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THE 
 
 CHEMISTRY OF PAINTS AND PAINTING 
 
THE 
 
 CHEMISTRY 
 
 OF 
 
 PAINTS AND PAINTING 
 
 BY 
 
 SIR ARTHUR H. CHURCH, K.C.V.O., F.R.S. 
 
 M.A., D.Sc., F.S.A. 
 
 Sometime Professor of Chemistry in the Royal Academy oj Arts in London 
 
 FOURTH EDITION 
 
 REVISED AND ENLARGED 
 
 O; 
 
 MD 
 
 LONDON 
 
 SEELEY, SERVICE & CO. LIMITED 
 
 38 Great Russell Street 
 
 1915 
 
[Dedication oj the First and Second Editions.] 
 
 TO 
 
 SIR FREDERIC LEIGHTON, BART., P.R.A. 
 
 WHO HAS ALWAYS SHOWN A DEEP INTEREST 
 IN ITS SUBJECT. AND HAS GREATLY 
 ENCOURAGED ITS AUTHOR, 
 
 THIS BOOK 
 
 IS. BY PERMISSION, DEDICATED. 
 
PREFACE 
 
 This handbook first appeared in the spring of i8go ; two 
 years afterwards a second and revised edition was pub- 
 lished. In 1901, when the work had been for some time 
 out of print, a thorough revision of its contents was 
 carried out, a good deal of new matter being introduced, 
 while a few pages, which had been occupied by a digest 
 of an important newspaper discussion on the effect of 
 light upon water-colour drawings, were not reprinted. 
 This account was omitted because it could no longer be 
 contended that many English water-colour drawings, ex- 
 posed to strong light for a considerable length of time, 
 had suffered no change in hue and depth. 
 
 Various additions and corrections have been made in 
 this, the fourth edition. A few of the paragraphs relating 
 to rather recondite subjects have been abridged or even 
 omitted. Indeed, an attempt has been made, in carrying 
 out the present revision, to simplify, so far as possible, 
 the way in which the results, obtained by chemists in the 
 study of painters’ materials, are presented to the artist 
 and the student of art. 
 
 In the year 1908 a German translation of the third 
 edition of this book was published in Munich. It was 
 
 vii 
 
PREFACE 
 
 viii 
 
 prepared and edited by the distinguished scientist Dr. 
 Wilhelm Ostwald. I have incorporated with the present 
 issue the substance of the paragraphs which he introduced 
 into my original text ; these are indicated by the sign H. 
 
 In preparing the following pages for the press, I have 
 to acknowledge, as on previous occasions, the help of 
 several friends and correspondents. Amongst these I 
 specially name Mr. J. Scott Taylor, many of whose 
 suggestions have been incorporated in the text, and also 
 Dr. A. P. Laurie, my successor in the chair of Chemistry 
 in the Royal Academy of Arts. 
 
 Of recent years the literature dealing with the subjects 
 to which the present handbook is devoted has greatly 
 increased. Several of the volumes named in my 
 ‘Bibliographical Notes’ are of sterling merit and contain 
 original material of no little importance. But I am 
 bound to confess that I have met with several disappoint- 
 ments when searching for records of new facts in recent 
 dictionary articles, reports of lectures, and treatises. On 
 perusal a familiar note seemed sometimes to be struck ; 
 and I ultimately identified not a little of the material as 
 my own. I will not dwell on this matter ; it is indeed 
 some consolation to feel that such transferences from my 
 pages would not have taken place had not the paragraphs 
 and tables and comments been deemed of some value. 
 But I trust that I myself shall not be thought guilty of 
 plagiarism because in 1914 I reprint something, say a 
 table or a classification, which I published in 1890, but 
 which appeared ten years or more later as having been 
 
PREFACE 
 
 lx 
 
 devised by another chemist. Another reason for limiting 
 the number of books included in my list of titles is to be 
 found in the extensive Bibliography appended to Pro- 
 fessor Laurie’s ‘ The Materials of the Painter’s Craft.’ 
 
 No very great differences will be found between the 
 present and the preceding edition, but I have endeavoured, 
 not only to introduce new matter which I think of import- 
 ance, but to simplify and make more exact the treatment 
 of the various subjects discussed ] and, in fine, to carry out 
 more fully the plan set forth in the Preface (here re- 
 printed) to the First Edition. 
 
 Arthur H. Church, 
 
 Kew Gardens, 
 
 yune 2, 1914. 
 
PREFACE TO THE FIRST EDITION 
 
 In the present volume the materials and methods of the 
 painter of pictures are viewed mainly from the chemical 
 standpoint. An attempt has been made to treat in orderly 
 sequence the various kinds of painting-grounds, the con- 
 stituents of vehicles and varnishes, the pigments them- 
 selves, and the chief processes of painting. Although 
 the artistic side of the numerous problems discussed has 
 not been neglected, the book is in no way intended to 
 teach manipulation to art students. It has been written 
 with the view of explaining to artists, whether they be 
 accomplished masters or commencing students, the chief 
 chemical and physical characters of the materials with 
 which they deal and of the operations they practise. In 
 many instances a sketch of the processes for preparing 
 certain pigments and varnishes is given, not in order to 
 turn the painter into a colour-maker or a varnish-manu- 
 facturer, but rather that he may acquire a clearer insight 
 into the nature and properties of the most important con- 
 stituents entering into the composition of his pictures. 
 With regard, however, to the tests for purity and 
 genuineness which I have described in the following pages, 
 
 xi 
 
xii PREFACE TO THE FIRST EDITION 
 
 my object in introducing them has been different, for I trust 
 that (in some cases, at least) the easy experiments I have 
 recorded will be tried, especially with suspicious pigments. 
 The operations require but little time; the pieces of ap- 
 paratus needed, like the chemicals, are few and inexpen- 
 sive. And when the ease with which these testings can be 
 made has been proved by practice, the experimenter may 
 perhaps be induced to proceed a little farther, preparing his 
 own siccative oil, selecting and purifying his spirit of tur- 
 pentine, and so forth. That the painter should test the 
 varnishes he buys for hardness and toughness, and the pig- 
 ments for durability, may, I hope, be taken for granted. 
 
 ‘ Titian managed pretty well without chemistry, did he 
 not ?’ A distinguished artist asked me this question the 
 other day. But not only were the conditions under which 
 the painters of Titian’s time worked simpler than those of 
 the nineteenth century, but grounds, paints, oils, and var- 
 nishes were generally prepared in the studios of the artists, 
 and under their own superintendence, so that the chances 
 of going wrong were comparatively limited. And it is not 
 to be denied that a better acquaintance with the nature of 
 the materials which many of the old masters employed 
 would have caused their works to be handed down in 
 sounder preservation to future generations. 
 
 It is possible — I hope, indeed, it is probable — that this 
 book may be found of service to students who are purpos- 
 ing to devote themselves to certain manufacturing and 
 technical pursuits. I am aware that to those who refer to 
 
PREFACE TO THE FIRST EDITION 
 
 xiii 
 
 its pages for the revelation of all the secrets of colour- 
 manufacturers it may prove in some measure disappoint- 
 ing ; yet I trust that, in the way of information and 
 suggestion, the study of this volume will not be unattended 
 with advantage. It must be remembered that it is con- 
 fessedly an elementary manual only, written with a defi- 
 nite aim, but covering a very wide area of inquiry. And if 
 chemists should conclude that it contains too little chem- 
 istry, artists may perhaps think that it contains too much. 
 
 There are repetitions in the following pages, for the 
 topics discussed in some of the chapters overlap one 
 another. I am perfectly aware of having made the same 
 statement, given the same figure, and expressed the same 
 opinion in more than one place. The scheme of the work 
 required such repetitions. I felt sure that many an artist 
 or student would turn to one section or other of the book 
 without caring to read the whole. One inquirer would 
 like to ascertain at once what pigments were safe, what 
 dubious, what fugitive, by a reference to the tables in 
 Chapters XXI. and XXII.; while another, anxious to learn 
 something of the evidence on which the several verdicts of 
 approval or condemnation were based, would expect to 
 find his requirements met in the pages devoted to trials of 
 pigments. Again, under the names of the individual pig- 
 ments, discussed in Chapters XIII. to XIX., some of the 
 changes described in the last part of the work are quoted. 
 Thus it happens that there are some materials common to 
 all of those sections of the book just named. 
 
XIV 
 
 PREFACE TO THE FIRST EDITION 
 
 Much of the substance of the lectures which I have 
 delivered before the Royal Academy since the year 1880 
 has been incorporated with the present manual, but it is 
 necessary to state that some of the original material to be 
 found in the following pages has been long before the 
 artistic world, and has found its way into the books and 
 essays of other writers. I say this, not for the purpose of 
 making reclamations of priority, but in order to prevent 
 myself from being charged with plagiarism. For instance, 
 so long ago as 1859, I described, for the first time, some of 
 the artistic uses of solid paraffin in a paper on the pro- 
 cesses of painting, read before the Oxford Architectural 
 Society ; further details were given in a lecture to the 
 Architectural Association in 1862. On many other matters 
 connected with the chemistry of paints and painting, new 
 investigations and studies were published by me between 
 the years 1867 and 1872, particularly in notes and essays 
 entitled ‘ Chemical Aids to Art,’ and ‘ The Chemistry of 
 the Fine Arts.’ But my statements and results, whether 
 contained in the above publications or in my Academy 
 lectures, have not been, in all instances, referred to their 
 source, or reproduced with accuracy, while some have 
 been overlooked or forgotten. 
 
 In preparing the present volume I have made consider- 
 able use of several of the works named in my Biblio- 
 graphical Notes ; I have consulted also the standard 
 chemical dictionaries of Watts and of Wurtz, the treatise 
 by Roscoe and Schorlemmer, besides many special papers 
 
PREFACE TO THE F[RST EDITION 
 
 XV 
 
 by other chemists. I wish I could have given an au- 
 thority for every statement not derived from my personal 
 experience, but in an elementary manual treating of 
 many diverse topics such a plan, even if it could have 
 been carried out, would have embarrassed my story with 
 a multitude of perplexing references. 
 
 I do not know of any one text-book which covers the 
 same ground as the volume now offered to the public. 
 Several small books on pigments — the most important of 
 all the materials employed by the artist— -have indeed been 
 lately published, but the chemical information they afford 
 is generally meagre, and sometimes far from exact. One 
 recent little brochure, which lies before me, has, I confess, 
 caused me some amusement not wholly unshaded with 
 regret. The writer does not pose as a humourist, yet he 
 tells us, when we test for lead in cadmium red, first to 
 mix the sample with white lead before applying the usual 
 test for that metal. Chinese vermilion, he informs us, is 
 sulphide of arsenic, though it is really sulphide of mercury. 
 The presence of sulphides of baryta and lime is stated in 
 one place to lend a softness to the chromates of lead ; as 
 these sulphides instantly blacken these brilliant chromates, 
 perhaps they may be said to soften them. Cceruleum, a 
 stannate of cobalt, is directed to be made of carbonate of 
 soda, powdered flint, and oxide of copper, its two essential 
 constituents, the oxides of tin and cobalt, not being named. 
 These and many other equally preposterous statements 
 and directions may afford merriment to the chemist, but 
 
XVI 
 
 PREFACE TO THE FIRST EDITION 
 
 it is indeed pitiable that such teaching should be seriously 
 offered to artists and art-students. 
 
 It is satisfactory to know that several accomplished 
 chemists are now devoting themselves to the practical 
 study and improvement of pigments. Mr. A. P. Laurie, 
 Mr. H. Seward, and Mr. J. Scott Taylor, are all doing 
 good work in this direction. 
 
 It remains for me to express the hope that the readers 
 of this volume will favour me with any material at their 
 disposal which may serve for the correction and improve- 
 ment of its pages. I am aware of having omitted to 
 notice many interesting matters ; amongst these I include 
 certain pigments, derived from coal-tar products, which 
 have not yet been sufficiently tested. Then, too, the 
 materials and methods of ceramic and glass painting have 
 been excluded from consideration, mainly because their 
 adequate treatment, while demanding much space, would 
 have appealed to a comparatively limited group of 
 students. 
 
 If painters and chemists will grant me their help, I 
 trust that I may further justify, by means of an improved 
 edition of my book, the favourable reception which I hope 
 may be accorded to the first. 
 
 A. H. Church. 
 
 Kew, March, 1890. 
 
BIBLIOGRAPHICAL NOTES 
 
 Blockx, J., ‘ Peinture a I’Huile.’ Pp. iv, 98. Gand, 
 
 1881. 
 
 Cennini, Cennino, ‘The Book of the Art.’ Translated 
 into English by Mrs. C. J. Herringham, with 
 Notes on Medieval Methods by the Translator. 
 Pp. xxxviii, 288. London, 1899. 
 
 Church-Ostwald, ‘Farben und Malerei’ Pp. xii, 376. 
 Miinchen, 1908. 
 
 Eastlake, Sir C. L., ‘ Materials for a History of Oil- 
 Painting.’ Series L, pp. xii, 561 ; Series II., pp. xv, 
 432. London, 1847, 1869. 
 
 Field, G., ‘ Chromatography,’ modernized by J. Scott 
 Taylor. Pp. viii, 207. Second edition. London, 
 1885. 
 
 Hurst, G. H., ‘ Painters’ Colours, Oils, and Varnishes.’ 
 Fifth edition, revised by Noel Heaton. Pp. xii, 528. 
 
 London, 1913. 
 
 Jametel, Maurice, ‘ L’Encre de Chine.’ Pp, xxx, 94. 
 Paris, 1882. 
 
 Lapparent, P. de, ‘ Les Alterations des Couleurs,’ 
 Pp. 36. Paris [1900]. 
 
 Laurie, A. P., ‘ The Materials of the Painter’s Craft in 
 Europe and Egypt.’ Pp. xvi, 444. London and 
 Edinburgh, 1910. 
 
 xvii 
 
xviii BIBLIOGRAPHICAL NOTES 
 
 Laurie, A. P., ‘ The Pigments and Mediums of the Old 
 Masters.’ Pp. xvi, 192. London, 1914. 
 
 Moreau-Vauthier, Ch., ‘ La Peinture.’ Pp. xii, 322. 
 Paris, 1912. 
 
 Ostwald, W., ‘ Letters to a Painter.’ Translated from 
 the German by H. W. Morse. Pp. viii, 162. 
 Boston, U.S.A., 1906. 
 
 Parry, Ernest J., and Coste, John H., ‘ The Chemistry 
 of Pigments.’ Pp. viii, 280. London, 1902. 
 
 Russell, W. J., and Abney, W. de W., ‘Action of Light 
 on Water-Colours ’ (Blue-Book). Pp. 78. Appendix 
 of 14 diagrams. London, 1888. 
 
 Solomon, Solomon J., ‘ The Practice of Oil-Painting.’ 
 Pp. xvi, 278. London, 1910. 
 
 Vasari, Giorgio, ‘On Technique.’ Translated by Louisa 
 S. Maclehose ; edited and annotated by Professor 
 G. Baldwin Brown. Pp. xxiv, 328. London, 1907. 
 
CONTENTS 
 
 INTRODUCTION - 
 
 PART I 
 
 PA INTING-GRO UNDS 
 
 CHAPTER 
 
 I. PAPER, VELLUM, IVORY - - - - 
 
 II. PLASTER, GESSO, STONE, SLATE, ETC. - 
 
 III. PANEL ------ 
 
 IV. . CANVAS ------ 
 
 PART II 
 
 VEHICLES AND VARNISHES 
 
 V. OILS - 
 
 VI. RESINS, WAXES, AND SOLID PARAFFINS 
 
 VII. YOLK AND WHITE OF EGG | SIZE ; GLUE 
 
 VIII. GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 
 
 IX. WATER-GLASS, LIME- AND BARYTA-WATER 
 
 X. SOLVENTS AND DILUENTS 
 
 XI. SICCATIVES OR DRYERS - - - - 
 
 XII. VARNISHES AND VEHICLES 
 
 PAGE 
 
 I 
 
 7 
 
 i8 
 
 29 
 
 34 
 
 45 
 
 68 
 
 84 
 
 91 
 
 TOO 
 
 106 
 
 125 
 
 130 
 
 XIX 
 
XX 
 
 CONTENTS 
 
 PART III 
 
 PIGMENTS 
 
 CHAPTER PAGE 
 
 XIII. WHITE PIGMENTS - - - . 145 
 
 XIV. YELLOW PIGMENTS - - - "157 
 
 XV. RED PIGMENTS - - - - 1 86 
 
 XVI. GREEN PIGMENTS - - - - 212 
 
 XVII. BLUE PIGMENTS - _ - . 226 
 
 XVIII. BROWN PIGMENTS - - - - 252 
 
 XIX. BLACK PIGMENTS . - - . 264 
 
 XX. CLASSIFICATION OF PIGMENTS - - 274 
 
 XXL TABLES OF PERMANENT, FUGITIVE, AND ALTER- 
 ABLE PIGMENTS . - - . 283 
 
 XXII. SELECTED AND RESTRICTED PALETTES - 290 
 
 PART IV 
 
 METHODS AND RESULTS 
 
 XXIII. PAINTING-METHODS - - - - 30I 
 
 XXIV. THE STUDY OF OLD PAINTINGS AND DRAWINGS 325 
 
 XXV. CONSERVATION OF PICTURES AND DRAWINGS - 342 
 
 XXVI. TRIALS OF PIGMENTS - - - - 359 
 
 INDEX 
 
 383 
 
THE CHEMISTRY 
 OF PAINTS AND PAINTING 
 
 INTRODUCTION 
 
 The materials employed by ‘ picture-makers’ are now very 
 numerous. Some of the old pigments, and painting-grounds, 
 and methods, have indeed fallen more or less completely 
 into disuse ; but, on the other hand, many new products, 
 both natural and artificial, have been added to the resources 
 of the artist, while several new processes of painting have 
 been introduced, or old methods modified. Nowadays it is 
 very seldom that a painter prepares for himself any one of 
 the materials which he uses, generally accepting, without 
 much hesitation and without examination, the paper, the 
 canvas, the paints, the oils, and the varnishes which his 
 colourman supplies, provided they respond, at first sight, 
 to his requirements. True he has abandoned, not without 
 regret, several of the mosttreacherous compounds by which 
 his immediate predecessors were seduced. ‘ Pure scarlet ’ 
 he has given up ; he is shy of asphalt ; tobacco-juice and 
 Spanish liquorice are no longer regarded as desirable 
 water-colours. He may go so far as to reject chromate 
 of lead, but he still employs the pigment called chrome 
 green, or green cinnabar, for he does not know that the 
 
 I 
 
2 
 
 INTRODUCTION 
 
 same chromate of lead enters largely into its composition ; 
 and he still thinks that madder yellow is a sound paint, 
 because it is called madder, while he rejects the yellow 
 lakes, which are derived from the same source. His 
 linseed oil is neither made from pure linseed, nor cold- 
 drawn ; his copal varnish may not have a particle of pure 
 copal in it ; but both are taken on trust. I do not expect 
 that artists should become chemists trained to test their 
 materials, but they will place themselves in a position of 
 comparative security by acquiring an elementary know- 
 ledge of the origin, the composition, and the character- 
 istics of the various products with which their works are 
 constructed. An architect is expected to recognise the 
 sound or unsound quality of the timber, the stone, the 
 brick, the iron, with which the edifice he designs is 
 constructed : why should the painter take everything on 
 trust ? The purchaser of a picture ought not to be dis- 
 tressed by doubts as to its stability. The concentration 
 of the artist’s attention on the definitely artistic side of 
 his practice must, of course, be in no wise interfered 
 with, but time may still be found for the acquisition of 
 such knowledge of his materials as shall enable him to 
 discriminate between the good and the bad. He may 
 even try, with great advantage, a few simple experiments 
 — experiments performed in a few minutes with the 
 simplest apparatus, and with the most innocent of re- 
 agents. These are the more necessary now that painters 
 no longer buy their raw materials, or make their own 
 paints, and oils, and varnishes, or prepare their own can- 
 vases and panels. Before colourmen generally under- 
 took such work, early in the seventeenth century, painters 
 were eager after receipts, and, there can be no doubt, 
 were ignorant of reasons : there was little exact science 
 
INTRODUCTION 
 
 3 
 
 underlying their art. Yet it would be unfair to the best 
 colourmen of the present day to assume that they do not 
 endeavour to provide, as far as possible, sound materials. 
 But they do not manufacture all they sell. They are not 
 paper-makers, nor, as a rule, are they manufacturers of 
 oils and varnishes. Many of the pigments they furnish 
 are not of their own make. If, for instance, you inquire 
 the source of the artificial ultramarine you purchase of 
 your colourman, you will find that it has probably been 
 made in a factory wholly devoted to the manufacture of 
 that pigment. The production of this material can 
 indeed be properly carried on only in special establish- 
 ments thoroughly equipped for a peculiar and difficult 
 work. In reality, this specialization ought to be, and 
 generally is, advantageous, but it renders the position of 
 the colourman somewhat difficult. He has to assume 
 responsibility for the soundness and genuineness of many 
 products of the history and preparation of which he 
 knows little or nothing. 
 
 This difficulty confronts him in many directions. I have 
 known cases in which importers or manufacturers’ travel- 
 lers have offered to artists’ colourmen speciously prepared 
 but spurious pigments, such as madder carmine and rose 
 madder made from artificial alizarin, ultramarine ash 
 containing not a particle of the native lapis-lazuli, and a 
 gold ochre owing its colour to a basic ferric sulphate 
 instead of a hydrate. Then, too, some of the original 
 localities of a few native earths, such as terre verte and 
 raw umber, are practically exhausted, and most of the 
 new sources yield products of inferior hue. Hence the 
 temptation to ‘ exalt ’ the hue of the commercial article 
 by some seductive though dangerous addition. 
 
 After these introductory observations, I may refer the 
 
4 
 
 INTRODUCTION 
 
 reader to the table of contents for the plan of the present 
 book, and to the prefaces for the object with which it has 
 been prepared. I would add, here, only this one remark, 
 that the materials with which a painting is constructed 
 are described in definite order, beginning with the 
 ground, then passing on to the medium and the pig- 
 ments, not omitting the final varnish, and finally closing 
 with a brief summary of methods of painting, and of the 
 experimental studies by means of v/hich the conclusions 
 given in the earlier portions of the volume have been 
 reached. 
 
PART I 
 
 PAINTING-GROUNDS 
 
 Chapter I. — Paper, Vellum, Ivory. Chapter II. — Plaster or Intonaco, 
 Stone, etc. Chapter III. — Panel. Chapter IV. — Canvas. 
 
CHAPTER I 
 
 PAPER, VELLUM, IVORY 
 
 As paper is used as the painting-ground for the vast 
 majority of works executed in water-colours, and as 
 this method of painting offers but slight protection to the 
 pigments employed against hostile influences, it becomes 
 of the greatest importance to ascertain that no unneces- 
 sary elements of danger are introduced in the paper itself. 
 We will now proceed to consider briefly the sources and 
 constituents of drawing-paper. 
 
 Linen from the common flax [himmi usitatissimuni), and 
 in the form of white rags, should be the basis of the pulp 
 used in the making of sound drawing-paper. In actual 
 practice the cheaper and weaker fibre of cotton (seed-hairs 
 of Gossypium sp.) has almost entirely displaced flax, 
 although during recent years a successful attempt has been 
 made in England to produce a high grade of hand-made 
 drawing-paper almost wholly composed of linen. Other 
 vegetable fibres might, no doubt, be employed for this 
 purpose. Thus, Japanese paper, prepared from the bast- 
 fibres of the paper-mulberry {Brotissonetia papyrifera), were 
 it made less absorbent by the introduction of a sufficiency 
 of size, would probably become an efficient, strong, and 
 durable substitute for linen-paper ; but at present linen- 
 papers, cotton-papers, and papers made from a mixture 
 
 7 
 
8 
 
 CONSTITUENTS OF PAPER 
 
 of these fibres, are the only kinds with which water- 
 colourists are practically concerned. 
 
 During his explorations of Chinese Turkestan, Sir Aurel 
 Stein recovered many examples of early manuscripts 
 written on felted vegetable fibre, that is, paper. In the 
 British Museum are two scraps of such paper, with 
 Chinese writing, which must be dated somewhere between 
 the years a.d. 25 and 220. They are the most ancient 
 specimens of paper known to exist in the world. But the 
 manufacture of linen-paper in Europe has not at present 
 been traced back farther than the second half of the twelfth 
 century. Mr. W. H. James Weale, formerly Keeper of 
 the Art Library in the Victoria and Albert Museum, 
 informed me that the two first paper-mills in France were 
 set going near Ambert, in the valley of the Valeyre, by 
 men who, during their captivity in the Holy Land, were 
 forced to work at the manufacture of paper at Damascus. 
 One of these French mills was called ‘ Damascus,’ the 
 other ‘Ascalon.’ This was previous to the year ii8g. 
 To Mr. Weale I am also indebted for an opportunity of 
 examining two early specimens, obtained from the ‘ Regis- 
 tre des Revenus de I’^lveche du Puy.’ As one of the 
 sheets contains contemporary entries of the year 1273 — 
 the other entries belonging to 1289 — these papers are, at 
 least, as early as the years named. Both papers present 
 the creamy hue, the translucency, and the gloss of vellum. 
 One hundred square inches of the earlier specimen weigh 
 127 grains ; of the later, 163. Both are heavily sized with 
 paste made from wheaten starch. The use of starch for 
 sizing paper has been revived of recent years, but animal 
 size or jelly is still extensively employed. Some paper is, 
 indeed, made from felted linen pulp alone without size ; 
 but it is blotting or filter paper, and is quite unfitted for 
 
ANALYSIS OF DRAWING-PAPER 
 
 9 
 
 water-colour work, for when a wash of pigment is passed 
 over it, the colouring matter and the water partially separ- 
 ate, while the outline of the brush-stroke is not preserved. 
 
 Before entering further into the question of what are 
 the essential and what the accidental and unnecessary con- 
 stituents of paper, I give the summarized results of six 
 analyses, which show the percentage proportions found in 
 good samples ; 
 
 ANALYSES OF DRAWING-PAPERS 
 
 
 Water 
 
 Size 
 
 Ash 
 
 Fibre 
 
 Hodgkinson, 1869 - 
 
 6-8 - 
 
 4-6 - 
 
 II 
 
 87-5 
 
 English, 1876 - 
 
 io’9 
 
 6'i 
 
 II 
 
 81 '9 
 
 Dutch, 1876 - 
 
 II'O 
 
 4-8 . 
 
 0-9 - 
 
 83-3 
 
 Whatman. 1885 
 
 7'4 - 
 
 6'3 - 
 
 I 'I 
 
 85 "2 
 
 Arnold, 1894 - 
 
 7'4 - 
 
 7-6 - 
 
 I '5 - 
 
 83-5 
 
 ‘ 0 . W.,’ 1897 
 
 8-7 - 
 
 5'5 - 
 
 i ‘7 ■ 
 
 84 •! 
 
 Water . — It should be noted that the percentages of 
 water shown in these analyses vary considerably by reason 
 of variations in the humidity, temperature, and pressure of 
 the atmosphere to which the different papers had been 
 exposed just before the analyses were made. There are, 
 however, slight permanent peculiarities in samples made 
 from different fibres or sized in different ways ; in conse- 
 quence the moisture-absorbing and moisture-retaining pro- 
 perties of different papers are not precisely identical under 
 identical atmospheric conditions. This hygroscopic mois- 
 ture does, indeed, vary inversely with the temperature, and 
 directly with the amount of water-vapour in the air ; it is 
 increased also by an increased barometric pressure. There 
 is no doubt that if it could be wholly excluded, the larger 
 number of changes which occur in the pigments of a water- 
 colour drawing would be prevented. It is most injuriously 
 active when a framed drawing is exposed to considerable 
 
10 
 
 ASH OF PAPER 
 
 ranges of temperature. Under these conditions the 
 moisture of the paper is first partly turned into vapour, 
 then condensed on the glass, and, lastly, is re-absorbed by 
 the paper, and, for a time, especially by the pigments lying 
 on its surface. This temporary condensation of an excess 
 of moisture upon the coloured surface does much injury 
 before hygroscopic equilibrium is once more re-estab- 
 lished. Much less harm would accrue were the vapour- 
 ized water allowed to escape. 
 
 Size . — The size must be considered next. It may be 
 applied to the pulp or to the sheet, and may consist of 
 gelatine with a little alum, of colophony or rosin dissolved 
 in soda-lye, followed by treatment with alum or alum-cake. 
 Sometimes starch is used along with alum or alum-cake. 
 From good drawing-papers, which are sized in the sheet 
 with animal size, the greater part of the size may be ex- 
 tracted by means of boiling distilled water, the solution 
 being usually neutral or faintly acid, sometimes faintly 
 alkaline, to test-papers. Gelatine and starch, to the extent 
 of about 5 per cent, of the weight of the paper, are the 
 safest sizing materials. 
 
 Ash . — The ash or mineral matter in paper may be 
 derived from three sources, namely, traces of the original 
 mineral substances taken up by the flax plant from the 
 soil, and still remaining associated with the felted pulp; the 
 mineral matters, such as soda and alum, introduced with 
 the size; and, lastly, the mineral compounds used to whiten, 
 to weight, or to finish the paper, or in bleaching the fibre 
 and as ‘ antichlors.’ In common and adulterated papers 
 the ash greatly exceeds i per cent., twelve parts per hun- 
 dred of paper being no unusual proportion. This ‘filling’ 
 may contain or consist of the following substances : kaolin 
 or china-clay, silicate of lime or ‘pearl-hardening,’ chalk or 
 
FIBRE OF PAPER 
 
 II 
 
 whitening, lead-white, baryta white or ‘ white dressing,’ 
 artificial gypsum or ‘ satin-dressing,’ and a mixture of alu- 
 minium hydrate with magnesium carbonate or with calcium 
 carbonate, known as ‘ satin finish ’ or ‘ satin-white.’ Other 
 substances which increase the amount of ash left when a 
 paper is burnt are blue colouring matters, introduced to 
 counteract the natural yellow tint of the pulp. These 
 include artificial ultramarine, smalt or cobalt blue, and 
 Prussian blue. 
 
 Fibre . — What is put down as fibre in the analyses of 
 paper previously cited, is a substance, or group of sub- 
 stances, to which the name of cellulose is given by 
 chemists. Cellulose consists of the three elements — 
 carbon, hydrogen, and oxygen ; it is, when pure, entirely 
 combustible, leaving no ash. 
 
 The source of this cellulose is by no means without in- 
 fluence on the durability, strength, and working quality of 
 drawing-paper. The fibres of linen and of cotton present 
 distinct differences of form and resistance to strain. When 
 working on a paper with a knife so as to develop high lights, 
 the water-colour painter soon discovers the weakness and 
 fluffiness of abraded cotton, while the clear-cut surfaces of 
 linen are equally obvious. Even in washing and in taking 
 out lights from a drawing by sponging and rubbing, the 
 superiority of linen-paper to cotton-paper is very marked; 
 in fact, papers into which a high proportion of the latter 
 fibre enters will not stand much worrying. The other 
 fibrous materials commonly forming the basis of ordinary 
 papers are, on one score or another, less desirable than 
 cotton. Nearly all of them require, in order to fit them for 
 paper-making, a very drastic treatment, which is liable to 
 leave behind it traces of injurious chemicals, or to yield 
 altered material of lessened strength and permanence. 
 
12 
 
 PAPER-MAKING 
 
 Wood-pulp, esparto, and straw-pulp belong to this cate- 
 gory. 
 
 Paper-making . — The technology of paper-making cannot 
 be discussed here, but a few references to the chemicals 
 employed in the process of manufacture may be usefully 
 given at this point. Amongst these chemical substances, 
 one or more of which will have been introduced into the 
 fibrous basis of the paper or into the size may be named; 
 caustic soda and caustic lime ; chloride of lime, magnesium 
 hypochlorite, moist chlorine gas, and sulphuric acid ; 
 alum, aluminium chloride, and aluminium sulphate ; 
 sodium sulphite; gelatin. Of course, it is possible to 
 cleanse and bleach the higher class of rags without 
 having recourse to any chemical treatment, but the 
 ‘ souring ’ with sulphuric acid and the employment of 
 some soda or sodium carbonate to remove grease are 
 usual ; while there is always a salt of aluminium present 
 in the size. Indeed, in the best and purest drawing- 
 papers, the alum, or its equivalent, is the one ingredient 
 upon which the chemist interested in painting will look 
 with suspicion. But the subject of the presence of chemi- 
 cals, injurious or innocuous, in the finished product of the 
 paper-mill may be relegated to the following paragraphs. 
 
 Paper -testing . — The simplest test of the suitability of 
 any sample of drawing-paper for water-colour work con- 
 sists in applying to its surface uniform and weak washes 
 of a chosen set of sensitive pigments. A sound standard 
 paper is taken for comparison ; this may be ‘ Whatman,’ 
 but it should be first swilled in cold distilled water for 
 five minutes, and then hung up to dry. In applying this 
 test, a strip of the sample to be tested and one of the 
 standard paper should be laid side by side, and then the 
 several colour washes, made with distilled water, carried 
 
TESTING PAPER 
 
 13 
 
 across both strips by means of a broad brush. The pig- 
 ments used may be French ultramarine, chrome yellow, 
 and carmine. Unless they are employed in very dilute 
 admixture, the changes produced by alum and other 
 chemicals will not be perceptible. There should be no 
 bleaching of the ultramarine or the carmine, or any 
 blueing of the latter, and no dulling of the chrome, even 
 after the lapse of a week from the date of the experiment. 
 Washes of tincture of azolitmin from litmus, tincture of 
 dahlia flowers, and tincture of methyl-orange may be 
 similarly applied to paper-strips ; in this case it will prob- 
 ably be found that the two former tests will show an 
 acid reaction, and the methyl-orange a basic or alkaline 
 reaction. This seemingly strange result has been found to 
 arise from the presence of a derivative of the alum in the 
 size, namely, an aluminium sulphate which is acid to some 
 tests and basic to others. This point has been established 
 by the experiments* of Messrs. Cross and Bevan, Mr. C. 
 Beadle, and Drs. P. N. Evans and Quirin Wirtz, who have 
 pr&ved that all the drawing-papers of well-known makers 
 which they have examined contained no free sulphuric 
 acid. Of course, the question remains, ‘ How far, if at all, 
 is the basic aluminium sulphate in drawing-paper injurious 
 to sensitive pigments ?’ This inquiry can, I think, be an- 
 swered by applying the colour-tests already described, not 
 onlytothe suspected papersthemselves, but also to extracts 
 from them made with cold distilled water and also with hot. 
 
 Other useful tests are the following : 
 
 1. Burn 100 grains of paper to a white ash; not more 
 than I ’5 grains of incombustible residue should be found. 
 
 2. Extract 100 grains of paper repeatedly with boiling 
 
 * Journal of the Society of Chemical Industry (1892), pp. 212, 213, 
 261. 
 
14 
 
 TESTING PAPER 
 
 distilled water. The united watery extracts, evaporated 
 to dryness, should not amount to 8 grains. 
 
 3. If straw or esparto fibre be present in a paper, it will 
 become red when immersed in a boiling i per cent, solution 
 of aniline sulphate. 
 
 Attempts have been made to size paper with casein dis- 
 solved in ammonia, and also with ‘ viscose,’ a modified 
 cellulose made out of the substance of the paper itself by 
 means of water, caustic soda, and carbon disulphide. At 
 present, however, gelatin-sizing holds its own. The neces- 
 sity of introducing alum, or an equivalent of some other 
 aluminium salt, into this size is its chief drawback, although 
 an animal product of the group to which gelatin belongs, 
 being prone to decomposition and to the attacks of micro- 
 scopic organisms, itself constitutes a source of danger. 
 Alum is used not merely as an antiseptic, but because it 
 exerts a peculiar liquefying effect upon the size. A little 
 alum solution added to gelatin solution increases its stiff- 
 ness, but further additions up to an easily ascertained point 
 make the solution more mobile. It is absolutely necessary 
 to keep the alum percentage low ; I found in a batch of 
 one well-known make of drawing-paper that exactly twice 
 as much alum had been employed as was necessary. My 
 remonstrance with the manufacturers had its due effect. 
 
 The roughness or smoothness of the surface of the paper, 
 or cardboard, is not without influence on the permanence of 
 water-colours. The pigments become less intimately asso- 
 ciated with the smooth surface of a hot-pressed paper than 
 with a comparatively rough natural surface. The rough 
 surface is, however, liable to wider and more rapid fluctua- 
 tions in the amount of hygroscopic moisture. 
 
 Some apparently sound papers deteriorate in strength 
 and tint on being kept. Such changes may occur even when 
 
SIZE IN PAPER 
 
 15 
 
 pure linen rags have been used for the pulp ; they may be 
 generally traced to the disintegrating action on the fibre of 
 the chemical bleaching agents employed. The development 
 of rust-spots, when not due to the mount or backing of a 
 drawing, arises from the presence of small particles of 
 metallic iron from the machinery having become em- 
 bedded in the pulp. These particles appear grey, brown, 
 or black ; they may be detected by placing a drop of oxalic 
 acid solution on the suspected spot, allowing it to dry, and 
 then moistening the place with a drop of a freshly-pre- 
 pared solution of tannin. If the particle be iron an ink- 
 stain will be produced. However, some dark spots con- 
 sist of blackened grease, or of tar, or of the paper-fungus 
 {Myxotvichum chartantm). 
 
 Naturally, there is a small quantity of oil or fat in 
 paper ; it varies from 3 to 5 parts in a thousand. The 
 difficulty experienced in immediately wetting a surface of 
 paper, caused by the presence of this trace of oil, may be 
 overcome by first washing the surface with distilled water 
 to which a drop or two of caustic ammonia has been added. 
 A solution of the natural mixture of alkaline organic salts, 
 known as oxgall, effects the same purpose. The use of 
 borax had better be avoided. It is always advisable to 
 wet the whole surface of the paper before beginning a 
 water-colour drawing. Thus any abrasions or defects of 
 the surface will become apparent. 
 
 As drawing-papers are sized in the sheet they occasion- 
 ally show a peculiar defect arising from the irregular dis- 
 tribution of the size. In such cases, when the surface is 
 scraped off, an absorbent layer of imperfectly sized pulp is 
 revealed beneath. When such paper is used for water- 
 colour painting the sinking-in and running of the pigments 
 produce disastrous results ; but it is easy to guard against 
 
i6 
 
 VELLUM AND IVORY 
 
 accidents of this sort by previously scraping and colouring 
 a corner of the sheet to be used. The peculiarity is gener- 
 ally owing to the too prolonged and slow drying of the 
 sheets of paper after they have been removed from the 
 warm sizing-bath and pressed. The solution of size is 
 brought to the surfaces from the interior of the sheet, and 
 remains there. Moreover, in very slow drying, the size is 
 apt to decompose with loss of its glutinous character and, 
 possibly, the formation of mildew. A good drawing-paper 
 will indeed have rather more size at the surface than in 
 the interior, this result being secured by a rate of drying 
 which is neither too rapid nor too slow. Let us add that 
 the strength of paper when completely wetted and in the 
 presence of free water, is very low. If, however, it has 
 been gelatin-sized and afterwards sprayed with a 40 per 
 cent, solution of formalin to coagulate the gelatin it be- 
 comes appreciably stronger. 
 
 As to vellum, parchment, and ivory, little need be said. 
 All three contain the characteristic ingredient ossein, an 
 insoluble nitrogenous organic substance, which by long 
 boiling with water is converted into gelatin : a solution of 
 gelatin constitutes ordinary size. Water-colour paints 
 placed upon any of these materials sink either very 
 slightly, or not at all into their substance — a very few, 
 such as aureolin, strontia-yellow, and madder carmine, 
 stain the superficial layer. The old method of preparing 
 vellum for the reception of water-colours consisted in 
 rubbing the surface with very finely-ground bone-ash, or 
 with pulverized sandarac. Pumice-stone or cuttle-fish, re- 
 duced to a minutely divided state by pounding, grinding, 
 and sifting, may be used for this purpose ; the infusorial 
 earth known as polishing silica, or kicselguhv, may also be 
 employed. 
 
VELLUM AND IVORY 
 
 17 
 
 Ivory which has become yellowish through age and se- 
 clusion from light may be safely bleached by contact with 
 an ethereal solution of hydrogen peroxide. The treatment 
 is best carried out in a wide-mouthed stoppered bottle, 
 care being taken to immerse the sheets of ivory wholly in 
 the liquid, and not to allow them to touch each other. 
 
 Much care is necessary in selecting tinted and coarse 
 coloured papers for water-colour work. The tints of the 
 former are often obtained by the introduction of fugitive 
 pigments into the pulp ; the latter are often made of in- 
 ferior and mixed fibres, and sometimes contain lead-white 
 and other m]m\ons fillings, ‘Turner’ paper, for example, 
 owes its grey-blue tint to the presence of indigo, while 
 ‘ Varley ’ paper contains about 20 per cent, of ‘ mechanical ’ 
 wood-pulp, a material which steadily darkens into brown 
 after but a short exposure to light. ‘ Sugar ’ paper, what- 
 ever its hue, should be avoided. Mill-board is often 
 made of wood-pulp, oakum and straw-pulp : its surface is 
 primed for oil-painting in the same way as canvas. 
 
CHAPTER II 
 
 PLASTER, GESSO, STONE, SLATE, ETC. 
 
 The painting-grounds to be considered in this chapter 
 consist mainly of mineral substances. However their con- 
 stituents may be varied, in accordance with the process to 
 be used in painting upon them, the wall or backing upon 
 which they are spread should fulfil certain conditions. It 
 must be naturally dry, free from soluble saline matters, and 
 not very porous. A damp-proof course above the level 
 of the ground is necessary, and the wall should be well- 
 built, and free from tremors. A double wall well-bonded 
 has been recommended : in this case the air enclosed 
 between its two divisions should not be stagnant. 
 
 Before being plastered, the wall, whether its surface be 
 of stone, bricks and mortar, roughened slate, or tiles, must 
 be thoroughly wetted with lime or baryta-water. The 
 plaster is applied in two or more coats, the coarsest and 
 thickest first. In the case of a ground for fresco the two 
 ingredients usually employed are (or rather were) pure 
 slaked lime, and clean sharp silicious sand. The sand 
 must be uniform in grain, white, and free from soluble 
 salts. The slaked lime is so important an ingredient in the 
 majority of plasters, that it is expedient to describe its 
 preparation once for all. Before doing so we may state 
 the relations subsisting between the three compounds 
 known generally as carbonate of lime (chalk), or mild lime, 
 
 i8 
 
COMPOUNDS OF LIME 
 
 19 
 
 burnt lime, or quicklime, and slaked lime. The first of 
 these is neutral and nearly insoluble in pure water, the 
 second and third are alkaline and caustic. When burnt 
 lime unites with water to form slaked lime it becomes 
 slightly soluble in pure water. In chemical language these 
 three compounds are called respectively calcium carbon- 
 ate, calcium oxide, calcium hydrate (or hydroxide). From 
 the first substance the others are readily obtained. If 
 calcium carbonate, often called carbonate of lime, be 
 heated to a sufficient temperature, it is decomposed, being 
 resolved into carbon dioxide (carbonic acid gas) which 
 escapes, and calcium oxide (lime) which remains : from 
 100 parts by weight of the carbonate 56 parts of lime, that 
 is, burnt lime, are obtained. Placed in water or exposed 
 to moist air this burnt lime combines with water, 56 parts 
 of it uniting with 18 parts of water to yield 74 parts of 
 slaked lime, calcium hydrate. In the ordinary country 
 atmosphere, which contains no more than 3 measures of 
 carbonic acid gas per 10,000, slaked lime or calcium 
 hydrate loses its combined water, slowly becoming once 
 more the carbonate from which it was originally produced : 
 74 parts of hydrate lose 18 parts of water and combine 
 with 44 parts of carbonic acid, and yield 100 parts of car- 
 bonate. Thus mild lime is formed once more from caustic 
 lime. By this change, if it be effected in the presence of 
 a sufficiency of free water — that is, if the hydrate of lime 
 be in the state of a firm paste — the whole substance 
 becomes a hard crystalline solid, like an opaque marble. 
 Advantage may be taken of this hardening or cementing 
 process to firmly incorporate other substances with the 
 lime. Silicious sand, infusorial earth, pumice, marble 
 powder, and many other mineral substances, may be thus 
 introduced. Such of these materials as are silicious may 
 
20 
 
 LIME-PUTTY 
 
 contain silica in a form which is known as ‘ soluble silica.’ 
 This substance further strengthens the plaster by forming 
 with a part of the lime an insoluble compound called sili- 
 cate of lime. To return to the preparation for artistic 
 purposes of hydrate of lime. White or black marble, 
 limestone, chalk, or other fairly pure forms of carbonate 
 of lime are first of all burnt, and then the quicklime pro- 
 duced is slaked with clean water. This is done in a 
 grouting box, having a sluice i or 2 inches from the bottom. 
 Run the thick cream of lime into a tank of slate and keep 
 it, covered loosely, for two months. At the end of this time 
 it will be ready for all the rougher purposes of plastering. 
 For finer work the grouting operation is to be repeated, and 
 the cream of lime strained through hair-sieves, and pre- 
 served in screw-top stoneware jars. Some water will accu- 
 mulate above the lime-putty, as it may be called, in these 
 jars ; it should be poured off or drawn off, from time to 
 time. The jars are kept tightly closed to prevent further 
 carbonation of the lime hydrate. This change, if carried 
 beyond a certain point, is undesirable, since the binding 
 and hardening powers of the lime would thereby be 
 lessened seriously, or even vanish altogether by its con- 
 version into mild lime : not more than one-third or at most 
 two-fifths of the lime should be converted into the car- 
 bonate. The lime-putty thus prepared may be used for 
 plaster and intonaco with the certainty that it will not give 
 rise to defects in the painting-grounds made therewith. 
 Much lime paste of this kind was prepared for the works 
 in fresco in the Houses of Parliament, and was kept in 
 the cellars under that building, where probably some of 
 it still remains. I have made many experiments with 
 samples from that source, and can speak with confidence 
 of its excellent quality. 
 
FRESCO GROUNDS 
 
 21 
 
 Bum’ Fresco , — A good mixture for the first application to 
 the moistened wall consists of 2 parts (by weight) of clean 
 sharp sand to one of lime-putty. When one or more coats 
 of this mixture have been duly laid and have set, then the 
 surface is ready to receive the final coat or intonaco, the 
 actual painting-ground. Before this is applied, the rougher 
 plaster below must be thoroughly wetted with distilled or 
 lime water. The sand in the intonaco is of finer and more 
 uniform grain than that previously employed; the intonaco 
 itself is only one eighth of an inch in thickness. All the 
 coats must be laid without having recourse to scraping or 
 ‘ floating’ ; the latter operation brings too much lime up to 
 the surface. Considerable practice and manual dexterity 
 are needed in these operations. The work of painting is 
 at once commenced when the intonaco has been laid, no 
 more being spread at one time than the artist can cover in 
 the day. Upon the wet soft plaster the cartoon is laid, and 
 the outlines and other important parts pounced in, trans- 
 ferred, or impressed by an ivory point. Rapidity and 
 firmness of execution, with the distribution of a uniform 
 thickness of pigment, are matters to which special atten- 
 tion must be paid. The chemistry of this method of 
 painting will be discussed in Chapter XXIII. 
 
 Many modifications in the preparation, proportions, and 
 materials of fresco painting-grounds have been introduced 
 or suggested from time to time. I have found the following 
 mixture to yield an excellent plaster for this purpose : 
 Three parts of burnt lime in very fine powder are ground 
 up with 2 parts of whitening or prepared chalk ; the mix- 
 ture is grouted, and then strained through hair-sieves ; 
 5 parts of the putty thus obtained are mixed with 5 parts 
 of sifted crushed marble, or with 5 parts of sharp, fine, 
 sifted sand, or with 3 parts of sifted pumice, or with the 
 
22 
 
 TEMPERA GROUNDS 
 
 same quantity of infusorial (silicious) earth ; the whole 
 being moistened with a sufficient quantity of lime-water 
 to render working easy. For the undercoats the sand, etc., 
 introduced may be coarser ; while a small quantity of the 
 most silky and whitest asbestos, cut with scissors into 
 short uniform lengths, will prove a desirable addition. 
 The asbestos* lessens the risk of any lack of continuity 
 in the undercoats. 
 
 Fresco-Secco and Tempera . — For fresco-secco the same 
 ground as that required for true fresco may be used, but it 
 is allowed time to dry and harden. So long as it contains 
 any caustic lime this ground is unfitted for work in tem- 
 pera, as its alkaline nature seriously limits the variety of 
 pigments which may be employed in this method. When 
 carbonation of the lime is complete it may be employed 
 for tempera-painting, the surface being first treated with 
 warm size. Many Greek and Byzantine paintings were, 
 however, executed upon a caustic lime ground, but the 
 pigments employed consisted chiefly of those natural 
 earths which are unaffected by alkalies. In these Greek 
 tempera-grounds slaked lime mixed with chopped straw, 
 flax, or cotton, formed the basis of the plaster. It is 
 scarcely necessary to remark that these vegetable 
 materials are liable to decay and to cause discoloration 
 of the ground. 
 
 The ordinary ground for Italian and Spanish tempera- 
 paintings consisted either of whitening and size, or of 
 burnt gypsum (that is, plaster of Paris), stirred well with 
 
 * Professor Laurie, in his ' Materials of the Painter’s Craft ’ 
 (p. 138), attributes this recommendation as to the use of asbestos 
 to Mr. James Ward, who names it in his book on ‘ Fresco Painting ’ 
 (p. 14) published in 1909. But the present author published the 
 same recommendation with fuller instructions in the year 1890 ; it 
 will be found on p. 18 of the first edition of the present handbook : 
 but he also may have been anticipated. 
 
TEMPERA GROUNDS 
 
 23 
 
 water so as to lose the power of setting, strained, and 
 mixed with size. Sometimes both whitening and slaked 
 burnt gypsum are found together as constituents of the 
 ground. The ground was laid directly on the panel, or 
 on the cloth which had been previously glued to the 
 wood. Great care was taken by sifting and washing to 
 secure the fineness and purity of the whitening (calcium 
 carbonate) and of the slaked plaster of Paris (calcium 
 sulphate united with two proportions of water). Various 
 kinds of size were used ; one of the best was made partly 
 from parchment, partly from the finer kind of fish-glue. 
 An excess of size will cause the ground to crack ; it must 
 never contain such a quantity as to be rendered non- 
 absorbent, All tempera-grounds of gesso were originally 
 absorbent ; in course of time they have become more so 
 owing to the decay of the size. Whether they were 
 afterwards to be painted in tempera or oil they were 
 always first sized. This sizing preserved the luminous 
 whiteness of the ground, which was unable to absorb the 
 oil of oil-paints or that present in the egg-yolks employed 
 in tempera. A proof of the existence of this layer of size 
 above the ground proper is obtained in the process of 
 transferring old tempera and oil pictures to canvas, for 
 in such cases we find discoloration of the ground under 
 cracks only where both the size and the paint above it 
 have become fissured. 
 
 It will have been gathered from what has been stated 
 in the preceding paragraph that a non-caustic tempera- 
 ground is suitable for work in oils. In the latter case, 
 however, it must be perfectly dry before the painting is 
 commenced. It should be gently warmed and rubbed 
 with a little clean spirits of turpentine before laying on 
 the first coat of oil-paint. 
 
24 
 
 STEREOCHROME GROUNDS 
 
 Steveochyomy . — The ground for stereochromy has been 
 modified several times since the first introduction of this 
 method of water-glass painting. Originally it was recom- 
 mended to use an undercoat containing 2 parts of sharp 
 sand, 2 parts of fine sand, and i part of slaked lime in 
 fine powder. Upon this was laid an intonaco of one-tenth 
 to one-eighth of an inch in thickness, made of 3 parts of 
 fine sand and i part of slaked lime. The fineness or 
 coarseness of the sand in the intonaco must, however, be 
 regulated by the nature of the surface required by the 
 artist. I see that nearly fifty years ago I recommended* 
 the employment of sifted white marble powder, and of 
 several other substitutes for sand, recommendations 
 which, within the last few years, have been again brought 
 forward by Herr Adolph Keim. Oxide of zinc may be 
 advantageously substituted for a part of the lime in the 
 intonaco, and it may be added to the pigments. Keim 
 recommends the wall to be first coated with a mixture of 
 I part of burnt lime (which is to be slaked with distilled 
 water), and 4 parts of a composition consisting of coarse 
 quartz sand, infusorial earth, and powdered marble. The 
 actual painting-ground, which is from one-eighth to a 
 quarter of an inch in thickness, is made of i part of 
 slaked lime, and 8 parts of a mixture of the finest quartz 
 sand, marble sand, marble meal, and infusorial earth. 
 Fine asbestos paper, wetted with lime-water, and firmly 
 pressed by rolling into a soft freshly-laid lime and sand- 
 plaster, makes an excellent ground for stereochrome 
 painting; but as a single breadth only of this paper can 
 be used, the size of the work that can be executed 
 upon it is somewhat limited. All the precautions as to 
 
 * ‘Chemistry of the Fine Arts’ in Cassell’s ‘Technical Edu- 
 cator.’ 
 
SPIRIT-FRESCO GROUNDS 
 
 25 
 
 dryness of the wall and purity of the materials, already 
 noted in the case of fresco-grounds, must be observed in 
 reference to those intended for stereochrome painting. 
 
 Spirit-Fresco . — The ground recommended by the late 
 Mr. Gambler Parry for that modified form of varnish- 
 painting to which he gave the name of ‘ Spirit-Fresco ’ is 
 identical with that required for true fresco. All the usual 
 precautions as to the dryness of the backing, and its 
 freedom from soluble salts, must be taken. The plaster 
 must be allowed to dry completely before the operation of 
 saturating it with the medium is commenced ; the lime in 
 it should also have become mild — that is, carbonated. 
 (See Chapter XXIII. for tests for alkalinity and moisture.) 
 Syringing the plaster with distilled water previously 
 charged under pressure with carbonic acid gas, though 
 it delays the drying, hastens the carbonation of the lime 
 materially. To complete the preparation of the ground, 
 it should, when quite dry, be soaked with a mixture of 
 two parts of the medium (Chapter XII.), and three of tur- 
 pentine. After two days, this treatment must be repeated. 
 A third application may be needed for very porous 
 grounds. Another period of forty-eight hours having 
 elapsed, the surface receives a coat of white paint, made 
 of equal parts of white lead and gilder’s whitening, 
 ground up with the medium diluted with one-fourth or 
 one-third its bulk of turpentine. This priming is re- 
 peated when the first coat is dry. After three weeks, the 
 painting may be commenced. Stone and terra-cotta, if 
 sufficiently porous, may be primed in the same way as 
 plaster. Under no circumstances should cements con- 
 taining plaster of Paris be introduced into the grounds 
 used for spirit-fresco. 
 
 During the last twenty years a considerable number of 
 
26 
 
 SLATE AND STONE 
 
 large mural paintings have been executed either in Gam- 
 bier Parry’s medium or in the paraffin-copal medium. 
 Some of these works have been painted directly on 
 plastered walls, some on canvases which have been 
 afterwards affixed by uiaronflage to the surfaces prepared 
 to receive them. To the latter category belong nearly 
 all the paintings in the Ambulatory of the Royal 
 Exchange, London. Each of the compartments has 
 been very carefully arranged with a view to secure dry- 
 ness and freedom from soluble saline matter. In front 
 of the wall itself has been fixed a slate slab slightly 
 inclined forwards at the top and having a ventilated air- 
 space behind it. Upon the slate the finished picture has 
 been attached (or maroufle) by means of a thick paste of 
 white-lead, oil, and copal-varnish, spread not only upon the 
 slate, but simultaneously upon the back of the canvas. It 
 may be affirmed that paintings so secured are free from all 
 risk of injury from the back. In an atmosphere like that 
 of London the surface of the painting must either be pro- 
 tected by glass or be periodically cleansed from deposits 
 of dust, soot, tarry mffiters, and the other impurities 
 which are described in Chapter XXV. of this handbook. 
 
 Several fresh materials have been recently employed as 
 painting-grounds. They are either patent or secret pre- 
 parations, dependent in general for their solidification upon 
 reactions between insoluble earthy and alkaline earthy 
 matters, such as china-clay, asbestos, .and compounds of 
 lime and magnesia, with solutions of such salts as mag- 
 nesium chloride, aluminium sulphate, and alum. There is 
 sometimes a lack of tenacity, and always a lack of tough- 
 ness in these mixtures, but some artists find them to pos- 
 sess precisely the texture and absorptive character they 
 desire in grounds not only for tempera, but also for oil- 
 
SLATE AND STONE 
 
 27 
 
 painting, and they may be spread on canvas as well as on 
 more rigid supports. There is some danger of want of 
 adhesion between the paint and the ground. It is also 
 necessary to make sure that the materials of the ground 
 do not affect sensitive pigments such as ultramarine. The 
 hardening or petrifying liquids which in most cases are 
 used in association with solid preparations to make the 
 grounds in question, are invariably acid to test-paper, 
 unlike the alkaline silicates described in Chapter IX. 
 
 Slate may be used as the ground for spirit-fresco and oil- 
 painting; but its freedom from crystals of iron-pyrites, 
 which present a brass-yellow colour, must be first ascer- 
 tained. The firm adhesion of any priming, or other layers 
 of oil-paint which may be applied subsequently, to slate 
 may be secured in the following manner. The slate is 
 slowly warmed in a water-oven, and thus becomes quite 
 dry. While still warm, it receives a very thin coat of 
 oil-copal varnish, largely diluted with turpentine or with 
 toluol, and applied warm. When this film is hard, the 
 painting may be carried out as in the ordinary way of 
 using oil-colours ; a priming of flake-white ground in oil 
 and mixed with a little copal- varnish and tqrpentine, may 
 be first applied, if desired. Terra-cotta and stone may be 
 treated in the same way, but, being more absorbent than 
 slate, the process recommended on p. 31 is preferable. 
 
 Owing to the presence of sulphuric acid in urban air 
 painting-grounds containing calcium carbonate arejliable 
 to an injurious change, the carbonate being turned in 
 part into the hydrous sulphate (gypsum) with a consider- 
 able increase of bulk. Then, through such expansion, 
 the surface-pigment becomes fissured and even detached. 
 It will be readily understood that grounds consisting 
 chiefly of sulphate of lime are not susceptible of such 
 
28 
 
 SLATE AND STONE 
 
 change. So, where damp can be excluded, they may be 
 used for mural paintings, ground flints or fine sand being 
 admixed with the burnt gypsum employed. The paint- 
 ings of the buried cities of Chinese Turkestan explored 
 by Sir Aurel Stein were executed on grounds of this kind 
 — grounds, that is, of nearly pure plaster of Paris. 
 
CHAPTER III 
 
 PANEL 
 
 ' Wood, as a backing for the painting-ground of works in 
 tempera and oil, presents some advantages over plaster and 
 canvas. Its chief merit lies, perhaps, in its comparative 
 immunity from mechanical injuries. The wood selected 
 must be hard, that its surface may resist blows and abra- 
 sion ; and it must not contain much resin, gum, colouring- 
 matter, or other ‘ extractives,’ as they are called, or else 
 discoloration of the painting-ground, or priming, may 
 occur. Wood grown in poor soils, in temperate climates, 
 and felled in winter, is the best. The Flemings used oak ; 
 the Italians white poplar. But oak often proves treacher- 
 ous, through irregular shrinkage; while poplar is too soft. 
 Italian painters employed, also, the wood of the stone 
 pine and chestnut. Leonardo da Vinci recommended 
 cypress, pear, and service-tree. Mahogany, which was 
 unknown to the old painters, is now generally employed. 
 Teak and cedar, and also American or black walnut, 
 deserve further trial. 
 
 The specific gravity of wood varies from 0-3 to i*3 ; the 
 lighter kinds contain large volumes of interstitial air. 
 The longitudinal contraction of wood is much less than 
 the transverse ; the distribution, form, and number of the 
 cracks in old panel-pictures is often to be traced to this 
 cause. 
 
 29 
 
30 
 
 PANEL 
 
 Wood contains (i) water, (2) ligno-cellulose, (3) extrac- 
 tives, (4) ash or mineral matter. The water, in thoroughly- 
 seasoned and air-dried wood, generally constitutes about 
 one-eighth part of its weight. The main constituent of 
 wood is the so-called ligno-cellulose, which is present to 
 the extent of from 75 to 85 per cent. It may be resolved 
 into two substances, which, for convenience’ sake, are here 
 called cellulose and lignose. The extractives belong to 
 two groups — one, soluble in alcohol and ether, consists 
 chiefly of resins ; the other, soluble in cold or hot water, 
 or else in very dilute alkalies, includes tannin, albu- 
 minoids, gum, and colouring-matters. The following 
 analyses of three kinds of wood in an air-dried state will 
 convey a fair idea of their constitution in 100 parts : 
 
 
 Mahogany 
 
 Oak 
 
 Pine 
 
 Water - 
 
 ■ I2'4 - 
 
 - 131 - 
 
 - 12 '9 
 
 Cellulose 
 
 - 490 - 
 
 - 395 ■ 
 
 - 533 
 
 Lignose ■ 
 
 - 276 - 
 
 ■ 34'3 - 
 
 - 28-2 
 
 Ash 
 
 I'l 
 
 I "2 - 
 
 • o ‘3 
 
 Resin 
 
 I'O - 
 
 - 0-9 - 
 
 I '6 
 
 Water-extract 
 
 - 8-9 - 
 
 - II'O - 
 
 - 37 
 
 The preparation of panels for painting requires much 
 time and trouble. The directions given by ancient authori- 
 ties are numerous, and not always accordant. One author 
 tells us to boil the wood ; another says we are to coat it 
 with mastic dissolved in twice-distilled turpentine and 
 mixed with white. Then it is to be treated twice or thrice 
 with spirits of wine, in which some white arsenic or corro- 
 sive sublimate has been dissolved ; coats of boiled oil, of 
 liquid-varnish * and white, and of verdigris and yellow are 
 subsequently mentioned. Probably the best method of 
 treating the harder woods intended for pictures is, after 
 
 * Made by boiling i part of sandarac in 3 parts of linseed-oil. 
 
PREPARATION OF PANELS 
 
 31 
 
 thorough seasoning, first of all to reduce the panel, by 
 planing and glass-papering both sides equally, to the desired 
 thickness. The panel is then soaked in water heated to 
 50° C., and then steamed. When dry, it receives a wash 
 on both sides of a solution of corrosive sublimate in 
 methylated spirit; it is again dried and seasoned in a warm 
 air-chamber. After these operations, the panel should not 
 require more than a slight rubbing with fine glass-paper, 
 in order to render both surfaces plane. For panels to be 
 used for oil-pictures, a priming is now applied, consisting 
 of white lead, a little copal-varnish, and drying linseed- 
 oil prepared by means of borate or oxalate of manganese. 
 Allow this coat, which is intended to fill up the cavities 
 and pores of the wood, to dry thoroughly, and then apply 
 another coat in the transverse direction; subsequent coats 
 should contain nothing but white lead (or other pigment) 
 and the drying oil. Repeated smoothings of each coat, 
 when hard, with fine pumice-powder are necessary; the 
 last coat may consist of zinc-white and drying-oil. Both 
 sides of the panel should be treated, as far as possible, 
 alike, so that they may be equally loaded, and equally 
 protected ; but the pumice-rubbings are, of course, not 
 required for the back of the panel. The object of priming 
 the back is twofold — the prevention of decay and of the 
 attacks of insects ; and the avoidance of that gradual cur- 
 vature whereby the protected front becomes convex, and 
 the unprotected back concave. This change occurs 
 through the slow loss of water from the back of the panel 
 — a loss which is generally accompanied by a loss of some 
 of the organic constituents of the wood through oxidation. 
 Here it may be mentioned that the original steaming of the 
 panel removes some of the extractives, and coagulates the 
 albuminoids present, which are generally the first cause 
 
32 
 
 PREPARATION OF PANELS 
 
 of decay. This decay is not primarily a chemical and 
 spontaneous one, but is commenced by certain minute 
 organisms, the growth and increase of which is, in part, 
 dependent upon the presence of available albuminoids, but 
 which involves also the destruction of some of the other 
 extractives, and even of the ligno-cellulose itself. The 
 corrosive sublimate employed helps to sterilize the wood, 
 and to prevent the inroads of animal organisms. 
 
 In order to avoid the disastrous effects of transverse 
 shrinkage upon compound panels, the old painters glued 
 linen cloth, or vellum, or parchment, or tinfoil to the front 
 surface of the wood, and on this they spread their gesso or 
 painting-ground. Gesso, made of plaster of Paris and size, 
 or of whitening and size, often lost its cohesion through 
 the decay of the binding material, and in consequence 
 became fragile and powdery ; the panel itself decayed, and 
 thus at last the linen or parchment remained as the best 
 preserved element of the composite structure. Were we 
 to avoid gesso and use lead-primed canvas glued to panel, 
 we should really be painting upon canvas backed or pro- 
 tected by wood. Panel is to be recommended for modern 
 workonly when a single piece of uniform and well-seasoned 
 wood of sufficient size can be secured. However, an 
 excellent cement for joining panels together was some- 
 times used with success. It consisted of lime and cheese, 
 both in fine powder, the latter having been grated, and 
 then washed with water. These materials intimately 
 mixed and then ground into a paste with water, yield a 
 tough and adhesive cement which becomes of rocky 
 hardness. 
 
 In order to prepare a panel for tempera work, it should 
 be treated in the manner above described, substituting 
 for the priming with oil, white lead and copal-varnish, a 
 
PREPARATION OF PANELS 
 
 33 
 
 mixture consisting partly of parchment-size, partly of 
 fish-glue, and whitening. 
 
 It is very probable that some of the hard, fine-grained 
 woods of British India and of North Borneo will furnish 
 excellent materials for picture-panels. At present experi- 
 ments in this direction cannot be regarded as more than 
 tentative and promising. 
 
 3 
 
CHAPTER IV 
 
 CANVAS 
 
 The usual, and probably the best fibre for the manu- 
 facture of canvas for painting is unbleached flax — that is, 
 linen ; hemp and cotton are decidedly inferior. The 
 material is woven in different ways, and with strands of 
 different degrees of fineness, so as to produce cloths of 
 various degrees of thickness and fineness, and having 
 several kinds of texture and surface. 
 
 The canvas is first treated with size or a solution of 
 glue ; this should be as free from colour as possible ; the 
 addition of honey to the size is undesirable. The priming 
 consists of two coats, the first containing whitening and 
 size, the second lead white and linseed oil. F uller primings 
 are often given where it is not desired to allow the texture 
 of the canvas to remain evident. Such primings are put 
 on alternately in directions at right angles to one another, 
 and are treated in the same way as the primings of panel. 
 If before the last priming be dry it be dusted with zinc 
 white, or if a very thin final priming of zinc white and 
 drying oil (free from lead) be given, the usual discoloration 
 of the canvas which occurs on keeping it, especially in the 
 dark, will be avoided. But such discoloration can always 
 be removed by leaving in contact with the priming a 
 piece of blotting-paper saturated with a solution of 
 
 34 
 
CANVAS 
 
 35 
 
 hydrogen peroxide : a slight warmth greatly hastens the 
 
 bleaching process. 
 
 Some painters in oil have employed with success a tem- 
 pera-priming on their canvases. This priming may be pre- 
 pared with a mixture of a strong, though elastic, size, with 
 whitening. A good composition of this sort may be made 
 by taking equal weights of fine whitening and of fine 
 plaster of Paris, which has been slaked in and soaked with 
 abundance of clean water, or of the preparation called 
 satin -finish, an artificial gypsum, used by paper-makers : 
 the warm size is incorporated with this mixture. When 
 the priming coats are dry the surface is dressed with a 
 layer of pure size, and allowed to harden thoroughly before 
 the picture is begun. 
 
 An ordinary primed canvas was examined with the 
 following results. The amount of moisture present was 
 5 ‘5 per cent, of its weight, the priming 25 per cent., and 
 the dry substance of the size 15. The dry fibre which 
 constituted the remaining constituent would weigh, there- 
 fore, about 54 parts. It was further found, with the same 
 canvas, in a dry heat of 100° C. (212° F.) continued for 
 twenty minutes, that a strip 20 inches long became shorter 
 by a quarter of an inch, changing in colour from a creamy 
 white to a pale buff. After immersion in boiling water 
 for twenty minutes a piece of this canvas 20 inches square 
 was found to have shrunk more than i inch in one direc- 
 tion, and in the other direction rather more than half an 
 inch. The piece was somewhat crinkled, and had become 
 yellow in patches. 
 
 A few remarks as to the bearing of the above observa- 
 tions on some of the phenomena presented by oil-paintings 
 on canvas may be here introduced. The water present in 
 canvas varies with the temperature, and in consequence 
 
36 
 
 PRESERVATION OF CANVAS 
 
 the dimensions of the canvas vary. As the contraction on 
 drying* and the expansion on taking up moisture are not 
 the same in the direction of the warp as in that of the woof, 
 there is an unequal strain upon the layers of paint upon the 
 surface. These may, tnerefore, become irregularly fissured, 
 and even loosened. The importance of selecting a canvas 
 so woven as to expand nearly equally in both directions is 
 evident, but the maintenance of a uniform temperature, and 
 of a suitable degree of moisture in the atmosphere where 
 pictures are hung, is also obvious. The absorption of 
 moisture by canvas occurs through the back, unless that 
 be also protected by paint. With the moisture deleterious 
 gases may also be absorbed, and these may easil}^ pass 
 through and affect the priming, even the picture. Canvas 
 protected by panel behind, or coated at the back with a 
 layer of white lead which has been ground up with starch 
 paste, escapes this injury in great measure, as the sulphur- 
 etted hydrogen, etc., are then intercepted. The colouring- 
 matter of the fibre and size of the canvas may move towards 
 the front and discolour the priming and even the picture. 
 An excess of damp and a high temperature are the chief 
 causes of this movement. When the first priming coat con- 
 tains size, though it may adhere firmly to the sized canvas, 
 it may not hold the subsequent oil-painting quite so tena- 
 ciously. Canvas is liable to accidental injuries from 
 mechanical causes: a double canvas mitigates the evil. The 
 elasticity of the priming may not suffice, when the canvas is 
 rolled up, to prevent cracking. A small addition of a non- 
 drying oil, such as almond or olive oil, to the linseed oil 
 used in the priming coats, proves useful, but such addition 
 
 * Note that this contraction occurs at ordinary temperatures, 
 and must be distinguished from the contraction caused by boiling 
 water. 
 
PRESERVATION OF CANVAS 
 
 37 
 
 should not exceed i part of non-drying oil to 20 of 
 drying oil. 
 
 There are two methods of preserving canvas from decay 
 by the application of solutions to the back after the priming 
 has been completed on the front. One of these solutions 
 contains corrosive sublimate (mercuric chloride) dissolved 
 in methylated spirit : a 5 per cent, solution is sufficiently 
 strong. The other solution is made by dissolving tannin 
 in methylated spirit. One or other of these solutions 
 should be applied once to the back of the canvas by means 
 of a broad stiff varnish-brush. When the spirit has 
 evaporated, the coating of white lead ground in starch 
 paste previously recommended in this chapter may be 
 applied. The two solutions we have named act by coagu- 
 lating some of the size in the canvas : the tannin turns it 
 into leather. Corrosive sublimate prevents the develop- 
 ment of mould or mildew, and is a good preservative 
 against the attack of animal organisms. 
 
 It may be observed that the employment of size in the 
 first preparation of canvas constitutes an element of weak- 
 ness. Many attempts have been made to substitute a less 
 hygroscopic and changeable substance. A plain collodion 
 containing a little ceresin (the hard paraffin from ozokerite, 
 or earth -wax) has been used for the purpose in question. 
 It is, however, very difficult to secure the adhesion to the 
 canvas of the film left behind when the collodion dries. 
 I have found that oil-paintings executed upon collodion- 
 ized canvas cannot be rolled up without damage. It 
 would probably be found that the formation of a viscose 
 film (see the account previously given of paper-sizing) 
 would prove a good substitute for ordinary size in the 
 first treatment of canvas. 
 
 H The majority of pictures nowadays are painted on 
 
38 
 
 PRESERVATION OF CANVAS 
 
 canvas, though it must be admitted that, especially in 
 respect of mechanical and chemical durability, it is a very 
 unsatisfactory material. Its light weight, its cheapness, 
 and the possibility of rolling up pictures painted upon it, 
 offer some advantages, no doubt, although the last charac- 
 teristic is of questionable value. On the whole, the draw- 
 backs to the use of canvas preponderate over its merits. 
 In this connexion special reference should be made to the 
 very marked alteration in dimension caused by damp (see 
 p. 36). This persistent working or movement of the ground 
 can be checked in the case of large collections gathered in 
 galleries duly equipped with the latest technical appliances 
 for the careful regulation of humidity and temperature. 
 But the case is different in private rooms where the move- 
 ment in question is practically unavoidable, and inevitably 
 leads to cracking in the course of time. This change is 
 still further promoted by the action of the oxygen in the 
 atmosphere, which attacks the painting both back and 
 front, and, by producing a gradual alteration in the binding 
 material, brings about a corresponding deterioration in 
 the adhesion and cohesion of the pigments. Moreover, 
 from the same cause, the linen or hemp fibre itself 
 becomes after a time so brittle that it is scarcely capable 
 of affording adequate support to the painted layer. When 
 it reaches such a state a picture must be ‘ relined ’ — i.e., 
 stretched on a fresh canvas. The painting itself may 
 thus prove more durable than the material base which 
 was designed to secure its durability. 
 
 ^ The stability of pictures painted on canvas is en- 
 hanced if the back be protected by a metallic coating, so 
 as to protect it in a measure, on that side at least, from the 
 inroads of oxygen. The simplest way to secure this result 
 is by coating the back with tinfoil, using to fix the metal 
 
PRESERVATION OF CANVAS 
 
 39 
 
 in position a strong solution of shellac* in spirits of wine. 
 In order to guard against the penetration of oxygen through 
 the accidental holes occurring in the tinfoil, a second 
 sheet of this metal may be added when the shellac solu- 
 tion has become dry. This treatment may be applied 
 generally to pictures painted on canvas, and virtually 
 doubles their span of life. 
 
 H But protection from mechanical injury is not ensured 
 by a thin coating of tinfoil. If that further protection be 
 desired the back of the painting may be lined with sheet 
 metal. According to the size of the picture, sheet copper 
 or brass, or even sheet iron coated with tin or zinc, may 
 be employed. Paintings executed on canvas may be 
 fastened to the sheet of metal by the shellac* cement 
 before named or with thick amber varnish. Thus the back 
 becomes protected both chemically and mechanically by 
 the same contrivance, and a high degree of durability is 
 thus assured for the picture. 
 
 H When it is a question of producing new pictures the 
 painting may be executed directly on metal. Such a 
 procedure applied to sheet copper was frequent with 
 Dutch miniaturists : the flawless condition of their works 
 justifies this method from the present point of view. Yet, 
 as this use of copper involves some risk that its green 
 and blue oxidation-products may give rise to discoloration, 
 a more appropriate painting-ground is offered by sheet 
 aluminium, which yields only colourless compounds. 
 Moreover, when aluminium is exposed to the atmosphere 
 there is formed on the surface a transparent and imper- 
 ceptible film of oxide which retains oil-colours very firmly. 
 Even on unprepared surfaces of aluminium it is possible 
 to paint very easily, for the metal possesses a peculiar 
 * Perhaps marouflage is preferable (see p. 26). 
 
40 
 
 LINOLEUM 
 
 ‘ tooth ’ in relation to the paint so that one can readily lay 
 on successive coats of paint, stroke by stroke. Some 
 years ago I covered a piece of sheet aluminium with a 
 coating of oil-paint and exposed it in the laboratory to all 
 the accidents of the place. The paint remains sound to 
 this day and shows no tendency to crack or peel. A 
 sketch executed on strong sheet aluminium stands in a 
 greenhouse, where it receives all available sunshine and is 
 exposed to great variations of temperature : after exposure 
 during six months of spring and summer it showed no 
 signs of change for the worse. There is therefore good 
 reason for contending that in sheet aluminium we 
 possess an ideal painting - ground, especially for work 
 in oils. 
 
 U Another material which seems to lend itself particu- 
 larly to decorative and monumental painting is linoleum. 
 This consists of a very strong fabric coated with a thick 
 layer of oxidized linseed oil mixed with cork-raspings and 
 other materials. It thus bears some resemblance to canvas 
 which has been primed for the reception of oil-colours, but 
 differs in its greater solidity and in the elastic substances 
 which it contains. The fact that the body of linoleum 
 consists mainly of the same substance that forms the bind- 
 ing material in ordinary oil-painting sufficiently guarantees 
 permanent union between picture and ground. From 
 another point of view the massive nature of the material 
 almost completely obviates the risk of mechanical injury, 
 and affords at the same time complete protection from the 
 attacks of air and damp at the back. If the brown colour 
 be not an objection, the surface can be used just as it is 
 as a painting-ground ; in this case the various rough and 
 smooth sorts of linoleum provide an agreeable choice of 
 surfaces from the artistic standpoint. But it will be 
 
LINOLEUM 
 
 4« 
 
 found better to lay on a thin coat of white oil-paint, 
 especially in the case of pictures intended to present a 
 bright general tone. Or a white pigment may be incor- 
 porated with the mass of the linoleum itself and so the 
 brilliancy of the applied colours may be enhanced. As 
 linoleum is manufactured several yards wide, it is possible 
 to paint very large pictures on a single piece, so that this 
 material seems more suitable for monumental or large 
 decorative works. It should not be fi.xed directly to the 
 wall, but attached to a metal framework covered with 
 galvanized iron wire netting and erected at a small dis- 
 tance from the wall ; the danger of injury from damp or 
 fracture is thus avoided. 
 
 With reference to the two materials, linoleum and sheet 
 aluminium, recommended in the preceding paragraphs for 
 use as painting-grounds, a few further observations may 
 be advisable. The variety of linoleum in which the 
 canvas-backing is omitted — solid linoleum — is not suit- 
 able for the purpose under discussion, for there is some 
 risk when large pieces are used of its sagging, and even 
 splitting, after the lapse of some time. And the experi- 
 ence of coach-builders is not altogether in favour of alu- 
 minium for the reception of a coating of oil-paint. In 
 some instances, at all events, there are signs of the dis- 
 integration of the metal and consequent cracking of the 
 superimposed layers of pigment. Possibly these draw- 
 backs may not occur where the painted surfaces are not 
 exposed to the external atmosphere. And it must be 
 remembered that the sheet aluminium of commerce varies 
 somewhat in its composition and properties. 
 
 ‘ Willesden canvas ’ appears to resist the attack of 
 moisture and of animal organisms : the copper-compounds 
 which it contains do not interfere with its use as a painting- 
 
42 
 
 ■ WILLESDEN CANVAS’ 
 
 ground, but the absence of soluble salts (chiefly sulphates) 
 from it should be ascertained. This test is easily made by 
 soaking a piece of the canvas weighing 50 grains in dis- 
 tilled water overnight, pouring off the clear liquid next 
 morning, heating it to boiling, and adding a few drops of 
 barium chloride solution and of dilute nitric acid. If a 
 distinct precipitate be formed the canvas cannot be em- 
 ployed safely, but a mere cloudiness may be disregarded. 
 It is just as well to test the watery extract for free acid by 
 means of litmus paper, because an attempt has been made 
 to remove the green colour of Willesden canvas by a bath 
 of dilute sulphuric acid, the presence of which is, on all 
 accounts, to be avoided. ‘ Willesden paper ’ possesses 
 properties similar to those of Willesden canvas, and may 
 sometimes be found serviceable for work in oil-colours. 
 
PART II 
 
 VEHICLES AND VARNISHES 
 
 Chapter V. — Oils. Chapter VI. — Resins, Waxes, Paraffin-Waxes. 
 Chapter VII.— Yolk and White of Egg, Size, Glue. Chapter VIII. 
 — Gums, Glycerin, Honey. Chapter IX. — Water-Glass, Lime- 
 and Baryta-Water. Chapter X. — Solvents and Diluents. Chap- 
 ter XI. — Siccatives and Dryers. Chapter XII. — Varnishes and 
 Oleo-Resinous Vehicles. 
 

CHAPTER V 
 
 OILS 
 
 The common usage of the term ‘oil ’ is wider and less 
 definite than that sanctioned by chemists. We must 
 exclude from the category of true oils petroleum and 
 the liquid paraffins, spirit of turpentine and the volatile 
 essences of plants, the hydrocarbons of coal naphtha, as 
 well as a number of other liquids which present certain 
 superficial resemblances to the oils proper. Fats, how- 
 ever, belong to the same group, their solidity at ordinary 
 temperatures being, so to speak, an accidental rather than 
 an essential difference. 
 
 The true oils are often called fixed oils, for they cannot 
 be boiled and distilled without change, thus differing from 
 really volatile liquids. They are glycerides — that is, com- 
 pounds from which glycerin, on the one hand, and fatty 
 acids, on the other, are obtainable. These glycerides are 
 named after the fatty acids which they yield. Thus olein 
 is the glyceride of oleic acid, linolein the glyceride of lino- 
 leic acid. In reality three kinds or varieties of glycerides 
 of each fatty acid are possible, but the oils used by painters 
 consist almost entirely of one of these kinds. The forma- 
 tion of one of these glycerides may be expressed in words 
 thus : One molecule of glycerin, reacting with three mole- 
 cules of a fatty acid, yields one molecule of the glyceride 
 
 45 
 
46 
 
 DRYING OILS 
 
 in question and three molecules of water. Conversely, 
 under other conditions, one molecule of a glyceride, re- 
 acting with three molecules of water, produces one mole- 
 cule of glycerin and three molecules of fatty acid. If, in 
 this last reaction, we substitute for the water three mole- 
 cules of an alkali, such as potash, we obtain glycerin as 
 before ; but, in lieu of the free fatty acid, we find that an 
 alkaline salt of the fatty acid has been formed — such salt 
 is a soap. Alkaline soaps, namely, those of potash, soda, 
 ammonia, are soluble in water, which fatty acids — at any 
 rate, those with which we are here concerned — are not. 
 There are, however, other soaps which are insoluble in 
 water, namely, the lime, lead, copper, and many similar 
 metallic salts of fatty acids. 
 
 Oils, though insoluble in water, are easily soluble in 
 spirit of turpentine and other volatile plant essences ; 
 in benzene, chloroform, and liquid paraffins ; they are, 
 in fact, miscible in all proportions with these liquids. 
 There are other liquids in which the oils are less soluble, 
 such as alcohol, acetone, and glacial acetic acid. 
 
 Oils are divisible into two classes, one of which includes 
 those which dry up and harden, forming a kind of elastic 
 varnish, by exposure to the air. The oils of the other 
 class do not harden, but become sticky, and rancid in 
 smell ; these oils, however, if submitted to the tempera- 
 ture of boiling water for some time, do in some instances 
 become dry and hard, but the varnish they yield under 
 these circumstances is dark in colour and brittle ; it has 
 been suggested that some of these should be grouped to- 
 gether in a third class as ‘semi-drying’ oils. The painter’s 
 concern is almost exclusively confined to the oils of the 
 first group, generally known as drying oils. To the most 
 important of these attention will be directed presently. 
 
LINSEED OIL 
 
 47 
 
 but the general methods of extracting them first demand 
 a few words of explanation. There are twO' different pro- 
 cesses in use. In one of these, which has been practised 
 widely from very early times, the oil is obtained by 
 pressure; in the other process, invented some seventy 
 years ago, the oil is extracted by means of an appropriate 
 solvent. We may dismiss this latter process almost 
 summarily, for the product which it yields, though much 
 greater in quantity, is decidedly inferior to that obtained 
 by pressure. It is less fluid, and contains a larger propor- 
 tion of solid fats. The solvent commonly employed to 
 dissolve out the oil from oil-yielding materials is carbon 
 bisulphide (CSg), a compound of carbon and sulphur, 
 which may be prepared cheaply by passing the vapour of 
 sulphur through red-hot charcoal. Of the pressure-process 
 for obtaining fixed oils there are two modifications. In 
 the more usually adopted of these, the oily seed or other 
 material is first heated, and then pressed while still hot ; 
 in the other modification the pressure is applied to the 
 cold seed, etc. Heat and pressure give a more abundant 
 yield of oil, but the product is less pure and less well fitted 
 for use in painting. The bulk of the oils of commerce are 
 thus obtained. Cold-pressed oils remain clear in cold 
 weather, are more fluid than hot-pressed oils, and con- 
 tain a smaller proportion of solid fats and of free fatty 
 acids. 
 
 The most important drying oils are those of linseed, 
 poppy-seed, and walnut kernels ; others are obtained 
 from niger-seed, sunflower-seed, and hemp-seed. The 
 first place is due to linseed oil. 
 
 Linseed oil is obtained from the seed of the common 
 cultivated flax (Linum usitatissiimmi). Linseed varies in 
 size and colour. The usual colours are a purplish-brown 
 
48 
 
 LINSEED OIL 
 
 and a reddish-brown, but there is a nearly white sort — a 
 mere sport or variety — which may be said to be straw- 
 coloured. It is grown along with the brown variety in 
 some parts of the North-West Provinces of India, par 
 ticularly in Nagpur, but no pains are taken to keep the 
 strain pure. Through the kind offices of the Director of 
 the Royal Gardens, Kew, the Government of India were 
 good enough to obtain a specially pure sample of some 
 hundredweights of white Nagpur linseed, and to place it 
 at my disposal. Attempts to grow it for seed in this 
 country and in Belgium failed, but a large quantity of 
 oil was expressed for trial and analysis. Messrs. Bell 
 and Co., of 225, Oxford Street, obtained several gallons 
 of oil by cold-pressure ; many artists have expressed 
 their approval of the product. One advantage of this 
 white seed is the ease with which the purity of a sample 
 may be recognised by the eye, any accompanying weed- 
 seeds differing widely in colour from the white linseed. 
 The skin of the seed is, moreover, thin, the cold-drawn 
 oil is nearly colourless, and the seed is particularly rich 
 in oil, containing no less than 45 per cent, of its weight, 
 although, of course, much less than this proportion is 
 obtainable by cold-pressure. In a hand-press about 
 25 per cent, was the average yield. Of the common or 
 brown linseed our chief supplies come from Russia and 
 India. The Russian seed is generally finer than the 
 East Indian ; it is, moreover, imported in a less mixed 
 and impure condition. By screening, the greater part of 
 the impurities are or may be removed, but it is sold on a 
 basis of 4 per cent, impurity. The impurities consist of 
 dirt, other oil-seeds, such as mustard, rape, and gold of 
 pleasure, and non-oily weed-seeds. The presence of the 
 last-named, though it reduces the yield, is not otherwise 
 
LINSEED OIL 
 
 49 
 
 objectionable,* but the same remark does not apply to 
 the foreign oil-seeds. Most of these contain non-drying 
 oils, which mingle with the linseed oil when the sample 
 is pressed and reduce its siccative character. Much 
 linseed now comes from the Argentine, Canada, and the 
 United States, as well as from India and Russia. 
 
 The percentage of oil in linseed varies between 28 and 
 45 : by cold-pressure 20 per cent, is the average yield ; by 
 hot-pressure, 27 per cent. ; by extraction with carbon 
 disulphide, 33 per cent. The linseed oil in common use 
 by artists is hot-pressed oil, and is very rarely, if ever, 
 obtained from absolutely pure seed. The seed should be 
 kept three months before it is pressed. The expressed 
 oil should be exposed to light in covered glass vessels or 
 tanks, and kept at a temperature of 212° F. for some 
 time. It thus loses colour and becomes clear, a slimy 
 deposit containing mucilage, albuminoid matter, and 
 traces of a cyanogenetic glucoside, being formed. When 
 thus bleached and clarified, the oil should be preserved 
 in corked bottles filled quite full ; the longer it is kept, the 
 better it becomes for painting, provided the access of air 
 is prevented. The specific gravity of good linseed oil 
 varies very little. At 60° F. (i5‘6° C.) it is '935 ; a bottle 
 which will hold 1,000 grains of water at this temperature 
 will therefore hold but 935 grains of linseed oil. It 
 expands considerably with heat, its specific gravity at 
 50° C. being -913 only. One part of linseed oil requires 
 36 parts of cold absolute alcohol for solution, but only 
 4 parts of boiling alcohol. It may be purified by solution 
 in boiling alcohol or in petroleum ether. Other methods of 
 purification are generally employed. Amongst these may 
 
 * Occasionally these weed-seeds give up, under pressure, certain 
 matters which deepen the colour of the expressed oil somewhat. 
 
 4 
 
50 
 
 LINSEED OIL 
 
 be named the following : Filtration through felt or carded 
 cotton and charcoal, and then through pyrolusite ; con- 
 tact for some weeks with 3 per cent, of a mixture of 
 equal parts of kaolin and aluminium hydrate, both these 
 compounds having been previously dried at about 50° C.; 
 agitation with a solution of common salt, followed by 
 washing w th water, and drying by a heat of 220° F. ; 
 treatment with one four-hundredth part of oil of vitriol, 
 addition of hot water, washing, and drying. Various 
 other processes and reagents have been employed for 
 purifying and bleaching linseed oil. Aqueous solutions 
 of sulphurous acid, green vitriol, potassium permangan- 
 ate, potassium bichromate, and peroxide of hydrogen 
 may be included in this list. The addition of 1 per cent, 
 of oil of turpentine to the oil, and then passing a mixture 
 of air and steam through it, has also been tried. What- 
 ever process be adopted, no acid, saline matter, or 
 moisture must be left in the oil. The general and usual 
 result of all the very different kinds of treatment to 
 which linseed oil is subjected, in the above-named and in 
 many other processes, seems to be the more or less com- 
 plete removal of impurities. The effect on the properties 
 of the purified oil is chiefly seen in its greatly increased 
 rate of absorbing oxygen and consequent hardening. 
 
 The chemical composition of linseed oil may now 
 engage our attention. Its ultimate analysis shows it to 
 vary according to the method of extraction adopted, cold- 
 pressed oil containing about 78 per cent, of carbon, 1 1 per 
 cent, of hydrogen, and ii per cent, of oxygen ; while the 
 hot-pressed oil contains nearly 3 per cent, less carbon, 
 and nearly 3 per cent, more oxygen — linseed oil, extracted 
 by carbon disulphide, is still poorer in carbon, and richer 
 in oxygen. It appears that linseed oil consists chiefly of 
 
LINSEED OIL 
 
 51 
 
 three glycerides, called, respectively, linolein, linolenin, 
 and olein. A small, but variable, amount of free fatty 
 acids, such as palmitic and arachidic, is also present. 
 The empirical formulae of the three fatty acids of the 
 above-named glycerides are, respectively : 
 
 Linolein, which is present in linseed oil to the extent of 
 about 20 per cent., is the glyceride of linoleic acid, and 
 has the formula (CjgH3j^O)g,C3H5,03 ; or, as it may be 
 written, C3H5(0,C^8H3i0)3. The relation of this glycer- 
 ide to glycerin may be seen when the latter body is ex- 
 pressed by the formula, C3H5(OH)g. It is probable that 
 the other main constituent of the oil — linolenin — is a 
 similarly constituted glyceride, and that it closely resem- 
 bles linolein in physical and chemical properties. When 
 loo parts of linseed oil are saponified by an alkali, they 
 yield from 9-4 to 10 parts of glycerin. 
 
 The most important chemical property of linseed oil, 
 from a painter’s standpoint, is its behaviour with oxygen. 
 Under certain circumstances, it absorbs oxygen to the 
 extent of 13 or even 14 per cent, of its weight, becoming 
 converted into a mixture of substances for which it is con- 
 venient to retain the old name linoxine. Linoxine is solid, 
 and not liquid ; it is far less soluble than linseed oil in any 
 solvent, and in many liquids it is insoluble. Linoxine 
 is, moreover, denser than the original oil; 100 grains of 
 linseed oil produce about 109 or no grains of linoxine. 
 Notwithstanding the greater density of linoxine, when 
 compared with the original oil, its formation is attended by 
 a considerable expansion. In consequence, a layer of raw 
 
 Linolenic Acid 
 Linoleic - 
 Oleic 
 
 CjaHanOo. 
 
52 
 
 LINSEED OIL 
 
 linseed oil spread upon glass becomes wrinkled during the 
 drying and oxidizing process. During the oxidation of 
 linseed oil, the small quantity of olein it contains remains 
 unoxidized — its presence confers elasticity upon the pro- 
 duct. 
 
 H The incidents associated with the hardening or solidi- 
 fying of drying oils have always been an attractive study, 
 but it is only through the chemico-physical researches of 
 recent years that their true nature has been made clear. 
 The most important points will now be briefly explained. 
 This hardening depends, as before stated, on a process of 
 oxidation— that is, on the absorption of free oxygen from 
 the atmosphere. During this process carbon dioxide and 
 other volatile organic compounds are formed and given 
 off, while simultaneously there are produced solid, non- 
 volatile bodies which constitute the dried and hardened 
 oil. These solids then, in their turn, by a further and 
 very slow oxidation, yield other volatile products. While 
 in the first stage, the gain in weight of the oil, due to the 
 absorption of oxygen, far more than compensates for the 
 loss which arises from the escape of volatile matters, in 
 the second stage there is a distinct diminution in bulk and 
 in weight, while the residue acquires a deepening brown 
 hue. This last phenomenon, however, does not seem to 
 be inevitable, for it occurs when light is excluded ; and 
 this yellowing or embrowning of the hardened oil may 
 often be remedied by subsequent exposure to light, 
 although it does occur in many pictures which hang on 
 well-lighted walls. As this change does not take place 
 always, it seems reasonable to conclude that, putting 
 aside discoloration through the deposition of dirt and 
 sooty matters, it must arise by an alteration in something 
 present which is not oil. Indeed, it seems to be trace- 
 
LINSEED OIL 
 
 53 
 
 able to the presence of lead introduced into the oil used 
 as a siccative or dryer. As equally efficient dryers may 
 be prepared without the employment of lead compounds, 
 it seems desirable that these should be rejected. 
 
 H If a thin layer of linseed oil be put into a bottle full 
 of air and provided with a contrivance for observing the 
 absorption of the oxygen, it will be seen that at first the 
 oxidation proceeds very slowly — this is Period I. The 
 absorption then becomes more and more rapid till it 
 reaches a maximum — this constitutes Period II. Once 
 more the absorption becomes slow — this is Period III. 
 It is only during this last period that the oil loses its 
 fluidity, becoming first viscous and finally solid. Oil 
 examined at the close of the second period or stage dries 
 quickly, and is often called varnish. 
 
 U The processes just described, if carried out in the 
 dark, occupy some weeks, but they may be hastened by 
 means of several different agents. For instance, by heat — 
 that is, by raising the temperature. It is a general law that 
 the rate of chemical action increases proportionately with 
 rise in temperature. Thus the higher the temperature at 
 which the linseed oil absorbs oxygen, the more rapid 
 does the action become. It is on this fact that the very 
 old process of varnish-making by boiling raw linseed oil 
 rests. The oil, heated in open vessels up to a fairly high 
 temperature (200° C. or more) absorbs oxygen rapidly, 
 while at the same time, principally through the overheating 
 of the sides of the vessels used, some brown decomposition 
 products, which give the varnish a dark colour, are formed. 
 If the heating be stopped when the oil is in its second 
 stage of oxidation, a product is obtained which, though 
 still fluid, has acquired the property of absorbing with 
 great rapidity the small amount of oxygen still needed to 
 
54 
 
 LINSEED OIL 
 
 render it solid. Oil thus treated dries, therefore, much 
 more quickly than raw oil, and is used when quick drying 
 is of importance ; it is known as linseed oil varnish. 
 However, along with the advantage of quick drying, its 
 dark colour constitutes a drawback. But this discolora- 
 tion, being due to excessive and unequal heating, can be 
 avoided by conducting the operation of limited oxidizing 
 at a moderately high temperature (say ioo° to 150° C.). 
 It may, too, be hastened by passing a stream of air 
 through the heated oil. In this way, not only is discolora- 
 tion avoided, but the oil is actually bleached, and a nearly 
 colourless varnish produced. If the treatment be stopped 
 at the right moment, a sufficiently fluid varnish is ob- 
 tained, while if the process is carried farther, viscous and 
 almost solid products are formed. Naturally this mode 
 of preparing the varnish takes more time, owing to the 
 lower temperature employed, than the old boiling process, 
 but the product is much better. 
 
 H The second agent which may be employed to hasten 
 the oxidation of oil is light, which acts energetically. On 
 this fact depends the process of transforming linseed oil 
 into varnish by exposing it to sunshine in shallow vessels, 
 so as to facilitate the access of light, care being taken to 
 exclude dust, while the oil is occasionally stirred in order 
 to prevent a skin being formed on the surface through a 
 superficial oxidation. If this skin be produced, it hinders 
 the access of oxygen to the oil beneath, while the product 
 is not homogeneous. It is on this action of light that a 
 common practice of artists is based, the placing a picture 
 in the sun that it may dry quickly. The converse prac- 
 tice, however, of keeping paintings soft and moist during 
 the time when the artist is not working upon them, by 
 excluding light from them, is less known. The best 
 
LINSEED OIL 
 
 55 
 
 means of securing this object consists in arranging a 
 sheet of aluminium in front of the picture so as not to 
 touch the surface ; it is light in weight, and rigid. 
 
 H A third agency which may be used to hasten the oxi- 
 dation of a drying oil is to be found in the presence of one 
 or other of a group of substances, the mere presence of 
 which when the oil is still in its first stage may reduce the 
 time required to reach a condition of solidity from days 
 to hours. Some compounds of lead and manganese are 
 the best known of these active materials. Innumerable 
 old recipes for varnish boiling and for preparing varnish 
 in the cold are based on the solution in oil, in one way or 
 another, of certain compounds of the metals just named. 
 Since it is only within comparatively recent times that the 
 conditions, under which the oxidation of drying oils pro- 
 ceeds, have been clearly understood, it is to be expected that 
 these old recipes should prescribe a number of superfluous 
 and, indeed, actually injurious operations. In order to 
 obtain a quickly drying oil it is requisite merely to dissolve 
 a suitable and generally a very small quantity of one of 
 these ‘ accelerators ’ in the oil, and to carry the oxidation 
 process no farther than to the second stage or period. 
 Lead, which has been longest known as a ‘ dryer,’ is best 
 used in the form of its linoleate or resinate, as these com- 
 pounds dissolve in oil, especially when warmed. Strong 
 solutions of this kind, generally dark in colour, are put on 
 the market as siccatives, and added by artists to their 
 oil-paints on the palette in a haphazard manner. Such is 
 an injudicious procedure and may have an injurious effect 
 on the durability of the picture. For when thus added 
 the dryer is more or less unevenly distributed, not only 
 throughout the picture as a whole, but even in different 
 portions of the same paint. Thus there ensues uneven 
 
56 
 
 LINSEED OIL 
 
 drying and the formation of cracks is promoted. It is 
 better to add the proper quantity of the dryer to the 
 paints in the first instance. 
 
 During recent years many improved methods of treating 
 raw linseed oil have been devised. The ‘ boiling ’ has 
 been carried out in aluminium vessels in lieu of those of 
 iron, which become much corroded through the action of 
 the free acids of the oil upon this metal. The iron com- 
 pounds thus formed are undesirable ingredients of the 
 boiled oil. Then, again, superheated steam has taken 
 the place of direct fire-heat in treating the oil, which is 
 mechanically stirred while a current of oxygen or of air 
 is at the same time sent through the liquid. In yet an 
 other process, the raw oil in the form of spray and heated 
 is brought into intimate contact with a stream of heated 
 air. There exists also an improved method of preparing 
 a drying oil by the agency of light. As it has been found 
 that sunlight acts mainly in virtue of its ultra-violet or 
 actinic rays, an artificial light, singularly rich in such 
 rays, has been substituted for the light of the sun. This 
 is found in the mercury lamp, in which an electric spark, 
 passing between two mercury poles enclosed in a quartz- 
 glass tube, originates a peculiar light of high activity. A 
 battery of such lamps is so arranged that their radiation 
 impinges upon the oil, which is at the same time kept at 
 a temperature of 8o° C., while a finely divided stream of 
 oxygen gas is forced through it. The pale, quickly drying 
 oil thus produced is said to possess the property of drying 
 uniformly throughout without the production of a skin on 
 the surface. 
 
 The changes which occur during the oxidation of 
 linseed oil, as described in the preceding paragraphs, 
 are, as will have been seen, complex ; but there is 
 some formic acid formed, so that the product is sour — 
 
LINSEED OIL 
 
 57 
 
 carbonic acid gas and water are also produced. It 
 has been shown that there are many ways of bringing 
 about this oxidation. A very common one is to heat 
 the oil to a temperature of at least ioo° C., and to blow 
 air through it, or air containing ozone. Many sub- 
 stances favour the absorption of oxygen by linseed oil 
 under the above conditions. Amongst these may be 
 named manganese dioxide, borate, oxalate, resinate, or 
 linoleate ; cobalt resinate •, red-lead, litharge, or lead ace- 
 tate ; green vitriol, iron in the presence of water, etc. It 
 is better to use one of the manganese compounds, and an 
 excellent result is obtained with the borate of this metal. 
 On the small scale, the operation may be thus carried out : 
 Tie up in a small piece of muslin 20 grains of dry and 
 powdered manganese borate. Suspend the bag in a glass 
 quart flask, into which a pint of linseed oil has been 
 placed, so that the bag is just covered by the oil ; lightly 
 plug the mouth of the flask with some carded cotton. 
 Stand the flask in a warm place, where the temperature 
 does not fall below 40° C., nor rise above 100° C. In a 
 fortnight’s time, the oil will have become strongly sicca- 
 tive, so that when it is spread in a thin layer on glass, or 
 paper, it will dry up to a tough varnish within twenty- 
 four hours. If the oil and manganese borate be main- 
 tained, by means of a water-bath, at a temperature of 
 100° C., the change will occupy less time, and the product 
 will be just as good ; but it is not advisable to boil the oil 
 with the borate, although the change may be thus effected 
 in less than an hour. The oxidation may be further 
 hastened by occasionally blowing a little air into the oil 
 through a glass tube kept permanently in the flask. When 
 the rapid- drying quality of the oil has been proved, by 
 experiments made with a drop or two withdrawn for that 
 purpose, the flask is allowed to get cold, and the oil 
 
58 
 
 SICCATIVE LINSEED OIL 
 
 poured into a corked glass bottle, so as to fill it. In the 
 course of the next few weeks, a slight deposit will be 
 formed in the bottle ; when this has occurred, the clear oil 
 should be poured off into other bottles, and preserved for 
 use. According to the purpose for which the prepared oil 
 is to be afterwards used, the treatment with the borate must 
 be more or less prolonged ; but care should be taken not to 
 carry it so far that the oil becomes ropy or viscous, unless 
 it is intended to make linseed oil varnish. In the subse- 
 quent chapters of this book we shall often refer to this 
 siccative linseed oil as ‘manganese oil.’ To the above 
 directions for preparing this oil may be added the remark 
 that if the operations be conducted in a strong light, the 
 oil will be bleached, as well as rendered highly siccative. 
 No satisfactory explanation of the action of the manganese 
 borate (and of many other substances used for the same 
 purpose) has been offered. But it seems probable that 
 the absorption of oxygen by the oil is favoured by the 
 removal of certain impurities, and this the borate of 
 manganese may effect : it has been suggested that the 
 action is in part catalytic. 
 
 The increasing specific gravity of the ‘ manganese oil,’ 
 as the process is prolonged, may be used as an indication 
 of the point at which the heating may be discontinued. 
 When the oil has acquired a specific gravity of •945, it is 
 generally sufficiently siccative for grinding with non- 
 drying pigments, and as an addition to certain varnishes. 
 For these purposes it may even attain a specific gravity 
 of ’96 ; but when it shows ’99, or '995, it constitutes a 
 thick varnish, which needs dilution with a suitable 
 solvent. It may be well to remark here that the various 
 processes for rendering linseed oil more rapidly-drying 
 may be regarded as resulting in two actions, partly con- 
 
TESTING LINSEED OIL 
 
 59 
 
 secutive, partly simultaneous. The first action, if it 
 could, or did, occur alone, would yield a purified oil apt 
 to dry quickly, but very slightly altered in composition ; 
 the second action is more profound, and gives rise to a 
 thickened, denser product, in which the drying process 
 has already commenced. In practice, the first action 
 occurs almost, but not quite, uncomplicated with the 
 second, when linseed oil is warmed with borate of man- 
 ganese in a vessel to which atmospheric air has very 
 limited access ; the second action, which is of necessity 
 associated with the first, takes place when a stream of 
 air is blown through warm linseed oil, even in the absence 
 of manganese borate, but far more quickly in its presence. 
 
 The superiority of the highly siccative oils prepared 
 with borate of manganese (or the oxalate, resinate, or 
 linoleate) over those in the manufacture of which lead 
 compounds are used, is so decided that all description of 
 the older and less satisfactory methods will be omitted. 
 But there are two other ways of rendering linseed oil 
 more siccative, which deserve a passing notice. Into a 
 clear-glass quart-bottle an ounce of distilled water and 
 an ounce of clean iron brads are first placed, and then 
 one pint of raw linseed oil, agitation being avoided. The 
 next day, the bottle, placed in as strong a light as possible, 
 is to be shaken frequently, the shaking being repeated 
 every day, until a drop of the oil, when tested, shows a 
 sufficient degree of drying character. Finally, the liquid 
 part of the mixture in the bottle is poured into a separating- 
 funnel, and the aqueous part allowed to run away. The 
 oil may require drying and filtration. In another similar 
 process green vitriol is substituted for the metallic iron, 
 the other directions being identical. 
 
 The most important property of linseed oil, and some 
 
6o 
 
 TESTING LINSEED OIL 
 
 methods for the further development of this property 
 having been discussed, we may now describe the remain- 
 ing characters of this oil. The cold-pressed oil is very 
 pale straw-coloured, or pale yellow, with occasionally a 
 faint greenish hue ; the hot-pressed oil is a darker yellow 
 or brown. The cold-pressed oil, when considerably 
 cooled, remains clear long after the hot-pressed oil has 
 become turbid. The fluidity of the oil is less than that 
 of water in the ratio of i : lo. The hot-pressed oil has a 
 much stronger taste and odour than the cold-pressed oil. 
 
 The adulteration of linseed oil with other oils may be 
 recognised with more or less precision by means of 
 several different tests. Most of these tests (oil of vitriol 
 test, nitric acid test, etc.) produce reactions in which the 
 oil and the acid acquire varied colours characteristic of 
 different oils. These tests must be applied under exactly 
 similar conditions of temperature, agitation, lapse of time, 
 strength of acid, etc. ; and even then, unless the experi- 
 menter is well- versed in the work, the indications obtained 
 are sometimes perplexing and difficult to interpret. The 
 amount of iodine absorbed by a given w'eight of linseed 
 oil is also a measure of its drying power as shown in its 
 capacity for absorbing oxygen. This ‘ iodine- value,’ as 
 it is called, is the amount of iodine absorbed from 
 chloride of iodine in the presence of glacial acetic acid, 
 by loo grammes of oil. The iodine-value for linseed oil 
 is somewhere near 200 ; the figures for walnut oil and 
 poppy oil are always lower, while the semi-drying and 
 the non-drying oils may not show half this value, and 
 these are the oils likely to be used as adulterants. But 
 such quantitative determinations can be properly per- 
 formed only by the skilled chemist. There is another 
 test known as Valenta’s acetic acid test, which has been 
 
POPPY OIL 
 
 6i 
 
 used for the detection of non-drying oils in linseed oil. 
 It is based upon the less solubility of the former oils in 
 glacial acetic acid. It is, however, not easy to secure 
 constant results with this test. Determinations of 
 volatile matters, of unsaponifiable substances, and of 
 insoluble bromine derivatives, afford valuable indications 
 as to the purity of samples of this oil. 
 
 The specific gravity of linseed oil also affords a valuable 
 means of testing its purity. At iy 6 ° C. (6o° F.) it is 
 denser than most other vegetable oils : 
 
 Name of Oil Spec. Grav. 
 Linseed - - '935 
 
 Gold-of- Pleasure- ‘931 
 Hemp-seed - - -930 
 
 *Cotton-seed- - ‘930 
 
 Walnut - - -927 
 
 The four oils marked with an a: 
 
 Name of Oil Spec. Grav. 
 Poppy-seed - - '926 
 
 Sunflower-seed - '925 
 
 ♦Black Mustard-seed- '921 
 
 ♦Ground-nut - - '918 
 
 *Colza-seed - - '914 
 
 risk are practically non-drying. 
 
 Poppy Oil . — This oil is obtained from the seed of the 
 opium-poppy, Papavev somniferum. It is of a very pale 
 straw-colour, often almost colourless, and is nearly free 
 from taste and smell. By filtration through hot animal 
 charcoal it may be completely decolourized. If the fluidity 
 of water be represented by 1,000, that of poppy oil at 
 15-6° C. is 74. Its specific gravity at the same tempera- 
 ture is ’926. Its chemical composition is near that of lin- 
 seed oil ; it contains the same three glycerides, but in 
 different proportions, for it is mainly made up of linolein 
 and olein. The large quantity present of olein causes 
 poppy oil to be a less rapidly drying oil than linseed. 
 Wolffen, in 1640, stated that poppy oil dries throughout in 
 four or five days, while linseed oil forms a pellicle upon the 
 surface. Joseph Petitot, writing from Geneva under date 
 January 14, 1644, stated that umber is a siccative for 
 
62 
 
 NUT OIL 
 
 poppy oil. Poppy oil was introduced into painting in the 
 beginning of the seventeenth century, after linseed and nut 
 oil. Later on in the same century the Dutch painters ac- 
 quired greater confidence in this more slowly drying oil, 
 employing it not only in the painting process, but also for 
 grinding their pigments, especially whites, blues, and pale 
 tints. 
 
 Nut Oil. — This oil is obtained from the kernels of the 
 common walnut, /i/g/sKs regia. Leonardo da Vinci directs 
 it to be made from the peeled kernels in order to avoid the 
 chance of darkening its colour, and also causing the subse- 
 quent alteration of the tone of the pictures painted with it. 
 The kernels were to be soaked in water first, before being 
 peeled and pressed. The introduction of nut oil into 
 painting followed that of linseed oil, and preceded that of 
 poppy. Cold-pressed nut oil is much paler in colour, and 
 has much less taste and smell than the hot-pressed oil ; it 
 also differs in composition much in the same way that cold- 
 pressed differs from hot-pressed linseed oil. The con- 
 stituent glycerides of nut oil are the same in kind as those 
 of linseed oil, but a larger proportion of linolein is present. 
 Nut oil closely resembles linseed oil in its physical charac- 
 ters ; its specific gravity, '929, is intermediate between 
 that of linseed and poppy oil : cold pressed oil from the 
 Black walnut (Jitglans nigra) has the specific gravity "922, 
 and is quite as good for painting purposes as oil from the 
 common walnut. Besides the three drying oils already 
 described we may name that expressed from niger-seed, 
 Guizotea oleifera. It is occasionally employed in grinding 
 artists’ colours as a substitute for linseed and poppy oil. 
 Tea-seed and camellia-seed oils, and the oils extracted in 
 Japan from the seeds of Perilla ocimoides and from the 
 kernels of Torreya nucif era, dire noi of sufficient importance 
 
ACTION OF PIGMENTS ON OILS 
 
 63 
 
 to demand description. There is, however, one remark- 
 able drying oil of recent introduction which ought to be 
 named here. This is Chinese Wood oil or Tung oil ob- 
 tained from the seeds of Aleurites cordata. It is distinguished 
 from the oils we have been discussing by the change 
 which it undergoes when heated to about 282° to 285° C. 
 After having been maintained at this temperature for a 
 few minutes the oil becomes a gelatinous mass, firm and 
 free from stickiness. Tung oil is heavier than any of the 
 oils hitherto described. It is probable that it may find 
 certain applications in artistic painting, for it has been 
 shown to yield a durable film when oxidized. 
 
 A few observations may now be offered as to (i) the 
 action of certain pigments on oils; (2) the different amounts 
 of oil needed for grinding with different pigments. 
 
 1. Action of Pigments on Oils . — The most common action 
 is a physical one, in which the opacity of a pigment is 
 gradually lessened in course of time by the more complete 
 interpenetration of the oil between the particles. Thus 
 yellow ochre and raw sienna, for example, darken in colour 
 because they become more translucent, just as a piece of 
 oiled cream-laid paper is darker and yellower than the 
 same paper when dry. The light which falls upon it 
 plunges into it more deeply, and on reflection is more 
 highly coloured. In the case of such pigments as we 
 have named, and several others, another cause is at work 
 darkening and modifying the colour : this is the yellowing 
 of the oil itself. And it is the pigments which require the 
 largest proportion of oil for grinding which exhibit in a 
 marked degree the phenomena in question. 
 
 A second action between a pigment and the oil with 
 which it has been ground is the peculiar gelatinous or 
 ‘ livery ’ condition quickly assumed by some oil-paints. 
 
64 
 
 OIL IN PAINTS 
 
 This change is particularly noticeable with the cochineal 
 and madder lakes. I have succeeded in obviating it, by 
 carefully drying the pigments at a temperature just under 
 ioo° C., before grinding them with oil, and by substitu- 
 ting for raw linseed oil a mixture of the ‘ manganese oil,’ 
 described in the present chapter, with some poppy oil. 
 Those pigments which dry easily should be ground with 
 more of the latter oil, those which dry with difficulty with 
 more of the former. Sometimes pigments harden quickly 
 in the tube itself ; this change is due either to the siccative 
 character of the pigments, or to the introduction of an 
 actual ‘ dryer,’ or to the too copious use of a strongly sic- 
 cative oil with those pigments which are naturally slow 
 in drying. 
 
 The third action between a pigment and the oil with 
 which it has been ground appears to be of a distinctively 
 chemical nature. The most striking example of it known 
 occurs with flake-white. When normal flake-white, that 
 is hydrato-carbonate of lead, is ground in oil and after- 
 wards exposed to the air, it gradually becomes very 
 hard — much harder than the great majority of other oil- 
 paints under the same conditions, zinc-white for example. 
 It is not the hardness of the lead-compound plus the 
 hardness of the oxidized oil, but a hardness combined 
 with toughness of a higher order. As those varieties of 
 white-lead which consist wholly of the carbonate do not 
 possess this quality in anything like the same degree, so 
 it must depend upon the lead hydrate which is intimately 
 associated with the carbonate in typical white-lead. It 
 has been usual to conclude that the phenomenon is due 
 to the formation of a lead soap, a linoleate of lead, by the 
 interaction of the free acids in the oil with some of the 
 lead hydrate. This view is supported by some, yet hardly 
 
ACTION OF PIGMENTS ON OILS 
 
 65 
 
 decisive, experimental evidence. Thus the longer the oil 
 and the lead-white remain in contact the more marked is 
 the change, especially if the temperature be raised some- 
 what above the normal. If a collapsible tube, filled with 
 ordinary flake- white ground in oil, be tightly closed so as 
 to exclude the air and then be submersed, in water kept 
 hot, for a few days, the change in question is hastened. 
 Consequently it becomes impossible to extract from the 
 paint so treated, by means of ether or other suitable 
 solvent, quite the amount of oil originally present. One 
 could understand this result had the paint been allowed 
 to absorb oxygen from the air, when some linoxine, in- 
 soluble in most solvents of oil, would have been pro- 
 duced. Whatever the action may be, and whatever the 
 true explanation, the phenomenon is beyond question 
 Further reference to this subject will be found in Chapters 
 XIII. and XXIII. 
 
 A fourth action between a pigment and the oil with 
 which it has been ground is occasionally observed with 
 certain colours of organic origin, which actually dissolve 
 in and stain the oil. Bitumen, gamboge, and several 
 alizarin preparations exhibit this phenomenon. 
 
 2. The different amounts of oil required by different pig- 
 ments may now be considered. As a rule, the densest or 
 heaviest pigments require the least oil. A few pigments 
 require an excess of oil in order to protect them from 
 moisture or other injurious agents. Different authorities 
 do not agree at all closely as to the amount of oil needed 
 to make a workable oil-paint from the same pigment. 
 The following list gives the weight required by 100 parts 
 in weight of 22 pigments : 
 
 5 
 
66 
 
 OIL IN PAINTS 
 
 
 According to 
 
 According to 
 
 Name of Pigment 
 
 C. Roberson and Co. 
 
 Winsor and 
 
 
 {1901) 
 
 Newton (1901 
 
 White Lead 
 
 - 16 - 
 
 - 15 
 
 Zinc White 
 
 - 19 - 
 
 - 23 
 
 Aureolin - 
 
 - 71 - 
 
 - 49 
 
 Chrome Yellow 
 
 - 35 - 
 
 - 56 
 
 Cadmium Yellow 
 
 - 37 - 
 
 - 67 
 
 Yellow Ochre - 
 
 - 59 - 
 
 - 63 
 
 Raw Sienna - 
 
 - 147 - 
 
 - 240 
 
 Vermilion 
 
 
 - 23 
 
 Light Red 
 
 - 69 - 
 
 - 70 
 
 Madder Lake - 
 
 - 103* ■ 
 
 - 55 
 
 Terre Verte - 
 
 - 49 - 
 
 - - 87 
 
 Viridian - 
 
 . 56 . 
 
 - 52 
 
 Prussian Blue 
 
 - 72 - 
 
 - 78 
 
 Cobalt Blue - 
 
 - 50 - 
 
 - 90 
 
 Ultramarine (artificial) - 34 - 
 
 - 43 
 
 Raw Umber - 
 
 - 97 - 
 
 - 95 
 
 Burnt Umber 
 
 - 97 - 
 
 - 87 
 
 Bitumen- 
 
 
 
 Brown Madder 
 
 - 81 - 
 
 - 93 
 
 Vandyke Brown 
 
 - 72 - 
 
 - 94 
 
 Burnt Sienna 
 
 - - 138 - - 
 
 - 150 
 
 Ivory Black - 
 
 . 88 - 
 
 - II 2 
 
 The discrepancies between the corresponding figures in 
 the vertical columns are due, amongst other causes, to 
 differences in the modes of preparation of the dry pig- 
 ments ; to natural variations in the native earths em- 
 ployed ; to the dissimilar standards of solidity or fluidity 
 aimed at in the finished paint ; and to several other causes 
 which it is needless to particularize, but amongst which 
 may be named different modes of grinding and the em- 
 ployment of different kinds of oil. 
 
 The great differences in the above amounts of oil do not 
 cause such serious results in the conduct of the process of 
 
 Figure for rose madder. 
 
OIL IN PAINTS 
 
 67 
 
 oil-painting as might have been expected at first, for they 
 correspond in a measure to the relative bulks of the 
 several pigments. We can use more copal or amber 
 varnish to balance the excess of oil in some pigments, and 
 so secure a uniformity of structure, texture, and rate of 
 drying in the different parts of the work. It is, however, 
 often convenient to remove some of the excess of oil from 
 a pigment before using it, especially with the colours pre- 
 pared by some makers.* This can be done by leaving 
 the oil-paint on a pad of blotting-paper ; but 3-inch cubes 
 of plaster-of-Paris afford a far cleaner and surer method 
 for the absorption of oil. It may be further remarked that 
 the quantities of oil required by some of the pigments in 
 the above table may be reduced by grinding them under 
 greater pressure. Raw sienna, burnt sienna, and ivory 
 black should be dried at 100° C. just before grinding, and 
 then yield workable paints with less oil. The subsidence 
 of vermilion from the oil in which it has been ground 
 may in some measure be prevented by using ‘ manganese 
 oil ’ instead of raw linseed oil, and adding to it a small 
 quantity of linoleate or oleate of alumina, or of beeswax, 
 or of hard paraffin wax or ceresin, having a melting point 
 not under 65° C. Some artists find it a good plan to keep 
 their tubes of vermilion and of other heavy pigments in 
 an inverted position — that is, with the cap downwards. 
 
 * Dr. H. Stockmeier, of Niimberg, found the following per- 
 centages of oil in certain oil-paints from different sources which he 
 
 analysed : 
 
 Flake-White (Roberson and 
 Co.) ... - i6’2 
 
 Light Red (Winsor and 
 Newton) - - - 419 
 
 Burnt Sienna (Dr. Schoen- 
 feld) - - - - 59 '2 
 
 Chinese Ochre (G. B. 
 Moeves) - - - -45 
 
CHAPTER VI 
 
 RESINS, WAXES, AND SOLID PARAFFINS 
 
 In commercial parlance resins are incorrectly termedgums. 
 The true gums (Chapter VIII.) are either soluble in water 
 or swell up in that liquid, but resins are not acted on by 
 water. The term resin is used throughout the present 
 volume in its proper sense, so that ‘ copal resin,’ ‘ mastic 
 resin ’ are spoken of, not ‘ gum copal,’ ‘ gum mastic.’ All 
 the resins used for making vehicles and varnishes are of 
 vegetable origin; they contain besides carbon and hydro- 
 gen a not inconsiderable proportion of oxygen. They are 
 related to the hydrocarbons known as terpenes, present in 
 many essential oils, but are of more complex constitution. 
 Some resins, such as gamboge, contain gum and are called 
 gum-resins ; others contain a hydrocarbon (or terpene, see 
 Chapter XI.) or an aromatic acid, and are called balsams ; 
 others are true resins, but even these rarely, if ever, con- 
 sist of a single definite compound, but are mixtures of at 
 least two, often of three, four, or five different bodies. 
 Generally these constituents of true resins differ as to their 
 degree of solubility in various liquids, such as alcohol, 
 ether, spirit of turpentine, benzene, petroleum spirit, and 
 heated fixed oils. They contain carbon, hydrogen, and 
 oxygen, with occasionally a little sulphur, and are usually 
 of an acid character, and are capable of forming soaps, 
 
 68 
 
AMBER 
 
 69 
 
 called resinates, with the alkalies. Resins differ much 
 from one another, not only in solubility but also in hard- 
 ness and in the temperature at which they melt. Those 
 which are least soluble are generally those which are 
 hardest, and which require the highest degree of heat to 
 bring them into fusion. Most true resins contain, besides 
 their proper resinous constituents, small quantities of 
 colouring-matter, of water, of crystalline aromatic acids, 
 and of a volatile hydrocarbon or terpene. All these im- 
 purities, save the first, may be removed, generally with 
 advantage, by the following treatment. The powdered 
 resin is thoroughly mixed with a little water and placed 
 in a large glass retort. A current of steam is then passed 
 into the mixture until the terpene and volatile acids 
 present have distilled over. To the contents of the retort 
 carbonate of soda is added (i part for each 100 of resin). 
 The mixture after agitation is allowed to cool and then 
 filtered through a fine cotton cloth. The purified resin is 
 then washed on the filter with distilled water, then dried 
 in the air and finally in the water-oven : the air-bath and 
 a temperature of 110° to 120° C. may be used for the 
 desiccation of the harder resins. 
 
 It might be thought that the subject of resins would be 
 sufficiently discussed from the painter’s standpoint by a 
 description of three kinds — amber, copal, mastic. But it 
 will be shown presently that copal and mastic are names 
 given to several distinct substances, and that there are some 
 other resins which cannot be excluded from our view. 
 
 Amber IS the most familiarly known of all the resins on 
 account of its long use in its natural state for ornamental 
 purposes. Amber beads have not infrequently been found 
 in early British graves ; on the Continent these and other 
 ornaments of amber have often been obtained from ancient 
 
70 
 
 AMBER 
 
 interments. At Naples I was shown some years ago a very 
 large number of antique fibulae carved out of this sub- 
 stance : they had just been disinterred from Etruscan 
 tombs. Such amber has often become brittle and far more 
 soluble in the usual solvents, especially so far as regards 
 the surface layers ; but in other instances the preservation 
 of the properties of this resin has been complete. The 
 chief localities where amber is found are the Prussian 
 shores of the Baltic Sea (particularly between Konigsberg 
 and Memel) and the neighbouring plains ; it has been 
 found in veins, and is regularly quarried. Some amber, 
 much of it having a dark colour, is found near Catania, 
 Sicily. Near Lemberg (Galicia in Austria) nodules of 
 amber occur in rock. It occurs in several places in Den- 
 mark, Sweden, Norway, and France. In the British 
 Museum collection of minerals there is a fine mass from 
 Cambridge. Excellent specimens occur in comparative 
 abundance on the seashore at Southwold in Suffolk, and 
 at several other places on the Suffolk, Norfolk, and Essex 
 coasts. The dark fossil resin found in Birma, often in 
 large masses, is not identical with Baltic and English 
 amber. The same observation may be made with respect 
 to the so-called ambers ofTravancore in the East Indies, 
 and of the Isle of St. Louis, Senegambia, Africa. In 
 fact, amber, instead of being, as commonly stated, the 
 fossil resin of a single species of tree of Tertiary age, has 
 obviously been derived from no inconsiderable number of 
 different plants. Goppert, so long ago as 1853, satisfied 
 himself that at least eight species of plants besides Pinites 
 succinifev have afforded this fossilized resin ; he also 
 enumerated 163 species of plants as represented by remains 
 in amber ; many others have been since recognised. 
 
 Amber has a specific gravity of about voj ; its hard- 
 
AMBER 
 
 71 
 
 ness is 2^ on the ordinary mineralogical scale. In most 
 of the usual solvents of resins it is either insoluble or but 
 partially soluble. When heated quickly on a spatula it 
 splits up and then fuses into a viscous liquid, the drops 
 which are formed rebounding as they fall upon a cold sur- 
 face : this behaviour serves as a distinguishing test be- 
 tween amber and copal. When crushed amber is heated 
 in a retort it fuses at about 280° C. (536° F.), gives off 
 water, succinic acid, marsh gas, a mixture of liquid hydro- 
 carbons (known as oil of amber), and, finally, at a very 
 high temperature, a yellow substance having a wax-like 
 consistence. Sulphuretted hydrogen and other sulphur 
 compounds are also evolved in small quantity, for amber, 
 like several other fossil resins, contains a little sulphur 
 (sometimes \ a part in 100) in organic combination. 
 Amber breaks with a conchoidal fracture. When frag- 
 ments of amber are being ground or powdered they emit 
 an aromatic odour. On being rubbed amber becomes 
 negatively electric in a high degree. 
 
 It is probable that true amber consists mainly of a 
 single resin (85 to 90 per cent, of the whole) represented 
 by the empirical formula wC^oH^gO. Small quantities of 
 two other resins which are soluble in alcohol and ether, 
 of a liquid hydrocarbon, and of succinic acid, are associ- 
 ated with the main constituent, which has received the 
 mineralogical name ‘ succinite.’ 
 
 The classical names for amber were -t)XeKTpov, lyncu- 
 rium, electnim, and sticcinum. In early mediaeval times 
 amber was called vernix, a term which at first was applied 
 also to sandarac, and later in the fifteenth century to san- 
 darac only, when amber was designated as glas, or glassa. 
 In modern French amber is distinguished from ambre gris 
 as ambre jaune, although it is also known as harabe and 
 
72 
 
 COPAL 
 
 sticcin. It is the Bernstein of the Germans. The word 
 ‘ amber ’ is probably derived, through the Spanish, from 
 the Arabic anbar, a term applied to ambergris. 
 
 Copal is a name given to a number of hard resins which 
 vary not only in their degree of hardness, but also in their 
 degree of solubility ; they are the produce of many dif- 
 ferent species, and even genera of trees, while the origin 
 of several of the kinds still remains unknown. One of the 
 hardest, palest, and best of all is known as Sierra Leone 
 copal, from the port of collection and shipment. It has 
 been identified as the resin produced by a tree, Copaifera 
 Guibotiriiana, which belongs to the sub-order Caesalpineae 
 of the order Leguminosae. It is probable that the hard 
 West African pebble copal is the resin of the same tree, 
 but it occurs in rolled pebbles with an abraded surface, 
 and is at least semi-fossil : it is collected from the beds 
 of streams. Pebble copal has more colour than Sierra 
 Leone copal, but yields as strong a varnish. The latter 
 resin occurs in irregular rounded lumps or masses, gener- 
 ally varying in size from that of a hazel-nut to that of a 
 walnut. It is hard and elastic. It consists of at least 
 two resins, one of which, present to the extent of 33 per 
 cent., is soluble in absolute alcohol and in spirits of tur- 
 pentine. The other resin constitutes nearly the whole of 
 the remaining part of the copal, and becomes soluble in 
 most of the usual solvents, as well as in hot linseed oil, 
 when it has been previously heated to its melting-point 
 or to a temperature of 180° to 221° C. (360° to 430° F.). 
 Another process for rendering this and other kinds of 
 copal soluble is reduction to a fine powder in the presence 
 of water and the subsequent exposure of this powder to 
 the air for several months, or even a whole year. The 
 time requisite for this change may be shortened by keep- 
 
COPAL 
 
 73 
 
 ing the powdered copal at a temperature higher than that 
 of the ordinary atmosphere. More will be said as to this 
 and other methods of increasing the solubility of copal in 
 the chapter on Varnishes. 
 
 Other species of the genus Copaifeva yield similar but 
 inferior resins to that produced by C. Giiihourtiana, but 
 C. Gorskiana is the source of Inhambane (near Mozam- 
 bique) copal ; Benguela copal, Angola copal, and Gaboon 
 copal are other sorts, varying in hue from straw-colour to 
 a dull reddish -orange, produced in all probability by 
 different species of Copaifeva. Much of the so-called 
 Manilla copal is the produce of Agathis lovanthifolia. 
 
 Zanzibar copal is another hard and valuable resin of 
 African origin : it is often called anime. It is produced 
 by another leguminous tree, Tvachylohium Hornemannia- 
 num, which belongs to the same sub-order, Caesalpinese, as 
 Copaifeva. Most of this Zanzibar copal occurs in a fossil 
 or semi-fossil state in the earth near the roots of the trees, 
 or in places where the trees have formerly stood. This 
 fossilized resin is covered when dug up with a semi- 
 opaque, rough, and dull-brown crust ; when this powdery 
 coat is removed the remainder of the mass appears of a 
 transparent yellow colour, with a surface covered with 
 small rounded elevations like those on the rind of an 
 orange : this is spoken of as ‘ goose-skin.’ Many of the 
 pieces are flat and tabular, with a thickness of a quarter 
 of an inch or more. The same resin, when occurring on 
 the bark of the living trees of the same species of Tvachy- 
 lohium, presents a smooth and glossy surface ; it is not so 
 hard as the fossil variety. Zanzibar copal melts at a 
 higher temperature than Sierra Leone copal, and is very- 
 hard. In order to render it soluble it may be treated in 
 the same manner as the Sierra Leone copal. Its chemical 
 
74 
 
 COPAL 
 
 nature requires further study. The varnish made with 
 Zanzibar copal, though darker in colour, must be re- 
 garded as at least equal in strength and durability to that 
 prepared with Sierra Leone copal. 
 
 A third resin, sometimes designated as copal, some- 
 times as anime, is produced by another leguminous tree, 
 Hymenaa courharil, a native of Brazil and other countries 
 of South America. It is rather softer and more soluble 
 than Zanzibar copal. The copal of Madagascar comes 
 from another species of the same genus, H. verrucosa. A 
 Mexican copal is probably the resin of an allied species. 
 The resin from H. courharil is generally known as West 
 Indian copal ; fine specimens have been received from 
 Demerara. 
 
 The Bungo tree of Sierra Leone, Daniellia thurifera, 
 affords a resin of inferior quality. It is probable that the 
 same leguminous tree is the source of some of the Niger 
 and Sudan copals. 
 
 A rather hard resin of comparatively recent introduction 
 is Kauri or Cowdi copal, produced by the Cowdi pine of 
 New Zealand, Dammara australis. This is a coniferous 
 tree belonging to the tribe Araucariae. The largest masses, 
 some of them occasionally over loo pounds in weight, are 
 found in the earth in many places far from those in which 
 the trees now grow. Kauri resin usually becomes more 
 transparent and yellower by keeping. It is generally 
 somewhat whitish, or streaked with opaque bands, when 
 first found. It is cleaned and scraped and then sorted 
 into several qualities. Great quantities were imported 
 into England for some years, and for a time it was largely 
 employed as the basis of most of the so-called copal 
 varnishes, on account of its abundance, its low price, and 
 its easy manipulation. But the varnish which it yields, 
 
DAMMAR 
 
 75 
 
 or of which it constitutes the chief resinous component, 
 is inferior in hardness, toughness, and durability to that 
 made from Sierra Leone copal or Zanzibar copal. 
 
 Kauri resin is sometimes spoken of as dammar, but this 
 name properly belongs to the resins produced by other 
 trees, not by Dammava australis. White or Singapore 
 dammar is the resin of Dammava orientalis. It is soft, and 
 may be scratched even by mica. ‘ Sal dammar ’ is produced 
 by Shorea robusta, the sal tree, widely distributed in India. 
 This resin, though soft, yields a good flexible paper 
 varnish. The tree belongs to the Dipterocarpeae. Valeria 
 indica, another Dipterocarp, yields piney resin or white 
 dammar : a similar resin is produced by another species, 
 V. acuminata, a Ceylon tree. Several kinds of Hopea {H. 
 niicrantka, H. odorata, etc.), which belong to the same 
 natural order, yield pale, transparent resins which are a 
 trifle harder than that of the sal tree. Black dammar or 
 Tinnevelly resin is produced by Canarium strictuni ; it is of 
 very inferior quality. This tree belongs to the Burseraceae : 
 several kinds of elemi resin are also furnished by plants 
 belonging to the same natural order. These elemis are 
 soft, sticky resins, occasionally employed in varnishes to 
 prevent them from becoming brittle and cracking. They 
 contain essential oils and other aromatic bodies, and vary 
 very much in composition and properties, although they re- 
 semble one another in their solubility in boiling alcohol and 
 in their easy alterability. They are unsatisfactory resins. 
 
 The resin first known as sandarac was probably juniper 
 resin, although the name was also applied to amber. It is 
 spoken of by the older authorities on painting as having 
 a red colour. Its hue is a dull reddish orange, and it yields 
 a dark-brown varnish when dissolved by the aid of heat in 
 a drying oil. The effect of this varnish in imparting an 
 
76 
 
 MASTIC 
 
 agreeable warm tone to pictures painted in tempera is very 
 evident, when the cold aspect of an old Italian unvarnished 
 tempera picture is compared with the glowing colour of a 
 painting which still retains its original sandarac varnish. 
 The resin now called sandarac is produced by another 
 coniferous plant [Callitvis quadrivalvis), a native of Algiers. 
 It is a pale yellow resin, when fresh resembling mastic in 
 colour, but becoming yellower with age. It is brittle and 
 melts easily. When finely powdered and sifted it forms 
 one of the kinds of pounce used in preparing the surface 
 of parchment and vellum for writing and illuminating. 
 It dissolves in alcohol and in acetone, incompletely in 
 petroleum spirit and benzol. 
 
 There is one more resin which requires mention. This 
 is mastic. The best and most important sort of mastic is 
 produced by a small tree {Pistacia Lentiscus), belonging to 
 the cashew-nut order or Anacardiaceas. This tree occurs 
 in Scio and other islands of the Greek Archipelago. Mastic 
 exudes in the form of tears from incisions made in the 
 bark. It occurs in small pea-like masses, and presents 
 when fresh a very pale straw-colour. It is so fragile that 
 it may be crushed to powder between the fingers. It has 
 an aromatic odour, and dissolves completely in boiling 
 alcohol and in spirits of turpentine. Its melting-point is 
 low, on an average about i io° C. It contains, besides its 
 resinous constituents, a small quantity of a volatile essen- 
 tial oil (a terpene) and of moisture. It yields a tender 
 but glossy varnish, largely employed for the final protec- 
 tion of pictures in oil. This varnish yellows with age, 
 and becomes fragile and fissured. 
 
 Resins, sometimes called mastics, are produced by other 
 trees of the same genus. These resins, which are of no 
 value for artistic purposes, are : 
 
COPALS 
 
 77 
 
 Indian mastic from Pistacia cabulica. 
 
 Bombay mastic from P. Khinjah. 
 
 Pistachio mastic from P. Terebinthus. 
 
 In the following table, compiled from the results of 
 Bottler, are comprised some particulars concerning twelve 
 of the resins commonly called ‘ copals.’ In the first 
 column the names are given, in the second the melting- 
 points, in the third the relative hardness (12 being the 
 hardest), and in the fourth and last column the degree of 
 solubility (xii being the least soluble). The specific 
 gravity of these copals depends so much upon the relative 
 freedom of the several kinds from cavities and bubbles 
 that the figures for this character are not included in the 
 table. It may, however, be mentioned that all these 
 resins are rather heavier than water, their specific gravi- 
 ties ranging from i'035 to I'OJ. 
 
 Name of Copal 
 
 Melting-point 
 
 Hardness 
 
 Solubility 
 
 Zanzibar - 
 
 - 275“ C. 
 
 12 
 
 xii 
 
 Red Angola 
 
 - 315 
 
 II 
 
 ix 
 
 Pebble Copal - 
 
 - 230 
 
 10 
 
 xi 
 
 Sierra Leone - 
 
 - 195 
 
 9 - 
 
 V 
 
 Yellow Benguela 
 
 - 180 
 
 8 - 
 
 vii 
 
 White Benguela 
 
 - 185 - 
 
 7 - 
 
 X 
 
 Congo 
 
 - igo 
 
 6 - 
 
 iv 
 
 Manila 
 
 - 145 - 
 
 5 - 
 
 ii 
 
 White Angola - 
 
 - 245 
 
 4 ■ 
 
 i 
 
 Kauri 
 
 - 150 - 
 
 3 - 
 
 iii 
 
 Demerara 
 
 - 90 
 
 2 
 
 viii 
 
 Brazilian - 
 
 - 95 
 
 - T 
 
 vi 
 
 All these numbers are approximative only ; and the 
 valuation of these resins for varnish-making ought to 
 take into account other properties not here recognised, 
 such as toughness after as well as before heating and 
 solution, liability to darkening in colour by lapse of time, 
 and durability. 
 
78 
 
 VENICE AND STRASBURG TURPENTINE 
 
 Turpentines, Oleo-Resins, and Balsams. — There is a group 
 of substances, many of them derived from coniferous 
 plants, which are, or have been, included under the term 
 balsam. Strictly speaking, this designation should be 
 limited to those resinoid exudates which contain benzoic 
 or cinnamic acid, while the term oleo-resin, or, better still, 
 the term turpentine, should be given to those soft and semi- 
 liquid natural exudates which consist of terpenes asso- 
 ciated with bodies of resinous character. The word 
 turpentine is, however, so generally connected with the 
 volatile hydrocarbons (terpenes) distilled from these 
 exudates, that it should be clearly understood that the 
 three vegetable products hereunder described are of 
 natural, not artificial, origin. It is in consequence 
 of the preservative influence upon certain pigments 
 which has been assigned, not without experimental 
 confirmation, to these bodies that they are noticed 
 here. 
 
 Venice Turpentine. — Under this name the resin of the 
 common larch is now known. It comes chiefly from Tirol. 
 Recent examination has shown it to consist mainly of three 
 groups of compounds, namely, about 63 per cent, of 
 resinous acids, 20 per cent, of terpenes, and 14 per cent, 
 of resins. The best specimens are never quite so clear 
 and free from colour as those of the next product to be 
 described. 
 
 Strashurg Turpentine is derived from Ahies pectinata, the 
 silver-fir, the best quality coming from the Italian side 
 of the Tirolese Alps. It contains about 57 per cent, of 
 resinous acids (not identical with those in larch turpentine), 
 28 per cent, of terpenes, and 13 per cent, of resins. This 
 turpentine is the true Olio d’Abezzo of Italian writers, and 
 when dissolved in a terpene was used as a varnish for 
 
WAX 
 
 79 
 
 pictures in tempera and oil, and for the special protection 
 of verdigris and of some other dangerous pigments. Some 
 specimens of this turpentine are beautifully clear and 
 colourless. It is decidedly superior to larch turpentine, 
 with which it has no doubt been often confused, and to 
 Bordeaux turpentine, obtained from Pinus Pinaster. The 
 chemical study of the olio d’abezzo has at present thrown 
 no light upon the specially protective or locking-up 
 qualities which are claimed for this turpentine. 
 
 Canada Balsam, from Abies balsamea, much resembles 
 Strasburg turpentine. The resinous acids which consti- 
 tute three-fifths of its weight are said to be different from 
 those already mentioned as existing in the turpentines 
 from the larch and silver-fir. 
 
 Wax . — The true waxes, unlike the oils described in 
 Chapter V., are not glycerides, and do not therefore yield 
 glycerin when they are saponified — that is, turned into 
 soaps by the action of alkalies. Ordinary beeswax is the 
 best known, and probably the most important of all the 
 different kinds ; but very few experiments have been made 
 as to the utilization of exotic and vegetable waxes in the 
 processes of painting. Crude beeswax requires purifica- 
 tion and bleaching in order to fit it for artistic use. The 
 first operation consists in melting the wax at nearly the 
 lowest temperature possible, and then pouring it in a 
 slender stream into a cold saturated solution of alum, 
 agitating the latter all the time. The granulated wax thus 
 prepared may be bleached by exposure for several days on 
 linen cloths to the action of the sunlight and dew; or it may 
 be treated with dilute chromic acid solution, or with hydro- 
 gen peroxide. All these processes succeed better when 
 the wax is in the form of thin sheets or ribbons. The 
 bleached wax, after thorough washing and drying, is to 
 
8o 
 
 fVAX 
 
 be re-melted. Its hardness is increased and its melting- 
 point raised by the above treatment. 
 
 Bleached beeswax melts at 62° or 64° C. (144° or 
 147° F.). It consists of four distinct substances, not 
 present in all samples in the same proportions. By boiling 
 wax with strong alcohol a substance called myricin 
 (myricyl palmitate) is left undissolved. The dissolved 
 portion is the larger ; the bulk of it, which crystallizes 
 out as the alcohol cools, was formerly called cerin. It is 
 a mixture of two fatty acids. The cold alcohol still 
 retains a small quantity of a fourth substance. 
 
 Beeswax, by long-continued exposure to atmospheric 
 influences, disintegrates and partially perishes by oxida- 
 tion. It is a constituent of Gambier-Parry’s spirit-fresco 
 medium, into which it is introduced in order to impart a 
 matt appearance to the painting. Excellent examples of 
 the use of melted wax as a binding material for pigments 
 may be seen in the National Gallery and the Victoria 
 and Albert Museum. They are encaustic portraits, exe- 
 cuted probably in the second and third centuries of our 
 era, and were discovered by Professor W. M. Flinders 
 Petrie, in the Hawara Cemetery, Fayum, Egypt. The 
 pigments were mixed with wax and laid on in the melted 
 state. The wax having become disintegrated in the 
 course of centuries has been re-melted, some fresh wax 
 having been added in several instances. 
 
 Wax is abundantly distributed in the vegetable world; 
 its production is, in many cases, stimulated by the 
 attacks of insects. Thus, Chinese wax is produced by 
 the puncture of Coccus Pela, living on Ligustrum lucidum 
 and Fraximis chitiensis. Chinese wax, which melts at 
 82° C. (180° F.), consists almost entirely of cerotyl 
 cerotate. Brazilian or Carnaiiba wax occurs naturally 
 
PARAFFIN WAX 
 
 8i 
 
 in thin films on the leaves of a palm [Copernicia cerifera ) ; 
 it melts at 84° C. (183° F.). Japanese or Ibota wax is 
 probably produced by the attacks of a coccus on Ligiistnm 
 Ibota ; it melts at 42° C. (108° F.). 
 
 Paraffin wax, hard paraffin, solid paraffin, and ceresin, 
 are names given to certain mixtures of hydrocarbons 
 occurring in native petroleum and in the ‘ mineral wax ’ 
 called ozokerite, and also in the tars produced by the 
 destructive distillation of wood, peat, lignite, bituminous 
 shales, and coals. The liquid hydrocarbons which 
 accompany the paraffin wax are described so far as 
 necessary in Chapter XL under the head of Solvents. 
 
 Paraffin wax, so far as its main or fundamental con- 
 stituents are concerned, contains no oxygen, and is a 
 mixture of several of the least alterable of all organic 
 compounds ; very few chemical reagents have any action 
 at all upon it. On this account it presents for artistic 
 purposes a marked superiority over beeswax or any 
 vegetable wax. Of the hydrocarbons occurring in large 
 quantity in paraffin wax the best known are those to 
 which the chemical formulae CggH^g, C^gHg^, 
 
 CgrHgg, CggHgg, and CggHg^ belong. The melting-point 
 of paraffin wax oscillates within wide limits, say, from 
 30° to 80° C. The higher the melting-point the harder, 
 the heavier, and the less crystalline is the material. For 
 artistic purposes, hardness and the absence of a tendency 
 to separate from solution in the form of large crystals 
 are desirable properties. Unfortunately the hardest 
 paraffin waxes of high melting-point are much less 
 soluble in oils, terpenes, and varnishes than the softer 
 varieties, and thus their usefulness is limited ; they are 
 also somewhat yellowish in hue. I have, however, 
 found that a pure paraffin wax from the Bathgate shale, 
 
 6 
 
PARAFFIN WAX 
 
 having the melting-point of 65-5° C. (150° F.), answers 
 every purpose. It is sufficiently hard and but indistinctly 
 crystalline, and yet may be dissolved in fair abundance 
 by the usual solvents. It is convenient to preserve it 
 for use in the form of small flattened globules, which 
 are easily prepared by melting the substance and pouring 
 it drop by drop on to the surface of a large sheet of glass 
 previously moistened by breathing upon it. When these 
 drops are shaken in a bottle they rattle like small pebbles, 
 and do not mark the glass ; when the softer solid paraffins 
 are thus treated, they fall with a thud, and leave streaks 
 and spots upon the interior surface of the vessel. This 
 difference of deportment affords a ready means of dis- 
 tinguishing between a paraffin wax suitable for artistic 
 uses and one which had better be rejected. 
 
 The manufacture or isolation of hard paraffin and its 
 purification are not described here. The processes em- 
 ployed — distillation, treatment with oil of vitriol, frac- 
 tional crystallization from solvents, etc.— involve the use 
 of complex apparatus. It may, however, be here stated 
 that commercial hard paraffins vary somewhat in purity. 
 Those obtained from mineral wax or ozokerite are nearly 
 free from oxygen compounds ; while those derived from 
 the products of the destructive distillation of shales, coal, 
 etc., sometimes contain as much as 3 per cent, of oxygen, 
 indicating the presence of other bodies besides hydrocar- 
 bons. Some of these bodies are of an acid nature ; these 
 may be separated by repeatedly boiling the commercial 
 paraffins in question with a 5 per cent, solution of caustic 
 potash. The following table shows the relations subsist- 
 ing between the melting-point and the specific gravity 
 (at 20° C.) of six different samples of hard paraffin, 
 generally known as ceresin, from ozokerite : 
 
PARAFFIN WAX 
 
 83 
 
 No. of 
 
 Melting- 
 
 Specific 
 
 No. of 
 
 Melting- 
 
 Specific 
 
 Sample 
 
 point 
 
 Gravity 
 
 Sample 
 
 point 
 
 Gravity 
 
 I - 
 
 - 56° C. - 
 
 ■ 0-912 
 
 4 - 
 
 72° C. - 
 
 - 0-935 
 
 2 - 
 
 ■ 61° - - 
 
 - 0-922 
 
 5 - 
 
 - 76° - - 
 
 - 0-939 
 
 3 - 
 
 - 67° - 
 
 - 0-927 
 
 6 
 
 - 82° - 
 
 - 0-943 
 
 A sample of ceresin made from ozokerite was furnished 
 to meat my request by the late J. Calderwood, of Price’s 
 Patent Candle Company. It has a setting-point of about 
 156° F. (69° C.), and is almost non-crystalline in appear- 
 ance. It possesses, however, a somewhat greasy feel and 
 a slight yellowish hue. I find by experiment that this 
 ceresin, with a small admixture of a refined paraffin 
 (from the same manufacturers) having a melting-point 
 of 147° F., forms an excellent substitute for the hard 
 paraffin wax (melting-point 150° F.), from Bathgate shale, 
 described on a preceding page, and unfortunately no 
 longer to be met with in commerce. 
 
 Hard paraffin wax may be used in the preparation of 
 painting mediums as a substitute for beeswax ; for pre- 
 venting the separation of heavy pigments, such as ver- 
 milion, from the oil in which they are ground ; and for 
 the preparation of certain painting-grounds. 
 
 H In practice it has been found that far smaller quan- 
 tities of beeswax than of paraffin wax are required to 
 prevent the subsidence of heavy pigments from the oil 
 in which they have been ground. Moreover, the working 
 of paints containing a small quantity of beeswax is more 
 agreeable than is the case with those into which paraffin 
 wax has been introduced. 
 
CHAPTER VII 
 
 YOLK AND WHITE OF EGG ; SIZE ; GLUE 
 
 The materials described in the present chapter owe their 
 peculiar properties — at least, in great measure — to the 
 presence of chemical compounds which contain the ele- 
 ment nitrogen. Now, this element is not a constituent of 
 any of the artists’ materials already described, nor, indeed, 
 of any others, except a few pigments, such as aureolin, 
 Prussian blue, and indigo. The presence of nitrogen in an 
 organic compound is very often accompanied by a measure 
 of instability, or proneness to change; the nitrogenous con- 
 stituents of eggs, and of size, afford illustrative examples. 
 Another source of weakness in the composition of the 
 nitrogenous constituents, both of the white and of the yolk 
 of eggs, lies in the presence of another element — namely, 
 sulphur. Part of this sulphur readily leaves the original 
 substance, yielding simpler compounds, such as sulphur- 
 etted hydrogen, and ammonium sulphide, which possess 
 the objectionable property of discolouring many of the 
 metallic pigments used by artists. On the other hand, all 
 these nitrogenous bodies are susceptible of coagulation, 
 whereby they become insoluble, and very much less prone 
 to change. Indeed, the majority of them may be turned 
 into a substance which is virtually leather, a material 
 which resists decay in the most marked manner. This 
 
 84 
 
WHITE OF EGG 
 
 85 
 
 tanning operation may be readily effected by treating the 
 substances in question with a solution containing tannin, 
 the active ingredient of oak-bark, sumach, nut-galls, etc. 
 
 We will first consider the composition of the yolk and 
 white of ordinary hen’s eggs. The percentage proportions 
 are, on the average : 
 
 Water - - - - 
 
 Yolk 
 
 - 51 '5 - 
 
 
 White 
 - 84 '8 
 
 Albumen, Vitellin, etc. 
 
 - i5’o - 
 
 - 
 
 - I2'0 
 
 Fat or Oil 
 
 - 22 'O - 
 
 - 
 
 0'2 
 
 Lecithin, etc. 
 
 - 90 - 
 
 - 
 
 - trace 
 
 Mineral Matter - 
 
 I 'O - 
 
 - 
 
 - 07 
 
 Other Substances 
 
 - I’5 - 
 
 - 
 
 - 2-3 
 
 The white, it will be seen, is characterized by the 
 presence of 12 parts per hundred of albumen, which is in 
 solution in the ropy liquid. When this solution is heated 
 to a temperature considerably below that of boiling water, 
 the albumen becomes insoluble, and is said to be coagu- 
 lated ; it is not capable of being again dissolved in its 
 original menstruum. Solutions of tannin, corrosive subli- 
 mate, and many other compounds, inorganic and organic, 
 produce a similar effect. But egg-white is not a pure 
 solution of albumen. For all practical purposes in the 
 arts, it may be sufficiently freed from extraneous matters 
 in the following manner : The necessary number of 
 ‘ whites ’ are mixed in a wide-mouth stoppered bottle, with 
 twice their bulk of water, and shaken up thoroughly ; 
 then a slip of yellow turmeric-paper is dropped into the 
 mixture. Drop by drop weak acetic acid is poured in, 
 until the reddened turmeric-paper ha.?, just, or nearly, re- 
 gained its original yellow hue. In this way the alkaline 
 reaction of the liquid is almost neutralized, and it becomes 
 thinner. After further agitation, the mixture is poured 
 upon a piece of well-washed muslin in a funnel. The 
 
86 
 
 COAGULATION OF ALBUMEN 
 
 clear liquid which drops through has been freed from 
 membranes, etc., and contains nearly 4 per cent, of albu- 
 men. It may be concentrated by cautious evaporation 
 at a temperature not exceeding 50° C. The albumen 
 which it contains is a very complex substance, containing, 
 besides carbon, hydrogen, nitrogen, and oxygen, about 
 I ‘6 per cent, of sulphur. A solution of albumen spread 
 upon glass, and allowed to dry slowly at the ordinary 
 temperature, leaves a residue of albumen in the form of a 
 nearly-transparent film. This, when quite dry, is brittle, 
 and easily cracks. If, before it be quite dry, it be heated 
 to 70° or 75° C., it cannot be again dissolved by water, 
 having been converted into the insoluble form. In this 
 condition it is much less prone to change. It will now 
 be seen how powdered pigments, if ground up with albu- 
 men solution and then used in painting, may be made to 
 cohere, and also to adhere to the painting-ground of cloth, 
 paper, or plaster, on which they have been spread. And 
 afterwards, by simply heating the work sufficiently, the 
 whole coloured layer may be rendered insoluble and irre- 
 movable by water. Advantage may also be taken of the 
 action of tannin on albumen to secure the same result 
 — the coagulation of the albumen. We may coat a piece 
 of fine linen cloth with albumen-solution, and before it is 
 quite dry we may paint upon it with pigments which have 
 been previously ground up with a weak solution of tannin. 
 If the work be carefully done, the colours will, when dry, 
 be found to have been fixed by the reaction between the 
 tannin and the albumen. If, however, the pigments be 
 laid on somewhat quickly, it may be found necessary to 
 give the whole surface a final coat of albumen-solution. 
 We have dwelt at some length upon this employment of 
 tannin, or of heat, to secure the coagulation of albumen, 
 
YOLK OF EGG 
 
 87 
 
 because it serves to illustrate the way in which paintings, 
 executed with egg-yolk, or size, as a medium, may be 
 fixed. For, as we shall now proceed to show, egg-yolk 
 and size possess many characters in common with 
 albumen-solution. 
 
 But the yolk of an egg contains other substances besides 
 albumen. First of all, the albumen present is accompanied 
 by another similar compound called vitellin, which re- 
 sembles it in composition and properties, and which, for 
 our present purpose, we need not further describe, except 
 so far as to state that, unlike albumen, it is not soluble in 
 water. Of albumen and vitellin, taken together, egg-yolk 
 contains, as we have seen, not less than 14 or 15 per cent. 
 But egg-yolk is something more than a solution of these 
 two similar bodies. It is, in fact, an oily emulsion, in which 
 innumerable minute globules of a thick, fatty oil are sus- 
 pended in an albuminous solution. And, moreover, the 
 amount of this oil is large ; there is about 22 per cent, of 
 it, and associated with this oil there is no less than 9 per 
 cent, of a curious compound called lecithin, which has 
 many of the physical properties of a fat. It seems to be 
 a triglyceride, including two fatty-acid radicles and one 
 phosphoric acid radicle. Associated with lecithin there is 
 a nitrogenous basic compound. Although lecithin re- 
 sembles oils and fats in its behaviour to most solvents, it 
 yet differs from them in this one particular, that it is very 
 hygroscopic and swells up in water, forming a kind of 
 emulsion. Now, 9 parts of lecithin with 22 parts of oil 
 make up nearly one-third of egg-yolk, or 31 parts of oily 
 or fatty matter per 100, as against 15 parts of albuminoid 
 matter, or vitellin and albumen taken together. Hence 
 it happens that egg-yolk, the usual vehicle for pigments in 
 the best kind of tempera- painting, must be regarded as 
 
88 
 
 SIZE AND GLUE 
 
 essentially an oil-medium. As it dries, the oil hardens, 
 and remains intimately commingled with the albuminous 
 substances left behind on the evaporation of the water 
 present. These albuminous substances coagulate and 
 become insoluble in the lapse of time — a change greatly 
 accelerated by the old practice of exposing the finished 
 tempera picture to sunshine previous to varnishing it. 
 
 Size and glue may be considered together. They consist 
 of two distinct yet similar compounds, known respectively 
 as gelatin and chondrin. These bodies consist of carbon, 
 hydrogen, nitrogen, and oxygen ; and, when pure, they 
 contain no sulphur. They are soluble in hot water, yet 
 are coagulable by tannin and by some other compounds, 
 organic and inorganic. Chondrin is thrown down from its 
 solution by alum, and, indeed, by several compounds which 
 do not precipitate gelatin. The latter body is obtained 
 from skin, tendons, and bones. These organized structures 
 contain a substance called ossein, or collagen, which, under 
 the influence of boiling water, dissolves, becoming changed 
 into gelatin. This conversion occurs more quickly when 
 the process is performed under a pressure somewhat 
 greater than that of the atmosphere, and, therefore, at a 
 temperature rather higher than ioo° C. In this way the 
 transformation of the organic tissue of ivory, bone, vellum, 
 parchment, fish -bladder, etc., into gelatin may be readily 
 effected. The purity of the product depends, in part, upon 
 the care with which the raw materials have been selected 
 and cleansed, in part upon the temperature and the dura- 
 tion of the extraction. If the temperature be too high, or 
 the boiling be much prolonged, the gelatin produced is 
 transformed partially into a substance which does not 
 gelatinize when its aqueous solution is cooled, Chondrin 
 is obtained from cartilage, which consists mainly of carti- 
 
SIZE AND GLUE 
 
 89 
 
 lagin, or chondrigen, by the same process which changes 
 collagen into gelatin. A hot solution of chondrin gelatin- 
 izes on cooling just like one of gelatin ; but it does not 
 yield, with the same amount of substance, so firm a jelly. 
 Size, glue, and commercial gelatin, consist of mixtures of 
 gelatin, chondrin, and the non-gelatinizing substances 
 produced by the long-boiling or the over-heating of their 
 solutions. Isinglass, vellum, and ivory-dust yield a size 
 which contains nothing but gelatin and a little mineral 
 matter ; the darker and stickier kinds of glue contain 
 many impurities, having been made from very varied 
 materials, such as ox-hoofs, horseflesh, old leather, etc. ; 
 they often contain sulphuric acid. 
 
 In selecting a size for artistic use, the special purpose 
 in view will indicate whether an insoluble (in cold water) 
 and strongly-gelatinizing, or a partially soluble and very 
 adhesive one should be selected. The former is less liable 
 to crack when dry than the latter. The very fine gelatins 
 used in photography will often be found suitable. A few 
 experiments, with cold water and then with hot, will soon 
 reveal the peculiarities of the samples submitted to ex- 
 amination. As caustic lime, caustic soda, chloride of lime, 
 sulphurous acid, and certain mineral acids, are frequently 
 employed in the manufacture of size, glue, and gelatin, it 
 is absolutely necessary to ascertain, before using these 
 materials in any process of painting, their freedom from 
 free acids, free alkalies, or bleaching agents. A hot-water 
 solution of the material must not redden blue litmus-paper, 
 nor bleach dahlia-paper, nor embrown tumeric-paper. 
 
 Glue and size may sometimes be purified and improved 
 by cutting up the solid or gelatinous mass into small 
 pieces, soaking them in distilled water for a few hours, 
 and then pouring off the liquid before dissolving them. 
 
90 
 
 PRESERVATION OF EGG-YOLK 
 
 The temporary preservation from putrefaction of the 
 solutions of the substances described in the present 
 chapter, may be effected in several ways. A lump of 
 camphor, or a few drops of eugenol (from oil of cloves), 
 is generally sufficient. I have preserved the egg-yolk 
 medium for tempera-work for many days in an agreeable 
 condition for use by the following plan : A saturated 
 solution of eugenol in 5 per cent, acetic acid is first made, 
 then this is added, drop by drop, with constant agitation, 
 to the required number of yolks in a wide-mouth bottle, 
 the point at which to stop further addition being learnt by 
 the change of colour of a slip of turmeric-paper. When 
 this paper just regains its original yellow colour, which 
 was turned brownish-red by the yolks, no more acetic 
 acid is wanted. Any water needed for thinning the 
 medium may now be added, together with a lump of 
 camphor, which will remain floating on the surface. 
 
CHAPTER VIII 
 
 GUM, STARCH, DEXTRIN, HONEY, AND GLYCERIN 
 
 The term gum is properly applied to a number of non- 
 crystalline, structureless substances, of vegetable origin. 
 They consist essentially of so-called hydrates of carbon, 
 and are either soluble in cold water, or swell up when left 
 therein for some time. The only gum of any importance 
 in painting is gum-arabic. This name is not, however, 
 exclusively applied to one variety only ; it is given to the 
 gums which exude from several species of Acacia. For 
 instance. Acacia arabica furnishes the Morocco, Mogador, 
 Brown Barbary, and East Indian gums of commerce. 
 But it should be noted that, although A . arabica is a native 
 of India, and is grown to some extent in many parts 
 of that empire, the gum it yields is rarely, if ever, exported 
 thence, the so-called East Indian gum-arabic being really 
 taken from Red Sea ports to Bombay, and thence re- 
 shipped to Europe. Acacia arabica, however, does not 
 furnish a strong and durable gum, and it is from another 
 species, A. Senegal, that we obtain the gum employed as a 
 binding material for water-colours. This gum is known 
 commercially as Kordofan, picked Turkey, white Sennaan 
 and Senegal gum. The tree which yields it is a native of 
 Senegal and the Sudan ; it grows to a height of twenty 
 feet. The supplies which come from Kordofan are of the 
 
 91 
 
92 
 
 GVM SENEGAL 
 
 finest quality, but all the grades of gum from A. Senegal 
 are superior to the produce of A . arabica in their greater 
 dryness, density, and adhesiveness, as well as in the 
 smaller amount of mineral matter which they contain. It 
 may be added in this place that, according to some authori- 
 ties, a part of the gum Senegal of commerce is produced 
 by other species of Acacia besides A. Senegal, such as 
 A . Adansoriii, A . alhida, A. dealbata, A . nilotica, A. Vereh, etc., 
 and even from species of Kaya, Spondias, and Stercidia. 
 Suakim gum, the produce oi Acacia stenocarpa and A. Seyal, 
 varies greatly in quality, but is largely imported into 
 England, and much used, though not generally available 
 for fine work. 
 
 Gum consists mainly of arabin, a mixture of the salts 
 of an acid called arabic acid, and of the free acid itself. 
 The salts are those of the three bases — potash, lime, and 
 magnesia ; water is also present. It is probable that, in all 
 varieties, even of the finest gum Senegal, other organic 
 acids, besides arabic acid, are present. An analysis of a 
 fine specimen of picked ‘ Turkey gum ’ gave 15 per cent, 
 of water, and 2-8 per cent, of ash, leaving 82'2 per cent, 
 for the arabic and other allied acids and organic matters. 
 The arabic acid was formerly expressed by the formula 
 C12H22O11, but the experiments of O’Sullivan indicate a 
 much more complex composition (Cg9Hj^20r4)- 
 
 Gum from Acacia Senegal, the only sort which ought to 
 be employed in painting, should be nearly free from colour, 
 and should dissolve in cold water without leaving an appre- 
 ciable residue. Its watery solution should be clear, and 
 should give no colour with tincture of iodine, but an abun- 
 dant precipitate with ammonium oxalate solution. If 
 iodine produce a purplish colour, adulteration with dextrin 
 is indicated ; the white precipitate thrown down by the 
 
GUM TRAGACANTH 
 
 93 
 
 oxalate shows the presence of calcium, a constant con- 
 stituent of the genuine gum. I have found that the 
 samples of gum sold to me as gum Senegal were of a more 
 pronounced yellowish colour than those bought as gum- 
 arabic and best Turkey : the lumps varied more in size, 
 often contained air-bubbles, and were less fissured. The 
 adhesiveness and toughness of these samples, moreover, 
 compared favourably with these properties as exhibited 
 by the finest and whitest ‘Turkey gum ’ obtainable. 
 
 For the preparation of water-colours, and for occasional 
 use in the operations of painting, it is convenient to have 
 at hand a standard solution of gum. This may be pre- 
 pared by dissolving i ounce of the selected gum reduced 
 to fine powder in 2 measured ounces of boiling distilled 
 water. The powdered gum should be very slowly added, 
 with constant stirring, to the boiling water. When the 
 whole is dissolved, the liquid is allowed to stand for at 
 least a day ; then it is decanted from any sediment that 
 may have been deposited into a wide-mouth bottle with- 
 out cork or stopper, but covered with a glass cap. It is 
 well to allow a lump of camphor to float in it, or to add 
 to it a couple of drops of eugenol, the active antiseptic 
 constituent of oil of cloves ; a still more effective pre- 
 servative is ^-naphthol. 
 
 Gum tragacanth is produced by certain leguminous 
 shrubs belonging to the genus Astragalus. Amongst these 
 may be named : A. gummifev, A. eriostylus, A. bvachycalyx, 
 and A, adscendens. Its constituents include a small quan- 
 tity of a gum soluble in cold water, a little starch and 
 cellulose, and a large proportion of a mucilaginous body 
 which swells up in cold water, but does not dissolve. 
 The substance having these properties is a compound of 
 carbon, hydrogen, and oxygen of very complex consti- 
 
94 
 
 STARCH 
 
 tution, which has been called hassorin. Gum tragacanth 
 contains from 12 to 15 per cent, of water, and leaves 2 to 
 3 per cent, of ash when burnt. A mucilaginous medium 
 made with gum tragacanth may be used for painting on 
 linen : it is not very easy to prepare so as to be of uniform 
 consistency. A fairly good plan is to place the finely- 
 powdered tragacanth in a bottle, and to add enough spirit 
 of wine to moisten it : then add the required amount of 
 water, and shake the mixture gently at intervals. Water 
 containing no more than 3 or 4 per cent, of the gum con- 
 stitutes a moderately thick mucilage. 
 
 ^ Tragacanth mucilage containing from i to 2 per cent, 
 of this gum serves as a binding medium in the making of 
 crayons for pastel work. 
 
 Other gums are of small importance. They commonly 
 contain much bassorin and but little arabin. The Aus- 
 tralian wattle gums from several species of Acacia are 
 perhaps thus constituted ; but if this be the case, the 
 bassorin present in them seems to present some points of 
 difference from the bassorin of tragacanth. Cape gum is 
 produced by Acacia horrida : it is inferior to gum-arabic, 
 as a substitute for which it is used in Cape Colony. 
 
 Starch comes next in our list. This important food- 
 substance occurs in commerce in a condition so nearly 
 pure that there is no need to describe its character. For 
 the limited uses to which it is put in artistic practice the 
 uncoloured or white starch should be selected. The 
 starch from rice, wheat, maize, or potatoes may be em- 
 ployed indifferently. Arrowroot may also be used. The 
 preparation of starch-paste does, however, require some 
 care. The best plan is to thoroughly agitate 50 grams of 
 the dry powdered starch with enough cold water to produce 
 a liquid of creamy consistence, and then to pour this 
 
STARCH 
 
 95 
 
 mixture slowly into a vessel in which about 300 cubic 
 centimetres of distilled water is kept in steady ebullition. 
 All but 2 per cent, of the starch will dissolve into a nearly 
 transparent homogeneous paste : the quantity of starch 
 must be reduced if a thin liquid be required. 
 
 H Although starch has not hitherto been much employed 
 in painting, its merits are such as deserve a more extended 
 use. As its constituent elements include neither nitrogen 
 nor sulphur, it is, on the one hand, more stable and less 
 liable to the attacks of micro-organisms than size, white 
 of egg, or casein ; while, on the other hand, its chemical 
 inertness is such that there is no fear of its exercising 
 any injurious effect on colouring matters. But ordinary 
 starch paste, owing to its viscous character, is not very 
 suitable as a binding material for pigments. However, 
 by means of certain treatments, as with ozone, glycerin, 
 or volatile acids, starch can be brought into a more soluble 
 and liquefiable form of great adhesiveness, and admirably 
 fitted as a binding material in water-colour painting. 
 Moreover, the various preparations of soluble starch 
 possess in a high degree the property of becoming in- 
 soluble in cold water after they have once become dry. 
 In consequence, a pigment laid on in admixture with a 
 soluble starch vehicle becomes, after it is dry, irremovable 
 by water, so that further washes of colour may be added 
 without disturbing the previous layers. 
 
 H Soluble starch may be obtained by dissolving 10 
 grams of caustic alkali in 400 cubic centimetres of water, 
 and then stirring in 100 grams of starch previously ground 
 into a paste with a little water. The mixture should then 
 be carefully and uniformly warmed until it has become 
 transparent. After heating for about fifteen minutes, 
 hydrochloric acid is added to the paste until it no longer 
 
96 
 
 STARCH 
 
 shows an acid reaction to litmus paper ; the addition of 
 a little ^-naphthol will protect the product from mould. 
 Similar preparations of starch can be bought under 
 various fancy names (such as vegetable glue). They are 
 produced in the way just described, and are used in the 
 preliminary priming of canvas instead of ordinary animal 
 size ; but before the artist employs any of them, the sample 
 should be tested with reddened litmus paper to see that 
 it has no alkaline reaction, and with blue litmus to learn 
 if an excess of acid be not present. For the careful and 
 necessary neutralization of the product is not unfrequently 
 omitted. 
 
 The drawback to the preparation of soluble starch by 
 treatment with caustic alkali lies in the presence of much 
 alkaline chloride in the product ; it is not desirable to in- 
 troduce sodium chloride, and still less potassium chloride, 
 into a coloured drawing. An entirely satisfactory variety 
 of soluble starch is obtained by the limited action of fresh 
 malt-extract, in very small quantity, upon starch-paste 
 at 75°. Or dilute sulphuric acid may be used, in the 
 same way, to produce the desired transformation, the 
 action being stopped directly the liquid becomes clear, 
 by stirring in an excess of precipitated barium carbonate, 
 which is subsequently removed by filtration. Still another 
 method of preparing soluble starch is by heating it with 
 glycerin. It is recommended to employ 6 grams of dry 
 potato starch and loo grams of glycerin, heated together 
 for about half an hour to 190° C., and then cooled down 
 to 120° C. The soluble starch may be thrown down 
 from this liquid by adding to it three times its bulk of 
 strong alcohol. It must be remarked that the so-called 
 ‘ soluble starch ’ prepared by the several methods just 
 described is not precisely an identical product. In its 
 
HONEY 
 
 97 
 
 most characteristic form it dissolves freely in hot water, 
 but is deposited as a white powder during the cooling of 
 the solution ; cold water holds about 3 per cent, in solu- 
 tion. It is stated that the variety prepared by means of 
 sodium peroxide is much more soluble in cold water. 
 
 Starch contains carbon, hydrogen, and oxygen only, 
 and is a carbohydrate having the empirical formula 
 wCgHj^Og. It is a stable compound. Commercial starch 
 always contains some water, generally from 12 to 18 per 
 cent. 
 
 Dextrin, or British gum, as met with in commerce, is 
 prepared from starch in one or other of several different 
 ways, and is a variable mixture of at least three varieties 
 of true dextrin, soluble or modified starch, starch, a sugar 
 called maltose, and certain minor ingredients and im- 
 purities. It will suffice for the purpose now in view, if 
 we select a commercial dextrin, free from acidity, dis- 
 solving nearly completely in cold water, and then yielding 
 a solution which, even when strong, has only a light 
 yellowish or brownish colour. When a filtered cold-water 
 solution of commercial dextrin is allowed to evaporate on 
 a glass plate, and the residue becomes air-dry, the film 
 of dextrin left differs from one of true gum by being less 
 friable. A solution of dextrin is, however, far less ad 
 hesive than one of true gum of the same strength. 
 
 Honey now claims our attention. It is a common in- 
 gredient in moist water-colours, and was often employed 
 in size-painting. It is used to counteract the brittleness 
 of gum or of size when dry, or, by its absorption and 
 retention of water, to keep a paint moist. Honey con- 
 sists of nearly equal quantities of two sugars known as 
 dextrose and laevulose, a little sucrose or common sugar, 
 small quantities of non-saccharine compounds, and about 
 
 7 
 
98 
 
 GLYCERIN 
 
 20 per cent, of water. As the useful properties of honey 
 depend entirely upon its lagvulose, a solution of this sugar 
 should be employed instead of the raw honey : this may 
 be easily prepared in the following way : Pure pale honey, 
 kept until it has become crystalline and semi-solid from 
 the separation of dextrose, is mixed gradually with four 
 times its bulk of proof spirit, and thoroughly shaken at 
 intervals for a few hours. The pale yellow alcoholic solu- 
 tion is then filtered : the filtrate is a solution of Isevulose, 
 accompanied by small quantities of the other sugars of 
 honey and of harmless impurities, and for some artistic 
 urposes is at once available. Should it be desired to 
 obtain a more concentrated solution of this substance, the 
 liquid may be evaporated to the desired consistency in 
 a porcelain basin, or it may be submitted to distillation 
 in a retort. The aqueous solution of laevulose may be 
 decolourized by filtration through warm animal charcoal. 
 
 Laevulose, when free from water, forms a glassy solid ; 
 but it is usually obtained as a thick syrup. Although 
 this sugar is capable of assuming the crystalline form, it 
 never does so under ordinary conditions. It has a strong 
 attraction for moisture ; on this property its usefulness 
 as a constituent of certain paints depends. 
 
 Glycerin was discovered in 1779 by Scheele as a by- 
 product in the preparation of lead-plaster ; for a long time 
 the comparatively small quantity of glycerin met with in 
 commerce was obtained in this way. It is now prepared 
 from oils and fats by distilling them in a current of super- 
 heated steam, sometimes by first saponifying them with 
 alkalies, or decomposing them with sulphuric acid, and 
 then submitting them to this distillation treatment. 
 
 Glycerin generally occurs as a thick syrup with a sweet 
 taste : when pure, it may be obtained in deliquescent 
 
GLYCERIN 
 
 99 
 
 crystals. Its empirical formula is CgHgOg. It is a 
 strongly hygroscopic or water-attracting substance, the 
 pure water-free glycerin being capable of absorbing more 
 than one-third its weight of water from the air. Com- 
 mercial glycerin always contains water ; the specific 
 gravity of the liquid affords a rough method of estimating 
 the amount. For pure glycerin at i5‘6° C. has the specific 
 gravity 1-265, while that which contains 20 per cent, of 
 water is reduced to 1-213 ; with 30 per cent, it is 1-186, 
 and with 40 per cent. 1-157. The presence of sugar, 
 a not uncommon adulterant, may be recognised by the 
 turbidity caused by mixing the glycerin, after evaporation 
 to remove water, with chloroform. Glycerin containing 
 lead darkens when sulphuretted-hydrogen water is added 
 to it, while the presence of acids may be recognised by 
 blue litmus-paper, which is not reddened by pure glycerin. 
 
 The water-attracting property of glycerin induced me 
 to use it as a substitute for honey in preparing moist 
 water-colours so long ago as 1856, but I am given to 
 understand that it was employed in 1847 by Messrs. 
 Winsor and Newton. Even in cake-colours a trace of 
 glycerin may be introduced with advantage, as it renders 
 them less friable and more easily rubbed down with water. 
 It prevents size, glue, and white of egg from becoming 
 brittle on drying, and on this account may be used in the 
 preparation of linen, canvas, etc., as painting-grounds. 
 Care must, however, be taken in every case not to add 
 more glycerin than is necessary to effect the purpose in 
 view. It is a useful addition to gum-water, i dram to 
 each ounce of gum present being sufficient ; some copying- 
 inks contain it. Modelling clay may be kept moist by 
 means of glycerin. 
 
CHAPTER IX 
 
 WATER-GLASS, LIME- AND BARYTA-WATER 
 
 The name water-glass appears to have been first applied 
 to those silicates of potash and of soda which are soluble 
 in water by Professor J. N. von Fuchs, in 1825 ; but 
 Glauber, so early as 1648, made a soluble potash silicate, 
 which he termed fluid silica. Van Helmont had prepared 
 a similar compound in 1640. The actual manufacture on 
 a commercial scale of these salts dates, however, from 
 1825 only, and the credit of originating their production 
 belongs to Von Fuchs. They differ from the compounds 
 constituting ordinary and insoluble glass by containing 
 no lime, baryta, alumina, or other earthy base. They 
 are made in several ways. The purest sand obtainable 
 is fused with carbonate of potash, or carbonate of soda, 
 or a mixture in the desired proportions of these two car- 
 bonates, in the presence of a little powdered charcoal. 
 The fused mass dissolves by long continued boiling in 
 water, and yields a heavy syrupy liquid of strongly alka- 
 line reaction. By evaporating this liquid to dryness, and 
 fusing the residue, the water-glass may be obtained in a 
 solid form, and then closely resembles ordinary glass in 
 appearance. Water-glass may also be made by heating 
 flints red-hot, quenching them in water, and then digest- 
 ing the powdered silica thus obtained with soda-lye or 
 potash-lye under pressure. 
 
 100 
 
WATER-GLASS 
 
 lOI 
 
 Three kinds of water-glass have been used in water- 
 glass painting or stereochromy. One of these is a potash 
 silicate, another is a soda silicate, the third is a mixture 
 of these two, or a potash-soda silicate, called double water- 
 glass. The solutions of the two former silicates as met 
 with in commerce vary a good deal in their relative pro- 
 portions of silica and alkali ; it is not desirable that they 
 should contain so much silica as was recommended in 
 the original papers of Von Fuchs, the inventor of stereo- 
 chromy, and of Kuhlmann, who subsequently modified 
 the process. Indeed, it has often been found useful to 
 add a little pure caustic potash or caustic soda-solution 
 or ammonia to the commercial solutions of water-glass 
 before diluting them with distilled water for use in this 
 process of painting. 
 
 A solution of water-glass, if allowed to dry upon a piece 
 of ordinary glass, leaves an opaque white irremovable 
 stain. Water-glass alters or destroys, in virtue of its 
 strong alkalinity, the great majority of organic pigments. 
 On the same account it cannot be used with flake-white, 
 aureolin, the chromates, vermilion, and several other 
 mineral pigments. It hardens zinc-white, some of the 
 ochres, earths, and terre verte, forming with them, or 
 with some of their constituents, double silicates, which 
 are quite insoluble in water. The fixative power of water- 
 glass in stereochromy depends indeed mainly upon actions 
 of this order which occur between it and ingredients of 
 the plaster or painting-ground, and of the pigments. It 
 was formerly supposed that when an alkaline silicate acted 
 upon carbonate of lime a double decomposition occurred, 
 of which the only products were an alkaline carbonate, 
 and lime silicate. But subsequent investigation has 
 proved that the change in question is more complex. 
 
102 
 
 LIME- WA TER 
 
 a considerable quantity of a double and insoluble silicate 
 of lime and alkali being produced. Similar double silicates 
 of potash or soda and zinc, of potash or soda and baryta, 
 and of potash or soda and alumina, have been proved to 
 exist in stereochromic work ; doubtless many others are 
 also present They are not only insoluble in water, but 
 are harder than the materials out of which they have 
 been formed. 
 
 Commercial solutions of water-glass contain from 28 to 
 60 per cent, of the alkaline silicate or silicates. They 
 should be carefully preserved from access of air, the 
 carbonic acid of which produces much alkaline carbonate 
 (often separating in crystals in the case of soda), and finally 
 causes the separation of gelatinous silica hydrates. The 
 entrance of calcareous matters, gypsum, zinc-white, etc,, 
 should also be guarded against. 
 
 The subject of water-glass is here treated very briefly, 
 partly because the various processes of stereochromy, even 
 with their latest improvements, are very little used in this 
 country, and partly because the preparations of water- 
 glass specially made for the use of painters may be trusted. 
 To this latter observation I might add the remark that the 
 problem of thoroughly examining a commercial water- 
 glass solution for strength, purity, and due proportion of 
 silica to alkali, is too complex to be undertaken except by 
 a trained chemist. 
 
 Lime-water is the name given to the solution in water 
 of slaked lime, called in chemical language hydrate of lime, 
 calcium hydrate, and calcium hydroxide. To prepare it, 
 quicklime, which has been made by burning (as it is com- 
 monly called) a pure marble, or, preferably, Iceland spar, 
 is slaked with distilled water. The calcium hydrate formed 
 is placed in a wide-mouth stoppered bottle, and covered 
 
LIME-WATER 
 
 103 
 
 with several times its bulk of distilled water. The object 
 of this treatment is to dissolve soda and some other soluble 
 impurities, the major part of which will be removed when 
 the watery liquid in the bottle is decanted from the un- 
 dissolved excess of calcium hydrate which should then be 
 again covered with distilled water which has been recently 
 boiled. The stopper should be well ground and smeared 
 with vaseline. The bottle should be shaken at intervals 
 in order that the water may take up as much calcium 
 hydrate as it can dissolve. After all, this amount is very 
 small, not exceeding, at 15° C., 0-172 part by weight per 
 hundred measures of lime-water. Thus a gallon of lime- 
 water, saturated at about 60° F., could not contain more 
 than 120 grains of calcium hydrate, corresponding to 
 go grains of pure lime or calcium oxide, CaO. In 
 ordinary practice such a perfectly saturated solution is 
 not attainable, while the most carefully prepared and 
 strongest solution is sure to become weakened each time 
 the stopper of the containing vessel is withdrawn by the 
 removal of some of the lime in solution in the form of 
 carbonate of lime. The clearest lime-water, from this 
 cause and from its action on glass, always appears turbid 
 after a time. 
 
 Although so dilute a solution, lime-water gives the most 
 marked reactions of an alkali ; it turns red litmus paper 
 blue, embrowns yellow turmeric paper, and imparts a 
 crimson hue to colourless phenolphthalein paper. It acts 
 energetically upon many organic and some inorganic 
 pigments, owing to its alkaline or basic properties. The 
 ease with which the lime in lime-water unites with car- 
 bonic acid, forming carbonate of lime ( = calcium car- 
 bonate), and the bearing of this action, and of other 
 properties of caustic lime upon the materials and 
 
104 
 
 BARYTA-WATER 
 
 processes of painting are discussed in Chapters II. and 
 XXIII. 
 
 Baryta-water has its uses, but cannot replace lime-water 
 in fresco-painting. It is a solution of hydrate of baryta, 
 barium hydrate, barium hydroxide, for these names all 
 belong to the compound, in distilled water. The distilled 
 water used should have been recently boiled and then 
 cooled out of contact with the carbonic acid of the air. 
 The barium hydrate used may be purchased in the form 
 of colourless crystals having the formula BaOjHg -1- 8 aq. 
 These, if not sufficiently pure, may be washed with cold 
 distilled water, or recrystallized from boiling water, in 
 which they dissolve very abundantly. A saturated cold 
 solution is made by placing rather more than i ounce of 
 these crystals in a bottle containing a pint of distilled 
 water : the bottle should be almost full, the stopper should 
 be smeared with a little vaseline. If the crystals dissolve 
 completely, after repeated agitation, a few more should 
 be added so as to leave a small excess at the bottom of 
 the bottle. If the solution be clear it may be used directly 
 from the bottle, as required ; if filtration be needed, a 
 glass plate should be placed on the funnel during the 
 operation to prevent free access of air, and the clear filtrate 
 should be received at once in the bottle in which it is 
 to be preserved. A solution of barium hydrate saturated 
 at 15° C., contains nearly 2'g grams of BaO in 100 cubic 
 centimetres, or 2,023 grains per gallon. It is thus about 
 seventeen times stronger than a solution of calcium hydrate 
 saturated at the same temperature. Baryta-water, as it 
 is called, is a powerfully alkaline liquid, becoming covered 
 with a film of white barium carbonate on exposure to the 
 air. By blowing air from the lungs through a glass tube 
 into baryta-water, a dense white precipitate is formed. 
 
BARYTA. WATER 
 
 105 
 
 Unfortunately, the binding power of barium carbonate is 
 almost nil, so that baryta-water in mural painting is of 
 service, not directly as a medium, but for destroying 
 traces of calcium sulphate (gypsum) in the plaster-ground, 
 and thus liberating a corresponding amount of lime-water. 
 It may also be used for testing the effect of an alkaline 
 earth on the powdered pigments which it is proposed to 
 use in the work, in order to see if they can withstand its 
 action ; those unaffected by baryta will prove to be 
 unchanged by lime. 
 
CHAPTER X 
 
 SOLVENTS AND DILUENTS 
 
 The liquids to which attention is directed in the present 
 chapter are, with very few exceptions, not miscible with 
 water. Of water itself it is not necessary to say anything 
 beyond this, that distilled water is best adapted for almost 
 every purpose to which this liquid is applied in the prepara- 
 tion of pigments, as a solvent for gum, honey, etc., and in 
 the practice of painting in water-colours. Next to dis- 
 tilled water may be ranked rain-water collected in the 
 open country, then the softer kinds of water yielded by 
 some streams, springs, and wells. Waters containing 
 more than 20 or 30 grains per gallon of solid matters in 
 solution should be avoided as far as possible. It should 
 be noted that very hard waters tend to curdle or precipi- 
 tate the particles of colouring matter in the water-colour 
 paints which they may be used to dilute. 
 
 Before considering the chief solvents and diluents, a 
 list of the most important of those which have been ob- 
 tained in a pure state or isolated may be given. Most of 
 these are artilicial or laboratory products, the natural 
 liquids employed in the processes of painting being mix- 
 tures, not infrequently both variable and complex. In 
 the following table the several definite compounds in- 
 cluded are arranged according to their boiling-points, those 
 
 106 
 
SOLVENTS 
 
 107 
 
 which boil at low temperatures being placed first : an 
 asterisk indicates that the liquid is miscible with water : 
 
 TABLE OF SOLVENTS 
 
 Name 
 
 Boiling-point 
 
 Specific 
 
 Gravity 
 
 Formula 
 
 Ether - - - 
 
 35° C. 
 
 = 95 ° F- 
 
 - 0-719 - 
 
 CdboO. 
 
 Carbon bisulphide 
 
 46° 
 
 = 115° 
 
 - 1-271 - 
 
 CS^. 
 
 *Acetone 
 
 56° 
 
 ^133° 
 
 - 0-798 - 
 
 C3HP. 
 
 Chloroform - 
 
 61° 
 
 = 142° 
 
 - I -500 - 
 
 CHCI3. 
 
 * Wood-spirit - 
 
 66° 
 
 = 151° 
 
 - 0-798 - 
 
 CHp. 
 
 ♦Alcohol 
 
 78° 
 
 - 172° 
 
 - 0-794 - 
 
 C,H, 0 . 
 
 Benzene 
 
 81° 
 
 = 178° 
 
 - 0-884 ■ 
 
 CeHe. 
 
 Toluene 
 
 iii° 
 
 = 232° 
 
 - o-86g - 
 
 C„Hg. 
 
 Epichlorhydrin 
 
 117° 
 
 = 243° 
 
 - 1-191 - 
 
 C3H5CIO, 
 
 Perchlorethylene - 
 
 121“ 
 
 = 250° 
 
 - I -620 - 
 
 C,Ch. 
 
 Amyl alcohol 
 
 131° 
 
 = 268° 
 
 - 0-814 - 
 
 CjHjjO. 
 
 Pinene - 
 
 160° 
 
 = 311° 
 
 - 0-859 - 
 
 
 Cineol = eucalyptol 
 
 173° 
 
 = 343 ° 
 
 - 0-930 - 
 
 
 Cymene 
 
 175° 
 
 = 347 ° 
 
 - 0-858 - 
 
 CiuHi 4 . 
 
 Sylvestrene - 
 
 176° 
 
 = 349 ° 
 
 - 0-851 - 
 
 C-ioHjg. 
 
 Limonene 
 
 177° 
 
 = 351° 
 
 - 0-850 - 
 
 CiqHjs. 
 
 Dipentene 
 
 177° 
 
 = 351° 
 
 - 0-846 - 
 
 CioFI]6 - 
 
 Citral - 
 
 228° 
 
 = 442° 
 
 - 0-897 ■ 
 
 CjoFIieO. 
 
 Geraniol 
 
 230° 
 
 = 446° 
 
 - 0-894 ■ 
 
 
 The pinene, sylvestrene, limonene, and dipentene named 
 in the above table are examples of what are now called 
 terpenes. Mixtures of these and of a few other terpenes 
 of less importance constitute what is generally known as 
 oil or spirit of turpentine. Terpenes are very frequent and 
 often very abundant constituents of the volatile, ethereal, 
 or essential oils extracted from plants. Some, however, 
 of these volatile and strong-smelling essences consist 
 mainly of liquids containing oxygen, such as cineol or 
 eucalyptol, CjgHjgO, which occurs to a large extent in the 
 oils distilled from many species of eucalyptus. Besides 
 the compounds in our list and a certain number of essen- 
 
io8 
 
 ETHER 
 
 tial oils from plants, we shall have to consider some of the 
 more volatile liquid constituents of natural petroleum and 
 of artificial paraffin oils. The fixed or fatty oils, which 
 are constantly used in painting and in the manufacture of 
 varnishes, have been already discussed in Chapter V. 
 
 Ether, often called sulphuric ether, is a very mobile 
 liquid of extreme volatility, and possesses a penetrating 
 odour. Its vapour, given off freely at ordinary tempera- 
 tures, forms with air a highly inflammable and explosive 
 mixture. Great care is therefore required in using this 
 liquid ; no light must on any account be brought near it. 
 It does not mix with water, but floats on the surface, 
 although it dissolves in water to the extent of about lo per 
 cent. Commercial ether contains water and alcohol along 
 with traces of other impurities. It is seldom necessary to 
 remove the alcohol from it (for varnish-making, etc.), but 
 it can be got rid of by repeatedly shaking the crude ether 
 with water, whereby much ether also is dissolved away. 
 The water present interferes seriously with the use of 
 ether as a solvent for resins, etc., but it may be removed 
 by careful rectification with fused calcium chloride, that 
 substance having previously been allowed to remain in 
 contact with the liquid for a day. A final distillation 
 from a little metallic sodium completes the drying of the 
 ether and also removes, if used in sufficient quantity, the 
 alcohol present. Great care is necessary in distilling 
 ether to secure, by a current of ice-cold water in the 
 condenser, the condensation of the vapour. 
 
 Carbon Bisulphide . — This heavy, oily but volatile liquid 
 readily gives off vapour at ordinary temperatures. It is 
 poisonous, and the same care in manipulating it must be 
 taken as that insisted upon in the case of ether. The 
 smell of the ordinary commercial bisulphide is most offen- 
 
ACETONE 
 
 109 
 
 sive, but it is now possible to purchase a specially purified 
 sort from which a particularly disagreeable sulphur-com- 
 pound of nauseous odour has been removed. Carbon 
 bisulphide sinks in water : it is a powerful solvent for 
 many resins, and mixes perfectly with the fixed and 
 essential oils in all proportions. 
 
 Acetone also occurs in crude wood-naphtha. It has a 
 penetrating but agreeable odour. It is miscible with 
 water, alcohol, oils, etc., and dissolves many resins, 
 camphor, fixed oils, and allied bodies. It is sometimes 
 serviceable as a solvent for discoloured varnishes on 
 pictures. Commercial acetone is very impure, containing 
 wood-spirit, empyreumatic oils, and water. 
 
 Chloroform is another powerful solvent of resins. It has 
 a pungent but sweet taste, is not miscible with water, and 
 is very heavy. Commercial chloroform often contains 
 alcohol and other foreign matters, from most of which it 
 may be purified by redistillation from a little oil of vitriol 
 followed by a second distillation from fragments of quick- 
 lime. For making varnishes neither water nor alcohol 
 should be present in chloroform, but there are other 
 impurities which do not interfere with its employment 
 for such a purpose. 
 
 Wood-spirit, or methyl-alcohol, is a constituent of wood- 
 naphtha, a product of the destructive distillation of wood. 
 It rarely occurs in commerce in a state even approaching 
 to that of purity. It is miscible with water in all propor- 
 tions, but not with fixed oils. When free from water it 
 may be used as a solvent for some resins, and for remov- 
 ing discoloured varnish from oil-paintings. Methylated 
 spirit now contains in 100 measures 9^ measures of crude 
 wood-spirit and \ measure of petroleum oil, the remainder 
 being rectified spirit of wine. 
 
1 10 
 
 ALCOHOL 
 
 Alcohol, or pure spirit of wine, is met with in commerce 
 practically free from all impurities save water. Proof 
 spirit, rectified spirits of wine, and methylated spirit, 
 though of service in cleaning oil-pictures and for many 
 other purposes, ought not to be used in the preparation of 
 varnishes. For this purpose pure alcohol, often called 
 absolute alcohol, is required ; but provided that it con- 
 tains no water the presence of wood-spirit is no drawback 
 to its use. In commerce, nearly absolute alcohol, made 
 both from spirits of wine and from methylated spirit, is 
 obtainable ; but it may be prepared by operating upon 
 the strongest available spirits of wine in the following 
 manner : The spirit is distilled in a water-bath until no 
 further strengthening of the alcoholic distillate is secured 
 by repetition of the process ; then a dry retort is half- 
 filled with small, clean, hard fragments of quicklime, the 
 strong spirit is poured upon these so as to somewhat 
 more than cover them, and then the whole is left over- 
 night ; distillation from a water-bath is then commenced, 
 when it will be found that a spirit comes over which con- 
 tains no more than one part of water in two hundred. 
 Even this small proportion may be removed by redistilling 
 the alcohol from a very little metallic sodium. The last 
 distillate, when a small portion of it is shaken up with its 
 own bulk of benzene, should mix perfectly with the latter, 
 causing no turbidity. But it should be borne in mind 
 that absolute alcohol is a very hygroscopic liquid, greedily 
 absorbing water from the air ; it must, therefore, be kept 
 in well-stoppered bottles, filled almost completely. In 
 absolute alcohol some of the more intractable resins, even 
 some kinds of copal, readily dissolve. The specific gravity 
 of absolute alcohol at 15° C. is • 794 > while, if it contains 
 but I per cent, of water, its specific gravity is distinctly 
 higher, namely, '797. 
 
BENZENE 
 
 III 
 
 Benzene is employed not only as a solvent, but as a 
 diluent of the medium or oil employed in painting. It is 
 obtained from the lighter naphtha separated in the frac- 
 tional distillation of coal-tar. The benzene (also called 
 benzol) of commerce is rarely pure. The presence of small 
 quantities of higher hydrocarbons of the same series is of 
 little moment, but it also contains about one half per cent, 
 of a sulphur compound called thiophene (C^H4S), to which 
 the offensive odour of ordinary benzene is partly due. 
 Thiophene is, however, much more soluble in cold oil of 
 vitriol than is benzene, and may be removed by several 
 treatments of the benzene with small quantities of this 
 powerful acid. Benzene thus purified can now be pur- 
 chased. Benzene is a mobile liquid, not miscible with 
 water, but dissolving readily in all proportions in most if 
 not all of the liquids now being described. It dissolves 
 oils and very many of the harder as well as all the softer 
 resins. 
 
 Toluene, commercially known as toluol, much resembles 
 benzene, and may be used for the same purposes, although 
 it is less volatile. Commercial toluene has a disagreeable 
 smell, arising from the presence of a sulphur compound 
 (thiotolene), which is more difficult to remove from the 
 liquid than the thiophene from benzene. 
 
 Toluene of good quality and at a moderate price may 
 be obtained from Kahlbaum of Berlin. It constitutes a 
 useful diluent and solvent when used with the spirit-fresco 
 medium. 
 
 Epichlorhydrin has been employed as a solvent for some 
 of the copals and other intractable resins in the manu- 
 facture of varnishes. Without further trials it would be 
 unwise to employ this liquid in artistic painting, yet the 
 resins dissolved in it seem to retain much of their original 
 
12 
 
 TERPENES 
 
 toughness and hardness. The same statement may be 
 made in reference to several other similar chlorine com- 
 pounds, which possess the merits of cheapness and non- 
 inflammability. 
 
 Amyl alcohol, the chief constituent of fusel-oil, is used 
 by picture-cleaners for the removal of discoloured varnish. 
 Its vapour is suffocating and even poisonous. 
 
 Pinene, Sylvestvene, Limonene, and Dipentene, with several 
 other similar compounds, are the main constituents of the 
 various liquids to which the ordinary name of turpentine, 
 or, rather, spirit or oil of turpentine, is applied. All these 
 liquids are hydrocarbons, having the same composition in 
 loo parts, expressed by the empirical formula Cj„Hjg. 
 But these liquids — of which about ten are known — differ 
 from one another in some of their chemical and physical 
 characters, such as oxidizability, boiling-point, specific 
 gravity, and action on light. The extreme importance 
 of turpentine in the process of oil-painting, and in the 
 manufacture of varnishes, warrants a somewhat full con- 
 sideration of its several constituents. 
 
 Tnvpeniine, properly so called, is not a liquid, but the 
 solid or semi-solid resinous secretion of many trees, chiefly 
 coniferous. Some exudes naturally, but much more is 
 obtained by artificial incisions. It consists of a mixture 
 of one or more true resins and resinous acids in which 
 oxygen is present, with one or more liquid hydrocarbons 
 which contain (as the name imports) nothing but carbon 
 and hydrogen, and therefore no oxygen. These hydro- 
 carbons are called in chemical language tevpenes, a term 
 by which they will be designated henceforth in the present 
 chapter. On distilling the crude turpentine or resins 
 alone or with water, or in a current of steam, the terpenes 
 distil over while the solid part remains behind ; this, on 
 
TERPENES 
 
 113 
 
 fusion, is called rosin or colophony. It need not be 
 further considered, as it is of no value in painting, being 
 friable and more or less strongly coloured ; it is, however, 
 employed in making certain ‘ dryers,’ known as resinates 
 (or better, rosinates), containing cobalt, manganese, etc. 
 We confine our attention, therefore, to the distillate or 
 terpenes. It should be added, however, that the leaves^ 
 cones, and other parts of many coniferous trees, them- 
 selves yield various terpenes when submitted to distil- 
 lation, and that many of the volatile or essential oils of 
 aromatic plants other than conifers contain or consist of 
 terpenes. The oils expressed from the rinds of lemons 
 and oranges afford illustrations of this remark. 
 
 Terpenes differ from one another in several obvious and 
 in several obscure ways. Even now the chemistry of 
 these liquids is not by any means clearly and completely 
 unravelled. We need not here concern ourselves with 
 those minute differences in chemical and physical pro- 
 perties by which the identity of individual terpenes is 
 established, but may confine our attention to their most 
 salient characteristics. Of these none is more important 
 than the behaviour of terpenes with regard to atmospheric 
 oxygen. Some of these liquids absorb oxygen readily, 
 and to a large extent, from the air, becoming thereby 
 resinified— in fact, they thus yield sticky, resinous, semi- 
 solid bodies, closely resembling the crude turpentine from 
 which they have been prepared. Everyone who has had 
 occasion to use spirit of turpentine frequently must have 
 noticed the production of a sticky substance about the 
 neck of the bottle in which this liquid has been kept. 
 Moreover, the spirit of turpentine itself will often have 
 been noticed to have become cloudy, viscid, or almost 
 solid, especially if it has been contained in a bottle fre- 
 
 8 
 
TERPENES 
 
 114 
 
 quently opened, and not quite full. Besides these obser- 
 vations another will have been made — different specimens 
 of spirit of turpentine will have been found to differ 
 much as to the rate at which these changes have taken 
 place. Some samples, even in half-full bottles, remain 
 clear and limpid for long ; others become thick, opaque, 
 and sticky in a few weeks. Such changes are undesirable 
 in a solvent, diluent, or painting medium, on many 
 grounds. The resin formed is an unsatisfactory one — 
 soft, sticky, and contractile. The liquid decreases so 
 greatly in mobility, and increases so greatly in viscosity, 
 that its utility in thinning oil pigments, and in making 
 fine touches, is greatly impaired. And this thickening of 
 the liquid is accompanied by the production of acid sub- 
 stances and of water, which affect injuriously the ease of 
 working and the stability of the picture. Spirit of tur- 
 pentine should disappear by evaporation quickly and 
 completely from the painting into which it has been intro- 
 duced. Now, if it be easily oxidizable, even if it be kept 
 from experiencing change before it is actually employed, 
 it will, during the very time in which it is being used, 
 attract oxygen ; so that though a great part of it will 
 escape by evaporation, the remainder will resinify on the 
 canvas itself, adding a sticky deposit to the drying oils 
 and hard resms which may have been used as the paint- 
 ing medium. It is clear, from all the above considera- 
 tions, that the greatest care ought to be taken in selecting, 
 in the first instance, such a sort of spirit of turpentine 
 as will resist oxidation under ordinary conditions. Even 
 an inferior spirit may be used, with a minimum of dis- 
 advantage, if immediately after distillation it be poured 
 into a number of small bottles, so as to fill each of them 
 completely ; they should be at once closed with sound 
 
TERPENES 
 
 115 
 
 corks. In this way the contents of a bottle may be used 
 up very soon after it has been opened. Another precau- 
 tion may be taken ; A few small fragments of hard quick- 
 lime may be placed in each bottle to absorb any moisture 
 produced by oxidation, and also the acid bodies which are 
 formed at the same time. Even with the choicer samples 
 of spirit of turpentine, which pass much less easily into 
 resins, this precaution is desirable ; but in this case the 
 employment of many small bottles is unnecessary, and 
 it will suffice to put a few hard pieces of lime, free from 
 powder, into a pint or quart bottle, and then to fill it 
 with the spirit. The clear liquid may be poured off as 
 required for use, any disintegrated particles of lime sink- 
 ing readily to the bottom of the vessel. 
 
 Before giving details as to the sources and character- 
 istics of the best terpenes, it may be useful to mention that 
 commercial samples of spirit of turpentine m.ay be tested 
 and compared by means of a very simple experiment. 
 Obtain the required number of small flat-bottomed, conical 
 glass flasks with wide mouths, one flask for each sample ; 
 these flasks are known as Erlenmeyer’s. Into the flasks 
 pour enough of the several samples to cover the bottom 
 to the depth of one-eighth of an inch ; label each flask 
 to correspond with the sample, and lightly close each 
 mouth with a plug of carded cotton — the date of the 
 experiment should be added on the label. Shake each 
 flask so as to cause a number of bubbles to be formed in 
 the liquid ; the more rapidly these bubbles break, the 
 better is the sample. Repeat the experiment of shaking 
 the samples at short intervals for a few weeks — notable 
 changes in the viscosity of the oils will be observed 
 sooner or later. Any sample which after one month 
 remains clear, and in which the bubbles formed on agita- 
 
TERPENES 
 
 1 16 
 
 tion break almost as quickly as at first, may be accepted 
 as of good quality. Another test for discriminating 
 between the samples, so far as their state at the time of 
 the experiment is concerned, is the very simple one of 
 placing one drop of each oil upon a sheet of writing- 
 paper, and gently warming the translucent stain it forms; 
 with a good oil the mark completely disappears. 
 
 Two other obvious characteristics of different samples 
 of spirit of turpentine may now be noticed — namely, 
 odour and boiling-point. Some samples have a much more 
 agreeable scent than others ; the vapour of these seems 
 to have a less marked tendency to produce headache 
 than that of the pungent and cruder-smelling varieties. 
 The range in boiling-point is not very extensive ; but 
 it may be taken as about 25° C., the figures ranging 
 from 155° to i8i.° Samples having lower boiling-points 
 evaporate more quickly than those which enter into 
 ebullition at higher temperatures. The solvent power 
 on resins differs with different kinds ; this is a property 
 which is of importance in varnish-making, but very little 
 accurate knowledge exists on this point. But there is one 
 characteristic almost peculiar to the terpenes which must 
 not be overlooked. When oxidizing they possess, unlike 
 the alcohols and benzene and petroleum spirit, a power of 
 starting or increasing the absorption of oxygen by linseed 
 or other drying oils; in fact, they act as siccatives. This 
 property is constantly utilized in oil-painting ; probably it 
 is connected with the formation of hydrogen peroxide which 
 passes on its surplus atom of oxygen to the oil present. 
 
 A few of the more important turpentine oils may now 
 be named ; 
 
 American oil, chiefly from ^Pinus palustris and P. 
 
 Tada. 
 
TERPENES 
 
 117 
 
 Austrian oil, partly from Pinus Lavicio, partly from 
 P. Pumilio. 
 
 Burmese oil, from Pinus Kliasya. 
 
 French oil, from Pinus Pinaster ( = P. maritima). 
 
 German oil, from Pinus sylvestris, P. Cemhra, P. Abies, 
 P. vulgaris, etc. 
 
 Juniper oil, from Junipertis communis. 
 
 Russian and Swedish oils, chiefly iroxn Pinus sylvestris 
 and P. Ledebourii. 
 
 Strasburg oil, from Abies pectinata. 
 
 The above-named turpentine oils are accompanied by 
 small amounts of various resins, camphor, and other 
 oxygenated bodies, from which they may be separated 
 by treatment with caustic potash, metallic sodium, and 
 fractional distillation. 
 
 From the above-named liquids a number of terpenes 
 have been isolated. Among the better known of these 
 the following may be mentioned. 
 
 1. Pinene, with a boiling-point of 160° C. It exists in 
 two forms, distinguished by their rotatory power on 
 polarized light : dextro-pinene is the chief constituent 
 of German and American oil of turpentine. The other 
 form of pinene, laevo-pinene, occurs in large proportion in 
 French oil of turpentine ; it absorbs oxygen less readily 
 than dextro-pinene, and therefore resinifies more slowly. 
 In consequence, it is more suitable for artistic uses, such 
 as the thinning of paints, or as an ingredient of varnishes, 
 
 2. Phellandrene. — Boiling-point 171° to 172°. This 
 terpene has been separated from eucalyptus oil, that is, 
 from the oil obtained by the distillation with water of 
 the leaves of one of the numerous species of eucalyptus, 
 E. amygdalina. It is one of the most alterable of all 
 terpenes, and the oils containing it should be avoided. 
 
ii8 
 
 TERPENES 
 
 3. Lintonene. — This terpene, like most of the others, 
 occurs in two forms or varieties, having opposite actions 
 on polarized light. It is sometimes called citrene. It 
 boils at 177°. It is best prepared from orange-peel oil, 
 which yields over 90 per cent, of dextro-limonene when 
 distilled from caustic potash. When pure it is less alter- 
 able than dextro-pinene and phellandrene, though it 
 resinifies after a time. 
 
 4. Sylvestrene. — Boiling-point 176°. When pure it has 
 the smell of bergamot, but generally presents the odour 
 of fir-wood. It is dextro-rotatory, and forms the chief 
 constituent of Russian and Swedish oil of turpentine, 
 and of some of the German oils. On exposure to air 
 it oxidizes readily, and leaves a sticky resin. It has 
 a particularly strong odour. 
 
 5. Dipentene, which boils at about 177° C., is optically 
 inactive, and may be made by heating some of the other 
 terpenes to 250° — 270° for some hours, or by mixing 
 dextro- and lasvo-limonene together. The only natural 
 product in which dipentene is known to occur is the 
 volatile oil which accompanies common camphor. Its 
 odour resembles that of citron oil : it resinifies to about 
 the same extent as limonene. 
 
 From the preceding descriptions it may be gathered 
 that of all the above terpenes, limonene and dipentene are 
 the least alterable. They have, however, somewhat high 
 boiling-points, and evaporate more slowly than most of 
 the other terpenes. 
 
 Here it may be mentioned that the presence of water 
 in a terpene, or a mixed essential oil, may be detected by 
 the cloudiness which it shows when mixed with thrice 
 its volume of benzine or of petroleum-spirit. To remove 
 traces of water from any of the less volatile liquids we 
 
TERPENES 
 
 iig 
 
 have been considering, without having recourse to distil- 
 lation from caustic potash, or from quicklime, the follow- 
 ing simple procedure may be adopted : A glass flask is 
 three-fourths filled with the liquid, and then it is kept at 
 a temperature of iio° to 120° C., so that the moisture 
 present is disengaged as vapour without the terpene or 
 essential oil itself boiling : drops of moisture will condense 
 in the neck of the flask, and may be removed from time to 
 time by means of a roll of blotting-paper. The mouth of 
 the flask should be loosely plugged with carded cotton. Of 
 course this process is applicable only to liquids which boil 
 at temperatures considerably over 120°, like the terpenes. 
 
 In connexion with the terpenes two other liquids and 
 one solid remain to be mentioned. The liquids are ‘ oil of 
 amber’ and ‘oil of copal.’ These are obtained by strongly 
 heating the resins in question. They are employed as 
 efficient solvents for the harder resins. Oil of amber may 
 be obtained in commerce at a moderate price. Its offen- 
 sive smell, partly due to compounds of sulphur, may be 
 lessened by adding to it some white lead and solid caustic 
 potash, and afterwards distilling it. It contains amongst 
 other liquid constituents at least one terpene. Its boiling- 
 point rises, as distillation proceeds, from 110° C. to 260°. 
 Camphor is expressed by the formula C^gH^gO, and is 
 obtained chiefly from Cinnamomum Camphom, a tree of 
 Formosa, China and Japan. It is a tough crystalline 
 solid of penetrating odour and pungent taste. It is 
 soluble in all the liquids named in the present chapter. 
 Although it boils at so high a temperature as 204° C., it 
 readily and rapidly volatilizes at ordinary temperatures. 
 It is used to aid the solution of some of the harder resins 
 in the making of varnishes, but its presence in a varnish 
 is objectionable, for it slowly escapes after the apparen- 
 
120 
 
 PET ROLE UM -SPIRIT 
 
 drying-up of the varnish, and thus causes a deterioration 
 of the lustre and continuity of the resinous film. 
 
 Petroleum -spirit. — When native petroleum and the 
 similar materials obtained in the distillation of bitumin- 
 ous shales, etc., are submitted to fractional distillation, 
 the more volatile portions which come over first con- 
 stitute the liquids variously known as benzine, gasoline, 
 benzoline, ligroine, petroleum-naphtha, petroleum-ether, 
 and petroleum-spirit. This liquid consists entirely of 
 hydrocarbons, some of which belong to the paraffin series, 
 while others are naphthenes. Their boiling-points are all 
 under 170° C., while some of them boil as low as 50°; 
 indeed, commercial samples of petroleum-spirit often 
 begin to enter into ebullition at a lower temperature even 
 than this. The series of petroleum products may be 
 roughly grouped thus : 
 
 Petroleum-spirit boils below 170° C.; specific gravity, 
 •6 to 
 
 Lamp-oil, kerosene, photogen, or paraffin-oil, boils 
 between 180° and 220°, and has a specific gravity of 78 
 to *82. 
 
 Solar-oil, lubricating-oil, vaseline, and paraffin-wax, are 
 heavier products, with a range of specific gravity from 
 •83 up to ‘94. Their viscosity increases with their density 
 until the semi-solid vaseline and the solid paraffin-waxes 
 are reached. The latter substances have been described 
 already, the former are not available in painting : in fact, 
 their presence even in traces in petroleum-spirit — an 
 extremely useful solvent and diluent — should be carefully 
 guarded against. They neither escape by evaporation 
 nor harden in the lapse of time. Thus petroleum-spirit 
 remains alone for further consideration. 
 
 As a solvent for resins, and as an extremely volatile 
 
PET ROLE UM -SPIRIT 
 
 I2I 
 
 and very thin liquid for diluting oily vehicles and paints 
 in the process of oil-painting, the variety of petroleum- 
 spirit which boils between 50° and 70° C. is the most 
 suitable. It contains hydrocarbons represented by the 
 formulae CgH^j and CgH^^. It must be used with great 
 caution on account of its easy inflammability and the 
 readiness with which it gives off a vapour, which, when 
 mingled with atmospheric air, is highly explosive. It 
 may be used for many purposes in lieu of benzene (from 
 coal-tar naphtha), being much cheaper and quite as 
 efficient. A drop of this variety of petroleum - spirit 
 on paper evaporates very quickly, leaving no greasy 
 stain. 
 
 Another variety of this petroleum-spirit is obtained 
 by collecting apart the fractions which boil between 
 100° C. and 130°. These contain heptane (C^H^g), octane 
 (CgHjg), heptylene and octylene (CgHjg), and 
 
 other hydrocarbons. This mixture is less volatile than 
 that just described, it dries more slowly, and is a less 
 energetic solvent. 
 
 A third variety boils between 130° and 170° and is avail- 
 able for many of the purposes for which turpentine-oil is 
 employed. It is not advisable, in my opinion, to use 
 fractions having a higher boiling-point than 170° C. as 
 additions to the pigments and vehicles of oil-painting, 
 for, though their slow drying is sometimes an advantage, 
 there exists the danger of their incomplete evaporation 
 from the painted surface. If they remain even in traces 
 in the finished work after it has been varnished, they may 
 give rise to the same accidents as are caused by the 
 treacherous though seductive asphalturn. 
 
 It should be remembered that the various petroleum 
 liquids just described do not resinify, nor do they leave 
 
122 
 
 OIL OF SPIKE LAVENDER 
 
 any permanent stain or mark upon paper which has been 
 moistened with them. 
 
 In the Table of Solvents on p. 107 three liquids contain- 
 ing oxygen and related to the terpenes find a place. Two 
 of these, cineol or eucalyptol, and geraniol, represented by 
 the empiric formula CigH^gO, are alcoholic in consti- 
 tution ; while the third, known as citral, belongs to the 
 aldehydes. These and several other allied oxidized com- 
 pounds, as well as a few ethereal salts known as esters, 
 enter largely into the composition of certain essential oils 
 occasionally used in oil-painting. We will introduce a 
 few remarks concerning some of these compounds under 
 the names of the essential oils of which they are important 
 components. 
 
 Oil of Spike Lavender IS, obtained by distillation from the 
 flowers of a species of lavender, Lavandula spica. Its 
 specific gravity varies from '905 to '918 : it dissolves in 
 three volumes of 70 per cent, alcohol. It contains about 
 30 to 40 per cent, of an alcohol, linalol (CjgHjgO), about 
 5 per cent, of an ester, linalyl acetate, a considerable 
 quantity of cineol (eucalyptol), and a small proportion 
 of terpenes. It is often adulterated with rosemary oil. 
 When spike oil is exposed for a long time to the air, the 
 part which does not evaporate gradually thickens, owing 
 to the oxidation of its constituents. This thickened oil, 
 although usefully employed in the application to porcelain 
 of enamel colours, is useless in oil and spirit-fresco 
 painting. To preserve spike oil in its thin and mobile 
 state, the precautions recommended in the case of tur- 
 pentine (p. 1 14) should be taken. Spike oil is a powerful 
 solvent of resins ; it is one of the components of Gambier- 
 Parry’s spirit-fresco medium. 
 
 Oils of Eucalyptus are derived from many species of 
 
OIL OF ORANGE 
 
 123 
 
 eucalyptus, and differ from one another widely as to the 
 relative proportions in which their components exist, and 
 also in their odour. Cineol, or eucalyptol, is the chief 
 and most characteristic constituent of the majority of 
 them, occurring to the extent of 50 to 65 per cent, in the 
 oil from E. globulus, the commonest of all kinds. On the 
 other hand, the oil from E. maculata, var. citriodora, some- 
 times contains no less than 95 per cent, of citronellal, an 
 alcohol. This oil is of particularly agreeable odour, as 
 are also the oils of E. cneovifolia, E. corymbosa, and E. 
 dealbata. For a diluent in oil-painting it is probable that 
 any one of these oils may be chosen with equal propriety, 
 our choice being guided by the odour of the sample. 
 
 Oil of Lemon . — Though the terpenes known as dextro- 
 and laevo-limonene constitute the main portion of this oil, 
 yet its characteristic odour is partly due to the presence 
 of 6 to 9 per cent, of the aldehyde citral mentioned above. 
 This compound is occasionally separated from lemon-oil ; 
 by its removal the remainder becomes richer in terpenes 
 and more fitted for the use of the painter. 
 
 Oil of Orange . — This essential oil, which, like that of 
 lemon, is obtained by expressing the rind of the fruit, is 
 remarkably rich in limonene (dextro-limonene). This, 
 with small quantities of other terpenes, makes up over 
 95 per cent, of the oil. Although the expressed oil pos- 
 sesses a yellow colour, it may be obtained absolutely free 
 from colour and of agreeable odour, by distillation under 
 reduced pressure. 
 
 Oil of Rosemary. — This oil varies in specific gravity 
 between -9 and -918. It contains about 20 per cent, of 
 an ester, bornyl acetate (CJ2H20O21), and 6 per cent, of 
 borneol. Its other constituents include lineol and two 
 terpenes. 
 
124 
 
 CYMENE 
 
 Cymene . — There are twenty or more varieties of the 
 hydrocarbon expressed by the empirical formula 
 The best known of these is the agreeable lemon-scented 
 liquid contained in cumin oil from the seeds of Cuniimm 
 cyminum. Its full sciemific name is paramethylisopropyl- 
 henzene, while its constitution is shown by the formula 
 CH3,C^,H^.CH(CH3)2. This hydrocarbon serves the 
 same purpose as a diluent as the terpenes, but is too 
 costly for general use. Doubtless some of the other 
 forms of the hydrocarbon might be similarly em- 
 
 ployed. The range of their boiling-points lies between 
 i68° and 204° C. Some are solid at ordinary temperatures. 
 
CHAPTER XI 
 
 SICCATIVES OR DRYERS 
 
 The terms ‘siccatives’ and ‘dryers’ are applied to three 
 classes of substances. Perhaps the most correct or appro- 
 priate application of these words is to those metallic com- 
 pounds which are used in order to increase the rate at 
 which the drying oils harden, but in the literature of the 
 subject w'e often find that drying oils which have been 
 thus treated, and likewise certain resinous solutions, are 
 spoken of as siccatives. In the present chapter we describe 
 the dryers proper only, referring our readers to the chapters 
 on oils and on varnishes for the necessary particulars con- 
 cerning the other materials which may be included in the 
 group under discussion. 
 
 Lead and several of its salts have been long and widely 
 used as dryers. Metallic lead in the form of foil, litharge 
 or lead protoxide, minium or red lead, lead peroxide, sugar 
 of lead or lead acetate, the basic lead acetate, and white 
 lead itself, have all been used in this way, chiefly for the 
 purpose of making linseed or other painting oil dry more 
 quickly. Some of these compounds, particularly sugar 
 of lead, have been introduced into the very picture itself. 
 It was a common practice to employ powdered sugar of 
 lead or a solution of this salt in water to hasten the drying 
 of vehicles and of slow-drying pigments which have been 
 
 125 
 
126 
 
 MANGANESE DRYERS 
 
 ground in oil. I have seen one of the results of this com- 
 mingling of sugar of lead with the medium or the paint 
 in the production of an immense number of small spots 
 in the picture, sometimes appearing through the surface- 
 varnish in the form of a white efflorescence. This 
 efflorescence consists at first of lead acetate in crystals, 
 but these soon attract carbonic acid from the air and 
 become lead carbonate, which, in its turn, is changed 
 into lead sulphide by the action of sulphuretted hydro- 
 gen. This tendency of the lead compounds to yield 
 brown or black lead sulphide is, indeed, the great draw- 
 back to any use of these substances as dryers. When 
 oil is left in contact with them, and especially when heat 
 is applied to the mixture, some of the lead dissolves, 
 forming, with the fatty acids of the oil, lead-soaps. These 
 soaps are distributed uniformly throughout the oil, and 
 help to make it dry and harden quickly. The same action 
 occurs when white lead is ground as a paint with oil, and 
 has been urged as an objection to the use of those white 
 leads which contain hydrate of lead, a compound which 
 acts upon oil more quickly and thoroughly than the car- 
 bonate of lead. 
 
 It will be seen, however, that while there may be 
 reasons for permitting the use of a single lead pigment 
 which possesses this peculiar property, there can be none 
 for introducing into every part of a picture oils or other 
 materials which contain a metal, like lead, so liable to 
 cause discoloration and darkening, when other and per- 
 fectly innocuous substances are available for producing 
 the same siccative effects. On this account we omit 
 further reference to the lead compounds, which have been 
 and are still employed in the preparation of strongly- 
 drying oils, etc., but pass on to the 
 
MANGANESE DRYERS 
 
 127 
 
 Manganese compounds, of which the dioxide, the 
 hydrated protoxide and sesquioxide, the borate, the 
 oxalate, and the linoleate are the most important. 
 
 Manganese dioxide, the black oxide, MnOg, is used in 
 the form of a powder obtained by grinding the mineral 
 pyrolusite. As the effectiveness of this compound is made 
 complete only by the use of oil of vitriol, which needs 
 subsequent neutralization with lime, it cannot be recom- 
 mended as a material for rendering linseed oil intended 
 for painting, or for making picture-varnish, more drying. 
 The difficulty of preparing the manganese hydrates above 
 mentioned constitutes an objection to their employment 
 for this purpose. But the borate, the linoleate, and the 
 oxalate of manganese may be obtained in commerce in a 
 state of sufficient purity for our present purpose, and it is 
 to them chat we wish to direct attention. Borate of 
 manganese may, moreover, be so easily prepared, that it 
 is worth while to give here the necessary directions. 
 One pound of pure manganese sulphate is dissolved in 
 six pints of distilled water, the solution being filtered if 
 cloudy. A few drops of the liquid are now to be tested 
 with caustic soda solution — the precipitate formed should 
 be white ; if it show a greenish, yellowish, or greyish hue, 
 iron is probably present, and it will be necessary to treat 
 the whole of the solution with caustic soda until a white 
 precipitate falls, and then to filter it again. In order to 
 produce manganese borate, a boiling saturated solution 
 of pure borax is added to the manganese sulphate solu- 
 tion until no more precipitate falls. The precipitate is 
 collected on a filter and washed with hot distilled water 
 until the wash-waters show no turbidity when a solution 
 of barium chloride and a few drops of dilute hydrochloric 
 acid are added to the last portion coming through the 
 
128 
 
 DRYERS 
 
 paper. The borate of manganese is then dried in a warm 
 place, and finally in the water-oven. One grain of it, 
 warmed with linseed oil, is sufficient to render an ounce 
 of the latter highly drying (see Chapter V.). The oxalate 
 or the linoleate of manganese may be used in the same 
 way, and there are also met with certain manganese 
 ‘ resinates ’ which may be employed similarly. Cobalt 
 resinate is also a powerful dryer. 
 
 IT The quantities of lead or manganese compounds 
 necessary to confer the drying character on oil are very 
 small. With -2 to I'o per cent, of the weight of the oil 
 the maximum effect is so nearly attained that any further 
 addition is unnecessary. If the manganese in the form 
 of resinate or linoleate be dissolved in ten times its weight 
 of turpentine, a siccative having very little colour but 
 possessed of great power is obtained ; this, when added 
 to the oil in the proportion of from i to 20, i to 50, or even 
 I to 100, confers the drying character upon it without 
 any further heating. Moreover, if this oil be allowed, 
 under carefully adjusted conditions, to absorb enough 
 additional oxygen for it to enter on the second period 
 (p. 53), it dries with great rapidity. Oil of this kind, pre- 
 pared with the smallest possible amount of a manganese 
 salt, is much to be commended for the use of the artist, 
 since it assures to the finished painting a longer life than 
 any other preparation of this kind. 
 
 Borate of lime and borate of zinc have been employed 
 not only for rendering oils more quickly drying, but also 
 in admixture with some of those oil-paints which dry with 
 difficulty. Being colourless they are well adapted for 
 use with white pigments, such as oxide of zinc. Several 
 of the siccative materials sold under various fancy names 
 consist of mixtures of these borates with carbonate of 
 
DRYERS 
 
 129 
 
 zinc or oxide of zinc, manganese compounds being also 
 sometimes added. Another dryer in common use is white 
 vitriol or sulphate of zinc. Its siccative character is very 
 slight. Most of the other siccatives employed by artists 
 owe their efficacy to lead, or are resinous preparations. 
 Siccatif de Courtrai is a very dangerous mixture, heavily 
 loaded with compounds of lead ; Siccatif de Haarlem is 
 a resinous preparation, which produces, on drying, a hard, 
 brilliant, and tough film. This acquires, in course of 
 time, a deep yellow hue, which, however, hardly affects 
 the colour of the paints with which the siccative has been 
 employed, because of the small proportion used. 
 
 H Here it may be mentioned that spirit of turpentine 
 may be regarded as a fairly efficacious dryer, especially 
 if the picture in which it has been employed is exposed 
 to sunlight. This property of turpentine (terpenes) is 
 not shared by the hydrocarbons of petroleum and of coal- 
 naphtha, such as petroleum spirit, benzene, and toluene. 
 This difference in chemical activity must be borne in 
 mind if we would correctly estimate and foresee the 
 results of employing these several liquids as vehicles or 
 diluents. 
 
 It may be well to remark in this place that many of 
 the volatile solvents, described in this chapter, are danger- 
 ously inflammable, and some are of a poisonous character. 
 
 9 
 
CHAPTER XII 
 
 VARNISHES AND VEHICLES 
 
 When an oil, such as linseed, walnut, or poppy, has been 
 purified and made more quickly drying by one or other of 
 the methods already described, it is often called ‘varnish.’ 
 It has acquired the property of rapidly solidifying, when 
 spread as a thin layer, into a tough transparent substance, 
 endowed with a considerable degree of cohesiveness and 
 elasticity, yet rather soft withal. N ow oil of this character, 
 although it has many uses in painting, is not quite hard 
 enough for some of the purposes for which a true varnish 
 may be required, but its defects may be amended by 
 associating with it one or more of the resins described in 
 Chapter VI, One class of varnishes is compounded in 
 this manner of two materials, oil and resin, both of which 
 are fixed or non-volatile. A second group of varnishes 
 consists of a resin dissolved in a volatile solvent. And 
 there are also mixed varnishes which contain at least three 
 ingredients — namely, a drying oil, a volatile solvent, and a 
 resin. As the varnishes which consist wholly of oil and 
 resin are thick and intractable, it is usual to thin these 
 according to the purpose for which they are intended, with 
 varying amounts of some volatile liquid or solvent, spirit 
 of turpentine being most frequently thus employed. In 
 order to avoid too elaborate a classification, it will be 
 
 130 
 
MASTIC VARNISH 
 
 131 
 
 advisable to describe those varnishes which contain oil as 
 oil or fat varnishes, and those which consist wholly of a 
 resin and a volatile solvent as spirit varnishes. We de- 
 scribe the latter first, as their manufacture is easier and 
 their constitution simpler. In order to avoid repeated 
 references to the descriptions already given of the several 
 materials employed in making varnishes, it will be con- 
 venient to state once for all that the oils used are described 
 in Chapter V., the resins in Chapter VI., and the solvents 
 in Chapter X. 
 
 Mastic Varnish . — This is usually prepared by dissolving 
 mastic in spirit of turpentine, although other volatile oils 
 and even absolute alcohol may be employed. In order 
 to prevent the mastic from agglutinating together, warm 
 powdered glass, or warm fine white quartz sand, may be 
 added to the resin before it is mixed with the solvent. The 
 spirit of turpentine should be absolutely free from mois- 
 ture, the mastic may be in tears, or, preferably, have been 
 purified and dried as before directed. The materials are 
 introduced into a capacious glass flask fitted with a cork, 
 tube and condenser so arranged that, when the flask is 
 heated in a water-bath, the vapours given off from the 
 solvent may be condensed and return to the vessel. The 
 temperature of the water-bath may be 100° C. if oil of 
 turpentine be used, but should not be allowed to rise 
 beyond 78° C. if absolute alcohol or 96 per cent, alcohol 
 (specific gravity ’806) be substituted for the oil of turpen- 
 tine. The following receipt gives a varnish which con- 
 tains nearly 25 per cent, of its weight of mastic, but the 
 proportion may easily be increased or diminished : 
 
 14 ounces of mastic, 
 
 44 ,, ,, spirit of turpentine, 
 
 6 ,, ,, powdered glass, or fine sand. 
 
132 
 
 MASTIC VARNISH 
 
 When the mastic has dissolved the varnish is allowed to 
 cool, and then poured oflf into a closed glass vessel, in 
 which it is allowed to rest until perfectly clear. Or it may 
 be clarified by filtration through a plug of dried carded 
 cotton fitted into a funnel. The funnel should be closely 
 covered with a ground-glass plate, but a specially con- 
 trived filtering apparatus has been designed for the pur- 
 pose of preventing any escape of vapour during the pro- 
 cess of filtration. 
 
 The varnish prepared according to this receipt is nearly 
 colourless, and leaves a brilliant glassy film when it evapo- 
 rates on a smooth surface. But this film is very brittle, and 
 easily abraded by gentle friction even with the finger, in 
 fact it consists of little more than the original mastic resin, 
 the fragility of which is well known. To obviate this 
 brittleness many plans have been devised. Sometimes 
 Venice turpentine, Canada balsam, or Elemi resin is 
 introduced in small quantity, not exceeding one-seventh 
 in weight of the mastic used. In consequence of such 
 admixture of a natural soft turpentine the varnish pro- 
 duced dries more slowly, and leaves a less brittle, tougher, 
 more adhesive, and more elastic film on evaporation. 
 Ultimately, however, these balsams become brittle like 
 mastic itself. This remedy is, tlierefore, of a temporary 
 character, but, at the same time, these additions do not 
 interfere with the ease with which the varnish, when old 
 and discoloured, can be removed from a painting by means 
 of solvents or of friction, without injuring the glazing pig- 
 ments which may lie immediately below it ; they also 
 render the varnish more easy of application. The other 
 classes of substances added to toughen the resinous film 
 left by the drying of a spirit varnish, are fixed oils, and 
 those liquid paraffins which boil at temperatures above 
 
COPAL VARNISH 
 
 133 
 
 170° C. A very small proportion of ‘ manganese ’ linseed 
 oil is, perhaps, the more effective and safer toughener of 
 the two, but its introduction involves the disadvantage 
 just named. In many French mastic varnishes camphor 
 is introduced for the same purpose to the extent of 5 to 
 8 parts for each 100 of mastic. The camphor, however, 
 gradually escapes by volatilization, the varnish losing its 
 fine lustre and becoming brittle and fissured. It should 
 be mentioned here that the more easily resinified varieties 
 of oil of turpentine, when used as solvents for mastic, 
 also toughen the resinous film left on the drying up of the 
 varnish, although the effect is not permanent. If alcohol, 
 benzene, light petroleum ether, or other non-oxidizable 
 solvents be substituted for any kind of essence of turpen- 
 tine in making mastic varnish, there is no doubt that the 
 brilliant films they yield are more brittle and less adhesive. 
 
 Sandarac and the various kinds of soft pale dammar may 
 be substituted wholly or in part for the mastic mentioned 
 in the receipt for spirit varnish above given. But if these 
 dammars be used great care must be taken that they are 
 themselves free from moisture, and that the oil of turpen- 
 tine or other solvent be also perfectly dry. It has been 
 recommended to employ oil of spike lavender instead of 
 oil of turpentine in making mastic varnish. The spike 
 oil in this case must be free from water, and freshly dis- 
 tilled : mastic varnish thus prepared has less tendency to 
 ‘ bloom ’ than the ordinary kind, but if pictures are var- 
 nished in a perfectly dry atmosphere and kept therein 
 till the surface has hardened, the formation of bloom is 
 minimized if not prevented. 
 
 A copal spirit varnish may be made by the use of 
 acetone, or of ether (both water-free), or of absolute 
 alcohol, light petroleum-ether, or benzene. The copal to 
 
134 
 
 COPAL VARNISH 
 
 be dissolved may be either Sierra Leone copal, Zanzibar 
 copal, or Demerara copal, the first two yielding the 
 harder varnish, but the last-named being easier of solu- 
 tion, or, rather, dissolving less incompletely. The pow- 
 dered copal, prepared as directed previously (by exposure 
 to the air, and heating), or first fused, or at least heated 
 till it has lost from lo to 20 per cent, of its weight, is kept 
 in contact with four times its bulk of the solvent until it 
 is nearly dissolved. Three measures of dry oil of turpen- 
 tine are then added, and the mixture submitted to distil- 
 lation from a water-bath until three measures of the 
 acetone or other original solvent have been drawn over ; 
 an efficient condenser must be used. If it be desired to 
 prepare a mixed varnish (partly oil or fat varnish), 
 I measure of ‘ manganese ’ oil, and 2 measures of oil of 
 turpentine may be used in lieu of the quantity of turpen- 
 tine above mentioned, the distillation being then proceeded 
 with as before. 
 
 In another method of preparing copal (and amber) spirit 
 varnishes the resins duly prepared and powdered are 
 heated with the selected solvent under pressure — that is, at 
 a temperature above that at which the particular solvent 
 used boils under ordinary conditions. With purified oil 
 of amber, oil of copal, oil of turpentine, oil of spike, or 
 the heavier petroleum spirit, and on a small scale, glass 
 tubes hermetically sealed and heated to 200° C. may be 
 used, but if a higher temperature or more volatile solvents 
 be employed, copper tubes with screw stoppers are 
 necessary. But operations of this order can be carried out 
 safely and successfully only in a well-equipped laboratory 
 or factory by skilled operators, and it is therefore unneces- 
 sary to furnish further particulars in a work like the 
 present. 
 
COPAL VARNISH 
 
 135 
 
 The preparation of fat or oil varnishes with the harder 
 resins is generally attended with considerable difficulty ; 
 but there is, as we have already mentioned, one way in 
 which the difficulty may be lessened. By the aid of one of 
 the powerful and very volatile solvents previously named, 
 we prepare a spirit copal or amber varnish ; we then add 
 the required amount of ‘ manganese ’ oil and draw off the 
 volatile solvent by distillation, thinning the resinous solu- 
 tion obtained with so much oil of turpentine as is necessary. 
 If the copal or amber employed has been first roasted or 
 fused, the varnish produced will be more or less dark in 
 tint ; it is on this account that the exposure of the powdered 
 resin to the air in a flat porcelain dish for seventy-two 
 hours, at a temperature (of 220° C.) which does not cause 
 discoloration, is recommended. But if, on the other hand, 
 the copal or amber be merely powdered, some part of it, 
 and that a considerable part, will probably remain undis- 
 solved though swollen, and will therefore be wasted. The 
 following process, in the main identical with one recom- 
 mended in the American edition of Mr. Erwin Andres’ 
 work on varnishes, yields a pale and durable varnish when 
 Sierra Leone copal or other hard copal is employed, and 
 is doubtless well adapted for the preparation of amber 
 varnish also. As will be seen, it is based upon the pre- 
 liminary partial solution of the hard resin in chloroform, 
 or in light petroleum spirit of about the same boiling- 
 point. It may be stated at once that the proportions of 
 the five ingredients used are approximately 10 parts by 
 weight of copal or other hard resin ; 5 parts by weight 
 of dried powdered glass or sand ; enough chloroform to 
 cover the above substances ; 35 parts by weight of oil of 
 turpentine, and 10 parts by weight of ‘ manganese ’ oil. 
 The following is an outline only of the process. The 
 
136 
 
 COPAL VARNISH 
 
 copal, after having been powdered and heated to 220° C. 
 for seventy-two hours, is mixed with the glass or sand, 
 and introduced into a retort ; chloroform in quantity 
 sufficient to cover the mixture is added. After the lapse 
 of twenty-four hours the dry oil of turpentine is poured 
 in, and an upright condenser is attached to the retort. 
 The retort is then heated to 50° or 60° C. for two hours, 
 so that the chloroform continually returns to the mixture. 
 Then the contents of the retort are allowed to cool, and 
 the condenser slanted downwards to allow of the chloro- 
 form being distilled over. This removal of the chloroform 
 having been effected at a temperature so low that very 
 little turpentine has come over, the remaining mixture in 
 the retort is heated once more with the condenser in an 
 upright position. The heat used must suffice to bring 
 the oil of turpentine into vigorous ebullition — in an hour 
 the whole of the copal should have dissolved. The ‘ man- 
 ganese ’ oil wanted should now be heated to 100° C., and 
 then the copal mixture, when it has cooled to 70° C., 
 added little by little to it with constant stirring, the tem- 
 perature of the oil being maintained at go° to 100°. When 
 the mixture is complete the source of heat is withdrawn, 
 but the varnish is still stirred for twenty minutes. Then 
 it is allowed to settle, until quite clear, in glass bottles, 
 or, if an appropriate filtering apparatus is available, it is 
 filtered. In the latter case a little hot oil of turpentine 
 may be used to extract any copal solution which may 
 remain with the powdered glass or the sand in the retort. 
 
 The older plan of preparing oil or fat varnishes with 
 hard resins is still that usually adopted ; but it yields 
 products which are darker in colour than those obtained 
 by the method just described, as the copal or amber used 
 has been previously heated or even fused, whereby it has 
 
COPAL VARNISH 
 
 137 
 
 lost one quarter of its weight. One way of carrying out 
 this plan consists in melting the copal in one vessel, and 
 heating the oil until it commences to give off small bubbles 
 in another ; then half the oil is poured in a very thin 
 stream into the melted resin, and incorporated therewith 
 by constant stirring. Complete union having been effected 
 between the two materials, the mixture is incorporated 
 with the remainder of the hot linseed oil, any portions 
 adhering to the vessel being afterwards dissolved by means 
 of oil of turpentine ; 30 parts of melted copal, 100 parts 
 of linseed oil, and 70 parts of oil of turpentine, are pro- 
 portions often employed in carrying out the process we 
 are describing. This process may now be completed by 
 adding to the solution of copal in linseed oil | of a part 
 of manganese borate, stirring continually, and heating for 
 two hours, or until the solution has acquired the character 
 of a thick gold-coloured syrup which can be drawn out 
 into threads. This point having been reached, the heating 
 is discontinued, and the contents of the boiler allowed to 
 cool to 60° or 70° C., and then is added the warm oil of 
 turpentine which has been used to dissolve out any of the 
 copal solution clinging to the vessel in which that resin 
 Avas melted. Finally, the remainder of the oil of turpen- 
 tine is very gradually introduced with constant stirring. 
 Copal varnish prepared in the above manner ought to 
 dry in twelve hours or sooner. It is scarcely necessary 
 to say that this method of preparing varnish with copal 
 or other hard resin is one that no inexperienced person 
 should attempt ; not only is there some chance of partial 
 or total failure, but there is serious risk of fire. An easier 
 and less dangerous process requires a specially constructed 
 heater, which is kept hot by a water-bath. Melted copal, 
 copal or amber oil, ‘ manganese ’ oil, and oil of turpentine, 
 
138 
 
 COPAL VARNISH 
 
 are the materials used. They are all introduced together, 
 and, as the temperature during the process of cohobation 
 does not exceed ioo°C., the time required is greater than 
 in the previously described process. 
 
 A good copal or amber varnish ought to leave a film 
 (on a sheet of glass) which combines the qualities of hard- 
 ness and toughness. The toughness is given by the oil, 
 the hardness by the resin. Such a film should not become 
 fissured even when it has been exposed to sunshine 
 during a year. Much of the copal varnish of commerce 
 is not made from true copal or anime at all, kowdi or 
 kauri resin (from Dammara australis), which is much 
 easier to dissolve, being employed instead — the product, 
 however, is decidedly inferior. Sometimes several resins 
 are mixed together in the preparation of a so called copal 
 varnish. A guarantee of genuineness, in which the name 
 or names and proportions of the resin or resins employed 
 is inserted, should always be demanded when buying 
 copal varnish. This ought to be furnished by the varnish- 
 maker himself, for artists’ colourmen rarely prepare oil- 
 varnishes themselves. 
 
 An ingenious process for rendering hard copals soluble 
 in oil without roasting them in the ordinary way has 
 been recently devised and patented by H. Terrisse. It is 
 based upon the fact that the solid hydrocarbon, naphtha- 
 lene, a by-product in the manufacture of coal-gas, shares 
 with some other organic bodies, liquids as well as solids, 
 the property of dissolving hard resins when heated with 
 them under pressure at a temperature not exceeding 
 300° C. In this way the greater part of the loss in- 
 curred when copals are roasted in the usual manner is 
 avoided, while the discoloration of the torrefied resin does 
 not occur. A mixture of i part of copal with 3 parts 
 of naphthalene is taken, and then heated for an hour or 
 
MEDIUMS FOR OIL-PAINTING 
 
 139 
 
 two until complete solution has been effected. The mass 
 is then transferred to a suitable still, when the naphtha- 
 lene, being volatile, along with a little moisture and some 
 oil of copal separated in the operation, are distilled off. 
 Subsequent operations are two — the incorporation, under 
 pressure, with the altered copal of the necessary propor- 
 tion of linseed oil ; and, secondly, the addition of spirit 
 of turpentine to thin the product, which is pale in colour 
 and yields a sound varnish. Hard copals treated by this 
 process suffer changes less profound than those brought 
 about by the higher temperature involved in roasting 
 them ; they consequently retain more of their original 
 qualities of hardness and toughness when finally turned 
 into varnishes. 
 
 For the general use of painters in oil nothing more is 
 wanted than true copal or amber oil-varnish, a drying oil, 
 and a diluent. Of these three liquids a mixed medium in 
 general use is compounded by taking equal measures of 
 the three — varnish, oil, spirit of turpentine — and mixing 
 them together in small quantities as required. But con- 
 sidering the large quantity of oil already associated with 
 oil-pigments and present in copal or amber oil-varnish, 
 one-third of oil in the medium seems a somewhat high 
 proportion. I have proved by numberless experiments 
 that it may be reduced with perfect safety to the perma- 
 nence of the picture, although the manipulation and 
 technique of a painter may demand the peculiar quality 
 in a medium which oil in considerable proportion can 
 alone supply. A formula which answers well is this : 
 
 2 measures of copal oil-varnish made from Sierra Leone 
 or Zanzibar copal ; 
 
 1 measure of poppy oil ; 
 
 2 measures of oil of turpentine or oil of spike. 
 
140 
 
 MEDIUMS FOR OIL-PAINTING 
 
 By substituting linseed oil for the poppy oil a more 
 quickly-drying medium is obtained ; still more rapid 
 drying is secured by means of ‘ manganese ’ oil. With 
 the same object in view, benzene may be used instead 
 of oil of turpentine. This latter ought, of course, in 
 all cases, to be one of the least resinifiable varieties 
 obtainable. 
 
 If an amber or copal varnish containing no oil be 
 available, a good medium may be prepared by mixing 
 3 measures of it with 2 measures of poppy or linseed oil, 
 and I measure of oil of turpentine or of spike. 
 
 Bell’s medium contains no resin, but consists of thick- 
 ened linseed oil dissolved in oil of spike. To prepare it, 
 pure linseed oil may be oxidized by having a current of 
 warm, moist air passed through it until it has acquired 
 the consistence of fresh honey : this change occurs slowly 
 when a layer of oil is exposed to the air in a large flask, 
 the mouth of which is lightly plugged with carded cotton. 
 The flask should be shaken occasionally to mix its 
 contents, and to prevent the formation of a pellicle on 
 the surface of the oil. 
 
 Paintings executed with this thickened oil medium do 
 not acquire the hardness and solidity of those carried out 
 with a vehicle containing a hard resin. 
 
 Roberson’s medium has now been in use for something 
 like seventy years. It has been and is a favourite vehicle 
 with many distinguished artists. A substitute for it is 
 sometimes prepared in the studio by mixing and warming 
 together strong copal varnish, poppy oil or linseed oil 
 and a trace of white wax. 
 
 Of megilp — a mixture of linseed oil and mastic varnish 
 — it is only necessary to say this ; that however agreeable 
 as a medium with which to work, it contains a poor and 
 
MEDIUMS FOR OIL-PAINTING 
 
 141 
 
 weak resin, which becomes in course of time yellow and 
 brittle, and is liable to be injuriously affected when a 
 picture, in which it has been used freely, is cleaned. 
 
 For painting in oil on plaster, slate, or stone, a perfectly 
 sound and convenient medium is made by warming 12 
 ounces of oil of spike, or of non-resinihable oil of turpen- 
 tine in a glass flask plunged in water heated to the boiling- 
 point, and then pouring into it in a slender stream 4 ounces 
 by weight of paraffin-wax (melting-point about 58° to 
 62“ C.), or of ceresin, or of a mixture of these materials. 
 The mixture becomes perfectly clear if it be thoroughly 
 agitated and maintained at a temperature of 80° C. Then 
 20 measured ounces of ‘ picture ’-copal varnish, or 16 
 ounces of oil-copal varnish, are slowly added, with con- 
 stant shaking, in the same way. It is of the highest 
 importance that the copal varnish used should contain a 
 sufficiency of oil. If a thin varnish with much terpene 
 be employed in preparing this medium the pigments may 
 lack coherence. I have found this defect counteracted 
 by using pigments ground in inspissated or blown linseed 
 oil, rather than in the medium itself. The ‘ paraffin- 
 copal ’ medium thus obtained may be diluted with oil of 
 turpentine exactly to the same extent as recommended 
 by the late Mr. Gambier-Parry, in the case of his ‘ spirit- 
 fresco ’ medium, and may be used in the same way and for 
 the same purpose. Paintings executed with this medium 
 present a perfectly dead or matt surface without the least 
 shine. This medium is superior to that used in spirit- 
 fresco, for it contains neither elemi-resin nor wax, the 
 two doubtful constituents of the latter preparation, but it 
 is not so pleasant in use. Moreover, if a painting executed 
 with this medium on canvas be rolled up, the paint seems 
 to have some tendency to crack. This accident may be 
 
142 
 
 SPIRIT-FRESCO MEDIUM 
 
 obviated if the rolling up and the unrolling afterwards 
 be carried out in a warm room. 
 
 Mr. Gambier-Parry’s medium, to which reference has 
 just been made, is prepared with five ingredients. The 
 original instructions are unnecessarily complicated, and 
 may be simplified while keeping to the original propor- 
 tions, and without modifying the nature of the product 
 in the slightest degree. Eight ounces of oil of spike are 
 warmed in a glass flask to 8o^ C., then 2 ounces by weight 
 of elemi are added, the mixture being warmed and shaken 
 till the elemi has dissolved. Some dirt and woody frag- 
 ments are sure to be introduced with the elemi, and so 
 the solution (still warm) must be filtered. Upon the filter, 
 when all the liquid has run through, 2 ounces by measure 
 of oil of turpentine, heated to 80° C., are now poured, and 
 the united filtrates are thoroughly mixed. The liquid is 
 then introduced into a flask, and heated to 80° C. ; then 
 4 ounces by weight of pure white wax (previously melted) 
 are poured in a thin stream into the solution of elemi and 
 thoroughly shaken. When the commixture is complete, 
 20 ounces by measure of ‘ picture ’-copal varnish, or 16 
 ounces of oil-copal varnish, are gradually introduced with 
 constant agitation. The water surrounding the flask is 
 now made to boil, and kept boiling for five minutes. The 
 flask is withdrawn, wiped dry, and allowed to cool. As 
 the cooling proceeds the flask is gently agitated from 
 time to time. When the mixture begins to get treacly in 
 consistence it is at once poured into the bottles (bottles 
 with wide mouths, holding 4 ounces apiece, are con- 
 venient) in which it is intended to preserve the medium 
 for use. The dilution of this medium and the mode of 
 using it are described in Chapter XXIII. on Painting 
 Methods. 
 
PART III 
 
 PIGMENTS 
 
 Chapter XIII. — White Pigments Chapter XIV. — Yellow Pigments. 
 Chapter XV. — Red Pigments. Chapter XVI. - Green Pigments. 
 Chapter XVII. — Blue Pigments. Chapter XVIII. — Brown Pig- 
 ments. Chapter XIX. — Black Pigments. Chapter XX. — Classifi- 
 cation of Pigments. Chapter XXI. — Tables of Permanent and 
 Fugitive Pigments. Chapter XXII. — Selected and Restricted 
 Palettes. 
 
CHAPTER XIII 
 
 WHITE PIGMENTS 
 
 Flake-White: White Lead — Ceruse — Blanc d' Argent — 
 Blanc de Plomb — Bleiweiss — Krernserweiss. 
 
 White lead was known to the ancients. A face-powder 
 or cosmetic, found, in its original pottery-box of about 
 400 B.C., in the neighbourhood of Athens, proved to be a 
 mixture of white lead and whitening. Theophrastus, 
 Pliny, and Vitruvius describe its manufacture from lead 
 and vinegar. It was designated by several names, such as 
 cerusa, cerussa, cerosa, psimuthion. In the first half of 
 the fourteenth century it is mentioned as ‘ minium album.’ 
 It has been called by divers names after the place or 
 method of its manufacture, or after persons who have 
 devised special processes for preparing it. 
 
 White lead still continues to be made for the most part 
 by processes which are essentially identical with the old 
 method, now generally known as the ‘ Dutch ’ process. 
 This consists in attacking metallic lead, in the form of 
 ‘crates,’ ‘grids,’ or spirals, simultaneously by acetic acid, 
 carbonic acid, atmospheric oxygen, and water-vapour. 
 The metal is gradually converted into a mixture or com- 
 pound of lead carbonate and lead hydrate. Other pro- 
 cesses, generally yielding an inferior product, containing 
 more carbonate and less hydrate, have been used. One 
 
 145 
 
 10 
 
46 
 
 FLAKE-WHITE 
 
 of these consists in passing a current of carbonic acid gas 
 through a solution of lead subacetate ; in another, 4 parts 
 of litharge, i part of common salt, and 16 parts of water, 
 are kept in contact for some hours with constant agita- 
 tion, and then carbonic acid gas is led into the mixture 
 until it becomes neutral to test-papers. 
 
 The best white lead contains two molecules of lead car- 
 bonate intimately associated with one molecule of lead hy- 
 drate, and is represented by the formula ePbCOg.PbHgOg. 
 This formula corresponds to about 70 per cent, of lead 
 carbonate, and 30 per cent, of lead hydrate. If the pro- 
 portion of hydrate rise above this percentage, the opacity 
 of the paint is lessened seriously ; if it fall much below 
 the above-named figure, the binding-power and working 
 quality of the white lead are impaired. Although the 
 normal lead hydrato-carbonate is probably constituted of 
 one molecule of each of its components, the formula 
 previously given may be taken to represent the highest 
 quality of white lead as a paint. It has been recently 
 stated that two molecules of lead hydrate associated with 
 three molecules of barium carbonate constitute a pigment 
 actually better than flake-white in some respects. 
 
 It is scarcely necessary to say that the metallic lead 
 used in the manufacture should be as nearly pure as 
 possible, such, for instance, as the lead from the Upper 
 Hartz, which contains but 2 parts of foreign metals per 
 1,000. These foreign metals, the presence of any one of 
 which in sensible quantity may cause a discoloration of 
 the product, are copper, bismuth, silver, cadmium, anti- 
 mony, nickel, and, more particularly, iron. But not only 
 must the raw material be pure, but it is necessary to 
 guard against the contamination of the white lead, during 
 its manufacture, by dust or sulphuretted gases. 
 
WHITE LEAD 
 
 147 
 
 The impurities and defects of white lead are (i) acci- 
 dental, (2) intentional. 
 
 (1) Of the accidental impurities and defects of white 
 lead made from pure metal, the following are the chief : 
 
 a. Metallic lead, imparting a grey hue to the pro- 
 
 duct. 
 
 b. Massicot or litharge, the yellow oxide of lead. 
 
 c. Minium or red lead, which gives a rosy hue. 
 
 d. Excess of lead hydrate, which causes translucency. 
 
 e. Excess of lead carbonate. 
 
 /. Lead acetate. 
 
 A simple experiment will suffice to show whether lead 
 acetate be present in objectionable proportion in any 
 sample. Some of the dry pigment is to be ground with 
 distilled water into a paste, thrown on to a wetted filter 
 and then washed with freshly-boiled distilled water. The 
 clear filtered liquid should give nothing more than a slight 
 cloudiness on the addition of a little dilute sulphuric acid. 
 Some samples of flake-white which had been insufficiently 
 washed contained from 2 to 1 1 per cent, of lead acetate 
 removable by distilled water. In order to ascertain 
 whether the lead carbonate and lead hydrate exist in due 
 proportion in a sample of white lead, a weighed portion 
 of the dry pigment, after having been dried at 212° F., 
 should be carefully roasted in a current of dry air, and 
 the water evolved (2 to 3 per cent.) intercepted by means 
 of a weighed calcium chloride absorption tube. This 
 operation, however, requires much manipulative experi- 
 ence, and, unless accurately performed, may lead to 
 erroneous conclusions. 
 
 (2) Of the intentional adulterations of white lead the 
 following are the most usual : 
 
WHITE LEAD 
 
 a. Heavy spar, that is, native barium sulphate ; or 
 
 the same compound artificially prepared (per- 
 manent white, blanc fixe). 
 
 b. Gypsum. 
 
 c. China-clay. 
 
 d. Whitening or chalk. 
 
 e. Lead sulphate. 
 
 The first of these adulterations is by far the most usual. 
 Barium sulphate, in the form of finely-ground barytes, or 
 heavy spar, is the material employed on the large scale 
 for cheapening the cost of production of ordinary white 
 lead ; precipitated, that is, artificially prepared, barium 
 sulphate is used in the case of the finer makes of this pig- 
 ment. In either case the sophistication is very readily 
 recognised. Pure flake-white, for example, loses 14I per 
 cent, of its weight when strongly heated so as to drive off 
 its carbonic acid and water, but ‘Venice’ white, which 
 is white lead and barium sulphate mixed in the proportion 
 of equal parts, loses, under such treatment, no more than 
 7-3 grains per 100. ‘ Hamburg ’ white, with 33 per cent, 
 
 only of white lead, loses q'S per cent., and ‘ Dutch ’ white, 
 of which three-fourths are barium sulphate, gives off no 
 more than 3'8 per cent. ‘ Crems,’ or ‘ Cremnitz ’ white, 
 is, or ought to be, pure white lead. The complete solu- 
 bility of pure white lead in dilute nitric acid may also be 
 made use of to detect the presence of barium sulphate, 
 which will remain undissolved as a dense white powder. 
 The adulterations with gypsum, china-clay, whitening and 
 lead sulphate, can be recognised only by further tests. 
 Gypsum, for instance, gives off water when heated, and 
 I part of it dissolves in 420 parts of water. China-clay 
 also gives off water when heated, but is insoluble in 
 water, and only slightly soluble in nitric acid. Whiten- 
 
WHITE LEAD 
 
 149 
 
 ing dissolves in all mineral acids, but lead sulphate is 
 practically insoluble. After all, the detection of barium 
 sulphate is the only point with which the painter need 
 concern himself. It will therefore suffice if he ascertain 
 that a sample of white lead is of first-rate colour and 
 body, contains no sensible quantity of lead acetate, loses 
 when heated i4|- per cent, of its weight, and dissolves 
 perfectly in dilute nitric acid. 
 
 It has been observed that white lead is less liable to be 
 blackened by sulphuretted hydrogen and by other sul- 
 phides when it contains a small quantity of baryta-white, 
 or of lead sulphate thoroughly incorporated with it by 
 grinding. This observation opens the door to adultera- 
 tion, it is true : and it is perhaps wiser to rely upon the 
 protection furnished by resinous mediums and a final 
 coat of mastic varnish rather than upon any admixture 
 with other white substances. 
 
 The drawbacks attendant upon the use of white lead as 
 a paint are its poisonous character, its sickly and noxious 
 smell when used with oil, and its liability to discolour when 
 exposed to sulphuretted hydrogen or any sulphide soluble 
 in water. On the other hand the quality of the whiteness 
 of the best flake-white is unimpeachable: the paint works 
 admirably in oil, and has great body ; moreover, flake- 
 white not only mixes perfectly and safely with the majority 
 of permanent pigments, but it serves to impart to slow- 
 drying colours its own strongly siccative character. 
 Besides all these merits white lead possesses a valuable 
 property, which has scarcely been clearly recognised or 
 duly appreciated. For when an old oil-picture is carefully 
 examined, it will generally be found that if any portion of 
 its surface (of the paint, not the varnish) show decided 
 contractions and cracks, these are precisely those portions 
 
150 
 
 WHITE LEAD 
 
 into which white lead has entered in smallest proportion, if 
 at all. The most translucent parts, the rich glazings and 
 the deepest shadows may be fissured, but not the high 
 lights : examples illustrative of this point are referred to 
 in Chapter XXIV. of the present volume. This property 
 of white lead seems to depend upon a combination taking 
 place between a part of the oil with which it is ground and 
 a part of the lead hydrate which it contains. A degree of 
 toughness and elasticity is thus imparted to those films 
 of oil paint into which lead-white enters to any consider- 
 able extent. 
 
 Flake-white becomes brown, grey or black when ex- 
 posed to the action of sulphuretted hydrogen, ammonium 
 sulphide, or any metallic sulphide soluble in water. This 
 discoloration, which is due to the formation of lead sul- 
 phide, occurs more readily in the presence of moisture : 
 it is favoured by darkness to such an extent that a piece 
 of perforated cardboard laid upon a dry oil-painted 
 surface of white lead will, after a few weeks’ exposure, 
 give a white pattern representing the perforations on a 
 buff ground, which corresponds to the solid parts of the 
 cardboard. But, after the removal of the perforated 
 card and subsequent exposure of the painted surface to 
 strong light, this pattern will disappear, the coloured 
 sulphide of lead being oxidized into the white sulphate. 
 The same change may be more speedily brought about 
 by means of a solution of hydrogen peroxide. By laying 
 a sheet of white filter-paper soaked in this liquid upon the 
 discoloured lead-priming of a prepared canvas the original 
 colour of the paint may be gradually brought back, 
 especially by the aid of a moderate degree of warmth. 
 This method is not available in the case of drawings or 
 water-colour paintings in which flake-white has black- 
 
LEAD SULPHATE 
 
 151 
 
 ened ; but even these may often be successfully treated 
 by exposure to moist ozone, or by light touches of a 
 solution of hydrogen peroxide in ether. The latter treat- 
 ment has been successfully applied to a series of archi- 
 tectural drawings in gouache by C. Clerisseau in the Soane 
 Museum. In these the high lights had become black. 
 Old silver-point drawings, in which the lights were height- 
 ened with lead-white, may sometimes be thus restored to 
 their pristine state. 
 
 The specific gravity of the best flake-white is 6'6; 100 
 parts by weight of it require from 1 1 to 15 parts of linseed 
 oil in order to form an oil-paint of suitable consistence. It 
 is sometimes ground with poppy oil when a particularly 
 pure white product is demanded. The yellowish tint of 
 some makes of white lead is occasionally neutralized by the 
 addition of a trace of indigo or of artificial ultramarine. 
 Burnt or roasted white lead is sometimes used as a pig- 
 ment. It is of a cream-colour, a buff, or a pale yellowish 
 salmon, according to the temperature at which it has 
 been prepared, or the length of time during which it has 
 been heated. 
 
 Lead Sulphate . — Many attempts have been made to 
 utilize the sulphate of lead (PbSOJ as a pigment. This 
 compound, which is nearly insoluble in water and in dilute 
 acids, is almost, if not entirely, destitute of poisonous pro- 
 perties owing to this insolubility, although as ordinarily 
 prepared it possesses neither the pure whiteness nor the 
 body of white lead. But under the name of Freeman’s 
 white lead, or non-poisonous white lead, a paint has been 
 introduced which may prove a rival to ordinary white 
 lead. It is essentially lead sulphate, and is prepared by 
 precipitating lead acetate solution with sulphuric acid. 
 But this precipitate is subjected to a special process of 
 
ZINC- WHITE 
 
 152 
 
 grinding with small quantities of zinc-white and barium 
 sulphate, and acquires thereby a considerable increase of 
 density and opacity, although both the latter compounds 
 are of less specific gravity than the lead sulphate to which 
 they have been added. Being, when ground in oil, not 
 only destitute of the disagreeable smell of white lead, but 
 much less readily darkened by sulphuretted hydrogen. 
 Freeman’s white possesses distinct advantages in these 
 respects over the more common paint. It may be mixed 
 with other permanent pigments without injuring them : 
 it is practically non-poisonous. On the other hand, it 
 does not possess the remarkable hardening and drying 
 powers of white lead. 
 
 Lead Oxychloride. — Pattinson’s white (PbClHO) does 
 not possess any advantage, as a white pigment for artists’ 
 use, over the ordinary flake-white. Similar verdicts may 
 be pronounced as to the eligibility of several other white 
 compounds of lead, such as the antinionite, the anti- 
 moniate, and the tungstate of this metal. 
 
 The blanc d’argent of the French is supposed to be 
 pure lead carbonate free from any hydrate, but the great 
 majority of the specimens which I have examined are 
 nothing but flake-white of good quality. For general use 
 as a white pigment, both alone and in admixture, the best 
 flake-white, with all its defects, presents distinct advant- 
 ages over pure lead carbonate free from lead hydrate. 
 
 Zinc-white ; Chinese white — Blanc de Zinc — Zinkweiss. 
 
 The substitution of carbonate of zinc for white lead 
 seems to have been first suggested by Courtois of Dijon 
 in 1787. After several unsuccessful attempts to introduce 
 either the carbonate or the oxide as an oil paint, the latter 
 began to be used about 1849-50, shortly after Leclaire had 
 
ZINC- WHITE 
 
 «53 
 
 shown how to prepare an oil suitable for making the paint 
 dry. We believe that it had been frequently employed as a 
 water-colour many years before 1849. So early as 1834 
 Messrs. Winsor and Newton prepared a peculiarly dense 
 form of this pigment under the name of Chinese white. 
 
 For the preparation of the best zinc-white it is essential 
 that the zinc be pure ; especially should it be as free as 
 possible from the metal cadmium. The zinc is heated to 
 the distilling-point in crucibles or retorts set in a furnace ; 
 the vapour, meeting with air, burns into the white oxide, 
 which condenses in a series of chambers. The contents 
 of these chambers vary somewhat in purity of tint ; the 
 presence of some metallic zinc generally imparts a greyish 
 hue to the zinc oxide nearest the crucibles or retorts. By 
 selecting the densest and whitest product, and then sub- 
 mitting this to powerful mechanical compression when 
 red-hot, an excellent pigment having a dense body is 
 obtained. Zinc-white prepared in the wet way, as by 
 the action of lime-water upon zinc chloride, is inferior in 
 substance to that made as above described, while that 
 obtained directly from blende is of bad colour. 
 
 As an oil-paint, zinc-white is a bad dryer. Instead of 
 being ground in raw poppy or linseed oil, an oil rendered 
 highly siccative by borate of manganese should be em- 
 ployed. In spite of its unquestionable merits, zinc-white 
 in oil cannot be recommended as a complete substitute for 
 flake-white. When used freely, it often shows a tendency 
 to crack and scale, besides becoming with age more trans- 
 lucent, or rather, less opaque. For water-colour painting, 
 tempera, and for fresco, zinc-white is practically perfect, 
 being unchangeable in hue or opacity under the most 
 adverse influences. Paper washed with zinc- white, either 
 alone or tinted with a coloured pigment, affords a good 
 
154 
 
 BARYTA-WHITE 
 
 ground for silver-point, platinum-point, or pencil draw- 
 ings. There is a peculiar ‘tooth’ in the zinc-white which 
 freely brings off the metal or graphite from the pencil) 
 and serves to fix it on the prepared surface. 
 
 The purity of zinc-white is easily tested. Heated in a 
 tube, it should yield no volatile product, and should suffer 
 no permanent change of hue. It should dissolve com- 
 pletely without effervescence in boiling dilute nitric or 
 hydrochloric acid. If, on heating, it acquires a permanent 
 yellowish hue, giving off moisture at the same time, white 
 lead is probably present. If it does not dissolve completely 
 in acid, it probably contains barium sulphate ; if efferves- 
 cence occurs during solution, either whitening, or white 
 lead, or zinc carbonate is present. Zinc carbonate, however 
 prepared, is inferior in whiteness and body to the oxide. 
 
 Zinc sulphide has been prepared as a paint ; its liability 
 to evolve sulphuretted hydrogen renders its use as an 
 artists’ pigment dangerous, for there are several other 
 colours upon which it would exert a deleterious action. 
 It has very considerable body. 
 
 Baryta-white ; Permanent white — Blanc Fixe — Permanent 
 
 Weiss. 
 
 The mineral known as heavy spar, or barytes, has been 
 used as a white paint, particularly as an adulterant for 
 white lead. However finely it may be ground, it is always 
 very inferior in body and covering-power to the artificially- 
 prepared barium sulphate — the true blanc fixe. To make 
 this, a cold solution of barium chloride of specific gravity 
 i-ig is prepared, and to it is gradually added in the cold, 
 and until no further precipitate is formed, dilute sulphuric 
 acid of I ‘245 specific gravity. The barium sulphate is 
 
MINOR WHITE PIGMENTS 
 
 155 
 
 washed with cold water until the wash-waters are entirely 
 free from acid ; for many purposes to which the product 
 is applicable (fresco and tempera painting) it should be 
 kept under water. 
 
 Baryta-white is absolutely unalterable by an impure at- 
 mosphere, and is without action upon other pigments. It 
 does not work well in oil, but a mixture of flake-white 
 and baryta- white, in the proportion of 2 to i, presents the 
 advantage of being very much less affected by sulphur- 
 etted hydrogen than flake-white. 
 
 The artificial baryta-white may be distinguished from 
 the natural by its much finer state of division, by its 
 greater body, and by the purity of its whiteness. Baryta- 
 white is not adulterated, but its almost absolute insolu- 
 bility in hydrochloric or nitric acid enables it to be at once 
 distinguished from zinc-white or white lead. 
 
 Several mixtures of barium sulphate and zinc sulphide 
 have been introduced as pigments ; they are not suitable 
 for the palette of the artist. The reaction by which the 
 majority of them are formed is brought about by mixing 
 together solutions of two soluble salts, barium sulphide 
 (BaS) and zinc sulphate (ZnSOJ, when two new salts 
 are precipitated, both insoluble, namely zinc sulphide 
 (ZnS) and barium sulphate (BaSO^). 
 
 Other white compounds used in painting are lime, 
 whitening, gypsum and China-clay. These have been con- 
 sidered in the chapter on Painting-Grounds. Amongst 
 white pigments which we need not describe are antimo- 
 nious oxide, antimonious oxychloride, lead sulphite, lead 
 tungstate, lead antimonite, and lead antimoniate. Not 
 only are these compounds difficult to prepare in a satis- 
 factory condition of purity and whiteness, but they are 
 liable to turn yellow or dull in impure air. 
 
150 
 
 MINOR WHITE PIGMENTS 
 
 It should be stated here that the tests described in the 
 present chapter, and in all the other chapters on pigments, 
 refer only to the dry material, or, at any rate, to pigments 
 mingled with no fluid other than water. If it be desired 
 to operate on paints, this can be done, as a rule, only after 
 the removal of the vehicle with which they have been 
 ground. Oil may be removed by means of benzene or 
 turpentine-spirit, gum by treatment with distilled water. 
 
CHAPTER XIV 
 
 YELLOW PIGMENTS 
 
 Yellow Ochre : Roman Ochre — Golden Ochre — Mineral 
 Yellow — Brown Ochre — Oxford Ochre — Ocre jaiine — 
 Gelber Ocher. 
 
 The distinction between the yellow ochres and the red 
 ochres, whether natural or artificial, depends upon a per- 
 fectly definite chemical difference. The colour of every 
 one of these pigments is due, indeed, to iron, and to iron 
 in the same state of oxidation ; but the iron oxide in the 
 yellow and brown ochres is chemically united to water, 
 while in the red ochres it is nearly or quite anhydrous — 
 that is, dry. In chemical language, then, we may say 
 yellow ochre is a ferric hydrate, red ochre a ferric oxide. 
 But, when we proceed to examine a number of samples 
 of yellow ochre, we find, not merely different proportions 
 of ferric oxide to combined water — that is, different ferric 
 hydrates — but we find also very variable proportions of 
 intruding or accessory constituents. In fact, yellow ochre 
 represents not less than three mineral species, and it 
 occurs associated with many impurities, the latter con- 
 sisting mainly of silica, of clay, of rocky debris, with 
 traces of gypsum, of iron or copper pyrites, and of humus 
 or peaty acids. There are, moreover, ochres in which 
 other compounds occur, as barium sulphate to the extent 
 
 157 
 
158 
 
 YELLOW OCHRE 
 
 of 75 per cent, in some American varieties. The three 
 fundamental minerals, in order of frequency, which may 
 be traced in various yellow ochres, are these : 
 
 Brown haematite, or limonite, consisting of two mole- 
 cules of ferric oxide combined with three molecules of 
 water, and represented by the formula 2Fe20g, 3H2O ; 
 
 Yellow haematite, or xanthosidente, consisting of one 
 molecule of ferric oxide combined with one molecule of 
 water, and represented by the formula FogOg, HgO ; 
 
 Bog-iron ore, or lymnite, consisting of one molecule of 
 ferric oxide and three molecules of water, and is repre- 
 sented by the formula FogOg, 3H2O j the separate exist- 
 ence and permanence of a hydrate having this formula 
 are, it must be owned, doubtful. 
 
 It is probable that all the numerous varieties of yellow 
 ochre, from the countless localities of this substance, 
 belong essentially to one or other of the above species of 
 iron minerals, although the frequent presence of such 
 impurities or accessories as silica, iron silicates, and clay 
 renders the identification very difficult. Moreover, there 
 are reasons for suspecting, in some ochres at least, the 
 presence of another and more complex compound, namely, 
 a distinct double iron-aluminium hydrate. 
 
 An analysis of a fine sample of yellow ochre, taken by 
 the author from a pit on Shotover Hill near Oxford, gave 
 the following percentages : 
 
 Hygroscopic moisture 
 
 - 7'i ; Magnesia - 
 
 - 03 
 
 Combined water 
 
 - 9'0 1 Silica 
 
 • 61 '5 
 
 Ferric oxide 
 
 - 1 3 '2 1 Calcium sulphate 
 
 - i '4 
 
 Alumina - 
 
 - 6'3 1 Undetermined - 
 
 - 1'2 
 
 The varying hues of yellow ochres depend mainly upon 
 two differences of composition. One of these is the amount 
 of white clay, silica, calcium sulphate, or barium sulphate 
 
YELLOW OCHRE 
 
 159 
 
 present in them — this lightens the colour ; the other is the 
 presence of ferric oxide, which gives them a ruddier or 
 warmer hue. All, when burnt— that is, calcined — lose 
 their essential water, and become converted into various 
 kinds of red ochre, light red, etc. The varieties which 
 contain much silica and clay (ingredients which, even in 
 good yellow ochres, often amount to two-thirds of their 
 weight) yield the less translucent and paler tints of some 
 of the burnt red ochres. India furnishes a great variety 
 of hues of yellow ochre, but our chief supplies come from 
 France, Italy, Germany and Spain. More recently excel- 
 lent ochres have been obtained from the district of Dubbo 
 in New South Wales. Some of the English ochres (from 
 Oxfordshire, Derbyshire, etc.) are of fine quality. Peri- 
 gord Yellow, a natural earth found in Perigord, is a fine 
 variety of yellow ochre : it yields when heated to 8 oo°- 
 1,000° C. a fine reddish orange, brighter than that of the 
 light red produced from any other ochre. 
 
 Yellow ochre is generally prepared for use as a pigment 
 first of all by careful selection of the best pieces, and then 
 by the familiar process of elutriation, or washing over. 
 Thus it is at once freed from sand or other coarse particles, 
 and from any soluble salts which it may contain. Imme- 
 diately before being ground in oil, it should, however, be 
 dried at a temperature a little below that of boiling water, 
 as it is liable to contain hygroscopic moisture in addition 
 to its necessary constitutional water. 
 
 Yellow ochre is one of the most ancient pigments, 
 having been used by the Egyptians, the Greeks, and the 
 Romans. It is the oichra of Theophrastus. Pots of yellow 
 ochre were found at Pompeii. It has stood, with very little 
 change, the test of centuries. It certainly does become, 
 in all media, but especially in oil, slightly darker and 
 
i6o 
 
 YELLOW OCHRE 
 
 warmer in hue after prolonged exposure to light. The 
 change, however, is slight ; moreover, it soon comes to a 
 stop. It is probably due in part to a slight loss of con- 
 stitutional water from the ferric hydrate, and in part to 
 increased translucency. It must be recollected also that 
 yellow ochre as an oil-paint contains 40 or more per cent, 
 of oil, and this becomes yellower and darker in time. 
 Yellow ochre, so long as it is exposed to air and light, is 
 not darkened by sulphuretted hydrogen. It is without 
 action on other pigments, although the statement has often 
 been made, on quite insufficient grounds, that paints which 
 are damaged by contact with metallic iron are likewise 
 damaged by yellow ochre and by the red oxide of iron. 
 For instance, true Naples yellow is undoubtedly spoilt by 
 contact with a steel spatula, because the metal of the latter 
 takes away oxygen from, or ‘reduces ’ the lead antimoniate 
 of which the former consists. But such an action is 
 impossible with yellow ochre, for this iron compound is a 
 stable substance, containing already all the oxygen it can 
 take up. It is possible, notwithstanding, that ochre may 
 injure the hue of some lakes, such as yellow lake and 
 crimson lake, by replacing in part some of the alumina 
 with which the colouring matter is united. But as such 
 lakes are worthless, from their extreme instability when 
 exposed to light, when used alone, such probable action 
 of ochre upon them need scarcely be considered. Still 
 the same action may occur in the case of the madders 
 and alizarin pigments. 
 
 Yellow ochre is little subject to adulteration, for it is 
 too cheap a pigment to make it worth while to substitute 
 other substances for it. But sometimes the golden and 
 richer coloured varieties have been found to have had 
 their colour enhanced by the addition of certain fugitive 
 
YELLOW OCHRE 
 
 i6i 
 
 or semi-permanent yellows of artificial or organic origin. 
 The majority of such additions may be detected by 
 pouring a little liquor ammonise mixed with spirits of 
 wine upon some of the ochre placed on a filter-paper in a 
 funnel : the liquid passing through will be colourless if 
 the ochre be genuine. An ochre which when heated in a 
 test-tube gives off, besides water, fumes which partially 
 condense into a coloured or tarry matter on the glass, 
 contains organic matter, naturally present or artificially 
 added, and is generally of inferior permanence. Of late 
 years a far more frequent adulteration of yellow ochre is 
 the addition of chrome yellow — that is, lead chromate. 
 This adulteration may be detected by boiling the sus- 
 pected ochre with sodium carbonate solution, filtering, 
 and adding to the filtrate enough acetic acid to neutralize 
 it, and then a few drops of lead-acetate. A yellow pre- 
 cipitate indicates the presence of a chromate. An artificial 
 yellow ochre is made by acting upon solutions of iron 
 salts with metallic zinc, and thoroughly washing the 
 precipitate obtained. 
 
 Brown ochre is an approximately pure limcnite : raw 
 sienna is very nearly related to it (see farther on), but 
 cologne earth, raw umber, Caledonian brown and vandyke 
 brown are distinct substances. An artificial brown ochre 
 is prepared by heating yellow ochre with 4 per cent, of 
 common salt to a low red heat. 
 
 Under the name of cypnisite a peculiarly bright lemon- 
 coloured earth has been imported from Cyprus as a 
 pigment : it consists essentially of a hydrated ferric 
 sulphate : it is not likely to prove a safe pigment for 
 artistic use. 
 
CADMIUM YELLOW 
 
 162 
 
 Cadmium Yellow: Orient Yellow — Aurora Yellow — 
 
 Daffodil — Orange Cadmium — Sulphide of Cadmium — 
 
 Jaiine Brillant — Jaune de Cadmium — Kadmiumgelb. 
 
 The metal cadmium, which is nearly related to zinc 
 both chemically and physically, was discovered by 
 Stromeyer in the year 1817. To one compound only of 
 cadmium, the sulphide, are due all the hues and tints 
 from the palest lemon cadmium to the fiery orange-red. 
 This compound is represented by the formula CdS, and 
 contains 112 parts by weight of cadmium to 32 parts of 
 sulphur. As comm.only prepared, cadmium yellow is of 
 an orange hue ; when this compound separates slowly 
 from a solution, or is made in any way to take a dense or 
 aggregated form, it becomes of a decided reddish orange. 
 The orange-yellow variety, when very finely ground, 
 becomes less red and more inclined to yellow. Some of 
 the palest cadmium yellows contain white pigments, or 
 flour of sulphur, added to reduce their depth of colour : 
 the presence of free sulphur is sufficient to make any 
 pigment ineligible. 
 
 There are two well-known processes for making 
 cadmium yellow. In one of these pure cadmium oxide 
 is heated in a covered crucible with pure sulphur in 
 excess. In the other process, which yields pigments of 
 greater brilliancy and beauty, a soluble salt of cadmium, 
 such as the chloride or sulphate, is precipitated in the 
 presence of a little free acid, by means of a solution of 
 sodium sulphide, or preferably, of a stream of sulphuretted 
 hydrogen. The hue of the product inclines to red when 
 the solution is strong, hot and faintly acid ; to yellow 
 when it is weak, cold, and neutral. It is necessary to 
 state that all the materials used must be pure. Iron, 
 
CADMIUM YELLOW 
 
 163 
 
 lead, bismuth, and any metals giving a coloured sulphide, 
 even in traces, are seriously detrimental to the beauty of 
 the product. The precipitate of cadmium sulphide, after 
 having been thoroughly washed with boiling distilled 
 water until the wash-waters no longer redden blue litmus 
 paper, is collected on filter-papers and dried in the water- 
 oven. In order to remove any free sulphur that may be 
 present, the dry cadmium yellow may now be digested in 
 a suitable vessel with pure carbon disulphide. After this 
 treatment the pigment is once more dried, and is then 
 ready for grinding in oil or other vehicle. Cadmium 
 yellow, prepared by the process last described, presents 
 a satisfactory degree of permanence, and has no action 
 on white lead when both pigments are ground together 
 in oil. But a curious change has been noticed when the 
 orange-red variety of this pigment, ground in oil, was 
 kept some time in the ordinary metallic collapsible tubes, 
 which formerly contained some lead, although of late 
 years they have been made of nearly pure tin. The 
 interior surface of the tube became darkened, sometimes 
 almost black, from the formation of lead sulphide. It is 
 certainly strange that a similar action does not occur 
 between white lead and these deep cadmiums. For I 
 found that the same sample of cadmium-red in oil which 
 had blackened the metallic tube, when some of it was 
 laid upon flake-white in oil, and kept for years, had not 
 darkened the lead compound anywhere, even at the 
 surface of contact. Moreover, cadmium yellows mixed 
 with flake-white prevent, as do many other substances, 
 such as baryta-white, lead sulphate, etc., the ready 
 darkening of this lead paint by sulphuretted hydrogen. 
 On the other hand, the cadmium yellows act with great 
 energy upon some of the pigments containing heavy 
 
CADMIUM YELLOW 
 
 164 
 
 metals. Emerald green, for example, is rapidly ruined 
 by cadmium sulphide, both in water and in oil ; cadmium 
 yellow and emerald green (Schweinfurt green) are abso- 
 lutely incompatible. Chrome yellow and true Naples 
 yellow are also darkened by admixture with cadmium 
 yellow, at least after a time. With oil colours, a sample 
 of yellow ochre, which was afterwards found to have 
 been adulterated with chrome yellow to the extent of 
 8 per cent., became yellowish-grey after admixture with 
 some cadmium yellow. 
 
 While the stability of what may be called the normal 
 cadmium yellow or orange is pretty well assured, both as 
 an oil and a water colour, a very different verdict must be 
 pronounced upon pale and lemon cadmium when used in 
 water-colour painting. When thus used these pigments 
 do not merely fade, but acquire a somewhat greyish hue. 
 The following observations throw some light upon these 
 changes. During the year 1876 I prepared a number of 
 samples of cadmium yellow and orange. All were obtained 
 by the action of sulphuretted hydrogen upon solutions of 
 cadmium chloride. The products ranged in hue from a 
 lemon colour to a deep orange, according to the strength 
 of the solution, the presence or absence of free acid, and 
 the temperature at which the precipitation of the pigment 
 took place. After due washing and drying the various 
 samples were put into bottles and preserved in my labora- 
 tory. They were never exposed to direct sunshine. On 
 examining them from time to time it was noticed that the 
 specimens of medium depth, having a yellowish orange 
 hue, kept their hue perfectly, while two or three of the 
 orange-red varieties exhibited a curious phenomenon of 
 alteration. The loose friable lumps into which the powder 
 had aggregated were distinctly paler on the outside than 
 
CADMIUM YELLOW 
 
 165 
 
 in the interior, while the parts of the contents of the 
 bottles which had been most exposed to light were paler 
 than those which had been comparatively shaded. But a 
 still more marked change had taken place in the samples 
 to which the term ‘ pale ’ cadmium might be applied. 
 These had generally become still paler, almost straw- 
 coloured, especially where most exposed to light ; but in 
 some of the specimens orange specks were observed, 
 resembling in hue what is usually called ‘ middle ’ cad- 
 mium. From the above observations it would seem that 
 there is a tendency in differently tinted ‘ wet process ’ 
 cadmium yellows to return to what we may call the 
 normal or medium hue, but that the palest varieties are 
 most subject to change. This change seems to arise in 
 part from oxidation and hydration, for the bleached speci- 
 mens gave indications of containing some white cadmium 
 hydrate, when heated giving off a little water, and be- 
 coming brownish from the formation of the brown oxide 
 of cadmium. Such a bleaching of pale cadmium, if my 
 explanation be correct, is in a measure explicable if we 
 recollect that this variety occurs in a very fine state of 
 division, and on this account is more liable to chemical 
 change. In water-colour painting, where there is no 
 effective protection through the presence of a hydrofuge 
 medium, this fading of ‘ wet process ’ pale cadmium is 
 notorious. In oils this cadmium, like the others, is generally 
 thought to be permanent. My faith in the inalterability 
 of cadmium pigments, even in oil and allied media, has, 
 however, been somewhat shaken during recent years. 
 Cadmium orange has almost perished where used in 
 Leighton’s lunette ‘ Arts of Peace,’ in the Victoria and 
 Albert Museum, a work executed in spirit-fresco. I 
 regard the passage of the pale and of the deep cadmium 
 
i66 
 
 CADMIUM YELLOW 
 
 yellow when in powder into the normal or middle variety 
 as dependent chiefly, if not entirely, upon molecular 
 changes. Moreover, the pale cadmiums are rarely found 
 free from admixture, and their alterability may be in part 
 owing to the foreign ingredients they contain. More 
 recent researches by G. Buchner and N. von Klobukoff 
 confirm the conclusions drawn from my early experiments. 
 There can be no doubt that cadmium sulphide exists in 
 two if not in three molecular states, differing not only in 
 colour but in crystalline form and in specific gravity. 
 Thus pale cadmium has the specific gravity 3'g to 4‘5, 
 while the red modification is denser — 4‘5 to 4’8. And 
 when the pale variety, dry and in powder, is rubbed 
 strongly with a piece of agate, its colour deepens and 
 reddens in a very decisive manner. The same change 
 occurs when a water-colour wash of cadmium yellow is 
 exposed for a year or so to sunlight in a perfectly dry 
 atmosphere. This phenomenon is clearly analogous with 
 that shown when the yellow mercuric iodide is altered 
 into the scarlet form by pressure. It is perhaps safer to 
 employ an ivory palette knife rather than one of steel in 
 manipulating the cadmium pigments. 
 
 Aurora yellow is a bright and beautiful pigment con- 
 sisting essentially of cadmium sulphide. It has more 
 opacity than most of the other varieties of cadmium and 
 possesses a pure yellow hue. Its stability is greater than 
 that of many other varieties of this pigment. Daffodil 
 yellow is the name given to another variety of cadmium 
 sulphide, prepared at a red heat and containing a small 
 quantity of magnesia. Neutral orange is a mixture of 
 cadmium yellow with Venetian red. 
 
 Cadmium yellows are sometimes adulterated with 
 Indian yellow, baryta and strontia chromates, and 
 
CADMIUM YELLOW 
 
 167 
 
 chromates of lead. Indian yellow shows its presence by 
 blackening and giving off tarry fumes when the pigment, 
 in the state of dry powder, is strongly heated in a test- 
 tube. The chromates may be detected by the green colour 
 produced when the sample is warmed with alcohol and 
 dilute sulphuric acid. The lead chromates or chrome 
 yellows, and the orange and red basic chromates of the 
 same metal will blacken when the substance in which 
 they are present is moistened with weak ammonium 
 sulphide. Free sulphur in pale cadmium yellows comes 
 off as a vapour when the sample is heated, but it may be 
 better detected by the solvent action upon it of carbon 
 bisulphide. Baryta-white may be detected by its insolu- 
 bility in hot strong hydrochloric acid, in which cadmium 
 sulphide dissolves. 
 
 Cadmium red and cadmium orange are slightly trans- 
 lucent when compared with the paler and yellower varie- 
 ties of this pigment, and possess very full and glowing 
 hues. They work well as oil and water colours. Mixed 
 with zinc-white or flake-white, deep and middle cad- 
 miums yield several beautiful colours, some of which 
 closely resemble the different varieties of true Naples 
 yellow, and are now employed very largely in lieu of the 
 latter pigment. Pure cadmium yellow, when heated 
 moderately, becomes orange-red or red, but regains its 
 pristine hue on cooling. If, however, the heat be con- 
 siderably raised in the presence of air, some of the sulphur 
 in the compound burns, and the residual mass presents 
 a dull brown colour. ‘ Manganese oil ’ accelerates the 
 drying of the cadmium colours, which is sometimes 
 inconveniently slow. 
 
A UREOLIN 
 
 1 68 
 
 Aureolin : Cohalt Yellow — Jaime de Cohalt — Kohaltgelb. 
 
 Origin and Composition. — This remarkable artificial 
 yellow pigment was discovered by Fischer. It is a com- 
 pound of the nitrites of cobalt and potassium. Usually 
 it is free from water, but it sometimes contains three 
 molecules, and is then represented by the formula 
 KgCo2(N02)i2) 3H2O. Other proportions of water also 
 occur; but when the compound contains four molecules, 
 its hue is somewhat greenish. The dry or anhydrous 
 variety is best made by mixing a solution of a cobaltous 
 salt, strongly acidified with acetic acid, wuth a concen- 
 trated solution of potassium nitrite, and keeping the 
 mixture warm. Perhaps a pigment of finer hue is 
 
 obtained by passing a stream of nitric oxide gas mixed 
 with air into a solution containing nitrate of cobalt and 
 a little acetate of potassium ; from time to time a little 
 potassium carbonate is added. 
 
 Another method of preparing a variety of aureolin 
 having a singularly bright yellow hue consists in adding 
 a solution of sodium cobaltinitrite acidified with acetic 
 acid to a dilute solution of potassium acetate or nitrate. 
 
 I have tried the experiment in accordance with the in- 
 structions given by Messrs. Adie and Wood (in the 
 ‘ Transactions of the Chemical Society,’ vol. Ixxvii., 1900, 
 p. 1076), but I have used sometimes other cobalt salts 
 instead of the acetate, and have also so arranged the 
 constituents of the two solutions that the precipitate of 
 aureolin is intimately associated with barium sulphate 
 precipitated at the same time. By this means an opaque 
 pigment of bright and light yellow hue is obtained. The 
 pure aureolin obtained by this process contains sodium 
 as well as potassium, and is represented by the formula 
 
A UREOLIN 
 
 169 
 
 K2NaCo(N02)6>H20. Its value as a pigment is at least 
 equal to that of the better-known varieties of aureolin. 
 The pure pigment prepared in the way indicated, without 
 any suggestion of its use in painting, by Messrs. Adie 
 and Wood, requires less oil than usual and dries well ; in 
 water-colour painting it shows one distinct advantage 
 over the older varieties of aureolin, for it is less soluble 
 in water and does not sink into the paper. The several 
 varieties of aureolin are not much affected by caustic 
 potash solution or by dilute hydrochloric or nitric acid, 
 and are very slowly attacked and blackened by solution 
 of sulphuretted hydrogen, but are at once destroyed by 
 ammonium sulphide. Ordinary aureolin is slightly soluble 
 in cold water. 
 
 Aureolin is of a pure yellow colour, and is almost trans- 
 parent whether used in water or oil painting. In oil some 
 samples dry with great difficulty, and become very dirty 
 if exposed to the air during the progress of desiccation ; 
 other samples dry and harden too quickly — the exact 
 cause of this difference of deportment has not been 
 ascertained. Moreover, as ordinarily ground in oil, some 
 varieties require a very large proportion of the medium. 
 These defects may be easily remedied by heating the 
 slow-drying variety of the ground pigment to 212 ° F. 
 immediately before the addition of the oil, and by using, 
 instead of raw linseed oil, the siccative linseed oil, pre- 
 pared by means of borate of manganese. Thus prepared, 
 aureolin not only dries quickly, but it retains its purity 
 of hue ; moreover, a surface of the dried oil pigment will 
 yield nothing to a wet cloth passed over it instead of 
 staining it yellow. The reason why this staining occurs 
 with ordinary aureolin ground in oil, even when it has at 
 last become dry, is that the oil does not suffice to pro- 
 
A UREOLIN 
 
 170 
 
 tect the particles of pigment from the solvent action of 
 moisture. The quick-drying variety of aureolin should 
 be ground in poppy oil. 
 
 I find that the variety of aureolin which contains sodium 
 as well as potassium (see above) dries perfectly well when 
 ground in purified linseed oil, even when the latter has 
 not been made siccative by special treatment. 
 
 Aureolin properly prepared in oil, as described above, 
 does not fade by exposure to sunlight, nor does it darken, 
 except so far as the admixed oil is concerned. As a 
 water-colour aureolin is practically permanent, even in 
 sunlight, as the following figures show : 
 
 Original intensity ... ... ... 10 
 
 After two and five years ... ... 10 
 
 After ten years ... ... ... 9 
 
 In the Burlington Club trials it was found that aureolin 
 
 stood perfectly for four years when exposed in an ordinary 
 frame or in air kept dry, but that it lost somewhat by 
 exposure, during the same time, in a hermetically sealed 
 tube in the presence of ordinary moist air. 
 
 The fading of fugacious organic pigments, such as the 
 lakes from cochineal, is accelerated by their commixture 
 with aureolin, which particularly hastens the destruction 
 of indigo, even in oil. The aureolin cannot so act without 
 being itself likewise affected ; it generally becomes, under 
 such circumstances, of a brownish hue. 
 
 It is easy to learn whether a sample of aureolin is free 
 from combined water by heating a small portion some- 
 what strongly in a long test-tube ; dew will condense 
 upon the upper part of the tube if water be present in the 
 pigment. The presence of yellow organic matters in 
 imitative or adulterated aureolins may generally be 
 
LEMON YELLOW 
 
 171 
 
 detected by mixing some powder of the suspected sample 
 with spirits of wine and a few drops of strong ammonia ; 
 the liquid becomes red orange, or yellow if the aureolin 
 be not pure. Aureolin containing chrome yellow is 
 blackened by a solution of sulphuretted hydrogen. 
 
 Aureolin is the first pigment described (in the present 
 manual) which illustrates the remarkable colouring power 
 of the element cobalt. The hues derived from this metal 
 acting as a chromogen range from yellow to green, blue 
 and violet or purple ; there is also a rose cobalt. Various 
 oxides, themselves colourless, serve as chromophores. 
 
 Lemon Yellow: Baryta Yellow — Barium Chromate — 
 Yellow Ultramarine — Permanent Yellow — Jaune d' Outre 
 mer — Zitronengelb. 
 
 Of all the chromates which have been used in painting, 
 barium chromate is the most stable. It has a pure 
 yellow colour, with a not inconsiderable degree of opacity. 
 It works smoothly. 
 
 Lemon yellow is often made by mixing solutions of 
 neutral potassium chromate and of barium chloride, both 
 liquids having been previously heated to 100° C. A still 
 better plan is to take equivalent proportions — namely, 
 25I parts by weight of pure crystals of barium chloride 
 and 21^ parts of pure crystals of neutral potassium 
 chromate — of these two compounds, and to grind them 
 together to very fine powder. Continue the grinding, and 
 then add gradually sufficient pure water to convert the 
 mixture into a thin paste. The paste is then heated to 
 100° for fifteen minutes, thrown on a filter, washed with 
 abundance of pure water, dried, and ground. 
 
 Properly prepared lemon yellow may be mixed with 
 most other stable pigments without suffering change. It is 
 
172 
 
 GAMBOGE 
 
 not blackened like the lead chromes by sulphuretted 
 hydrogen, but it has a tendency, as a water-colour, to 
 become greenish when long exposed to this gas or to 
 impure air. In oils it is very useful, for although some 
 organic pigments may give it a greenish cast by reducing 
 it in part to green chromic oxide, yet it may be safely 
 associated with aureolin, with madder carmine, and with 
 Prussian blue. Lemon yellow may be used in fresco. 
 
 Strontium chromate is very often — we may say gener- 
 ally — substituted for true lemon yellow, but it is less 
 stable, and has the further defect (for water-colour work) 
 of being decidedly soluble even in cold water, so that 
 light washes of it may be found to sink into the paper 
 and to partially disappear. The most common adultera- 
 tion of lemon yellow is with pale chrome ; of course, 
 sulphuretted hydrogen detects this falsification by darken- 
 ing or blackening the pigment. Strontium chromate is 
 distinguished from barium chromate by its dissolving in 
 boiling water to such an extent as to yield a solution 
 having a strong yellow colour. It may be prepared in 
 the same way as the chromate of barium. Zinc chromate 
 and calcium chromate are yellow pigments of inferior 
 value. A mixture of zinc chromate with barium chromate 
 is sold as primrose yellow. 
 
 Gamboge : Gomme-gutte — Gmnmigutt. 
 
 Origin . — This gum-resin is produced by several species 
 of Garcinia. Siam gamboge comes from G. Hanhuryi 
 (Hook, f.) ; Ceylon gamboge from G. Morelia (Desv.). 
 There are other species from which the same product is 
 obtained in various parts of India, as G. Carnbogia 
 (Desrouss.) and G. dliptica. The fine, deep-coloured 
 
GAMBOGE 
 
 173 
 
 gamboge, produced by the Burmese G.heterandra (Wall.), 
 may prove to be superior to Siam gamboge, but it has 
 not yet become an article of European trade. Gamboge 
 is a mixture of a gum soluble in water, and a resin which 
 is soluble in alcohol, chloroform, ether, etc. The pipe- 
 gamboge of Siam, which is as pure as any variety met 
 with in commerce, contains about 78 per cent, of resin 
 and 18 of gum. The resin, which is the true colouring- 
 matter, may be easily obtained pure by crushing pipe- 
 gamboge into fine powder, mixing it with a little water, 
 and then shaking up the mixture with ether ; the ether 
 dissolves the resin alone. From the ethereal solution the 
 colouring-resin is recoverable by evaporation ; but it is 
 better to add a little drying-oil and some copal-varnish 
 before driving off the ether by means of a very gentle 
 heat. The coloured, semi-fluid mass which then remains 
 may be preserved in bottles or tubes for use as an oil- 
 paint. The resin of gamboge has the properties of an 
 acid, and forms yellow, orange, or brown compounds, 
 with soda, lime, baryta, and other bases. Some of these 
 compounds might prove useful as paints. 
 
 Gamboge was used by the early Flemish oil-painters. 
 In the seventeenth century it was largely employed to 
 give a golden hue to the embossed leathers for which 
 Amsterdam was famous. 
 
 In water-colour painting gamboge is not trustworthy. 
 It is unaffected by sulphur compounds, but is darkened 
 by ammoniacal fumes, and slowly bleached by strong 
 light. Some samples prove, however, far less fugitive 
 than others. In two years’ exposure to sunlight, one 
 sample of cake-gamboge lost more than half its original 
 intensity ; while a sample of moist gamboge, bought at 
 the same time from the same maker, retained nine-tenths. 
 
174 
 
 INDIAN YELLOW 
 
 The same sample of moist gamboge, after seven years, 
 still showed seven degrees out of the original ten of 
 intensity. 
 
 As an oil-colour, gamboge affords a rich, transparent, 
 golden or amber hue ; it has some claims to the con- 
 sideration of artists. To secure its permanence, ad- 
 mixture with oil alone does not, however, suffice ; a resin 
 such as copal, or Strasburg turpentine, or wax, or 
 paraffin, must be used also. Some of Sir Joshua 
 Reynolds’ trials of gamboge prove this, those with oil 
 alone being a name only now ; while those with resin, or 
 wax, retain their original hue very fairly, though they 
 were spread upon the canvas in 1772. It must, there- 
 fore, be remembered that reliance cannot be placed upon 
 the permanence of the ordinary gamboge oil-paint as 
 met with in commerce. 
 
 Gamboge, from its resinous nature, shows, when laid 
 on thickly as a water-colour, a rather shining surface. 
 It appears to have little or no chemical action on other 
 pigments (with the exception, perhaps, of white lead), 
 although, if it be mixed with anything which contains 
 lime, or other alkaline compounds, it becomes brownish, 
 and darkens. Gamboge forms beautifully clear and rich 
 greens with Prussian blue or indigo, but its place in 
 water-colour painting may be advantageously taken by 
 aureolin, and even by Indian yellow. When mixed with 
 baryta yellow or cadmium yellow, the permanency of 
 gamboge is enhanced. 
 
 Indian Yellow : Pinri, Purree, Peori — Jaime Indien — 
 Indischgelh. 
 
 This remarkable pigment is obtained at Monghyr, a 
 town in Bengal, from the urine of cows which have been 
 
INDIAN YELLOW 
 
 175 
 
 fed upon mango-leaves. It generally occurs in the 
 bazaars of the Panjab in the form of large balls, having 
 an offensive urinous odour. 
 
 Indian yellow is an impure magnesium salt of euxanthic 
 acid. The essential part of it is a compound containing 
 4‘5 per cent, magnesia, 18-7 per cent, water, and 78-7 
 per cent, euxanthic anhydride ; but this substance is 
 always associated, even in the most carefully purified 
 samples of prepared Indian yellow, with various im- 
 purities both mineral and organic. The pure mag- 
 nesium euxanthate is represented by the formula 
 5H2O. 
 
 For artistic purposes the crude imported Indian yellow 
 is thoroughly powdered, and then washed with boiling 
 water, until the liquid filtered from it is no longer 
 coloured ; a brown impurity, and much of the evil smell, 
 are thus removed. The colour of the washed product is 
 enriched by leaving it in contact for a day or two with a 
 saturated solution of sal-ammoniac, and then repeating 
 the treatment with hot water. 
 
 Thus purified, this pigment presents a translucent 
 orange-yellow colour of great depth and beauty. Ground 
 in oil, some specimens are practically unchanged, even 
 after long exposure to sunlight, any darkening they show 
 being due either to imperfect purification, or to the 
 change of the associated oil. Such change is reduced to 
 a minimum if poppy oil be substituted for linseed oil, or 
 if the latter be previously treated with manganese borate. 
 On the other hand, I have met with specimens of Indian 
 yellow ground in oil which, after five years’ exposure, 
 have lost nearly one-third of their original depth, and 
 have, at the same time, become rather reddish-brown in 
 hue. As a water-colour, Indian yellow retains its hue 
 
i;6 
 
 INDIAN YELLOW 
 
 unimpaired when exposed to diffused daylight ; sunlight 
 very slowly bleaches it, the hue it acquires being some- 
 what brownish. The rate of alteration and of reduction 
 in force caused by sunlight may be approximately repre- 
 
 sented by these figures : 
 
 Original intensity ... ... ... lo 
 
 After 2 years ... ... ... 9 
 
 After 5 years ... ... ... 7 
 
 After 7 years ... ... ... 6 
 
 After 10 years ... ... ... 5 
 
 When this water-colour pigment is exposed to sunlight 
 in the presence of air maintained in a state of perfect 
 dryness it loses its colour much more rapidly than under 
 ordinary conditions. For this reason it may be advisable 
 to incorporate an extra proportion of glycerin with Indian 
 yellow when prepared as a water-colour. 
 
 As a general rule, Indian yellow suffers no change by 
 admixture with any pigment itself permanent, nor is it 
 affected by sulphur compounds. True Naples yellow, 
 however, most of the chromates, and probably aureolin 
 also, tend to embrown it to some extent. 
 
 Indian yellow which has been adulterated with lead 
 chromate (chrome yellow) becomes dark-brown when 
 moistened with ammonium sulphide. 
 
 A fine yellow pigment may be prepared from the 
 euxanthic acid, which is the characteristic constituent of 
 Indian yellow, by throwing it down in combination with 
 the two bases — alumina and magnesia. The following 
 directions may be followed : Dissolve i part of pure 
 eu.xanthic acid in just sufficient dilute ammonia. Pour 
 the solution into a liquid prepared by dissolving 45 parts 
 of potash-alum, 15 parts Epsom salts, and 6 parts sal- 
 
MARS YELLOW 
 
 177 
 
 ammoniac in 250 parts of water. Now cautiously add 
 dilute ammonia to the mixture, stirring all the time, and 
 avoiding any excess of ammonia. The precipitated pig- 
 ment is to be thoroughly washed, and then pressed, dried, 
 and ground. 
 
 Mars Yellow: Mars Orange — Artificial Ochre — Jaune 
 de Mars. 
 
 This pigment is a kind of yellow ochre prepared arti- 
 ficially. It may be made by precipitating a salt of iron 
 mixed with alum by means of caustic soda, or potash, 
 or lime. The salts of iron used are either green vitriol 
 (ferrous sulphate) or the ferric chloride. If green vitriol 
 be employed the precipitate formed gradually becomes 
 yellow on exposure to the air. Upon the proportion of 
 alum mixed with the iton salt depends the depth of the 
 yellow colour in the product, for the alumina precipitated 
 with the iron hydrate acts as a diluent of the colour. 
 When lime is used as a precipitant for the iron com- 
 pound (if this be green vitriol or ferric sulphate), calcium 
 sulphate, that is, gypsum, comes down along with the 
 ferric hydrate and basic ferric sulphate, and serves to 
 lighten the colour. 
 
 By submitting the different varieties of Mars yellow 
 to various degrees of heat, with or without a little nitre, 
 a number of products of different hues are obtained, in- 
 cluding Mars orange. Mars red. Mars brown, and Mars 
 violet. All these preparations require very thorough 
 washing to fit them for use on the palette of the artist. 
 
 The Mars colours are permanent when carefully pre- 
 pared and thoroughly purified from soluble salts. They 
 seem sometimes to have a slightly injurious effect upon 
 a few of the best semi-permanent pigments of organic 
 
178 
 
 NAPLES YELLOW 
 
 origin, such as the madder colours. This action may be 
 due to the ferric hydrate in them combining with the 
 colouring matter, and displacing some of the alumina 
 previously united with it. In this direction it is probable 
 that Mars yellow will be more active than the deeper- 
 coloured pigments produced by calcining it at various 
 temperatures. 
 
 Naples Yellow : Jaime de Naples — Jaime d' Antimoine 
 ■ — Neapelgelb — Giallo di Napoli. 
 
 Under this name three different substances are in- 
 cluded. The pigment generally sold in England as 
 ‘ Naples yellow ’ is an excellent imitation made by mixing 
 cadmium yellow or deep cadmium with a white, prefer- 
 ably a zinc white. But a true Naples yellow, which is 
 a basic lead antimoniate, is still procurable from some 
 artists’ colourmen. This preparation is sometimes made 
 by heating together for two hours a mixture of i part 
 tartar emetic, 2 parts nitrate of lead, and 5 parts common 
 salt, all the ingredients being of the purest quality, and 
 the heat not exceeding that at which common salt fuses. 
 A more recent process, in which zinc oxide is introduced 
 among the materials which are heated together, yields a 
 paler but excellent product. A bright pale variety of 
 yellow ochre seems to have formerly gone under the 
 name of Naples yellow. 
 
 This antimonial yellow has been known from very early 
 times as an enamel colour. It has been found upon 
 Babylonian bricks at least 2,500 years old. Persian 
 pottery as early as the thirteenth century of our era is 
 occasionally decorated with antimonial yellow. 
 
 In oil the genuine and the imitative Naples yellows 
 
NAPLES YELLOW 
 
 179 
 
 are quite permanent, so far as light is concerned, but the 
 genuine kind is liable to be darkened, like other lead 
 compounds, by air containing sulphuretted hydrogen. In 
 water-colour painting genuine Naples yellow is quite in- 
 admissible, for it blackens rapidly, but irregularly, in the 
 presence of mere traces of sulphur compounds. This 
 blackening, like that of lead white under similar con- 
 ditions, is much more marked in darkness than in light. 
 
 Naples yellow, in contact with metallic iron, tin, 
 pewter, zinc, and several other metals, is discoloured and 
 blackened. An ivory instead of a steel spatula, or palette 
 knife, should be used with this pigment. The darkening 
 in question is due in part to attrition, owing to the 
 extreme hardness of the particles of the lead antimoniate, 
 however finely the material may have been ground, and 
 partly to the reducing effect of the above-named metals 
 upon this antimoniate. Iron in the form of its oxide or 
 hydrate (as in light red or yellow ochre), or in complex 
 combinations (such as Prussian blue), does not exert any 
 effect upon Naples yellow. A statement to the contrary 
 effect has crept into a large number of technical manuals, 
 but I have been unable to discover the slightest experi- 
 mental evidence in favour of such a view. Naples 
 yellow, however, is injured by and does injure some of 
 the organic pigments, such as the cochineal reds and the 
 numerous yellow lakes. But as Naples yellow cannot 
 be used as a water colour, and as the above-named 
 organic pigments ought to be entirely excluded from the 
 palettes of all artists, the action in question is of little 
 importance. Naples yellow acts upon indigo also. 
 Indigo, however, is a pigment, to which a very high 
 degree of permanence cannot be assigned ; there is, 
 moreover, no reason why it should be associated with 
 
i8o 
 
 YELLOW LAKE 
 
 Naples yellow, as other yellow pigments may be safely 
 used to modify its hue. 
 
 Another pigment also is sold as jaune d’antimoine. It 
 is a mixture of the oxychlorides of bismuth and lead with 
 lead antimoniate. When carefully prepared it yields a 
 rich paint of good body, but its use cannot be recom- 
 mended to artists. 
 
 Yellow Lake; Brown Pink — Citrine Lake — Yellow 
 Madder — Italian Pink — Quercitron Lake — Gelber Lack. 
 
 Origin. — The sources of yellow lake are numerous, but 
 the best kind is obtained from quercitron bark from 
 Quercus tinctoria, Qu. nigra, and Qu. citrina, three species 
 of North American oak. A hot- water decoction is made, 
 and this is precipitated by a solution of alum and dilute 
 ammonia. A richer yellow pigment is obtained by 
 extracting the powdered bark and alburnum with boiling 
 dilute sulphuric acid instead of with water. The original 
 colouring matter of the bark (quercitrin) is thus changed 
 into a more stable compound known as quercetin. The 
 former substance is a glucoside, the latter has the 
 character of an acid ; both may be converted into lakes 
 by bringing them into contact with precipitating or pre- 
 cipitated hydrate of alumina. Yellow lake was formerly 
 made from the fruits of various species of buckthorn, 
 known as Persian, Turkish, or Avignon berries. The 
 species yielding these fruits are Rhamnus infectoriiis, 
 R. oleoides, R. saxatilis, R. amygdalinus, R. catharticus. The 
 bark of R. frangula and of R. catharticus also yields a 
 yellow pigment. ‘ Stil de grain,’ and several of the con- 
 tinental yellow lakes, are made from the above-named 
 berry. 
 
BROWN PINK 
 
 i8i 
 
 Italian pink, Dutch pink, and deep yellow madder are 
 names usually given to the richer yellow lakes of quer- 
 citron, although some of these pigments are occasionally 
 prepared from Turkish or Avignon berries. 
 
 Beautiful and useful as many yellow lakes undoubtedly 
 are, they should be rigorously excluded from the artist’s 
 palette. In oil most of them are very bad driers, as well 
 as fugitive : in v/ater-colour they generally lose nine- 
 tenths of their colour within two years of exposure to 
 sunlight : the residual stain is ultimately of a bluish-grey. 
 
 The following observations as to the behaviour of 
 several members of this group, on exposure for two years 
 to sunlight, apply to the colours as ground in oil, and as 
 mixed with flake-’ 
 
 Name 
 
 Laque Robert — hell 
 gelb 
 
 Laque Robert — dun 
 kelgelb - 
 Laque brun-jaune 
 Laque brun-fonce 
 Pale yellow madder 
 Deep yellow madder 
 
 The same pigments used as glazing colours over flake- 
 white have faded to about the same extent, but their 
 change of hue is, in one or two cases, rather less marked. 
 
 The so-called brown pink is usually a deep quercitron 
 lake, although it was formerly made from the berries of 
 one of the kinds of buckthorn (Rhamnus) previously 
 named. I have never met with a specimen of it which 
 would stand a year’s exposure to sunlight without suffer- 
 ing almost complete change or loss of colour both in water 
 and in oil. And it further presents the awkward effect of 
 
 white in tint : 
 
 In Oil only 
 
 With Original 
 
 Flake-white Intensity =io 
 
 - Lemon yellow - Pale straw - 
 
 Deep lemon 
 Salmon - 
 Yellowish-grey 
 Pale orange 
 Greyish salmon 
 
 - 4 
 
 Stone - 
 Pale rose - 
 Smoke-grey - 8 
 Pale buff - - 7 
 
 Pale greyish pink 6 
 
CHROME YELLOW 
 
 182 
 
 becoming ultimately of a cool bluish-grey hue, a change 
 particularly unfortunate when it has been freely used to 
 represent foreground vegetation, or the golden lights on 
 the near foliage of trees. Yet I am bound to confess 
 that in Mr. W. Simpson’s fifteen years’ trial of certain 
 water-colour pigments, the brown-pink has suffered com- 
 para,tively little alteration. Had a portion of the original 
 cake-colour employed been preserved for examination it 
 might have been possible to have discovered the cause 
 of this anomalous behaviour of the particular specimen 
 in question. 
 
 Chrome Yellow; Chvome — Chromate of Lead — Jaune de 
 Chrome — Chromgelb. 
 
 This pigment, when of a pure yellow hue, is the neutral 
 lead chromate. By associating it with an additional 
 quantity of lead oxide it may be obtained of various 
 orange and reddish orange hues. It may be made by the 
 mutual action of a soluble lead salt, such as the acetate 
 or nitrate, and the chromate or bichromate of potassium. 
 Or white lead in fine powder (2 kilos.) may be boiled with 
 a solution of bichromate of potassium kilo.) in water 
 (10 litres). Alum and baryta-white, or lead sulphate, are 
 also employed in the preparation of some of the paler 
 chrome yellows. Lemon chrome is a mixture of lead 
 chromate and sulphate. Orange chrome and chrome red 
 are prepared from a mixture of lead acetate (6f kilos.), 
 litharge (5^ kilos.), neutral potassium chromate (6 kilos.), 
 caustic potash being sometimes used in addition. Chrome 
 red may be obtained also by the direct action of caustic 
 soda in solution upon the yellow lead chromate : its 
 chemical formula is PbCrO^, PbO, or Pb 2 CrOj. 
 
VANADIUM YELLOW 
 
 183 
 
 The chromates of lead are peculiarly liable to change, 
 and are quite unfitted for use in tempera or water-colour 
 painting. In oil, especially if protected by varnish, or 
 locked up in a resinous vehicle, these pigments show a 
 certain measure of permanence, except when they are 
 mingled with paints of organic origin. In fact there are 
 two causes which militate against the integrity of the lead 
 chromates. One of these is the tendency which they 
 possess towards reduction, that is, the loss of oxygen by 
 their chromic constituent, by which the green or lower 
 oxide of chromium is formed. This change is brought 
 about by many kinds of organic matter, notably by such 
 animal or vegetable pigments as are themselves prone to 
 oxidation. The other cause of deterioration is the pres- 
 ence of certain sulphur compounds which act upon the 
 lead chromates in the same way as they act upon white 
 lead, producing lead sulphide of a dark brown, or a grey 
 colour. 
 
 Of late years the respective merits as oil-paints of 
 cadmium yellow and chrome yellow have been warmly 
 contested ; the tendency at present, especially among 
 artists rather than among chemists, is to give a verdict 
 in favour of the latter pigment. 
 
 Vanadium Yellow. 
 
 It has been proposed to employ the beautiful golden- 
 bronze crystals of meta-vanadic acid as a pigment. They 
 possess, when finely ground, an intense colour, like that 
 of a very rich golden ochre, but less earthy, and more 
 brilliant. This pigment has remarkable covering power, 
 and works admirably both as an oil and a water-colour. 
 Although the material is somewhat costly, the price for 
 which it could be prepared need not preclude its use. 
 
KINGS’ YELLOW 
 
 184 
 
 But, unfortunately, this colour is not permanent. A few 
 hours’ exposure to sunshine of a water-colour wash of 
 vanadium yellow suffices to change and deteriorate its 
 hue in a marked degree. 
 
 Kings’ Yellow: Orpiment — Jaune Royal — Kdnigsgelh. 
 
 The yellow arsenious sulphide (AsgSg), though extremely 
 beautiful in hue, cannot be relied on as a pigment. Even 
 in oil or varnish its colour fades: Sir Joshua Reynolds’ 
 experimental canvas shows some pale brown patches 
 which have once been kings’ yellow, but which now have 
 almost entirely disappeared. Strange to say, in one of 
 his trials, a few quite visible crystals of orpiment are 
 preserved. As it cannot be imagined that he used this 
 pigment in this exceedingly coarse form, it would seem 
 that a molecular aggregation of a part of the orpiment 
 has taken place in the lapse of years. If this change has 
 not occurred, then we may conclude that only the largest 
 particles of the kings’ yellow have escaped alteration. 
 Under any circumstances the inadmissibility of kings’ 
 yellow to the palette of the artist is obvious : moreover, 
 it cannot be safely mixed with any pigment containing 
 lead or copper. It was known to the Egyptians. 
 
 Another compound of arsenic and sulphur (AsgSg) has 
 been employed as a pigment. It is of an orange-red hue 
 and is known as realgar. Not only is it extremely poison- 
 ous, but it suffers change on exposure to light, and acts 
 injuriously upon colours containing copper or lead. It was 
 used by the Romans : I identified a fragment of it amongst 
 the objects discovered at Silchester in the year 1896. 
 
PURE ORANGE 
 
 tSS 
 
 Pure Orange : Mangold — Alizarin Yellow — Alizarin 
 Orange. 
 
 Under the above names a pigment of great richness 
 and beauty has been introduced. It is a kind of lake, 
 and consists of a coal-tar colour known to chemists as 
 ^-nitro-alizarin thrown down upon an aluminous base. 
 Nitro-alizarin, as its name implies, is a derivative of 
 alizarin, one of the least changeable of all organic pig- 
 ments, and the chief tinctorial product of madder. There 
 is no doubt about the beautiful hue of this paint, a deep 
 brownish gold : the trials first made as to its permanence 
 in oil promised well, but on continuing the exposure to 
 light of this pigment ground in oil it became evident that 
 it suffered considerably. The deterioration was more 
 marked when the paint had been mixed with flake white, 
 but even as a glazing colour it is not safe. 
 
CHAPTER XV 
 
 RED PIGMENTS 
 
 Vermilion : Cinnabar — Vermilion — Zinnoher. 
 
 The mineral cinnabar, or mercuric sulphide, occurs in 
 many parts of Europe, and abundantly in China, and is 
 extensively worked in New Almaden in California ; it 
 would be tedious to recount the numerous localities in 
 which it has been, or is, found. Its colour in the mass 
 varies from cochineal-red and red-brown to lead-grey ; its 
 powder is usually scarlet, or red. Its hardness lies 
 between that of gypsum and that of calc-spar. It seldom 
 contains even i part in loo of impurities, but consists in 
 loo parts of very nearly 14 parts of sulphur by weight, 
 united with 86 of mercury, or i atom of each element. 
 The density of native vermilion is about 9. Vermilion 
 was formerly known as vermiculus, cinnabaris, ceno- 
 brium, and minium ; the last name is now appropriated 
 to red lead. Vermilion and vermiculus are derived from 
 the Latin vermes, a name originally designating the 
 ‘kermes’ insect found on the ilex or evergreen oak, which 
 is still used for the preparation of a red dye. From 
 kermes, in its turn, the words crimson and carmine are 
 derived. The name cinnabar is supposed to be of 
 Oriental origin (compare the Persian zanjifrah), and was 
 used sometimes to designate dragon’s blood, a red resin. 
 
 186 
 
VERMILION 
 
 187 
 
 Theophrastus informs us that two kinds of cinnabar were 
 known to the Greeks. One of these was undoubtedly 
 real cinnabar (chiefly from Spain), the other was red 
 lead. Pliny’s ‘ cinnabar ’ or ‘ minium ’ was true ver- 
 milion, so was the ‘ minium ’ of Vitruvius. Theophilus 
 calls it ‘cenobrium,’ Wyclif ‘cynoper,’ Hakluyt ‘ cinaper,’ 
 and Ben Jonson ‘ cinoper.’ 
 
 One of the most curious facts concerning vermilion is 
 that it is identical in the nature and proportion of its 
 two constituent elements with an artificial black sub- 
 stance, ‘ ^thiop’s mineral.’ The red substance may be 
 changed into the black, and vice versd, and this without 
 any loss or gain, or any alteration of chemical com- 
 position, the change being a physical or molecular one 
 merely. The black substance is amorphous, the red 
 crystalline. 
 
 The pigment vermilion may be made by simply grind- 
 ing selected pieces of native cinnabar, or it may be 
 obtained artificially by combining the two elements 
 sulphur and mercury. 
 
 All the methods of preparing vermilion artificially may 
 be grouped under two divisions. The first of these is the 
 dry way, the other the wet way. In the former method 
 metallic mercury 42 parts, and sulphur 8 parts, are inti- 
 mately mixed and agitated together in revolving drums 
 until they have combined. The brownish-black powder 
 thus obtained is then submitted to sublimation in vertical 
 iron cylinders, surmounted by heads which are connected 
 with receivers. On sufficient heating, the mercuric sul- 
 phide sublimes as cinnabar or vermilion, the best part 
 condensing in the retort-heads. The rest of the sublimed 
 product (which has travelled farther) contains free sul- 
 phur, and is of inferior colour. The selected portions are 
 
VERMILION 
 
 1 88 
 
 next ground, moistened with water, warmed with a little 
 caustic potash solution or nitric acid, and then thoroughly 
 washed with boiling water. In another dry process the 
 mercury is gradually added to the proper proportion of 
 melted sulphur in an iron basin. When the combination 
 (which is accompanied by a violent evolution of light and 
 heat) is complete, the fused blackish mass is poured out, 
 broken into fragments, heated until excess of sulphur has 
 been driven off, and then sublimed in the way already 
 described. Some makers add to the crude sulphide, pre- 
 vious to sublimation, i per cent, of antimony sulphide, 
 with the object of improving the colour ; the product is 
 afterwards ground, digested with liver of sulphur, and 
 then washed with hydrochloric acid. 
 
 There are numberless processes for preparing vermilion 
 by the wet way. One of the best of these consists in 
 grinding, in the presence of water, loo parts of mercury 
 with 38 parts of flowers of sulphur until these elements 
 have united. The black product is then triturated at 
 45° C. for many hours with a solution of 25 parts of 
 caustic potash in 150 parts of water. When the product 
 has attained its maximum of redness and beauty, it is 
 thrown into water, and thoroughly washed by decantation. 
 In a second process mercury, sulphur, and potassium 
 pentasulphide are boiled together for three or four hours, 
 and then the mixture is kept at a temperature of 50° C. 
 for several days. Vermilion may also be prepared from 
 the black sulphide obtained by precipitating a mercuric 
 salt with a soluble sulphide, from ‘ white precipitate,’ and 
 from metallic mercury itself, by warming any one of these 
 substances with a solution of an alkaline pentasulphide, 
 and then purifying the product by means of a potash- 
 solution heated to 45° C. It has also been found that ver- 
 
VERMILION 
 
 189 
 
 milion is produced when a mixture of mercurous chloride 
 (calomel) and zinc sulphate is heated to 45° — 50° C. with 
 an excess of a solution of sodium thiosulphate. 
 
 Except where carmine or realgar (red sulphide of 
 arsenic) is present, a very simple test suffices to ascertain 
 whether vermilion be pure or not. A small pinch should 
 be heated over a spirit-lamp on a fragment of hard porce- 
 lain ; no appreciable residue will be found, unless red- 
 lead, red iron oxide, brickdust, or other non-volatile 
 adulterants be present. Carmine, which is sometimes 
 added to scarlet vermilions to approximate their hue to 
 that of the crimson varieties such as the Chinese, may be 
 detected by laying a pinch of the powdered pigment on a 
 small pad of white blotting-paper, and moistening the 
 substance with a few drops of strong ammonia-water ; a 
 crimson stain will appear on the paper if carmine or 
 crimson-lake be present. The colour of a good vermilion 
 is not changed by moistening it with nitric acid. The 
 accidental impurities which impair the hue of vermilion 
 are free sulphur, and compounds of iron and lead ; that 
 prepared in the wet way often retains alkaline salts, 
 owing to imperfect washing. A spurious vermilion, 
 called anti-vermilion or antimony vermilion, is made by 
 warming antimonious chloride with sodium thiosulphate 
 solution. It is the chief material used in colouring red 
 rubber. 
 
 Vermilion prepared from the mineral or native cinnabar 
 is probably less liable to change than the artificial pro- 
 ducts, whether obtained by the dry way or the moist way ; 
 but ‘ moist way ’ vermilions are certainly the most alter- 
 able. And it may also be remarked that the more finely 
 a vermilion is ground, the less stable it is — at least, as a 
 water-colour paint. Thus it happens that, other things 
 
VERMILION 
 
 190 
 
 being equal, an orange-vermilion is inferior in perma- 
 nence to a scarlet, and a scarlet-vermilion to one inclining 
 to crimson. As an oil-pigment, vermilion does not dry 
 well, but suffers, especially if it be locked up in copal or 
 paraffin, no change by light or impure air ; 100 parts of 
 the dry substance require less than 20 parts of oil. Owing 
 to its great density, vermilion tends to separate from the 
 oil with which it has been ground. This result may be 
 obviated by the addition to the oil of a little aluminium 
 oleate or linoleate, or by the employment of oxidized and 
 thickened oil in which a small quantity of beeswax or 
 ceresin has been dissolved by the aid of heat. In water- 
 colour painting most vermilions are found to be changed 
 on exposure, the solar rays gradually converting the red 
 into the black modification of mercuric sulphide, without, 
 of course, producing any chemical alteration. This 
 change occurs even in the absence of air and of moisture. 
 Impure air, per se, even if sulphuretted hydrogen be 
 present, does not discolour vermilion. 
 
 Anyone who has examined old illuminated manuscripts 
 must have noticed the apparent capriciousness with which 
 the ornaments, and especially the initial letters, painted 
 with vermilion, have been affected. I have more than 
 once observed that, while all the vermilion used in one 
 part of a missal or choral-book has remained red, a leaden 
 hue has spread irregularly over the rest of the work in 
 places where this pigment has been used. This may be 
 due to the use by the illuminator of a sample of vermilion 
 adulterated with minium or red lead, but sometimes to a 
 change in the technique, as a change in the style or handi- 
 work is often associated with the difference above de- 
 scribed. In oil-painting there are no permanent pigments, 
 save the copper-greens, with which vermilion may not be 
 
VERMILION 
 
 igi 
 
 safely mixed. Only when it contains impurities, such as 
 free sulphur, does it darken flake-white. 
 
 Vermilion prepared from native cinnabar is found per- 
 fectly preserved in the flesh-tints of Italian tempera- 
 paintings of the thirteenth and fourteenth and fifteenth 
 centuries. It has stood in the wall-paintings of Pompeii, 
 where it often seems to have been waxed. A compara- 
 tively recent but instructive instance of the permanence 
 of vermilion in oil is furnished by a portrait, dated 1758, 
 in the National Portrait Gallery. It represents the painter, 
 Hogarth, with his palette set before him. The second of 
 the dabs of colour thereon is vermilion, perfectly intact. 
 In the same collection there is a portrait by Marc Ghee- 
 raedts of Mary Sidney, Countess of Pembroke, in which 
 the vermilion has stood. This work was painted in 1614. 
 Scores of earlier and later examples might be cited. 
 
 The variations in hue observable in different specimens 
 of vermilion are mainly due to the differing degrees of 
 fineness in which the pigment occurs. The coarsest grain 
 corresponds with a crimson hue, and then we have every 
 variety of colour ranging from scarlet to reddish orange 
 or orange. The processes of regrinding and ‘washing- 
 over ’ enable us to obtain the kinds separately. And if we 
 repeat these operations often enough, we may ultimately 
 convert the whole of a crimson vermilion into the orange 
 form. It was formerly supposed that the latter material 
 was a mere scum, or impurity, or at least differed from the 
 crimson kind in composition. When any vermilion is 
 mixed in tint with white, an opposite effect to that of 
 further grinding is produced. For, as the early writer 
 Eraclius states : ‘ If you mix white with vermiculus, car- 
 mine is made ’ — that is, the hue of the mixture becomes 
 more rosy, and therefore further removed from orange. 
 
MADDER PIGMENTS 
 
 192 
 
 Madder : Pink Madder — Rose Madder — Madder Carmine 
 
 — Madder Red — Rubens' Madder — Madder Purple — 
 
 Madder Lake — Madder Brown — Carniin de Garance — 
 
 Laque de Garance — Krapplack. 
 
 Some authorities assert that madder was used in dyeing 
 long before its employment in painting. But there is some 
 evidence, derived from ‘ finds ’ of pigments and from paint- 
 ings, that the ancient Greeks and Romans were acquainted 
 with a pink pigment derived from madder, while there 
 are good reasons for believing that such substances were 
 widely known in Europe as early as the thirteenth century. 
 Even in England, such a pigment is almost certainly re- 
 ferred to, under the name ‘ sinopis,’ in the middle of the 
 fourteenth century. Now Alcherius (close of fourteenth 
 century) tells us that ‘ sinopis is a colour redder than ver- 
 milion, and it is made from varancia.’ ‘Varancia’ is 
 clearly garance — that is, madder — the same material being 
 named ‘ warancia ’ and ‘ waranz ’ in a British Museum 
 manuscript (Sloane, No. 416) v/hich contains recipes of 
 the fourteenth century. Besides ‘ sinopis ’ (strictly, a red 
 earth), madder-lake was called, in English account-rolls of 
 the fourteenth century, ‘ sinopre ’ and ‘ cynople.’ It is, 
 however, difficult, if not impossible, to ascertain the pre- 
 cise date at which pigments derived from madder came 
 into use in the various schools of painting in Europe. For 
 the nomenclature of pigments has always been somewhat 
 vague, while the evidence furnished by existing pictures 
 does not at present enable us to trace back with absolute 
 certainty the mediaeval use of madder paints to an earlier 
 time than the fifteenth century. Eraclius does not men- 
 tion madder, nor does Cennini, who lived at a much later 
 time. Mr. R. Hendrie, in his notes to ‘ Theophilus,’ 
 
MADDER 
 
 193 
 
 speaks of an English manuscript of the fourteenth century 
 in which directions are given for extracting the colouring 
 matter of ‘ madyr.’ From these directions we are, per- 
 haps, justified in concluding that the preparation of a kind 
 of liquid paint was intended. 
 
 The European madder-plant, a native of Greece, belongs 
 to the tribe Galieae, of the order Rubiaceae ; it is the Ruhia 
 tinctornm of Linnaeus. Several other species of this genus 
 are used or grown in India for the sake of the red dye they 
 afford. Among such species, Ruhia covdifolia (Linn.) and 
 R. sikhimensis (Kurz.) may be named, but the European 
 madder is also cultivated extensively in India. Much 
 madder was formerly grown in the Levant, in Holland, 
 and in the south of France ; but the manufacture by arti- 
 ficial means from the anthracene of coal-tar of its two chief 
 colouring matters, alizarin and purpurin, has almost en- 
 tirely extinguished the cultivation of the madder-plant in 
 Europe. We shall have something to say presently con- 
 cerning the artificial products above named. 
 
 The root of madder contains a much larger proportion 
 of the colouring matters (or, it would be more correct to 
 say, colour-making substances) than the other parts of 
 the plant. They occur dissolved in the yellow cell-con- 
 tents of the soft tissue of the root. The finest madder 
 w^as grown in the ‘ Palud,’ a chalky valley near Vaucluse. 
 But the cultivation of this plant was carried out in great 
 perfection in Zeeland during the eighteenth century. 
 
 The colouring matters obtained from madder exist in 
 the plant in the form of glucosides. These glucosides are 
 resolved by the fermentation, brought about by a peculiar 
 ferment in the plant itself, and by many chemical agents, 
 such as mineral alkalies and acids, mainly into glucose on 
 the one hand, and on the other into the several colouring 
 
 '3 
 
194 
 
 MADDER LAKES 
 
 principles. Of such colouring principles the glucosides in 
 madder yield at least three, of which the most important 
 are these two : 
 
 1. Alizarin, Cj^4HgO^. 
 
 2. Purpurin, C^^HgOg. 
 
 Both alizarin and purpurin are now manufactured arti- 
 ficially from anthracene. This compound, which occurs in 
 coal-tar, is a crystalline fluorescent hydrocarbon, 
 
 By a series of processes this substance gives rise to alizarin 
 and purpurin, which are in all respects identical with these 
 colouring matters as derived from the madder plant itself. 
 The artificial alizarin of commerce contains several other 
 colouring matters, two of which are better known than the 
 others ; these are anthrapurpurin (C^^HgOg) and purpuro- 
 xanthin (Cj4Hg04). Purpuroxanthin is also present in the 
 natural pigments derived from madder, but it exists in 
 small proportion. Of all these compounds alizarin is the 
 most important and the best known, and yields lakes 
 having various hues of crimson, rose, purple, violet and 
 marone, according to its purity, its concentration, and the 
 nature of the base (alumina, aluminium phosphate, iron 
 oxide, manganese oxide, copper oxide, or lime with 
 alumina) with which it is associated. The purpurin and 
 anthrapurpurin resemble one another closely, and give 
 pigments which are generally characterized by more 
 orange or red hues than those obtained with alizarin. 
 The rose and pink madders and the madder carmines of 
 commerce are generally so manufactured as to include, 
 for their colouring constituents, much alizarin and very 
 little purpurin. A few indications of the ordinary methods 
 of preparing these lakes may first be given. 
 
 The material used is often that called ‘ madder flowers,’ 
 which consists of the finely ground dried root after it has 
 
MADDER LAKES 
 
 195 
 
 been submitted to the action of dilute sulphuric acid and 
 washed. Four pounds of this madder are taken and 
 warmed for two or three hours on a steamer, with a solu- 
 tion of I pound of pure alum in i gallon of water. The 
 mixture is placed in a filter-press, and the liquor obtained 
 (which must be perfectly clear) precipitated by the gradual 
 addition of a solution of sodium carbonate. The first 
 portions of madder lake which fall, being the best, should 
 be collected apart. All the precipitates should be 
 thoroughly washed with rain or distilled water till the 
 wash-waters are no longer troubled on the addition of 
 barium chloride solution ; they are then moulded into small 
 cones, drops, or discs, and carefully dried at a moderate 
 temperature. Another process for preparing madder lakes 
 is a modification of the above. Four pounds of madder- 
 root in powder, after having been fermented and then 
 washed with a weak solution of sodium sulphate, are 
 boiled for fifteen minutes with 4 gallons of a 10 per cent, 
 solution of pure alum, the whole is filtered, and at a tem- 
 perature of 45° partially neutralized with a solution in 
 water of about 8 ounces of pure sodium carbonate. The 
 liquor is now brought nearly to the boiling-point ; the 
 madder lake which is then deposited is to be thoroughly 
 washed and then dried : it is much denser than that pro- 
 duced by the preceding process. In the manufacture of 
 alizarin lakes it is customary to introduce a small quantity 
 of a preparation known as Turkey-red oil or sulphated 
 castor oil. This is made into a soap and added to the 
 alkaline solution employed to precipitate the lake. 
 
 By the employment in various proportions of solutions 
 of alum and calcium chloride, by the substitution of 
 sodium phosphate for the carbonate, and by choosing 
 various qualities of madder-root, a number of hues and 
 
MADDER LAKES 
 
 196 
 
 tints of rose and pink madder may be obtained when one 
 or other of the methods above described is adopted. The 
 oxides of iron, manganese and copper, when used in asso- 
 ciation with more or less alumina as a base for receiving 
 the various colouring matters of madder, give other hues, 
 including madder purple and madder brown. 
 
 But occasionally the pigments sold under these names 
 are mixtures. For instance, burnt sienna and copper ferro- 
 cyanide have been found in samples of madder brown; the 
 presence of copper in madder brown seems, however, to 
 be usual, but it arises from the employment of copper 
 sulphate in its preparation along with alum. 
 
 From alizarin and from purpurin (either natural or 
 artificial) lakes may be readily prepared by dissolving 
 these substances in the smallest necessary quantity of an 
 alkali, such as ammonia or sodium carbonate, and then 
 adding a solution of a pure aluminium salt or some pure 
 freshly precipitated and thoroughly washed aluminium 
 hydrate. Another and more recent process consists in 
 dissolving the colouring matter in a solution of sodium 
 aluminate, and then precipitating the ‘ lake ’ by adding 
 dilute sulphuric acid or, better, a solution of alum. 
 
 The best artificial alizarin of commerce occurs as a 
 yellowish powder, presenting the aspect of raw sienna. It 
 may, however, be obtained in yellow or orange red crystals, 
 either by repeated crystallization from a solvent or by 
 sublimation in vacuo. Its colour is always brighter than 
 that of purpurin, which in powder has about the hue of 
 Venetian red. But when solutions are made of these two 
 substances in alkalies, then it is seen that the colours are 
 reversed — alizarin yielding a crimson verging upon purple, 
 and purpurin a red verging upon crimson. Differences of 
 colour will be noticed in the lakes prepared with these two 
 
1 
 
 ALIZARIN AND PURPURIN 
 
 197 
 
 bodies. The directions for preparing pigments from the 
 above-named bodies are practically identical with those 
 already given in outline, but the minute details of manip- 
 ulation can be learned only in actual practice. The 
 following process gives an ardficial red madder of excel- 
 lent hue : Equal weights of pure alum (absolutely free 
 from iron and lime) and of the purest artificial purpurin 
 in powder are ground together, and then washed with cold 
 water until the washings are colourless ; then the residue 
 on the filter is boiled with a 5 per cent, solution of pure 
 alum, filtered while boiling, and immediately neutralized 
 with pure sodium carbonate solution (also boiling) until 
 red flocks appear. These are filtered off, and constitute, 
 when washed and dried, a fine pigmmnt of a rich red hue. 
 By heating the mother liquor to 80°, and adding more 
 sodium carbonate, a further and equally good product is 
 obtained. The purpurin residue, when again heated with 
 more alum-solution and precipitated as above directed, 
 yields a further quantity. The final residue, after several 
 such exhaustions, produces an impure lake, having a 
 brownish-red hue. A very "large number of commercial 
 preparations of alizarin and of other dye-stuffs closelyallied 
 to it are now available for the preparation of the so-called 
 ‘ madder lakes.’ Some of these preparations when dis- 
 solved and then precipitated on a suitable basis, yield pig- 
 ments of great richness and stability, others, especially 
 those which possess a yellow, orange, or red-brown hue, 
 are less permanent. Here it may be remarked that, 
 broadly speaking, the true or ‘ root ’ madders are complex 
 so far as their colour-constituents are concerned and 
 simple as regards their base, while the converse is true 
 of the alizarin lakes. 
 
 Although the madder colours are very much less affected 
 
 
198 
 
 MADDER LAKES 
 
 by light than are the pigments derived from cochineal, yet 
 it cannot be affirmed that any of them are absolutely per- 
 manent when continuously exposed. The following figures 
 show approximately the amount and nature of the change, 
 observed after certain intervals, in the case of several 
 madder pigments used as water-colours : 
 
 Name of Pigment 
 
 Original 
 Intensity = 10 
 
 Change of Hue 
 
 ♦Madder Carmine, -A 
 
 After I 
 
 year. 
 
 10 
 
 - Very slight. 
 
 j> )> B 
 
 > > 
 
 I 
 
 > > 
 
 8 
 
 - Much more purplish. 
 
 „ c 
 
 ■ )) 
 
 5 
 
 1 1 
 
 2 
 
 - 
 
 c 
 
 > > 
 
 7 
 
 r 1 
 
 0 
 
 - 
 
 „ F 
 
 - ,, 
 
 4 
 
 > J 
 
 10 
 
 - More purplish. 
 
 Madder Red - - - 
 
 5 > 
 
 I 
 
 fi 
 
 6 
 
 - Less red, more blue. 
 
 Rose Madder - - - 
 
 
 I 
 
 
 8 
 
 - Slightly more purplish. 
 
 )! j> B - - 
 
 > i 
 
 2 
 
 5 j 
 
 3 
 
 - 
 
 n B - - 
 
 - 
 
 5 
 
 ) 
 
 I 
 
 - Smoke grey. 
 
 „ B - - 
 
 > > 
 
 7 
 
 t 
 
 I 
 
 - Grey. 
 
 F - - 
 
 ) ) 
 
 4 
 
 1 
 
 8^ 
 
 - Slightly more purplish. 
 
 Pink Madder - - - 
 
 - J, 
 
 2 
 
 t 
 
 I 
 
 - 
 
 Purple Madder, A - 
 
 > J 
 
 I 
 
 )) 
 
 7 
 
 - Duller, less red, more 
 
 » „ c - 
 
 f f 
 
 2 
 
 ft 
 
 6 
 
 - More bluish. [blue. 
 
 .. D - 
 
 - ,, 
 
 5 
 
 > 5 
 
 7 
 
 - 
 
 „ c - 
 
 - ,, 
 
 7 
 
 
 2 
 
 - 
 
 *„ E - 
 
 > 5 
 
 7 
 
 
 9 
 
 - Somewhat puce. 
 
 ♦Brown Madder, A 
 
 “ 1 1 
 
 I 
 
 
 9 
 
 - Less red, more yellow. 
 
 .. B 
 
 ) > 
 
 2 
 
 
 I 
 
 - Grey. 
 
 n „ B 
 
 “ 1 • 
 
 5 
 
 ) > 
 
 I 
 
 - 
 
 )> >) B 
 
 - 
 
 7 
 
 
 0 
 
 - Grey. 
 
 The letters A to F indicate different samples of the several 
 pigments, which were in all cases ‘ moist ’ colours ; a 
 parallel but less complete series with ‘ cake ’ colours gave 
 practically the same results. The five samples marked * 
 are instances of exceptional stability, and are of import- 
 ance as showing the possibility of obtaining some, at all 
 events, of the madder pigments in a satisfactory form. 
 It is noticeable that the paler (pink and rose) madders. 
 
MINERAL LAKE 
 
 igg 
 
 which contain much water, are generally more perishable 
 than the concentrated madder carmine ; the comparative 
 trials having, of course, been made with washes of nearly 
 the same depth of tint. 
 
 A study of this table inclines one to think that the 
 genuineness and purity of some of these pigments are 
 doubtful, yet one specimen only (Madder Carmine C) was 
 not tested. In this case the material used was not available 
 for analysis, but I have no reason to doubt its authenticity. 
 
 Mineral Lake: Pink-Colonv — Potters' Pink — Laqiie 
 Minerale — Minerallack. 
 
 Attempts have been made to obtain mineral pigments of 
 absolute permanence in order to acquire substitutes for 
 the reds and purples of vegetable origin. None of them 
 equals in intensity and splendour of colour the derivatives 
 of madder. One of the best of these substitutes is mineral 
 lake. This compound may be made in many ways. In 
 some recipes stannic oxide, chalk and a little potassium 
 chromate are directed to be heated together : in one pro- 
 cess the operations are begun by precipitating a solution 
 of neutral potassium chromate by means of a solution of 
 stannic chloride. The precipitate is collected on a filter 
 and thoroughly washed. Still moist, it is ground into a 
 paste with half its bulk of pure nitre and some stannic 
 oxide, and allowed to dry. The dry mixture is projected, 
 little by little, into some nitre heated to low redness in a 
 crucible. When the basic chromate of tin has settled, the 
 nitre, still fused, is poured off, and the residue washed 
 thoroughly with water. The product thus obtained 
 requires calcination for two hours at a high tempera- 
 ture in a luted crucible, in order to develop its colour, 
 which much resembles that of almond-blossom when 
 
200 
 
 LIGHT RED 
 
 the matter is finely ground. It appears much richer in 
 hue and less opaque when used as an oil-colour. It 
 constitutes an unalterable pigment. 
 
 Under the name of Potters’ Pink Mr. W. Burton, of 
 Pilkington’s Tile Works, has introduced to the notice of 
 artists a ceramic pigment which is a variety of that which 
 has been just described. He says of it that it was 
 ‘ invented in Staffordshire by an unknown potter about 
 a hundred years ago. It is obtained by calcining a 
 mixture of oxide of tin and lime with a mere trace of 
 oxide of chromium. It is a semi-opaque colour, unlike 
 any usually supplied to artists. It should be particularly 
 valuable in paintings in which it is undesirable to use 
 madder or alizarin pigments.’ It is scarcely necessary 
 to add to this account that Potters’ Pink is not only a 
 permanent pigment which may be used in all methods of 
 painting (including fresco), but that it is without action 
 on other pigments. 
 
 Light Red: Burnt Ochre — Rouge Anglais — Brtin Rouge 
 — Englischrot. 
 
 Light red is, or ought to be, yellow ochre burnt — that is, 
 calcined. The different varieties of yellow ochre yield, as 
 might be expected, products having various hues and 
 tints of this rather pale an ' dull brownish or orange red. 
 Moreover, these hues depend in some measure upon the 
 temperature at which the calcination is effected. To 
 prepare light red, the selected yellow ochre is usually 
 crushed and then roasted on an iron plate heated to red- 
 ness. When the desired tint has been attained the 
 material is thrown into cold water, ground, and washed. 
 Light red may also be made by conducting the finely- 
 divided yellow ochre suspended in a current of air into a 
 
VENETIAN RED 
 
 201 
 
 heated chamber or furnace. Light red consists, then, of 
 yellow ochre deprived of its water of hydration by means 
 of heat. It is necessary to employ yellow ochre as free 
 as possible from organic matter and from lime if a bright- 
 coloured product be desired. 
 
 Light red possesses a considerable degree of opacity. 
 Its hue may be defined as a scarlet, modified by a 
 little yellow and grey. It is perfectly permanent and 
 without action upon other pigments. 
 
 Light red boiled with hydrochloric acid will, if genuine, 
 yield a solution, which after filtration will give no pre- 
 cipitate, but merely a slight cloudiness, on the addition 
 of a few drops of barium chloride solution. The terms 
 ‘ rouge Anglais ’ and ‘ Brun rouge ’ are not infrequently 
 applied to artificially prepared iron reds. 
 
 Venetian Red : Rouge — Cwcus — Colcothar — Caput 
 Movtuum V iinoli — V endianischfot. 
 
 Originally Venetian red consisted of a native ferric 
 oxide or red haematite, less purplish in its tints and 
 washes than Indian red. But of recent years the name 
 appears to have been transferred to a particular quality of 
 artificial ferric oxide, made by calcining green vitriol. 
 When this salt is heated in a crucible the upper portion 
 of the product, which has been less strongly heated than 
 the lower, is of a brighter red than the remainder, and 
 after washing and grinding is sold as Venetian red. If 
 moistened with a solution of nitre, again heated, and then 
 ground and washed, the red tint of the product becomes 
 somewhat brighter. 
 
 The hue of Venetian red is less brownish than that of 
 light red, and not at all purplish like that of Indian red. 
 
 Venetian red, whether artificial or natural, is a per- 
 
202 
 
 INDIAN RED 
 
 manent pigment which may be mixed with other permanent 
 pigments without fear of injuring them ; but it must be 
 perfectly free from soluble salts and from any trace of 
 sulphates. The presence of the latter may be detected by 
 the test described under ‘ Light Red’ and ‘ Indian Red.’ 
 But few commercial samples will stand this test, however, 
 and we consequently find that many samples of Venetian 
 red, owing to the presence therein of sulphates, exert an 
 injurious action upon some of the organic pigments used 
 as water-colours — notably, upon indigo. 
 
 A very fine native red ochre comes from Tuscany and 
 from Krasso in the Banat, Hungary. It is represented 
 by the formula 2Fc203, HgO, and goes under the minera- 
 logical name of turgite. Its hue is that of a fine Venetian 
 red : it is probable that the fine native Indian reds and 
 red ochres sometimes consist of or contain this hydrated 
 ferric oxide, and are not really anhydrous. 
 
 Indian Red : Persian Red — Indian Red Ochre — Indischrot. 
 
 Indian red is a variety of red ochre, or red haematite, 
 containing about 95 per cent, of ferric oxide, and having a 
 slightly purplish hue. It varies somewhat in quality, and 
 often requires sifting through a fine silk sieve, followed by 
 washing over, in order to fit it for use as a pigment. Most 
 of the Indian red imported from India is a natural pro- 
 duct, but some has been prepared by calcination. Some so- 
 called Indian red is imported from Ormuz in the Persian 
 Gulf; some is an English haematite from the Forest of 
 Dean. 
 
 A recent recipe for making an artificial Indian red 
 directs that a mixture of 75 parts of green vitriol be taken 
 and dried at a moderate heat previous to mixing it with 
 18 parts of calcined magnesia and 7 parts of common 
 
INDIAN RED 
 
 203 
 
 salt, all the ingredients being in fine powder. The mix- 
 ture is then ignited, preferably under reduced pressure, 
 and the residuum thoroughly washed with water. By the 
 introduction into the original mixture of a little aluminium 
 sulphate the purple hue of the product may be enhanced ; 
 indeed, it is quite possible in this way to obtain the pig- 
 ment known as Mars violet. 
 
 Indian red, when genuine, is a perfectly permanent pig- 
 ment in all media, and is without action upon other colours. 
 It was extensively employed by the older masters of the 
 English Water-Colour School, in association with true 
 ultramarine, with Prussian blue, with indigo, or with indigo 
 and yellow ochre, to produce the lilac greys of stormy 
 clouds. The indigo in some of these greys having often 
 perished, the Indian red (and the yellow ochre where 
 employed) remains intact, giving a hot and frequently 
 foxy red to spaces which were originally cool in hue, and 
 comparatively neutral. This change has been incorrectly 
 attributed to an action exerted upon the indigo by the 
 Indian red. But as indigo disappears when used alone, or 
 when a thin wash of it on a sheet of gelatine is placed 
 over, but not in contact with, a wash of Indian red, the 
 current explanation of the phenomenon in question cannot 
 be true. Greys made with light red or Venetian red show 
 similar alterations of colour. Colcothar, or jewellers’ rouge, 
 the red oxide of iron obtained as a residue when green 
 vitriol (ferrous sulphate) is calcined, has sometimes been 
 called Indian red, and substituted for the native oxide. 
 Those portions of the above-named residue which have 
 been more strongly heated generally present something of 
 the purplish red hue which belongs to the true native 
 Indian red. And this peculiar hue may be imparted to 
 ordinary rouge by moistening it with a weak solution of 
 
204 
 
 RED OCHRE 
 
 potassium chlorate, drying, and then calcining the mass 
 once more. It generally contains basic ferric sulphate, 
 and then should be looked upon with suspicion, for it may 
 seriously damage the indigo and other organic pigments 
 with which it is associated. If a small pinch of Indian 
 red be boiled with hydrochloric acid, thrown on a filter, 
 and the filtrate tested with barium chloi'ide solution, the 
 genuineness of the pigment will be proved by the absence 
 of any white precipitate of barium sulphate. 
 
 Red Ochre : Red Hcematite — Red Ivon Ove — Scarlet Ochre 
 
 — Red Chalk — Ruddle — Bole — Sinoper — Sinopis — Riibrica 
 
 —Miltos — Terra Rosa — Arrahida Red — Bolus. 
 
 The pigments above-named are native ferric oxide (or 
 iron peroxide) associated with variable proportions of 
 mineral impurities such as clay, chalk, and silica. They 
 differ from the yellow and brown ochres described on 
 page 1 57, by not containing combined water, in other 
 words, the iron to which they owe their colour is ferric 
 oxide, not ferric hydrate, except in the case of turgite, 
 named on page 202. They occur in very many localities 
 accompanying or even constituting some of the most im- 
 portant iron ores. Their colour varies with their physical 
 state, and with their purity ; some are iron grey, or even 
 black, until they are finely ground, when they assume a 
 cherry-red hue. Cappadocia yielded to the ancient Greeks 
 some at least of their sinopis, or red ochre, but they were 
 familiar with the process of calcining yellow ochre in 
 order to redden its hue ; and they thus prepared the pig- 
 ment to which the name ‘ light red ’ is now assigned. 
 
 An unusually bright red variety of haematite from 
 Cumberland gave me on analysis, in 100 parts, ferric 
 oxide, 947; alumina, 2-0; silica, 2’2, and moisture, I’l. 
 
INDIAN LAKE 
 
 205 
 
 But some almost equally rich red ochres contain much 
 less iron oxide, a ‘ sinopis ’ from Anatolia, analysed by 
 Klaproth, having been found to contain 21 per cent, 
 only, and others, from other localities, not above 40. 
 The paler varieties of a reddish brown or yellow brown 
 hue often consist of mixtures of haematite and yellow 
 ochre. A very fine red ochre from Tuscany, the Banat, 
 Hungary, and from the Urals, contains about 5 per cent, 
 of water, and is considered to belong to a distinct mineral 
 species called turgite, as mentioned before under the 
 heading ‘ Venetian Red.’ 
 
 When red chalk (from Hunstanton, Norfolk) is calcined 
 at a high temperature it loses its red colour, and becomes 
 of a dull olive green hue, a change due in this case to 
 the production of calcium ferrite, a compound of lime 
 and ferric oxide. 
 
 The terra rosa of Italy owes its pinkish red hue to 
 ferric oxide, but it is probably often, if not always, an 
 artificial product. 
 
 All the pigments described under the title ‘ red ochre ’ 
 are permanent, and without action on other pigments. 
 
 For the substitution of artificially prepared ferric 
 oxide, or colcothar, for red ochre, and for the method of 
 detecting it, reference should be made to page 202, under 
 * Indian red.’ 
 
 Indian Lake : Lac Lake — -Lack-Lack. 
 
 Lac is a resinous secretion produced by certain plants 
 when punctured by the larvae of the Coccus lacca, an 
 East Indian hemipterous insect. Amongst the trees 
 which the insect chiefly attacks are Butea fvondosa. Ficus 
 religiosa, and F. bengalensis, Schleicher a trijuga, Shorea 
 robusia, and Zizyphus jujuba. The lac, though a secretion 
 
206 
 
 INDIAN LAKE 
 
 primarily derived from the tree on which the insects 
 feed, is yet profoundly modified, particularly with respect 
 to its colour, during its passage through the animal’s 
 body. It varies in colour with the species of tree, but 
 always consists mainly of three substances — namely, a 
 resin, a colouring matter, and a wax. The resin, which 
 constitutes two-thirds of the substance, is obtained in the 
 form known as ‘ seed-lac ’ by pounding in water the lac 
 which has been removed by pressing with a roller the 
 encrusted twigs on a floor. The water becomes red ; 
 from it, by evaporation, the crude ‘ lac-dye ’ is obtained. 
 This is made into cakes, and dried. 
 
 The lac-dye of commerce contains nitrogenous and 
 mineral matters, as well as several dark-coloured 
 impurities, and some resin. In order to prepare a lake 
 from it, it should be first powdered, and then digested in 
 spirit of turpentine, or benzene. The purified residue 
 is, when dry, extracted with sodium carbonate solution : 
 the liquor is afterwards filtered and precipitated with 
 alum solution. The precipitate thus formed is washed 
 and dried in the dark. 
 
 Indian lake was used by the Venetian and Flemish 
 painteis of the sixteenth century, but it does not seem, 
 so far as one can gather from the notices of it in the 
 work of De Mayerne, and in the Secreet-Boeck, to have 
 been often obtained of good colour. It is even spoken 
 of as a ‘ light brown.’ 
 
 Indian lake is inferior in beauty, and in variety of 
 hues, to the colours from madder ; it is also more affected 
 by light. But it is distinctly less fugitive than crimson 
 lake and the other cochineal pigments. 
 
 I do not know from direct experiment whether the com- 
 parative stability of the red colouring matter from kermes 
 
COCHINEAL LAKES 
 
 207 
 
 when used as a dye for animal fibres belongs also to all 
 the lakes prepared from this substance : anyhow, kermes 
 pigments are, so far as I can learn, not met with in com- 
 merce at the present time. Their use in European paint- 
 ing seems to have been displaced, first of all by Indian 
 lac lakes, and then by cochineal lakes. The colouring 
 matters produced by these three kinds of coccus are 
 closely allied chemically. 
 
 Carmine and the Cochineal Lakes : Carmin — Laque 
 Cramoisie, or Crimson Lake — Purple Lake, etc. — Karmin. 
 
 Cochineal consists of the dried wingless females of a 
 species of coccus (C. cacti) which feeds upon several kinds 
 of Opuntia, or cactus. The best quality comes from Tene- 
 riffe, and contains about half its weight of colouring 
 matter. This colouring matter is a glucoside, to which 
 the name of carminic acid has been given. When this 
 substance is treated with weak sulphuric acid, it is 
 resolved into a sugar and another colouring matter called 
 carmine red. 
 
 The carmine of commerce is prepared directly from 
 cochineal, and is the most concentrated and purest form of 
 any of the pigments derived from this source. The 
 methods of preparation differ, but in all the colouring 
 matter is extracted from the insects by means of boiling 
 water, with the subsequent addition of small quantities of 
 alum, or nitre, or potassium oxalate, or cream of tartar ; 
 occasionally a small quantity of stannous chloride is em- 
 ployed also. The liquor, after a repose of some days or 
 even weeks, deposits a great part of the colouring matter 
 as a deep crimson-red powder, which is then thrown on a 
 filter, washed and dried in the dark. However prepared, 
 it contains fat, albuminoid matter, mineral salts, and 
 
208 
 
 COCHINEAL LAKES 
 
 other impurities ; the finest varieties, however, dissolve 
 perfectly in strong liquor ammoniae. The liquor, which 
 has deposited the carmine, gives up the remainder of its 
 colouring matter to freshly - precipitated aluminium 
 hydrate, or, after having been rendered alkaline by 
 potassium carbonate, to a solution of alum. Lakes are 
 thus formed. Lakes are also made by directly precipi- 
 tating cochineal extract with solutions of potassium car- 
 bonate and alum. A purplish tinge is given to the product 
 by a small quantity of lime ; other hues, generally dull, 
 are imparted by the presence of iron, manganese, or 
 copper in the solutions employed. The cochineal lakes 
 always contain a larger quantity of water and of alumina 
 (or other mineral basis) than carmine, and are conse- 
 quently weaker. Scarlet lake is usually a mere mixture 
 of crimson lake and vermilion, but alizarin lake may 
 replace the former. 
 
 Beautiful and rich as are the colours prepared from 
 cochineal, not one of them should ever find a place upon 
 the palette of the artist. They all become brownish, and 
 ultimately almost disappear after a short exposure to 
 sunlight or the more prolonged attack of strong diffused 
 daylight. In six hours of sunshine a strong wash of fine 
 crimson lake on Whatman paper lost 8 per cent, of its 
 original intensity ; this was on April 12. The loss during 
 a second period of six hours’ exposure was much less, but 
 after the lapse of four months less than 5 per cent, of the 
 original colour remained. In the case of carmine, from 
 one to two years was required for the complete oblitera- 
 tion of every trace of the original crimson from a deep 
 wash of this pigment. All the cochineal pigments be- 
 come somewhat brownish during the course of fading, 
 but ultimately, when all the red has disappeared, either 
 
I 
 
 BURNT CARMINE 209 
 
 a greenish-grey or a faint sepia-like brown is the sole 
 residue. 
 
 The term ‘ lake ’ belongs to all colouring-matters 
 thrown down upon such a basis as alumina ; but when 
 purple, crimson, or scarlet is prefixed to the word lake, 
 cochineal colours are always understood. So carmine used 
 alone refers to cochineal carmine, although it is a general 
 term for a group of rich pigments, of which madder car- 
 mine and indigo carmine are perfectly distinct examples, 
 derived from madder and indigo respectively. 
 
 It is not necessary to say more about the various 
 cochineal pigments, nor to point out their many falsifica- 
 tions, for their value as artists’ colours is very small. No 
 artist who cares for his work and hopes for its permanency 
 should employ them. 
 
 Burnt Carmine. 
 
 This preparation should rather be called ‘ roasted car- 
 mine.’ It is obtained by carefully heating the carmine 
 made from cochineal. It possesses a beautiful hue, but 
 is quite as fugitive as the product which yields it. Two 
 years’ -exposure to sunlight completely destroyed a strong 
 wash of cake-burnt carmine on paper. The moist pig- 
 ment had lost nine-tenths of its intensity at the end of 
 the same period, while the small residual proportion of 
 the colour had suffered no further change in depth at the 
 end of a further lapse of three years. Burnt carmine is 
 rather less fugitive in oil than in water colour. Experi- 
 ments in the latter medium gave, after exposure to 
 sunlight, the following residual intensities out of ten : 
 
 Moist, after two years ... ... i 
 
 Cake, after two years ... ... o 
 
 Moist, after five years ... ... i 
 
 14 
 
210 
 
 RED LEAD 
 
 A sample of burnt carmine purchased of Messrs. New- 
 man about the year 1815 was found (as might have been 
 anticipated) to have retained its colour in the cake per- 
 fectly to the present year ; but a wash of it on paper 
 possessed no greater nor less degree of permanency than 
 a wash of the same pigment prepared by the same 
 makers in 1886. 
 
 Red Lead : Minium — Saturnine — Mine Rouge, Mine 
 Orange — Mennige — Rosso Saiurno. 
 
 This beautiful orange-red pigment approaches in com- 
 position a compound of two molecules of protoxide of lead 
 with one molecule of binoxide, and may be approximately 
 represented by the formula PbgO^. The paler and more 
 orange-tinted varieties contain an excess of protoxide of 
 lead, often accompanied by a little carbonate. 
 
 This pigment is peculiarly liable to discoloration in the 
 presence of sulphuretted hydrogen : it acts energetically 
 upon some paints, on the cadmium yellows, for example. 
 It is quite inadmissible as a water-colour, and cannot be 
 considered as safe in oil. 
 
 Cobalt Red ; Rose de Cohalt — Cohalt Violet — Kohaltrot. 
 
 This little-used pigment should consist of the oxides of 
 magnesium and cobalt. It is prepared at a high tempera- 
 ture and is quite permanent. One method of making 
 this pigment involves the use of magnesium carbonate or 
 oxide, which is made into a paste with a solution of pure 
 cobalt nitrate. This paste is then slowly dried, and ulti- 
 mately calcined in a crucible. Different preparations of 
 this pigment differ considerably in hue ; a purplish cast 
 is sometimes due to the accidental presence of alumina. 
 
COBALT RED 
 
 2II 
 
 Pigments consisting of cobalt arseniateare occasionally 
 called ‘ cobalt red ’ ; the term ‘ cobalt violet ’ is usually 
 and may be more fitly applied to them. The hue they 
 present is rather bluer (or less red) than that of the 
 flowers of the common foxglove. Cobalt violet has been 
 made from the mineral known as erythrite, or cobalt- 
 bloom, which has the formula COgAsgOg, SHgO ; an 
 artificial cobalt arseniate is also made by oxidizing cobalt 
 sulph-arsenide, which is first reduced to powder and then 
 roasted with twice its weight of potassium carbonate. 
 After further treatment, the final product obtained by 
 grinding and washing constitutes a pigment of a rather 
 coarse grain which does not work smoothly as a water- 
 colour, but has the advantage of complete stability in all 
 vehicles. A sample of this cobalt violet of good quality 
 was found to contain no water and to suffer no change 
 when heated to a red heat in the air ; along with cobalt 
 arseniate it contained some phosphate. 
 
CHAPTER XVI 
 
 GREEN PIGMENTS 
 
 Terre Verte : Green Earth — Terre de Verone — Grilne 
 Erie — Terra Verde. 
 
 There are two rather indefinite minerals, probably not 
 really distinct — namely, glauconite and celadonite — which 
 furnish the raw material from which the artists’ pigment, 
 generally known as terre verte, is prepared. The form, 
 or variety, celadonite is the rarer of the two ; it is softer 
 than glauconite : both minerals are probably mixtures. 
 Green earth of very good quality is found at Bentonico, 
 to the north of Monte Baldo, near Verona, where it occurs 
 in cavities in an amygdaloid rock. The best samples 
 possess a deep olive-green colour ; inferior specimens are 
 celandine or apple-green. Green earth is obtained from 
 a large number of European and American localities, and 
 varies much in chemical composition. From its greenish 
 hue it has been assumed to consist chiefly of a ferrous 
 silicate — that is, a silicate of protoxide of iron, and in this 
 way it is represented in the older analyses. But more 
 exact analyses have shovm that green earth contains but 
 a small part of its iron in the protoxide condition, and that 
 it is mainly a ferric silicate. A choice specimen of fine 
 hue from Monte Baldo gave the following results on 
 analysis, the numbers representing parts in one hundred: 
 
 212 
 
TERRE VERTE 
 
 213 
 
 Water, given off at 100° C. 4’i 
 Water, given off at a red heat 4'2 
 Ferric oxide (FcjOj) - 20 3 
 
 Ferrous oxide (FeO) - - 2-6 
 
 Alumina - - - • i‘7 
 
 Lime - 
 
 - 
 
 - 
 
 - I ‘I 
 
 Magnesia - 
 
 - 
 
 - 
 
 - 5‘6 
 
 Potash 
 
 - 
 
 - 
 
 - 64 
 
 Soda - 
 
 - 
 
 - 
 
 - 2’3 
 
 Silica 
 
 
 - 
 
 - 517 
 
 Green earth is thus allied to the hornblendes, differing 
 mainly in the partial replacement of soda by potash and in 
 the presence of water. Being itself an alteration-product, 
 it is not likely to be amenable to further change, particu- 
 larly as the iron in it is for the most part fully oxidized. 
 
 Terre verte occurs in ancient Roman wall-paintings (the 
 prepared pigment was found in the ruins of Pompeii), and 
 was largely employed by the early artists of Italy in their 
 works in tempera, fresco, and oil. But amongst the green 
 pigments found in ancient wall-paintings in Rome and 
 Pompeii there occurs also a substance of a richer and 
 deeper hue than that possessed by terre verte. It was 
 made by grinding into fine powder a kind of green jasper ; 
 it has proved quite permanent. 
 
 Terre verte is prepared by carefully selecting the richest- 
 coloured and most uniform specimens of the mineral, 
 grinding them to fine powder, and washing the pulverized 
 material with rain-water ; it is then dried. Sometimes the 
 selected fragments are heated, and then quenched in very 
 dilute hydrochloric acid to remove ochre and other im- 
 purities ; the undissolved portion is then ground, washed 
 thoroughly, and dried. Most samples of terre verte are 
 found to be perfectly stable both in water-colour and oil- 
 painting. It is a semi-opaque or translucent pigment, 
 without much body in oil. It has no action on, nor is it 
 affected by, other permanent pigments. When used in 
 oil or tempera as a ground-colour or in the under-painting, 
 terre verte sometimes becomes more conspicuous in the 
 
214 
 
 GREEN OXIDE OF CHROMIUM 
 
 course of time, owing partly to the deepening of its own 
 hue and partly to the increased translucency of the pig- 
 ments which have been laid over it. Some samples of 
 terre verte seem to be liable to become slightly rusty 
 when brought into contact with lime hydrate in true 
 fresco painting. This is probably due to the further 
 oxidation of some of the ferrous oxide they contain. Cal 
 cined terre verte is known as Verona brown. 
 
 Terre verte is rarely adulterated. A pure sample is not 
 affected when drenched with liquor ammonias, becoming 
 neither more bluish (presence of copper compounds), nor 
 more brownish (presence of Prussian blue). But although 
 adulterated terre verte is rarely met with I have found that 
 a well-known firm of artists’ colourmen sell, or have sold, 
 a mixture with green ultramarine under the name of 
 terre verte. Tubes of oil-colour of this sort have been 
 submitted to me for analysis. This substitution is unfair 
 to the artist, who has a right to obtain the material he 
 demands. Green ultramarine freed from oil gives sul- 
 phuretted hydrogen when moistened with hydrochloric 
 acid, which has no such action on terre verte. 
 
 Green Oxide of Chromium ; Chromium Sesquioxide — 
 True Chrome Green — Opaque Oxide of Chromium — Vert 
 de Chrome — Griines Chromoxyd. 
 
 The so-called native oxide of chromium, or chrome 
 ochre, is a mere greenish clay, containing not more than 
 10 per cent, of chromium oxide. But another mineral 
 (from Okhansk, in Siberia) is of a deeper green, and 
 sometimes contains one-third of its weight of this oxide. 
 We are not aware that any attempt to employ these 
 minerals as pigments has ever been made. 
 
 The green oxide of chromium, CrgOg, varies in hue, in 
 
GREEN OXIDE OF CHROMIUM 
 
 215 
 
 depth of colour, and in opacity according to the process 
 of its preparation. It may be made either in the ‘ dry ’ 
 way or the ‘ wet ’ way. Perhaps the finest quality is that 
 produced by heating mercurous chromate in a retort till 
 the whole of the mercury has been distilled off. This is 
 an expensive process, but the product is excellent in colour 
 and body. Ammonium bichromate gently heated, in small 
 portions at a time, yields a dull-coloured but a useful 
 variety of this pigment ; but there is a similar, though more 
 economical process, yielding a better-coloured product. 
 This consists in gently heating together and then calcining 
 a mixture of 3 parts of neutral potassium chromate with 
 2 parts of ammonium chloride. The mass is to be 
 thoroughly washed with hot water, dried, and again ignited. 
 Two other processes for preparing this pigment in the dry 
 way may be commended. In both of them potassium 
 bichromate (free from iron) is used, but in the one case 
 sulphur, in the other starch, is employed, in order to effect 
 the reduction of the chromic salt to the condition of ses- 
 quioxide. The sulphur method yields at once a good pig- 
 ment, which needs nothing but a thorough washing, first 
 with very dilute sulphuric acid and then with water, fol- 
 lowed by grinding, to fit it for use, but a second calcination 
 is required in the starch process. In order to prepare 
 oxide of chromium by the wet way, a solution of an 
 alkaline chromate or bichromate is to be reduced by 
 sulphur or other reducing agents, or a sesquisalt of 
 chromium is precipitated by ammonia or a fixed alkali. 
 The hydrated sesquioxide is thrown down ; after having 
 been washed, this substance is gently calcined. The 
 hydrate itself, when air-dried, constitutes one of the forms 
 of ‘ transparent oxide of chromium.’ 
 
 The ordinary or opaque oxide of chromium usually 
 
2i6 
 
 VIRIDIAN 
 
 occurs in the form of a greyish-green powder of consider- 
 able body. It is quite permanent under all conditions of 
 exposure and of commixture with other pigments, and is 
 available in all the processes of painting. Its tints with 
 flake-white, and the yellowish greens which it yields 
 with aureolin, are peculiarly valuable to the landscape- 
 painter. 
 
 Green oxide of chromium is rather imitated than adul- 
 terated. This pigment when genuine is not altered in 
 colour either by ammonium sulphide or caustic potash. 
 But under the name of chrome-green mixtures of Prussian 
 blue and lead chromate are constantly sold. These prep- 
 arations generally contain some barium sulphate, often a 
 considerable quantity of gypsum, and, occasionally, alu- 
 mina. The term ‘chrome-green’ cannot be justly applied 
 to these mixtures, which are greatly inferior in stability 
 to the pigments under discussion, and are all discoloured 
 by lime and alkalies. 
 
 ViRiDiAN : Emerald Oxide of Chromium — Vert Pannetiev — 
 
 Vert de Guig7iet — Vert Emeraiide — Mittler’s Green — 
 
 Feuriges Chromoxyd. 
 
 About the year 1838 Pannetier and Binet began to make 
 a beautiful chromium green by means of a secret method. 
 Many years afterwards M. Guignet discovered and 
 patented a process by which this admirable pigment 
 could be manufactured. About 8 parts of crystallized 
 boracic acid and 3 parts of potassium bichromate are 
 thoroughly mixed and calcined. The mass obtained is 
 treated with cold water, washed by decantation, ground 
 wet, washed with hot water, and carefully dried. The 
 product is a hydrated chromium sesquioxide, in which a 
 variable amount of the boracic constituent is often re- 
 
VIRIDIAN 
 
 217 
 
 tained. Viridian is, however, essentially a hydrated ses- 
 quioxide of chromium, having the formula Cr^O^, 2H^O. 
 In the preparation of this pigment it often happens that 
 sufficient care is not taken to wash it perfectly free from 
 all soluble salts. I have known the metal tubes in which 
 this moist water-colour has been kept to be corroded by 
 these salts and to fall to pieces in a few months. The 
 presence of such saline matter is easily detected by mixing 
 the moist or cake colour with water and noting if coagu- 
 lation or curdling takes place. 
 
 It would be difficult to exaggerate the value of this ad- 
 dition to the artist’s palette. The colour of viridian is a 
 very deep bluish green of great purity and transparency. 
 It furnishes, with aureolin on the one hand and with ultra- 
 marine on the other, an immense number of beautiful hues, 
 adapted to represent the colours of vegetation and of water. 
 It is quite unaffected by sunlight and sulphuretted hydro- 
 gen, and it has no action on other pigments. Moreover, 
 it may be safely used with all the different painting media, 
 and upon all kinds of painting-grounds. 
 
 Viridian is the name by which this pigment is perhaps 
 now best known in England. It is unfortunate that it 
 should be called ‘ Vert Emeraude ’ in France, since it has 
 little in common with the poisonous emerald green of our 
 colourmen. This pigment is sometimes adulterated with 
 baryta yellow in order to modify its hue. This substance 
 may be readily detected by moistening the pigment with 
 dilute hydrochloric acid, when a yellow solution is ob- 
 tained. 
 
 Arnaudon’s chrome green is of a somewhat opaque 
 green hue, rather like that of Schweinfurt ; it is a phos- 
 phate of chromium. A similar product is Mathieu-Plessy’s 
 chrome green ; but under the name of ‘ chrome green,’ 
 
2i8 
 
 COBALT GREEN 
 
 ‘green cinnabar’ and ‘griiner Zinnober,’ spurious pig- 
 ments are constantly sold, the commonest of them con- 
 sisting of mixtures of chrome yellow and Prussian blue. 
 They are worthless in comparison with viridian. 
 
 A clear and bright green called ‘ vernalis’ is one of the 
 potters’ pigments introduced to the notice of artists by 
 Mr. Wm. Burton. It is formed at a very high tempera- 
 ture and is perfectly permanent. It contains lime but 
 owes its colour to chromium. 
 
 Cobalt Green ; Rinmanns Green — Vert de Cohalt — Vert 
 de Zinc — Kohaltgriin. 
 
 It has long been known that the oxide or a salt of zinc, 
 moistened with a solution of cobalt nitrate, and then 
 strongly heated before the blow-pipe, gives a porous mass 
 of a beautiful green hue. This compound or mixture of 
 the oxides of zinc and cobalt may be prepared by : (i) Pre- 
 cipitating with an alkaline carbonate a mixture of the 
 nitrates of cobalt and of zinc, and then strongly heating 
 (after washing) the precipitate formed ; (2) Making a paste 
 of zinc oxide and water, and adding to it a solution of 
 nitrate or sulphate of cobalt, or of roseo-cobaltic chloride ; 
 the mass is then dried, calcined at a dull red heat, thrown 
 into water, ground, washed, and dried. Method No. 2 
 gives a finely coloured product, the depth of hue being 
 proportional to the percentage of cobalt oxide. If the 
 latter oxide amount to one-third of that of zinc the colour 
 is a very deep bluish green ; with no more than one-sixth 
 the colour is still rich. Some specimens do not contain 
 more than one-twentieth — sometimes even less — of cobalt 
 oxide, and yet they are far from pale. An excellent deep 
 sample contained 12 per cent, of cobalt oxide. 
 
 When properly prepared, cobalt green is a pigment of 
 
EMERALD GREEN 
 
 219 
 
 great beauty and power.* The deeper tones of cobalt 
 green are almost transparent in oil. The pigment works 
 well, is quite permanent, and has no action on other pig- 
 ments. Cobalt green is, in fact, one of the too-rare pigments 
 which is at once chemically and artistically perfect ; such 
 at least is the conclusion I reached from my own trials, 
 but Mr. J. Scott Taylor tells me that cobalt green fades a 
 good deal when exposed to damp, although it stands light 
 well. It must be admitted, however, that it may be 
 exactly imitated by a mixture of viridian and artificial 
 ultramarine with a little zinc white. 
 
 Cobalt green is again coming into artistic use, as it is 
 equally adapted for all the methods of painting. It was 
 discredited for awhile by the inferiority of the product 
 obtained by Rinmann’s original process (No. i above). It 
 ought not to be an expensive pigment. 
 
 Sometimes cobalt green is prepared by precipitating a 
 cobalt salt with an alkaline arseniate or phosphate, and 
 then heating the precipitate with zinc white. 
 
 Emerald Green : Cupric Acdo-Avsenite — Schweinftirt 
 Green — Vert Paul Veronhe — -Schweinfurter Griin. 
 
 This pigment was discovered in 1814 during the course 
 of experiments made with the object of preparing an im- 
 proved Scheele’s green. It may be prepared by half a 
 dozen slightly differing processes, but in all verdigris (or 
 vinegar and blue vitriol) and white arsenic are the two 
 essential materials employed. Generally verdigris is dis- 
 solved in acetic acid, and added to a boiling aqueous 
 
 * One sample of deep transparent cobalt green which I obtained 
 from a Paris colour-manufacturer contained both viridian and 
 ultramarine, added to enrich the colour of the cobalt green which 
 formed the basis of the pigment. 
 
220 
 
 EMERALD GREEN 
 
 solution of white arsenic : on continued ebullition a de- 
 posit of emerald green occurs. Sometimes copper sul- 
 phate, potassium arsenite, and acetic acid are employed. 
 Whatever the method, it is necessary that the coloured 
 product be washed with boiling water to remove the last 
 traces of soluble salts. 
 
 The hue of this pigment is a nearly normal green, slightly 
 verging upon bluish green ; it is brighter and more opaque 
 than Scheele’s green, and, like it, is a deadly poison. It is 
 less attacked by sulphuretted hydrogen than Scheele’s 
 green, but as a water-colour, does not long remain untar- 
 nished in impure air. In oil it is practically permanent, 
 both alone and when used with the majority of permanent 
 pigments. It is, however, quickly blackened by the cad- 
 mium yellows. Emerald green cannot be relied upon as 
 permanent in fresco and tempera painting. Its use in 
 wall papers and in the decoration of all domestic furniture 
 and fabrics is to be deprecated, by reason of its poisonous 
 character ; but is, happily, at the present time, in great 
 measure abandoned. 
 
 Emerald green, if pure, dissolves perfectly in boiling 
 dilute nitric or hydrochloric acid ; the solutions thus 
 made should yield no precipitate with a few drops of 
 barium chloride solution. An undissolved residue gener- 
 ally shows the presence of baryta white. 
 
 Emerald green may be distinguished from Scheele’s 
 green by a simple experiment. If a small pinch of the 
 dry powder be warmed with a few drops of moderately 
 strong sulphuric acid (half oil of vitriol, half water), acid 
 vapours, having the smell of vinegar, will be given off only 
 when true emerald green is the subject of the experiment. 
 
 On the Continent, Vert ^Imeraude is the name given to 
 viridian, the emerald oxide of chromium. 
 
SCHEELE'S GREEN 
 
 221 
 
 Scheele’s Green : Cupric A rsenite — Swedish Green — 
 Mitis Green — Scheeles Griin. 
 
 This pigment, discovered in 1778, is an arsenite of cop- 
 per with an excess of copper oxide. It is best prepared by 
 dissolving, in separate portions of hot water, white arsenic 
 and blue vitriol. The solutions are then mixed, and to the 
 mixture is added, in small successive portions, a solution 
 of potassium carbonate. These additions are stopped when 
 the precipitated pigment has attained its maximum of 
 colour intensity. In another process, a hot solution of 
 potassium arsenite is added to a hot solution of blue 
 vitriol. This pigment needs thorough washing with hot 
 water, and must be dried at a moderate temperature. 
 
 Scheele’s green presents nearly the same characteristics 
 as emerald green, but is in every way inferior to that 
 pigment. It is eminently poisonous. It should not find 
 a place on the palette of the artist. 
 
 Vienna green, Mitis green, and Veronese green are 
 names which have been given to specially prepared 
 varieties of this cupric arsenite ; but there are very many 
 other designations by which pigments of essentially the 
 same composition are known. They are prepared by 
 slightly modified processes, and frequently contain such 
 foreign matters as chalk, heavy spar, or gypsum. 
 
 Malachite : Green Verditer — Green Bice — Mountain Green 
 — Green Carbonate of Copper — Vert de Montagne — Berg- 
 griin — M alachitgriin. 
 
 This green copper mineral was employed as a paint by 
 the ancients. It often accompanies the blue carbonate, 
 and occurs in many European, Asiatic, African, and 
 
222 
 
 MALACHITE 
 
 American localities. The mines at Ekaterinburg and 
 Nischne Tagilsk in Russia, and at Burra Burra in South 
 Australia, furnish malachite of fine colour ; it also occurs 
 abundantly in Namaqualand. Its variations in depth of 
 colour are due less to impurities than to differences in its 
 state of aggregation. Its specific gravity is about 4. Its 
 composition is that of a hydrate and carbonate of copper. 
 It may be represented by the formula CuC03,CuH202. It 
 contains, therefore, less of the copper carbonate than 
 azurite, or blue verditer. 
 
 Malachite requires no other treatment than careful 
 grinding to fit it for use as an artists’ pigment. The raw 
 material must, however, be carefully selected, and all 
 visible impurities, such as ochreous veins and deposits, 
 and azurite, completely removed. An artificial malachite 
 was prepared and largely used in the seventeenth century, 
 and is still often substituted for the mineral ; but it is in- 
 ferior in colour and stability to the native form. 
 
 Malachite as an oil-paint has often proved to be per- 
 manent, although it may seem to acquire a dull, brownish 
 hue, owing to the darkening and yellowing of the oil; 
 sometimes, however, it becomes somewhat olive in 
 colour. In admixture with cadmium yellow it is liable to 
 blacken. It is so easily injured by impure air when un- 
 protected by any hydrofuge, that it is quite inadmissible 
 as a water-colour. In old tempera paintings it is some- 
 times found to have stood well ; but the sulphur from 
 the egg-medium and from the size has not infrequently 
 browned it. 
 
 Malachite is sometimes adulterated with baryta white ; 
 sometimes a mixture of that pigment and an arsenical 
 green is substituted for it. The former falsification may 
 be detected by boiling the sample In hydrochloric acid. 
 
ii 
 
 VERDIGRIS 
 
 223 
 
 when the malachite dissolves, leaving the baryta white 
 as a sediment. To detect an arsenical green, a small 
 portion of the sample should be mixed with powdered 
 charcoal, gently warmed at first in a long narrow test- 
 tube to drive off moisture, and then strongly heated ; a 
 dark sublimate of metallic arsenic will form on the cooler 
 part of the tube. 
 
 Verdigris : Basic Copper Acetate — Vert-de-Gris—Verdet 
 de Montpellier — Grimspan. 
 
 This green copper pigment was called by the writers 
 of the fourteenth century ‘ viride Graecum,’ or, more 
 simply, ‘ viride,’ ‘ viride terrestre ’ being used for green- 
 earth — that is, ‘ terre verte.’ ‘ Vert-de-Grfece ’ — that is, 
 verdigris — was used by the ancient Romans as a pig- 
 ment, and has been detected in the wall-paintings of 
 Pompeii. It occurs in early Italian tempera pictures ; 
 but it has frequently injured the gesso-ground on which 
 it has been laid, forming calcium acetate with the calcium 
 carbonate, and disintegrating the surface. The blackness 
 of the shaded parts in many Venetian and Spanish pictures 
 of the_ sixteenth and seventeenth centuries has been attri- 
 buted to the changes which this pigment suffers in oil. 
 The medieval writers on the practice of painting en- 
 deavoured to show how the peculiar liability of verdigris 
 to change could be obviated by locking it up in some 
 hydrofuge substance, such as a resin or balsam. But the 
 problem actually possesses little practical interest to-day, 
 though of real moment in the study of old pictures. In 
 the modern palette the place of verdigris is taken by per- 
 manent greens derived from chromium and from cobalt : 
 concerning the safety of these we need not be anxious. 
 The large proportion of resinous matter employed by 
 
224 
 
 VERDIGRIS 
 
 early painters for the protection of verdigris from alter- 
 ation, and the success of this precautionary measure, 
 may be seen in the green drapery in several pictures by 
 Van Eyck and Mabuse in the National Gallery and at 
 Hampton Court. It should, however, be stated that the 
 older processes for preparing verdigris often yielded a 
 product much more alterable in the presence of damp 
 than is the verdigris which for a century or more has 
 been made at Montpellier. 
 
 Verdigris is commonly called in chemical language a 
 basic acetate of copper. In fact, it is a mixture of three 
 such acetates, its varying hues, ranging from green to 
 greenish blue, being dependent upon the relative pro- 
 portions of these acetates. The most blue basic acetate 
 contains i molecule of copper acetate, and i of copper 
 hydrate, with 5 molecules of water ; the greenest has 
 twice as much acetate. Average verdigris contains in 
 100 parts about 29 parts of anhydrous acetic acid, 43 of 
 copper oxide, and 27 of water. It is nearly insoluble in 
 cold water ; but by continuous washing, or by continuous 
 exposure to moist air, is ultimately decomposed. 
 
 The Montpellier process for making verdigris consists 
 in exposing thin strips of metallic copper to the vapours 
 arising from grape marc undergoing the acetic fermenta- 
 tion. The operation is conducted in a moist, warm 
 atmosphere ; finally, the whole substance of the metallic 
 copper is transformed into verdigris. 
 
 An impure atmosphere containing sulphuretted hydro- 
 gen blackens verdigris ; it is also affected by moisture 
 and by carbonic acid. As a water-colour, it is quite 
 inadmissible ; in oil, it stands pretty well if ‘ locked up ’ 
 in the way already described. But it acts energetically 
 upon several important pigments, and is very poisonous. 
 
VERDIGRIS 
 
 225 
 
 For these reasons its employment in artistic painting 
 
 ought to be abandoned. 
 
 Verdigris, if pure, dissolves perfectly in liquor ammoniae, 
 any gypsum or barytes present as diluents or adulterants 
 remaining undissolved. If blue vitriol has been added to 
 verdigris, it also will dissolve in the ammonia ; but this 
 falsification may be detected by acidifying the ammoniacal 
 solution with hydrochloric acid, and then adding solution 
 of barium chloride — a white precipitate of barium sul- 
 phate indicates the presence of copper sulphate. 
 
 There are many composite green pigments sold by 
 artists’ colourmen ; none is of real value. Green lake, a 
 mixture of quercitron lake and Prussian blue ; Hooker’s 
 green — gamboge and Prussian blue ; olive green — Indian 
 yellow, umber and indigo ; and olive lake, a mixture of 
 quercitron lake, bone brown and ultramarine — all these 
 belong to the same category. However, there is one 
 mixed pigment, the so-called ‘ Cadmium-green ’ on which 
 a favourable judgment may be passed : it consists of 
 viridian and cadmium yellow. 
 
 15 
 
CHAPTER XVII 
 
 BLUE PIGMENTS 
 
 Ultramarine: Lapis Lazuli Blau — Lasurstein Blau — 
 Otitremer — Bleu d'Azur. 
 
 There are at least three mineral species, closely allied in 
 chemical composition, and generally presenting a more or 
 less marked blue colour, which contain as their essential 
 constituents the five elements, silicon, aluminium, sodium, 
 sulphur, and oxygen, and which owe their characteristic 
 hue to the same compound. From one of these minerals, a 
 variety of ‘ hauyne,’ often called ‘ lapis-lazuli,’ the true or 
 native ultramarine is obtained. This stone occurs, of very 
 varying purity and colour, at Bucherei,Transbaikal,andin 
 many other Siberian localities ; at Ditro, in Transylvania ; 
 in the Andes of O valla, Rio Grande; and in several regions 
 of Persia, Tibet, and China. It is the ‘sapphire’ of ancient 
 authors. Small golden specks of iron-pyrites are frequently 
 irregularly scattered through its substance ; it is also very 
 frequently associated intimately with portions of the rocky 
 gangue, or matrix (limestone, syenite, granite, etc.), in 
 which it occurs. Very fine lapis-lazuli comes from Tibet. 
 
 To prepare a pigment from this mineral, selected pieces 
 of small size, as free as possible from pyrites or other im- 
 purities, are heated in a crucible and quenched (etonn6) 
 in cold water, or very weak vinegar. The m.aterial, thus 
 
 226 
 
ULTRAMARINE 
 
 227 
 
 disintegrated, is washed by decantation, and then dried 
 and carefully ground. The powder is then purified by 
 elutriation, or ‘ washing over,’ the several wash-waters 
 depositing pigments of different depths of colour, and of 
 different degrees of fineness. Some manufacturers adopt 
 an old process, and make the powder into a soft mass with 
 a little rosin, linseed oil and beeswax, and knead, beat, or 
 macerate the lump, secured in a bag of coarse muslin 
 under very weak potash, or soda-lye — the alkaline water 
 carries off or withdraws the greater part of the pigment, 
 and deposits it on standing. The richness of the blue 
 product obtained depends primarily upon the original 
 quality of the stone, but several grades are always pro- 
 curable from the same raw material by means of the 
 above-described processes, bluish-grey and grey powders, 
 known respectively as ultramarine ash and mineral grey, 
 being the last and the least valuable products, while the 
 deepest and finest pigments are deposited from the 
 earliest wash-waters. 
 
 Optically, the superb blue of native ultramarine ap- 
 proaches more closely than the blue of any other pigment 
 to the pure normal blue of the solar spectrum ; it shows 
 very little violet and in this respect is unlike most speci- 
 mens of artificial ultramarine. Ultramarine is somewhat 
 harsh and granular in texture, a characteristic which may 
 be reduced by a small admixture of Chinese white, but 
 which becomes more marked when it is used as a light 
 wash, or in conjunction with transparent pigments, in 
 water-colour painting. It more nearly approaches trans- 
 parency when used in oil, and is then of excellent working 
 quality. 
 
 It is generally considered that ultramarine withstands 
 the action of light, moisture and sulphuretted hydrogen 
 
228 
 
 ULTRAMARINE 
 
 perfectly, and that it neither affects nor is affected by any 
 other pigments. I have, however, been informed by an 
 English landscape-painter in oil, who has largely employed 
 native ultramarine in the skies of his pictures, that he has 
 lost faith in its inalterability. But the question arises, 
 ‘ Was the pigment used always authentic ?’ It dries well 
 in oil. It is decolourized at once by a hot solution of 
 alum, and ultimately even by a saturated cold solution, 
 which, however, bleaches very quickly all but the most 
 stable varieties of the artificial pigment. All mineral 
 acids, save carbonic, and all the common organic acids, 
 such as acetic, oxalic and citric, discharge the colour of 
 native ultramarine. It is only by a combination of 
 several tests in the hands of a skilled chemist that the 
 discrimination of genuine from spurious ultramarine may 
 be with certainty accomplished. 
 
 It may, however, be mentioned here that when a current 
 of hydrogen gas is passed over true ultramarine heated in 
 a glass tube the powder retains its colour wholly or par- 
 tially for an hour or more, while the best artificial pig- 
 ment similarly treated becomes grey or greenish grey. 
 
 In the works — both in fresco and tempera, and in oil — 
 of many of the old masters, and in a large number of 
 illuminated manuscripts, the permanence of true ultra- 
 marine may be seen. If in some cases it has acquired a 
 greenish or dull hue in oil-painting, such change is due to 
 the yellowing of the oil and varnish, and not to any 
 deterioration of the pigment. 
 
 The price of genuine ultramarine is very high. This 
 is due less to the scarcity of the original lapis-lazuli from 
 which it is derived, than to the small yield and to the 
 elaborate and tedious operation by means of which the 
 pigment is prepared. But when every allowance is made 
 
ARTIFICIAL ULTRAMARINE 
 
 229 
 
 on account of the troublesome and lengthy process of 
 manufacture, the cost of ultramarine is unwarrantably 
 excessive. 
 
 Artificial Ultramarine: New Blue — French Blue — 
 Permanent Blue — Gmelins Blue — Guimet’s Blue — Kiinst- 
 liches U Itramarin. 
 
 In the year 1814a blue coloration, subsequently proved 
 to be due to ultramarine, was noticed in the soda (black- 
 ash) furnaces of St. Gobain. About fourteen years after- 
 wards a method of making the same blue substance at will 
 v/as discovered by Christian Gmelin, and by Guimet ; this 
 method was founded in part upon chemical analyses of 
 natural ultramarine, and in part upon a study of the con- 
 ditions under which the above-named blue coloration 
 occurred. By successive improvements in its manufac- 
 ture artificial ultramarine is now produced at a cost of no 
 more than a few pence per pound. It is chiefly made in 
 Germany and in F ranee. 
 
 The raw materials employed in the preparation of ultra- 
 marine are kaolin, or China-clay, silica, sodium sulphate, 
 sodium carbonate, sulphur, charcoal and rosin. Some 
 makers omit the sodium sulphate, others the rosin, while 
 calcined alum is occasionally substituted for the kaolin. 
 These materials are heated together in closed crucibles in 
 a furnace, and slowly cooled. A greenish porous cake is 
 the product: this is powdered and gently roasted, after the 
 addition of a little sulphur, for some hours. The material 
 is again powdered, and then washed and dried : further 
 calcination is sometimes required to develop the proper 
 blue colour. 
 
 In preparing artificial ultramarine for use as an artists’ 
 pigment it must be very finely ground, and verythoroughly 
 
230 
 
 ARTIFICIAL ULTRAMARINE 
 
 washed with water free from lime. The grinding not only 
 improves the colour, but renders working with the paint 
 less difficult to manage ; the washing removes soluble 
 sulphates and certain sulphur-compounds, which are liable 
 to discolour some of the pigments (those containing lead 
 or copper) with which the ultramarine may afterwards be 
 associated in a picture. 
 
 The hue of artificial ultramarine is commonly of a less 
 pure quality than that of the natural pigment, verging 
 somewhat towards a purple. But its range of hue is 
 considerable, from a greenish-blue to a decided violet. 
 The greenish-blue and blue varieties are not affected in 
 hue by admixture with zinc white, but the varieties 
 which incline towards violet become remarkably enfeebled 
 in richness of colour by this admixture, such weakening 
 being out of all proportion with the dilution of tint which 
 would be expected to ensue from this addition of white. 
 However, other white substances do not produce this 
 curious result. 
 
 Weak acetic acid, and a saturated cold solution of 
 alum, which are without immediate action upon natural 
 ultramarine, generally change the hue, and always ulti- 
 mately decolourize the artificial product. Those kinds 
 which have a somewhat violet tinge resist the destructive 
 action of the above reagents longer than the pure blue 
 and greenish-blue varieties. Neither sulphuretted hydro- 
 gen, nor caustic lime or other alkaline substance, affects 
 the colour of artificial ultramarine. 
 
 Although the colour of ultramarine is certainly due to 
 a substance containing sulphur, the precise chemical 
 composition of this blue substance has not yet been 
 determined. Some chemists are of opinion that it is a 
 compound of aluminium, sodium, sulphur, and oxygen ; 
 
ARTIFICIAL ULTRAMARINE 
 
 231 
 
 others regard it as a sulphide of aluminium. There is 
 little doubt, however, that it contains sulphur in two 
 conditions. Some curious derivatives of blue ultra- 
 marine, of various colours, have been obtained, in which 
 it is believed that the sodium of the original compound 
 has been replaced by other metals ; such is the yellow 
 ‘ silver-ultramarine,’ prepared by keeping blue ultra- 
 marine in a solution of silver nitrate. These bodies are, 
 however, useless as pigments. The function of the silica 
 in ultramarine is not known, although it forms from 
 30 to 45 per cent, of the total weight of all the varieties, 
 and although it has been found by experience that ultra- 
 marines rich in silica resist the action of alum better 
 than those which are poor in this constituent ; these 
 silicious ultramarines are sometimes sold under the name 
 of ‘ Oriental Blue.’ 
 
 Artificial ultramarine, when properly prepared, is 
 permanent both in water and oils. When thin washes 
 on paper appear to lose strength as they dry, or soon 
 afterwards, the change is due to the chemical action of 
 the alum, or other aluminium compound, present in the 
 size of the paper. If an ultramarine should discolour 
 emerald green, chrome yellow, Naples yellow (true), or 
 flake white, it probably contains free sulphur, or has 
 been insufficiently washed. 
 
 In order to test the purity of ultramarine, an easy plan, 
 useful so far as it goes, is this : Boil a small quantity of 
 the sample with distilled water in a wide test-tube for 
 five minutes. Pour the liquid on to a wetted Swedish 
 filter-paper fitted in a funnel. Divide the clear filtrate 
 which runs through into 2 parts — to one add a few drops 
 of basic acetate of lead ; to the other a few drops of 
 barium chloride solution. No darkening should occur in 
 
232 ARTIFICIAL ULTRAMARINE 
 
 the first case, nor any white cloudiness in the second. 
 Besides the white adulterants, gypsum and heavy spar, 
 both chessylite and Prussian blue have been found in 
 artificial ultramarine. If chessylite be present, its 
 presence may be detected by warming the sample with 
 ammonia solution, when a blue solution will be obtained. 
 Ultramarine containing Prussian blue acquires a brown 
 hue v/hen warmed with caustic soda solution, while it 
 does not completely lose its blue colour when treated 
 with dilute hydrochloric or sulphuric acid. 
 
 When an acid (such as hydrochloric or oxalic) acts upon 
 ultramarine, it disengages both sulphur and sulphuretted 
 hydrogen ; a good deal of silica is also, in most cases, then 
 separated in a gelatinous form. The sulphur separated 
 as such may amount to as much as lo per cent, of the 
 weight of the pigment taken, or it may be less than a half 
 per cent. The sulphur disengaged as sulphuretted hydro- 
 gen through the action of an acid varies between a half 
 per cent, and 6 per cent. As these variations have no 
 relation to the depth of colour in the several samples, it is 
 evident that a great proportion of this sulphur does not 
 form an essential part of the blue pigment itself. Other 
 things being equal, it is well to select samples of ultramarine 
 which contain as little as possible of sulphur in any 
 state. 
 
 The ultramarines known as ‘ Guimet’s ’ and ‘ Heu- 
 mann’s ’ are of fine quality. Large quantities of this 
 pigment are manufactured in Germanyand France, smaller 
 amounts in Belgium and England. The green, violet, 
 lilac, purple and red ultramarines of commerce are per- 
 manent pigments of some artistic value. They are or 
 may be produced in the manufacture of the blue variety, 
 the green being its precursor and the others being formed 
 
ARTIFICIAL ULTRAMARINE 
 
 233 
 
 by further heating or treatment of the blue kind. The 
 final product is a greyish-white body. 
 
 There are two easily applied tests which, taken together, 
 enable one to estimate the relative values of a set of 
 samples of ultramarine in powder. These tests have dis- 
 tinct objects in view. In one, resistance to alteration is 
 determined — in the other, the colouring power. The 
 quantity operated on is only 5 centigrams, so the best 
 plan is to begin by weighing out, with the aid of a sensi- 
 tive balance, two portions of -05 gram a-piece from each 
 sample. One of each of these portions is thoroughly 
 mixed, by means of an ivory spatula, on highly glazed 
 white paper, with 2 grams of pure kaolin : the tints of 
 the several kinds are then compared. For the other test 
 we require a number of small precipitating glasses or 
 large test-tubes, and a supply of a saturated solution of 
 potash alum in distilled water. The five centigrams of 
 each sample of ultramarine are put into the duly labelled 
 glasses and a measured quantity (say 50 cubic centi- 
 metres) of the alum solution is poured on with constant 
 stirring. The change or loss of colour is duly noted at 
 intervals of time, some samples opposing a resistance of 
 days to the destructive influence of the alum, while others 
 are injured by a contact of a few hours, or, in some 
 extreme cases, of a few minutes. It is scarcely necessary 
 to add that the contents of each test-glass should be 
 thoroughly stirred at regular intervals. To avoid this 
 necessity, and at the same time to improve the accuracy 
 of the results, a slight modification of the method may be 
 introduced. Ten grams of the purest agar-agar are dis- 
 solved by the aid of heat in a litre of the alum solution. 
 Just before this liquid has become a jelly by cooling, a 
 measured portion is poured upon the necessary quantity 
 
234 
 
 COBALT BLUE 
 
 of ultramarine : the mixture after thorough agitation is 
 allowed to set, so that the pigment remains suspended 
 throughout the mass ; any changes of colour can be 
 easily recognised. 
 
 Cobalt : Cohalt Blue — Bleu de Thenard — Kohalthlau. 
 
 Excluding smalt, which owes its colour to a cobalt 
 silicate, there are at least three pigments which go under 
 the name of ‘ cobalt ’ or ‘ cobalt blue.’ The best known 
 of these is a combination of alumina and cobalt oxide ; 
 then comes Leithner’s or Thenard’s blue, a cobalt phos- 
 phate on an aluminous base ; lastly, there is an aluminous 
 cobalt arseniate very much like the phosphate. 
 
 The original and simplest form of cobalt blue, or 
 Wenzel’s blue, may be made by calcining strongly an 
 intimate mixture of aluminium hydrate and cobalt oxide. 
 A better way consists in moistening freshly-precipitated 
 aluminium hydrate with a solution of cobalt nitrate, dry- 
 ing and then strongly igniting the mass. It may likewise 
 be prepared by precipitating a solution of sodium alumi- 
 nate by means of cobalt chloride solution. Thenard’s blue 
 may be prepared by mixing about 8 parts of aluminium 
 hydrate with i part of cobalt phosphate, both in the moist 
 condition, then drying and strongly calcining the mixture ; 
 cobalt arseniate may replace the phosphate. Another 
 variety of Thenard’s blue is obtained by adding sodium 
 phosphate solution to a solution of alum containing a little 
 cobalt sulphate. In all the above methods, the complete 
 freedom from iron and nickel of the materials used is 
 essential to the purity and beauty of the blue pigment 
 formed. 
 
 The cobalt blues work well in all media. They are un- 
 affected by light, moisture, and oxygen. The best samples 
 
CCERULEUM 
 
 235 
 
 of them are practically permanent even in impure air, but 
 ammonium sulphide tends to discolour them. If they 
 appear changed in hue in any oil-paintings, the yellowing 
 of the admixed or overlying oil or varnish must be regarded 
 as the cause. Cobalt blues may be used in fresco-painting ; 
 they are unaffected by commixture with other pigments. 
 Cobalt blues do not lose their colour when boiled with 
 alum solution, nor when treated with moderately strong 
 acids. 
 
 Cobalt blue as an oil-colour is usually ground with about 
 three-fourths its weight of linseed or poppy oil. 
 
 Cobalt blue examined optically is found to reflect much 
 green and violet light as well as blue. Viewed by candle 
 or gas light it acquires a very marked purplish hue. 
 Burton’s cobalt, originally prepared for the use of potters, 
 is of fine quality and of more than usual stability. 
 
 The introduction of cobalt blue to the palette of the 
 artist may be said to have created a revolution in the 
 style of painting, especially obvious in water-colour land- 
 scapes. 
 
 CcERULEUM : Cerulium — Cerulean Blue — Coelinhlau — 
 Bleu Celeste. 
 
 When oxide of tin is moistened with cobalt nitrate solu- 
 tion and strongly heated, a greenish-blue mass is obtained, 
 which, after powdering and washing, constitutes one of 
 the varieties of the pigment known as coeruleum. There 
 are other ways of preparing this substance. One of these 
 consists in precipitating potassium stannate with cobalt 
 chloride, collecting and washing the precipitate, and then 
 mixing it with some pure silica and heating it. A good 
 specimen of coeruleum contained in 100 parts : 49^7 tin 
 binoxide, i8'6 cobalt oxide, and 317 silica. Some samples 
 
236 
 
 PRUSSIAN BLUE 
 
 contain calcium sulphate, or lead sulphate, in place of the 
 silica ; they are of inferior quality. 
 
 Coeruleum is a permanent pigment of a rather greenish- 
 blue colour, without any tendency to the violet cast, so 
 noticeable with other cobalt blues (page 235), when viewed 
 by gas or candle light. It suffers little, if any, change by 
 exposure to light or impure air, or by commixture with 
 other pigments. It is a sub-opaque, rather earthy pig- 
 ment, with a moderate tingeing power. Although some 
 painters find it useful, cceruleum may be imitated so 
 nearly by a mixture of ultramarine, viridian, and white 
 that its presence on the palette can easily be dispensed 
 with. 
 
 Prussian Blue : Turnbull’s Blue — Antwerp Blue — Berlin 
 Blue — Prussiate of Iron — Chinese Blue — Saxon Blue — 
 Bleu de Bevlin — Paviser-hlau. 
 
 Although the chemical constitution of this pigment can 
 hardly be said to have been absolutely ascertained, yet it 
 is generally believed that there are at least three different 
 though closely allied chemical compounds included under 
 the above names, not to mention those varieties of this 
 pigment which contain added or extraneous substances, 
 such as alumina, plaster-of- Paris, or zinc-white. The 
 three typical and distinct compounds are : 
 
 I. Soluble Prussian Blue. — This is made by pouring a 
 solution of ferric chloride or ferric nitrate into an excess 
 of potassium ferrocyanide solution (yellow prussiate of 
 potash), or by pouring ferrous sulphate solution into 
 excess of potassium ferricyanide solution. The blue 
 precipitate formed is washed with distilled water until 
 the wash-water begins to acquire a blue tint. The com- 
 position of the pigment thus prepared is, when dry, 
 
PRUSSIAN BLUE 
 
 237 
 
 represented by the formula K2Fe2(CN)j^2F®2- 
 tains potassium, and is, in reality, a double ferrocyanide 
 — a ‘ potassio-ferric ferrocyanide.’ It is less stable than 
 either of the other kinds of Prussian blue, while its solu- 
 bility in water causes it to stain the paper on which it is 
 spread in water-colour painting. It should invariably be 
 rejected by artists, although it must be owned that it 
 works very smoothly both in water and in oil. It may 
 always be distinguished from the superior kinds of 
 Prussian blue by very simple tests. One of these con- 
 sists in roasting a small portion of the dry powdered pig- 
 ment in a porcelain basin or iron tray, allowing the 
 brown residue to cool, and then throwing it into a little 
 pure water. Then place the mixture on a wetted filter 
 contained in a funnel, and see whether the clear filtrate 
 is alkaline by dipping a piece of yellow turmeric paper 
 into it ; if the yellow tint of this paper is reddened, then 
 the Prussian blue belongs to this section. Another test 
 is applied by simply washing some of the powdered blue 
 with warm distilled water on a Swedish filter — the filtrate 
 becomes blue. 
 
 11 . . Insoluble Prussian Blue may be prepared by boiling 
 No. I. (the soluble kind) with a solution of ferric chloride, 
 by mixing solutions of ferrocyanic acid and ferric chloride, 
 by pouring potassium ferrocyanide solution into an excess 
 of a solution of ferric chloride, or of ferric nitrate, and 
 heating the mixture for some time, or by precipitating a 
 watery solution of Blue No. I. with an excess of either 
 of the above-named iron salts. It may also be obtained 
 by oxidizing Turnbull’s blue (No. III.) with chlorine 
 water or nitric acid. The chemical composition of this 
 pigment is very complex, the simplest empirical formula 
 for it being Fe/CN)^g: it will be seen that it contains no 
 
238 
 
 TURNBULL’S BLUE 
 
 potassium. It always contains some combined water, 
 which cannot be driven off by heat without decomposition 
 of the salt. This blue is more permanent than No. I. 
 
 III. Timihiill’s Blue . — The chief constituent of the 
 original Turnbull’s blue (more properly, Gmelin’s blue) 
 closely resembles ordinary soluble Prussian blue, and, 
 like it, contains potassium. But the potassium may be 
 removed from it by stannous chloride solution, a sub- 
 stance being produced having the empirical formula 
 Fe5(CN)i2, but containing some water. Or the same 
 body may be made by precipitating a solution of ferri- 
 cyanic acid with a solution of ferrous sulphate or ferrous 
 chloride. This blue is of good colour, but is more diffi- 
 cult to obtain pure than No. II., the other insoluble 
 Prussian blue. Exposed to light, all the forms of Turn- 
 bull’s blue, pure and impure, have a more decided ten- 
 dency to become greenish or to fade than No. II. 
 
 The ordinary commercial Prussian blue is a mixture, 
 in varying proportions, of the three blues above de- 
 scribed. It is made by adding green vitriol (ferrous 
 sulphate) solution to a solution of yellow prussiate of 
 potash (potassium ferrocyanide). The precipitate formed 
 (which varies in colour from a light to a deep blue, 
 according to the amount of ferric salt present in the 
 green vitriol) is then oxidized by means of dilute nitric 
 acid or of a solution of bleaching powder. After having 
 been washed, the substance is treated with hydrochloric 
 acid, and is then again washed with water. 
 
 All the above blues are of a very deep blue colour 
 in powder or in the lump, but when pressed or rubbed 
 they all show a coppery lustre. The only one fit for 
 artists’ use is the insoluble variety (No. II.), the others 
 being less stable or having other defects. The insoluble 
 
PRUSSIAN BLUE 
 
 239 
 
 form is, moreover, the only one which yields, when 
 roasted, a perfectly satisfactory ‘ Prussian brown.’ 
 
 Prussian blue is a transparent colour of great force and 
 
 richness, and works well in oil as well as in water. In 
 thin washes or layers it has a slightly greenish hue. Its 
 colour is changed by lime and by the weakest alkalies, so 
 that it cannot be employed in fresco or on newly-plastered 
 walls . Long-continued exposure to strong light weakens 
 and alters the colour of Prussian blue, but the insoluble 
 varieties are less affected than the soluble. When this 
 fading of the pigment in water-colour washes has taken 
 place, a brief sojourn in darkness generally suffices to 
 restore the hue almost to its original depth and quality. 
 This strange phenomenon, which awaits explanation, has 
 been long familiar to artists’ colourmen. The influence 
 of moisture in determining the fading of Prussian blue 
 under solar exposure is seen in three comparative trials 
 with water-colour washes on paper. In a sealed tube 
 with ordinary air the intensity was reduced from 10° to 
 1°, and the colour became sea-green in thirteen months ; 
 after four years a part of the same wash retained its full 
 depth when the slip was exposed in air kept dry ; another 
 portion was reduced to 8-5° by four years’ exposure in 
 an ordinary frame. A sample of Prussian blue (as 
 ordinarily made) in oil, after five years’ exposure, had 
 become somewhat greenish, with a loss of about one- 
 tenth of its depth. These changes were more obvious in 
 the pure transparent pigment than in its tint with flake- 
 white. A second specimen, from another maker, similarly 
 exposed, was rather less affected, both as to loss of colour 
 and as to change of hue. 
 
 Prussian blue was discovered in 1704 by a colour- 
 maker of Berlin, Diesbach by name. When, as is some- 
 
240 
 
 CYANINE 
 
 times the case, this pigment is found in water-colour 
 paintings of the seventeenth century, it is scarcely neces- 
 sary to state that its presence betrays the brush of the 
 restorer or the forger. 
 
 Antwerp blue is a sort of Prussian blue lake, the pig- 
 ment consisting of a colourless base dyed with Prussian 
 blue. According to one method of preparation, a solution 
 of I part of green vitriol and 2 parts of zinc sulphate in 
 40 parts of water is precipitated by adding to it a solution 
 of 4 parts of potassium ferrocyanide in 40 parts of water. 
 The blue colour of the precipitate deepens as it is washed. 
 Alumina is sometimes used as the base upon which the 
 blue pigment is thrown. Antwerp blue is less transparent 
 and less intense in colour than Prussian blue ; it has 
 about the same degree of stability. 
 
 Cyanine ; Leitclis Blue. 
 
 A mixture of Prussian blue and cobalt blue has been 
 sold under the name of cyanine. It would seem from 
 some recent experiments made with this mixed pigment 
 that it is fairly permanent, even in water-colour painting. 
 It is, of course, not adapted for use in fresco, as the Prus- 
 sian blue in it at once yields rust through the action of the 
 lime of the intonaco. Mixed pigments cannot, however, 
 be recommended, as it is in nearly all cases better for the 
 artist himself to associate together those paints which he 
 wishes to mingle. This plan gives him the opportunity 
 of ascertaining the purity and quality of the several com- 
 ponents of his mixtures. In the case of cyanine, it 
 appears that the more permanent constituent, the cobalt, 
 partially protects the Prussian blue from change — a result 
 which is still better seen when a separate wash of cobalt 
 is laid over a wash of Prussian blue. In this case the 
 
INDIGO 
 
 241 
 
 light which has penetrated through the cobalt particles 
 would seem to have been deprived of those rays which 
 effect the decomposition of the Prussian blue beneath. 
 Such a phenomenon is not unusual, and has been ob- 
 served in the case of several pairs of pigments having 
 very closely-allied hues. 
 
 Indigo. 
 
 Indigo has been used either as a pigment or a dye from 
 very early times in India and in Egypt. It is referred to 
 under the name of indicmi by Pliny ; later on the Byzantine 
 writers called it azorium Romanim. ‘ Indigo bagadel ’ — 
 that is, indigo of Bagdad — is named as early as 1228 in 
 the Marseilles tariffs ; in the early English accounts rela- 
 ting to painting works (1274) it is called ‘ indebas.’ In 
 the fourteenth century it was designated as ‘ ind,’ ‘ inde,’ 
 and ‘ ynde.’ ‘ Endego ’ and ‘ indico ’ were used in the 
 sixteenth and seventeenth centuries. It was first largely 
 imported from India into Europe in the seventeenth cen- 
 tury by the Dutch. 
 
 A large number of different plants yield true indigo. 
 This pigment was once obtained in considerable quantity 
 from a crucifer, Isatis tinctoria, the dyers’ weed or woad, 
 the ‘ pastel ’ of the French ; but the chief source is now 
 Indigofeya tinctoria, a leguminous shrub, probably of 
 Indian, or at least Asiatic, origin. 
 
 Indigo (CjgHjpNgOj) does not exist ready-formed in the 
 plants which yield it, but occurs in the form of a colourless 
 compound, or ghicoside, which, by combining with water, 
 splits up into a sugar and indigo. It is prepared from the 
 freshly-cut plants, or from the dried foliage, by maceration 
 in water and fermentation, followed by boiling (sometimes 
 lime-water is first added) ; the dark precipitate which forms 
 
 16 
 
242 
 
 INDIGO 
 
 is thrown on to cloth-strainers, and finally pressed and 
 dried. The mineral impurities which commercial indigo 
 contains are derived partly from the plant itself, partly 
 from the water used in preparing it, and partly from the 
 lime-water above mentioned ; moreover, it is sometimes 
 adulterated. Indigo is easily oxidized by a very large 
 number of substances rich in oxygen, yielding a yellow 
 product called isatine ; it is converted into a colourless 
 body (CjgHjjNgOg) by many reducing agents. 
 
 Indeed, several of the processes of purifying indigo 
 depend upon the reduction of the blue colouring sub- 
 stance, or ‘ indigotin,’ into ' white indigo,’ and the subse- 
 quent precipitation of the blue matter by exposure to the 
 oxygen of the air. Green vitriol is the commonest reducing 
 agent, and is used in association with lime. The purified 
 indigo prepared by this process, though of fair colour, does 
 not, however, work so well as a paint as the best Bengal 
 indigo treated successively with acid, alkali, acid, and 
 alcohol. Indigotin, if quite pure, has a somewhat purplish 
 cast in thick water-colour washes ; this hue is observable 
 with this substance whether obtained by sublimation or 
 by Fritzche’s process with grape-sugar, caustic soda, and 
 alcohol. 
 
 The impurities in commercial indigo constitute from 
 20 up to 70 or 80 per cent, of its total weight — the 
 average is about 50. They consist mainly of mineral 
 matter, indigo red, indigo brown, and nitrogenous com- 
 pounds. Much of the mineral matter may be removed 
 by digestion in hydrochloric acid, followed by treatment 
 with boiling water. Sodium hydrate solution dissolves 
 the indigo brown, while strong alcohol takes away the 
 indigo red, which amounts to nearly 4 parts in 100 of 
 the original indigo. After treatment with these three 
 
INDIGO 
 
 243 
 
 solvents, the residual purified indigo is of an intense and 
 very beautiful hue. Java indigo is generally of very 
 good quality, that from Bengal comes next, and then 
 the indigo from Oudh, Kurpah, and Madras. Japanese 
 indigo is generally poor. 
 
 Indigo frequently receives no purifying treatment 
 previous to its being ground into a fine powder suitable 
 for admixture with oil or with gum and the other media 
 of water-colours. The necessity of choosing the purest 
 and finest samples of the commercial dye-stuff is of 
 course evident, but it is better in every case to adopt the 
 processes of purification named in the preceding para- 
 graph. No sample of purified indigo should leave, after 
 being burnt, more than 3 per cent, of ash. 
 
 This rich and transparent blue is, unfortunately, 
 gradually oxidized and browned when exposed to light. 
 In thin washes of water colour it disappears rapidly in 
 the sun’s rays, much more slowly when submitted to 
 diffused daylight. The following figures approximately 
 represent the reduction in force of a sample of indigo as 
 a moist water-colour when exposed to sunlight : 
 
 Original intensity ... ... ... 10 
 
 After two years ... ... ... i 
 
 After ten years ... ... ... o 
 
 Other trials with other samples gave in some cases less 
 unfavourable results. 
 
 Indigo in cake is sometimes less affected by sunlight 
 than the moist preparations. As an oil-colour, indigo 
 loses from one-third to one-half of its intensity when 
 exposed to sunlight for five years, its hue being at the 
 same time altered, in different specimens, either to a 
 greyish or a greenish blue ; the change is more con- 
 
244 
 
 INDIGO 
 
 spicuous when the indigo has been mixed in tint with 
 flake or other white. Locked up in copal or amber 
 varnish it is more slowly changed. The fading is due to 
 oxidation. 
 
 Indigo may be replaced advantageously by ultramarine 
 mixed with a trace of viridian, or by a good Prussian 
 blue, either being associated with a little ivory-black. 
 
 Several pigments, such as aureolin, true Naples yellow, 
 and all the chromates, have a very marked effect upon 
 indigo. 
 
 In order to ascertain whether the fading of indigo as a 
 water-colour, on exposure to sunshine, was increased by 
 the presence of alum in the paper, a series of comparative 
 experiments were made. A pale tint of indigo was 
 spread upon (i) paper free from alum; (2) paper washed 
 with alum solution ; (3) paper containing a trace of 
 alum ; (4) paper which had been washed with weak 
 ammonia- water after having received an alum -size. 
 After six months’ (April to September inclusive) exposure 
 to sunlight, all the four specimens showed complete 
 extinction of the blue pigment, the disappearance of the 
 colour from No. 2 having, however, been a trifle more 
 rapid than in the other cases. Honey and glycerin, 
 owing to their hygroscopic character, appear to hasten 
 the fading, so does water-vapour ; for a dried slip of 
 indigo-washed paper sealed up in a glass tube loses its 
 colour less quickly than one in its ordinary moist con- 
 dition, when both are exposed side by side to sunshine. 
 A tightly-framed water-colour drawing presents, of course, 
 a close analogy to the second or more unfavourable set of 
 conditions. When a medium tint of indigo on paper was 
 exposed for four years to sunlight in a tube containing air 
 kept dry by a water-absorbing agent, its original depth of 
 
INDIGO 
 
 245 
 
 colour was perfectly preserved. An identical experiment 
 
 in an ordinary glazed frame resulted in a reduction of 
 tone from 10° to 1°, while the residual hue was a greenish 
 
 grey. 
 
 The effect, if any, of the several iron reds, such as light 
 red, Venetian red, and Indian red, in accelerating the 
 fading of indigo in sunshine has been tested in many ways. 
 Provided the three red pigments above-named be free 
 from soluble salts, and especially from sulphates, they are 
 equally innocuous ; the indigo disappears with or without 
 them at the same rate. In one instance only a wash of 
 Venetian red with indigo lost its indigo completely three 
 weeks before the destruction of the blue in the parallel 
 experiments was complete, which was the case in six 
 months. It is impossible to assert that this result was 
 not due to a smaller amount of indigo having been pres- 
 ent in this particular case, but I believe it to have been 
 due to this sample of Venetian red having been an imita- 
 tive one prepared from colcothar. 
 
 In comparing under the same conditions the relative 
 stability, when exposed to light, of different indigoes, it 
 appears that ‘ Bengal refined ’ is superior to the best ‘ raw 
 Bengal,’ and even to the indigotins obtained by the green 
 vitriol and glucose processes. 
 
 The superiority, when exposed to light, of refined indigo 
 — that is, of indigo which has been purified by the treat- 
 ment with acid and the other solvents already named — 
 although observed in recent experiments, seems to have 
 been ascertained in the time of De Mayerne. One of the 
 authorities (Elias Feltz, of Constance) quoted by De 
 Mayerne affirms that this pigment may be rendered safe 
 by steeping it in vinegar and exposing it to the sun for 
 several days ; the vinegar is then to be poured off, and 
 
246 
 
 INDIGO 
 
 the paste when dry ground in oil. Another plan recom- 
 mended (in a note, dated 1642) by Feltz consists in grind- 
 ing the indigo with a little calcined alum ; this plan is, 
 however, objectionable for several reasons. The treatment 
 of the indigo with the solvents previously named, which 
 are adapted to remove its natural impurities, is the only 
 legitimate plan. It is scarcely necessary to add that there 
 is abundant evidence to prove that in De Mayerne’s day 
 indigo was generally regarded as an unstable colour. 
 Under all circumstances no indigo should be employed in 
 painting unless it be completely free from acids. 
 
 Although it is not possible to ascertain the exact rich- 
 ness in indigotin of commercial indigoes by any tests save 
 those in use by professional chemists, yet it is easy to 
 learn a good deal about any particular sample by means 
 of a few simple experiments. A good sample should 
 appear homogeneous, and should float on water. Dried 
 at 100° C., it should not lose more than 6 parts per 100 of 
 moisture. When rubbed with a hard smooth substance 
 it should show a coppery lustre. One hundred grains 
 when burnt should not leave more than 10 grains of grey 
 ash. It should dissolve perfectly in four times its weight 
 of fuming sulphuric acid. Starch, gypsum, clay, chalk, 
 steatite, and Prussian blue are amongst the adulterants of 
 indigo. 
 
 Indigo dissolved in four times its weight of fuming oil 
 of vitriol (kept cool) forms a liquid from which, after 
 slight dilution and filtration through asbestos cloth, potas- 
 sium carbonate precipitates a fine blue compound, which 
 has been used in water-colour painting under the name of 
 indigo carmine. It is not a safe pigment. 
 
 The artificial or synthetic indigo, although characterized 
 by freedom from impurities, both organic and inorganic, 
 
INDIGO 
 
 247 
 
 does not offer any advantages over the natural product, 
 if properly purified, when employed as a paint in water- 
 colour or oil. It may be added that those derivatives of 
 indigotin, in which some of the hydrogen atoms have been 
 substituted by bromine or chlorine, are no more perma- 
 nent than the original dyestuff. This is the case with 
 that form of dibrom-indigotin (the punicin of the late 
 H. E. Schunck), which occurs naturally in, or rather was 
 obtained from, certain marine molluscs [Purpura lapillus 
 and Murex hrandaris), and which has been known for 
 many centuries as Tyrian Purple. The very minute yield 
 of the natural pigment would have made its general use 
 impracticable, but now that the identical substance can 
 be freely made from indigo, it is found that its lack of 
 permanence should exclude it from the ‘selected’ palette 
 of the artist of to-day. 
 
 In examining old water-colour drawings, it will often be 
 found that the parts protected by the mount or frame show 
 the indigo used in compounding the greys of clouds and 
 the greens of vegetation perfectly intact, while it has com- 
 pletely left the exposed parts. In many cases where indigo 
 is supposed to have withstood long exposure to light, it 
 will be found that the blue used has been Prussian blue, 
 modified by admixture with other pigments. But in many 
 old pictures and drawings it will be found that the un- 
 natural bluish hue of the foliage represented is due to the 
 complete loss of rapidly evanescent yellows, rather than to 
 the entire stability of the indigo with which the greens have 
 been compounded. Nor must it be forgotten that indigo 
 was not the only blue in such mixed greens, blue carbonate 
 of copper and even lapis-lazuli having been extensively 
 employed at that time. The latter pigment is perfectly 
 permanent except in the presence of acids and alum. 
 
248 
 
 SMALT 
 
 Smalt : Royal Blue — Dumont's Blue — Zaffre — Bleu de 
 Smalte — Smalte — Zaffer. 
 
 Glass and vitreous mixtures containing cobalt, and of 
 a rich blue colour, have been known for ages, although 
 copper, not cobalt, was the colouring principle of most of 
 the antique materials of this class. The smalt now made 
 is a very deep-blue glass (appearing black in the lump), 
 consisting essentially of cobalt and potassium silicate. It 
 generally contains, in 100 parts, silica, 65 to 71 ; potash, 
 16 to 21 ; and cobalt oxide, 6 to 7 parts: a little alumina 
 is always present. In the inferior varieties the oxides of 
 iron and nickel always occur. 
 
 In order to prepare a pigment from the dark cobalt glass, 
 it is fused, and then poured into cold water. After the 
 disintegration thus effected, the glass is ground into a 
 moderately fine powder, and submitted to the process 
 called elutriation, or washing-over. The finest particles, 
 which take longest to settle from the wash-waters, are 
 the palest in colour ; the larger particles, though of richer 
 hue, are very difficult to use as a paint. 
 
 Smalt is rarely employed now as an artists’ pigment, 
 cobalt blue and artificial ultramarine having been very 
 advantageously substituted for it. For not only is it a 
 difficult pigment with which to work, in both water and 
 oil, but it is gradually altered by moisture and by the 
 carbonic acid of the air, becoming paler and greyer ; more- 
 over, the finer the state of division in which it exists, the 
 more rapid is the change. It will be found that even 
 spring or distilled water is competent to start the decom- 
 position of smalt. For if a little of this pigment be placed 
 on a'piece of yellow turmeric-paper, and moistened with 
 clean water, there will soon be formed a red stain beneath 
 
CHESSYLITE 
 
 249 
 
 the smalt — proof of the liberation of some of the alkaline 
 constituent (potash) of this blue glass. 
 
 Chessylite : Blue Verditer — Bice — Mountain Blue — 
 
 A zuvite — Cendves Bleues — Berghlau. 
 
 This copper mineral differs from malachite in containing 
 less hydrate, or more carbonate of the metal, its composi- 
 tion being represented by the formula aCuCOg, CuHgOj. 
 Its best-known locality is Chessy, near Lyon, in France, 
 but very fine specimens are found at Wallaroo and 
 Burra-Burra, in South Australia, and in the district of 
 Perm, Siberia. 
 
 This blue pigment has been prepared artificially, but 
 the natural substance is far less liable to change on 
 exposure to impure air. The introduction of cobalt blue, 
 and more particularly of artificial ultramarine, has 
 practically caused the disuse of blue verditer, or rather 
 of chessylite ( = azurite), this beautiful native blue pig- 
 ment, which, when used in illuminated manuscripts, as 
 was largely the case between the thirteenth and six- 
 teenth centuries, has kept its hue unimpaired to the 
 present day. 
 
 Under the name of Bleu Lumifere a beautiful turquoise- 
 coloured paint was introduced to artists. It consists 
 mainly of an artificial copper hydrate along with some car- 
 bonate. It becomes greenish by exposure to sunlight or 
 a very moderate degree of heat. Like all similar artificial 
 compounds of copper it proves to be untrustworthy. 
 
 Many old pictures, especially those in tempera, afford 
 evidence of the blue hydrato-carbonates of copper having 
 become green. With the extensive range of more per- 
 manent blues at the command of the modern artist, 
 there is no need to retain this pigment on the palette. 
 
250 
 
 BLUE PIGMENTS 
 
 Egyptian Blue. 
 
 A beautiful and permanent blue pigment, generally 
 known as Egyptian blue, has been studied by many 
 chemists. It is found on objects of Egyptian origin 
 from the time of the fourth Dynasty onwards, and 
 was in use during the time of the Roman Empire. 
 Specimens have been found in Pompeii and other Roman 
 sites; also in Britain, at Wroxeter, in Syria, and in 
 Crete. Our knowledge of this pigment has become more 
 exact in consequence of the researches* of Professor A. 
 P. Laurie, who has re-determined its chemical composi- 
 tion as well as its physical properties, and has, moreover, 
 ascertained the precise conditions under which it is pro- 
 duced. In one of Professor Laurie’s trials he took i8o 
 parts of fine sand, 48 copper carbonate, 36 calcium car- 
 bonate, and 20 parts of ‘ fusion mixture.’ A few grams 
 were submitted to definite temperatures in an electric 
 furnace for some hours, the mass being cooled, re-ground, 
 and re-heated. Finally it was found that the optimum 
 temperature for the production of the crystalline blue 
 was somewhere about 830° — 850° C. The crystals, 
 which are transparent and dichroic, and have a density of 
 3, consist of a double silicate of calcium and copper, 
 represented by the formula Cu0,Ca0,4Si02, but gener- 
 ally containing about 2 per cent, of potash and soda, as 
 substituents for a part of the copper and calcium oxides ; 
 the actual percentage of copper oxide present in the 
 pure blue is therefore usually somewhat lower than the 
 theoretical. It should be added that the interest at- 
 tached to the subject of Egyptian blue is rather academic 
 
 * Proceedings of the Royal Society, A. (1914), vol. 89, pp. 418-429. 
 
MANGANESE VIOLET 
 
 25 ‘ 
 
 than practical, for this pigment is not now made except 
 on a small laboratory scale, and has not found for many 
 centuries a place on the palette of the artist. 
 
 Manganese Violet: Mineral Violet — Permanent Violet - — 
 N iimhergerviolett . 
 
 This pigment is rarely met with on the palette of the 
 artist ; it is, however, quite permanent and has a truer 
 violet hue than cobalt violet, which is redder as well as 
 brighter. Its preparation is somewhat tedious. It is 
 made by means of manganous chloride and phosphoric 
 acid, solutions of these compounds being mixed together, 
 evaporated to dryness, and then the residual mass fused. 
 The fused mass is broken up and boiled with a solution 
 of ammonium carbonate. The turbid liquor is allowed 
 to settle, and then the clear portion is decanted or filtered 
 off and evaporated to dryness, and the residue fused. By 
 grinding the fused mass and boiling it with water a fine 
 precipitate of ‘ manganese violet ’ separates : it is re- 
 moved by filtration and thoroughly washed and dried. 
 It appears to be essentially manganous metaphosphate, 
 although by no means pure. 
 
 Two other violet or purple pigments of a permanent 
 character have been already described. One of these is 
 violet cobalt (page 211), the other violet ultramarine 
 (page 232). 
 
CHAPTER XVIII 
 
 BROWN PIGMENTS 
 
 Raw Umber: Levant Umber — Terre d’Ombre — Umbraun — 
 U m bra — T err a 0 mbra . 
 
 This earth is found in several localities; the best variety 
 has come for some time past from Cyprus. A consider- 
 able number of Cypriote specimens, of several nuances, 
 some excellent, were shown in the Colonial and Indian 
 Exhibition of 1886. It differs chemically from the yellow 
 and brown ochres in several particulars, notably in the 
 presence of a considerable quantity of one of the higher 
 oxides of manganese (Mn^O^, or Mn02), and in the small 
 proportion of water which it contains. Samples from 
 English localities are poor in iron ; one Derbyshire 
 specimen gave Mr. G. H. Hurst no less than 30 per 
 cent, of barium sulphate. An analysis of my own, made 
 with a choice sample from Cyprus, showed the following 
 percentages : 
 
 Water, lost at 100° C. - 4'8 
 
 Water, lost at a red heat*- 8 '8 
 Iron oxide (Fe203) - - 48'5 
 
 Manganese dioxide (Mn02) ig'o 
 Lime - - - - - i '4 
 
 Magnesia - 
 
 - o'5 
 
 Alumina - 
 
 - 21 
 
 Phosphorus pentoxide 
 
 - 09 
 
 Silica- 
 
 - 137 
 
 Carbon dioxide, etc. - 
 
 ■ 0-3 
 
 This sample had the peculiar greenish hue so much 
 
 * Includes a little organic or bituminous matter. 
 252 
 
RAW UMBER 
 
 253 
 
 prized by artists. It should be stated that a part of the 
 manganese probably existed as MogO^. 
 
 Before being used as a paint, this brown mineral is 
 finely ground, washed with water, and then dried at 
 ioo° C., or at a slightly higher temperature. When, by 
 a stronger heat, the whole of its water has been expelled, 
 
 the umber acquires a reddish hue, and is then the pig- 
 ment known as burnt umber. This change of colour is 
 due to the passage of the brown ferric hydrate into the 
 red ferric oxide, and to an increase in the proportion of 
 the red-brown manganese oxide present. 
 
 Raw umber in powder, after having been purified, soon 
 acquires a very slight reddish hue on exposure to light 
 and air ; it is a good plan to place the undried, finely- 
 ground mineral on trays in the sunshine before completing 
 its desiccation and mixing it with oil or other medium. 
 
 Raw umber is permanent when used with each or any 
 of the painting media : the slight yellowish or dull aspect 
 which it acquires in oil may be traced to the augmented 
 translucency of the paint, and to the yellowing of the 
 associated oil. Umber is without action on other pig- 
 ments. A very few samples of umber, used as a water- 
 colour, have been observed to fade slightly after from 
 five to ten years’ exposure to sunlight. But this 
 deterioration is due to the presence of traces of brown 
 peaty acids, or ‘ humus ’ substances, which occasionally 
 occur in the umbers from certain localities. 
 
 Raw umber possesses a semi-opaque, citrine-brown 
 colour ; it works and dries well in oil. Associated with 
 transparent blues, it yields soft, quiet green hues ; it is 
 invaluable both in figure and landscape painting. As a 
 priming or first painting-ground, it is apt, like most dark 
 pigments, to become more conspicuous in time, owing 
 
254 
 
 RA W SIENNA 
 
 chiefly to the translucency which the superimposed 
 painting gradually acquires. 
 
 Raw umber is not subject to adulteration, but a ferru- 
 ginous brown coal has been occasionally substituted for 
 the true mineral. The great variation in quality shown 
 by the umbers of commerce is due, in great part, to the 
 difficulty of securing, even from the same mine, con- 
 tinuous supplies of the same excellence. 
 
 Burnt Umber. 
 
 It has before been pointed out that raw umber, from 
 which burnt umber is prepared by calcination, is not an 
 ordinary ochre, but owes its colour in great measure to 
 the presence of a considerable amount of some compound 
 of manganese. The exact constitution of raw umber is 
 not, however, known, although the slight change in hue 
 which occurs when it is roasted negatives the idea that 
 it contains any considerable proportion of the ordinary 
 ferric hydrates. If these were present in notable propor- 
 tions, roasting would certainly redden raw umber much 
 more than is actually the case. 
 
 Burnt umber differs in quality and hue from the raw 
 earth mainly in being more translucent, and of a warmer 
 brown. Although some Continental authorities affirm 
 that this pigment darkens and becomes purplish in course 
 of time, I cannot regard it as otherwise than perfectly 
 permanent, and as exerting no action on stable pigments. 
 
 Raw Sienna : Ter ye de Sienne — Terra di Siena — Rohe 
 Sienna. 
 
 This earth, which is found chiefly in Tuscany and the 
 Hartz, is a particularly rich variety of yellow ochre, and 
 contains a large proportion of a ferric hydrate. The late 
 
RA W SIENNA 
 
 255 
 
 G. H. Hurst (‘ Chem. News,’ vol. lix., p. 172) gave three 
 analyses of raw sienna. In these the range in the 
 percentages of the more important constituents is as 
 follows : 
 
 Raw sienna is prepared for use by crushing, sifting to 
 remove sand, grinding and washing in the same way as 
 in the case of yellow ochre. It should be noted that 
 when lumps of fresh raw sienna are first broken and 
 exposed to the air, their surfaces acquire a slight olive- 
 green nuance. In order to avoid any disadvantage which 
 might arise from such an alteration taking place subse- 
 quently, it is a good plan to expose the crushed earth to 
 the air and light previous to its final preparation as a 
 pigment. Before grinding it in oil, it should be cautiously 
 dried at 60° C. to remove the greater part of the accidental 
 or hygroscopic moisture. 
 
 Raw sienna in thick washes is somewhat deeper in 
 tint and of a warmer and browner hue than yellow ochre. 
 Owing to a trace of organic or peaty matter which it 
 contains, raw sienna is liable to become rather less brown 
 and more yellow by long-continued exposure to strong 
 light. It is generally without action on other pigments, 
 and is available for water-colour, oil, and tempera paint- 
 ing ; it sometimes fails in fresco. A given weight of raw 
 sienna requires a larger proportion of oil than any other 
 pigment ; the finished oil-paint contains only 30 per cent, 
 of pigment. 
 
 Manganese dioxide 
 Iron oxide (FegOg) 
 Silica ... 
 
 Hygroscopic water 
 Combined water* 
 
 8-2 to 17-5 
 g-o „ 12-4 
 0-6 „ 1-5 
 
 45-8 „ 597 
 5'o .. i7'4 
 
 Includes traces of organic matter. 
 
256 
 
 CALEDONIAN BROWN 
 
 Raw sienna is not subject to adulteration, but it is well 
 to be certain that the pigment has been well washed. 
 
 Burnt Sienna, 
 
 The roasting or calcination of raw sienna produces a 
 very great change in its hue as well as in the depth of its 
 colour. The ferric hydrate of the raw earth becomes 
 wholly converted into ferric oxide, this change being 
 accompanied by a great increase in the translucency and 
 depth of the colour. 
 
 When small fragments (or the coarse powder) of raw 
 sienna are calcined, it will be noticed that the change of 
 hue which occurs is not quite uniform, some points being 
 of a brighter and redder brown than others. A very fine 
 powder, thoroughly stirred during roasting, shows this 
 peculiarity in a much less marked degree. 
 
 Burnt sienna possesses a very beautiful, warm, reddish- 
 brown hue, which cannot be exactly imitated in trans- 
 lucency and depth by mixtures of other pigments. It is 
 permanent, without action on other pigments, and not 
 liable to adulteration. It is available for use in every 
 method of painting. Some fine and permanent foliage- 
 greens may be made by associating viridian with burnt 
 sienna. 
 
 Caledonian Brown. 
 
 This brown, although a natural earth, presents very 
 much the appearance of burnt sienna. It contains a 
 small quantity of combined moisture. It consists mainly 
 of the brown hydrates and oxides of manganese and iron. 
 When calcined it loses its ruddy hue and becomes almost 
 black — a black with a slight brownish hue. 
 
 Caledonian brown, whether raw or burnt, is a per- 
 
VANDYKE BROWN 
 
 257 
 
 manent and innocuous pigment, which is well adapted 
 for oil and tempera painting. It is said that the original 
 source of this pigment is exhausted, and that an imita- 
 tive mixture of burnt sienna and bituminous Vandyke 
 brown is sold in lieu of Caledonian brown. 
 
 Vandyke Brown. 
 
 Three brown pigments pass in commerce under the 
 name of Vandyke brown. The first is made by calcining 
 certain very ferruginous earths or brown ochres ; the 
 second is nothing more than a dark-brown variety of 
 colcothar ; the third is a kind of brown earth containing, 
 along with some iron oxide and hydrate, a good deal of 
 organic substance in the form of humus or bituminous 
 matter. The first and second kinds are permanent and 
 innocuous, but the third kind will not resist the pro- 
 longed action of light, becoming paler and redder in the 
 course of time. The discrepancies in the published state- 
 ments as to the permanence of this pigment are thus 
 readily explained ; it is to be regretted that most of the 
 samples of Vandyke brown now met with in England 
 belong to the third kind, and therefore fade quickly in 
 water-colour, more slowly in oil. This sort may be 
 recognised by the dark sublimate which it yields when 
 its powder is heated in a test-tube, as well as by the 
 change in colour and great loss of weight which it then 
 shows. We shall designate this less satisfactory variety 
 in the Tables of Permanent and Fugitive Pigments in 
 the present volume as Vandyke brown B., the other kinds 
 being called Vandyke brown A. It is unfortunate that 
 the colour-value of the perishable variety is incom- 
 parably greater than that of the more permanent sort. 
 
 17 
 
258 
 
 CAPPAGH BROWN 
 
 Cologne or Cullen earth, and Cassel brown or Cassel 
 earth, are soft, impure varieties of brown coal or lignite. 
 They vary in fixity, some of them being even more easily 
 bleached by light than Vandyke brown B. ; these should 
 not find a place on the palette of the artist. When 
 slightly roasted, a part of the brown organic matter in 
 these earths is charred or carbonized, and the substance 
 becomes darker, duller, and decidedly less alterable by 
 exposure. Some of the so-called Cologne earth now sold 
 is merely Vandyke brown B., slightly changed by gentle 
 roasting ; it is then rather less alterable. We have met 
 with some specimens of Cassel earth which proved prac- 
 tically permanent in oil, but even these faded quite 
 distinctly when exposed to strong light after having been 
 mixed with flake-white. 
 
 Cappagh Brown: Eiichrome — Mineral Brown. 
 
 This earth was found on the estate of Lord Audley, in the 
 Cappagh Mine, which was opened in the year 1814, and is 
 situated about ten miles west of the town of Skibbereen, in 
 the county of Cork. In composition and general characters 
 it resembles raw umber, but has a more reddish hue. It 
 contains ferric hydrate and ferric oxide, with a consider- 
 able amount of one of the oxides or hydrates of manganese. 
 It gives off a good deal of water when heated to 100° C., 
 and acquires a rich reddish-brown colour, not unlike that 
 of burnt sienna, and almost identical with that of Cale- 
 donian brown. The specimens examined contained mere 
 traces of organic matter, so that it cannot be regarded as 
 a kind of bog-earth or peat, although it is, of course, 
 possible that there may be another mineral found in the 
 same locality which might be correctly so designated. The 
 
BISTRE 
 
 259 
 
 following analysis represents the composition in 100 parts 
 of a characteristic specimen of this pigment : 
 
 Water, lost at 100° C. - 187 Alumina ... - 2 6 
 
 Water, lost at a red heat - n '6 i Lime i i 
 
 Iron oxide (Fe203) - - 34'4 j Silica - - - - - 4 ’6 
 
 Manganese dioxide (MnOj) aya | Phosphorus pentoxide(P20j) o‘4 
 
 It is probable that a part of the manganese really exists 
 in the form of the red oxide (MngOJ, and a part of the iron 
 as ferrous oxide (FeO). I have, however, calculated both 
 these metals into their higher oxides. In this way it 
 happens that the added percentages exceed 100, even when 
 the traces of magnesia and potash present in Cappagh 
 brown are not included in the total. The large quantity of 
 water present in this mineral in a loosely-attached form 
 (hygroscopic), amounting to nearly one-fifth of the weight 
 of the pigment, indicates the desirability of cautiously 
 drying the substance previous to grinding it in oil. A 
 temperature of 60° C. should not be exceeded. 
 
 Cappagh brown works well in oil, particularly if it be 
 dried at a heat below that of boiling water before it be 
 ground in oil. It is an innocuous pigment, but its perma- 
 nence has scarcely been sufficiently tested. A rub of 
 Cappagh brown in oil, exposed to strong sunlight for 
 one month, lost a little of its yellow, assuming a some- 
 what ruddier hue ; the change, however, was very slight, 
 and did not appear to have increased after continued 
 exposure for five months more. 
 
 Bistre : Bister — Brauner Lack — Russbraim. 
 
 Bistre is prepared from the tarry soot of certain woods, 
 especially from that of beech-wood, by the following pro- 
 cess : The soot is finely ground and sifted, and then the 
 
26 o 
 
 ASPHALTUM 
 
 powder is digested with successive portions of hot water 
 until the latter no longer acquires a brown or yellow tint ; 
 the residue is then ground with suitable quantities of gum- 
 water and glycerin, and preserved in the moist state. To 
 form cake-bistre the glycerin is omitted, but more gum is 
 employed. Bistre is not used as an oil-colour. 
 
 The tarry matter in bistre is its element of weakness. 
 By exposure to strong light this tarry matter oxidizes, and 
 the residual pigment becomes cooler in hue and paler. 
 Professor Ogden Rood, experimenting with a weak water- 
 colour wash of bistre, found that it lost ig parts of its 
 original intensity of 25 by an exposure of three and a 
 half months to the summer sun. I have not found so 
 considerable a change to occur with the samples of bistre 
 which I have tried ; but this pigment varies much in 
 composition, being obtained from the soot of different 
 woods as well as from that of peat. The most fugitive 
 preparations are those made from samples of soot con- 
 taining the highest proportions of tarry matters. 
 
 Asphaltum : Bitumen — Mineral Pitch — Antwerp Brown — 
 Mummy — Mumie. 
 
 Asphalt, asphaltum, or mineral pitch, has long been 
 used as a pigment. The best known is that from the 
 Dead Sea (^Lacus asphaltites). Other abundant sources of 
 this carbonaceous mineral occur in Trinidad ; Caxitambo 
 and Berengela, in Peru; Val de Travers, Neufchatel; 
 Avlona, in Albania, etc. 
 
 Asphalt is rather a mixture of minerals than a single 
 mineral ; it is, moreover, very variable in the nature, 
 character, and proportion of its constituents. Essentially 
 it consists of a number of liquid, semi-solid and solid, 
 colourless hydrocarbons (related to the paraffins), asso- 
 
ASPHALTUM 
 
 261 
 
 ciated with certain ill-understood dark-brown or black 
 substances, which constitute the useful part of the raw 
 material. The best varieties for artistic use are those 
 which contain the smallest proportion of the above- 
 described hydrocarbons, for to the presence of these the 
 treacherous character of asphalt as a pigment is due. On 
 this account the hardest, most earthy and most brittle 
 kinds should be chosen, and the crushed samples should 
 always be submitted to a temperature of at least 250° C. 
 before being ground in oil or turpentine. The operation 
 of roasting native asphalt — keeping it over a slow fire 
 ‘ till it will boil no more and becomes nearly a cinder ’ 
 — was recommended by Williams in his ‘ Essay on the 
 Mechanic of Oil-Colours’ (1787), and furnishes a perfectly 
 satisfactory and safe product. 
 
 If carefully-selected asphalt be submitted to either of 
 the processes named above, and then be moistened with 
 spirits of turpentine, and ground in drying-oil (prepared 
 with borate of manganese), a paint is obtained which 
 neither cracks nor moves on the canvas like the unpurified 
 material. Its fixity is further ensured by mixing it with a 
 little copal varnish, and more particularly by associating 
 it with a denser pigment, such as umber or flake-white. 
 It is superior to the imitative asphalts made from coal- 
 tar, now largely sold in lieu of the original and genuine 
 product. The disadvantages attending the use of these 
 coal-tar browns and of ordinary asphalt are two-fold. 
 Not only are they treacherous on account of their easy 
 fusibility, but they are liable to stain contiguous pigments 
 by reason of their solubility in oil or varnish. When 
 used successfully by the older artists they were always 
 introduced sparingly, or were largely commingled with 
 more solid paints. 
 
262 
 
 ASPHALTUM 
 
 ‘ Mummy,’ as a pigment, is inferior to prepared, but 
 superior to raw, asphalt, inasmuch as it has been sub- 
 mitted to a considerable degree of heat, and has thereby 
 lost some of its volatile hydrocarbons. Moreover, it is 
 usual to grind up the bones and other parts of the mummy 
 together, so that the resulting powder has more solidity 
 and is less fusible than the asphalt alone would be. A 
 London colourman informs me that one Egyptian mummy 
 furnishes sufficient material to satisfy the demands of his 
 customers for twenty years. It is perhaps scarcely neces- 
 sary to add that some samples of the pigment sold as 
 ‘ mummy ’ are spurious. Mummy was certainly used as 
 an oil-paint at least as early as the close of the sixteenth 
 century. 
 
 Asphalt, after having been heated to drive off the 
 hydrocarbons previously alluded to, cedes to ammonia a 
 considerable quantity of a dark-brown colouring-matter, 
 which in this way may be made available for water-colour 
 painting. The ammoniacal solution is either evaporated 
 slowly, to the consistence of a thick syrup, after the addi- 
 tion of a little gum and glycerin, or it is precipitated with 
 acetic acid, and the precipitate (after washing) is mixed 
 with gum and glycerin, and then partially dried until it 
 has acquired a suitable degree of consistency. But the 
 water-colour paint thus made is not permanent. 
 
 Merimee’s process for preparing asphalt for use as an 
 oil-colour cannot be recommended. He introduces shellac, 
 white wax, and Venice turpentine into the mixture, as 
 well as a large proportion of boiled linseed-oil. This 
 preparation constitutes a very treacherous pigment. 
 
PRUSSIAN BROWN 
 
 263 
 
 Prussian Brown. 
 
 This pigment, as usually met with in commerce, con- 
 tains a considerable quantity of a soluble salt of potash, 
 and is not fitted for the use of artists. But this impurity 
 need not be present, as it may be removed by a thorough 
 washing of the powdered colour with boiling water. A 
 still better plan is to prepare Prussian brown from one 
 of those varieties of Prussian blue which contain no 
 potassium. It is made by throwing small pieces (the size 
 of hazel-nuts) of Prussian blue upon a plate of iron main- 
 tained at a red heat. Each fragment burns like tinder, 
 and if care be taken to employ the right heat for the 
 proper time, will show a mixed hue, partly yellowish 
 brown, partly reddish brown, and partly black. The 
 product, still hot, is thrown into water, ground, washed, 
 and dried. Prussian brown thus made has a rich 
 colour of considerable translucency and good drying 
 character. In hue it is warmer than asphalt. It is quite 
 permanent. 
 
CHAPTER XIX 
 
 BLACK PIGMENTS 
 
 Indian Ink: Chinese Ink — Japanese Ink — Encve de Chine 
 — Chinesische Tusche. 
 
 This ink has been prepared in China for at least 2,000 
 years. It consists essentially of a very fine lamp-black, 
 associated with gelatin, and scented with musk, camphor, 
 cloves, or rose-water. The lamp-black employed is 
 derived from the imperfect combustion of oil or of pine- 
 wood. The oils chiefly used are those of Sesamum indi- 
 cum, Cannabis sativa, and Dvyandvia cordata; but in some 
 factories rape-oil, bean-oil, or the oil of Gleditschia sinensis 
 is employed. According to the treatise of Chen-ki-suen, 
 which was written a.d. 1398, these oils are burnt in 
 small earthenware lamps in the presence of a limited 
 supply of moist air. The smoke is collected in earthen- 
 ware conical covers; from these the condensed soot is 
 removed at short intervals, care being taken to preserve 
 those portions only which are free from tarry products. 
 The soot is finally sifted, and reduced to an extremely 
 fine powder. Lac-resin, rock-oil, as well as many kinds 
 of wood, have been employed for the preparation of this 
 carbonaceous basis of China ink in different parts of the 
 empire, and at different times. It would appear that 
 from all of these combustibles, if due care be taken, an 
 
 264 
 
INDIAN INK 
 
 265 
 
 excellent product may be obtained. The next step in 
 the manufacture consists in the incorporation of the soot, 
 prepared as above described, with the necessary amount 
 of size. The size employed should be made from a 
 mixture of clean fish-glue and parchment-size ; this is 
 thoroughly mixed, while warm, with the fine soot. The 
 paste thus formed is made into balls, which are heated 
 for some time at the temperature of boiling water, and 
 then fashioned roughly into sticks. These are subjected 
 to repeated blows — some hundreds, at least — from a 
 hammer ; they are re-heated occasionally during this 
 operation, in order to prevent them from becoming hard. 
 The perfume, consisting of musk and camphor, mixed 
 with a little rose-water, is incorporated with the mass. 
 The material, after further pounding and beating, may 
 then be pressed into the wooden moulds which are to 
 give it its final form. A tedious process of drying 
 follows next, the sticks of ink being finally packed in 
 the ash of rice-straw frequently renewed. After the 
 removal of adhering ash, the sticks are cleaned, gilt or 
 otherwise ornamented, and polished with an oily brush. 
 
 If the soot used in the manufacture of this ink be con- 
 taminated with tarry or empyreumatic matters, it yields 
 a brownish-black product ; the purer and the finer the 
 state of division of the carbon, the more intense is the 
 black, and the more neutral are the greys which it yields 
 on dilution with water, or by admixture with opaque 
 white pigments. 
 
 There are many qualities of this ink made in China. 
 The best kinds are hard and homogeneous ; they show a 
 lustrous black fracture, and, when rubbed with water, 
 do not give rise to the separation of any curdy particles. 
 Those having, in tint with water, a bluish or violet tinge 
 
266 
 
 INDIAN INK 
 
 are the most esteemed ; the pure black come next, and 
 the brownish or yellowish black last. 
 
 A stick of Indian ink should be rubbed on the palette, 
 in straight lines, backwards and forwards. A very con- 
 venient ink-slab for this purpose forms part of the fittings 
 of the Japanese writing-case or box, called ‘ suzuri-bako.’ 
 It consists of an oblong block of dark slate, in which a 
 sloping cavity has been hollowed out. The slight 
 ‘ tooth,’ or roughness of the surface, greatly helps the 
 rubbing-down of the ink. A strong wash of this ink, on 
 sized paper, should not be affected, when once dry, by 
 having water brushed freely over it. Bluish-black and 
 pure black Indian ink is permanent under prolonged 
 exposure to sunlight or impure air ; but the brownish 
 varieties become paler, less brown, more neutral, by 
 the action of light. Like most carbonaceous matters, 
 Indian ink occasionally tends to absorb to a small 
 extent some of the organic pigments which may be 
 brought into contact with it in the process of colouring a 
 drawing. 
 
 Indian ink is available for tempera-painting, but can- 
 not be used with oil. 
 
 Indian ink has been imitated with fair success in 
 France. The chief difficulty in preparing it seems to 
 lie in the preparation of a suitable gelatinous medium 
 with which to mix the purified lamp-black. A size 
 prepared from washed fish-glue (by partial precipitation 
 with tannin, and subsequent solution of the precipitate 
 in more size) affords a good binding material. The size, 
 in true Chinese ink, forms a very large part of the total 
 weight, varying from one-fourth to over one-third ; but 
 the European imitations rarely contain as much. Japan- 
 ese ink is generally inferior to Chinese. 
 
LAMP-BLACK 
 
 267 
 
 Chinese amateurs sometimes form collections of rare 
 and old kinds of Chinese ink, occasionally giving for 
 sticks bearing the marks of renowned makers not less 
 than their weight in gold. Such specimens are prized 
 for their rarity, not on account of any special merits 
 as pigments v»?hich they may possess ; and a Chinese 
 ink collector regards it as an unpardonable offence to 
 moisten any of his specimens with a view to testing their 
 quality. 
 
 Lamp-Black ; Noir de Lanipe — Noiv de Fumee — Noir de 
 Houille — Russ — Lampenschwartz. 
 
 When resins, resinous woods, fatty oils and fats, 
 paraffin and paraffin oil, or coal-tar oils, are burnt with 
 an insufficient supply of air, a considerable part of the 
 carbon they contain may be deposited in the form of soot. 
 This soot is not, however, pure carbon, but retains 
 variable proportions of the tarry products of imperfect 
 combustion or destructive distillation ; these impart to 
 lamp-black a more or less pronounced warm brownish 
 hue, except in the cases in which it has been prepared 
 by processes specially devised to intercept the tarry 
 and oily products in question. Sometimes small fur- 
 naces, sometimes large lamps with long wicks are 
 employed in its manufacture, the soot given off being 
 collected in two or more receivers ; the soot first de- 
 posited contains the larger part of the impurities. This 
 point may be illustrated by the simple experiment of 
 depressing a white porcelain plate into the flame of a 
 candle ; the nearer the plate to the wick, the browner 
 will be the soot deposited. 
 
 Lamp-black carefully made is an unalterable pigment ; 
 
268 
 
 CHARCOAL-BLACK 
 
 but its employment for pictorial purposes has frequently 
 been objected to by writers on artistic practice as 
 tending to heaviness and opacity in the shadows. 
 With the exception of a few pigments of organic 
 origin, which in water-colour painting have a tendency 
 to cede some of their colouring matter to any kind 
 of carbonaceous black, lamp-black exerts no injurious 
 influence upon any pigments which are stable when used 
 alone. 
 
 Numerous carbonaceous substances have been used as 
 black or brown-black pigments. Amongst these anthracite 
 and common bituminous coal may be named. Van Man- 
 der and De Mayerne both mention forge or pit coal. Black 
 shales and black slates have long been employed in the 
 preparation of dark grey pigments. These minerals owe 
 their colour in part to carbon or compounds of carbon, 
 in part to very finely divided iron pyrites. They are 
 permanent, so far as the carbon present is concerned. 
 
 Charcoal-Black ; Blue-Black — Vine-Black — Frankfort- 
 Black — Noir de Vigne — Rebschwartz. 
 
 When non-resinous woods and woody tissues are 
 strongly heated in crucibles or other almost completely- 
 closed vessels, the residue contains the greater part of the 
 carbon of the original material, and preserves its form. 
 As the charcoals thus made contain some soluble mineral 
 matter, particularly potash salts, they should be coarsely 
 ground and thoroughly washed with hot water previous to 
 their being finally converted into paints. They are also 
 hygroscopic, and therefore need to be dried before being 
 ground in oil. 
 
 Amongst the best materials for producing these char- 
 coal or vegetable blacks may be named the hard shells or 
 
CHARCOAL-BLACK 
 
 269 
 
 stones of plums, almonds, and similar fruits; coco-nut shell 
 broken into small pieces; cork cuttings, and the twigs of 
 beech and shoots of vine. Coco-nut yields the densest, 
 most velvet-like black ; vine-shoots a less solid black, 
 having a bluish hue. Washed wine-lees yield a rich black 
 — Frankfort-black. 
 
 When charcoal has been prepared at a sufficiently high 
 temperature, and then has been thoroughly washed, there 
 is no question as to its permanence as a pigment in all 
 media. But if it retains tarry matters, or has been im- 
 perfectly carbonized, then it may become greyer or less 
 brown (when used in thin washes) after long exposure to 
 light. This change is due to the oxidation of the tarry 
 matters, or of the brown substances which are interme- 
 diate in composition between the original vegetable 
 materials and the carbon, which is the final product of 
 their torrefaction out of contact with the air. And one 
 peculiar property, possessed in varying degrees by char- 
 coal of every kind, must not be lost sight of. Charcoal 
 withdraws the majority of organic colouring matters from 
 suspension, and even from solution in water. A pale tint 
 of rose-madder in water, if a pinch of coco-nut or vine- 
 black be added, becomes rapidly decolourized, the pig- 
 ment being completely absorbed, although not really 
 destroyed. Animal charcoal (bone-black, ivory-black) 
 exerts a still more energetic action of this character ; 
 but lamp-black is less powerful. 
 
 It is to be regretted that the beautiful bluish blacks, 
 derived from such materials as the shoots of the vine and 
 beech, are frequently fraudulently imitated by mixtures of 
 lamp-black and indigo. The purple vapours of indigotin, 
 given off when such a mixture is heated in a test-tube, 
 betray the adulteration at once. 
 
270 
 
 IVORY BLACK 
 
 Ivory Black : Noir d’Ivoire — Elfenheinschwartz. 
 
 Waste ivory, in the form of turnings, shavings, and saw- 
 dust, if charred in closed vessels, leaves a black residue, 
 which, however, consists essentially of bone-earth (calcium 
 carbonato-phosphate), stained by the presence of a few per 
 cents, of carbon. On exposure to the air, ivory black 
 absorbs, not only the gases of the atmosphere, but also a 
 very considerable proportion of moisture. On this account 
 ivory black, just previous to its being ground in oil, should 
 always be thoroughly dried. As this substance has a strong 
 decolourizing power when placed in contact with moist 
 organic pigments, it is better adapted for use in oil paint- 
 ing than with water colours. This decolourizing property 
 belongs also to the animal blacks obtained by charring 
 horn and bone shavings — products which are frequently 
 substituted for genuine ivory black. Sir Charles Eastlake 
 tells us that in a collection of specimens of water-colour 
 tints inserted in the Mayerne manuscript the ‘hartshorn’ 
 black, made from cormi cervinimi, remains very intense. 
 
 Ivory and bone black are perfectly permanent black 
 pigments ; the latter is quite free from the bluish tinge 
 which characterizes most of the vegetable charcoals. 
 Both are better adapted for oil than for water-colour 
 painting, for which vine black is preferable. 
 
 Black Lead : Plumbago — Graphite — Graphit. 
 
 The material of which so-called black-lead pencils are 
 made is essentially nothing but one of the three forms in 
 which the element carbon occurs ; diamond is another ; 
 lamp-black may be taken as a good representative of the 
 third form. Graphite is the most appropriate name for 
 the mineral commonly known as black lead, but which 
 
GRAPHITE 
 
 271 
 
 in reality contains no lead, and is in no way related to 
 that metal. Graphite was found of good quality at 
 Borrowdale in Cumberland, a locality which has been 
 stated, probably erroneously, to be now exhausted ; but 
 excellent supplies of this mineral come from the Albert 
 Mine, Siberia, Mount Alibert in the Ural, Ceylon, and 
 many other places. Graphite, however, is never found 
 in a state of perfect purity, always leaving, when burnt, 
 some incombustible matter or ash. 
 
 In order to prepare graphite for use as a pigment, the 
 purest pieces should be selected ; these should be at first 
 broken into small fragments in order that obviously con- 
 taminated bits may be rejected before the material is 
 ground. Inferior qualities of graphite may be purified 
 by being coarsely ground, and then heated with strong 
 hydrochloric acid to remove iron and alumina. After 
 washing, the thus-far purified material should be placed 
 in a leaden or platinum vessel and gently warmed with 
 a solution of hydrofluoric acid to remove silica. The 
 graphite, after this treatment, is to be washed with 
 abundance of water, and ground to a very fine powder, 
 which is then ready for admixture with gum water or, 
 after drying, with oil. The addition of a little china clay 
 during the grinding of graphite in oil tends to produce a 
 more manageable paint. 
 
 Graphite has a very dark-grey colour, and forms pure 
 tints of grey with white pigments. It is equally well 
 adapted for use in water-colour, oil, fresco, and tempera 
 painting. It is absolutely permanent, and without action 
 on other pigments. 
 
 Graphite is sometimes adulterated with charcoal or 
 lamp-black. When a very thin layer of the suspected 
 pigment — freed from oil or other vehicle — is spread on a 
 
272 
 
 SEPIA 
 
 piece of platinum foil and strongly heated over a lamp^ 
 the lamp-black will burn away, leaving the true graphite 
 unaltered. If a change of hue or tint occurs, this is a 
 sign of the presence of the above-named adulterant. 
 
 Sepia. 
 
 The dark-brown colouring-matter from the ink-bag of 
 Sepia officinalis, Loligo tunicata, and other species of cuttle- 
 fish common in the Mediterranean and Adriatic, has not 
 been thoroughly investigated from a chemical point of 
 view. The pure pigment, which constitutes four-fifths 
 of the weight of the dried ink-bags as they occur in com- 
 merce, partakes of the character of a weak organic acid, 
 and is soluble in alkalies and precipitated by acids. In 
 preparing the substance for artists’ use, it is commonly 
 first removed from the sacs containing it, dissolved in 
 soda or ammonia solution, and then, after straining the 
 solution, thrown down by neutralizing the alkali with 
 hydrochloric acid ; the precipitate is then washed by de- 
 cantation, and dried. Sometimes the filtered ammoniacal 
 solution is used directly as a liquid ink. The chief 
 impurities of the natural sepia are salts of lime and 
 magnesia, which may be partly removed by washing the 
 dried and crushed sepia first with dilute hydrochloric 
 acid and then with water, previous to dissolving it. 
 
 Sepia is of a redder or warmer brown hue than bistre, 
 but it is not so reddish as Vandyke brown. Of these 
 three pigments, there is no question that sepia is the least 
 alterable. It is not, however, permanent when exposed 
 to sunshine, although in darkness or in diffused daylight 
 it suffers no appreciable change either in depth or quality. 
 It might, indeed, have been supposed that sepia would 
 prove unalterable, from the consideration of the observed 
 
SEPIA 
 
 273 
 
 fact of the pigment from the ink-bags of fossil cuttle-fish 
 showing now, when used as a water colour, the same 
 hue and the same chemical characters as recent sepia 
 from the Mediterranean cuttle-fish of to-day. But it 
 must be recollected that this fossil pigment has been 
 excluded completely from the adverse influence of light, 
 and in great measure from that of air, during the long 
 ages which have elapsed since it was embedded in rock. 
 And it is light which, in the case of the majority of 
 organic pigments, is the determining cause of the changes 
 brought about by the combined presence of moisture and 
 atmospheric oxygen. 
 
 Sepia is not employed as an oil colour. 
 
 There are several grey pigments which, being com- 
 pounded of other paints already described, need hardly 
 be mentioned here. Amongst these are neutral tint and 
 Payne’s grey, which in water-colour are still prepared 
 by commingling indigo, crimson lake, and ivory black, 
 but which have been replaced in oil by artificial ultra- 
 marine, ochre and ivory black — an entirely trustworthy 
 mixture. Slate grey, prepared from a rather soft and 
 very dark-coloured slate, is a satisfactory pigment both 
 in artistic quality and in stability. 
 
 18 
 
CHAPTER XX 
 
 CLASSIFICATION OF PIGMENTS 
 
 The painter naturally classes pigments according to their 
 colour, or more exactly according to what are called the 
 constants of colour — namely, hue, brightness and purity. 
 He also takes into account transparency and opacity, 
 although these terms are conventional and comparative 
 only, since no pigment is perfectly transparent, none 
 perfectly opaque. Another basis of classification, and a 
 very important one, that of stability, will be considered 
 in the next chapter ; at present we are concerned with 
 none of these methods of grouping pigments, but with 
 others founded either upon their origin, or their physical 
 characters, or their chemical composition. 
 
 Pigments are often classified into two groups — the 
 mineral, and the organic. It is necessary to divide these 
 groups further, in some such way as this : 
 
 Mineral Pigments. 
 Organic Pigments. 
 
 / Natural ; as ochre, terre verte, ultramarine. 
 \ Artificial ; as aureolin, viridian, cobalt blue. 
 / Animal : as Indian yellow, carmine, sepia. 
 
 \ Vegetable ; as gamboge, sap green, indigo. 
 ’ Artificial : as Prussian blue, verdigris. 
 
 Such a classification brings into prominence one 
 marked distinction between the two groups, for, in 
 accordance with one’s expectation, the mineral pigments 
 
 274 
 
CLASSIFICATION OF PIGMENTS 
 
 275 
 
 are, as a rule, characterized by a much higher degree of 
 permanence than those of organic origin. [The chemist 
 looks upon all compounds containing carbon, save the 
 carbonates, as organic ; but at the same time the dis- 
 tinction between organic and inorganic, or organic and 
 mineral, is nothing more than a convenient convention ] 
 
 Other bases of classification are afforded by physical 
 or mechanical characters. Pigments may be fixed or 
 volatile, soluble or insoluble, crystalline or amorphous, 
 substantive or adjective. There are difficulties in carry- 
 ing out these schemes of classification, and it will be 
 found that distinctions of physical character are utilized 
 to the best purpose when connected with such a chemical 
 classification as is offered below. 
 
 The simplest chemical classification is this : 
 
 Elements ; as graphite, lamp-black, gold. 
 
 Compounds ; as aureolin, viridian, vermilion. 
 
 Mixtures; as yellow ochre, brown pink, rose madder. 
 
 After considerable expansion and some rearrange- 
 ment, the differences just indicated afford a reasonable 
 basis for a chemical classification which will prove of 
 real service in judging of the degrees of stability, and of 
 the possible interaction of pigments.* The mixed and 
 
 * In a pamphlet by M. Paul de Lapparent there is an ingeniously 
 constructed diagram giving, at one view, a list of pigments which, 
 in the judgment of the author, react upon one another. If we omit 
 from the list red lead, we shall be able to cancel nearly one-third 
 of the black marks assigned to mixtures of two pigments ; but we 
 shall still include two conspicuous offenders, namely, pale cadmium 
 and Prussian blue. Pale cadmium is stated to be incompatible 
 with Indian red, Venetian red, burnt sienna, the native earths, 
 ivory black, Prussian blue, and cobalt violet ; while Prussian blue 
 is marked as affecting, or as affected by, Venetian red, burnt sienna, 
 deep cadmium, orange cadmium, pale cadmium, aurora yellow, 
 
CLASSIFICATION OF PIGMENTS 
 
 27b 
 
 even indefinite character of many pigments, and the 
 chemical solitariness of others, preclude the formation of 
 groups having equal rank and precise group-characters : 
 thus the proposed chemical classification, though con- 
 venient, has no pretension to completeness. I suggest 
 the following nine groups : 
 
 Group I. — Elements 
 
 Ivory black 
 Charcoal black 
 Lamp black 
 Indian ink 
 Graphite 
 
 ■ Contain carbon. 
 
 Silver. 
 
 Gold. 
 
 Platinum. 
 
 Aluminium. 
 
 Zinc white - - 
 
 Green oxide of\ 
 chromium / 
 
 Burnt umber 
 
 Cobalt green 
 Cobalt red - - 
 
 Cobalt blue - - 
 
 Group II 
 
 ZnO. 
 
 Cr203. 
 
 Oxides of Fe 
 and Mn. 
 CoO,«ZnO. 
 CoO,«MgO. 
 CoOjwAloOj. 
 
 — Oxides 
 Cceruleum 
 Red lead - - 
 
 Venetian red 
 Light red 
 Indian red 
 Burnt sienna 
 
 - CoO.HSnOj. 
 
 - Pb304. 
 
 |-Chiefly Fe 203 . 
 
 Group III. — Sulphides 
 
 Cadmium yellow - - - CdS. 
 
 Kings’ yellow - . - . AsgSg. 
 
 Realgar AsgSj. 
 
 Vermilion HgS. 
 
 Ultramarine -v Contain 
 
 Artificial ultramarine I Si, Al, 
 Green ultramarine j Na, O 
 Red ultramarine and S. 
 
 the native earths, ivory black, white lead, zinc white, and viridian. 
 On the other hand, M. de Lapparent allows that vine black is an 
 entirely innocuous and permanent pigment. My experience is not 
 in general agreement with the judgments of M. de Lapparent as 
 embodied in the diagram under consideration. For instance, I do 
 not find that aureolin reacts with white lead or with ultramarine, 
 nor can I admit that Prussian blue deserves the bad character 
 assigned to it. Possibly the purity of the particular pigments with 
 which our author dealt was not assured in all cases. Might there 
 not have been free sulphur in his pale cadmium and free acid in his 
 Prussian blue ? 
 
CLASSIFICATION OF PIGMENTS 
 
 277 
 
 Group IV.— Hydrates 
 
 Yellow ochre 
 
 Raw sienna 
 Raw umber 
 
 - FePg.wHgO. 
 l Oxides and hy- 
 drates of Fe 
 I and Mn. 
 
 Emerald oxide\ 
 of chromium/ 
 Mountain blue - 
 
 CrjO-jjaHjO. 
 
 CuHjOg. 
 
 Group V. — Carbonates 
 
 Flake white - 2PbC03,PbH202. 
 
 Whitening - CaC03. 
 
 Group VI. 
 
 -r . f Silicate of Fe, K, 
 
 Terre verte f , 
 
 \ Mg. 
 
 Egyptian blue CuO,CaO,4Si02- 
 
 Group VII. — Chromates 
 
 Baryta yellow - - - BaCr04. | Chrome red - - - - PbgCrOj. 
 Strontia yellow - - SrCr04- | Zinc chromate - - ZnCr04. 
 Chrome yellow - - PbCr04. j 
 
 Chessylite - CuC03,CuH202. 
 Malachite - 2CuC03,CuH202- 
 
 -Silicates 
 
 Smalt 
 
 f Silicate of Co 
 I and K. 
 
 Group VIII.— Various Inorganic Salts 
 
 Baryta white 
 Lead sulphate 
 Aureolin - 
 Naples yellow 
 
 - BaS04. 
 
 - PbS04. 
 
 - K^CojiaNOj. 
 
 - Contains Pb, 
 
 Sb, O. 
 
 Schweinfurt green 
 Tungsten green 
 
 { 
 
 { 
 
 Manganese violet 
 = Nurnberg violet 
 
 Contains 
 Cu, As, O. 
 
 Chromium 
 
 tungstate. 
 
 Manganese 
 
 metaphos- 
 
 phate. 
 
 Group IX.— Organic Compounds 
 
 Indian yellow. 
 Yellow lake. 
 Gamboge. 
 
 Pure orange. 
 Rose madder. 
 Madder carmine. 
 Rubens madder. 
 Madder red. 
 Purple madder. 
 
 Brown madder. 
 Scarlet alizarin. 
 Crimson alizarin. 
 Carmine. 
 Crimson lake. 
 Scarlet lake. 
 Purple lake. 
 
 I Sap green. 
 
 ' Verdigris. 
 
 Emerald green. 
 Indigo. 
 
 Prussian blue. 
 Antwerp blue. 
 Bitumen. 
 
 Bistre. 
 
 Sepia. 
 
 Vandyke brown B. 
 
278 
 
 SULPHIDES 
 
 One of the chief lessons to be learnt from this 
 classification is this, that the members of each class, as 
 a general rule, exert no action upon one another. This 
 is explained easily. The oxides of Group II., having 
 already taken up the full complement of oxygen which 
 they can acquire under ordinary conditions, are not likely 
 to be oxidized by admixture with other oxides of similar 
 character. In the same manner the sulphides of 
 Group III. neither give sulphur to, nor receive it from 
 the other sulphides, for all but one of them have been 
 produced in the presence of excess of sulphur. The 
 following characteristics of each group may prove useful 
 in the study of their chief members : 
 
 Group I. : Elements. — All the black pigments in 
 ordinary use consist of or contain the element carbon, 
 and are not subject to change : graphite is a form of 
 carbon and is unalterable and inert. Gold, if pure or 
 nearly free from alloy, is not liable to chemical change, 
 but silver readily tarnishes by combining with sulphur ; 
 drawings in silver-point are frequently found to have 
 altered in hue from this cause. The best metal-point for 
 fine drawing is pure platinum. 
 
 Group II. : Oxides. — These have generally been 
 prepared at a high temperature, and are not easily 
 amenable to chemical or physical change : they are, 
 moreover, not liable to affect other pigments, being 
 practically inert. 
 
 Group III. : Sulphides. — Some of these may give up 
 sulphur to the metallic bases of other pigments. Thus 
 cadmium yellow blackens emerald green, producing 
 copper sulphide. One of these pigments, vermilion, is 
 prone to a molecular change, whereby the red crystalline 
 form passes, without chemical alteration, into the black 
 amorphous variety. The members of this group some- 
 
I 
 
 VARIOUS INORGANIC SALTS 
 
 279 
 
 , times contain free sulphur, or inj urious sulphur com- 
 pounds. 
 
 Group IV. : Hydrates. — The water present in these 
 I compounds exists in two states, essential and hygro- 
 
 ^ scopic. Sometimes a part of the former may be lost, and 
 
 ; a change of hue occur in consequence, but the alteration 
 
 j is rare, save in the pigments which owe their colour to 
 
 j the presence of copper hydrate. In the case of raw 
 umber, the water present acts rather in aiding the oxygen 
 j of the air, under the influence of sunlight, to oxidize 
 I some of the peaty or bituminous matter sometimes 
 I present in this pigment. 
 
 ) Group V. : Carbonates. — Three out of the four 
 
 carbonates included in this group are liable to suffer 
 change on account of the metal they contain (lead or 
 ' copper) combining with sulphur, and so forming a brown 
 j or black sulphide. 
 
 I Group VI. : Silicates. — These are generally inert 
 
 bodies little prone to suffer or cause change. Some of 
 the ochreous earths contain silicates of iron, manganese, 
 j and alumina, as well as the hydrates of the two former 
 metals, and so might be placed in this group, 
 j Group VII. : Chromates. — This group consists of 
 
 I compounds rich in oxygen. When in contact with some 
 of the more alterable organic pigments belonging to 
 I Group VIII. the chromates occasionally lose oxygen. 
 
 [ On this account they show a tendency to acquire a 
 
 greenish or greyish hue, the result of the reduction of 
 the red oxide of chromium to the green oxide. This 
 change is accompanied by a corresponding injury to the 
 colour of the organic pigment which has been involved 
 I in the reaction. 
 
 Group VIII.: Various Inorganic Salts. — A num- 
 ber of miscellaneous compounds having no chemical 
 
28 o 
 
 CLASSIFICATION OF PIGMENTS 
 
 relationship have been thrown into this group. One, a 
 sulphate, is insoluble and inalterable ; another, potassium 
 cobalti-nitrite, is generally inert, but, owing to its nitrous 
 constituent, acts injuriously upon some organic pigments, 
 notably on indigo. The members of the group which 
 contain lead or copper may darken in the presence of 
 sulphuretted hydrogen and of some other sulphur com- 
 pounds. 
 
 Group IX. : Organic Compounds. — This group in- 
 cludes many more pigments than any other ; not one of 
 its members possesses the permanency belonging to the 
 majority of the mineral pigments, while some are so 
 fugitive that they may even be used for producing a 
 photographic picture by being exposed to sunlight under 
 a negative. This fading is generally due to the com- 
 bined action of water and oxygen : in oily and resinous 
 media it is lessened, retarded, or even prevented by the 
 hydrofuge character of these vehicles. 
 
 It should be noted that members of each group, 
 though presenting one or more characters in common, 
 often exhibit certain chemical and physical differences of 
 deportment. Here is a list of the chief changes which 
 they are capable of suffering, with illustrative examples : 
 
 Molecular rearrangement 
 
 Subsidence 
 Volatilization 
 Solution 
 Fusion 
 Oxidation ... 
 
 Reduction... 
 
 Sulphuration 
 
 Vermilion ; cadmium sul- 
 phide. 
 
 Smalt. 
 
 Kings’ yellow. 
 
 Strontia yellow ; aureolin. 
 Asphalt. 
 
 Carmine; Vandyke brown. 
 Naples yellow; chromates. 
 White lead ; emerald green. 
 
CLASSIFICATION OF PIGMENTS 281 
 
 The effect of pulverization upon pigments may be 
 mentioned in this connexion. Generally, the more 
 finely an alterable pigment is ground, the more suscep- 
 tible does it become to chemical injury : its colour 
 becomes at the same time paler, and may even change 
 in hue as well as in tone. Continued grinding, beyond 
 the degree necessary to develop the proper colour, im- 
 proves some pigments, but injures others. 
 
 In the chemical classification of pigments which has 
 been sketched in the present chapter there comes out in 
 rather striking relief one point to which no allusion has 
 yet been made. It is indeed a point which touches the 
 chemist rather than the artist, and yet it seems to merit 
 a passing reference in this place. I refer to the number 
 of gaps in the table — to the number of elements and of 
 classes of salts which have no place therein. The 
 scientist will not, indeed, expect to find amongst these 
 9 groups any substances possessed, to a marked degree, 
 of the property of solubility in water, for he will recog- 
 nise the unfitness of such bodies for use as paints. But 
 he will probably observe, with some surprise, that there 
 are no compounds of fluorine, chlorine, bromine, or iodine 
 in our lists, but two sulphates, only one substance con- 
 taining tungsten, and not one containing nickel, uranium, 
 molybdenum, or vanadium. Coloured insoluble com- 
 pounds indeed exist of all these elements ; several of such 
 compounds have been proposed and even employed as 
 pigments, but instability or injurious action upon other 
 pigments has banished these candidates from the palette 
 of the artist. 
 
 A few words may be added here as to the distinction 
 between substantive and adjective pigments. Of the 
 former class aureolin, vermilion and malachite may be 
 
282 
 
 CLASSIFICATION OF PIGMENTS 
 
 cited as examples ; to the latter all the lakes belong. 
 Substantive pigments are homogeneous, definite sub- 
 stances, simple or compound, but not separable into two 
 bodies, having differing optical qualities. On the other 
 hand, adjective pigments contain two substances, one 
 coloured, and another generally colourless, through which 
 the former is disseminated or over which it is extended 
 as on a background. 
 
CHAPTER XXI 
 
 TABLES OF PERMANENT, FUGITIVE, AND ALTERABLE 
 PIGMENTS 
 
 By several different methods, data may be obtained which 
 enable us to classify pigments — roughly, it is true — in 
 accordance with their varying degrees of stability. Such 
 data are derived partly from the known chemical and 
 physical constitution of the various substances ; partly 
 from a study of old paintings and drawings in which they 
 have been used ; and partly from special experimental 
 tests of permanency to which they have been subjected. 
 Selections from these data are given in Chapters XX., 
 XXIV., and XXVI., of the present work ; but much 
 additional information has been furnished by other trials, 
 conducted by the author and other experimenters, for 
 which space could not be found in this volume. Tables 
 constructed from such data must not be regarded as 
 affording exact values, but merely approximations. From 
 some minute and often obscure cause differences of deport- 
 ment, under exposure to hostile influences, will occasion- 
 ally be observed in the case of two specimens of the same 
 pigment having the same hue. And, further, the group- 
 ing of pigments into a small number of classes is a 
 conventional and convenient arrangement which cannot 
 accurately represent the numerous degrees of stability or 
 instability which characterize the several pigments under 
 
 283 
 
284 
 
 TABLES OF PIGMENTS 
 
 discussion. For when we leave the practically unalter- 
 able mineral pigments, we have to deal with a number of 
 preparations which fall by irregular and often barely recog. 
 nisable steps from the almost permanent to the hopelessly 
 fugitive. One example of this difficulty in classification 
 must suffice : aureolin is almost worthy of a place in 
 Class I., Indian yellow scarcely deserves inclusion in 
 Class II. The action of mixed pigments upon one another, 
 though not as frequent as it is supposed to be, creates 
 another difficulty in our classification, so also does the 
 medium employed in painting, which may either protect 
 an alterable pigment from change or aid in its destruction. 
 In fact, each method of painting, if really distinct, requires 
 a special classification of the pigments to be employed in 
 carrying it out. 
 
 In the annexed classification, a limit of three orders of 
 stability has been adopted, the first class including the 
 practically permanent pigments ; the second class those 
 which, though liable to a variable measure of change, may 
 yet generally be allowed ; and the third class those which 
 should be definitely excluded from the palette : 
 
 CLASSIFIED TABLE OF PIGMENTS FOR OIL PAINTING 
 
 Class I 
 
 Baryta white. 
 Zinc white. 
 
 Flake white. 
 
 Yellow ochre. 
 Raw sienna. 
 Baryta yellow. 
 Naples yellow. 
 Cadmium orange. 
 
 Class II 
 White 
 
 Yellow 
 
 Aureolin. 
 
 Indian yellow. 
 Strontia yellow. 
 Chrome yellow. 
 Cadmium yellow. 
 
 Class III 
 
 Kings’ yellow. 
 Yellow madder. 
 Brown pink ; yellow 
 lake. 
 
 Gamboge. 
 
 I Zinc chromate. 
 
TABLES OF PIGMENTS 
 
 2 ^ 
 
 Class I 
 
 Vermilion. 
 
 Indian red. 
 Light red. 
 
 Venetian red. 
 Red ochre. 
 
 Cobalt violet. 
 
 Mars violet. 
 
 Violet ultramarine. 
 
 Emerald oxide of 
 chromium. 
 
 Green oxide of chro- 
 mium. 
 
 Cobalt green. 
 
 Green ultramarine. 
 
 Ultramarine. 
 Artificial ultra- 
 marine. 
 
 Cobalt. 
 
 Coeruleum. 
 
 Burnt sienna. 
 
 Raw and burnt um- 
 ber. 
 
 Cappagh brown. 
 Verona brown . 
 Prussian brown. 
 Vandyke brown A. 
 
 (earthy). 
 
 Ivory-black. 
 
 Charcoal-black. 
 
 Lamp-black. 
 
 Graphite. 
 
 Class II 
 
 Red 
 
 Madder carmine. 
 Rubens’ madder. 
 Rose madder. 
 Madder red. 
 
 Purple madder. 
 Scarlet lake (ali- 
 zarin). 
 
 Violet 
 
 Manganese violet. 
 
 Green 
 
 Emerald green. 
 Terre verte. 
 Malachite. 
 
 Madder green. 
 
 Blue 
 
 Smalt. 
 
 Prussian blue. 
 Antwerp blue. 
 Chessylite. 
 
 Brown and Black 
 Madder brown. 
 Cologne earth. 
 
 Class III 
 
 Crimson lake. 
 Carmine and burnt 
 carmine. 
 
 Indian lake. 
 
 Scarlet lake (cochi ■ 
 neal). 
 
 Purple lake, 
 j Violet carmine. 
 
 Verdigris. 
 
 Sap green. 
 
 ' Green vermilion,’ 
 etc. 
 
 Green verditer. 
 
 Indigo. 
 
 Blue verditer. 
 
 Blue ochre. 
 
 Vandyke brown B. 
 
 (bituminous). 
 
 Bistre. 
 
 Sepia. 
 
 Bitumen ( = asphalt). 
 
286 
 
 TABLES OF PIGMENTS 
 
 In order to adapt the foregoing classified table to water- 
 colours, some changes and additions must be made. 
 Flake white, Naples yellow (true), cadmium (pale), and 
 vermilion (artificial), must be removed from the Class (I.) 
 of permanent pigments and placed in Class III., to which 
 also must be relegated several pigments from Class II., 
 namely, chrome yellow, malachite, and madder brown. 
 Of course, it should be clearly understood that no pigment 
 belonging to Class III. should be employed in artistic 
 painting. One satisfactory addition, and one only, can 
 be made to Class I. in the table. Indian ink is a pigment 
 available for water-colour painting, and when it is free 
 from a brownish hue may be safely used. Bistre and 
 sepia are likewise used only as water-colours, but they are 
 both fugitive, and must be placed in Class III. Almost 
 the same modifications of the table are required in the 
 case of tempera-painting as in water-colour painting. 
 With fresco- painting the exclusion of many more pigments 
 is an absolute necessity, as they are completely ruined by 
 caustic lime. Not only are all the chromates inadmissible, 
 as well as all the pigments which cannot be trusted as 
 water-colours, but likewise Prussian blue and Antwerp 
 blue, while the madder colours are much altered in hue 
 when used in this process. In stereochromy the number 
 of available pigments is still further reduced. 
 
 It may not be uninstructive if we cite in this place the 
 classification of pigments as used in oil which M. Decaux 
 has published. The order followed by this experimenter 
 is that of stability ; the figures prefixed to the names of 
 the individual pigments indicate the degree of perma- 
 nence, I marking out the materials which are quite 
 unchangeable, while 45 is the most fugitive of all : 
 
TABLES OF PIGMENTS 
 
 287 
 
 DECAUX’S TABLE 
 
 OF PIGMENTS FOR 
 
 OIL-PAINTING 
 
 
 Class I 
 
 
 I. Zinc white. 
 
 I. Green oxide of chro- 
 
 4. Cobalt green. 
 
 I. Flake white. 
 
 mium. 
 
 5. Mars yellow. 
 
 I. Yellow ochre. 
 
 I. Ivory black. 
 
 6. Mars orange. 
 
 I. Naples yellow. 
 
 I. Terre verte. 
 
 7. Burnt umber. 
 
 I. Cadmium (deep). 
 
 I. Green ultramarine. 
 
 8. Viridian. 
 
 I. Raw sienna. 
 
 I. Cobalt blue. 
 
 9. Indian red. 
 
 I. Red ochre. 
 
 I. Artif. ultramarine. 
 
 10. Mars violet. 
 
 I. Mars red. 
 
 I. Ivory black. 
 
 1 1 . Indian yellow. 
 
 I. Venetian red. 
 
 2. Mars brown. 
 
 12. Emerald green. 
 
 I . Burnt Italian earth. 
 
 3. Burnt sienna. 
 
 
 
 Class II 
 
 
 13. Malachite green. 
 
 17. Prussian blue. 
 
 26. Madder ‘ rose 
 
 14. Scheele’s green. 
 
 18 to 23. Various madder 
 
 doree.’ 
 
 13. Raw umber. 
 
 lakes. 
 
 27. Brown madder. 
 
 16. Vandyke brown. 
 
 24. Madder carmine. 
 
 29. Cassel earth. 
 
 
 Class III 
 
 
 30. Pale chrome. 
 
 35. Asphalt. 
 
 43. Yellow lake. 
 
 31. Zinc chromate. 
 
 36. Brown pink. 
 
 44. Carmine. 
 
 32. Pale cadmium. 
 
 38. Vermilion. 
 
 45. Crimson lake. 
 
 33. Orange chrome. 
 
 42. Burnt carmine. 
 
 
 On comparing this classified list with that previously 
 given a general accordance will be perceived, the low 
 position given to raw umber and to vermilion, as well as 
 the very high place assigned to Indian yellow and to 
 terre verte, constituting the chief exceptions. 
 
 In closing this chapter it may be useful to state that 
 the pigments to which a place in our Class I. has been 
 assigned have stood the very severe test of long exposure 
 to direct sunlight. On a subsequent page it will be shown 
 that this method of determining the stability of pigments 
 
288 
 
 TABLES OF PIGMENTS 
 
 is not in all cases a fair one, because changes brought 
 about by such exposure may not occur at all when the 
 temperature does not rise beyond a particular point, and 
 when the radiant energy of light and actinism does not 
 exceed a moderate measure of intensity. So far, then, as 
 exposure to light is concerned, it may happen that some 
 of the pigments in Class II. really deserve a higher posi- 
 tion than that assigned to them in our table. In this 
 connexion we may give some of the conclusions which 
 Messrs. Winsor and Newton have published as to the 
 stability of oil colours when exposed, not to sunshine, but 
 to a strong north light. It will be noticed that the class 
 of permanent pigments has been greatly enlarged as the 
 result of the milder ordeal through which the materials 
 have passed : 
 
 Class I. — Permanent 
 
 Zinc white. 
 Aureolin. 
 Cadmium yellow. 
 Yellow ochre. 
 Raw sienna. 
 Baryta yellow. 
 Mars yellow. 
 Vermilion. 
 Venetian red. 
 Light red. 
 
 Indian red. 
 Alizarin lakes. 
 Crimson madder. 
 
 Madder carmine. 
 Pink madder. 
 
 Rose madder. 
 
 Purple madder. 
 Brown madder. 
 Rubens’ madder. 
 Scarlet lake (new). 
 Burnt lake (madder). 
 Cobalt green. 
 
 Oxide of chromium. 
 Viridian. 
 
 Cerulean blue. 
 Cobalt blue. 
 
 Ultramarine. 
 Manganese violet. 
 Cobalt violet. 
 Prussian brown. 
 Caledonian brown. 
 Cappagh brown. 
 Burnt umber. 
 Burnt sienna. 
 Vandyke brown. 
 Bone brown. 
 
 Black lead. 
 
 Blue black 
 Ivory black. 
 
 Class II. — Moderately Permanent 
 
 Flake white. 
 
 Chrome yellow. 
 Naples yellow (imi- 
 
 Indian yellow. 
 Green cinnabar. 
 Emerald green. 
 Malachite. 
 
 Leitch’s blue. 
 Prussian blue. 
 Antwerp blue. 
 Asphaltum. 
 
 tative). 
 
 Kings’ yellow. 
 
 Rose doree. 
 
 Brown pink. 
 
TABLES OF PIGMENTS 
 
 289 
 
 Class III.— Fugitive 
 
 Citron yellow 
 
 (ZnCr 04 ). 
 Yellow lake. 
 Gamboge. 
 
 Primrose yellow. 
 Carmine. 
 
 Burnt carmine. 
 Crimson lake. 
 Indian lake. 
 Purple lake. 
 Violet carmine. 
 
 Green lake. 
 Sap green. 
 Verdigris. 
 Indigo. 
 Italian pink. 
 
 19 
 
CHAPTER XXII 
 
 SELECTED AND RESTRICTED PALETTES 
 
 It is by no means easy to construct a palette which shall 
 be at once artistically and scientifically perfect. For it 
 is impossible to exclude every pigment which is suscep- 
 tible of change, and it is unwise to include every pigment 
 for which the fancies and partialities of particular painters 
 desire to find a place. An artist discovers how to obtain 
 a required hue by means of a special pigment, and is 
 naturally reluctant to learn by tedious experimenting 
 whether it cannot be secured by means of a more complex 
 commingling of the ordinary paints. And although some 
 great masters have done marvellous things with five, four, 
 or even three pigments only, there is no sound argument 
 which can be urged in favour of so severe a restriction. 
 If much mixing of paints be bad, then a reasonable en- 
 largement of the palette will render such mixing unneces- 
 sary. And the artist wants something more than a mere 
 match in hue : he knows that there is a peculiar quality 
 of colour to be sought as well. He can make a trans- 
 parent pigment opaque, but the reverse operation is im- 
 practicable. Scumbling of one opaque colour thinly over 
 another which is also opaque very imperfectly attains the 
 effect of translucency. So the artist demands, in addition 
 to a chromatic series of opaque pigments, a second series 
 
 290 
 
SELECTED PALETTES 
 
 291 
 
 possessed of transparency, or, at least, of translucency. 
 Thus he adds to his cadmium yellow, aureolin ; to his 
 vermilion, madder carmine ; to his emerald green, virid- 
 ian ; to his coeruleum or cobalt, ultramarine. And, 
 moreover, he has to take account of the peculiar and 
 often unexpected effects produced by the lightening of 
 the tone of a pigment by commixture with white, and by 
 the darkening due to the addition of black. Two nearly 
 identical translucent reds may yield with white two dif- 
 ferent hues, one verging on salmon, the other on rose. 
 Charcoal-black yields with aureolin or Indian yellow a 
 series of greens quite distinct from those obtained by 
 mixing these yellow pigments with ivory-black. So the 
 artist in making his first choice from the whole number 
 of trustworthy pigments at his command, will proceed 
 towards his final selection by two stages. He first re- 
 tains those pigments which commend themselves to his 
 judgment for their own chromatic qualities when un- 
 mixed ; he then proceeds to test the characteristics of 
 the remainder by trying the tints which they severally 
 produce with white, the shades they yield with black, 
 and the mixed hues to which they give rise by commix- 
 ture with one another in twos and threes. To this set of 
 experiments he adds another, in which these pigments 
 are mixed, after the same manner, with those belonging 
 to the first series. As the result of these trials the artist 
 will be enabled to exclude several paints which would 
 merely serve to encumber his palette. 
 
 Before deciding finally as to the elements which shall 
 be retained for our fundamental palette, it will be in- 
 structive to study the selections of pigments which from 
 time to time have been employed by artists of recent 
 times and of the present day. The obvious weakness of 
 
2gi 
 
 SELECTED PALETTES 
 
 many of such palettes lies in their inclusion of a few 
 treacherous pigments, such as asphaltum, and of a few 
 evanescent pigments, such as carmine, crimson lake, and 
 the bituminous variety of Vandyke brown. Nevertheless, 
 in making our selection of pigments from the classified 
 list previously given, we may obtain many useful hints 
 from the palettes employed by artists with whose works 
 we are familiar. It is particularly interesting to observe 
 how extremely restricted were the sets of pigments used 
 by several painters who are distinguished for the refine- 
 ment and for the rich variety of hues shown in their 
 works. In the following paragraphs the names of all 
 decidedly fugitive and alterable pigments are printed in 
 italics. 
 
 Sir Joshua Reynolds, although too fond of varying his 
 practice by the introduction of many dangerous com- 
 pounds, and by the use, in the same picture, of incom- 
 patible media and methods, executed many works between 
 the years 1770 and 1775 with one or other of these five 
 restricted palettes, containing from four to eight pig- 
 ments : 
 
 i. Flake white. 
 
 Yellow ochre. 
 
 Lake. 
 
 Ultramarine. 
 
 Black. 
 
 ii. Flake white. 
 
 Yellow ochre. 
 Orphnent. 
 
 Lake. 
 
 Carmine. 
 
 Ultramarine. 
 
 Black. 
 
 Blue black. 
 
 iii. Flake white. 
 
 Yellow ochre. 
 Naples yellow. 
 
 Carmine. 
 
 Vermilion. 
 
 Ultramarine. 
 
 Black. 
 
 iv. Flake white. 
 
 Asphaltum, 
 
 Vermilion. 
 
 Blue. 
 
 
 V. Flake white. 
 
 Naples yellow. 
 
 Lake. 
 
 Minium, 
 
 Aspkaltujn. 
 
 
 Paul Delaroche and H. Vernet employed these eleven 
 pigments : 
 
 Flake white. Yellow ochre. Vermilion. Artificial ultra- Blue black. 
 
 Naples yellow. Lake. marine. Ivory black. 
 
 Raw sienna. Brun rouge. 
 
 Burnt sienna. 
 
SELECTED PALETTES 
 
 293 
 
 W. Etty, R.A., used twelve pigments : 
 
 Flake white. Naples yellow. 
 
 Yellow ochre. 
 
 Vermilion. 
 Light red. 
 Indian red. 
 Lake. 
 
 Terre verte. Raw umber. 
 
 Blue verditer. Burnt umber. 
 
 Black. 
 
 Samuel Palmer employed in oil painting the following 
 pigments, twenty-eight in all : 
 
 Flake white. Naples yellow. Field ’svermilion. 
 
 Yellow ochre. Vermilion. 
 
 Raw sienna. Light red. 
 
 Cadmium i, 2, 3. Venetian red. 
 
 Aureolin. Indian red. 
 
 Madder carmine. 
 Pink madder. 
 Rose madder. 
 
 Ultramarine. Vine black. 
 
 Ultramarine Ivory black. 
 
 ash. Brown madder. 
 
 Cobalt. Raw umber. 
 
 Antwerp blue. Burnt sienna. 
 
 Terre verte. 
 
 Green oxide 
 chromium. 
 
 Emerald green. 
 
 Thomas Wright, of Derby, employed fourteen pigments, 
 and, it is to be presumed, flake-white also : 
 
 Naples yellow. Vermilion. Carmine. Ferraceum blue. Ivory 
 
 Brown pink. Burnt ochre. Lake, Ultramarine. black. 
 
 Indian red. Burnt lake. Prussian blue. 
 
 Light red. Lake azure (?). 
 
 From the Portfolio of 1875-6 we obtain the particulars 
 given below concerning the pigments used by several 
 well-known artists : the palettes quoted have been chosen 
 as representative of different types. 
 
 P. H. Calderon, R.A., employed fifteen pigments : 
 
 Flake white. Naples yellow. Vermilion. 
 
 Yellow ochre. Venetian red. 
 
 Cadmium yellow. Pink madder. 
 Raw sienna. 
 
 Mars yellow. 
 
 Cobalt blue. Burnt sienna, 
 Antwerp blue. Raw umber, 
 
 Vandyke brown. 
 Ivory black. 
 
 W. C. T. Dobson, R.A., ten pigments : 
 
 Flake white. Yellow ochre. Vermilion. Cobalt blue. 
 Raw sienna. Rose madder. 
 
 Purple lake. 
 
 Raw umber. 
 Vandyke brown. 
 Ivory black. 
 
 The following are water-colour palettes ; 
 
 Alfred W. Hunt, seventeen pigments, and in addition 
 Chinese white ; 
 
 Lemon yellow. Vermilion. Terre verte. Cobalt. Madder brown. 
 
 Ga 7 nboge. Light red. Ultramarine. Raw umber. 
 
 Yellow ochre. Indian red. Ultramarine ash. Burnt sienna. 
 
 Raw sienna. Madder lake. Smalt. Burnt umber. 
 
294 
 
 SELECTED PALETTES 
 
 Sir John Gilbert, R.A., fifteen pigments: 
 
 Chinese white. Yellow ochre. Vermilion, Cobalt. Burnt sienna. 
 
 Raw sienna. Light red. Artificial ultra- Vandyke brcnvn, 
 
 Venetian red. marine. Ivory black. 
 
 Indian lake. Indigo, 
 
 Prussian blue. 
 
 Antwerp blue. 
 
 The selection of a good set of permanent or fairly per- 
 manent pigments must depend to some extent upon the 
 idiosyncrasy of the artist, upon his training and methods 
 of work, upon the class of subjects with which he deals. 
 As a good general working set for oils, the following selec- 
 tion is offered. It is arranged in two sections, the second 
 including what may be called ‘ supplementary ’ pigments : 
 
 Section I. 
 includes 
 12 pigments. 
 
 Flake white. 
 Cadmium yellow. 
 Aureolin. 
 
 Yellow ochre. 
 
 Vermilion. 
 Madder car- 
 mine. 
 
 Light red. 
 
 Section II. 
 
 includes 
 12 pigment.s. 
 
 f 
 
 1 
 
 Raw sienna. 
 Naples yellow. 
 Baryta yellow. 
 
 Purple madder. 
 Madder brown. 
 Cobalt violet. 
 
 Viridian. Raw umber, 
 
 Artificial ul- Cappagh brown, 
 tramarine. Ivory Mack. 
 
 Green oxide Cobalt. 
 
 chromium. Prussian blue 
 Terre verte. (insol.). 
 
 Cobalt green, Burnt sienna, 
 light. 
 
 Emerald green is excluded, since it cannot be safely 
 associated with cadmium yellow, but there is no reason 
 why several more pigments should not be added in Sec- 
 tion II., other than the desirability of limiting the number 
 of paints to those really required. Garance doree, Rubens’ 
 madder, deep cobalt-green, burnt umber, Verona brown, 
 vine black, and graphite might be added to the list. On 
 the other hand, further restrictions become by practice 
 possible. One does not know what white, vermilion, 
 yellow, and vine or charcoal black can do until one has 
 purposely debarred one’s self from the employment of 
 any other coloured pigments. Here are two such re- 
 stricted palettes : 
 
 I. Flake-white, yellow ochre, light red, cobalt, ivory- 
 black. 
 
RESTRICTED PALETTES 
 
 295 
 
 2. Flake-white, cadmium yellow, vermilion, ultra- 
 marine, ivory-black. 
 
 A third restricted palette, containing ten pigments 
 instead of five, is thus constituted : 
 
 3. Flake-white, yellow ochre, cadmium yellow, aureolin, 
 vermilion, madder carmine, ultramarine, viridian, Cap- 
 pagh brown, ivory-black. 
 
 It is scarcely necessary to say that the capacity of No. i 
 for representing the range of natural hues is extremely 
 limited ; indeed, it is fitted only for ‘ dead colouring,’ and 
 for the ‘ first painting.’ With No. 3, however, we can 
 imitate with a near approach to exactness all the pigments 
 excluded from this palette, and we may therefore regard 
 it as practically complete. Some of the hues obtained by 
 the mixtures which it is necessary to employ for this pur- 
 pose will be a little less luminous than the originals, since 
 these hues will have been produced by the increased ab- 
 sorption of certain elements of the incident white light — 
 they are consequently duller, or have more grey in them. 
 This palette. No. 3, is nearly the same as one devised by 
 the late Mr. P. G. Hamerton {Portfolio, 1876, p. 132), which 
 was constituted of flake-white, pale cadmium, yellow 
 ochre, vermilion, rose madder, artificial ultramarine, 
 emerald oxide of chromium, Vandyke brown, black. I 
 have added one pigment, aureolin, and have substituted 
 for pale cadmium, full cadmium yellow ; for rose madder, 
 the more stable madder carmine ; and for Vandyke brov/n, 
 Cappagh brown. Mr. Hamerton tested the range of his 
 restricted palette by imitating with its constituents many 
 of the excluded pigments. I give some of his results, as 
 modified by my own experiments with my palette No. 3. 
 
 Naples Y ellow. ~lm.ita.ted by flake-white, with cadmium 
 yellow and a trace of yellow ochre ; exact. 
 
296 
 
 RESTRICTED PALETTES 
 
 Lemon Yellow. — Flake-white, cadmium yellow, with a 
 trace of viridian : less brilliant than the original. 
 
 Cadmium Orange. — Cadmium yellow, with vermilion : 
 less brilliant. 
 
 Light Red. — Vermilion, yellow ochre, Cappagh brown. 
 
 Venetian Red. — Vermilion, yellow ochre, madder car- 
 mine, a little Cappagh brown : exact. 
 
 Indian Red. — Vermilion, trace of yellow ochre, madder 
 carmine, ivory black : a good match, but less translucent. 
 
 Cobalt Blue. — Artificial ultramarine, flake-white, a little 
 viridian : less translucent ; does not match cobalt blue by 
 artificial light. 
 
 Prussian Blue. — Ultramarine, black, a trace of viridian : 
 lacks the translucency and depth of the original. 
 
 Raw Sienna. — Yellow ochre, aureolin, Cappagh brown. 
 
 Burnt Sienna. — Madder carmine and Cappagh brown, 
 with a trace of vermilion ; less translucent. 
 
 Emerald Green.— White, cadmium yellow, viridian, 
 artificial ultramarine : not so brilliant as the original. 
 
 Malachite. — White, cadmium yellow, yellow ochre, 
 viridian, ultramarine. 
 
 Terre Verte.—Y\!hite, aureolin, viridian, ivory-black. 
 
 Cohalt Green. — Ultramarine, viridian, trace of flake- 
 white. 
 
 Indigo. — Ultramarine, with black and trace of viridian : 
 very close. 
 
 Vandyke Brown. — Cappagh brown, with much madder 
 carmine and a little ivory-black. 
 
 It is needless to multiply further our illustrations of the 
 resources at the command of the painter who limits him- 
 self to our restricted palette of ten pigments (No. 3, 
 page 295), as experimental trials of its capacity are 
 easily made. 
 
RESTRICTED PALETTES 
 
 297 
 
 So far, then, as regards selected and restricted palettes 
 of oil colours. Some modifications must be made in our 
 list in order to devise corresponding palettes of useful 
 and enduring water-colours. In the more extended list 
 (p. 294), zinc-white must replace flake-white, while 
 vermilion, purple madder, brown madder, and cobalt 
 violet must be discarded. In the limited palette (No. 3), 
 the changes to be made comprise the substitution of 
 zinc-white ( = Chinese white) for flake- white, the replace- 
 ment of vermilion by one of the brightest native varieties 
 of iron reds (the mineral turgite is perhaps the best kind), 
 Cappagh brown by Mars brown, and of ivory-black by 
 Indian ink. The two palettes (A. and B.) will then 
 
 finally assume the following forms for water-colours : 
 
 Zinc white. Light red. Viridian. Raw umber. 
 
 Cadmium yellow. Indian red. Artificial ultra- Burnt sienna. 
 
 Aureolin. Madder car- marine. Indian ink. 
 
 Yellow ochre. mine. Cobalt. 
 
 Raw sienna. Red ochre. Prussian blue Mars brown. 
 
 (insol.). Ivory black. 
 
 Doubtless artists will especially miss from this palette 
 six pigments, namely, gamboge, vermilion, rose madder, 
 brown madder, Vandyke brown, and indigo. But after 
 the overwhelming evidence adduced in Chapter XXVI. as 
 to the want of permanence shown by these water-colour 
 paints, one feels compelled to exclude them. Our second 
 and more restricted palette (B.) is thus composed : 
 
 (B.) Chinese Yellow ochre. Red ochre. Ultramarine, Mars brown, 
 
 white. Cadmium orange. Madder car- Viridian. Indian ink. 
 
 Aureolin. mine. 
 
 Although it is obvious that with these limited palettes 
 it is impossible to produce exact imitations of every ex- 
 cluded pigment, yet there are two considerations which 
 must not be forgotten in estimating the influence of this 
 
 (A.) 
 
 Section I. 
 includes 
 13 pigments. 
 Section II. 
 
 includes 
 5 pigments. 
 
298 
 
 RESTRICTED PALETTES 
 
 defect on artistic painting. Foremost may be placed the 
 fact that pigments are rarely employed wholly unmodified 
 by admixture with others ; then it must be noted that the 
 differences between our imitations and the original pig- 
 ments which they are intended to replace are rather those 
 of lessened brightness, translucency, and depth than those 
 of hue. 
 
PART IV 
 
 METHODS AND RESULTS 
 
 Chapter XXIII. — Painting Methods. Chapter XXIV. — Study of 
 Old Paintings and Drawings. Chapter XXV. — Conservation 
 of Pictures. Chapter XXVI. — Trials of Pigments. 
 
CHAPTER XXIII 
 
 PAINTING-METHODS 
 
 As the grounds, vehicles, and pigments employed in 
 painting have been already described in Parts I., II., 
 and III. of this volume, it will not be necessary to do 
 more in the present chapter than give a summary or 
 general view of the chemistry of each method of employ- 
 ing these materials. 
 
 These methods are six in number, and may be thus 
 defined : 
 
 Methods 
 
 1. Tempera 
 
 2. Fresco 
 
 3. Stereochromy 
 
 4. Oil - Painting 
 
 AND Spirit- 
 Fresco 
 
 5. Water-Colour 
 
 6. Pastel, 
 
 Charcoal, 
 
 Plumbago, 
 
 Silver-Point 
 
 I. Tempera- painting, or painting in distemper, is gener- 
 ally assumed to include two, if not three, methods of 
 procedure, in which different vehicles or media are em- 
 ployed. These vehicles all contain a nitrogenous con- 
 stituent ; but in one of them — and that the most important 
 
 301 
 
 Vehicles 
 
 Egg-yolk emulsion ; solution of gelatin \ 
 
 or albumen / 
 
 Lime-water, in both buon’ fresco and 
 fresco secco - - - _ - 
 
 Aqueous solutions of alkaline silicates - 
 
 Oil, and solutions of resin, wax, paraffin 
 
 Aqueous solutions of gum, glycerin, 
 honey ...... 
 
 None 
 
 Changes 
 during Fixing 
 J Desiccation or 
 \ coagulation. 
 
 Carbonation, 
 Formation of in- 
 soluble silicates. 
 ^Oxidation, 
 
 I Resinification, 
 
 I Evaporation, 
 
 V Solidification. 
 
 Desiccation, 
 
 None. 
 
302 
 
 TEMPERA -PA INTING 
 
 — oil or fat is present in addition. Tempera-grounds 
 must be rigid, tenacious, and firm; they need not be dry, 
 but if organic pigments are to be used, they should not 
 contain caustic lane. Thus, a surface of plaster made 
 with slaked lime and sand must have been so long 
 exposed to the air as to have absorbed the amount of 
 carbonic acid necessary to convert the hydrate of lime 
 present into ‘mild lime’ — that is, the carbonate. To 
 detect the existence of caustic lime in such a painting- 
 ground recourse may be had to test-papers. Three kinds 
 are available for this purpose. Thus, yellow turmeric-paper, 
 first wetted and laid upon the surface of the plaster, 
 should show no change of colour ; if it become reddish, 
 the presence of caustic lime is indicated. Under the 
 same circumstances red litmus-paper turns blue or purple, 
 while phenolphthalein-paper acquires a crimson hue. If 
 these tests show the absence of caustic lime, the painting 
 may be commenced, otherwise the surface must be car- 
 bonated by syringing it or washing it with water charged 
 with carbonic acid gas. These precautions are, of course 
 unnecessary in cases where the painting-ground has been 
 prepared with plaster -of- Paris or other neutral com- 
 positions of which caustic lime is not a component. 
 Before commencing work the painting-ground must be 
 slightly and uniformly moistened with distilled water, 
 and then coated with weak size. The pigments to be 
 employed are those recommended for use as water- 
 colours; they are thoroughly mixed with the medium 
 to be employed, namely, egg-yolk emulsion, or size, or 
 prepared white of egg. These media serve not only to 
 bind the pigments to the ground, but also the coloured 
 particles to one another. To render the egg-yolk more 
 tractable, its alkaline reaction should be exactly neutral- 
 
TEMPERA -PA INTING 
 
 303 
 
 ized by the cautious addition of a very few drops of white 
 vinegar — hg-tree sap or white wine was sometimes 
 formerly employed for the same purpose. Some artists 
 content themselves with diluting the egg-yolks with a 
 little water, others add a small proportion of white of egg, 
 previously shaken with a little water and filtered. To 
 keep the egg-emulsion sweet, a lump of camphor or a 
 few cloves may be put into it. Size and also white of 
 egg have been employed in tempera-painting. The white 
 of egg needs dilution with water, thorough shaking, and 
 then filtering through muslin. When egg-yolk is used 
 in this method of painting, the oil in it gradually hardens, 
 while the albuminoid matters which accompany it be- 
 come partly insoluble and coagulated. As the amount 
 of oil in egg-yolk is twice as great (31 per cent.) as the 
 albuminoid matters (15 per cent.), this vehicle presents 
 considerable resemblance to those employed in oil- 
 painting, the albuminoid matters corresponding in a 
 measure to the resins often used in the latter method. 
 This vehicle does not act so effectually as oil and varnish 
 in ‘ locking up ’ pigments, and so the protection against 
 change which it affords is less. Moreover, instances have 
 been observed in which the sulphur present in the albu- 
 minoids of egg-yolk has acted injuriously upon some of 
 the pigments of the picture ; but by excluding, as we 
 now do, all paints containing lead and copper from the 
 tempera-palette, accidents of this kind are prevented. A 
 finished tempera-picture was often — one might almost 
 say generally — rubbed with a cloth and then varnished, 
 the varnish being often made by dissolving sandarac in 
 oil. The tone of the colours was thus warmed, while 
 further protection was at the same time afforded against 
 moisture and impure air. 
 
304 
 
 FRESCO-PAINTING 
 
 2. In fvesco-painting — both buon’ fresco and fresco secco 
 — the ground must not only be wet, but caustic. In true 
 fresco the pigments are applied to the last and freshly- 
 spread coat of plaster before it has had time to absorb 
 more than a trace of carbonic acid from the air ; the 
 painting-ground is in fact saturated with an aqueous 
 solution of hydrate of lime, while there remains a large 
 reserve of this compound in an undissolved condition. 
 When on such a surface a layer of pigment mixed with 
 water is placed, as that water evaporates the lime-water 
 in the ground diffuses into the paint, soaks it through 
 and through, and gradually takes up carbolic acid from 
 the air, thus producing carbonate of lime, which acts as 
 the binding material in this method. As there still exists 
 an ample reserve of hydrate of lime in the ground, wetting 
 the painted surface with pure water will cause more of 
 this hydrate to enter into solution, and so the liquid 
 present in the plaster will be reinforced with a fresh 
 supply of the binding material. Ultimately the ground 
 and the pigment become incorporated and harden together. 
 If more binding material be required, it may be intro- 
 duced by means of lime-water itself, or even by baryta- 
 water, which contains about twenty times as much 
 hydrate of baryta as the strongest lime-water contains of 
 hydrate of lime ; these liquids or hydrate of lime may 
 also be mixed with the pigments used. Although the 
 chief binding material in fresco-painting is this carbonate 
 of lime, yet with some plasters and with some pigments 
 another substance is produced. This is silicate of lime, 
 produced by the action of caustic-lime in solution upon 
 the soluble silica of the plaster or of the pigments. 
 Some sands, infusorial earths, and ochreous pigments, 
 contain such soluble silica, but it is certainly not present 
 
FRESCO.PAINTING 
 
 305 
 
 in every case. Silicate of lime as a binding material is 
 more permanent than the carbonate. 
 
 In fresco secco the plaster is allowed to harden, and, in 
 some measure, to dry, and the operation of painting may 
 be continued at leisure. The ground immediately before 
 beginning work is moistened with lime- or baryta-water, 
 and the pigments are mixed with one or other of these 
 liquids, or with a little slaked lime. This modified pro- 
 cess is far easier of execution than true fresco j but the 
 fixation of the pigments, though resulting from the same 
 cause, is less complete. 
 
 In the treatises of Cennini and other later writers the 
 expression ‘ painting in secco ’ is generally employed to 
 designate any process of tempera-painting, but the fresco 
 secco described in the preceding paragraph was practised 
 before and during the thirteenth century as the precursor 
 of buon’ fresco, and is briefly mentioned in Theophilus 
 (‘Schedula,’ Book L, chapter xv.). 
 
 The protection afforded to the pigments by the binding 
 material in fresco-painting is not generally very efficient. 
 In the case of a dry wall, free from soluble saline matter, 
 and exposed to a pure atmosphere, it may remain good 
 for centuries. But in air contaminated with the products 
 of the combustion of coal and gas, and with tarry and 
 sooty impurities, a fresco picture soon perishes. The 
 binding carbonate of lime is converted into the sulphate, 
 breaking up the paint, and becoming itself disintegrated 
 in the process of change. Through the same cause, and 
 through the production of sulphate of magnesia from the 
 carbonate of magnesia in the plaster, even the layer of 
 paint itself may scale off, while the lodgment of dirt and 
 soot upon the surface obscures such colours as still remain 
 in their place. And fresco-paintings often show scaling- 
 
 20 
 
3o6 
 
 FRESCO-PAINTING 
 
 off, by reason of the interposition of a film of carbonate 
 of lime between the coats of paint — a film formed during 
 the completion of the picture. 
 
 True fresco did not come into use in mediaeval times 
 until the close of the fourteenth century. About the year 
 1390, Pietro d’Orvieto painted some subjects from Genesis 
 in the Campo Santo at Pisa. In 1503, Pinturicchio, at 
 Siena, began some works in fresco, which he finished in 
 tempera with lakes and other pigments injured by lime. 
 This mixed method was much used in Italy to a late 
 period, as it enabled a greater richness of effect to be 
 attained. For the palette of the painter in true fresco is 
 severely restricted in certain directions, very few colours 
 of organic origin withstanding the decomposing action of 
 lime. It is a good plan to test each pigment intended to 
 be employed in this method : The pure pigment is thinly 
 painted over a slab of plaster-of-Paris, and then half of it 
 is to be moistened with lime- or baryta-water. No change 
 of hue, only a lightening of the tone, should be observed, 
 after drying, in the treated portion. Prussian blue may 
 be named amongst the pigments most quickly and seriously 
 altered by lime ; it becomes a mere stain of rust. 
 
 Although it might have been expected that the earthy 
 pigments, terre verte, yellow ochre, and raw sienna, would 
 prove peculiarly suitable for use in fresco-painting, the 
 examination of works executed in this method, during 
 the last half-century in England, does not confirm this 
 expectation. Indeed, it is found that the most friable 
 portions of such frescoes are precisely those in which 
 these pigments have been freely employed. This remark 
 applies particularly to terre verte, which is found to have 
 become swollen and easily detachable. 
 
 As lime in the caustic state acts strongly upon wood. 
 
FRESCO-PA INTING 
 
 307 
 
 it is necessary to employ palettes of zinc or glazed 
 earthenware ; bone or ivory palette-knives are preferable 
 to those of steel. 
 
 Asiatic Fresco . — The remarkably successful explorations 
 of Sir Aurel Stein among the buried sites of Chinese 
 Turkestan have brought to light numerous examples of 
 a peculiar variety of fresco-painting. In the brief ‘ Guide 
 to the Stein Exhibition of 1914,’ in the British Museum, 
 the method is vaguely described thus : ‘ A preparation of 
 lime is spread over a foundation of mud and chopped 
 straw, and the pigments applied to the surface while it 
 is wet.’ In reality the process adopted in these works, 
 dating from the third to the tenth century of our era, may 
 be more exactly described in the following words : On 
 a backing of the ordinary local loess mixed with the 
 chopped stems and leaves of the common reed, there 
 was spread a thin flat coating of impure burnt gypsum 
 made into a cream with water. Pigments such as an 
 iron red, malachite, a charcoal grey and an ochre, some- 
 times mixed with the cream of burnt gypsum, were then 
 painted on while the surface was still moist. On drying 
 the colours became fixed, not by carbonation, as in true 
 fresco work, but simply by loss of the solvent water 
 present and the crystallization of its content of gypsum. 
 As I made numerous analyses for Sir Aurel Stein of 
 painted plaster, from sites at Kadalik, Miran,and Mingoi, 
 I can speak with confidence of the essential distinction 
 between Asiatic and European fresco : the former is 
 essentially a plaster-of-Paris method. 
 
 3. In stereochromy, or water-glass painting, a process 
 introduced more than sixty years ago, the fixative em- 
 ployed is an alkaline silicate dissolved in water. From 
 time to time different experimenters have improved the 
 
STEREOCHROMY 
 
 joS 
 
 painting-grounds, the preparation of the pigments, and 
 the mode of applying the fixing liquid ; but the main 
 chemical actions involved in this method of painting are 
 identical in all the modifications which have been intro- 
 duced. The constituents and preparation of painting- 
 grounds adapted for this process have been discussed in 
 Chapter II. The pigments should be treated, as recom- 
 mended by Kuhlmann, with some of the fixing liquid, 
 and then reground ; in some cases they require the previous 
 addition of oxide of zinc, powdered marble, powdered glass, 
 carbonate of baryta, soluble silica, hydrate of alumina, etc., 
 in order that their natural inaptitude for equal fixation by 
 the alkaline silicate should be remedied. Opinions differ 
 as to the desirability of treating the painting-ground with 
 some of the water-glass solution before laying on the 
 colours ; but it is essential that if a solution of this silicate 
 be used at this stage, it should be very dilute. The finished 
 painting is sprayed with a warm dilute solution of potash 
 water-glass or potash-soda water-glass, to which has been 
 added liquor ammoniae. The surface is shortly afterwards 
 washed repeatedly with hot distilled water ; and, if neces- 
 sary, the application of the water-glass solution, and the 
 subsequent washing, are repeated. The final result of 
 these operations is to bind the particles of pigment to 
 one another, and to the ground, by means of an insoluble 
 double silicate. This silicate, formed partly out of some 
 of the constituents of the ground, of the pigments, and of 
 the water-glass, mainly consists of silica, lime, and potash ; 
 it often contains zinc, magnesia, and alumina. The soluble 
 salts removed by washing the painting with water are the 
 carbonates of potash and ammonia; when, however, soda 
 is present in the water-glass, carbonate of soda has been 
 formed, and is removed at the same time. The pigments 
 
OIL.PA INTING 
 
 309 
 
 employed in stereochromy are more limited in number 
 even than those available in fresco-painting, and consist 
 chiefly of natural oxides and earths, the artificial oxides 
 and hydrates of chromium and iron, cobalt green, ultra- 
 marine, cobalt blue, and ivory-black. 
 
 4. Oil-Painting and Spirit-Fresco . — The essential charac- 
 teristic of these methods is to be found in the use of a 
 binding material -which is in itself insoluble in water. 
 The painting-ground employed should be dry, and free 
 from alkali and from soluble salts. If it be primed 
 canvas or panel, it is a good plan to cleanse it with oxgall 
 and water, or with a very weak solution of carbonate of 
 ammonia, before commencing work. A discoloured lead- 
 priming should be restored to its original brightness by 
 laying a sheet of white blotting-paper upon it, and then 
 just saturating this paper with a solution of peroxide of 
 hydrogen. The moist surface is now exposed to a 
 moderate degree of heat — as by holding it in front of a 
 fire — which greatly quickens the activity of the peroxide. 
 When the paper has become dry, it may be removed, and 
 the bleaching of the tarnished ground will be found to 
 have been effected, the brown sulphide of lead having 
 been oxidized into the white sulphate. In order to learn 
 whether a plaster-ground or a wall is sufficiently dry to 
 be safely painted upon in oil or spirit-fresco, the gelatin- 
 test may be employed. A small oblong piece of coloured 
 sheet-gelatin is held firmly and closely against the plaster 
 or wall, by means of a stick applied at the centre. If 
 hygroscopic equilibrium have been established between 
 the wall and the air, the gelatin will remain flat ; if the 
 wall be moister than the air, the sheet will curl outwards, 
 the inner surface becoming highly convex. Slate and 
 several other suitable painting-grounds may be dried and 
 
310 
 
 OIL-PAINTING 
 
 further prepared for work in oil or spirit-fresco by heating 
 them gradually in a water-oven up to the temperature of 
 boiling water, and then rubbing them with a piece of 
 hard paraffin-wax. The slate is again heated in the water- 
 oven, withdrawn, and then at once rubbed with a dry, 
 warm cloth, so as to remove all excess of paraffin-wax. 
 Other methods of treating stone, etc., for the reception of 
 oil-colours have been previously given. A very con- 
 venient means of neutralizing the residual alkalinity of a 
 lime-plaster ground intended for oil or spirit-fresco painting 
 is afforded by linoleic acid.* This liquid fatty acid is an 
 article of commerce, moderate in price, and easily obtain- 
 able. A wide-mouth tin of it is placed in a vessel of 
 boiling water ; when the linoleic acid is hot, it is paid on 
 to the surface of the plaster with a wide brush, any excess 
 being removed by wiping the ground with a cloth. Solid 
 stearic acid may be melted and used in the same way, 
 but its effect is inferior. 
 
 The vehicles employed in these methods of painting are 
 not miscible with water — are, in fact, hydrofuge materials 
 repellent of moisture. If an absorbent ground or other 
 porous material be soaked with water, and then covered 
 with oil, as the water evaporates the oil penetrates, and 
 at last completely takes its place. But, on the other 
 hand, the reverse process cannot be carried out, since the 
 water outside will not displace the oil inside. These 
 vehicles are either oils or else solid substances in solution 
 — solids which, though insoluble in water, may be dis- 
 solved with more or less ease in one or other of a long 
 series of liquid solvents (Chapters V., VI., XI., and XII.). 
 The changes experienced by these vehicles and their 
 
 * By linoleic acid is here meant the mixture of fatty acids 
 obtainable from raw linseed oil. 
 
OIL-PAINTING 
 
 3'i 
 
 constituents during the painting process may be thus 
 summarized ; 
 
 (a) The oils used absorb oxygen from the air, increasing 
 in weight thereby to the extent of lo or ii per cent. — 
 such increase in weight being accompanied by a consider- 
 able increase in bulk. This latter change is clearly shown 
 when a layer of a drying oil, spread upon glass, is allowed 
 to dry ; it then becomes rippled or wrinkled from ex- 
 pansion ; such expansion, owing to the viscosity of the 
 oil, takes place mainly in a direction perpendicular to 
 that of the surface of the glass. 
 
 (d) The above-described absorption of oxygen by the oil 
 employed in painting results in the formation of a sub- 
 stance or mixture of substances called linoxine. Now this 
 product is not only solid instead of liquid, but it is almost 
 insoluble in the usual solvents of oils unlike the oil from 
 which it has been formed. But there are circumstances, 
 not yet accurately defined, in which linoxine itself occa- 
 sionally suffers a peculiar change, finally becoming brown 
 in colour, tacky in consistence, and soluble even in spirits 
 of wine. This degradation of linoxine is, however, of very 
 rare occurrence in the ordinary practice of oil-painting. 
 A singular circumstance connected with the transformation 
 of ‘ linolein ’ into ‘ linoxine ’ has been noticed ; this change 
 is accompanied by the formation of hydrogen peroxide, a 
 compound which is also produced during the oxidation of 
 the terpenes. The continuous production of the peroxide 
 may be recognised on the surface of an oil-painting long 
 after it has been completed by the blue colour which it 
 develops in starch-paste containing potassium iodide. 
 
 (c) The resins present in varnishes and media contract 
 for some time after the major part of their volatile solvent 
 has escaped by evaporation, and thus leave a residue which 
 
3'2 
 
 OIL-PAINTING 
 
 becomes fissured. In a properly-proportioned medium 
 this contraction should be balanced, or rather more than 
 balanced, by the expansion of the oil present. Hence the 
 desirability of associating a varnish (or a resin dissolved 
 in a volatile solvent) with a drying oil, in this method of 
 painting. 
 
 {d) Waxes and solid paraffins, when once deposited from 
 a solution by the escape of the .solvent, neither expand 
 nor contract by desiccation or oxidation, but only through 
 changes of temperature. 
 
 (e) Most of the liquid solvents simply evaporate, leaving 
 no fixed residue due to their previous presence. But spirit 
 of turpentine and oil of spike generally behave differently. 
 Some kinds of spirit of turpentine differ from the majority 
 in this particular, but the remainder suffer two simul- 
 taneous changes. A portion evaporates ; another portion 
 absorbs oxygen from the air, becoming converted into a 
 sticky, yellow, and resinous substance, which remains 
 behind. The resin thus formed is a very objectionable 
 constituent in the structure of a picture, and its production 
 should be avoided either by employing a variety of tur- 
 pentine not subject to easy resinification, or by using a 
 freshly-distilled turpentine which has been secluded from 
 the air, and in which a few lumps of freshly-burnt lime 
 have been placed, to remove water and such resinous 
 matters as may be produced. 
 
 An important precaution to be observed in the ‘conduct ’ 
 of a painting during its progress is based upon the two 
 actions just referred to, namely, the oxidation of the oil 
 during its hardening, and the escape of volatile solvents. 
 The latter action takes place more easily than the former, 
 and so if a picture is to be carried on rapidly to comple- 
 tion, the earlier and lower paintings should contain las 
 
OIL-PAINTING 
 
 313 
 
 oil than those nearer the surface, into which more oil and 
 less resin (copal or amber), dissolved in some volatile 
 solvent, should be introduced. If the reverse order be 
 followed, the highly oleaginous layers below, having had 
 no sufficient opportunity for oxidizing, drying, and harden- 
 ing, will be rent by the strong and quickly-drying resinous 
 layers above them. 
 
 The harder resins, paraffin-wax, wax, and oil, possess 
 in varying degrees the power of ‘ locking-up ’ the pigments 
 with which they are mingled, in such a way that these 
 become much less liable to act upon one another, and to 
 suffer injury from external agencies. In a measure they 
 repel and exclude moisture and oxygen — two of the chief 
 agents of chemical change. But the value of these 
 ‘ locking-up ’ materials has been exaggerated : they often 
 prove quite ineffectual in preventing the oxidation or 
 other change suffered by non-permanent pigments and the 
 inter- action of pigments. For instance, the oil which 
 surrounds each particle of cadmium yellow and emerald 
 green, in a mixture of these two oil-paints, is not capable 
 of preventing the formation of the black sulphide of 
 copper. And Dr. A. P. Laurie has found that when a 
 layer of linseed-oil is interposed between these oil-colours 
 separately spread, it is the emerald green which appears 
 to travel towards the cadmium yellow — perhaps owing to 
 its solubility in the medium. In consequence, the pro- 
 duction of spots of black sulphide of copper occurs chiefly, 
 if not entirely, on that side of the oil-layer which is in 
 contact with the cadmium yellow. To Dr. Laurie we are 
 also indebted for a very ingenious method of comparing 
 the locking-up function of various oils and resins. Dr. 
 Laurie prepared some anhydrous sulphate of copper which 
 is white, but acquires a blue colour when exposed to 
 
314 
 
 OIL-PAINTING 
 
 moisture. He ground this white sulphate with various 
 media, painted glass slides with the mixtures, dried them 
 in a desiccator, and then exposed them to moist air. A 
 solution of amber in turpentine proved superior, in its 
 power of resisting the access of moisture, to boiled linseed- 
 oil, oil-copal varnish, amber dissolved in oil, resin or 
 mastic dissolved in turpentine. Another set of trials, in 
 which the test substance was ground in linseed-oil, allowed 
 to harden in a desiccator and then coated with different 
 varnishes, indicated a temporary superiority on the part 
 of mastic in turpentine, and of oil-copal varnish over 
 amber or copal in turpentine. The inferiority of the latter 
 solutions may be due to the rupture in continuity of the 
 resinous films which they leave on evaporation. (See 
 Journal of Chemical Industry, June, i8go.) But it must 
 not be forgotten that many an old oil-picture furnishes 
 distinct evidence of the value of resinous matters (such 
 as Strasburg and Venice turpentine) in locking up such 
 changeable and destructive pigments as verdigris and 
 orpiment. The slow and laborious execution of such 
 paintings constituted an important element in the success 
 achieved, for each layer dried and hardened before the 
 next was applied. 
 
 It should be noted that different oil-paints contain very 
 different percentages of oil. This fact should be taken 
 into account, so far as possible, in adjusting the amount 
 of resinous matter to be introduced during the course of 
 work upon an oil-picture. A table giving approximately 
 the quantities of oil required in grinding lOo parts of 
 various dry pigments as oil-paints will be found on 
 page 66. Further information concerning such pigments 
 is given in Chapters XIII. to XIX. 
 
 In completing an oil-picture, the three operations of 
 
OIL-PAINTING 
 
 315 
 
 ‘ glazing,’ ‘ oiling out,’ and ‘ varnishing ’ remain to be con- 
 sidered. As to glazing and oiling out, it should be stated 
 that drying oil, with a little copal or amber varnish, should 
 alone be employed — mastic varnish should never be added 
 to the oil. Of course oil-paints are used in admixture 
 with oil and copal for glazing purposes. If mastic be 
 introduced, a risk is incurred of its partial removal during 
 any cleaning operation to which the picture may be after- 
 wards subjected. The question of the kind of varnish to be 
 finally applied to an oil-picture has been much discussed. 
 Our choice lies between a strong irremovable varnish, and 
 a weak one capable of being abraded by friction, or of being 
 dissolved by the application of a suitable solvent, which 
 will not touch the true painting beneath. Mastic dissolved 
 in turpentine fulfils the latter conditions ; copal or amber 
 dissolved in oil and thinned with turpentine, and mixed with 
 a little oil, constitutes a strong, hard, irremovable protec- 
 tion to the surface, and becomes a part of the picture itself. 
 Under no circumstances should any varnish be applied to 
 the painting until the latter has become thoroughly hard 
 and dry ; the danger of tearing the layers of paint by 
 such application will then have been reduced to a mini- 
 mum. A further advantage of delay in varnishing a picture 
 accrues through the increasing insolubility with age of 
 the oxidized oil present therein, the pigments associated 
 therewith becoming less liable to removal by any treat- 
 ment to which the work may afterwards be submitted. 
 
 The chemistry of Gambier-Parry’s spirit-fresco method, 
 and of the process in which paraffin-wax and copal varnish 
 are employed as the vehicle, is essentially the same as that 
 of oil painting. The wax or paraffin-wax is introduced 
 merely to secure a matt surface. Pictures executed in 
 these methods are, of course, never varnished. The 
 
SPIRIT-FRESCO PAINTING 
 
 method of spirit-fresco was devised by the late Mr. 
 Gambier-Parry with the object of obtaining such effects 
 in mural paintings as are realized in true fresco, but with 
 greater ease in working, and greater permanence under 
 adverse atmospheric conditions. He desired to exclude 
 linseed or other fixed drying oils completely from the 
 medium and other materials employed. With this end 
 in view, he directed that the pigments used should be 
 ground up, not with oil, but with the medium itself. He 
 was apparently unaware that the copal varnish, which 
 enters largely into the composition of his vehicle, contains 
 a greater proportion of oil than of any other ingredient 
 (see Chapter XII.). So, after all, the medium used in 
 spirit-fresco differs from that generally employed in oil- 
 painting rather in the proportions than in the nature of its 
 ingredients. Thus in working with it we shall find that 
 its binding character is obtained as a result of the same 
 two changes which cause the fixing and solidification of an 
 oil painting, namely, the oxidation of the oil, and the 
 desiccation of the resin. The wax present suffers no 
 chemical alteration at first, but merely solidifies, although 
 after the lapse of years it is liable to produce a kind 
 of exudation or bloom ; indeed, in the course of years the 
 wax may wholly disappear. It should be added that the 
 painting-ground for this method of working is first 
 prepared with the medium diluted with oil of turpentine 
 (see Chapter II.). 
 
 The method of painting with the paraffin-copal medium 
 involves the same chemical and physical changes as 
 those which occur in the use of the spirit-fresco vehicle, 
 and is carried out in the same manner. Colours stiffly 
 ground in oil may be used or in a mixture of the medium 
 with oil : dry colours ground in the medium generally 
 
WATER-COLOUR PAINTING 
 
 317 
 
 are to be preferred. The medium may be diluted to any 
 desired consistency with spirit of turpentine or with oil 
 of spike, but no dilution further than that required to 
 secure perfect freedom in the manipulation and use of the 
 paints is desirable, while it is important to remember that 
 the use of abundance of medium is necessary to bind 
 the particles of pigments firmly together. Artists have 
 sometimes found that a picture painted in spirit-fresco 
 will cede colour to a cloth used in rubbing its surface. 
 This result is due either to excessive use of a diluent 
 in working with this medium, or to a deficiency of oil 
 in the copal-varnish used. I have never known a friable 
 surface to be formed where the colours employed had 
 been ground in oil instead of in the medium, or where 
 a little extra oil had been added to the latter. 
 
 5. Water-colour Painting . — The usual binding material 
 in this method is gum ; glycerin and honey are also 
 employed to some extent. Raw honey should never be 
 used, but only one of the sugars it contains, known to 
 chemists as Icevjilose (Chapter VIII.). Great care must 
 be taken not to introduce any unnecessary excess of 
 either glycerin or laevulose, as these materials attract 
 moisture from the air, and we know that moisture 
 is one of the most potent agents in causing injury to 
 works in water-colour. Glycerin and laevulose are, 
 however, useful, when employed in moderation, for pre- 
 serving the pigments in working condition, and in counter- 
 acting the tendency of gum to crack. The media used 
 in water-colour painting, consisting wholly of aqueous 
 solutions, afford very slight protection to the pigments 
 used. In the presence of the moisture of the ground 
 (paper often contains naturally 10 per cent, of water) 
 and of the air, water-colour pigments have abundant 
 
3i8 
 
 WATER-COLOUR PAINTING 
 
 opportunities, not only of acting upon one another^ 
 wherever from their chemical constitution such action 
 is possible, but also of being acted upon by external 
 agents. Thus it comes to pass that several pigments 
 (vermilion, for instance, and emerald green) useful in 
 oil-painting cannot be safely used as water-colours. 
 Again, there are a few pigments (such as strontia yellow) 
 which are soluble in water, and which consequently may 
 gradually sink into the paper, and so partially disappear 
 from the surface. 
 
 Assuming the paper-ground to be of linen-pulp, and 
 free from ‘ filling,’ from bleaching substances, from anti- 
 chlors, and from fragments of iron, it will still contain 
 about 5 per cent, of size. When in preparation for 
 painting it is moistened with water, this size swells, and 
 on the subsequent application of washes of pigments, 
 enters partially into mechanical union with them, so 
 that the various coloured materials applied to the sur- 
 face become associated with the size rather than with 
 the paper-fibres. One paint, Indian ink, itself contains 
 size, and for this reason when washes of it are laid upon 
 paper previously damped, their incorporation with the 
 size of the latter is so intimate that their removal is 
 impracticable. The size in a water-colour drawing be- 
 comes in time partly coagulated and insoluble ; the gum 
 merely dries. Instances are known where the size has 
 in some degree ultimately perished. 
 
 6. Pastel, Charcoal, Plumbago, Silver-point . — The com- 
 mon characteristic of all the processes which form our 
 sixth group is the absence of any vehicle or binding 
 material. The usual ground on which drawings in 
 the above-named substances are executed is paper 
 (Chapter I.); but as the hold of coloured chalks and 
 
PA ST EL-PA IN TING 
 
 319 
 
 of charcoal is very precarious, the paper is generally 
 mounted on some comparatively rigid backing, such as 
 millboard, cardboard, copper, or panel. If a chalk or 
 charcoal drawing be carried out on paper which has first 
 received a wash of gum-water or of dextrin-solution, it 
 is easy to effect a partial fixation of the powdery pigment 
 by subsequently steaming the finished work, although it 
 is usual to employ a fixing solution in the form of very 
 fine spray to the finished drawing. For pastel work a 
 specially prepared paper is now generally employed. 
 This has a surface of finely-powdered pumice, which 
 affords an efficient tooth, and helps in securing the 
 coloured chalks or clays. This result is further aided 
 by the plan of working in and mingling the pigments by 
 means of rubbing with the fingers and the palm of the 
 artist’s hand. Pastel-paper is often made of inferior 
 pulp, and lacks strength. It should be less sized than 
 paper intended for water-colours. Pastel colours are 
 generally made with a basis of purified chalk or pipe-clay 
 mingled with the usual pigments in powder, a slight 
 degree of cohesion being secured by making up the 
 crayons with starch-paste or gum-tragacanth. 
 
 11 For fixing pastel-drawings it is convenient to use 
 the following medium: Pound 15 grams dry casein and 
 3 grams of borax together, and then shake the powder 
 with constant stirring into 100 cubic centimetres of dis- 
 tilled water. After some hours a syrupy mass will have 
 been formed. Dilute this with more water so as to 
 make the liquid up to 750 cubic centimetres ; then add 
 250 cubic centimetres of spirits of wine. After a time 
 a white precipitate may form ; pour off the somewhat 
 opalescent liquid from this sediment. This fixative is to 
 be sprayed on to the face of the pastel, care being taken 
 
320 
 
 PASTEL-PAINTING 
 
 to prevent the liquid from gathering in actual drops upon 
 any part of the drawing. When the surface looks moist 
 and shiny, it shows that it has been sufficiently dosed 
 with the fixative. The more completely the ground is 
 protected by the colour laid on, the less risk there is of 
 the fixation affecting the appearance of the picture. If, 
 however, the effect of the work has been obtained by a 
 mere whiff of the powdery pigment, it is wiser to omit 
 the fixing procedure, for the delicacy of such very fine 
 layers of colour would thus be impaired. In any case, 
 the artist who is concerned for the permanence of his 
 work will always try to obtain his effects by building up 
 as solid a layer of colour as possible. 
 
 H Pastels, as already mentioned, containing no binding 
 material, or next to none, drawings made with them are 
 exempt from the drawbacks inseparable from the use of 
 vehicles. Consequently there is no fear of the surface 
 cracking, darkening, blooming, becoming brown, or other- 
 wise altering. When we further consider that pastel- 
 drawings, unlike water-colours, depend for their effect on 
 the presence of a fairly solid layer of pigment, and that 
 many colours which are unstable when employed in 
 other methods of painting, have proved to be durable in 
 pastel, we are bound to admit that this beautiful technique 
 is not only simple in method but expressive in the effects 
 which it commands ; but is only capable of producing 
 drawings which last better than most others, provided 
 they are protected by glass, and are not exposed to 
 damp. 
 
 U Since the pastel crayons of the shops bear usually no 
 indication of the pigments employed to colour them, and 
 frequently contain unstable coal-tar dyes, special care 
 must be taken to test their permanence when exposed to 
 
PASTEL-PAINTING 
 
 321 
 
 light. To do this it will suffice to expose to direct sun- 
 shine in bright weather one half of a strip on which clear 
 tones of the set of coloured pastels which we wish to use 
 have been spread and fixed. It is possible, if the sun- 
 shine be strong, to detect the more alterable pastels after 
 a few days’ exposure. For serious work the artist should 
 use only such pastels as have stood the test. It is 
 fortunate that, owing to the absence of any medium, 
 chemical interaction between pastel -pigments when 
 mixed together in the process of painting is virtually 
 non-existent. 
 
 Details concerning the making at home of pastel- 
 crayons will be found in W. Ostwald’s ‘ Letters to a 
 Painter,’ English edition, pp. 22-27. Here we need add 
 only the following memoranda ; Excellent pastel-grounds 
 may be prepared by laying, on Bristol board or stout 
 drawing paper, a thin and even coat of powdered pumice 
 mixed with liquefied starch (see p. 95). Or the same 
 coat may be spread upon a surface of a fine fabric, such 
 as thin calico, linen, or silk, previously secured to the 
 board or paper by means of starch-paste. 
 
 In plumbago (lead-pencil) and silver-point work, the 
 mechanical adhesion of the coloured particles is naturally 
 less imperfect than in pastel, a portion of the plumbago 
 or silver becoming, in fact, incorporated with the fibres 
 of the paper-ground. This is particularly the case with 
 silver-point, in which method the ground receives a 
 particular preliminary preparation. One of the best 
 materials for this purpose is Chinese white (oxide of 
 zinc). An even wash of this pigment in the form of 
 ‘ moist ’ water-colour is first spread over the paper. As 
 a silver-point drawing is often heightened with touches 
 of Chinese white, it is desirable to bring these into promi- 
 
 21 
 
J22 
 
 SILVER-POINT DR A WING 
 
 nence by tinting the ground. For this purpose a small 
 quantity of some permanent pigment is mixed with the 
 wash of Chinese white. Yellow ochre, raw umber, green 
 oxide of chromium, Mars violet, ultramarine with a little 
 ivory-black, may be used. The ‘ tooth ’ of surface which 
 increases the attrition of the silver-point is, however, 
 furnished by the presence of the Chinese white. It 
 should be added that the silver used should be free from 
 any alloy of copper, which hardens the metal, but may 
 advantageously contain a few per cents, of metallic lead ; 
 an alloy of 2 parts of lead with i part of tin was some- 
 times used instead of silver. The silver in silver-point 
 drawings is liable to become brown from the sulphur 
 compounds in impure air. The blackening of the high 
 lights in old silver-point drawings is due to the tarnishing 
 of the lead white employed ; it may be got rid of by 
 keeping the drawing for some time in an atmosphere of 
 moist ozone, or by a careful treatment with a solution of 
 hydrogen peroxide in ether. 
 
 A pointed pencil of pure gold is occasionally used 
 instead of one of silver or graphite. It produces on a 
 prepared paper surface the same grey line, and is theo- 
 retically a perfect material for drawing purposes. But, 
 strange to relate, gold-point drawings have been observed 
 to suffer change, becoming nearly invisible, not by reason 
 of any chemical action on the metal, but in consequence 
 of a rearrangement of the metallic particles whereby 
 their grey hue disappears and the original yellow lustre 
 of the gold is resumed. Drawings in platinum-point are 
 not susceptible of this change. The platinum employed 
 must be pure, otherwise this metal is too hard for com- 
 fortable manipulation. 
 
 Pastel or coloured chalk drawings frequently show a 
 
PA ST EL-PA INTING 
 
 323 
 
 j higher degree of preservation, so far as certain hues are 
 I concerned, than contemporary works executed in oil. One 
 I can easily account for the pure and fresh air of old pastel 
 j drawings, knowing that they have been carefully mounted 
 
 j and framed, and that there has been no oil or resin to 
 
 ! yellow and darken the pigments. But how can the remark- 
 j able state of preservation in which the ‘ carnations ’ are 
 j found in so many examples be explained ? Has the 
 intimate commixture of chalk or of clay with crimson lake 
 preserved the latter from the destructive action brought 
 about by light ? If there have been such a preservative 
 action, has it been physical rather than chemical ? 
 Answers to such questions must be reserved until the 
 chemistry of coloured pastels has been thoroughly studied. 
 It should, however, be recollected that the white basis of 
 coloured pastels is not always the same. In the eighteenth 
 century it seems to have been invariably purified chalk, 
 that is, ‘ whitening ’ or ‘ whiting,’ which is essentially 
 calcium carbonate. But, on examining lately a well-known 
 make of French pastels, a considerable percentage of 
 calcium sulphate was recognised, in addition to chalk, 
 j Further experiments seem to show that the colouring 
 i matter used is first ground up with a mixture of chalk and 
 j plaster-of-Paris, and that, in consequence, the subsequent 
 j| addition of water causes the whole to set into a mass of 
 j| just sufficient tenacity to hold together, though very soft 
 and fragile. In this way the use of starch-water as a 
 binding material is obviated. In other pastels pipe-clay 
 ■ or china-clay has been employed as the basis for the 
 j colouring matter. 
 
 Paintings and drawings executed in fresco, in tempera, 
 and in water-colours, may be protected from the hostile 
 attacks of impure air and moisture by applying to the 
 
324 
 
 PA STEL-PA INTING 
 
 finished work a coating of pure hard paraffin-wax. If 
 such an after-treatment is contemplated in the case of a 
 work executed in water-colour the amount of vehicle em- 
 ployed (gum, etc.) should be reduced to the necessary 
 minimum. The mode of applying the paraffin-wax is 
 described further on at the end of Chapter XXV., 
 pages 356-357. 
 
CHAPTER XXIV 
 
 THE STUDY OF OLD PAINTINGS AND DRAWINGS 
 
 The study of old pictures, with the view of discovering 
 the causes of the physical and chemical changes which 
 have taken place in them, is fraught with interest. The 
 material on which they are executed, the medium em- 
 ployed, the pigments which can be identified, and the 
 varnish which has been applied to the surface, all these 
 matters demand attention. The dates of the various 
 works examined, the countries in which they have been 
 produced, the conditions under which they have been 
 preserved, and the treatment to which they have been 
 subjected, constitute elements in the investigation which, 
 whenever possible, should be kept in view. But the 
 adequate treatment of this extensive subject requires 
 not a brief chapter, but a whole volume. And then our 
 materials, though in some directions most abundant, are 
 in great measure inaccessible. We must confine our 
 attention to such specimens as are shown in our public 
 galleries. Even then we find ourselves hampered by the 
 impossibility of making the thorough investigation which 
 is desirable, and by the too frequent absence of certain 
 important data. In the present chapter we limit ourselves 
 to some general remarks, and to a few brief observations 
 upon a certain number of pictures in the National 
 
 325 
 
326 
 
 CHANGES IN PICTURES 
 
 Gallery, the National Portrait Gallery, and the Victoria 
 and Albert Museum ; and our selection will be confined 
 to paintings in oil, tempera, and water-colour, as the 
 available works in fresco in England are too few and too 
 fragmentary to furnish the information for which we are 
 seeking. 
 
 It will hardly be necessary, with respect to changes 
 in painting-grounds, to do more than refer the reader to 
 what has been already said on this subject in Part I. of 
 the present work. The causes of the decay of panels and 
 of the convexity which their painted surface shows in so 
 many cases have been already discussed. The disruption 
 of the ground and of the superposed layer of paint con- 
 sequent upon this convexity needs no further explanation. 
 The staining of the white priming which has been laid on 
 certain kinds of wood has been traced to dark-coloured 
 exudations of soluble organic matters. The grain of 
 some kinds of wood, notably of oak in pictures of the 
 Dutch and Flemish schools, often becomes painfully con- 
 spicuous in course of time, and gives to the surface-cracks 
 a peculiar character. The microscopic structure of 
 certain woods and the peculiar distribution of their histo- 
 logical constituents serve to explain these appearances. 
 The causes of the decay and cracking of gesso-grounds 
 in which size has been used, and the injurious mechanical 
 and chemical alterations which paper and primed canvas 
 may exhibit, have been already touched upon. The 
 other conspicuous changes which may be observed in 
 old pictures are connected with the medium, the pig- 
 ments, or the varnish. All these matters have been 
 referred to in Parts II. and III., yet there are three points 
 on which further discussion may not be out of place. I 
 refer to the number and character of the pigments used 
 
OLD PAINTINGS 
 
 327 
 
 in early works, to the manipulation of the paint, and to 
 the employment of white lead. Now, the pigments to 
 which the earlier painters were restricted were not only 
 few in number, but were mainly of mineral origin. At 
 the first glance one sees that the Italian artists of the 
 thirteenth century, and of the first half of the fourteenth, 
 worked almost exclusively in natural inorganic pigments, 
 two of which stand out in their works in startling promi- 
 nence, namely, vermilion and ultramarine ; and their 
 pigments were nearly all opaque or semi-opaque. The 
 absence of any pure and brilliant yellow, opaque or 
 transparent, from their pictures is another noticeable 
 characteristic. In the works of Jan van Eyck and 
 Rogier van der Weyden, and in those of many of the 
 Italian painters of the fifteenth century, the range of 
 colours is more extensive. Pigments which could not be 
 used in tempera or size, or which were semi-opaque when 
 employed with these vehicles, gave great richness and 
 variety to their works in oil. This tendency to press 
 into the service of pictorial art other coloured materials 
 besides those of mineral origin, namely, animal and vege- 
 table pigments in considerable variety, became more 
 marked as time went on. And during the nineteenth 
 century the progress of synthetical chemistry placed at 
 the disposal of the picture-maker a long series of pigments 
 — good, bad, and indifferent, — so that the chances of 
 introducing dangerous and fugitive colours have been 
 enormously increased. It is to this increase in the 
 number of pigments, and to their greatly extended range 
 of composition, rather than to their mode of preparation, 
 that one should attribute in great part the frequent 
 deterioration of modern paintings. 
 
 But the second point to which reference has been made 
 
328 
 
 OLD PAINTINGS 
 
 is concerned with the mode of laying on colours. The 
 exquisitely minute and careful manipulation of Jan van 
 Eyck, of Fra Giovanni Angelico, of Hans Memlinc, of 
 Gerard Dou, of Gerard Terborch, and of many another 
 old master, could not have been hurried. It was solid 
 but smooth ; the paints hardened gradually into one 
 organic whole. And we could name several oil-painters 
 of the eighteenth century, and even of the present day, 
 whose work is executed in the same safe manner, and 
 which, were it not for the occasional introduction of 
 dubious materials, would be sure to remain sound for 
 hundreds of years, provided, of course, that the painting- 
 ground be satisfactory. But this careful mode of painting 
 does not suit the temperament, nor is it capable of 
 expressing the ideas of many artists. The thick impasto 
 and loaded colour, the effective brush-work, the juicy 
 pencil, and the dashing haste of several painters often 
 prove to be elements of danger. 
 
 The third point, concerning which a few remarks seem 
 advisable, is connected with the use of flake-white. There 
 are many old oil-paintings in which the only perfectly- 
 preserved parts of the v/ork are those in which flake- 
 white has been used with considerable freedom. Here 
 the continuity of the layer of pigment is intact, elsewhere 
 there are cracks and roughnesses and scalings-off. To 
 what cause is the preservation of the high lights and of 
 the paler flesh-tints attributable ? The association of 
 hardness and cohesiveness which these parts show is 
 traceable to the white lead. This pigment was formerly 
 always prepared in such a way as to contain a consider- 
 able quantity of lead hydrate. The particles of this 
 hydrate do not lie, as it were, side by side with those 
 of the chief constituent (the lead carbonate), but are so 
 
ACTION OF WHITE LEAD 
 
 329 
 
 united with the latter as to form one complex compound. 
 This compound acts upon the linseed or other drying oil 
 with which it is ground, forming a substance of great 
 hardness and durability. 
 
 This substance — that is, the entire mass of the white- 
 lead ground in oil which has become solid, tough, and 
 hard— seems to contain a small percentage of a lead- 
 soap, formed probably out of the free fatty acids of the 
 linseed-oil. But whatever the complete explanation of 
 this hardening action may prove to be, there can be no 
 doubt that we must attribute to the simultaneous presence 
 of oil and the hydrato-carbonate of lead the preservation 
 of the continuity of surfaces of the whites, and of the pale 
 tints into which white lead enters, in many an old picture. 
 No other pigment in common use is capable of solidifying 
 the admixed oil to anything like the extent that character- 
 izes white lead. Now there are modern preparations of 
 white lead made chiefly by precipitation or the ‘ wet way,’ 
 which produces a pigment containing little or no lead 
 hydrate. Some writers on pigments advocate the use 
 of these newer products. ‘ Why,’ say they, ‘ should you 
 carefully exclude from your pictures oils, and varnishes, 
 and siccatives which contain lead in solution, and then 
 introduce the same or a like substance in your white lead 
 ground in oil ?’ Many years ago I tried to answer such 
 a question as this by means of experiment. I was actu- 
 ated by a desire, based on theoretical considerations, of 
 preventing altogether the formation of lead-soaps. I 
 tried comparative experiments with zinc oxide, pure lead 
 carbonate, and the Dutch-made lead hydrato-carbonate, 
 or ordinary flake-white. The two lead pigments (with 
 which alone we are now concerned) were washed 
 thoroughly with distilled water and dried before being 
 
330 
 
 ACTION OF WHITE LEAD 
 
 ground in linseed oil. The oil-paints thus prepared were 
 spread in duplicate series upon glass, paper, and primed 
 canvas ; one set was kept in a dark box, the other was 
 exposed to strong light. So decided was the superiority 
 of the ordinary flake-white over the pure carbonate, when 
 both series of specimens were examined after the lapse of 
 various intervals of time, that I was reluctantly compelled 
 to abandon my recommendation of the latter. Ease in 
 working, solidity of body, and rapidity of drying, were 
 not the only points of superiority ; for the films of paint, 
 after having been kept a year, showed differences in 
 hardness and in smoothness of surface which were all in 
 favour of the hydrated carbonate. No discoloration was 
 observed in the specimens exposed to light, except in the 
 case of the pair upon paper ; the absorbent ground had 
 withdrawn some of the protecting oil, and both specimens 
 had equally darkened. In darkness all the specimens 
 had become of a somewhat greyish yellow, the discolor- 
 ation being about equal in all the pairs, the pair spread 
 on paper having, as in the previous case, become darker 
 than the others. The late Mr. G. W. Wigner tried a 
 somewhat similar series of experiments, and came to the 
 same conclusions. I should add that these deductions 
 were corroborated by the results of other trials, in which 
 numerous permanent coloured pigments mixed in pale 
 tints with these two lead whites were treated in the same 
 way. If, however, we feel bound to recommend the 
 ordinary flake-white instead of pure lead carbonate, that 
 recommendation does not prevent us from excluding lead- 
 containing oils from our pictures, seeing that we possess 
 perfect substitutes for them, and that there is no reason 
 for thus multiplying the causes of possible change. 
 
 Before commenting on some of the lessons to be drawn 
 
ILLUMINATED MANUSCRIPTS 
 
 331 
 
 from individual pictures, it may be desirable to make a 
 few observations on some of the changes frequently ob- 
 servable in old illuminated manuscripts and choral books. 
 The tarnishing of lead and copper pigments laid on with- 
 out any protection but that of gum is very frequently 
 seen. The darkening of vermilion is apparently capri- 
 cious,* but is really explicable in part by the substitution 
 of red lead for vermilion, and in part by the molecular 
 change which the latter pigment is known to suffer, and 
 which has been already described. Ultramarine always 
 stands out absolutely intact ; sometimes it acquires extra- 
 ordinary prominence by reason of every other pigment 
 on a page having altered. The red cochineal and kermes 
 lakes have either gone or become paler and brownish. 
 Sometimes fruits painted in vermilion have been shaded 
 or dotted with a crimson lake, but the latter has dis- 
 appeared, leaving nothing but a slight gummy appearance 
 upon the scarlet ground. Blue flowers painted in smalt 
 and veined with indigo show scarcely a trace of the latter 
 pigment. Verdigris, which is partly soluble in water, 
 has run and discoloured the vellum, and at the same time 
 has acquired a brownish hue. Sap-green, from buck- 
 thorn berries, has faded greatly. Lilien-grun (of the 
 seventeenth century), from the flowers of Iris germanica, 
 has disappeared. 
 
 We now cite a few pictures, out of a large number 
 which have been studied for the purpose of observing the 
 present state of the materials which have been used in 
 their production. We begin with some works in the 
 National Gallery, Trafalgar Square. 
 
 * An initial letter in vermilion, painted in the fifteenth century, 
 and perfectly unchanged, became black by one year’s exposure to 
 sunshine. 
 
332 
 
 OLD PAINTINGS 
 
 Margaritone di Magnano (1216-1293). No. 564. In 
 the very limited palette of this early painter in tempera 
 we note that the vermilion, a yellow earth, lamp-black 
 and a puce colour are well preserved ; the last-named 
 pigment may be a form of iron oxide, and corresponds 
 in hue to the artificially prepared oxide called ‘ Mars 
 violet.’ 
 
 Giovanni da Milano (late fourteenth century). No. 
 579A. The crimson on the robes of two of the three 
 figures which occupy these panels seems to be derived 
 from madder, and is well preserved. 
 
 Jan van Eyck (1390 ?-i44i). No. 186 (dated 1434). 
 The green robe in this famous picture shows distinct 
 cracks, which differ in character and are larger in size 
 than any others in the work. The flesh-tints are per- 
 fectly preserved as to texture. I suspect that verdigris 
 has formed a constituent of the green paint employed. 
 
 Fra Giovanni Angelico (1387-1445). No. 663. The 
 translucent reds and purples in this work have faded 
 somewhat ; the green, which appears to be malachite — 
 ‘ green bice ’ — has stood. On the whole this exquisite 
 work in tempera is remarkably well preserved. 
 
 Dierick Bouts (1410 ?-i475). No. 664. Painted on 
 linen which had received a vevy thin priming ; the pre- 
 servation of this work, which has never been varnished, 
 is remarkably good except in two particulars — the red 
 pigment used for the sleeves, linings of robes, etc., having 
 faded, and the white paint on the dress of the Virgin 
 having partially scaled off. From certain peculiarities 
 in the touch, and from the minutely wrought details of 
 the landscape, I conclude that the medium used could 
 scarcely have been the usual egg-yolk tempera, but was 
 rather a thin size. 
 
OLD PAINTINGS 
 
 333 
 
 Bennozzo Gozzoli, School of (fifteenth century). No. 
 
 591. The vermilion in this tempera picture is preserved 
 in startling brilliancy ; the translucent reds have become 
 rather faded and embrowned. 
 
 Melozzo da Forli (1438-1494). No. 755. It is prob. 
 able that verdigris was employed in painting the green 
 carpet in this work. If so, the cracks in this part of the 
 picture (more conspicuous here than in other parts) would 
 be due to the corrosive action of this dangerous pigment, 
 
 Tuscan School (end of fifteenth century). No. 781. 
 The lining of the cloak of Tobias in this picture seems to 
 have been painted with verdigris ; it is now very dark, 
 in parts nearly black, although the pigment used has 
 evidently been mingled with much protective resin, as its 
 thickness is excessive when compared with that of other 
 parts of the work. 
 
 Gregorio Schiavone (fl. 1470). No. 630. The madder 
 and vermilion in the robe of one of the figures in this 
 tempera picture are well preserved. This is also the 
 case in another work by the same artist in the author’s 
 possession. 
 
 Gheeraert David (1460-1523). No. 1,045. The fine 
 crimson glazings of madder-lake in this oil picture are in 
 perfect preservation. The same remark may be made 
 concerning another picture (No. 1,432) by the same artist. 
 
 Michelangelo Buonarroti (1475-1564). No. 790. This 
 unfinished tempera picture affords an instance of the 
 stability of vermilion mixed with red-lead (in the robe of 
 one of the figures), of terre verte and of madder-lake. 
 The last-named pigment is also to be noted in the well- 
 preserved hatchings and stipplings on the robes of two of 
 the angels in No. 809. 
 
 Ridolfo del Ghirlandaio (1483-1561). No. 1,143. This 
 
334 
 
 OLD PAINTINGS 
 
 oil picture, originally painted on wood but transferred to 
 canvas, has been repaired and repainted in several places. 
 But the red glazings, apparently madder-lake, and the 
 green colour, seemingly verdigris on malachite, are, if 
 original, well preserved. The preservation of verdigris 
 when glazed on malachite is not unusual ; the two pig- 
 ments are closely related chemically, and are not likely 
 to react upon or injuriously affect each other. 
 
 In the National Gallery there are ten portraits in wax- 
 pigments from the Hawara Cemetery in the Fayum, 
 Egypt. A few of these portraits from this Cemetery are 
 on canvas, but the great majority on panels of wood. 
 There is a rich purple paint in several of these works, a 
 purple which one might perhaps be inclined to identify 
 with Tyrian purple from Purpura lapillus and other mol- 
 luscs, but which the examination of certain specimens of 
 ancient pigments leads one to conclude to be a madder 
 derivative. Anyhow, it has lasted, apparently unchanged, 
 for some eighteen centuries. But it must be rem.embered 
 that these remarkable paintings (Nos. 1,260-1,265, and 
 1,267-1,270) have been preserved in darkness almost from 
 the time when they were executed by Roman artists in 
 the period 80 to 180 a.d. The other pigments in these 
 paintings are yellow, red and brown ochre, charcoal 
 black, a blue consisting of a copper-calcium silicate, a 
 green from malachite, and perhaps verdigris also. An 
 orange-red pigment may be either red lead or realgar. 
 The pigments, incorporated with wax, were laid on, in a 
 fused condition, upon a distemper priming. 
 
 It happens that some information as to the pigments 
 actually employed by a Greek or Graeco- Roman artist of 
 the second century is furnished by six specimens found in 
 one of the Hawara graves by Professor W. M. Flinders 
 
OLD PAINTINGS 
 
 335 
 
 Petrie. These pigments were : white, mainly gypsum ; 
 yellow ochre having, however, almost the precise hue of 
 true antimony yellow ; red lead ; dark red due to ferric 
 oxide ; pink, probably derived from madder; and the lime- 
 copper silicate, known as Egyptian blue. 
 
 As to British pictures in the National Gallery, we can 
 afford space for a few words only. The works of Sir Joshua 
 Reynolds generally show the fading of the crimson lake 
 (from cochineal) in the flesh tints, the vermilion and 
 mineral yellows alone remaining. The picture of the 
 ‘ Infant Samuel ’ may be cited as an example of the large 
 and wide cracks caused by the free use of bitumen (in the 
 dark background). Two paintings by J. M. W. Turner 
 may be particularly mentioned. In No. 560, ‘ Chichester,’ 
 the bright lake-reds in the sky have become reduced to 
 brown stains — anything but luminous. In No. 534, the 
 ‘ San Benedetto, looking towards Fusina,’ we notice how, 
 in a group of small clouds near the top of the picture, 
 where vermilion and lake have been introduced, the 
 vermilion remains, but the lake is now a pale yellowish 
 brown. 
 
 The good condition of the great majority of the pictures 
 in the National Gallery of British Art at Millbank is worthy 
 of note. In this category may be placed the works of 
 Mr. G. F. Watts, R.A., and a number of other paintings 
 out of which I select a very few for special mention. ‘ The 
 Death of Chatterton,’ by Mr. Henry Wallis (No. 1,575), 
 painted in 1856, was retouched subsequently, so far as 
 the breeches of the dead poet are concerned, the crimson 
 lake originally employed having practically perished. 
 No. 1,685, ‘Christ Washing St. Peter’s Feet,’ by Ford 
 Madox Brown, was completed half a century ago. It 
 shows, so far as one can judge, no signs of deterioration. 
 
336 
 
 OLD PAINTINGS 
 
 Of ‘ The Annunciation,’ by D. G. Rossetti (No. 1,210), 
 painted in 1849, the same observation may be made. 
 Anyone familiar with Lord Leighton’s practice and with 
 his extreme care in the choice of permanent pigments, 
 would not expect to see any change in No. 1,574, ‘The 
 Bath of Psyche,’ a work, moreover, which was finished 
 so recently as 1890. To the critic of pigments, paintings 
 of flowers afford much information, partly because they 
 are generally pitched in a very high key, and partly 
 because the living flowers themselves are generally avail- 
 able for comparison with their representations in paint. 
 Two of the pictures by George Lance (Nos. 443 and 1,184) 
 betray the free use made by this accomplished artist of 
 such fugitive pigments as carmine, crimson lake, gamboge 
 and yellow lake. 
 
 We may now pass on to some instructive examples pre- 
 served in the National Portrait Gallery: 
 
 Marc Gheeraedts (1561-1635), No. 64. In this portrait, 
 painted probably in 1614, while the vermilion has stood, 
 the translucent reds appear to have faded and changed. 
 The white sleeves of the dress are ornamented with small 
 sprigs, which are now brown, and were probably originally 
 painted in some vegetable yellow. The reddish pattern of 
 conventional foliage on the cloak now clashes with the 
 colour of the chair, the curtain, and the table ; the hues 
 of all or some of these parts must have altered. 
 
 Sir Peter Lely (1617-1680). No. 509. A well-preserved 
 picture in most respects, but it is probable that crimson- 
 lake has been used for the satin dress, which is now a 
 pinkish grey, and clashes with the flesh tints. This work 
 was probably painted about 1669. 
 
 William Hogarth (1697-1764). No. 289. This portrait 
 of Hogarth, painted in 1758 by himself, affords some in- 
 
OLD PAINTINGS 
 
 337 
 
 |! 
 
 ii 
 
 ij 
 
 ■;| 
 
 'I 
 
 ii 
 
 ) 
 
 ‘I 
 
 i 
 
 !| 
 
 (j 
 
 Ii 
 
 l 
 
 . 
 
 formation as to the pigments he employed. He holds in 
 his left hand a mahogany palette ‘set’ with eight colours. 
 The first of these is white lead, and remains unchanged ; 
 so also is the second, vermilion ; the third is a pale warm 
 brown, precisely the hue of faded crimson lake ; the fourth 
 is now nearly black and undeterminable ; the fifth is yellow 
 ochre, slightly embrowned ; the sixth is a pale yellow, 
 well preserved — much like true N aples yellow ; the seventh 
 is a grey-blue, probably much changed ; and the eighth 
 and last a fair lavender blue colour. The seventh pigment 
 may have been indigo, and the last possibly smalt. The 
 cap on the artist’s head has certainly faded in colour ; 
 probably it was painted with cochineal lake. 
 
 William Hoare, R.A. (1706-1792). No. 112. This por- 
 trait of Alexander Pope, in coloured crayons on grey 
 paper, shows the blues apparently intact. 
 
 Thomas Phillips, R.A. (1770-1845). No. 269. This 
 portrait of Faraday, painted in 1842, shows a large number 
 of cracks, many of them wide. Where flake-white has 
 been introduced somewhat freely, as in the face and hands, 
 the shirt and collar, and the galvanic battery on the table, 
 the paint has not lost its continuity. 
 
 John Partridge (1789-1872). No 342. ‘ Meeting of the 
 Royal Fine Arts Commission.’ This picture was painted 
 in 1846. Almost every part of it is very badly cracked 
 through the use of bitumen, and perhaps also of much 
 megilp. Even the shaded portions of the faces have not 
 escaped, although the high lights have been preserved 
 where the proportion of white lead present has been large. 
 
 Many instructive illustrations of the degrees of stability 
 shown by pigments are furnished by examples in the 
 Wallace Collection at Hertford House. 
 
 Philippe de Champaigne (1602-1674). No. 119. This 
 
 22 
 
338 
 
 WATER-COLOUR DRAWINGS 
 
 picture is remarkable not only for the perfection of its 
 technique, but for the extraordinary state of conservation 
 of all the pigments, which cover a wide range of colours, 
 and include a transparent amber-yellow and a rose. 
 
 Sir Joshua Reynolds (1723-1792). No. 47. Here the 
 fatal asphaltum asserts itself, the background resembling 
 a dissected map. 
 
 J. L. E. Meissonier (1815-1891). No. 291. Generally 
 the works of this careful painter are well preserved, but 
 in this small example there are to be seen a few thin long 
 cracks, which seem to have arisen in consequence of the 
 premature application of varnish to the picture before the 
 oil-paint was hard. 
 
 In Sir John Soane’s Museum the two fine series of well- 
 preserved oil-paintings by W. Hogarth (1697-1764) will 
 repay careful study from the point of view now being 
 considered. 
 
 The remaining works to which attention is now called 
 are a few of the water-colour drawings shown in the 
 Victoria and Albert Museum. 
 
 William Daniell, R.A. (1769-1837). In one of the 
 water-colours by this artist the blue and green elements 
 have disappeared, save just in one little bit of smalt blue 
 in a sailor’s clothes. In another drawing the sky is now 
 a mere dirty laboured stain. 
 
 William Green (1761-1823). No. 685. An iron red 
 has here become too prominent. 
 
 Samuel Howitt (1765-1822). No. 3,019, 1876. Ap- 
 parently well preserved, but, on further scrutiny, it seems 
 that the ultramarine in the shaded parts of some of the 
 rocks and trees stands out more prominently than it 
 could have done originally. 
 
 Anne Frances Byrne (177,5-1837). No. 1,358, 1874. 
 
I 
 
 I WATER-COLOUR DRAWINGS 339 
 
 i In this fruit and flower piece the indigo in the sky has 
 I gone, while the yellow pigments and the red lakes have 
 j suffered greatly ; the roses are blanched, and the purple 
 I grapes have lost their crimson element, 
 j John James Chalon, R.A. (1778-1854). No. 570. The 
 ;j ‘ River Scene in Devonshire,’ painted in 1808, shows the 
 1 shaded parts of the clouds pink, from the loss of indigo. 
 
 I The hills are now too pale for the trees dotted upon them, 
 I through the fading of sap-green and gamboge, which have 
 j! been used in painting the grass. The shadows under the 
 i| ripples of the water have greatly altered, from the change 
 of indigo and other pigments ; they now show dirty stains 
 [ and elaborate brushwork. 
 
 No. 54, 1887, ‘At Hampstead Heath,’ by the same 
 artist, is, on the other hand, a well-preserved drawing, 
 
 I which has been more recently acquired by the museum, 
 ij The blues are particularly good, although the vegetable 
 •| yellows may perhaps have faded somewhat in spite of 
 ’i the care which has been taken with the drawing. 
 
 ,| John Cristall (1767-1821). No. 142, 1890. This 
 
 II drawing seems to have kept its hues well, and affords 
 tj a good example of the style of colouring of the period 
 l| and school to which it belongs. 
 
 j Jacob Xavery (painted in 1757). No. 15, 1872. This 
 has faded woefully. The sickly peaches and spectral 
 ! grapes proclaim the evanescence of crimson lake, gam- 
 i boge, and indigo. 
 
 I Mary Moser, R.A. (1744-1819). No. 160, 1881. Very 
 little is left of the original colour here ; the ‘ roses and 
 j other flowers ’ are a complete wreck. 
 
 I Francis Danby, A.R.A. (1793-1861). No. 480. The 
 I blue in the sky unchanged, but the pigments which once 
 I modified its hue have fled. 
 
340 
 
 WATER-COLOUR DRAWINGS 
 
 John Varley (1778-1842). No. 381. Hot iron reds 
 show themselves in great force in clouds and elsewhere — 
 even in the river ; the modifying organic pigments with 
 which they were mixed have nearly disappeared. 
 
 George Cattermole (1800-1868). No. 503. The crimson 
 lake seems to have faded from the face in this drawing. 
 In No. 507, painted in 1850, we have a good illustration 
 of the warm brownish hues produced by the deterioration 
 of crimson lake. 
 
 Samuel Prout (178 >1852). Nos. 1,473, 1869, and 3,056, 
 1876, afford examples of the stability of true ultramarine. 
 The skies in both these drawings are now quite out of 
 harmony with the architectural features, some of the pig- 
 ments in which must have faded. These drawings should 
 be compared with others by the same artist which hang 
 beside them, and in which the blues of the skies, as well 
 as some of the pigments in other parts, have faded. Here 
 it may be convenient to remark upon the startling prom- 
 inence of the skies, and sometimes of the blue distances, 
 in many water-colour drawings. The first glance on 
 entering a room in which such works are gathered reveals 
 the permanence of ultramarine and cobalt blue, the latter 
 pigment being, of course, of comparatively recent intro- 
 duction. But the want of harmony in such drawings 
 furnishes evidence at the same time of the decay of many 
 other pigments — of liquorice and tobacco-juice, of yellow 
 lake and brown pink, of indigo and rose pink. 
 
 William Henry Hunt (1790-1864). No. 1,031, 1873. 
 Some of the ruddy hue from the cheeks of the boy appears 
 to have gone. In 1,525, 1869, some of the pink in the 
 apple-blossom has faded ; the primrose-flowers are greener 
 and less yellow than they once were, probably from a 
 change in lemon yellow. The 'lawthorn-blossom in 1,470, 
 
WATER-COLOUR DRAWINGS 
 
 341 
 
 1869, has lost the faint rosy blush that was once visible 
 in some of the flowers — a delicate hue which I can dis- 
 tinctly recall. 
 
 The above examples, selected almost at random, must 
 suffice. But I may point to a different kind of injury, 
 from which water-colour drawings sometimes suffer, by 
 citing the case of W. Delamotte’s ‘ View of Christ Church, 
 Oxford.’ This seems to have been pasted on wood, and 
 to have been stained in consequence ; at least, it appears 
 likely that the brown spots in the sky may be traced to 
 the mount. A work by T. Barker (No. 134, 1878) and 
 the ‘ Dieppe ’ of J. S Cotman (No. 3,013, 1876) furnish 
 additional examples of the same kind of damage. 
 
CHAPTER XXV 
 
 CONSERVATION OF PICTURES AND DRAWINGS 
 
 It is generally conceded that a finished oil painting is 
 best kept in such a position that it is exposed to daylight 
 of just sufficient intensity for it to be well seen, the direct 
 beams of the sun being excluded. In darkness, or even 
 in approximate darkness, the lead-whites may tarnish, 
 and the oil and resins darken. Even with the most 
 moderate illumination, however, the more fugitive pig- 
 ments, such as the cochineal and quercitron lakes, will 
 in no long time alter and fade to such a serious extent 
 as to destroy the ‘ keeping ’ of the work. But there is 
 really no need to introduce these evanescent pigments, 
 for every nuance the artist can desire may be produced 
 with paints having a sufficient if not perfect degree of 
 permanence. The question of artificial lighting here 
 comes in. Against oil lamps, properly constructed and 
 managed so as to avoid the production of smoke and 
 soot, nothing can be urged ; the same opinion may be 
 given in reference to the use of electric incandescent 
 lamps. The introduction of electric arc lamps seems 
 less safe, even when the illumination they afford is reduced 
 to the necessary minimum, for the light they emit is richer 
 in those rays which, as a general rule, are peculiarly 
 effective in bringing about chemical changes in the less 
 stable pigments. But the light by which pictures are to 
 
 342 
 
CONSERVATION OF PICTURES 
 
 343 
 
 be seen is but one of the conditions out of several which 
 have to be considered in their conservation, though 
 perhaps the most important. The mode of securing a 
 picture in its frame is not an altogether trivial matter. 
 In the majority of cases the expansion and contraction 
 with variations of moisture and temperature, of panel 
 and canvas, do not correspond accurately with the similar 
 changes of the frame. In consequence, too great rigidity 
 in the system of fixing adopted should be avoided. Duly 
 adjusted springs or blocks of indiarubber (^not vulcanized), 
 secured in the rebate, afford convenient means of obtain- 
 ing the necessary freedom of movement, while preventing 
 the jar caused by accidental concussions. An equable 
 temperature is another important condition ; on no 
 account should currents of hot or of cold air impinge 
 directly upon the front or back of a painting. Moreover, 
 this is not a mere question of temperature, for such 
 currents of air may bring in particles of dust and other 
 impurities, while their hygroscopic condition is sure to 
 vary. This question of moisture is of some moment. 
 For if freshly- warmed air, which is pretty sure to be 
 comparatively dry air, is allowed to come in contact with 
 panels or canvases, it will withdraw from them some of 
 their necessary hygroscopic moisture, and thus cause 
 capricious and hurtful changes of size. Such changes, 
 often repeated, cannot but result in the production of 
 cracks and fissures in the oil paintings subjected to these 
 varying conditions. The hygroscopic balance between 
 picture and air can be maintained only by a due supply 
 of moisture to the warmed air before the latter comes in 
 contact with the painting ; the warmer the air the more 
 moisture must be added to it. The same reasoning 
 applies to the entrance of cold air, but in this case, care 
 
344 
 
 CONSERVATION OF PICTURES 
 
 must be taken that it is sufficiently dry not to deposit 
 water upon the picture. For the purpose of regulating 
 the hygroscopic condition of the atmosphere in a picture- 
 gallery, the introduction of a dew-point thermometer is 
 advisable. And there is another contrivance by means 
 of which the presence of the right proportion of moisture 
 in the air may be recognised. A strip of drawing-paper, 
 another of primed canvas, and another of mahogany, all 
 three being in a normal hygroscopic state, are to be 
 separately balanced by means of counterpoises. When 
 the air gets too dry, the strips will rise, owing to their 
 loss of water ; when excess of moisture is present, they 
 will sink. So long as the equilibrium of the beams to 
 the ends of which the strips are attached remains practi- 
 cally true, the air may be regarded as in a satisfactory 
 hygroscopic condition. Three pairs of ordinary apothe- 
 caries’ scales (or spring-balances) suffice for the construc- 
 tion of this apparatus, which should be protected by a 
 glass case to which the air has free access. This ques- 
 tion of the due amount of moisture in the air — neither 
 in excess nor in defect — has scarcely received the atten- 
 tion it deserves. But it will be allowed on all hands 
 that few conditions are more trying to pictures in oil or 
 water-colour than those caused by currents of hot, dry 
 air rising directly below them during the day, succeeded 
 by currents of cold, moist air descending upon them 
 down the surfaces of the walls at night. 
 
 The covering of an oil picture with glass, whatever 
 objections may be urged against it from an artistic point 
 of view, certainly secures the protection of its surface 
 from the solid and liquid and, to some extent, from the 
 gaseous impurities in the air. But the backs of pictures, 
 especially of those painted on canvas, are often forgotten. 
 
FRAMING AND MOUNTING OF PICTURES 
 
 345 
 
 yet excess of moisture and deleterious vapours and gases 
 often enter from behind, and seriously discolour the 
 painting-ground, and even the paint itself. Mention has 
 previously been made of methods by which this cause of 
 injury may be prevented by means of a double canvas, 
 or a layer of white lead in powder mixed with starch - 
 water, applied to the back of the original canvas ; 
 American leather cloth, or even parchment-paper, affixed 
 to the frame behind is nearly as effective. 
 
 A few words only are requisite as to the mounting and 
 framing of water-colour paintings. On no account must 
 the back of the paper on which a drawing is executed 
 come into contact with any kind of wood, or even with 
 an inferior sort of paper or mounting-cardboard. Injurious 
 substances in the latter may travel forwards into the 
 painting-ground, and affect the pigments, while wood may 
 cause stains. Iron brads produce rust-spots. Flour-paste 
 is not a sound material for mounting drawings ; far better 
 is an antiseptic size, which may also be used for fixing to 
 the back of the frame the sheet of paper which is there 
 placed to exclude dust. If we could secure a water-colour 
 drawing from dust, and yet allow of the escape of any 
 water set free in the form of vapour when the drawing 
 gets, from whatever cause, somewhat warmer than usual, 
 we should have effected an improvement upon the ordinary 
 plan of framing. In this, the moisture liberated from the 
 paper and mount cannot escape, but condenses upon the 
 glass when it cools, only to be reabsorbed by that surface 
 of the paper which carries the pigments, where it favours 
 chemical and physical changes, until the hygroscopic 
 equilibrium of the whole system — frame, mount, lining, 
 paper, etc. — is once more re-established. I have used 
 with advantage grey linen in lieu of brown paper at the 
 
 } 
 
346 
 
 PRESERVATION OF DRAWINGS 
 
 back of frames, and, by means of a few strips of thick 
 drawing-paper, have established an air-communication 
 between the space in front of the drawing and that at 
 the back. Thus the ventilation of the system is arranged 
 for, yet dust is excluded. To hermetically seal a framed 
 drawing, to the entire exclusion of all moisture and all 
 air, is not possible. That under such conditions a greatly 
 increased number of pigments would prove unalterable 
 has been long known. We should add to these observa- 
 tions upon the conservation of works in water-colour that 
 they should certainly be kept in a rather drier atmosphere 
 than that recommended for oil paintings. 
 
 The plan of preserving the water-colour drawings of 
 Turner, devised by the late John Ruskin, may fitly be 
 mentioned here. It was described in a letter to the 
 editor of the Times (October 28, 1856). The recom- 
 mendation is to enclose each work in a light wooden 
 frame, under a glass, the interior surface of which is pre- 
 vented from coming in contact with the drawing by 
 means of a raised mount. A number of such frames 
 (five to fifteen) are kept together in cases, which can be 
 carried or wheeled to any part of the room where the 
 drawings are to be studied. Each frame slides vertically 
 into grooves in the case. Professor Ruskin’s reasons 
 include the following : ‘ A large number of the drawings 
 are executed with body colour, the bloom of which any 
 friction or handling would in a short period destroy.’ 
 This argument, it will be seen, is directed against the 
 keeping of such works, in their unframed state, in port- 
 folios. Another reason given by Mr. Ruskin is that in 
 the case of these drawings ‘ their delicate tones of colour 
 would be destroyed by continuous exposure to the light, 
 or to smoke and dust.’ He fortifies his position in refer- 
 
PRESERVATION OF DRAWINGS 
 
 347 
 
 ence to such exposure in a letter to the Literary Gazette 
 (November 13, 1858), in which he says that ‘the officers 
 of both the Louv're and of the British Museum refuse to 
 expose their best drawings or missal-pages to light, in 
 consequence of ascertained damage received by such 
 drawings as have been already exposed ; and among the 
 works of Turner I am prepared to name an example in 
 which, the frame having protected a portion, while the 
 rest was exposed, the covered portion is still rich and 
 lovely in colour, while the exposed spaces are reduced 
 in some parts nearly to white paper, and the colour in 
 general to a dull brown.’ ‘ That water-colours are not 
 injured by darkness is also sufficiently proved by the 
 exquisite preservation of missal paintings, when the 
 books containing them have been but little used. Observe, 
 then, you have simply this question to put to the public : 
 “ Will you have your Turner drawings to look at when 
 you are at leisure, in a comfortable room, under such 
 conditions as will preserve them to you for ever, or will 
 you make an amusing exhibition of them {if amusing, 
 which I doubt) for children and nursery-maids ; dry your 
 wet clothes by them and shake off the dust from your 
 feet upon them for a score or two of years, and then send 
 them to the wastepaper merchant?”’ Mr. Ruskin in 
 another letter to the Times, which appeared on October 21, 
 1859, wrote thus : ‘ I take no share in the responsibility 
 of lighting the pictures either of Reynolds or Turner with 
 gas ; on the contrary, my experience would lead me to 
 apprehend serious injury to those pictures from such a 
 measure ; and it is with profound regret that I have 
 heard of its adoption.’ Although considerable weight is 
 rightly given to the opinions of Mr, Ruskin above quoted, 
 it must not be forgotten that all paintings of the modern 
 
348 LIGHTING OF PICTURE-GALLERIES 
 
 school are not to be classed with those of Turner and 
 Reynolds in respect to susceptibility to the injurious 
 action of the products of the burning of gas and of con- 
 tinuous exposure to moderate light. When, therefore, 
 Mr. Ruskin wrote (in the Daily Telegraph, July 5, 1876) : 
 
 ‘ I do not think it necessary to repeat my former state- 
 ments respecting the injurious power of light on certain 
 pigments rapidly, and on all eventually,’ I find myself 
 compelled to reject so sweeping an assertion. That light 
 injures all pigments eventually cannot for one moment 
 be conceded. And if we could but succeed in so modify- 
 ing the light that illuminates our pictures as to remove 
 from it certain particularly active beams, we might con- 
 siderably augment the list of permanent pigments. 
 Experiments on a small scale prove that several fluor- 
 escent substances, such as a solution of quinine sulphate, 
 while intercepting dangerous rays, do not sensibly modify 
 the colour of the light, and yet lessen its chemical 
 activity. In the first edition (published 1890) of the 
 present handbook, I wrote : ‘ Possibly a transparent 
 screen of this character will some day be used for our 
 picture-galleries.’ Since then an arrangement of coloured 
 glass — peacock blue and yellow — has been devised by 
 Sir W. Abney and introduced into one of the galleries of 
 the Victoria and Albert Museum, with the object of pre- 
 venting the entrance through the skylight of a great part 
 of the injurious rays. Thirteen years ago I used the 
 following words in relation to this subject : ‘ It is in- 
 structive to note how much difference exists between 
 different specimens of apparently colourless glass in their 
 absorptive power for the so-called chemical rays. These 
 differences may be tested by framing a strip of paper 
 washed with carmine and covering it crosswise with the 
 
LIGHTING OF PICTURE-GALLERIES 
 
 349 
 
 samples of glass to be valued, adding for comparison a 
 plate of rock-crystal. Under the last-named material the 
 fading is nearly as rapid as it is where the pigment is 
 without any cover. It may be safely affirmed that 
 miniatures should be protected by glass, not by rock- 
 crystal. Further experiments on the selection of pro- 
 tective glasses and the construction of transparent screens 
 are needed. A partial discussion of this subject will be 
 found in the next chapter, and to this I would refer my 
 readers.’ In this connexion a paper by Sir William 
 Crookes, P.R.S., may be named. It was published in 
 the Phil. Trans, of the Royal Society, Vol. 213A, and is 
 entitled ‘ The Preparation of Eye-Preserving Glass for 
 Spectacles.’ 
 
 The question of the lighting of a gallery or room where 
 pictures are to be displayed has been touched upon already 
 at the beginning of the present chapter. We would now 
 add that actual skylights are not without drawbacks. 
 One of these, especially in the case of water-colours, is 
 the presence in large proportion in the light from the 
 zenith of those rays which act most energetically upon 
 pigments. A few observations as to gas cannot be ex- 
 cluded. Gas, before and after burning, is bad for pic- 
 tures. The evil effects of an occasional escape of unburnt 
 gas are less to be dreaded than those caused by the pro- 
 ducts of gaseous combustion. These products are sul- 
 phuric acid, sulphurous acid, carbonic acid, and the 
 moisture which is formed at the same time. Thence 
 results a hot, moist atmosphere laden with these corrosive 
 compounds. The water-vapour condenses into the liquid 
 form and dissolves a part of the acids named above ; the 
 drops which trickle down are very injurious to paper, 
 wood, canvas and pigments. In any case, all the pro- 
 
350 
 
 AIR IN PICTURE-GALLERIES 
 
 ducts of the combustion of gas should be removed from 
 the room as they are formed. For even when there may 
 be no visible condensation of liquid, the vapours formed 
 are often absorbed as such by paper, canvas, etc., and do 
 in that form their destructive work. An illustration of 
 this fact is furnished by an analysis of the leather back 
 of an old calf-bound volume. Owing to its absorption of 
 the products of the burning of gas this back had decayed 
 and fallen off, and was found to contain over 6 per cent, 
 of free sulphuric acid. 
 
 With respect to the building itself in which pictures 
 are to be kept, our aim should be to secure as far as pos- 
 sible pure air, an equable and agreeable but moderate 
 temperature, and freedom from dust and dirt. Solidity 
 of construction, a continuous damp-proof course, a certain 
 degree of elevation above the ground-level, and double 
 walls enclosing an air-space, are desirable as conducing 
 to uniformity of temperature, and preventing the con- 
 densation of moisture upon the interior of the rooms. 
 Due provision should be made for excluding from the 
 galleries themselves the dust and dirt which may be 
 brought in by visitors. And it cannot be too strongly 
 urged that the supply of fresh air should not, as it were, 
 accompany the visitors, but be brought in from an inde- 
 pendent source. The place of in-take of such supply 
 should not be gratings near to, or on the level of the 
 ground, in out-of-the-way and dirty corners, the certain 
 depositories of uncertain rubbish. From such sources 
 air laden with organic and inorganic impurities can alone 
 come. The question of the exclusion of fog and city- 
 smoke may be mentioned here. Some kind of air-filter 
 is useful. It is astonishing how effectively the solid and 
 liquid particles suspended in a yellow fog may be strained 
 
RESTORATION OF PICTURES 
 
 351 
 
 off and intercepted by passing the air through a layer of 
 loosely packed carded cotton enclosed between two sheets 
 of perforated zinc — this air-filter of course requires 
 occasional renewal. Moist white lead, that is, white 
 lead in powder reduced to a paste by admixture with 
 water, will absorb the sulphuretted hydrogen as well as 
 the sulphuric and sulphurous acid present in town air. 
 And if the walls of the galleries are coated with a dis- 
 temper paint containing white lead, this absorption of 
 impurities goes on continually. For these impurities are 
 more readily absorbed by an unprotected and properly- 
 prepared distemper than by the pigments in the pictures. 
 To secure this result the distemper should be made, not 
 with size, but with starch-water, just sufficiently strong 
 to bind the particles together and to the wall. For 
 further particulars as to these and other arrangements for 
 the conservation of pictures, especially in public galleries, 
 the reader is referred to a paper on the subject in the 
 Portfolio for 1882, pp. 106- 108. 
 
 The conservation of pictures naturally leads us on to 
 their restoration. Picture-restoration, like some other 
 kinds of restoration, often involves injury, often renewal. 
 It is frequently difficult, sometimes impossible, to re- 
 establish the pristine state of the work. The operations 
 involved should never be undertaken by the inexperienced 
 amateur. And picture-restorers themselves are too often 
 artists who have mistaken their profession, or who have 
 been imperfectly trained. Many possess no power or 
 appreciation of accurate draughtsmanship. Look, for 
 illustrations, at those crucial parts, the hands and feet, 
 in ‘restored’ pictures. Nor have they that exquisite 
 sense of quality in colour and of delicate hues which will 
 enable them to fill up properly actual gaps in a painted 
 
354 
 
 REMOVAL OF VARNISH 
 
 has received, a year after completion, the thinnest pos- 
 sible layer of drying-oil containing a little copal-varnish, 
 and then, after the lapse of a twelvemonth, its final coat 
 of mastic-varnish, cannot be injured by the chafing pro- 
 cess just described. And, even under less favourable 
 conditions, it is the only method which can be recom- 
 mended for general adoption. But it has its risks, and is 
 not easily applicable in the case of pictures where the 
 texture of a coarse canvas, or the grain of a panel, is con- 
 spicuously evident on the surface. To these remarks on 
 the chafing process, we may add that it is sometimes ad- 
 visable to re-varnish a picture with fresh mastic before 
 commencing to remove the old ; a day or two afterwards 
 both layers may be removed together. 
 
 The removal of old varnish by the use of solvents is a 
 hazardous, though easy, operation. The liquid usually 
 employed for this purpose is spirits of wine, of about 
 6o° overproof, diluted with one-fourth of its bulk of 
 distilled water. It is applied by means of wads of 
 carded cotton, the action of the solvent being arrested, 
 when necessary, by instantly moistening the spot with 
 spirit of turpentine on another wad, or, in some cases, 
 with linseed-oil. But when mastic megilp has been 
 used as the painting-medium, it also, as well as the 
 pigments associated with it, may be removed by treat- 
 ment with these solvents. And it must be remembered 
 that some artists introduce layers or touches of water- 
 colours in their oil-pictures ; these are almost certain to 
 be affected by spirits of wine. Sometimes further injury 
 to them may be arrested by the application of linseed-oil. 
 Whenever a solvent is used in cleaning a picture, the 
 cotton tufts employed should be examined carefully from 
 time to time, in order to see that no actual pigment has 
 
RESTORATION OF PICTURES 
 
 355 
 
 coloured them — that they are stained by nothing but the 
 brown varnish. Other solvents besides those named are 
 sometimes used in cleaning pictures, particularly where 
 hard or oily varnishes have to be removed. Such sol- 
 vents are acetone, fusel-oil, amyl-acetate, benzene, 
 chloroform, and solutions of caustic alkalies. Great 
 risk of injury attends their employment — indeed, the 
 application of any kind of solvent is fraught with danger, 
 and should never be attempted by the inexperienced. 
 
 The usual plan of filling up actual gaps in the priming 
 or gesso-grounds of old pictures is by means of plaster- 
 of-Paris. When this has set, its surface is levelled by 
 gentle attrition with a cork and dry whitening, or cuttle- 
 fish. Great care is needed in order to prevent the 
 pigments surrounding the place from being abraded. I 
 have found asbestos-putty to be an excellent substitute 
 for plaster in many cases ; its surface is made smooth 
 and level by means of a painting palette-knife. But it 
 cannot be tinted with water- or tempera-colours ; in 
 order to make it match the hues of the neighbouring 
 parts of the picture oil-colours must be used. In any 
 necessary replacements of lost colours in old oil-paintings, 
 it has been recommended to use not oil-colours, but 
 water-colours, as these can always be distinguished from 
 the old work, and, if necessary, removed; this can be 
 done on ‘ stoppings ’ of whitening and size, as well as on 
 those of plaster. Tempera-pictures should, I think, be 
 repaired with dry pigments mixed with egg-yolk, as in 
 this case, when the final varnish is applied, a general 
 harmony of effect is produced. If water-colours are 
 introduced in repairing an oil-painting, the coat of varnish 
 subsequently added is sure to deepen and darken them, 
 unless this change has been allowed for during the pro- 
 
356 
 
 RESTORATION OF PICTURES 
 
 gress of the work, by no means an easy thing to manage. 
 When in any kind of repainting oil-paints are used, they 
 should be mixed stiffly with a very little copal-varnish 
 and spirit of turpentine, and should be rather lighter 
 and less yellow in tone than the colours they are intended 
 to match, since darkening and yellowing in some degree, 
 however slight, are sure to occur subsequently. 
 
 The cleansing and restoration of paintings executed in 
 fresco require special care. Additions to supply colour 
 which has scaled off are best made in tempera. When a 
 fresco has become grimy by exposure to the smoky air 
 of a city, methylated spirits of wine, applied freely on 
 tufts of carded cotton, removes the tarry and sooty im- 
 purities which a previous careful brushing of the painted 
 surface has failed to dislodge. Attempts to clear the 
 clouded portions of an injured fresco by means of dis- 
 tilled water or aerated distilled water are usually attended 
 with but slight success. The films which obscure the 
 surface in such cases sometimes consist of sulphate of 
 lime, produced from the carbonate of lime present by the 
 action of the sulphuric acid occurring in the atmosphere 
 of places where gas and coal are burnt. In getting rid 
 of this somewhat opaque film by means of water, portions 
 of the pigment are commonly removed. When a fresco 
 has been dusted and then cleansed with spirits of wine it 
 should be allowed to dry thoroughly, the lost colours 
 renewed in tempera, and then the whole surface coated 
 with a preparation of hard paraffin-wax. This prepara- 
 tion, which has the consistency of an ointment, is made 
 by melting together 4 parts of hard paraffin-wax 
 (melting-point above 150° F.}, i part of spirit of turpen- 
 tine, and 1 5 parts of toluol. When cold, this mixture is 
 to be spread uniformly over the painted surface, and then 
 
RESTORATION OF PICTURES 
 
 357 
 
 allowed to remain until its volatile constituents have 
 disappeared. Afterwards the paraffin-wax left on the 
 surface is to be melted and driven in by the local applica- 
 tion of a moderate heat. By this treatment the dead or 
 matt surface of the fresco is preserved, the obscuring 
 films are rendered translucent, and the picture may, 
 when cleansing is again required, be safely sponged with 
 pure water or weak spirits of wine. If any cloudiness of 
 the surface still persists after the application of the 
 paraffin-wax paste described above, the effect of treat- 
 ment with the Gambier- Parry medium (see p. 142), 
 largely diluted, may be tried. 
 
 The treatment of an injured fresco, in accordance with 
 the plan just outlined, was pursued in the case of Sir 
 Edward Poynter’s fresco painted in 1872-73 on the south 
 side of the chancel in St. Stephen’s Church, Dulwich, 
 That the work done upon this damaged fresco has been 
 successful may be learnt from the way in which 
 Mr. James Ward wrote in 1909 of the then state of the 
 painting in his book ‘ F resco Painting,’ on page 30. He 
 there says that this fresco is ‘ in a perfectly sound con- 
 dition, and is almost as fresh-looking and bright as when 
 first painted ; ... it shows no sign of deterioration ; on 
 the contrary, the surface looks, and feels to the touch, 
 more like terra cotta, or of the texture and firmness of 
 biscuit porcelain than anything else one can think of.’ 
 Mr, Ward would have come to a very different conclu- 
 sion as to the permanence of fresco had he seen this 
 painting when I took it in hand some four years before 
 his approval was published ! 
 
 An example of the treatment of a greatly damaged 
 oil-painting on a plaster ceiling may be here cited. This 
 work, in the Saloon of the Queen’s House at Greenwich, 
 
358 
 
 RESTORATION OF PICTURES 
 
 was painted between the years 1626 and 1635 by Orazio 
 Gentileschi, a Pisan artist invited over to this country 
 by Inigo Jones. It was reported in 1853 to be ‘ much 
 damaged ’ ; and fifty years afterwards, when I first 
 examined it, its condition seemed well-nigh hopeless. 
 The plaster ground had swollen, and had broken up and 
 loosened the layer of oil-paint applied to it. This injury 
 was due to the action of atmospheric sulphuric acid upon 
 the calcium carbonate of the plaster. By spraying the 
 whole surface with Gambier-Parry’s spirit fresco medium 
 considerably diluted, the coloured flakes which were 
 ready to fall were secured in position, and then the lost 
 portions were replaced by pigments ground in the same 
 medium. These operations were carried out between 
 the years 1907 and 1909. In cases of such serious 
 damage as this of Gentileschi’s ceiling, further treat- 
 ments are necessary, as the injury to the plaster is a 
 continuing one. 
 
CHAPTER XXVI 
 
 TRIALS OF PIGMENTS 
 
 The testing of pigments for genuineness and for purity 
 has been discussed incidentally in Chapters XIII. to XIX. 
 of the present volume. Though genuineness and purity* 
 have often an important bearing upon the question of 
 permanence, this last quality must be ascertained by 
 independent experiments of another order. The study 
 of old paintings often furnishes us with results of some 
 value, the results of unintentional testings. But for the 
 purpose of securing complete and wholly trustworthy 
 information, we must know precisely all the materials 
 and all the conditions of our trials. Not only must the 
 painting -grounds, the mediums, and the pigments, be 
 chemically examined, but we must be in a position to 
 state the character of the atmosphere in which they have 
 been exposed, and the nature and amount of the solar or 
 other radiations to which they have been subjected. In 
 the great majority of these trials accurate data as to 
 
 * The chromatic values of pigments — their approach in hue, etc.^ 
 to recognised standards of excellence — are not here taken into 
 account. Such data may be obtained by the use of Lovibond’s 
 Tintometer when once the chromatic elements of a pigment in 
 terms of the degrees of the standard glasses employed in this 
 instrument have been determined. But really exact determinations 
 of this kind require complex scientific apparatus, which cannot be 
 profitably used except by an expert manipulator. 
 
 359 
 
TRIALS OF PIGMENTS 
 
 360 
 
 materials and conditions are wholly wanting ; even the 
 South Kensington report affords us no information as to 
 the composition of the pigments employed, nothing more 
 than their commercial names, so that we have to take on 
 trust their genuineness and purity. However, in this 
 same most important series, quite unusual, if not un- 
 precedented, care was taken in order to determine the 
 conditions, physical and chemical, under which the pig- 
 ments were tested. In my own experiments, carried on 
 between 1856 and 1879, in somewhat desultory fashion, 
 and extended and improved since 1880, the influence of 
 purity of sample, of the presence of moisture and of oxygen, 
 and of the nature of the ‘ light,’ has not been neglected ; 
 the full details of the methods adopted, and of the results 
 obtained, could not be appropriately introduced into an 
 elementary manual. Mention will be made of the chief 
 conclusions reached in the present chapter ; there are 
 also numerous references to them in Chapters XIII. 
 to XXII. 
 
 In many early treatises on painting we find observations 
 as to the degrees of stability possessed by various pig- 
 ments, along with suggestions as to methods of treatment 
 by which in certain cases greater permanency may be 
 attained. To some of these observations and suggestions 
 reference has been made in those chapters of the present 
 volume which deal with pigments ; many of the remainder 
 are now without practical importance, referring as they 
 do to pigments which have been rightly discarded. 
 
 It is only of recent years that trials of pigments have 
 been made with any approach to exactness. But in the 
 majority of cases no information has been secured con- 
 cerning the purity and genuineness of the pigments with 
 which the experiments have been made. I have not been 
 
TRIALS OF PIGMENTS 
 
 361 
 
 able to find a single chemical analysis of any one of the 
 pigments tested. The chromatic analysis of the light they 
 severally reflect has, however, been recorded in the case 
 of the water-colour paints examined by Dr. Russell and 
 Sir W. Abney, who have likewise furnished some par- 
 ticulars as to the intensity of the solar radiations to which 
 the pigments were subjected. 
 
 More than a century ago Sir Joshua Reynolds tested, 
 in a rough way, the stability of some of the paints he 
 employed. Two causes detract from the value of his 
 results. In the first place, the information furnished con- 
 cerning the nature of many of the pigments he tried is too 
 imperfect to be of any use ; secondly, we are not ac- 
 quainted with the conditions under which his specimens 
 have been kept during the whole period since they left 
 his hands. Two of his trial canvases are preserved in 
 the Royal Academy. Although the darkening and em- 
 browning of the surface are general, and though the 
 names of the pigments employed are often undecipherable 
 or meaningless, yet something useful remains. From 
 the experiments made in 1772 we may gather the follow- 
 ing facts : The proper hues of several pigments remain 
 in a measure — orpiment, or kings’ yellow in crystals ; 
 yellow lake, with wax and drying oil ; gamboge, with 
 lake and Venice turpentine ; gamboge, with (Venice) 
 terpentine ; prepared gamboge, with wax ; and verditer, 
 with varnish. On the other hand, gamboge with oil, 
 lake with oil, and many other pigments of organic origin, 
 when unmixed with wax or varnish, are names only, or, 
 at the most, brown discolorations. 
 
 M. J. Blockz, in his ‘ Peinture a I’Huile,’ gives the 
 results of a number of experiments made by M. J. Dyck- 
 man. He condemns, for various reasons, not only asphalt. 
 
362 
 
 MR. ANDREW'S EXPERIMENTS 
 
 but also terre verte, cobalt green, emerald green, raw 
 sienna, raw umber, ivory brown, and all burnt madders. 
 Cassel earth was slightly changed; brown ochre, burnt 
 sienna. Mars brown, ivory black, and vine black, proved 
 to be permanent. His lists of incompatible pigments are 
 somewhat unnecessarily extended, not being justified, in 
 all particulars, by further and more careful experiments. 
 
 The experiments of the late F. W. Andrew, formerly 
 of the Victoria and Albert Museum, have been carried on 
 since 1876, but have been confined to water-colours, both 
 moist and cake. His chief results will be found recorded 
 along with my own, in Part HI., in the paragraphs 
 devoted to the consideration of the several pigments. His 
 water-colour washes, generally spread on Whatman paper, 
 or Whatman board, were exposed for periods varying 
 from twenty-eight to eighty-two months, in a south 
 window, to all the sunshine available ; half of each wash 
 was doubled back, and so far excluded from light. In 
 some cases a third part of the coloured slip was exposed 
 to the air and light without the protection of glass. The 
 chief paints which were unaffected, at all events, so far 
 as some specimens were concerned, by the exposure, are 
 included in the following list : Yellow ochre, raw sienna, 
 deep cadmium. Mars red, light red, Indian red, oxide of 
 chromium, Leitch’s blue, cobalt, artificial ultramarine, 
 Prussian blue, raw umber, burnt umber. Naples yellow 
 (true) became blackish in darkness, but was unaltered in 
 light, while orange chrome showed dark patches. F urther 
 details must be given as to the pigments which were 
 affected. In the tabular statements appended a selection 
 from the results afforded by eleven sets of experiments 
 is recorded, the letters C and M prefixed to the entries 
 respectively denoting the employment of cake or moist 
 
TRIALS OF WATER-COLOURS 363 
 
 colours. The numerical values representing the residual 
 hues are rough approximations only, but in some instances 
 they were determined by means of comparisons with 
 standard coloured liquids, contained in glass cylinders 
 graduated into ten equal parts. Hellige’s colorimeter or 
 the tintometer of Mr. J. W. Lovibond, of Salisbury, may 
 be employed with advantage in these estimations. 
 
 CHANGES IN WATER-COLOURS 
 
 
 Name of 
 
 Months of 
 
 Residual Depth Residual Hue 
 
 
 Pigment 
 
 Exposure 
 
 (Original = 
 
 10) and Remarks 
 
 M. 
 
 Aureolin ... 
 
 28 
 
 10 . 
 
 . Verges on orange- 
 
 M. 
 
 Aureolin 
 
 62 
 
 10 
 
 [yellow. 
 
 M. 
 
 Aureolin ... 
 
 82 
 
 9 
 
 
 C. 
 
 Gamboge ... 
 
 28 
 
 4 
 
 
 M. 
 
 Gamboge... 
 
 28 
 
 9 
 
 
 M. 
 
 Gamboge . . 
 
 82 
 
 7 
 
 
 M. 
 
 Yellow lake 
 
 62 
 
 2 
 
 Yellowish grey. 
 
 M. 
 
 Yellow lake 
 
 82 
 
 0 
 
 
 C. 
 
 Yellow madder .. 
 
 28 
 
 I 
 
 
 M. 
 
 Yellow madder .. 
 
 28 
 
 3 . 
 
 . Pinkish grey. 
 
 M. 
 
 Yellow madder .. 
 
 62 
 
 I 
 
 
 C. 
 
 Indian yellow .. 
 
 28 
 
 ... 8,9 
 
 
 M. 
 
 Indian yellow 
 
 28 
 
 9 
 
 
 M. 
 
 Indian yellow 
 
 60 
 
 7 
 
 
 M. 
 
 Indian yellow 
 
 82 
 
 6 
 
 
 M. 
 
 Pale cadmium . . 
 
 82 
 
 I . 
 
 . Pale buff. 
 
 M. 
 
 Vermilion 
 
 62 
 
 — . 
 
 . Blackish. 
 
 M. 
 
 Vermilion 
 
 82 
 
 — . 
 
 . Black. 
 
 M. 
 
 Carmine ... 
 
 28 
 
 0 . 
 
 . Pale grey. 
 
 M. 
 
 Crimson lake 
 
 28 
 
 0 . 
 
 . Greenish grey. 
 
 M. 
 
 Burnt carmine . . 
 
 28 
 
 I . 
 
 • 
 
 C. 
 
 Pink madder 
 
 28 
 
 I 
 
 
 M. 
 
 Rose madder 
 
 28 
 
 3 
 
 
 M. 
 
 Rose madder 
 
 62 
 
 I . 
 
 Pinkish grey. 
 
 M. 
 
 Rose madder 
 
 82 
 
 I . 
 
 
 M. 
 
 Madder carmine 
 
 62 
 
 2 
 
 
 M. 
 
 Madder carmine 
 
 82 
 
 0 
 
 
 M. 
 
 Purple madder ... 
 
 28 
 
 4 ■ 
 
 . A pale wash. 
 
364 
 
 MADDER VERSUS COCHINEAL 
 
 Name of 
 
 Months of 
 
 Residual Depth Residual Hue 
 
 Pigment 
 
 Exposure 
 
 {Original = 
 
 10) and Remarhs 
 
 M. Purple madder 
 
 62 
 
 7 
 
 
 M. Purple madder 
 
 82 
 
 2 
 
 
 C. Brown madder 
 
 28 
 
 I . 
 
 Warm grey. 
 
 M. Brown madder 
 
 28 
 
 I . 
 
 » 
 
 M. Brown madder 
 
 82 
 
 0 
 
 
 C. Indigo 
 
 28 
 
 5 - 
 
 . Greenish grey. 
 
 M. Indigo 
 
 62 
 
 I 
 
 
 M. Raw umber 
 
 60 
 
 9 ■ 
 
 Rather yellower 
 
 M. Vandyke brown 
 
 28 
 
 7 
 
 
 M. Vandyke brown 
 
 60 
 
 I 
 
 
 M. Bone brown 
 
 62 
 
 8 
 
 
 The pigments containing lead, such as the ordinary 
 chromes, and those having a copper basis, like emerald 
 green, had altered capriciously, losing part of their 
 original colour, and becoming tarnished or embrowned in 
 patches. Brown pink faded like the yellow lakes, but 
 acquired a bluish-grey residual hue. 
 
 The testing of the madder colours is so important that 
 I introduce here a few additional experiments selected 
 from my own note-books. The washes of the moist-colour 
 paints were, as far as possible, of the same depth of tone, 
 and they were all exposed together in a glazed frame to 
 one year’s sunshine : 
 
 I. 
 
 3 - 
 
 4 - 
 
 5 - 
 
 6 . 
 
 Name of 
 Pigment 
 Rose madder 
 Madder carmine 
 Madder carmine 
 
 Madder red 
 Purple madder 
 Brown madder 
 
 Residual Depth , 
 
 (OyiginalJio) Change of Hue, etc. 
 
 8 ... Slightly more purplish. 
 
 ... 10 ... Almost unchanged. 
 
 8 ... Much more purplish. This sample 
 
 was from another source. 
 
 6 ... Less red, more purplish. 
 
 7 ... Duller, less red, more blue. 
 
 8 ... Less red, more yellow-brown. 
 
 In contrast to the above results with madder carmine, 
 the following experiment with the ordinary carmine 
 
PROFESSOR ROOD'S EXPERIMENTS 
 
 365 
 
 (prepared from cochineal) is instructive. On a sheet of 
 Whatman paper, a space of 10 inches in length by 4 inches 
 in width was covered with a uniform wash of the moist 
 paint, having a depth of tint about equal to that of the 
 petals of the old China rose. This coloured strip was 
 then subjected to summer sunshine in such a way that 
 successive single inches of its length received the light 
 (during the same hours of similarly bright days) for periods 
 of 2, 4, 8, 12, 20, 26, 30, 40, and 100 hours, one single 
 inch at one end being, however, protected completely from 
 all access of light. The exposure of 100 hours sufficed 
 to bleach the last breadth completely, but had the rate of 
 fading been in a simple arithmetical progression, a much 
 shorter exposure would have sufficed. In fact, the 
 bleaching action was far more energetic during the first 
 period of two hours than during the second, about 20 per 
 cent, of the original colour having been destroyed during 
 these two first hours, while during the second equal 
 period the loss of depth did not exceed one-tenth of this 
 amount. Moreover, it was noticed that the change of 
 hue consequent upon the first exposure was different in 
 kind to that which occurred subsequently. 
 
 Professor O. N. Rood’s Experiments. — In his ‘ Modern 
 Chromatics,’ pages 90 and 91, Professor Rood gives the 
 results of a few trials which he made as to the effect on 
 washes of water-colours laid on ordinary drawing-paper 
 of three and a half months’ exposure to summer sunlight. 
 
 These pigments were unaffected ; 
 
 Cadmium yellow, yellow ochre, Roman ochre. 
 
 Indian red, light red, Jaune de Mars. 
 
 Terre verte. 
 
 Cobalt, French blue, smalt. 
 
 Burnt umber, burnt sienna. 
 
366 
 
 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 The following pigments were all affected. The sequence 
 represents the amount of alteration, the list commencing 
 with those colours which suffered but little change : 
 
 Name Nature 
 
 of Pigment of Change 
 
 1. Chrome yellow Slightly greenish. 
 
 2. Red lead • • Less orange. 
 
 3. Naples yellow- Slightly greenish 
 
 brown. 
 
 4. Raw sienna • Fades, yellower. 
 
 5. Vermilion - - Darkens^ brownish. 
 
 6. Aureolin - • • Fades slightly. 
 
 7. Indian yellow • Fades slightly. 
 
 8. Antwerp blue - Fades slightly, 
 
 9. Emerald green Fades slightly. 
 
 10. Rose madder * Fades slightly, pur- 
 
 plish. 
 
 11. Sepia- - • - Fades slightly. 
 
 12. Prussian blue - Fades somewhat. 
 
 Name Nature 
 
 of Pigment of Change 
 
 13. Hooker’s green - More bluish. 
 
 14. Gamboge - - - Fades, greyish. 
 
 15. Bistre - - - . Fades, greyish. 
 
 16. Brown madder • Fades. 
 
 17. Neutral tint - - Fades. 
 
 18. Vandyke brown Fades, greyer. 
 
 19. Indigo - - - - Fades. 
 
 20. Brown pink • - Fades greatly. 
 
 21. Violet carmine - Fades greatly, 
 
 brownish. 
 
 22. Yellow lake - - Fades greatly 
 
 brownish. 
 
 23. Crimson lake • Fades out. 
 
 24. Carmine • • - Fades out. 
 
 Professor Rood adds that rose madder, brown madder, 
 and purple madder were all a little affected by an exposure 
 to sunshine for seventy hours, and that pale washes were 
 completely obliterated by a much shorter exposure to sun- 
 shine in the case of carmine, dragon’s blood, yellow lake, 
 gall-stone, brown pink, Italian pink, and violet carmine. 
 
 W. N. Hartley’s Experiments. — On September 4^ 
 1886, the late Sir W. N. Hartley read, before the 
 British Association at Birmingham, a paper on ‘ The 
 Fading of Water Colours.’ His trials as to the effect on 
 pigments of a comparatively brief exposure to intermittent 
 sunshine in pure air may be thus summarized. Washes on 
 the best drawing-paper were the subject of the experi- 
 ments : 
 
 Gamboge. — Pale washes were completely bleached in 
 three days ; in a week strong washes were much lightened 
 in colour, and rendered dull, even three hours’ exposure 
 producing a very visible effect. 
 
 Crimson lake. — Six hours’ exposure to sunlight and air 
 almost bleaches pale washes, while three days or eighteen 
 to twenty-four hours of intermittent sunshine cause dark 
 
PROFESSOR HARTLEY'S EXPERIMENTS 367 
 
 crimson tones to become very much lighter, the hue of 
 the pigment being altered. 
 
 Light red, Indian red, and vermilion were unaffected. 
 
 Olive green and brown pink were rendered lighter in 
 colour by six hours’ exposure, the former pigment be- 
 coming bluish and the latter brownish in hue. 
 
 Indigo, cobalt, and artificial ultramarine were unaffected. 
 
 Brown madder became rather lighter after eight days’ 
 or forty-eight hours’ exposure. 
 
 Bistre faded with great rapidity, a light wash appearing 
 much paler after six hours. 
 
 Sepia. — A pale wash became colder in hue, but not very 
 perceptibly paler. 
 
 In a second series of experiments, sectors of paper discs, 
 washed with various pigments, were enclosed between 
 glass-plates, the edges of which were fastened with 
 gummed paper. Under these circumstances, crimson 
 lake and bistre were found to have been considerably 
 altered by five hours’ exposure — somewhat more so, 
 indeed, than was the case when these pigm.ents were 
 freely exposed to the air. 
 
 All the results above noted are in practical accord with 
 those obtained by other observers. The exposure to 
 intermittent sunshine ‘ for six hours a day during fourteen 
 days,’ does not produce a sensible effect upon vermillion 
 and indigo. Had Sir W. N. Hartley extended his obser- 
 vations a few weeks longer, his conclusions as to these 
 pigments must have agreed with those which we have 
 given, and therefore with the unanimous verdict of all 
 other scientific observers. His statement that ‘ indigo is 
 permanent’ (British Association Report, 1886, p. 581) 
 must, therefore, be modified into, ‘ indigo appears to have 
 suffered no change after fourteen days’ exposure to inter- 
 
368 PROFESSOR HARTLEY'S EXPERIMEHTS 
 
 mittent sunshine.’ A similar alteration is demanded with 
 regard to the stability of vermilion. 
 
 Sir W. N. Hartley’s experiments with water-colour 
 washes on paper enclosed between glasses require a few 
 words of comment. He is clearly and rightly dissatisfied 
 with this method of trial. A supply of atmospheric 
 oxygen, and of hygroscopic moisture, amply sufficient for 
 large chemical alteration and oxidation of the enclosed 
 pigments, was certainly present. And the glasses did 
 accelerate the action, not because of ‘ the very slight tint 
 of the plate-glass,’ but in spite of it. This acceleration 
 of change is mainly caused by the continued presence of 
 moisture in the confined space between the two glasses — 
 it cannot escape as it freely, and to a very great extent^ 
 does escape, when a piece of tinted paper is exposed to 
 sunshine in free air. I showed, indeed, in my lectures 
 at the Royal Academy, so long ago as 1880, that the 
 fading of many fugitive pigments is greatly lessened, when 
 not altogether prevented, by enclosing the paper washed 
 with them in a glass tube, the air of which is kept dry by 
 means of some strongly hygroscopic substance. When 
 both moisture and air are excluded (using a sealed 
 vacuum tube), the suspension of fading and alteration of 
 hue is still more marked and general. 
 
 It should be added here that Sir W. N. Hartley found 
 that cadmium yellow and Indian yellow are bleached by 
 peroxide of hydrogen, and changed into a muddy yellow 
 by sulphurous acid. This reagent bleaches artificial ultra- 
 marine and dulls vermilion. He attributes the partial or 
 complete destruction of the blue component of the hues 
 in certain old drawings, which have been long exposed to 
 air and light, to the presence of acids or acid substances in 
 the air, in the paper, or in the red ferruginous pigments 
 with which the blue colouring substances in question have 
 
MR. W. SIMPSON'S EXPERIMENTS 
 
 369 
 
 been associated. These blue pigments could have been 
 nothing other than Prussian blue, indigo, or natural ultra- 
 marine. I have ascertained, by direct experiments on old 
 drawings, that the latter was but rarely employed for 
 mixed tints, but it is quite probable that the reds prepared 
 from colcothar, with which it may have been occasionally 
 mingled, would sometimes contain enough acid salts 
 (certain ferric sulphates) to destroy its colour. The pro- 
 ducts of the burning of gas and of coal would also be rich 
 enough in sulphuric acid to produce the same effect. I 
 am unable to endorse Sir W. N. Hartley’s statement that 
 the best drawing-papers contain free sulphuric acid, at all 
 events when fresh from the mill, but they soon acquire 
 it when kept in an urban atmosphere. 
 
 Mr. W. Simpson’s Experiments. — Some washes of 
 water-colour, of thirty-one different kinds, were made 
 upon cards by the late Mr. W. Simpson. He so cut the 
 cards as to divide each coloured strip in half ; one 
 section was preserved in darkness, the other was exposed 
 in an eastern aspect on the shutter of a house in London 
 for fifteen years, but the sun did not shine upon the 
 specimens after ten o’clock in the morning. As they 
 were not tightly framed, the cards became a good deal 
 discoloured by the absorption of noxious vapours and 
 dirt. The results were : 
 
 Name 
 of Pigment 
 Yellow ochre- - 
 Indian yellow 
 Lemon yellow - 
 ‘Newman’s per- 
 manent yellow ’ 
 Cadmium yellow 
 Chrome yellow - 
 Brown pink - - 
 *Vermilion - - - 
 Light red - - - 
 Indian red - • 
 Crimson lake • - 
 Carmine - - - 
 Madder lake - - 
 
 Nature 
 of Change 
 None. 
 
 Faded considerably. 
 None perceptible. 
 
 None. 
 
 Perhaps browner. 
 Faded considerably. 
 Faded. 
 
 None. 
 
 None. 
 
 None. 
 
 Gone. 
 
 Gone. 
 
 More purplish. 
 
 Name 
 of Pigment 
 Purple madder - 
 *Brown madder - 
 Emerald green - 
 Cyanine blue 
 ^Prussian blue 
 French blue - - 
 Cobalt - - - - 
 Ultramarine - • 
 Indigo, rather 
 deep .... 
 Burnt sienna - - 
 ^Vandyke brown - 
 *Sepia - - - - 
 ^Bistre - - - . 
 
 Nature 
 of Change 
 Hue altered. 
 
 Loss of redness. 
 Slight. 
 
 Apparently none. 
 None. 
 
 Faded very slightly. 
 None. 
 
 None. 
 
 Very pale grey. 
 None. 
 
 None. 
 
 Faded very slightly. 
 None. 
 
 24 
 
370 
 
 TRIALS OF PIGMENTS 
 
 It will be noted that the above results are for the most 
 part in agreement with those recorded by other experi- 
 menters ; the chief exceptions are marked with a star. 
 Vermilion is usually blackened, but it is possible that 
 the sample employed in these experiments was the less 
 changeable native form or cinnabar. The Vandyke 
 brown, too, was probably the earthy rather than the 
 bituminous variety ; the slightness of the change recorded 
 for madder brown and sepia, and the absence of any 
 alteration on the part of bistre, are less easy of explana- 
 tion. The madder pigments seem to have stood more 
 than usually well, but they often exhibit large differ- 
 ences of stability. Nor must it be forgotten, in assigning 
 values to the above results, that this trial of fifteen years’ 
 exposure was not of the severest kind. Although, on the 
 one hand, there was the imperfect exclusion of an in- 
 jurious London atmosphere, on the other hand, the 
 energy of the solar radiation was much reduced by the 
 prevalent condition of the smoky air, while the inter- 
 mittent and capricious sunshine of the Metropolis never 
 fell on the trial cards after ten a.m. 
 
 The late Mr. R. H. Soden-Smith kindly placed at my 
 disposal a large number of specimens of old water-colour 
 cakes and of powder colours intended for oil-painting. 
 One set consists now of eleven cakes or fragments 
 of cakes (in their original box) bought about the year 
 1815 of Newman, in Soho Square. This set is peculiarly 
 interesting as the colours, which all bear the name of 
 the maker and his device, represent those used by many 
 of the best English water-colour painters during the first 
 quarter of the nineteenth century. The cakes are ; 
 Indian yellow, raw sienna, raw umber, burnt sienna, 
 burnt umber, vermilion, carmine, burnt carmine, pink 
 
SOUTH KENSINGTON REPORT 
 
 371 
 
 madder, ultramarine, indigo ; neutral tint and sepia are 
 missing. On comparing the hues of the first nine of 
 these paints and of the indigo with the hues of the 
 corresponding cake-colours as sold by the same house 
 in 1886, no appreciable differences were detected save 
 in the case of the raw umber. Here the pigment of 
 1815 showed a more beautiful nuance than that of 1886. 
 On making comparative tests of the stability, under 
 exposure to sunshine, of the two sets of pigments, the 
 results were found to be practically identical. One cannot, 
 therefore, claim for the water-colour paints in use one 
 hundred years ago a degree of permanence greater than 
 that possessed by their representatives of to day. 
 
 By far the most important series of trials of water- 
 colour paints yet published is that to be found in the 
 report by the late Dr. Russell and Captain (now Sir W.) 
 Abney to the Science and Art Department (1888). The 
 reporters endeavoured to give precision to their ex- 
 periments and their conclusions by a careful comparison 
 of the effective radiation from different sources of light. 
 The first part of their report contains a very useful 
 discussion of the relative values of direct sunlight, light 
 from clouds, and from an overcast or clear sky, and light 
 from artificial sources. Several cognate subjects are also 
 discussed therein, such as the number of years of ex- 
 posure which pigments would require, if in the picture 
 galleries of South Kensington, in order that they might 
 suffer the same changes as those caused by three or 
 twenty-two months’ exposure in a southern aspect out- 
 side the Museum. Part II. of the report contains the 
 results of twelve sets of experiments with various pig- 
 ments. In all the series the same paper (Whatman’s) 
 was used. In the paragraph relating to this subject 
 
372 
 
 SOUTH KENSINGTON REPORT 
 
 there is, however, one curious error, and one obscure 
 statement (p. 27). It is quite impossible that the 
 paper used — its weight per ream is not given — could 
 have contained so little as ‘nearly i grain’ of sizing 
 matter per square foot ; 10 grains is a more probable 
 quantity. The sentences next following do not state 
 the condition of the papers which absorbed from a moist 
 atmosphere from 12-07 12-46 per cent, ‘of their weight 
 
 of water.’ Were they dried previously, and, if so, at 
 what temperature ? We ought to have been told within 
 what limits the percentage of water in these papers varied 
 during the course of the trials: I have pointed out for 
 many years past the importance of this hygroscopic 
 moisture in paper in reference to the fading of pigments* 
 Eight tints of each pigment were applied to strips of 
 paper 8 inches long by 2 inches wide ; they were exposed 
 in tubes open at both ends, but having the upper ex- 
 tremity curved downwards so as to exclude wet and 
 dirt. Of course, exposure on a wall facing nearly south 
 constituted a very severe test, yet the circulation of air 
 In the tubes was more advantageous to the pigments than 
 would have been the steamy heat of a closed vessel, or 
 even of an ordinary paper-backed picture-frame. But on 
 the other hand, this arrangement allowed the free access 
 to the pigments of any noxious gases, such as sulphurous 
 and sulphuric acids, and sulphuretted hydrogen, which 
 might have been at any time present in the atmosphere. 
 The general results of this first series of trials are 
 gathered in the following table, the exposure in all cases 
 asting from May, 1886, until March, 1888. The pig- 
 ments are arranged in the order of instability, the most 
 fugitive being placed first : 
 
SOUTH KENSINGTON REPORT 
 
 373 
 
 ^Carmine. 
 *Crimson lake. 
 ♦Purple madder. 
 *Scarlet lake. 
 •Payne’s grey. 
 ♦Naples yellow. 
 ♦Olive green. 
 ♦Indigo. 
 
 ♦Brown madder. 
 ♦Gamboge. 
 ♦Vandyke brown. 
 ♦Brown pink. 
 ♦Indian yellow. 
 
 Cadmium yellow. 
 Leitch’s blue. 
 ♦Violet carmine. 
 ♦Purple carmine. 
 ♦Sepia. 
 
 Aureolin. 
 
 Rose madder. 
 Permanent blue. 
 Antwerp blue. 
 Madder lake. 
 Vermilion. 
 Emerald green. 
 Burnt umber. 
 
 Yellow ochre. 
 Chrome yellow. 
 Lemon yellow. 
 Raw sienna. 
 Indian red. 
 Venetian red. 
 Burnt sienna. 
 Terre verte. 
 Chromium oxide. 
 Prussian blue. 
 Cobalt. 
 
 French blue. 
 Ultramarine ash. / 
 
 r o 
 a 
 
 o 
 
 ja 
 
 CO 
 
 D 
 
 OC 
 
 C! 
 
 U 
 
 The pigments marked with an asterisk were found to 
 have distinctly altered either in depth or hue by a much 
 shorter exposure, from May to August 14, 1886. 
 
 In a second series of trials the tinted papers were 
 dried, and then introduced into the tubes, which had 
 been previously heated ; the specimens were [then sealed 
 up hermetically ; as no moisture-absorbing material was 
 enclosed with the papers, traces of water must have been 
 present. My own much earlier results were abundantly 
 confirmed by those obtained in this series, for the number 
 of pigments which proved to be permanent under these 
 conditions was double that of the first series. Brown 
 madder and Prussian blue were, however, acted upon in 
 this second series. Dr. Russell and Sir W. Abney make 
 the remark that of the eight colours which remained 
 unchanged in dry air, but were acted on in ordinary air, 
 all, with the single exception of madder lake, are mineral 
 colours. But this is not correct, for the pigments named 
 are — madder lake, olive green, Payne’s grey, sepia, Naples 
 yellow, cadmium yellow, emerald green, and burnt umber, 
 and of these the first four are either v/holly or partly of 
 organic origin, while the seventh contains an acetate. 
 
374 
 
 SOUTH KENSINGTON REPORT 
 
 In the next series of experiments, the pigments were 
 exposed in the presence of moisture-laden air. Very few 
 colours withstood this test — none of organic origin ; both 
 Prussian blue and Antwerp blue were entirely destroyed. 
 
 An atmosphere of moist hydrogen gas was employed 
 in the fourth series. Under these conditions carmine, 
 crimson lake, madder lake, brown madder, olive green, 
 indigo, Payne’s grey, sepia, and Vandyke brown, suffered 
 no change. 
 
 When, as in the fifth series, both moisture and oxygen 
 were excluded, scarcely any even of the most fugitive 
 pigments were affected. Vermilion, however, as in all 
 the other experiments, became black. We know that 
 the reason for the change is physical, not chemical. 
 
 In the sixth series it was proved that the addition of 
 ox-gall had no beneficial effect in lessening the change of 
 hue and tone in fugitive pigments. 
 
 The remaining series, save the twelfth and last, were 
 devised in order to learn what influence upon the stability 
 of pigments might be exerted by admixture with Chinese 
 white, by exposure to the light of the electric arc, by 
 heat without light, by heat and light together, and by 
 exposure to the light transmitted through coloured 
 glasses. Amongst the results recorded, we may note 
 the decided changes in several pigments caused by ad- 
 mixture with Chinese white, and by heating the prepared 
 paper slips in sealed tubes for seven hours a day for 
 three weeks, all light being excluded. In a twelfth series 
 of trials, the pigments were exposed in a picture-frame 
 under glass in such conditions, and to such an amount of 
 light, as might be taken to represent the ordinary cir- 
 cumstances in which pictures are kept. The frame was 
 exposed from August 6, 1886, until May 6, 1888, to very 
 
SOUTH KENSINGTON REPORT 
 
 375 
 
 bright light, but not to sunshine. Gamboge, indigo, 
 
 I' Naples yellow, brown pink, carmine, and Vandyke brown, 
 had faded in varying degrees. Some remarks on these 
 results will be found further on in the present chapter ; 
 they are of extreme importance, considering the large use 
 j that has been made of these pigments by our water- 
 colourists, and the mild treatment to which they were 
 subjected during the short period of twenty-one months. 
 
 For the results obtained with mixtures of pigments 
 j under varied conditions of exposure, we must refer our 
 
 ;j readers to the report itself. It may, however, be re- 
 
 ,1 marked that, in the great majority of cases, the changes 
 of tone and hue which occurred were such as might have 
 been predicted from the known degrees of stability of 
 the several constituents of the mixtures. Here, as else- 
 where in the report, we find frequent mention of the 
 strange, but long known, recovery in darkness of its colour 
 by Prussian blue which has been bleached by sunlight. 
 
 In the fourth appendix to this report is an instructive 
 list of the pigments employed by some of the most dis- 
 . tinguished artists using water-colours. Forty-six painters 
 j replied to the invitation of the Science and Art Depart- 
 ment; from their answers we learn that a large proportion 
 of them include in their palettes many pigments which 
 must be unhesitatingly condemned on account of their 
 want of stability. Thus no less than seventeen out of 
 the forty-six artists who responded to the appeal employ 
 three of the most fugitive pigments in the series — 
 namely, gamboge, brown madder, and indigo. Converted 
 into percentages, we may say that 37 out of 100 
 painters in water-colours use these three untrustworthy 
 pigments, besides others which are worse, and others 
 which are little better ; of course, they employ also 
 
 (j 
 
376 
 
 SOUTH KENSINGTON REPORT 
 
 certain colours as to the stability of which there is no 
 question. The following tabular statement gives the 
 proportion of artists, per loo, who use the eleven perish- 
 able pigments named below : 
 
 Gamboge ... 
 
 ... 70 ... 
 
 Faded to 7. ' 
 
 Indian yellow 
 
 ... 24 ... 
 
 Faded to 6. 
 
 Vermilion ... 
 
 ... 70 ... 
 
 Gone black. 
 
 Carmine 
 
 ... 8 ... 
 
 Gone, 
 
 Crimson lake 
 
 ... 22 
 
 Gone. 
 
 Purple madder 
 
 ... 28 ... 
 
 Faded to 8. > 
 
 Brown madder 
 
 ... 74 ... 
 
 Faded to 3, 
 
 Brown pink 
 
 II 
 
 Faded to 7, 
 
 Vandyke brown 
 
 ... 74 ... 
 
 Gone. 
 
 Sepia 
 
 ... 65 ... 
 
 Faded to 8. 
 
 Indigo 
 
 ... 52 ... 
 
 Faded to 8., 
 
 / I represents the 
 lightest tint, 8 the 
 darkest. The washes 
 of pigment were fully 
 exposed for twenty- 
 Uwo months. 
 
 We call these pigments perishable with good reason. 
 For, according to the report under review, all of them were 
 found to have faded, materially and conspicuously, after 
 twenty-two months’ full exposure in a south aspect, while 
 three of them had entirely disappeared, and another (ver- 
 milion) had become black. But this is not all. For under 
 a less severe trial (p. 45) — namely, exposure for the 
 same time, not to direct sunlight, but to a very bright 
 light from a window, ‘ under conditions approximating to 
 those to which pictures are usually subjected ’ — six out 
 of the eleven pigments had faded, though in varying 
 degrees. With these figures and results before us, it is 
 impossible to resist the conclusion that a life of 100 years 
 is too much to allow to many of the water-colour drawings 
 of the present day. What shall we say, then, as to the 
 stability of the works of the earlier masters of the English 
 water-colour school ? How much care in the exclusion 
 of ‘ the more fugitive colours ’ was taken by the water- 
 colourists of 1780 to 1850 ? Could it be honestly said of 
 any large number of such works, in which gamboge* 
 
TRIALS OF WATER-COLOUR PAINTS 
 
 377 
 
 brown pink, crimson lake, sap-green, indigo, and sepia, 
 were generally employed without stint, ‘ that about a 
 century of exposure would have to be given to water- 
 colour drawings in galleries lighted as are those at South 
 Kensington before any marked deterioration would be 
 visible in them ’? * (Report, p. 46.) 
 
 Dr. Russell and Sir William Abney add, indeed, the 
 proviso, ‘ If painted with any but the more fugitive 
 colours.’ But this condition cannot be said to have been 
 fulfilled by the v/orks in question ; for in the great 
 majority of them, most of the six fugitive pigments which 
 we have just named were freely employed. And it is 
 these very pigments which have been proved by the 
 reporters themselves to suffer ‘marked deterioration’ by 
 an exposure of twenty-one months only to strong daylight 
 without direct sunshine. Moreover, it must not be for- 
 gotten that the fading of a single important pigment in a 
 water-colour drawing is ruinous to the whole effect, de- 
 stroying the balance of the chromatic scheme of the artist 
 more effectually than a slight, but equal, degradation of 
 all the hues. 
 
 An instructive set of trials of water-colour paints was 
 commenced in May, 1894, and continued for four years 
 
 * In the preceding brief resume of certain parts of the South 
 Kensington Report no reference has been made to an argument, 
 developed in §§ x. to xv., in which it is contended that ‘ if a certain 
 tint be exposed to an intensity of radiation which we will call 100, 
 and which bleaches it in, say, i hour, then, if a similar tint be 
 exposed to an intensity i, it will require 100 hours’ exposure to it 
 to effect the same bleaching.’ The universal applicability of this 
 conclusion cannot be conceded by those who are familiar with 
 numerous instances in which no chemical or physical change 
 occurs when certain substances are exposed continuously for long 
 periods to a particular temperature, yet, when they are heated but 
 a degree or two higher, instantly alter, decompose, or react, as the 
 case may be. 
 
378 
 
 TRIALS OF WATER-COLOUR PAINTS 
 
 by a sub-committee of the Burlington Fine Arts Club. 
 The results of these experiments have been embodied in 
 three reports. Winsor and Newton’s moist water-colours 
 were used, flat washes on Whatman’s ‘ not hot pressed ’ 
 paper of the year 1888 being exposed to light in the 
 windows of the billiard-room of the club. One of the sets 
 so exposed was in an ordinary glazed frame, another set 
 was enclosed in hermetically sealed glass tubes containing 
 ordinary air; while a third set was contained in similar 
 tubes, but the atmosphere present was maintained in a 
 dry state by means of a reservoir of burnt lime which 
 absorbed all or almost all traces of water in the pigments, 
 the paper, and the mount. The final comparisons were 
 made with parallel sets which had been kept in absolute 
 darkness. We give here, in tabular form, the condition 
 of the paints at the end of the fourth year of exposure : 
 reference must be made to the original reports for infor- 
 mation as to the results of six months’ and of thirteen 
 months’ exposure to sunshine. 
 
 RESULTS OF EXPOSURE FOR FOUR YEARS, FROM 
 MAY 25, 1894, TO MAY 25, 1898 
 
 (Original depth = 10 ) 
 
 Pigment 
 
 Set in Dry 
 Air 
 
 Set in Moist 
 Air 
 
 Set in Flame 
 
 Aureolin 
 
 No change. 
 
 Faded to g. 
 
 No change. 
 
 Gamboge 
 
 Faded to i . 
 
 Faded to i. 
 
 Faded to i. 
 
 Indian yellow 
 
 Gone. 
 
 Faded to i. 
 
 Faded to i. 
 
 Cadmium yellow 
 
 Deeper orange. 
 
 No change. 
 
 No change. 
 
 Vermilion 
 
 Greyish. 
 
 Greyish. 
 
 Greyish. 
 
 Crimson lake ... 
 
 Faded to o‘ 5 . 
 
 Gone. 
 
 Gone. 
 
 Rose madder ... 
 
 Faded to 8 ' 5 . 
 
 Faded to 8 'o 
 
 Faded to 8-5 
 
 
 
 and purplish. 
 
 and purplish. 
 
 Indian red 
 
 No change. 
 
 No change. 
 
 No change. 
 
 Madder carmine 
 
 Faded to g. 
 
 Darker, more 
 
 Darker, more 
 
 
 
 purplish. 
 
 purplish. 
 
TRIALS OF WATER-COLOUR PAINTS 
 
 379 
 
 Pigment 
 
 Set in Dry 
 Air 
 
 Set in Moist 
 Air 
 
 Set in Frame 
 
 Madder brown 
 
 Faded to 9. 
 
 F aded to 6, 
 
 Faded to 8, 
 
 
 
 purple gone. 
 
 purple gone. 
 
 Madder purple 
 
 Faded to 8. 
 
 Faded to 4. 
 
 Faded to 5. 
 
 Prussian blue ... 
 
 No change. 
 
 Faded to i. 
 
 Faded to 8 5. 
 
 French blue 
 
 No change. 
 
 No change. 
 
 No change. 
 
 Indigo 
 
 No change. 
 
 Faded to i, 
 
 Faded to i, 
 
 
 
 greenish grey. 
 
 greenish grey. 
 
 Vandyke brown 
 
 Faded to 2, less 
 
 Faded to i. 
 
 Faded to i. 
 
 
 yellow. 
 
 
 
 Sepia 
 
 Indigo with In- 
 
 Faded to 8. 
 
 Faded to i. 
 
 P'aded to 4. 
 
 dian red 
 
 No change. 
 
 Indigo gone. 
 
 Indigo gone. 
 
 The most striking results of these trials was the com- 
 plete stability of Prussian Blue and of Indigo when exposed 
 
 in air kept dry. The further remark may be made that 
 moist air, that is, ordinary air containing moisture and 
 confined in a sealed tube, inflicts more injury upon 
 alterable pigments than ordinary air enclosed in a frame 
 which does admit of some amount of ventilation occurring. 
 There is no difficulty in so constructing a frame as to 
 introduce a water-absorbing substance which may be 
 renewed from time to time. Thus we shall be able to 
 employ with confidence in water-colour painting madder 
 brown, madder purple, Prussian blue, indigo and sepia — 
 five pigments which under ordinary conditions of ex- 
 posure to sunshine suffer serious changes. But no method 
 has yet been devised by means of which we may safely 
 use gamboge, Indian yellow, vermilion, crimson lake and 
 Vandyke brown, although it must be stated that instances 
 have been recorded in which vermilion as a water-colour 
 has stood very severe exposure-tests, especially when 
 v/hite of egg has been mixed with it. 
 
 Amongst the series of trials of oil-paints made by the 
 author of this handbook, one set first arranged in 1880 
 
38 o 
 
 EXPERIMENTS WITH OIL-PAINTS 
 
 may be described here. Chance’s colourless plate-glass 
 was employed as the painting-ground, so as to avoid all 
 interference with the pigments from the surface on which 
 they were spread ; glass presents the further advantage 
 of permitting a complete examination of the back of each 
 specimen, and of changes in its translucency, opacity, or 
 texture. Each glass measured 8 inches by 6 ; the com- 
 plete series was prepared in duplicate — one for preserva- 
 tion in darkness, the other for exposure to all the light 
 that could be secured (in Kew) during five years in a 
 window facing nearly south-west. The majority of the 
 paints tried were obtained from four firms (Messrs. Winsor 
 and Newton, Messrs. Roberson and Co., M. Edouard of 
 Paris, and Schoenfeld of Diisseldorf). Specimens of 
 each pigment were reserved for further examination and 
 analysis. Some of the chief results obtained are given 
 in the annexed table ; a few remarks on the changes 
 observed in some of the pigments which had been mixed 
 with flake white are added : 
 
 p. , Years of Residual Depth Change of Hue 
 igmen Exposure (Original =io) and Remarks 
 
 Yellow ochre ... 5 
 
 10 . 
 
 . . Browner ; more translu- 
 cent. 
 
 Aureolin ... ... 5 
 
 9 .. 
 
 .. None. 
 
 Indian yellow ... 5 
 
 8 ., 
 
 , . Slightly brownish. 
 
 Naples yellow (true) 5 
 
 10 ., 
 
 . . None. 
 
 Pale yellow madder 2 
 
 7 . 
 
 Greyish salmon when 
 mixed with flake white. 
 
 Deep yellow madder 2 
 
 6 . 
 
 Dirty pink when mixed 
 with flake white. 
 
 Laque brun jaune ... 2 
 
 7 .. 
 
 Lost much yellow. 
 
 Laque brun fonce ... 2 
 
 8 .. 
 
 . Lost much yellow. 
 
 Laque Robert, No. 5 2 
 
 2 .. 
 
 . Warm grey when mixed 
 with flake white. 
 
 Laque Robert, No. 6 2 
 
 4 • 
 
 Warm grey when mixed 
 with flake white. 
 
 Scarlet lake ... ... 5 
 
 7 .. 
 
 ,. Dull pinkish red. 
 
TRIALS OF OIL-PAINTS 
 
 381 
 
 Years of Residual Depth Change of Hue 
 Exposure {Original =10) and Remarks 
 
 Crimson lake 
 
 5 
 
 1 ... 
 
 Almost gone. 
 
 Madder red 
 
 2 
 
 10 ... 
 
 None. 
 
 Madder carmine ... 
 
 5 
 
 9'5 
 
 None. 
 
 Madder brown 
 
 2 
 
 9 ••• 
 
 Rather duller. 
 
 Prussian blue 
 
 5 
 
 8 - 5 ... 
 
 Slightly greener. 
 
 Indigo 
 
 5 
 
 8 ... 
 
 Slightly greener. 
 
 Artificial ultramarine 
 
 5 
 
 10 ... 
 
 None. 
 
 A series of trials of seventeen 
 
 madder colours in oil 
 
 was carried out in 
 
 1893. 
 
 These 
 
 were all prepared by 
 
 Lefranc of Paris. 
 
 The 
 
 samples 
 
 were spread on thin 
 
 lantern glass 4 in. x 4 in., and when dry each glass was 
 cut in half. One half was exposed to sunshine from 
 March 26 until October 26, the other half of each specimen 
 being kept in darkness. At the end of the seven months 
 the halves of each sample were rejoined and carefully 
 mounted, and thus an instructive set of slides obtained. 
 The results are given in the following table, in which I 
 have grouped together those varieties of ‘ laque de garance ’ 
 which resembled one another in their degree of stability : 
 
 Name 
 
 Laque de garance fence 
 
 ,, ,, rose intense 
 
 , , , , brun rouge 
 
 ,, ,, rouge brun 
 
 Laque de garance rose 
 
 , , , , rose dore 
 
 ,, ,, brun pourpre ... 
 
 Laque de garance pourpre ... 
 
 ,, ,, pourpre concentre 
 
 Carmin de garance ... 
 
 Laque de garance brun de madder 
 
 ,, ,, brun 
 
 , , , , brun fonce 
 
 „ jaune capucine 
 ,, ,, brun jaune 
 
 ,, ,, nuance bitume 
 
 Little or no change. 
 
 j-Slight change. 
 
 I Marked change. 
 
 Lost from 40 to 80 per 
 - cent, of their original 
 depth. 
 
382 
 
 TRIALS OF OIL-PAINTS 
 
 In the fourth or least stable group, comprising the 
 varieties of madder brown, it was noticeable that the 
 yellow constituent of the colour was most affected by 
 exposure, the hvmt fonce and the nuance hitunie losing all 
 their characteristic beauty of hue and becoming of a dull, 
 poor, rusty tint and not retaining over 20 per cent, of 
 their original depth. Even in Group II. the golden hue 
 of the rose doree was the only chromatic element of this 
 madder paint which had been lost to an appreciable 
 extent during the six months’ exposure. 
 
 Experiments as to the degree of stability possessed by 
 many other oil-paints have been made ; the results will 
 be found for the most part incorporated with the accounts 
 given of the several pigments in Part III. One remark 
 may perhaps be usefully introduced in this place with 
 reference to the differences observable in the quality and 
 behaviour of pigments bearing the same name but ob- 
 tained from different artists’ colourmen. It is a good 
 plan to place side by side on three trial-plates several 
 ‘ makes ’ of the same paint and to keep one set in dark- 
 ness, and to expose a second set to sunshine and a third 
 set to strong diffused daylight. It will sometimes be 
 found that the fascinating colour-quality which at the 
 first glance recommends one sample is not preserved 
 after exposure, although the reverse experience is not 
 uncommon. It must not be forgotten that although the 
 composition and constituents of the vast majority of pig- 
 ments, both natural and artificial, are known, yet there 
 are differences in the methods of preparation which, in 
 some cases at least, are kept secret, and which result not 
 in differences of nuance only, but in differences of stability 
 also. 
 
INDEX 
 
 Abney, Sir W., 348, 371 
 Acetic acid, 85, 234 
 Acetone, 109 
 Actinic rays, 56, 348 
 Adjective pig-ments, 281 
 Albumen, 85 
 Alcohol, no 
 Alizarin, 194, 196 
 ,, crimson, 194 
 „ lakes, 196 
 „ orange, 185 
 ,, yellow, 1 85 
 Alterable pigments, 283 et seq. 
 Alum in paper, 12, 14 
 Alumina, hydrate, 50 
 
 „ linoleate, 67, 190 
 
 „ oleate, 67, igo 
 
 Aluminium, sheet, 39, 41 
 Amber, 6g 
 
 ,, oil of, 71 
 ,, varnish, 135 
 Amyl acetate, 355 
 ,, alcohol, 112 
 Andrew, F. W., the late, 362 
 Anime, 73 
 Anti-vermilion, 189 
 Arabic acid, 92 
 Arnold paper, 9 
 Arrabida red, 204 
 Arsenic sulphides, 184 
 Asbestos, 26 
 
 ,, in plaster, 22 
 Asphaltuni, 260 
 Aureolin, 168 
 Aurora yellow, 166 
 Azurite, 249 
 
 Back, the, of pictures, 31, 38, 345 
 Balsams, 78 
 
 Barium chromate, 171 
 ,, hydroxide, 104 
 ,, sulphate, 148 
 Baryta-water, 104 
 ,, white, 148 
 ,, yellow, 171 
 Bassorin, 94 
 Beeswax, 79 
 Bell’s medium, 140 
 Benzene, in 
 Bistre, 259 
 Bitumen, 260 
 Black, ivory, 270 
 ,, lead, 270 
 ,, pigments, 264 
 Bleaching oil, 56 
 Bleu lumi^re, 249 
 Blockz, J., 361 
 Blue, Antwerp, 240 
 ,, black, 269 
 ,, cobalt, 234 
 ,, Egyptian, 250 
 „ indigo, 241 
 „ pigments, 226-251 
 „ Prussian, 236 
 ,, Turnbull’s, 238 
 ,, verditer, 249 
 Brown, Caledonian, 256 
 „ Cappagh, 259 
 ,, pigments, 252-263 
 „ pink, 181 
 „ Vandyke, 257 
 Burlington Club trials, 378 
 Burnt carmine, 209 
 ,, lime, 19 
 ,, sienna, 256 
 „ umber, 254 
 Burton’s cobalt, 235 
 
 ,, potters’ pink, 200 
 
 383 
 
INDEX 
 
 384 
 
 Cadmium, green, 225 
 „ pale, 162 
 
 ,, red, 166 
 
 ,, versus chrome, 183 
 
 ,, yellow, 162 
 
 Calcium carbonate, 19, 23 
 ,, hydroxide, ig 
 ,, oxide, 19 
 ,, silicate, 20, 304 
 
 „ sulphate, 23, 27, 307, 356 
 Caledonian brown, 256 
 Camphor, 119 
 Canada balsam, 79 
 Canvas, 34 
 
 ,, back of, 37 
 
 ,, preservation of, 36-39 
 
 „ priming of, 34 
 
 ,, Willesden, 41 
 
 Cappagh brown, 258 
 Carbon bisulphide, 108 
 Carbonate of copper, 221, 249 
 ,, lead, 145 
 ,, lime, 19 
 Carbonates, 277, 279 
 Carmine, 207 
 Cassel brown, 258 
 Cellulose, ii 
 
 Ceramic pigments, 200, 218, 235 
 Ceresin, 81 
 
 Cerulean blue or cerulium, 235 
 Chafing varnish, 353 
 Charcoal black, 268 
 Chessylite, 249 
 Chinese ink, 265 
 
 ,, vermilion, 189 
 ,, white, 152 
 Chloroform, 109 
 Chromates, 279 
 Chrome green, 214, 216 
 ,, yellow, 182 
 Chromium, green oxide of, 214 
 Cineol, 107, 123 
 Cinnabar, 187 
 Citral, 123 
 
 Coagulation of albumen, 85 
 Cobalt blue, 234 
 
 „ ,, Burton’s, 235 
 
 ,, green, 218 
 ,, resinate, 57 
 ,, violet, 211 
 ,, yellow, 168 
 Cobaltinitrites, 168 
 Coccus cacti, 207 
 ,, ilicis, 207 
 
 Coccus lacca, 205 
 Cochineal lake, 207 
 Coeruleum, 235 
 Collodion, 37 
 
 Conservation of pictures, 38^^ seq., 342 
 Copal, Angola, 73 
 „ Benguela, 73 
 ,, Kauri, 74 
 „ oil of, 139 
 ,, oil-varnish, 135 
 ,, pebble, 72 
 ,, Sierra Leone, 72 
 
 ,, spirit varnish, 133 
 
 ,, West Indian, 74 
 ,, Zanzibar, 73 
 Copals compared, 77 
 Cotton paper, 1 1 
 Cowdi resin, 74, 138 
 Cremnitz white, 148 
 Crimson lake, 208 
 Cyanine, 240 
 Cymene, 124 
 Cyprusite, 161 
 
 Dammar, 74 
 Dextrin, 97 
 Dextrose, 97 
 Diluents, 106-124 
 Dipentene, 118 
 Distilled water, 106 
 Dryers, 55, 57, 125 
 
 Egg-medium, 85 
 
 Egyptian blue, 250 
 
 Elements, 275, 276, 278 
 
 Elemi, 142 
 
 Emerald green, 219 
 
 Emerald oxide of chromium, 216 
 
 Emulsions, 87 
 
 Epichlorhydrin, iii 
 
 Esparto, 12 
 
 Ether, 108 
 
 Ethereal hydrogen peroxide, 17, 15 1 
 Eucalyptol, 123 
 Eucalyptus oils, 122 
 
 Ferrocyanides, 236 
 Flake white, 145-15 1, 328 
 
 ,, action on oil, 64, 328 
 Freeman’s white, 151 
 Fresco grounds, 21, 22. 
 
 ,, method, 303 
 ,, secco, 22, 305 
 Frescoes, Asiatic, 28, 307 
 
INDEX 
 
 385 
 
 Frescoes, protected and restored, 356 
 Fugitive pigments, 284, 287, 289 
 
 Galleries, picture, 38, 342, 349 
 
 Gambier Parry’s medium, 142, 315 
 
 Gamboge, 172 
 
 Gelatin, 10, 88 
 
 Geraniol, 107 
 
 Gesso, 32 
 
 Glass, protective, 348 
 Glue, 35, 88 
 Glycerides, 51 
 Glycerin, 51, 98 
 Gold-point, 322 
 Graphite, 270 
 Green, chrome, 214 
 ,, madder, 285 
 ,, oxide of chromium, 214 
 „ ultramarine, 232 
 „ verditer, 221 
 Gum arabic, 91 
 ,, British, 97 
 „ Cape, 94 
 ,, Senegal, 92 
 „ Suakim, 92 
 ,, tragacanth, 93 
 Gypsum, 22, 23, 27 
 
 Hartley, the late Sir W. N., 366 
 Hellige’s colorimeter, 363 
 Hodgkinson paper, 9 
 Honey, 97 
 
 Hydrate of alumina, 50, 194, 208 
 Hydrates of copper, 249 
 „ iron, 157, 202 
 Hydrocarbons, 81, in, 1 12-1 17 
 Hydrogen peroxide, 35, 151 
 Hydroxides or hydrates, 279 
 
 Illuminated manuscripts, 190, 331 
 Indian ink, 264 
 ,, lake, 205 
 ,, red, 202 
 ,, yellow, 174 
 Indigo, 241 
 
 ,, brominated, 247 
 „ synthetic, 247 
 Infusorial earth, 16 
 Ink, Indian, 264 
 Intonaco, 21 
 
 Iron, compounds of, 157, 177, 200- 
 205 
 
 Ivory, 19 
 ,, black, 270 
 
 Kauri, 74, 138 
 Kermes lake, 207 
 Kieselguhr, 16 
 Kings’ yellow, 184 
 Kowdi, 74, 138 
 
 Laevulose, 97 
 Lamp-black, 267 
 Lapis lazuli, 226 
 
 Laurie, Prof. A. P., viii, 22, 250, 313 
 Lavender, oil of, 122 
 Lead antimoniate, 178 
 ,, chromate, 182 
 „ dryers, 55, 59 
 ,, oxychloride, 152 
 ,, red, 210 
 ,, sugar of, 125 
 ,, sulphate, 151 
 „ white, 145-151 
 Lecithin in egg-yolk, 87 
 Leitch’s blue, 240 
 Lefranc’s madders, 381 
 Lemon, oil of, 123 
 ,, yellow, 171 
 
 Light, action of, 56, 342-349, 358-382 
 ,, red, 200 
 Lime, burnt, 19, 20 
 „ carbonate, 18 
 „ caustic, 19, 22 
 ,, hydrate, 19 
 ,, mild, 19 
 ,, -putty, 20 
 ,, slaked, 19 
 „ sulphate, 23, 27 
 ,, -water, 19, 102 
 Limonene, 118, 123 
 Linen fibre, 7,11 
 Linoleic acid and linolein, 5: 
 Linoleum, 40 
 Linoxine, 51 
 Linseed, 47 
 Linseed oil, 47-51 
 
 „ ,, siccative, 57 
 
 ,, ,, testing, 60 
 
 ,, white, 48 
 Litmus, 13 
 
 Lovibond’s tintometer, 359 
 
 Madder brown, 196, 198 
 ,, lakes, 194 
 ,, rose, 198 
 Malachite, 221 
 Manganese borate, 57 
 „ dryers, 57 
 
 25 
 
INDEX 
 
 386 
 
 Manganese oil, 58 
 
 ,, resinate, 57 
 
 ,, violet, 251 
 
 Manuscripts, illuminated, 190, 331 
 Marouflage, 26 
 Mars violet, 177, 203 
 ,, yellow, 177 
 Mastic, 76 
 
 ,, varnish, 131 
 Mediums, 139-142 
 Megilp, 140 
 Mercury lamp, 56 
 Methylated spirit, 109 
 Mineral lake, 199 
 ,, pink, 200 
 
 ,, violet, 251 
 Mixed varnishes, 130 
 Mummy, 262 
 
 Naphthalene as resin-solvent, 138 
 Naples yellow, 178 
 National Gallery, 331 
 
 „ ,, British Art, 335 
 
 „ „ Portrait, 336 
 
 Newman’s colours, 370 
 Nut-oil, 62 
 
 Ochre, chrome in, 161 
 „ Perigord, 159 
 ,, red, 204 
 ,, yellow, 157 
 Oil, action on paints, 63 
 ,, amber, 1 19 
 ,, copal, 1 19 
 ,, drying, 46 
 ,, eucalyptus, 122 
 ,, extraction, 47 
 ,, in egg-yolk, 87 
 ,, in paints, 65 
 ,, lavender, 122 
 ,, lemon, 123 
 ,, linseed, 47-51 
 ,, manganese, 58 
 ,, nut, 62 
 ,, orange, 123 
 ,, painting, 309 
 ,, poppy, 61 
 ,, rosemary, 123 
 ,, semi-drying, 46 
 ,, siccative, 46, 57 
 ,, turpentine, 1 12 
 „ tung, 63 
 ,, varnishes, 135 
 Oils, essential, 122 
 
 Oils, drying, 46 
 „ fixed, 45 
 Old paintings, 325-341 
 Orange, oil of, 123 
 Organic pigments, 277, 280 
 Orpiment, 184 
 Ossein, 16 
 
 Ostwald, Dr. W., notes by, 37-40, 52- 
 55 , 319-321 
 O. W. paper, 9 
 Oxides, 276, 278 
 
 Painters’ materials, l 
 Painting methods, 301 
 
 >y >} 
 
 , Central Asian, 28, 
 
 
 . 307 
 
 , distemper, 22, 301 
 
 ,, ,, 
 
 fresco, 21, 304 
 
 yy yy 
 
 Gambier Parry, 25, 
 
 
 309 
 
 oil, 309 
 
 >> >> 
 
 pastel, 318-321 
 
 
 stereochromy, 24, 
 
 „ 
 
 307 
 
 tempera, 22, 301 
 
 yy yy 
 
 water-colour, 317, 
 
 yy yy 
 
 362 
 
 water-glass, 24, 307 
 
 Panels, 29 
 
 ,, preparation of, 30 
 Paper, 7 
 
 ,, acid in, 13, 369 
 ,, alum in, 10, 13, 14 
 ,, analyses of, 9 
 ,, ash of, 10 
 
 ,, cotton, 1 1 
 
 ,, fibre in, 1 1 
 
 ,, linen, 9, 1 1 
 
 ,, size in, 10, 14 
 
 ,, sugar, 17 
 
 ,, testing, 12 
 
 ,, Turner, 17 
 
 ,, Varley, 17 
 
 ,, water in, 9 
 
 ,, wood-pulp in, 12, 17 
 Paraffin, 81, 120 
 
 ,, copal medium, 141 
 ,, on frescoes, 357 
 
 „ paste, 356 
 
 Parchment, 16 
 Pastel painting, 318-321 
 Payne’s grey, 273 
 Perigord, orange and raw, 159 
 Permanent pigments, 2S4-288 
 
INDEX 
 
 387 
 
 Peroxide of hydrogen, 150, 338 
 Petroleum spirit, 120 
 Phellandrene, 117 
 Pigments classified, 274 
 „ interacting, 275 
 Pinene, 117 
 Piuri, 174 
 Plaster, 18-28 
 Platinum-point, 322 
 Poppy oil, 61 
 Potters’ pink, 200 
 Primrose yellow, 172 
 Prussian blue, 236 
 ,, brown, 263 
 Punicin, 247 
 
 Purple, Tyrian, 247, 334 
 Purpurin, 194 
 
 Queen’s House, Greenwich, 358 
 
 Raw sienna, 254 
 „ umber, 253 
 Red lead, 210 
 ,, ochre, 204 
 ,, pigments, 186-2 u 
 Resin, 68 
 
 ,, amber, 69 
 
 „ anime, 73, 74 
 
 ,, copal, 72-77 
 
 ,, cowdi, 74 
 
 ,, dammar, 75 
 
 ,, kauri, 74 
 
 ,, mastic, 76 
 
 ,, sandarac, 75 
 
 Resinates, 55, 59, 69, 1 13 
 Restoration of pictures, 351 
 Restricted palettes, 294-298 
 Reynolds, Sir Joshua, 292, 338, 361 
 Roberson’s medium, 140 
 Rock crystal to be avoided, 349 
 Rood, Prof. O. N., 365 
 Rose madder, 198 
 Rosemary, oil of, 123 
 Rosin, 1 13 
 
 Rosinates, 55, 59, 113 
 Royal Exchange panels, 26 
 Ruskin, John, 347 
 
 Russell, Dr. W. J., the late, 371, 373 
 
 Sandarac, 75 
 
 ,, varnish, 76 
 Scheele’s green, 221 
 Schweinfurt green, 219 
 Selected palettes, 290 
 
 Sepia, 272 
 
 Siccatives, 55, 125-129 
 Sienna, burnt, 256 
 „ raw, 254 
 Silicates, 277, 279 
 
 ,, alkaline, 100, 307 
 Silver-point method, 321 
 Simpson, W., the late, 369 
 Size, 35, 88 
 Size-painting, 303, 332 
 Slate, 27 
 Slate-grey, 273 
 Smalt, 248 
 
 Soane Museum, 15 1, 338 
 Solvents, 106-124 
 
 South Kensington Museum, 338, 348 
 „ „ Report, 371 
 
 Spike, oil of, 122 
 Spirit-fresco grounds, 25 
 ,, medium, 142 
 ,, method, 142, 315 
 Starch, 94 
 
 ,, soluble, 95 
 Stein, Sir Aurel, 8, 28, 307 
 Stereochromy, 24, loi, 307 
 Stone, 18, 27 
 Strasburg turpentine, 78 
 Straw in paper, 12 
 Substantive pigments, 281 
 Sugar- paper, 17 
 Sulphides, 276, 278 
 Sylvestrene, 118 
 
 Taylor, Mr. J. Scott, viii, 218 
 Tempera-grounds, 22 
 ,, method, 301 
 Terpenes, 1 12-123 
 Terre verte, 212 
 ,, ,, adulterated, 214 
 
 Testing paper, 12 
 ,, pigments, xi 
 ,, turpentine, 115 
 Toluene, 11 1 
 Turnbull’s blue, 238 
 Turner paper, 17 
 Turpentine, 112 
 
 ,, oil of, 1 16 
 
 ,, Strasburg, 78 
 
 ,, _ Venice, 78 
 
 Turpentines, 112 
 
 Ultramarine, 226 
 
 „ artificial, 229 
 
 ,, ash, 227 
 
INDEX 
 
 388 
 
 Ultramarine, green, 232 
 „ Ulac, 232 
 
 „ red, 232 
 
 „ testing-, 233 
 
 ,, violet 232 
 
 Ultra-violet rays, 56, 318 
 Umber, 252 
 
 Vanadium yellow, 183 
 Varley paper, 1 7 
 Varnish, amber, 133, 135 
 „ copal, 133-140 
 
 ,, mastic, 131 
 
 „ oil, 131, 135 
 
 ,, sandarac, 133 
 
 „ spirit, 131, 133 
 
 Varnishes, 130-139 
 Vellum, l6 
 Venetian red, 201 
 Venice turpentine, 78 
 Verdigris, 223 
 Verditer, 221, 249 
 Vermilion, artificial, 187 
 
 ,, instability of, 190 
 
 ,, native, 186 
 
 „ tested, 189 
 
 Vernalis, 218 
 
 Victoria and Albert Museum, 338, 
 
 348 
 
 Vine black, 269 
 Violet, cobalt, 211 
 ,, manganese, 251 
 
 ,, ultramarine, 232 
 
 Viridian, 216 
 Viscose, 14 
 
 Wallace Collection, 337 
 Ward, Mr. James, 357 
 Water, 106 
 
 „ baryta-, 18, 104, 304 
 
 Water in drawings, 345 
 „ in paper, 9, 317 
 
 ,, in resins, 69 
 
 ,, lime-, 19, 102, 304 
 
 Water-colour method, 317 
 Water-glass, 100 
 Wax, bees’, 79 
 ,, Brazilian, 80 
 
 ,, Ceresin, 81 
 
 ,, Chinese, 80 
 
 ,, Japanese, 81 
 
 ,, -painting, 80 
 
 ,, paraffin, 81 
 
 Whatman paper, 9, 12, 371, 378 
 White-lead, 145 
 
 ,, ,, action on oil, 64 
 
 ,, ,, adulteration of, 147 
 
 ,, ,, bleaching discoloured, 
 
 ,, ,, defects of, 149 
 
 ,, ,, impurities in, 147 
 
 White of egg, 85 
 White pigments, 145-156 
 Willesden canvas, 41 
 Wood, 29-33 
 
 ,, pulp, mechanical, 17 
 j ,, spirit, 109 
 
 i Yellow, cobalt, 168 
 
 ; „ kings’, 184 
 
 ‘ ,, lake, 180 
 
 ,, madder, 181, 185 
 ,, ochre, 157 
 „ pigments, l57->85 
 
 I Zinc borate, 128 
 ,, chromate, 172 
 ,, oxide, 152 
 ,, sulphate, 129 
 ,, sulphide, 154 
 ,, white, 152 
 
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