The Chemistry 
 
 of Paints and Painting 
 
 A. H CHURCH, FR.S. 
 
<e 
 
 NJ 
 
 •V 
 
THE CHEMISTRY 
 
 OF PAINTS AND PAINTING 
 
THE 
 
 CHEMISTRY 
 
 PAINTS AND PAINTING 
 
 A. H. CHURCH, M.A., F.R.S. 
 
 Professor of Chemistry in tlie Royal Academy of Arts in London 
 
 1500 
 
 '89o 
 
 LONDON 
 
 SEELEY AND CO. LIMITED 
 
 ESSEX STREET, STRAND 
 
 "2 »■■ 
 
THE GETTY CENTER 
 LIBRARY 
 

 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 
 
 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 themselves, 
 and the chief processes of painting. Although the artistic 
 side of the numerous problems discussed has not been neg- 
 lected, the book is in no way intended to teach manipula- 
 tion 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-manufacturer, but rather that he may acquire a 
 clearer insight into the nature and properties of the most 
 important constituents entering into the composition of his 
 pictures. With regard, however, to the tests for purity and 
 
PREFACE 
 
 genuineness which I have described in the following pages, 
 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 apparatus 
 needed, like the chemicals, are few and inexpensive. 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 further, preparing his own sicca- 
 tive oil, selecting and purifying his spirits of turpentine, and 
 so forth. That the painter should test the varnishes he 
 buys for hardness and toughness, and the pigments 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 purposing 
 to devote themselves to certain manufacturing and technical 
 pursuits. I am aware that to those who refer to its pages 
 

 PREFACE ix 
 
 for the revelation of all the secrets of colour-manufacturers 
 it may prove in some measure disappointing ; 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 confessedly an elementary 
 manual only, written with a definite aim, but covering a very 
 wide area of inquiry. And if chemists should conclude that 
 it contains too little chemistry, 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 require- 
 ments met in the pages devoted to trials of pigments. 
 Again, under the names of the individual pigments, dis- 
 cussed 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. 
 
 Much of the substance of the lectures which I have 
 
PREFACE 
 
 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 processes 
 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 investiga- 
 tions 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 repro- 
 duced 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 Bibliographical 
 Notes ; I have consulted also the standard chemical diction- 
 aries of Watts and of Wurtz, the treatise by Roscoe and 
 Schorlemmer, besides many special papers by other chemists. 
 I wish I could have given an authority for every statement 
 not derived from my personal experience, but, in an elemen- 
 
PREFACE 
 
 tary manual treating of many diverse topics, such a plan, 
 even if it could have been carried out, would have em- 
 barrassed my story with a multitude of perplexing refer- 
 ences. 
 
 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, per- 
 haps they may be said to soften them. Coeruleum, 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 it is 
 jindeed pitiable that such teaching should be seriously offered 
 ito artists and art-students. 
 
 It is satisfactory to know that several accomplished 
 
xii PREFACE 
 
 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 improvement of its 
 pages. I am aware of having omitted to notice many 
 interesting matters ; amongst these I name 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 con- 
 sideration, mainly because their adequate treatment, while 
 demanding much space, would have appealed to a com- 
 paratively 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, \i 
 

 BIBLIOGRAPHICAL NOTES 
 
 Andes, L. E., ' Oel und Buchdruckfarben.' Pp. viii., 271. 
 Leipzig, 1889. 
 
 Andres, E., ' Volatile and Fat Varnishes,' Brannt's transla- 
 tion. Pp. xx., 346. Philadelphia, 1882. 
 
 Blockz, J., 'Peinture a l'Huile.' Pp. iv., 98. Gand, 1881. 
 
 Cennini, Cennino, 'A Treatise on Painting in Fresco, Secco, 
 Oil and Distemper.' Completed in 1437 ; first pub- 
 lished (in Italian) in 182 1 ; translated into English by 
 Mrs. Mary P. Merrifield. Pp. lxx., 177. London, 
 1844. 
 
 Eastlake, Sir C. L., 'Materials for a History of Oil-Painting,' 
 Series I., pp. xii., 561 ; Series II., pp. xv., 432. London, 
 1847, 1869. 
 
 Field, G., ' Chromatography, a Treatise on Colours and 
 Pigments.' Pp. xix., 276. London, 1835. 
 
 Field, G., 'Chromatography,' edited by T. W. Salter. 
 Pp. vii., 436. London, n.d. 
 
 Field, G, ' Chromatography,' modernized by J. S. Taylor. 
 Pp. viii., 207, 2nd edit. London, 1885. 
 
BIBLIOGRAPHICAL NOTES 
 
 Gentele, J. G., c Lehrbuch der Farben-Fabrikation,' 2te 
 
 Auflage. Braunschweig, 1880. 
 Lefort, J., ' Chimie des Couleurs.' Pp. 344. Paris, 1855. 
 Merrifield, Mrs. M. P., ' Original Treatises (of the twelfth to 
 
 the eighteenth century) on the Arts of Painting,' with 
 
 Introduction and Notes. Two vols. ; pp. cccxii., 918. 
 
 London, 1849. 
 Mierzinski, S., ' Die Erd- Mineral- und Lackfarben,' 4te 
 
 Auflage. Pp. viii., 500. Weimar, 1881. 
 Riffault, Vergnaud and Toussaint, ' A Practical Treatise on 
 
 the Manufacture of Colours for Painting.' Revised by 
 
 M. F. Malepeyre ; translated by A. A. Fesquet. Pp. xvi., 
 
 659. Philadelphia, 1874. 
 Russell, W. J., and Abney, W. de W., ' Action of Light on 
 
 Water-Colours' (Blue-Book). Pp. 78. Appendix of 
 
 14 diagrams. London, 1888. 
 Theophilus, or Rugerus, ' An Essay upon Various Arts ' 
 
 (eleventh century). Translated, with Notes, by 
 
 R. Hendrie. Pp. xxxviii., 447. London, 1847. 
 
CONTENTS 
 
 INTRODUCTION 
 
 l'AGE 
 I 
 
 PART I 
 
 PA INTING-GRO UNDS 
 
 CHAPTER 
 
 I. PAPER, VELLUM, IVORY 
 
 II. PLASTER OR INTONACO, STONE 
 
 III. PANEL - - - - 
 
 IV. CANVAS ... 
 
 7 
 
 14 
 22 
 26 
 
 PART II 
 
 VEHICLES AND VARNISHES 
 
 V. OILS ----- 
 VI. RESINS, WAXES, PARAFFIN-WAX 
 VII. YOLK AND WHITE OF EGG, SIZE, GLUE 
 VIII. GUMS, GLYCERIN, HONEY 
 IX. WATER-GLASS, LIME- AND BARYTA-WATER 
 X. SOLVENTS AND DILUENTS 
 XL SICCATIVES OR DRYERS 
 XII. VARNISHES AND OLEO-RESINOUS VEHICLES 
 
 31 
 
 47 
 60 
 66 
 
 73 
 78 
 
 93 
 97 
 
■^^■H 
 
 ■H 
 
 CONTENTS 
 
 PART III 
 
 PIGMENTS 
 
 CHAPTER PAGE 
 
 XIII. WHITE PIGMENTS - - - - III 
 
 XIV. YELLOW PIGMENTS - - - -122 
 XV. RED PIGMENTS - - - - 1 46 
 
 XVI. GREEN PIGMENTS - - - - 1 68 
 XVII. BLUE PIGMENTS - - - - 180 
 XVIII. BROWN PIGMENTS .... 200 
 XIX. BLACK PIGMENTS - - - - 2IO 
 XX. CLASSIFICATION OF PIGMENTS- - - 219 
 XXI. TABLES OF PERMANENT AND FUGITIVE PIG- 
 MENTS ----- 225 
 XXII. SELECTED AND RESTRICTED PALETTES - 229 
 
 PART IV 
 
 METHODS AND RESULTS 
 
 XXIII. PAINTING-METHODS -- 239 
 
 XXIV. STUDY OF OLD PAINTINGS - - - 255 
 XXV. CONSERVATION OF PICTURES AND DRAWINGS - 268 
 
 XXVI. TRIALS OF PIGMENTS - - - - 28 1 
 
 INDEX ------ 307 
 
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 most treacherous 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 same chrc- 
 
INTRODUCTION 
 
 mate 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 knowledge of the origin, the composition, and 
 the characteristics of the various products with which their 
 works are constructed. An architect is expected to recog- 
 nise the sound or unsound quality of the timber, the stone, 
 the brick, the iron, with which the edifice he designs is con- 
 structed : why should the painter take everything on trust ? 
 The purchaser of a picture ought not to be distressed 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 in- 
 nocent of reagents. 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 
 canvases and panels. Before colourmen undertook 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 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 
 
INTRODUCTION 
 
 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 pig- 
 ments 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 
 establishments thoroughly equipped for a peculiar and diffi- 
 cult 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 responsi- 
 bility for the soundness and genuineness of many products 
 of the history and preparation of which he knows little or 
 nothing. 
 
 After these introductory observations, I may refer the 
 reader to the table of contents for the plan of the present 
 book, and to the preface 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 pigments, not omitting 
 the final varnish, and finally closing with a brief summary of 
 methods of painting, and of the experimental studies by 
 means of which 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 em- 
 ployed against hostile influences, it becomes of the greatest 
 importance to ascertain that no unnecessary 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 {Linum usitatissimuni) and 
 in the form of white rags is, or should he, used in the manu- 
 facture of paper-pulp. Other vegetable fibres might no 
 doubt be successfully employed for this purpose. For 
 instance, the Japanese paper, prepared from the bast-fibres 
 of the paper-mulberry (Broussonetrd papyri/era), 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 it is the latter kind 
 with which alone water-colourists are practically concerned. 
 Its manufacture in Europe dates as far back as the latter 
 half of the twelfth century.* To the kindness of Mr. W. H. 
 
 * Mr. Weale informs 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, had been forced to work at the manu- 
 
CONSTITUENTS OF PAPER 
 
 James Weale I am indebted for an opportunity of examining 
 two early specimens, obtained from the 'Registre des Re- 
 venues de l'Eveche 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 water colour work, for 
 when a wash of pigment is passed over it, the colouring 
 matter and the water partially separate, 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 three 
 analyses, which show the percentage proportions found in 
 good samples : 
 
 ANALYSES OF DRAWING-PAPERS 
 
 English, 1876 
 
 Dutch, 1876 
 
 Whatman, 
 
 1885 
 
 Water - 10 '9 - 
 
 - I IT) - 
 
 ■ 7 "4 
 
 
 Size - 61 - 
 
 - - 4-8 - 
 
 - - 6-3 
 
 
 Ash - i*i - 
 
 - 0-9 - 
 
 i*i 
 
 
 Fibre - 81*9 - 
 
 - - 83-5 - 
 
 - 85-2 
 
 
 The four constituents of paper named above may be 
 regarded as essential. The water or hygroscopic moisture 
 varies inversely with the temperature, and directly with the 
 
 facture of paper at Damascus. One . of these French mills was called 
 ' Damascus,' the other ' Ascalon.' This was previous to the year 1189. 
 
ASH OF PAPER 
 
 amount of water-vapour in the air. 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 ranges of tem- 
 perature. 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 equi- 
 librium is once more re-established Much less harm 
 would accrue were the vapourized water allowed to escape. 
 
 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 and soda, of resin, soda, starch, 
 and alum. From good drawing-papers, which are sized in 
 the sheet with animal size, the greater part of the size may 
 be extracted by means of boiling distilled water, the 
 solution being usually neutral, but sometimes faintly acid or 
 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. 
 
 The ash or mineral matter in paper may be derived from 
 three sources, namely, traces of the original mineral sub- 
 stances 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 in bleaching the 
 fibre or as 'antichlors.' In common and adulterated papers 
 the ash greatly exceeds 1 per cent., twelve parts per hundred 
 of paper being no unusual proportion. This 'filling' may 
 contain or consist of the following substances : kaolin or 
 
TESTING PAPER 
 
 china-clay, silicate of lime or ' pearl-hardening,' chalk or 
 whitening, lead-white, baryta white or ' white dressing,' and 
 artificial gypsum or ' satin-dressing/ 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 ultra- 
 marine, smalt or cobalt blue, and Prussian blue. 
 
 What is put down as fibre in the analysis of paper pre- 
 viously given, is a substance, or group of substances, to 
 which the name of cellulose is given by chemists. Cellulose 
 consists of the three elements, carbon, hydrogen, and oxy- 
 gen ; it is, when pure, entirely combustible, leaving no ash. 
 
 The most useful chemical tests to be applied to drawing- 
 paper may be thus indicated. 
 
 A piece of paper, having a surface of ioo square inches, 
 is w r eighed in its ordinary hygroscopic condition ; it is then 
 heated in the water-oven to the boiling-point of water for 
 one hour, then rolled up into a glass tube, having a sliding 
 glass tube for cover, and again heated to ioo C. for ten 
 minutes. It is allowed to cool, in the double tube arrange- 
 ment mentioned, in a desiccator, wherein the air is kept dry 
 by means of a water-absorbing substance, such as oil of 
 vitriol. Finally, it is weighed, still in the tubes. The 
 weight of the latter having been previously ascertained, the 
 weight of the dry paper can be found. The difference 
 between this weight and that of the original paper repre- 
 sents the water which it has lost : the loss should not exceed 
 12 parts in too. 
 
 ioo grains of paper should not lose, by repeated extrac- 
 tion with boiling distilled water, more than seven per cent, 
 of the original weight. 
 
 ioo grains of paper, when burnt to a white ash, should 
 not leave more than i'2 grain of incombustible residue. 
 
TESTING PAPER 
 
 A few hundred grains of paper should be exhausted with 
 warm distilled water : it is best to leave the water and paper 
 in contact for an hour at least. The watery extract is sub- 
 mitted to the following tests : To one half of it a few drops 
 of tincture of dahlia or violet flowers is added : if the purple 
 tint of the tincture changes to blue, alkali is present ; if to red, 
 acid ; if it is lightened or bleached, then the presence of chlor- 
 ine, of sulphurous acid, or of thiosulphate of soda is indicated. 
 A sound paper will yield an extract which will exert no action 
 upon a sensitive vegetable colouring matter. The remainder 
 of the warm-water extract is tested for alum or for the chloride 
 of aluminium, by adding to it a drop or two of liquor am- 
 monias and then boiling it ; a flocculent or gelatinous pre- 
 cipitate of hydrate of alumina indicates the presence of one 
 or other of the above-named compounds. 
 
 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 
 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 embedded in the 
 pulp. These particles appear grey, brown, or black ; they 
 may be detected by placing a drop of dilute acetic acid on 
 the suspected spot, allowing it to dry, and then moistening 
 
SIZE IN PAPER 
 
 the place with a drop of a freshly-prepa ed solution of yellow 
 prussiate of potash. If the particle be iron a stain of Prussian 
 blue will be produced. However, some dark spots consist 
 of blackened grease, or of tar, or of the paper-fungus (Myxo- 
 trichum chartaruni). 
 
 Naturally, there is a small quantity of oil or fat in paper ; 
 it varies from 3 to 5 parts in a thousand. The difficulty ex- 
 perienced 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. 
 
 As drawing-papers are sized in the sheet they occasionally 
 show a peculiar defect arising from the irregular distribution 
 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 paint- 
 ing the sinking-in and running of the pigments produce 
 disastrous results ; but it is easy to guard against accidents 
 of this sort by previously scraping and colouring a corner of 
 the sheet to be used. The peculiarity is generally 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. More- 
 over, 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. 
 
VELLUM AND IVORY 
 
 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 recep- 
 tion of water-colours consisted in rubbing the surface with 
 very finely-ground bone-ash, or with pulverized sandarac. 
 Pumice-stone or cuttle-fish, reduced to a minutely divided 
 state by pounding, grinding, and sifting, may be used for 
 this purpose. 
 
 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 inferior 
 and mixed fibres, and sometimes contain lead-white and 
 other injurious fillings. Mill-board is often made of wood- 
 pulp 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 rain or distilled 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 
 

 COMPOUNDS OF LIME 
 
 15 
 
 of lime, or mild lime, burnt lime, 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 carbonate, 
 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 con- 
 tains 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 carbonate. 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 contain silica in a form which is known as 
 
1 6 
 
 LIME-PUTTY 
 
 1 soluble silica.' This substance further strengthens the 
 plaster by forming with a part of the lime an insoluble com- 
 pound called silicate 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 quick- 
 lime produced 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 preserved in screw-top stoneware jars. Some 
 water will accumulate 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 conversion into mild lime : not more than one-third or 
 at most two-fifths of the lime should be converted into the 
 carbonate. 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. 
 
 A good mixture for the first application to the moistened 
 
FRESCO GROUNDS 
 
 n 
 
 wall consists of 2 parts (by weight) of clean sharp sand to 
 one of lime-putty. When one or nlore 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 added, 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 com- 
 menced 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 out- 
 lines and other important parts pounced in, transferred, or 
 impressed by an ivory point. Rapidity and firmness of 
 execution, with the distribution of an uniform thickness of 
 pigment, are matters to which special attention 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 mixture 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 same 
 quantity of infusorial (silicious) earth • the whole being 
 
TEMPERA GROUNDS 
 
 moistened with a sufficient quantity of lime-water to render 
 working easy. For the undercoats the sand, etc., intro- 
 duced 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. 
 
 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 tempera, 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 paint- 
 ings 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 discolouration of the ground. 
 
 The ordinary ground for Italian and Spanish tempera- 
 paintings consisted either of whitening and size, or of burnt 
 gypsum, stirred well with 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). 
 
STEREOCHROME GROUNDS 
 
 ■9 
 
 Various kinds of size were used ; one of the best was made 
 partly from parchment, partly from 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 discolouration 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. 
 
 The ground for stereochrome has been modified several 
 times since the first introduction of this method of water- 
 glass painting. Originally it was recommended to use an 
 undercoat containing 2 parts of sharp sand, 2 parts of fine 
 sand, and 1 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 1 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 
 
 2 — 2 
 
SPIRIT-FRESCO GROUNDS 
 
 twenty 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 1 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 stereo- 
 chrome 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 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. 
 
 The ground recommended by the late Mr. Gambier 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 
 
 * ' Chemistry of the Fine Arts ' in Cassell's 'Technical Educator.' 
 
SLATE AND STONE 
 
 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 
 turpentine. 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 repeated 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 containing plaster of Paris be introduced into the 
 grounds used for spirit-fresco. 
 
 Slate may be used as the ground for oil-painting ; but its 
 freedom from crystals of iron-pyrites, which present a brass- 
 yellow colour, must be first ascertained. The firm adhesion 
 of any priming or other layers of oil-paint which may be 
 applied subsequently to slate may be secured in the follow- 
 ing manner. The slate is slowly warmed in a water-oven, 
 and thus becomes quite dry. While still warm, it receives 
 a thin coat of oil-copal varnish, largely diluted with turpentine, 
 or it is rubbed with a bit of hard paraffin-wax. When this 
 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 turpentine, 
 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 at the close of the preceding 
 paragraph is preferable. 
 
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 abrasion; 
 and it must not contain much resin, gum, colouring-matter, 
 or other ' extractives,' as they are called, or else discoloura- 
 tion of the painting-ground, or priming, may occur. The 
 Flemings used oak ; the Italians white poplar. But oak 
 often proves treacherous, through irregular shrinkage ; while 
 poplar is too soft. Italian painters employed, also, the wood 
 of the stone pine. 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. Wood grown in poor soils, in temperate climates, 
 and felled in winter, is the best. 
 
 The specific gravity of wood varies from 0*3 to 1*35 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. 
 
 Wood contains (1) water, (2) ligno-cellulose, (3) extractives, 
 
PANEL 
 
 23 
 
 (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, albuminoids, 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 
 
 Water - - - 124. - 
 
 Cellulose - - - 49 - o - 
 
 Lignose - - - 2 7 '6 - 
 
 Ash - - it - 
 
 Resin - - i - o - 
 
 Water-Extract - 8'o. - 
 
 The preparation of panels for painting requires much 
 time and trouble. The directions given by ancient authorities 
 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 corrosive 
 sublimate has been dissolved ; coats of boiled oil, of liquid- 
 varnish* and white, and of verdigris and yellow are sub- 
 sequently mentioned. Probably the best method of treating 
 the harder woods intended for pictures is, after thorough 
 seasoning, first of all to reduce the panel, by planing and 
 glass-papering both sides equally, to the desired thickness. 
 
 * Made by boiling 1 part of sandarac in 3 parts of linseed-oil. 
 
 Oak 
 
 Pine 
 
 131 - 
 
 - I2'9 
 
 39 - 5 - 
 
 - 53'3 
 
 34-3 - 
 
 - 28-2 
 
 I"2 - 
 
 - 0-3 
 
 0"9 - 
 
 - r6 
 
 iro - 
 
 - 37 
 
24 
 
 PREPARATION OF PANELS 
 
 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 curvature 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 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 
 
PREPARATION OF PANELS 
 
 25 
 
 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 protected by wood. 
 Panel is to be recommended for modern work only 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 sometimes 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 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 will furnish excellent materials for 
 picture-panels. At present experiments in this direction 
 cannot be regarded as more than tentative and promising. 
 
CHAPTER IV 
 
 CANVAS 
 
 The usual, and probably the best fibre for the manufacture 
 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 
 priming consists of two coats, the first containing whitening 
 and size, the second lead white and linseed-oil. Fuller 
 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 final priming of zinc white and drying oil 
 (free from lead) be given, the usual discolouration of the 
 canvas which occurs on keeping it, especially in the dark, will 
 be avoided. But such discolouration can always be removed 
 by leaving in contact with the priming a piece of blotting- 
 paper saturated with a solution of peroxide of hydrogen. 
 An ordinary primed canvas was examined with the 
 

 CANVAS 
 
 27 
 
 
 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 con- 
 stituted the remaining part would weigh, therefore, about 
 44 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 pnle 
 buff. After immersion in boiling water for twenty minutes 
 a piece of this canvas 20 inches square was found to have 
 shrunk rather more than 1 inch in one direction, 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 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, therefore, 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 easily 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 
 
PRESERVATION OF CANVAS 
 
 paste, escapes this injury in great measure, as the sulphuretted 
 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 contains 
 size, though it may adhere firmly to the sized canvas, it may 
 not hold the subsequent oil-painting quite so tenaciously. 
 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 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 coagulating some of the 
 size in the canvas : the tannin turns it into leather. Corro- 
 sive sublimate prevents the development of mould or mil- 
 dew, and is a good preservative against the attack of animal 
 organisms. 
 
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. Chapter XL — 
 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 ex- 
 clude from the category of true oils petroleum and the 
 liquid paraffins, spirits 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, however, 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, oil 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 linoleic 
 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 in 
 
32 
 
 DRYING OILS 
 
 question and three molecules of water. Conversely, under 
 other conditions, one molecule of a glyceride, reacting with 
 three molecules of water, produces one molecule of glycerin 
 and three molecules of fatty acid. If, in this last reaction, 
 we substitute for the water three molecules 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 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, benzene, chloroform, liquid paraffins, and 
 volatile plant essences ; they are, in fact, miscible in all pro- 
 portions with these liquids. There are other liquids in 
 which the oils are less soluble, such are alcohol, ether, 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 temperature of boil- 
 ing water for some time, do in some instances become dry 
 and hard, but the varnish they yield under these circum- 
 stances is dark in colour and brittle. 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, but the general 
 methods of extracting them first demand a few words of ex- 
 planation. There are two different processes in use. In 
 one of these, which has been practised widely from very 
 early times, the oil is obtained by pressure ; in the other 
 
LINSEED OIL 
 
 33 
 
 process, invented some fifty years since, 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 proportion of solid fats. The solvent commonly 
 employed to dissolve out the oil from oil-yielding materials 
 is carbon bisulphide (CS 2 ), 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 mere 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 contain 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 usitatissimnni). Linseed varies in 
 size and colour. The usual colours are a purplish-brown 
 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, particularly in 
 Nagpur, but no pains are taken to keep the strain pure. 
 Through the kind offices of the Director of the Royal 
 
 3 
 
34 
 
 LINSEED OIL 
 
 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. At- 
 tempts 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 advan- 
 tage 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 screen- 
 ing, 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 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 deteriorate its quality. 
 
 The percentage of oil in linseed varies between 28 and 
 45 : by cold-pressure 20 per cent is the average yield; by 
 
 * Occasionally these weed-seeds give up, under pressure, certain 
 matters which deepen the colour of the expressed oil somewhat. 
 
LINSEED OIL 
 
 35 
 
 hot-pressure, 27 per cent. ; by extraction with carbon di- 
 sulphide, 2>3 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 80° or even ioo° F. for some time. It 
 thus loses colour and becomes clear, a slimy deposit 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 6o° F. (15*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 be named the 
 following : Filtration through felt or carded cotton and 
 charcoal, and then through pyrolusite ; agitation with a 
 solution of common salt, followed by washing with water, 
 and drying by a heat of 220° F. ; treatment with one four- 
 hundredth part of oil of vitriol, addition of hot water, wash- 
 ing, and drying. Various other processes and reagents 
 have been employed for purifying and bleaching linseed oil. 
 Aqueous solutions of sulphurous acid, green vitriol, potas- 
 sium permanganate, 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. 
 
 3- 2 
 
36 
 
 LINSEED OIL 
 
 Whatever 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 complete 
 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 accord- 
 ing to the method of extraction adopted, cold-pressed oil 
 containing about 78 per cent, of carbon, 11 per cent, of 
 hydrogen, and 1 1 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. 
 Linseed oil consists chiefly of four glycerides, called, 
 respectively, linolein, linolenin, isolinolenin, and olein. A 
 small, but variable, amount of free fatty acids is also 
 present. The empirical formulae of the four fatty acids of 
 the above-named glycerides are, respectively : 
 
 Linolenic Acid\ 
 Isolinolenic J 
 
 - C 18 H 30 O 2 . 
 
 Linoleic- 
 Oleic - 
 
 - C 18 H 32 2 . 
 
 Linolein, which is present in linseed oil to the extent off 
 about 20 per cent, is the glyceride of linoleic acid, and has, 
 the formula, (C 18 H 31 0) 3 ,C 3 H 5 ,0 3 ; or, as it may be written, 
 C 3 H 5 (0,C 18 H 31 0) 3 . The relation of this glyceride to> 
 glycerin may be seen when the latter body is expressed by 
 the formula, C 3 H (OH) 3 . It is probable that the two other 
 main constituents of the oil — linolenin and isolinolenin — 
 are similarly constituted glycerides, and that they closely 
 
LINSEED OIL 
 
 37 
 
 resemble linolein in physical and chemical properties. 
 When ioo 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 12 or 13 per cent, of its weight, becoming converted into 
 a mixture of substances for which it is convenient 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, and is also more bulky ; 100 grains of 
 linseed oil produce about 108 or 109 grains of linoxine. 
 During the oxidation of linseed oil, the small quantity of 
 olein it contains remains unoxidized, and its presence con- 
 fers elasticity upon the product. The changes which occur 
 during this oxidation are complex and ill-understood ; but 
 there is some formic acid formed, so that the product is 
 sour— carbonic acid gas and water are also produced. 
 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 substances favour the absorption of oxygen 
 by linseed oil under the above conditions. Amongst these 
 may be named manganese dioxide, borate, oxalate, or 
 linoleate ; red-lead, litharge, or lead acetate ; green vitriol 
 or white vitriol, 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 
 
38 
 
 SICCATIVE LINSEED OIL 
 
 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 siccative, 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 
 maintained, by means of a water bath, at a temperature of 
 100° C., the change will occupy less time, and the pioduct 
 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 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 is to 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 subsequent 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 
 
SICCATIVE LINSEED OIL 
 
 39 
 
 that the absorption of oxygen by the oil is favoured by the 
 removal of certain impurities, and this the borate of man- 
 ganese may effect. 
 
 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 consecutive, 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 composi- 
 tion \ 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, w r hen 
 linseed oil is warmed with borate of manganese 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) over those in the 
 manufacture of which lead compounds, or white vitriol, 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 
 
4 o 
 
 TESTING LINSEED OIL 
 
 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, agita- 
 tion 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 drcp 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 
 methods for the further development of this property hav- 
 ing been discussed, we may now describe the remaining 
 characters of this oil. The cold-piessed 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 :io. 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 experimenter is 
 well-versed in the work, the indications obtained are some- 
 times perplexing and difficult to interpret. The amount of 
 
TESTING LINSEED OIL 
 
 41 
 
 bromine absorbed by a given weight of linseed oil, or better, 
 of the fatty acids obtained from it, affords a valuable test 
 of purity. This amount of bromine is unusually high, 
 much higher than that absorbed in the case of the oils 
 likely to be used as adulterants. But such quantitative 
 determinations can be properly performed only by the 
 skilled chemist. Valenta's acetic acid test is, however, 
 more easily managed. To apply this, take equal volumes, 
 three cubic centimetres of each, of the oil and of glacial 
 acetic acid (specific gravity, 105 6 '2) ; mix thoroughly and 
 gradually, heat the mixture until the oil has completely 
 dissolved, or the boiling-point is reached. Immerse a 
 thermometer in the liquid, allow it to cool slowly, and note 
 the temperature at which cloudiness appears. The following 
 temperatures are those at which this turbidity is produced in 
 the case of several different oils : 
 
 Tame of Oil 
 
 Temperature of Turbidity 
 
 Niger-seed - - - - 
 
 - - 49° C. 
 
 Linseed - - - - 
 
 • 57° 
 
 Sesame-seed 
 
 - - 87° 
 
 Almond -. - - - 
 
 - IIO° 
 
 Ground-nut 
 
 - 1 1 2° 
 
 Rape-seed, Mustard-seed, etc. 
 
 - Not dissolved. 
 
 It will be seen from these figures that of these six oils that 
 of linseed is, with one exception, the most soluble ; and 
 that the presence of such usual impurities as the oils of 
 sesame, rape and mustard, tends to reduce the solubility, 
 and hence to develop turbidity in the acetic acid sooner — 
 that is, at a higher temperature. 
 
 The specific gravity of linseed oil also affords a valuable 
 means of testing its purity. At 15 '6° C. (60° F.) it is denser 
 than most other vegetable oils : 
 
4 2 
 
 
 
 NUT OIL 
 
 
 Name of Oil 
 
 Spec. 
 
 Grav. 
 
 Name of Oil Spec. Grav 
 
 Linseed 
 
 - 
 
 "935 
 
 Poppy-seed 
 
 •926 
 
 Gold-of-Pleasure 
 
 - 
 
 •931 
 
 Sunflower-seed - 
 
 •925 
 
 Hemp- seed 
 
 - 
 
 •930 
 
 *Black Mustard-seed - 
 
 •921 
 
 Cotton-seed 
 
 
 •930 
 
 *Ground-nut 
 
 •918 
 
 Walnut - 
 
 - 
 
 •929 
 
 *Colza-seed 
 
 •914 
 
 The four oils marked with an asterisk are non-drying. 
 
 Poppy Oil. — This oil is obtained from the seed of the 
 opium-poppy, Papaver 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 temperature is "926. Its 
 chemical composition is near that of linseed oil ; it contains 
 the same four 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, states 
 that umber is a siccative for 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 acquired 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, Juglans 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- 
 
ACTION OF PIGMENTS ON OILS 
 
 43 
 
 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 characters ; 
 its specific gravity "929 is intermediate between that of lin- 
 seed and poppy oil. 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 ocymoides and from the 
 kernels of Torreya nucifera, are not of sufficient importance 
 to demand description, 
 
 A few observations may now be offered as to (1) 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 
 oecause 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 
 
44 
 
 OIL IN PAINTS 
 
 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 pheno- 
 mena 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. 
 This change is particularly noticeable with the cochineal and 
 madder lakes. I have succeeded in obviating it, by care- 
 fully drying the pigments at a temperature just under ioo° C, 
 before grinding them with oil, and by substituting 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 siccative 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 is of a distinctively chemical 
 nature. The most striking example of it known occurs 
 with flake-white. The lead hydrate in normal lead-white 
 saponifies the oil, forming lead-soaps with the fatty acid 
 which it contains, and, at the same time, setting free a small 
 quantity of glycerin. References to this curious action will 
 be found in Chapters XIII. and XXIII. 
 
 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 
 
OIL IN PAINTS 
 
 45 
 
 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 amount required by ioo parts in 
 weight of 19 pigments : 
 
 
 
 According 
 
 'to 
 
 According 
 
 r to Winsoi 
 
 ante of Pigment 
 
 M. 
 
 von 
 
 Pettenkofer 
 
 and 
 
 Newton (1882) 
 
 White Lead - 
 
 - 
 
 - 
 
 12 
 
 - 
 
 - 
 
 - 
 
 15 
 
 Zinc White 
 
 - 
 
 • 
 
 14 
 
 - 
 
 - 
 
 - 
 
 — 
 
 Aureolin - 
 
 ■ 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 200 
 
 Chrome Yellow 
 
 - 
 
 - 
 
 19 
 
 - 
 
 - 
 
 - 
 
 32 
 
 Yellow Ochre - 
 
 - 
 
 - 
 
 75 
 
 - 
 
 - 
 
 - 
 
 75 
 
 Raw Sienna 
 
 - 
 
 - 
 
 240 
 
 ■ 
 
 - 
 
 - 
 
 180 
 
 Vermilion 
 
 - 
 
 - 
 
 25 
 
 - 
 
 - 
 
 - 
 
 20 
 
 Madder Lake - 
 
 - 
 
 - 
 
 62 
 
 - 
 
 - 
 
 - 
 
 125 
 
 Terre Verte 
 
 - 
 
 - 
 
 IOO 
 
 - 
 
 - 
 
 - 
 
 70 
 
 Viridian - 
 
 - 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 75 
 
 Prussian 31ue - 
 
 - 
 
 - 
 
 112 
 
 - 
 
 - 
 
 - 
 
 75 
 
 Cobalt Blue - 
 
 - 
 
 - 
 
 125 
 
 - 
 
 - 
 
 - 
 
 75 
 
 Ultramarine (Art 
 
 ficial) 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 37 
 
 Raw Umber 
 
 - 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 IOO 
 
 Burnt Umber - 
 
 - 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 90 
 
 Bitumen - 
 
 - 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 126 
 
 Brown Madder - 
 
 - 
 
 - 
 
 — 
 
 - 
 
 - 
 
 - 
 
 87 
 
 Burnt Sienna - 
 
 - 
 
 - 
 
 181 
 
 - 
 
 - 
 
 - 
 
 195 
 
 Bone Black 
 
 - 
 
 - 
 
 112 
 
 - 
 
 - 
 
 - 
 
 no 
 
 The great differences in the above amounts of oil do not 
 cause such serious results in the conduct of the process of 
 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 an 
 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 prepared by some 
 
46 
 
 OIL IN PAINTS 
 
 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 rem irked that the quantities of oil 
 required by some of the pigments in the above table may be 
 reduced by grinding them under greater pressure. Aureolin 
 requires only 80 parts of 'manganese oil' for each 100 of 
 dry pigment, instead of 200 of linseed oil, and then yields 
 a quick-drying and perfectly protected paint. Yellow ochre, 
 raw 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 be prevented by using ' manganese 
 oil ' instead of raw linseed oil, and adding to it a small 
 quantity of hard paraffin wax having a melting-point not 
 under 65° C. 
 
 * Dr. H. Stockmaier, of Niirnberg, has found the following per- 
 centages of oil in certain oil-paints from different sources which he has 
 analysed : 
 
 Flake-White (Roberson and 
 
 Co.) - 16-2 
 
 Light Red (Winsor and 
 
 Newton) - - - 41 "9 
 
 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 termed gums. 
 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, and are probably oxidation-products of 
 certain hydrocarbons in essential oils. Some resins, such 
 as gamboge, contain gum and are called gum-resins ; others 
 contain a hydrocarbon (or terpene, see Chapter XL) or an aro- 
 matic acid, and are called balsams ; others are true resins, 
 but even these rarely, if ever, consist of a single definite com- 
 pound, 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 car- 
 bon, hydrogen, and oxygen, with occasionally a little sulphur, 
 and are usually of an acid character, and are capable of 
 forming soaps, called resinates, with the alkalies. Resins 
 differ much from one another, not only in solubility but also 
 in hardness and in the temperature at which they melt. Those 
 
48 
 
 AMBER 
 
 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 impurities, 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 ioo 
 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 no° 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 
 interments. At Naples I was shown some years ago a very 
 large number of antique fibulae carved out of this substance : 
 they had just been disinterred from Etruscan tombs. Such 
 amber has often become brittle, especially so far as regards 
 
AMBER 
 
 49 
 
 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 Denmark, 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 probably not 
 identical with Baltic and English amber. The same obser- 
 vation may be made with respect to the so-called ambers of 
 Travancore 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 incon- 
 siderable number of different plants. Goppert, so long ago 
 as 1853, satisfied himself that at least eight species of plants 
 besides Pinites succinifer 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 1*07 ; its hardness 
 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 surface : this 
 behaviour serves as a distinguishing test between amber and 
 
 4 
 
5o 
 
 COPAL 
 
 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 hydrocarbons (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 fragments 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 «C 10 H 16 O. Small quantities of two other 
 resins which are soluble in alcohol and ether, of a liquid 
 hydrocarbon, and of succinic acid are associated with the 
 main constituent, which has received the mineralogical 
 name ' succinite.' 
 
 The classical names for amber were tfXixrpov, lyncurium, 
 electrum and succimim. 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 sandarac only, 
 when amber was designated as g/as, or glassa. In modern 
 French amber is distinguished from ambre gris as ambrc 
 jaune. 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 different species, 
 and even genera of trees, while the origin of several of the 
 kinds still remains unknown. One of the hardest, whitest, 
 
COPAL 
 
 5i 
 
 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 Guibourtiana, which 
 belongs to the sub-order Csesalpinea? of the order Legumi- 
 nosag. 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, generally 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 
 thirty-three per cent., is soluble in absolute alcohol and in 
 spirits of turpentine. 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 keeping 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 Copaifera yield similar but 
 inferior resins to that produced by C. Guibourtiana, but 
 C. Gorskia?ia is the source of Inhambane copal ; Benguela 
 copal, Angola copal, and Gaboon copal are other sorts, vary- 
 ing in hue from straw-colour to a dull reddish-orange, pro- 
 duced in all probability by different species of Copaifera. 
 
 4—2 
 
52 
 
 COPAL 
 
 Zanzibar copal is another hard and valuable resin off 
 African origin : it is often called anime. It is produced by 
 another leguminous tree, Trachylobium Hornanannianum v 
 which belongs to the same sub-order, Cassalpineae, as Copai- 
 fera. 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 thick- 
 ness of a quarter of an inch or more. The same resin, whera 
 occurring on the bark of the living trees of the same species 
 of Trachylobium, presents a smooth and glossy surface ; ilt 
 is not so hard as the fossil variety. Zanzibar copal melts ait 
 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 nature 
 requires further study. 
 
 A third resin, sometimes designated as copal, sometimes 
 as anime, is produced by another leguminous tree, Hyme'- 
 ncea courbaril, 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 fronn 
 another species of the same genus, H. verrucosa. A 
 Mexican copal is probably the resin of an allied species;. 
 The resin from H. cowbaril is generally known as Wesit 
 Indian copal : fine specimens have been received froir.i 
 Demerara. 
 
 The Bungo tree of Sierra Leone, Daniellia /huriferat, 
 affords a resin of inferior quality. It is probable that the 
 
DAMMAR 
 
 S3 
 
 
 isame 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 Araucarieae. The largest masses, 
 some of them occasionally over ioo 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 some- 
 what whitish, or streaked with opaque bands, when first 
 found. It is cleaned and scraped and then sorted into 
 several qualities. Its use has greatly extended of recent 
 years. It is now 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 is inferior in hardness, toughness, and dura- 
 bility 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 Dammara australis. White or Singapore dammar is 
 the resin of Dammara 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. Vateria 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. micrantha , 
 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 
 
54 
 
 MASTIC 
 
 produced by Canarium strictum ; 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 composi- 
 tion and properties, although they resemble one another in 
 their solubility in boiling alcohol and in their easy alter- 
 ability. 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 
 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 (Callitris quadrivalvis), a native of Algiers. 
 It is a pale yellow resin, when fresh resembling mastic in 
 colour, but becoming yellower with age. It is soft and 
 brittle. When finely powdered and sifted it forms one of 
 the kinds of pounce used in preparing the surface of parch- 
 ment and vellum for writing and illuminating. It melts at 
 130 C. (266° F.), exhaling an aromatic odour. It partly 
 dissolves in alcohol, and is wholly soluble in oil of spike 
 and in several terpenes ; acetone also dissolves it. 
 
 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 
 
WAX 
 
 55 
 
 the cashew-nut order or Anacardiaceai. 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. It contains, 
 besides its resinous constituents, a small quantity of a volatile 
 essential oil (a terpene) and of moisture. It yields a tender 
 but glossy varnish, largely employed for the final protection 
 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 : — 
 
 Indian mastic from Pistatia cabulica. 
 Bombay mastic from P. Khinjak. 
 Pistachio mastic from P. Terebinthus. 
 
 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 lew experiments have been made as to the 
 utilization of exotic and vegetable waxes in the processes of 
 painting. Crude beeswax requires purification and bleach- 
 ing 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 
 
56 
 
 WAX 
 
 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 hydrogen 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 be re-melted. Its hardness is 
 increased and its melting-point raised by the above treat- 
 ment. 
 
 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 in- 
 fluences, disintegrates and partially perishes by oxidation. 
 It is a constituent of Gambier-Parry's spirit-fresco medium, 
 into which it is introduced in order to impart a matt appear- 
 ance 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 South Kensington Museum. 
 They are eticaustic portraits, executed probably in the second 
 and third centuries of our era, and were discovered by Mr. 
 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 
 
PARAFFIN WAX 
 
 57 
 
 insects. Thus, Chinese wax is produced by the puncture of 
 Coccus Pela living on Ligustrum lucidum and Fraxinns 
 c/wiensis. Chinese wax, which melts at 82° C. (180 F.), 
 consists almost entirely of cerotyl cerotate. Brazilian or 
 Carnaiiba wax occurs naturally in thin films on the leaves of 
 a palm (Copemicia cerifera) ; it melts at 84° C. (183° F.). 
 Japanese or Ibota wax is probably produced by the attacks 
 of a coccus on Ligustrum Ibota ; it melts at 42 C. 
 (108 F.). 
 
 Paraffin wax, hard paraffin, and solid paraffin, 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 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 
 C 22 H 4(; , C 24 H 50) C 26 H 52) C 27 H 56 , C 28 H 58 , and C 30 H 60 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 
 
5§ 
 
 PARAFFIN WAX 
 
 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, 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 distinguishing 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, fractional 
 crystallization from solvents, etc. — involve the use of com- 
 plex 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 hydrocarbons. 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 subsisting between the melting- 
 

 PARAFFIN WAX 
 
 59 
 
 point and the specific gravity (at 20 C.) of six different 
 samples of hard paraffin from ozokerite : 
 
 No. of 
 Sample 
 
 Melting- 
 point 
 
 Specific 
 Gravity 
 
 No. of 
 Sample 
 
 Melting- 
 point 
 
 Specific 
 Gravity 
 
 1 
 
 2 
 3 " 
 
 - 56 D C. - 
 
 - 6i° - - 
 
 - 67 - - 
 
 - 0912 
 
 - 0*922 
 
 - 0*927 
 
 4 " 
 
 5 " 
 
 6 - 
 
 - 72° C. ■ 
 
 - 7 6° - - 
 
 - 82 - - 
 
 ■ 0-935 
 • 0-939 
 - 0-943 
 
 Hard paraffin wax may be used in the preparation of 
 painting mediums as a substitute for beeswax ; for prevent- 
 ing the separation of heavy pigments, such as vermilion, 
 from the oil in which they are ground ; and for the prepara- 
 tion of certain painting-grounds. 
 
■ 
 
 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 element 
 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 sulphuretted 
 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 tanning operation may be 
 
WHITE OF EGG 
 
 6 1 
 
 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 hens' eggs. The percentage proportions 
 
 are, on the average : 
 
 Yolk White 
 
 Water ----- 51-5 - - . 84-8 
 Albumen, etc. - - - 15-0 - - - 12*0 
 
 Fat or Oil .... 30-0 - - - o"5 
 Mineral Matter - - - 1*4 - - - i'2 
 Other Substances - - - 2"l - - - 1*5 
 
 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 coagulated ; 
 it is not capable of being again dissolved. Solutions of 
 tannin, corrosive sublimate, 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 ex- 
 traneous 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 has just, or ?iearly, 
 regained 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 clear 
 liquid which drops through has been freed from membranes, 
 
62 
 
 COAGULATION OF ALBUMEN 
 
 etc., and contains nearly 4 per cent, of albumen. 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 albumen 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 suffi- 
 ciently, the whole coloured layer may be rendered insoluble 
 and irremovable 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 thickly, it may be found 
 necessary to give the whole surface a final coat of albumen- 
 solution. We have dwelt at some length upon this employ- 
 ment of tannin, or of heat, to secure the coagulation of 
 albumen, because it serves to illustrate the way in which 
 paintings, executed with egg-yolk, or size, as a medium, may 
 
SIZE AND GLUE 
 
 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 closely 
 resembles it in composition and properties, and which, for 
 our present purpose, we need not further describe. 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 suspended in an 
 albuminous solution. And, moreover, the amount of this 
 oil is large; for there is 30 per cent, of it. as against 15 per 
 cent, of albumen and vitellin taken together. Hence it 
 happens that egg-yolk, the usual vehicle for pigments in the 
 best kind of tempera-painting, must be regarded as 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 
 
6 4 
 
 SIZE AND GLUE 
 
 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 duration 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 cartilagin, or chondrigen, by the 
 same process which changes collagen into gelatin. A hot 
 solution of chondrin gelatinizes 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 usage, the special purpose in 
 view will indicate whether an insoluble (in cold water) and 
 strongly-gelatinizing, or a partially soluble and very adhesive 
 
GLUE AND SIZE 
 
 65 
 
 one should be selected. The former is less liable to crack 
 when dry than the latter. A few experiments, with cold 
 water and then with hot, will soon reveal the peculiarities 
 of the samples submitted to examination. As caustic 
 lime, caustic soda, chloride of lime, sulphurous acid, and 
 certain mineral acids, are frequently employed in the manu- 
 facture 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 turmeric-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. 
 
 The temporary preservation from putrefaction of the solu- 
 tions 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 suffi- 
 cient. 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 five 
 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 
 oni the surface. 
 
 5 
 
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 paint- 
 ing 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 Sennaar, 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 finest quality, but all the grades of 
 
GUM SENEGAL 
 
 67 
 
 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 authorities, a part of the gum Senegal of commerce 
 is produced by other species of Acacia besides A. Senegal, 
 such as A. Adansonii, A. albida, A. dealbata, A. nilotica, A. 
 Verek, etc., and even from species of Kaya, Spondias, and 
 Stercnlia. 
 
 Gum is essentially a mixture of the salts of an acid called 
 arabic acid. 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 is generally expressed by the formula C 12 H 22 11 , 
 but the experiments of O'Sullivan indicate a much more 
 complex composition (C 89 H 14l2 O r4 ). 
 
 Gum Senegal, the only sort which should be employed in 
 paiinting, should be nearly free from colour, and should dis- 
 solve in cold water without leaving an appreciable residue. 
 Its watery solution should be clear, and should give no 
 colour with tincture of iodine, but an abundant precipitate 
 with ammonium oxalate solution. If iodine produce a 
 purplish colour, adulteration with dextrin is indicated ; the 
 white precipitate thrown down by the oxalate shows the 
 presence of calcium, a constant constituent 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 
 tha.n those bought as gum-arabic and best Turkey : the lumps 
 varied more in size, often contained air-bubbles, and were 
 
 5—2 
 
68 
 
 GUM TRAGACANTH 
 
 less fissured. The adhesiveness and toughness of these 
 samples, moreover, compared favourably with these pro- 
 perties 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 prepared 
 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 without 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. 
 
 Gum tragacanth is produced by certain leguminous shrubs 
 belonging to the genus Astragalus. Amongst these may be 
 named : A. gummifer, A. eriosiylus, A. brachycalyx, and A. 
 adscendetis. It is only partially soluble in cold water. It 
 consists of arabin and bassorin — that is, of arabates of the 
 same compounds which constitute the bulk of gum-arabic 
 to the extent of half its weight, along with meta-arabates, 
 which latter probably have the same composition as the 
 corresponding arabates, but are insoluble in cold water : 
 there is also some starch in gum tragacanth. It contains 
 from T2 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 : 
 
STARCH 
 
 6 9 
 
 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 constitutes a moderately thick 
 mucilage. 
 
 Other gums are of small importance. They commonly 
 contain much bassorin (probably identical with the meta- 
 arabates), and but little arabin (or arabates). The Australian 
 wattle gums from several species of Acacia are perhaps 
 thus constituted; but if this be the case, the bassorin 
 present in them seems merely to swell up without dissolving 
 even when boiled for a long time with water, and so differs 
 from the bassorin of tragacanth. Cape gum is produced by 
 Acacia horrida : A. stcnocarpa yields Suakin gum. So far 
 as I know, no use has at present been made, in the fine arts, 
 of these gums. 
 
 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 employed 
 indifferently. Arrowroot may also be used. The prepara- 
 tion 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 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 thinner liquid be required. 
 
 Starch contains carbon, hydrogen and oxygen only, and is 
 a carbohydrate having the empirical formula «C H 10 O 5 . It 
 
70 
 
 HONEY 
 
 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 impurities. It 
 will suffice for the purpose now in view, if we select a 
 commercial dextrin, free from acidity, dissolving 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 adhesive than one of 
 true gum of the same strength. 
 
 Honey now claims our attention. It is a common 
 ingredient 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 consists 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 20 per cent, of 
 water. As the useful properties of honey depend entirely 
 upon its laevulose, 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 solution is; 
 
GLYCERIN 
 
 7i 
 
 then filtered: the filtrate is a solution of Isevulose, accom- 
 panied by small quantities of the other sugars of honey and 
 of harmless impurities, and for some artistic purposes 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 
 aqiueous 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 attrac- 
 tion for moisture ; on this property its usefulness as a con- 
 stittuent of certain paints depends. 
 
 (Glycerin was discovered in 1779 by Scheele as a by-pro- 
 duict in the preparation of lead-plaster ; for a long time the 
 comparatively small quantity of glycerin met with in com- 
 mence was obtained in this way. It is now prepared from 
 oils and fats by distilling them in a current of superheated 
 ste;am ; sometimes by first saponifying them with alkalies, or 
 decomposing them with sulphuric acid, and then submitting 
 the:m to this distillation-treatment. 
 
 (Glycerin generally occurs as a thick syrup with a sweet 
 tasite : when pure, it may be obtained in deliquescent 
 crystals. Its empirical formula is C 3 H 8 3 . It is a strongly 
 hygroscopic or water-attracting substance, the pure water- 
 frete glycerin being capable of absorbing more than one- 
 thiird its weight of water from the air. Commercial glycerin 
 always contains water : the specific gravity of the liquid 
 affords a rough method of estimating the amount. For 
 pure glycerin at 15 - 6° C. has the specific gravity i'2 64, while 
 thait which contains 20 per cent, of water is reduced to 
 
72 
 
 GLYCERIN 
 
 I '2 1 ; with 30 per cent, it is 1*183, and with 40 per cent. 
 1 '156. 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, when I recommended its em- 
 ployment for this purpose to the late Mr. Winsor. 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, 
 1 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, 
 sco early as 1648, made a soluble potash silicate, which he 
 termed fluid silica. Von Helmont had prepared a similar 
 ctompound in 1640. The actual manufacture on a com- 
 mercial scale of these salts dates, however, from 1825 only, 
 a.nd the credit of originating their production belongs to 
 Von Fuchs. They differ from the compounds constituting 
 OTdinary and insoluble glass by containing no lime, baryta, 
 a.lumina, or other earthy base. They are made in several 
 ways. The purest sand obtainable is fused with carbonate 
 df potash, or carbonate of soda, or a mixture in the desired 
 proportions of these two carbonates, in the presence of a 
 lnttle powdered charcoal. The fused mass dissolves by long 
 continued boiling in water, and yields a heavy syrupy liquid 
 of strongly alkaline reaction. By evaporating this liquid to 
 dryness, and fusing the residue, the water-glass may be 
 Oibtained in a solid form, and then closely resembles 
 ordinary glass in appearance. Water-glass may also be 
 miade by heating flints red-hot, quenching them in water, 
 a:nd then digesting the powdered silica thus obtained with 
 sioda-lye or potash-lye under pressure. 
 
74 
 
 WATER-GLASS 
 
 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 proportions 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 stereochromy, 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 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 pig- 
 ments. 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 pro- 
 ducts were an alkaline carbonate, and lime silicate. But 
 subsequent investigation has proved that the change in 
 question is more complex, a considerable quantity of a 
 double and insoluble silicate of lime and alkali being pro- 
 
 
LIME-WATER 
 
 75 
 
 duced. 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 are 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, is slaked with distilled water. 
 The calcium hydrate formed is placed in a wide-mouth 
 stoppered bottle, and covered 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 
 
7 6 
 
 BARYTA-WATER 
 
 which will be removed when the watery liquid in the bottle 
 is decanted from the undissolved 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 6o° F., could not contain 
 more than 120 grains of calcium hydrate, corresponding to 
 90 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 pig- 
 ments owing to its alkaline or basic properties. The ease 
 with which the lime in lime-water unites with carbonic acid 
 forming carbonate of lime ( = calcium carbonate), and the 
 bearing of this action, and of other properties of caustic 
 lime upon the materials and processes of painting are 
 discussed in Chapters II. and XXIII. 
 
 Baryta-water may sometimes advantageously replace lime- 
 water in fresco-painting. It is a solution of hydrate of 
 baryta, barium hydrate, barium hydroxide, for these names 
 
BARYTA. WATER 
 
 77 
 
 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 Ba0. 2 H 2 + 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 that 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 2-9 
 parts by weight of Ba0 2 H 2 , in 100 measures, or 2,023 
 grains per gallon. It is thus very many times stronger than 
 a solution of calcium hydrate saturated at the same tempera- 
 ture. Baryta-water, as it is called, is a powerfully alkaline 
 liqiuid, 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 
 preciipitate is' formed. 
 
CHAPTER X 
 
 SOLVENTS AND DILUENTS 
 
 The liquids to which attention is directed in the present 
 chapter are, with very few exceptions, those which are 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 wnich this liquid is applied in 
 the preparation of pigments, and as a solvent for gum, 
 honey, etc. Next to distilled water may be ranked rain- 
 water collected in the open country ; then the softer kinds 
 of water yielded by 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. 
 
 Before considering the individual solvents to which 
 attention is directed in the present chapter, a list of the 
 most important of those which have been obtained in a 
 pure state may be given. These liquids are arranged in the 
 following table according to their boiling-points, those which 
 boil at low temperatures being placed first : an asterisk 
 indicates that the liquid is miscible with water : 
 
 Name 
 
 Ether - 
 
 Carbon bisulphide - 
 *Wood-spirit - 
 
 TABLE OF SOLVENTS 
 
 Boiling- Specific 
 
 point Gravity 
 
 35°C.= 95° F. - 702 
 
 46 =115° - 1-272 
 
 55 =131° - -8i 4 
 
 Formula 
 
 C 4 H ]0 O. 
 CS,. 
 
 ch 4 o. 
 
ETHER 
 
 79 
 
 TABLE OF SOLVENTS {continued) 
 
 Name 
 
 Boiling- 
 
 Specific 
 
 Formuk 
 
 
 point 
 
 Gravity 
 
 
 * Acetone 
 
 - 56° C 
 
 = 133° F. 
 
 - -802 - 
 
 C 8 H„0. 
 
 Chloroform 
 
 - 6i° 
 
 = 142° 
 
 • i'S25 - 
 
 CHC1 3 . 
 
 * Alcohol - 
 
 - 7§° 
 
 ^-= 1 72° 
 
 - 794 - 
 
 CoH 6 0. 
 
 Benzene 
 
 - 8i° 
 
 = 176° 
 
 - -89 - 
 
 C 6 H 6 . 
 
 Toluene 
 
 - in° 
 
 -=232° 
 
 - "873 - 
 
 C 7 H 8 . 
 
 Pinene - 
 
 - i6o° 
 
 = 320° 
 
 - -864 - 
 
 ^10 "16- 
 
 Sylvestrene 
 
 - 175° 
 
 -=347° 
 
 - -858 - 
 
 CioH 16 . 
 
 Dipentene 
 
 - i8i° 
 
 = 358° 
 
 - -846 - 
 
 Clo"l6- 
 
 The three liquids last named in the above table are 
 examples of what are now called terpenes. Mixtures of 
 these and other terpenes constitute what is generally known 
 as oil or spirit of turpentine. Terpenes are very general 
 and very abundant constituents of the volatile, ethereal or 
 essential oils extracted from plants. Besides the compounds 
 included in our list and certain volatile oils, we shall have 
 to consider some of the liquid and more volatile constituents 
 of natural petroleum and of artificial paraffin oils. The 
 fixed or fatty oils, which are constantly used in painting as 
 solvents, have been already treated of in Chapter V. 
 
 Ether, often called sulphuric ether, is a very mobile 
 liquid, having a penetrating odour, and of extreme volatility. 
 Its vapour is given off freely at ordinary temperatures, and 
 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 10 per cent. 
 Commercial ether always contains water and alcohol. The 
 latter, which it is seldom necessary to remove (for varnish- 
 making, etc.), can be got rid of only by repeatedly shaking 
 the crude ether with water, whereby much ether also 
 
8o 
 
 ACETONE 
 
 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- 
 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. 
 
 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 proportions, 
 but not with fixed oils. When free from water it may be 
 used as a solvent for some resins, and for removing dis- 
 coloured varnish from oil-paintings. Methylated spirit is 
 spirit of wine, to which some crude w r ood-spirit has been 
 added. 
 
 Acetone also occurs in crude wood-naphtha. It has a 
 denetrating but agreeable odour. It is miscible with water, 
 alcohol, oils, etc., and dissolves many resins, camphor, fixed 
 
ALCOHOL 
 
 8 1 
 
 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 quicklime. 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. 
 
 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 contains 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 pre- 
 pared 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 quick- 
 lime, the strong spirit is poured upon these so as to some- 
 what more than cover them, and then the whole is left 
 over-night ; distillation from a water-bath is then com- 
 menced, when it will be found that a spirit comes over which 
 contains no more than one part of water in two hundred. Even 
 
 6 
 
S2 
 
 TOLUENE 
 
 this small proportion may be removed by redistilling the 
 alcohol from a very little metallic sodium. The last distil- 
 late, 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 
 1 per cent, of water, its specific gravity is distinctly higher, 
 namely, 797. 
 
 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 fractional 
 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 4 H 4 S), to which the 
 offensive odour of ordinary benzene is partly due. Thio- 
 phene 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 purchased. 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 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 
 
TERPENES 
 
 83 
 
 of a sulphur compound (thiotolene), which is more difficult 
 to remove from the liquid than the thiophene from benzene. 
 
 Pinene, Sylvestrene, and Dipentefie, 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 100 parts, 
 expressed by the empirical formula C 10 H 16 . 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 full consideration of its several con- 
 stituents. 
 
 Turpentine, 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 in which oxygen is present, with 
 one or more liquid hydrocarbons which contain (as the 
 name imports) nothing but carbon and hydrogen, and there- 
 fore no oxygen. These hydrocarbons are called in chemical 
 language terrenes, 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 fusion, is called rosin or colophony. It 
 need not be further considered, as it is of no value in paint- 
 ing, being friable and more or less strongly coloured. 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, themselves yield various 
 
 6—2 
 
8 4 
 
 TERPENES 
 
 terpenes when submitted to distillation, 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, or obtained by the 
 distillation with water of the flowers of lavender, 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 un- 
 ravelled. We need not here concern ourselves with those 
 minute differences in chemical and physical properties 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 spirits of turpentine 
 frequently must have noticed the production of a sticky 
 substance about the neck of the bottles 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 frequently opened, and not quite full. Besides these 
 observations another will have been made — different speci- 
 mens of spirits 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. 
 
TERPENES 
 
 S5 
 
 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 substances and of water, which 
 affect injuriously the ease of working and the stability of 
 the picture. Spirits of turpentine should disappear by 
 evaporation quickly and completely from the painting into 
 which it has been introduced. Now, if it be easily oxidisible, 
 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 very canvas itself, adding a sticky deposit to the 
 drying oils and hard resins which may have been used as 
 the painting medium. It is clear, from all the above con- 
 siderations, that the greatest care ought to be taken in 
 selecting, in the first instance, such a sort of spirits of 
 turpentine as will resist oxidation under ordinary conditions. 
 Even an inferior spirit may be used, with a minimum of 
 disadvantage, 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 
 corks. In this way the contents of a bottle may be used 
 up very soon after it has been opened. Another precaution 
 may be taken : A few small fragments of hard quicklime 
 may be placed in each bottle to absorb any moisture pro- 
 duced by oxidation, and also the acid bodies which are 
 formed at the same time. Even with the choicer samples 
 of spirits of turpentine, which pass much less easily into 
 resins, this use of quicklime is desirable ; but in this case 
 the employment of many small bottles is unnecessary, and 
 
86 
 
 TERPENES 
 
 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 sinking readily 
 to the bottom of the vessel. 
 
 Before giving details as to the sources and characteristics 
 of the best terpenes, it may be useful to mention that com- 
 mercial samples of spirits of turpentine may 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 corre- 
 spond 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 agitation break as quickly as at first, 
 may be accepted as of good quality. Another test for dis- 
 criminating between the samples 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 
 spirits of turpentine may now be noticed — namely, odour 
 and boiling-point. Some samples have a much more agree- 
 able scent than others ; the vapour of these seems to have 
 
TERPENES 
 
 87 
 
 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 181 °. 
 Samples having lower boiling-points evaporate more quickly 
 than those which enter into ebullition at higher temperatures; 
 each type will have its appropriate use in the process of 
 painting. 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. 
 
 A few of the more important turpentine oils and essential 
 oils containing terpenes may now be named : 
 
 Russian and Swedish oils, chiefly from Pinus sylvestris. 
 Austrian oil, partly from Pinus Laricio, partly from 
 
 P. Pumilio. 
 American oil, chiefly from Pinus australis and P. tceda. 
 French oil, from Pinus Pinaster. 
 German oil, from Pinus sylvestris, P. Cembra, P. Abies, 
 
 P. vulgaris, etc. 
 Strasburg oil, from Abies pedinata. 
 Juniper oil, from Juniper us communis. 
 Eucalyptus oil, from Eucalyptus globulus and other 
 
 species. 
 Orange oil, from Citrus Aurantium and its varieties. 
 Lemon oil, from Citrus medica, var. I.inionum. 
 Spike-lavender oil, from Lavandula spica. 
 
 The above-named turpentine oils and fragrant essences 
 are accompanied by various resins, camphor, and other 
 oxygenated bodies, from which they may be separated by 
 treatment with caustic potash, metallic sodium, and fractional 
 distillation. The oil of spike, however, yields a compara- 
 
TERPENES 
 
 tively small amount of terpene, although more than English 
 oil of lavender, which is distilled from the flowers of another 
 species of Lavandula, L. vera. Whether the liquid oxygen- 
 ated compounds present in eucalyptus oil and spike oil t.re 
 in themselves valuable as diluents and solvents has not been 
 ascertained, and these oils are, in fact, used for painting 
 purposes without any preliminary treatment save that of 
 redistillation. 
 
 From the above-named liquids a number of terpenes have 
 been isolated. Among the better known of these the 
 following may be mentioned. 
 
 i. Pinene, with a boiling-point of 160° C. It forms the 
 chief constituent of German and American oil of turpentine, 
 and occurs in considerable quantity in the volatile oils of 
 eucalyptus, rosemary, and juniper. It is an easily alterable 
 and resinifiable terpene, and should not be employed either 
 in thinning paints, or as an ingredient of varnishes. 
 
 2. Phellandrene. — Boiling-point 170°. 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 : whether it occurs in 
 all eucalyptus oils has not been ascertained. It is one 
 of the most alterable of all terpenes, and the oils containing 
 it should be avoided. 
 
 3. Limonene, — This terpene, like some others, occurs in 
 two forms or varieties, having opposite actions on polarized 
 light. It is sometimes called citrene. It boils at 175°. It 
 is best prepared from orange-peel oil, which yields over 
 80 per cent, of dextro-limonene when distilled from caustic 
 potash. It is rather slow in drying, but is less alterable 
 than pinene and phellandrene, though it resinifies after a 
 time. 
 
 4. Sylvestrene has a boiling-point which is variously given 
 
OIL OF SPIKE 
 
 as 1 73 to 178°. When pure it has the smell of bergainot, 
 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. 
 It is one of the most satisfactory of all the terpenes, being 
 stable and little prone to resinify. 
 
 5. Dipentefie, which boils at about 18 1° 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 lsevo-limonene together. It occurs in small 
 quantity in the oils distilled from Swedish and Russian 
 pine-wood tar — in other words in these turpentine oils. It 
 ranks with sylvestrene as a solvent and diluent, being very 
 slightly alterable in the presence of air. Its odour resembles 
 that of citron oil. 
 
 From the preceding descriptions it may be gathered that 
 of all the above terpenes sylvestrene, and the oils in which 
 it abounds, are at once accessible and excellent : dipentene 
 comes next, and then limonene, but the slow rate of evapora- 
 tion of the last-named limits its application in oil-paint- 
 ing. 
 
 A few more words may be added in reference to oil of 
 spike-lavender. The terpenes present in this agreeably- 
 smelling liquid sometimes amount to 4*0 per cent., part at 
 least of the remainder consisting of liquids in which oxygen 
 as well as carbon and hydrogen occur. It is a powerful 
 solvent for many resins, and forms a part of Gambier- 
 Parry's spirit-fresco medium. It should not be redistilled 
 from caustic potash, but from a few lumps of quicklime, 
 which have been in contact with it for twenty-four hours. 
 And 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 
 
go 
 
 CAMPHOR 
 
 volume of benzene or of petroleum spirit. To remove 
 traces of water from any of the less volatile liquids we have 
 been considering, without having recourse to distillation 
 from caustic potash, or from quicklime, the following simple 
 procedure may be adopted : A glass flask is three fourths 
 filled with the liquid, and then it is kept at a temperature of 
 no° to i2o° 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 con- 
 siderable over 120°, like the terpenes. 
 
 In connection 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 offensive 
 smell may be partly removed 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 10 H ](i O, and is obtained chiefly from Cinnamomum cam- 
 phora, a tree of 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 O, 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, 
 
PETROLEUM SPIRIT 
 
 9i 
 
 for it slowly escapes after the apparent drying-up of the 
 varnish, and thus causes a deterioration of the lustre and 
 continuity of the resinous film. 
 
 Petrolai7)i-spi*it. — When native petroleum and the similar 
 materials obtained in the distillation of bituminous shales, 
 etc., are submitted to fractional distillation, the more volatile 
 portions which come over first constitute the liquids variously 
 known as gazoline, benzoline, ligroine, petroleum-naphthn, 
 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, 
 o"6 to 0-7. 
 
 Lamp-oil, kerosene, photogen, or paraffin-oil, boils between 
 180° and 220°, and has a specific gravity of 078 to o'82. 
 
 Solar-oil, lubricating-oil, vaseline, and paraffin-wax, are 
 heavier products, with a range of specific gravity from C83 
 up to C94. 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 pre- 
 sence 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 and 
 very thin liquid for diluting oily vehicles and paints in the 
 
92 
 
 PETROLEUM SPIRIT 
 
 process of oil-painting, the variety of petroleum-spirit which 
 boils between 50 and 70 C. is the most suitable. It con- 
 tains hydrocarbons represented by the formula? C 6 H 12 and 
 C 6 H 14 . 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 ioo° C. 
 and 1 30°. These contain heptane (C 7 H K; ), octane (C 8 H 1S ), 
 heptylene (C 7 H 14 ), and octylene (C 8 H ]G ), and other hydro- 
 carbons. This mixture is less volatile than that just de- 
 scribed, 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 frac- 
 tions 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 
 asphaltum. 
 
 It should be remembered that the various petroleum 
 liquids just described do not resinify, nor do they leave any 
 permanent stain or mark upon paper which has been moist- 
 ened with them. 
 
CHAPTER XI 
 
 SICCATIVES OR DRYKRS 
 
 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 we 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 concerning 
 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 had been ground 
 
94 
 
 MANGANESE DRYERS 
 
 in oil. I have seen one of the results of this commingling of 
 sugar of lead with the medium or the paint in the pro- 
 duction 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 car- 
 bonic acid from the air and become lead carbonate, which, 
 in its turn, is changed into lead sulphide by the action 
 of sulphuretted hydrogen. This tendency of the lead com- 
 pounds to yield brown or black lead sulphide is, indeed, the 
 great drawback 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 pig- 
 ment 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 discolouration 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 compounds, of which the binoxide, the 
 
MANGANESE DRYERS 
 
 95 
 
 hydrated protoxide and sesquioxide, the borate, the oxalate, 
 and the linoleate are the most important. 
 
 Manganese binoxide, the black oxide, MnOo, is used in 
 the form of a powder obtained by grinding the mineral 
 pyrclusite. 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 men- 
 tioned 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 
 that 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 solu- 
 tion — 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 solution 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 paper. The borate of manganese 
 is then dried in a warm place, and finally in the water-oven. 
 
9 6 
 
 DRYERS 
 
 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. 
 
 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 zinc 
 or oxide of zinc, manganese compounds being also some- 
 times added. Another dryer in common use is white 
 vitriol or sulphate of zinc. This is used either in the 
 form of the hydrated salt, which contains 7 molecules of 
 water (ZnS0 4 , 7H 2 0), or less after ge?itle heating by which 
 some of the water is driven off. It is, however, less effective 
 and advantageous than the manganese compounds abov 
 recommended. Most of the other siccatives employed by 
 artists owe their efficacy to lead, or are resinous mixtures. 
 Such are Siccatif de Courtrai, Siccatif de Haarlem, and 
 terebene. 
 
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. Now 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, spirits 
 of turpentine being most frequently thus employed. In 
 order to avoid too elaborate a classification, it will be 
 
 7 
 
MASTIC VARNISH 
 
 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 spirits 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 mixture of resin and solvent. The spirits of 
 turpentine should be absolutely free from moisture, 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 ioo° C. if oil of turpentine be used, 
 but should not be allowed to rise beyond 8o° C. if absolute 
 alcohol or 96 per cent, alcohol (specific gravity "806) be sub- 
 stituted for the oil of turpentine. The following receipt gives 
 a varnish which contains nearly 25 per cent, of its weight of 
 mastic, but the proportion may easily be increased or 
 diminished : 
 
 14 ounces of mastic, 
 44 „ „ spirits of turpentine, 
 6 „ ,, powdered glass, or fine sand. 
 
MASTIC VARNISH 
 
 99 
 
 When the mastic has dissolved the varnish is allowed to 
 cool, and then poured off 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 contrived filtering 
 apparatus has been designed for the purpose of preventing 
 any escape of vapour during the process of filtration. 
 
 The varnish prepared according to this receipt is nearly 
 colourless, and leaves a brilliant glassy film when it evapor- 
 ates 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 brittle- 
 ness 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 produced 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, 
 therefore, 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 pigments which may lie immediately 
 below it : they also render the varnish more easy of applica- 
 tion. 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 tempera- 
 tures above 170 C. A very small proportion of ' manganese ' 
 linseed oil is, perhaps, the more effective and safer toughener 
 
 7—2 
 
COPAL VARNISH 
 
 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-oxidisable 
 solvents be substituted for any kind of essence of turpentine 
 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 turpentine 
 or other solvent be also perfectly dry. It has been recom- 
 mended 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 distilled : 
 mastic varnish thus prepared has less tendency to ' bloom ' 
 than the ordinary kind, but if pictures are varnished in 
 a perfectly dry atmosphere and kept therein till the surface 
 has hardened, the formation of bloom is minimized. 
 
 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 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 solution. The powdered 
 
COPAL VARNISH 
 
 copal, prepared as directed previously (by exposure to the 
 air, and heating), or first fused, or at least heated till it has 
 lost from i o to 20 per cent, of its weight, is kept in contact 
 with lour times its bulk of the solvent until it is nearly 
 dissolved. Three measures of dry oil of turpentine are 
 then added, and the mixture submitted to distillation from 
 a water-bath until three measures of the acetone or other 
 original solvent have been drawn over : an efficient con- 
 denser must be used. If it be desired to prepare a mixed 
 varnish (partly oil or fat varnish) 1 measure of ' manganese ' 
 oil, and two measures of oil of turpentine may be used in 
 lieu of the quantity of turpentine 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 unnecessary to furnish 
 further particulars in a work like the present. 
 
 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 
 
COPAL VARNISH 
 
 
 the required amount of ' manganese ' oil and draw off the 
 volatile solvent by distillation, thinning the resinous solution 
 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 fiat porcelain dish for seventy- 
 two hours, at a temperature (of 220 C.) which does not 
 cause discolouration, 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 
 undissolved though swollen, and will therefore be wasted. 
 The following process, in the main identical with one 
 recommended 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 preliminary partial solution of the hard resin in chloro- 
 form, 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 
 powdered glass or of sand ; enough chloroform to cover 
 the above substances ; 35 parts by weight of oil of turpen- 
 tine, and 10 parts by weight of 'manganese' oil. The 
 following is an outline only of the process. The 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 
 
COPAL VARNISH 
 
 i°3 
 
 then heated to 50 or 6o° 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 con- 
 denser slanted downwards to allow of the chloroform being 
 distilled over. This removal of the chloroform having 
 been effected at a temperature so low that very little turpen- 
 tine has come over, the remaining mixture in the retort is 
 heated once more with the condenser in an upright posi- 
 tion. 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 ' manganese ' oil 
 wanted should now be heated to ioo° C, and then the 
 copal mixture, when it has cooled to 70° C, added little by 
 little to it with constant stirring, the temperature of the oil 
 being maintained at 90° to ioo°. 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 appro- 
 priate 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 previous heated or even fused, whereby it has 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 
 
104 
 
 COPAL VARNISH 
 
 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 proportions 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 3 parts of litharge in fine powder, or |- 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 6o° 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 was 
 melted. Finally, the remainder of the oil of turpentine 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, 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 pre- 
 viously described process. 
 
 A good copal or amber varnish ought to leave a film (on 
 a sheet of glass) which combines the qualities of hardness 
 
MEDIUMS FOR OIL-PAINTING 
 
 10; 
 
 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 of the resin 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. 
 
 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, spirits of turpentine — and mixing them 
 together in small quantities as required. But considering 
 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 permanence 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 
 copal ; 
 
 i measure of poppy oil ; 
 
 2 measures of oil of turpentine or oil of spike. 
 
io6 
 
 PARAFFIN-COPAL MEDIUM 
 
 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 
 the one of the least resinifiable varieties obtainable. 
 
 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 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. 
 
 A good medium, consisting of copal oil-varnish and 
 poppy oil with a trace of white wax, is a favourite amongst 
 some artists, and may be recommended as perfectly safe. 
 
 For painting in oil on plaster, slate, or stone, a perfectly 
 sound and convenient medium is made by warming 1 2 
 ounces of non-resinifiable oil of turpentine 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 62° C). The mixture becomes 
 perfectly clear if it be thoroughly agitated and maintained 
 at a temperature of 8o° C. Then 20 measured ounces of 
 ' picture '-copal varnish, or 16 ounces of oil-copal varnish, 
 are slowly added, with constant shaking, in the same way. 
 The ' paraffin-copal ' medium thus obtained may be diluted 
 with oil of turpentine exactly to the same extent as recom- 
 mended by the late Mr. Gambicr-Parry, in the case of his 
 ' spirit-fiesco ' 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 MEDIUM 
 
 107 
 
 spirit-fresco, for it contains neither elemi-resin nor wax, the 
 two doubtful constituents of the latter preparation. 
 
 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 proportions, 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 fragments 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 8o° 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 convenient) 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 anc 
 Fugitive Pigments. Chapter XXII. — Selected and Restricte 
 Palettes. 
 
CHAPTER XIII 
 
 WHITE PIGMENTS. 
 
 Flake-White : White Lead — Ceruse — Blanc d' Argent— Blanc 
 de Plomb — Kremser Weiss. 
 
 White lead was known to the ancients. A face-powder or 
 cosmetic, found, in its original pottery-box of about B.C. 400, 
 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 the name of 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 compound 
 of lead carbonate and lead hydrate. Other processes, 
 generally yielding an inferior product containing more 
 carbonate and less hydrate, have been used. One of these 
 consists in passing a current of carbonic acid gas through 
 
FLAKE-WHITE 
 
 a solution of lead subacetate ; in another, 4 parts of litharge, 
 1 part of common salt, and 16 parts of water, are kept in 
 contact for some hours with constant agitation, 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 
 carbonate intimately associated with one molecule of lead 
 hydrate, and is represented by the formula 2PbC0 3 , PbH 2 2 . 
 This formula corresponds to about 70 per cent, of lead 
 carbonate, and 30 per cent, of lead hydrate. If the propor- 
 tion 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. 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 dis- 
 colouration of the product, are copper, bismuth, silver, 
 cadmium, antimony, 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. 
 
 The impurities and defects of white lead are (1) accidental, 
 (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 gray hue to the product. 
 
 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. 
 
WHITE LEAD 
 
 i'3 
 
 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 absorp- 
 tion tube. This operation, however, requires much manipu- 
 lative experience, and, unless accurately performed, may 
 lead to erroneous conclusions. 
 
 (2) Of the intentional adulterations of white lead the 
 following are the most usual : 
 
 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 
 
 8 
 
H4 
 
 WHITE LEAD 
 
 used in the case of the finer makes of this pigment. In 
 either case the sophistication is very readily recognised. 
 Pure flake-white, for example, loses 14! 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 4*8 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 solubility 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 1 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. Whitening 
 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 14! 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 sulphides 
 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 adulteration, it is true : and it 
 is perhaps wiser to rely upon the protection furnished by 
 
WHITE LEAD 
 
 "5 
 
 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 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 illustra- 
 tive of this point are referred to in Chapter XXIV. of the 
 present volume. This property of white lead seems to 
 depend upon the combination which takes place between a 
 part of the oil with which it is ground and a part of the 
 lead hydrate which it contains. A kind of lead-soap (lead 
 linoleate) is thus formed ; this compound imparts a degree 
 of toughness and elasticity to those films of oil paint into 
 which lead-white enters to any considerable extent. A very 
 pretty and instructive experiment proving the formation of 
 this lead-soap is made thus. On a sheet of glass a smear of 
 flake-white in oil is spread ; then a few drops of weak 
 sulphuric acid (10 per cent, of the real acid) are mixed 
 
 8—2 
 
n6 
 
 WHITE LEAD 
 
 thoroughly with it by means of a glass rod or glass spatula. 
 The whole may be easily incorporated into a cream-like 
 mixture, for the acid decomposes the lead-soap and destroys 
 the oily or hydrofuge character of the paint. No such 
 commixture of acid can be made with zinc white in oil or 
 baryta white in oil, for in these paints the oil has not been 
 saponified. 
 
 Flake-white becomes brown, grey or black when exposed 
 to the action of sulphuretted hydrogen, ammonium sulphide, 
 or any metallic sulphide soluble in water. This discoloura- 
 tion, which is due to the formation of lead sulphide, occurs 
 more readily in the presence of moisture : it is favoured by 
 darkness to such an extent that a piece of perforated card- 
 board laid upon a dry oil-painted surface of white lead will, 
 after a few weeks' exposure, give a white pattern on a buff 
 ground. 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 oxidised 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. This method is not 
 available in the case of drawings or water-colour paintings in 
 which flake white has blackened ; but even these may often 
 be successfully treated by exposure to moist ozone, or by 
 light touches of a solution of hydrogen peroxide. Old silver- 
 point drawings having the lights heightened with lead-white 
 may sometimes be thus restored to their pristine state. 
 
 The specific gravity of the best flake-white is 6 - 6 ; ioo 
 parts by weight of it require from u to 13 parts of 
 linseed oil in order to form an oil-paint of suitable consis- 
 
PATTINSON'S WHITE 
 
 U7 
 
 tence. 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 ultra- 
 marine. Burnt or roasted white lead is sometimes used as a 
 pigment. 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 pre- 
 pared 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 lately 
 introduced which is likely to prove a formidable 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 grinding with small quantities of zinc white and barium 
 sulphate, and acquires thereby a considerable increase of 
 density and opacity. 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 over the more common 
 paint. It may be mixed with other permanent pigments 
 without injuring them. 
 
 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 pro- 
 nounced as to the eligibility of several other white com- 
 
n8 
 
 ZINC WHITE 
 
 pounds of lead, such as the sulphate, the antimonite, the 
 antimoniate, 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 pig- 
 ment, both alone and in admixture, the best flake-white, 
 with all its defects, presents distinct advantages over pure 
 lead carbonate free from lead hydrate. 
 
 Zinc-white : Chinese-white — Blanc de Zinc — Zinkzveiss. 
 
 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 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 submitting this to 
 powerful mechanical compression when red-hot, an excellent 
 
ZINC SULPHIDE 
 
 119 
 
 pigment having a dense body is obtained. Zinc-white pre- 
 pared 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 employed. 
 In spite of its unquestionable merits, zinc-white in oil can- 
 not be recommended as ti complete substitute for flake-white. 
 When used freely, it often shows a tendency to crack and 
 scale, besides becoming with age more translucent, 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 ground for silver-point or pencil 
 drawings. There is a peculiar ' tooth ' in the zinc-white 
 which freely brings off the silver 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 completely 
 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 pro- 
 bably contains barium sulphate; if effervescence 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' 
 
120 BARYTA WHITE 
 
 pigment dangerous, for there are several other colours upon 
 which it would exert a deleterious action. It has very con- 
 siderable body. 
 
 Ba ryta-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-pre- 
 pared barium sulphate. To make this, a cold solution oi 
 barium chloride of specific gravity 1*19 is prepared, and to it 
 is gradually added in the cold, and until no further precipitate 
 is formed, dilute sulphuric acid of 1*245 specific gravity. 
 The barium sulphate is 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 1, presents the ad- 
 vantage of being very much less affected by sulphuretted 
 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 insolubility in hydro- 
 chloric 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.. 
 
MINOR WHITE PIGMENTS 121 
 
 Amongst other white pigments which we need not de- 
 scribe are antimonious oxide, antimonious oxychloride, lead 
 sulphite, lead tungstate, lead antimonite, and lead antimoni- 
 ate. Not only are these compounds difficult to prepare in 
 a satisfactory condition of purity and whiteness, but they are 
 liable to turn yellow or dull in impure air. 
 
 It should be stated here that the tests described in the 
 present chapter, and in all the other chapters on pigments, 
 can be tried 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 jaune — 
 Gelben Ocker. 
 
 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 consti- 
 tuents. In fact, yellow ochre represents not less than three 
 mineral species, and it occurs associated with many im- 
 purities, the latter consisting mainly of silica, of clay, of 
 rocky debris, with traces of gypsum, of iron or copper pyrites, 
 and of humus or peaty acids. The three fundamental 
 minerals, in order of frequency, which may be traced in 
 various yellow ochres, are these : 
 
YELLOW OCHRE 
 
 123 
 
 
 Brown haematite, or limonite, consisting of two molecules 
 of ferric oxide combined with three molecules of water, and 
 represented by the formula 2Fe^0 3 , 3H 2 0. 
 
 Yellow haematite, or xa?ithosiderite, consisting of one 
 molecule of ferric oxide combined with one molecule of 
 water, and represented by the formula Feo0 3 , H 2 0. 
 
 Bog iron ore, or lymniie, consisting of one molecule of 
 ferric oxide and three molecules of water, and represented 
 by the formula Fe^Oy, 3H 2 0. 
 
 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. 
 
 An analysis of a fine sample of yellow ochre, from the pit 
 on Shotover Hill near Oxford, gave the following percent- 
 ages : 
 
 Hygroscopic moisture ... ... ... 7'i 
 
 Combined water ... ... ... ... 9"o 
 
 Ferric oxide .. . ... ... ... ... i3'2 
 
 Alumina ... ... ... ... ... 6 "3 
 
 Silica 61-5 
 
 Calcium sulphate ... ... ... ... 1*4 
 
 Undetermined ... ... ... ... i'5 
 
 The varying hues of yellow ochres depend mainly upon 
 two differences of composition. One of these is the amount 
 of white clay or of silica 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 
 
124 
 
 YELLOW OCHRE 
 
 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. Quite recently excel- 
 lent ochres have been obtained from the district of Uubbo 
 in New South Wales. Some of the English ochres (from 
 Oxfordshire, Derbyshire, etc.) are of fine quality. 
 
 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. Immedi- 
 ately 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, 
 slightly darker and 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 constitutional water from the ferric hydrate, and in part 
 to increased translucency. 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 
 
YELLOW OCHRE 
 
 125 
 
 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 con- 
 sidered. With reference to the darkening or embrowning 
 of yellow ochre in oil, this change is in part due to the 
 change of the oil, of which this paint usually contains as 
 much as 43 per cent., and in part to an increase in the 
 translucency of the mixed paint. 
 
 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 turmeric, or of certain other 
 fugitive or semi-permanent yellows of organic origin. The 
 majority of such additions may be detected by pouring a 
 little liquor ammonia; 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. An artificial yellow ochre is made by acting 
 
126 
 
 CADMIUM YELLOW 
 
 upon solutions of iron salts with metallic zinc, and thoroughly 
 washing the precipitate obtained. 
 
 Brown ochre is an approximately pure limonite : raw 
 sienna is very nearly related to it (see further 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 cyprusite a peculiarly bright lemon- 
 coloured earth has been imported from Cyprus as a pig- 
 ment : it consists essentially of a hydrated ferric sulphate : 
 it is not likely to prove a safe pigment for artistic use. 
 
 Cadmium Yellow: Orie?it Yellow — Aurora Yelloiv — Orange 
 Cadmium — Sulphide of Cadmium — -Jaime Brillant—Jaune 
 de Cadmium — Cadmium Gelb. 
 
 The metal cadmium, which is nearly related to zinc both 
 chemically and physically, was discovered by Stromeyer in 
 the year 181 7. 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 commonly 
 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 
 
CADMIUM YELLOW 
 
 127 
 
 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. 
 The presence of a little zinc is immaterial ; but iron, lead, 
 bismuth, and any metal giving a coloured sulphide, even in 
 traces, are seriously detrimental to the beauty of the pro- 
 duct. 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 free sulphur 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 satis- 
 factory degree of permanence, and has no action on white 
 lead when both pigments are ground together in oil. But 
 a curious change is noticeable when the orange-red variety 
 of this pigment, ground in oil, is kept some time in the 
 ordinary metallic collapsible tubes. The interior surface of 
 the tube becomes 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 
 
128 
 
 CADMIUM YELLOW 
 
 kept for years, had not darkened the lead compound any- 
 where, 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 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 absolutely incom- 
 patible. Chrome yellow and true naples yellow are also 
 darkened by admixture with cadmium yellow, at least after 
 a time. 
 
 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. 
 Several years ago 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, 
 and the temperature at which the precipitation of the pig- 
 ment 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 the orange-red varieties 
 exhibited a curious phenomenon of alteration. The loose 
 
CADMIUM YELLOW 
 
 129 
 
 friable lumps into which the powder had aggregated were 
 distinctly paler on the outside than 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 ex- 
 posed to light ; but in some of the specimens orange specks 
 were observed, resembling in hue what is usually called 
 ' middle ' cadmium. From the above observations it would 
 seem that there is a tendency in differently tinted 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 from oxidation and hydration, 
 for the bleached specimens gave indications of containing 
 some white cadmium hydrate, when heated giving off a little 
 water, and becoming 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 pale cadmium is notorious. In oils 
 this cadmium, like the others, is practically permanent. I 
 regard the passage of the deep cadmium yellow when in 
 powder into the normal or middle variety as dependent 
 chiefly, if not entirely, upon a molecular change. More- 
 over, the pale cadmiums are rarely found free from admix- 
 ture, and their alterability may be in part owing to the 
 foreign ingredients they contain. It is perhaps safer to 
 employ an ivory palette knife rather than one of steel in 
 manipulating the cadmium pigments. 
 
 9 
 
13° 
 
 CADMIUM YELLOW 
 
 Cadmium yellows are sometimes adulterated with Indian 
 yellow, baryta and strontia chromates, and 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, 
 hut it may be better detected by the solvent action upon it 
 of carbon bisulphide. Baryta white may be detected by its 
 insolubility in hot strong hydrochloric acid, in which cadmium 
 sulphide dissolves. 
 
 Cadmium red and cadmium orange are slightly translucent 
 when compared with the paler and yellower varieties 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 cadmiums 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 considerably raised in the presence of air, some of the 
 sulphur in the compound burns, and the residual mass pre- 
 sents a dull brown colour. ' Manganese oil ' accelerates the 
 drying of the cadmium colours, which is sometimes incon- 
 veniently slow. 
 
 As the metal cadmium can be purchased for five shillings 
 a pound, and as this amount will yield twenty ounces of the 
 
A UREOLIN 
 
 131 
 
 dry pigment, cadmium yellow should be obtainable at a 
 moderate price. 
 
 Aureolin : Cobalt Yellow — -Jaune de Cobalt — Kobaltgelb. 
 
 Origin and Composition. — This remarkable artificial yellow 
 pigment was discovered by Fischer. It is a compound 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 K ( .Co 2 (NO Q ) ] . ; , 
 3H 2 0. 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 strong solution of a cobaltous salt, acidified with 
 acetic acid, with a concentrated 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 potas- 
 sium carbonate is added. It is not much affected by caustic 
 potash solution or by hydrochloric or nitric acid. It is very 
 slowly attacked and blackened by solution of sulphuretted 
 hydrogen, but is at once destroyed by ammonium sulphide. 
 It 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 it dries 
 with great difficulty, and becomes very dirty if exposed to 
 the air during the progress of desiccation. Moreover, as 
 ordinarily ground in oil, it requires a very large proportion of 
 the latter medium — nearly 2 parts (by weight) for 1 part of 
 aureolin powder. These defects may be easily remedied by 
 heating 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, prepared by means of borate of 
 
 9-2 
 
132 
 
 A UREOLIN 
 
 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, though pre- 
 sent to the extent of 67 per cent., does not suffice to protect 
 the particles of pigment from the solvent action of moisture. 
 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 
 
 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 somewhat 
 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 adul- 
 terated aureolins may generally be 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. 
 
LEMON YELLOW 
 
 *33 
 
 Lemon Yellow: Baryta Yellow — Barium Chromate 
 
 Yellow Ultramarine — Permanent Yellow. 
 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 ioo° C. A still 
 better plan is to take equivalent proportions — namely, 25? 
 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 gradu- 
 ally sufficient pure water to convert the mixture into a thin 
 paste. The paste is then heated to ioo° 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 not 
 blackened like the lead chromes by sulphuretted hydrogen, 
 but it has a tendency 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, generally 
 
 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 
 
134 
 
 GAMBOGE 
 
 found to sink into the paper and to partially disappear. 
 The most common adulteration of lemon yellow is with 
 pale chrome ; of course, sulphuretted hydrogen detects this 
 falsification by darkening 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. 
 
 Gamboge : Gomme-gutte. 
 
 Origin. — -This gum-resin is produced by several species 
 of garcinia. Siam gamboge comes from G. Ha?iburyi 
 (Hook, f.) ; Ceylon gamboge from G. Morella (Desv.). 
 There are other species from which the same product is 
 obtained in various parts of India, as G. Cambogia (Desrouss.) 
 and G. elliptica. The fine, deep-coloured gamboge, pro- 
 duced 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. It 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 
 
GAMBOGE 
 
 135 
 
 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 com- 
 pounds 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 heat. 
 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. 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, amber hue ; it has some claims to the con- 
 sideration of artists. To secure its permanence, admixture 
 with oil alone does not, however, suffice ; a resin such as 
 copal, 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, therefore, 
 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 
 
i3 6 
 
 INDIAN YELLOW 
 
 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 advan- 
 tageously 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—Jawie Indien — 
 Indisch-gelb . 
 
 This remarkable pigment is obtained at Monghyr, a town 
 in Bengal, from the urine of cows which have been 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, 187 per cent, water, and 787 
 per cent, euxanthic anhydride ; but this substance is always 
 associated, even in the most carefully purified samples of 
 prepared Indian yellow, with various impurities both mineral 
 and organic. The pure magnesium euxanthate is repre- 
 sented by the formula C 19 H 1(3 Mg0 11 ,5H 2 0. 
 
 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, is 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 
 
INDIAN YELLOW 
 
 *37 
 
 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 unimpaired when exposed to 
 diffused daylight ; sunlight very slowly bleaches it, the hue 
 it acquires being somewhat brownish. The rate of altera- 
 tion and of reduction in force caused by sunlight may be 
 approximately represented by these figures : 
 
 Original intensity 
 
 10 
 
 After 2 years ... 
 
 9 
 
 After 5 years .. 
 
 7 
 
 After 7 years ... 
 
 6 
 
 After 10 years 
 
 • • 5 
 
 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, how- 
 ever, 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 constiiuent of Indian yellow, 
 
138 
 
 NAPLES 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 euxanthic 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-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 pigment is to be thoroughly washed, and 
 then pressed, dried, and ground. 
 
 Mars Yellow : Mars Orange — Artificial Ochre— Jatme 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 (or 
 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 iron 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 compound (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, including 
 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. 
 
NAPLES YELLOW 
 
 139 
 
 The Mars colours are permanent when carefully prepared, 
 and thoroughly purified from soluhle salts. They seem 
 sometimes to have a slightly injurious effect upon a few of 
 the best semi-permanent pigments of organic 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 : Jaune de Naples — Jaune d'A/itwwifie — 
 Neapel-gelb — Giallo di Nafioli* 
 
 Under this name three different substances are included. 
 The pigment generally sold in England as ' Naples yellow ' 
 is an excellent imitation made by mixing cadmium yellow or 
 deep cadmium with a white, preferably a zinc white. But a 
 true Naples yellow, which is a basic lead antimoniate, is 
 still procurable from some artists' colourmen.* This pre- 
 paration is sometimes made by heating together for two 
 hours a mixture of 1 part tartar emetic, 2 parts nitrate of 
 lead, and 4 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 Baby- 
 lonian bricks at least 2,500 years old. Persian pottery as 
 
 * Roberson ; Edouard, of Paris ; Schonfeld, 
 others. 
 
 of Diisseldorf ; and 
 
140 
 
 NAPLES YELLOW 
 
 early as the thirteenth century of our era is occasionally 
 decorated with antimonial yellow. 
 
 In oil the genuine and the imitative Naples yellows 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 conditions, 
 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 experimental 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 red 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 
 
YELLOW LAKE 
 
 141 
 
 be assigned ; there is, moreover, no reason why it should be 
 associated with 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 recommended to 
 artists. 
 
 Yellow Lake : Brown Pink — Citrine Lake — Yellow 
 Madder — Italian Pink — Quercitron Lake. 
 
 Origin. — The sources of yellow lake are numerous, but 
 the best kind is obtained from quercitron bark from Querciis 
 tinctoria, Qu. nigra, and Qu. citri?ia, 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 precipitated 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 infeciorius, 
 R. oleoides, R. saxa tills, 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 conti- 
 nental yellow lakes, are made from the above-named berry. 
 
 Italian pink, Dutch pink, and deep yellow madder are 
 names usually given to the richer yellow lakes of quercitron, 
 
142 
 
 BROWN PINK 
 
 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 water-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 one year to sunlight, 
 apply to the colours as ground in oil, and as mixed with 
 flake-white in tint : 
 
 Name 
 
 Original 
 Colour 
 
 Acquired Original 
 Colour Jntettsity =10 
 
 Laque Robert — 
 
 
 
 
 hell-gelb - - 
 
 Lemon yellow 
 
 Pale straw - - - 
 
 2 ""i 
 
 
 Laque Robert— 
 
 
 
 
 
 dunkel-gelb - 
 
 Deep lemon - 
 
 Stone - - - - - 
 
 4 
 
 .o 
 
 Laque brun- 
 
 
 
 
 3 
 
 jaune - - - 
 
 Salmon 
 
 Pale rose - - - - 
 
 7 
 
 ]3 
 
 Laque brun- 
 
 
 
 
 
 fonce - - - 
 
 Yellowish-grey - 
 
 Smoke-grey - 
 
 8 
 
 g 
 
 Pale yellow 
 
 
 
 
 & 
 
 madder - - 
 
 - Pale orange - - 
 
 Pale buff - - - - 
 
 7 
 
 ft; 
 
 Deep yellow 
 
 
 
 
 
 madder - - 
 
 - Greyish salmon - 
 
 Pale greyish pink 
 
 6 , 
 
 
 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 suffering almost complete 
 loss of colour both in water and in oil. And it further 
 
CHROME YELLOW 
 
 14.: 
 
 presents the awkward effect of 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 comparatively little alteration. Had a portion of 
 the original cake-colour employed been preserved for ex- 
 amination it might have been possible to have discovered 
 the cause of this anomalous behaviour of the particular 
 specimen in question. 
 
 Chrome Yellow : Chrome — Chromate of Lean — -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. Orange 
 chrome and chrome red are prepared from a mixture of lead 
 acetate (6| 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 PbCr0 4 , PbO, or 
 Pb L ,Cr0 5 . 
 
 The chromates of lead are peculiarly liable to change, 
 
144 
 
 VANADIUM YELLOW 
 
 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 presence 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. 
 
 As the artist had better avoid the employment of these 
 pigments, further details concerning their characteristics 
 need not be given. 
 
 Vanadium Yfllow. 
 
 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. 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. 
 
KING'S YELLOW 
 
 145 
 
 King's Yellow : Orpiment— Jaune Royal — Konigsgelb. 
 
 The yellow arsenic sulphide, 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 king's yellow, but which now have almost entirely dis- 
 appeared. 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 king's yellow have escaped 
 alteration. Under any circumstances the inadmissibility of 
 king's yellow to the palette of the artist is obvious : more- 
 over it cannot be safely mixed with any pigment containing 
 lead or copper. 
 
CHAPTER XV 
 
 RED PIGMENTS 
 
 Vermilion : Cinnabar — Vermilion — Zinnober. 
 
 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 ioo of im- 
 purities, but consists in ioo parts of very nearly 14 parts of 
 sulphur by weight, united with 86 of mercury, or 1 atom of 
 each element. The density of native vermilion is very 
 nearly 9. Vermilion was formerly known as vermiculus, 
 cinnabaris, cenobrium, 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, 
 and 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 Indian 
 origin, and was used sometimes to designate dragon's blood, 
 a red resin. Theophrastus informs us that two kinds of 
 cinnabar were known to the Greeks. One of these was 
 

 VERMILION 
 
 147 
 
 undoubtedly real cinnabar (chiefly from Spain), the other 
 was red lead. Pliny's 'cinnabar' or 'minium' was true 
 vermilion, so was the 'minium' of Vitruvius. Theophilus 
 calls it 'cenobrium.' 
 
 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 substance, 
 ' .'Ethiop's mineral.' The red substance may be changed 
 into the black, and vice versa, and this without any loss or 
 gain, or any alteration of chemical composition, the change 
 being a physical or molecular one merely. The black sub- 
 stance is amorphous, the red crystalline. 
 
 The pigment vermilion may be made by simply grinding 
 selected pieces of native cinnabar, or it may be obtained arti- 
 ficially 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 ivet 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 sulphide 
 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 sulphur, and is of 
 inferior colour. The selected portions are 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 accom- 
 panied by a violent evolution of light and heat) is complete, 
 
148 
 
 VERMILION 
 
 the fused blackish mass is poured out, broken into frag- 
 ments, heated until excess of sulphur has been driven off, 
 and then sublimed in the way already described. Some 
 makers add to the crude sulphide, previous to sublimation, 
 i percent, 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, ioo 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 pentasulphide of potassium 
 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 vermilion is produced when a mixture of 
 mercurous chloride (calomel) and sulphate of zinc is heated 
 to 45° — 50 C. with an excess of a solution of sodium thio- 
 sulphate. 
 
 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 porcelain ; no ap- 
 preciable residue will be found, unless red-lead, red iron 
 
VERMILION 
 
 149 
 
 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 anti- 
 monious chloride with sodium thiosulphate. 
 
 Vermilion prepared from the mineral or native cinnabar 
 is probably less liable to change than the artificial products, 
 whether obtained by the dry way or the moist way ; but 
 ' moist way ' vermilions are certainly the most alterable. 
 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 being equal, 
 orange-vermilion is inferior in permanence 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. 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 altera- 
 tion. 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. 
 
ISO 
 
 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 a different 
 sample of vermilion having been employed, but sometimes 
 to a change in the technique, as a change in the style or 
 handiwork is often associated with the difference above 
 described. In oil-painting, there are no permanent pig- 
 ments with which vermilion may not be 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 comparatively 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 Gheeraedts 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 fine- 
 ness in which the pigment occurs. The coarsest grain cor- 
 responds with a crimson hue, and then we have every variety 
 of colour ranging from scarlet to reddish orange or orange. 
 
MADDER PIGMENTS 
 
 I5 1 
 
 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 pro- 
 duced. For, as the early writer Eraclius states : ' If you 
 mix white with vermiculus, carmine is made ' — that is, the 
 hue of the mixture becomes more rosy, and therefore further 
 removed from orange. 
 
 Madder : Pink Madder — Rose Madder — Madder Carmine 
 — Madder Red — Rubens' Madder — Madder Purple — 
 Madder Lake — Madder Brown — Carmin de Gara?ice — ■ 
 Laque de Garance — Krapp-lack. 
 
 Some authorities assert that madder was used in dyeing 
 long before its employment in painting. But if the ancient 
 Greeks and Romans were unacquainted with a red pigment 
 derived from madder, yet there are good reasons for believ- 
 ing that such substances were known in Europe as early as 
 the thirteenth century. Even in England, such a pigment 
 is almost certainly referred 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 vermilion, and it is made from varancia.' ' Var- 
 ancia ' is clearly garance — that is, madder — the same 
 material being named ' warancia ' and ' waranz ' in a British 
 Museum manuscript (Sloane, No. 416) which contains re- 
 cipes 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.' 
 is, however, difficult, if not impossible, to ascertain the pre- 
 
15* 
 
 MADDER 
 
 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 the use of madder paints 
 to an earlier time than the close of the fifteenth century. 
 Eraclius does not mention madder, nor does Cennini, who 
 lived at a much later time. Mr. R. Hendrie, in his notes 
 to ' Theophilus,' speaks of an English manuscript of the 
 fourteenth century in which directions are given for extract- 
 ing the colouring matter of ' madyr.' From these directions 
 we are, perhaps, 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 Rubiacese ; it is the Rubia 
 tinctorum 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, Rubia cordifolia (Linn.) and 
 R. sikkimensis (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 artificial 
 means from the anthracene of coal-tar of its two chief 
 colouring matters, alizarin and purpurin, has almost entirely 
 extinguished the cultivation of the madder-plant in Europe. 
 We shall have something to say presently concerning 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-contents of the soft 
 tissue of the root. The finest madder was grown in the 
 ' Palud,' a chalky valley near Vaucluse. 
 
 The colouring matters obtained from madder exist in the 
 
MADDER 
 
 153 
 
 plant in the form of glucosides. These glucosides are re- 
 solved 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 
 principles. Of such colouring principles the glucosides in 
 madder yield at least three, of which the most important are 
 these two : 
 
 1. Alizarin, C 14 H 8 4 . 
 
 2. Purpurin, C 14 H s 5 . 
 
 Both alizarin and purpurin are now manufactured arti- 
 ficially from anthracene. This compound, which occurs in 
 coal-tar, is a crystalline fluorescent hydrocarbon, C 14 H 10 . 
 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 14 H s 5 ) and purpuro- 
 xanthin (C 14 H 8 4 ). 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, 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 
 
*54 
 
 MADDER LAKES 
 
 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 
 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 solution 
 of i pound of pure alum in i gallon of water. The mix- 
 ture 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 solu- 
 tion ; 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 modifica- 
 tion 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 temperature of 45° partially 
 neutralized with a solution in water of about 8 ounces of 
 pure sodium carbonate. The liquor is now brought 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 produced by the preceding process. In order to 
 prepare a madder carmine in which there is little earthy base, 
 the following plan is frequently adopted : Some of the very 
 finest madder root is fermented in the usual way, dried, 
 ground, and treated with four times its weight of sulphuric 
 acid, diluted till it shows a strength of 55° Beaume. The 
 vessel in which the mixture is made is kept cold. After 
 
MADDER LAKES 
 
 155 
 
 three hours some water is added to the mass, and then the 
 whole is filtered through asbestos cloth. The filtered liquor is 
 allowed to drop into a large quantity of rain or distilled water ; 
 the madder carmine will separate and collect at the bottom of 
 the water. It is to be thrown on a filter, washed, and dried. 
 
 By the employment in various proportions of washed, 
 moist aluminum hydrate, and by choosing various qualities 
 of madder root, a number of hues and 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 association with more 
 or less alumina, as a base for receiving the various colour- 
 ing 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. 
 
 I select from a number of analyses of madder pigments 
 the two following as illustrative of some peculiarities in the 
 composition of these important preparations : 
 
 Rose Madder Madder Carmine 
 Water given off at 100° C. - - - i2 - o - 
 Water, combined, etc. - 28 - i 
 
 Colouring matter- - icro - 
 
 Alumina ------ ^g-g . 
 
 According to some authorities the finest rose madders 
 and madder carmines consist mainly of anthrapurpurin, 
 associated with a base of alumina. But my own experiments 
 with anthrapurpurin do not confirm this view. The follow- 
 ing is a brief account of my chief results. The three colour- 
 ing matters — anthrapurpurin, purpurin, and alizarin — were 
 
 13-0 
 15-0 
 
 22*6 
 
 49 "4 
 
1 5 6 
 
 MADDER LAKES 
 
 first prepared in a state of the greatest possible purity, the 
 two last-named substances having been obtained from 
 madder-root, the anthrapurpurin from anthracene. An alka- 
 line solution of each of these three colouring matters was 
 then made, ammonia being the solvent alkali in one set of 
 trials, and caustic potash being used in another series. No 
 more alkali was employed than was necessary to effect the 
 solution of the substances. The various coloured liquids 
 were then precipitated by means either of a solution of pure 
 potash alum, or by boiling them with pure gelatinous 
 aluminium hydrate, care being taken to use about the same 
 proportion of alumina to colouring matter in each set of 
 experiments. The lakes obtained were characterized by the 
 following hues : 
 
 Anthrapurpurin lake ; red, nearly pure. 
 Purpurin lake ; red, tending towards orange. 
 Alizarin lake ; crimson red. 
 
 I must confess that even my alizarin lake was not of so 
 pink or rosy a hue as that known in commerce as rose- 
 madder and madder-carmine, and which, when genuine, is 
 certainly made directly from preparations of the madder 
 root, and in which I have been unable to detect any colour- 
 ing matters besides alizarin, although small quantities of 
 fatty acids are occasionally present. The advantage of 
 using for artistic purposes those madder lakes which have 
 been prepared with alizarin is not confined to the beauty 
 and purity of the colours they furnish, for experiment 
 shows that these lakes are the least affected by light of 
 all the pigments derived from madder. The manufacture of 
 the above-named choice pigments for artists appears to be 
 the only reason which prevents the cultivation of the Rubia 
 tinctorum from being wholly extinguished through the ener- 
 getic competition of the artificial chemical product. 
 
ALIZARIN AND PURPURIN 
 
 157 
 
 From alizarin and from purpurin (either natural or arti- 
 ficial) madder 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 hy- 
 drate. 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 ; 
 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 bodies. The directions for 
 preparing pigments from the above-named bodies are prac- 
 tically identical with those already given in outline, but the 
 minute details of manipulation can be learned only in actual 
 practice. One peculiarity, however, distinguishing purpurin 
 from alizarin, may be here noticed. It will be found that, 
 while alizarin is practically insoluble in cold saturated alum- 
 water, and but slightly soluble in the same liquid even when 
 boiling, purpurin dissolves to a marked extent in this solvent. 
 From this purpurin solution, which possesses a crimson 
 colour and exhibits a fine orange red fluorescence, alkalies 
 throw down a pure red-coloured lake. The following pro- 
 cess gives a red madder of excellent 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 colour- 
 less ; then the residue on the filter is boiled with a 5 per cent, 
 solution of pure alum, filtered while boiling, and immediately 
 
•58 
 
 MADDER LAKES 
 
 neutralized with pure sodium carbonate solution (also boil- 
 ing) until red flocks appear. These are filtered off, and 
 constitute, when washed and dried, a fine pigment of a rich 
 red hue. By heating the mother-liquor to 8o°, 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 madder lake, having a 
 brownish red hue. 
 
 Although the madder colours are very much less affected 
 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 Figment 
 *Madder Carmine, 
 
 A 
 
 OH 
 
 Ititens 
 
 After l ) 
 
 olna 
 ity = 
 ear, 
 
 / 
 
 ■ 10 
 IO • 
 
 Change of Hue 
 Very slight. 
 
 Madder Red - 
 
 
 B 
 C 
 C 
 
 " i) I 
 
 - » 5 
 
 - » 7 
 
 - » i 
 
 ii 
 
 8 • 
 
 2 
 O 
 
 6 
 
 Much more purplish. 
 Less red, more blue. 
 
 Rose Madder - 
 
 „ >, B 
 
 „ „ B 
 
 ., B 
 
 Pink Madder - 
 
 - 
 
 - 
 
 - >, i 
 
 - >, 2 
 
 - » 5 
 
 - ,. 7 
 
 - ,, 2 
 
 ii 
 
 8 • 
 
 3 
 i 
 i 
 i 
 
 Slightly more purplish. 
 
 Smoke- grey. 
 Grey. 
 
 Purple Madder, 
 
 A 
 
 - 
 
 - ,, I 
 
 a 
 
 7 
 
 Duiler, less red, more blue 
 
 )> >> 
 
 C 
 
 - 
 
 - » 2 
 
 ii 
 
 6 
 
 More bluish. 
 
 11 11 
 
 11 11 
 
 D 
 C 
 
 . 
 
 - » 5 
 " » 7 
 
 " 
 
 7 
 
 2 
 
 
 Brown Madder, 
 
 E 
 A 
 
 - 
 
 - .. 7 
 
 - ,. i 
 
 J> 
 
 9 
 9 
 
 Somewhat puce 
 - Less red, more yellow. 
 
 ,, ,, 
 
 B 
 
 - 
 
 ■ )i 2 
 
 J> 
 
 i 
 
 - Grey. 
 
 11 i > 
 
 B 
 B 
 
 ■ 
 
 - » 5 
 
 - ,. 7 
 
 " 
 
 i 
 
 o 
 
 Grey. 
 
LIGHT RED 
 
 159 
 
 The letters A to E 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 two samples marked * are instances 
 of exceptional stability, and are of importance 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, which contain much water, 
 are generally more perishable than the concentrated madder 
 carmine ; the comparative trials having, of course, been 
 made with washes of the same depth of tint. 
 
 Light Red : Burnt Ochre — Rouge Anglais — Brun Rouge. 
 
 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 and dull brownish or orange red. More- 
 over, these hues depend in some measure upon the tempera- 
 ture 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 redness. 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 sus- 
 pended in a current of air into a 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. 
 
i6o 
 
 VENETIAN RED 
 
 Light red boiled with hydrochloric acid will, if genuine, 
 yield a solution, which after filtration will give no precipitate, 
 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 pre- 
 pared iron reds. 
 
 Venetian Red : Rouge — Crocus — Colcothar — Caput Mor- 
 tuuvi Vitrioli. 
 
 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 permanent 
 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. 
 
INDIAN RED 
 
 161 
 
 Avery fine native red ochre comes from the Banat, Hungary. 
 It is represented by the formula 2Fe.>0.>, H 2 0, and goes 
 under the mineralogical name of turgite. Its hue is that of 
 a fine Venetian red, but 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. 
 
 Indian red is a variety of red ochre, or red haematite, con- 
 taining 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 product, 
 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. 
 
 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. 
 
 1 1 
 
l62 
 
 RED OCHRE 
 
 Greys made with light red or Venetian red show similar 
 alterations of colour. Colcothar, or jewellers' rouge, the re:d 
 oxide of iron obtained as a residue when green vitriol (ferrouis 
 sulphate) is calcined, has sometimes been called Indian re(d, 
 and substituted for the native oxide. Those portions of thie 
 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 potassium chlorate, drying, and then 
 calcining the mass once more. It generally contains bassic 
 ferric sulphate, and then should be looked upon witth 
 suspicion, for it may seriously damage the indigo and othner 
 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 chloritde 
 solution, the genuineness of the pigment will be proved Iby 
 the absence of any white precipitate of barium sulphate. 
 
 Red Ochre : Red Hcematite — Red Iron Ore — Scarlet Ochire 
 — Red Chalk — Ruddle — Bole — ■ Sinoper — Sinopis — Rlu- 
 brica — Miltos — Terra Rosa. 
 
 The pigments above-named are native ferric oxide ((or 
 iron peroxide) associated with variable proportions of minerral 
 impurities such as clay, chalk, and silica. They differ froum 
 the yellow and brown ochres described on page 122, by mot 
 containing combined water, in other words, the iron to 
 which they owe their colour is ferric oxide, not ferric hydratte. 
 They occur in very many localities accompanying or evren 
 constituting some of the most important iron ores. Theeir 
 colour varies with their physical state, and with their puritxy ; 
 some are iron grey, or even black, until they are fimeely 
 ground, when they assume a cherry-red hue. Cappad<occia 
 
RED OCHRE 
 
 163 
 
 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 
 tthus prepared the pigment to which the name ' light red ' is 
 mow assigned. 
 
 An unusually bright red variety of haematite from Cumber- 
 Hand gave me on analysis, in 100 parts, ferric oxide, 947 ; 
 alumina, 2*0; silica, 2*2, and moisture, i*i. But some 
 almost equally rich red ochres contain much less iron oxide, 
 ai ' 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 
 rreddish brown or yellow brown hue often consist of mixtures 
 cof haematite and yellow ochre. A very fine red ochre from 
 TTuscany, the Banat, Hungary, and from the Urals, contains 
 aibout 5 per cent, of water, and is considered to belong to a 
 ddistinct mineral species called turgite. 
 
 When red chalk (from Hunstanton. Norfolk) is calcined 
 ait a high temperature it loses its red colour, and becomes of 
 ai dull olive green hue, a change due in this case to the 
 production of calcium ferrite, a compound of lime and ferric 
 ojxide. 
 
 The terra rosa of Italy owes its pinkish red hue to ferric 
 ODxide, but it is probably often, if not always, an artificial 
 pDroduct. 
 
 All the pigments described under the title ' red ochre ' 
 aire permanent, and without action on other pigments. 
 
 For the substitution of artificially prepared ferric oxide, or 
 ccolcothar, for red ochre, and for the method of detecting it, 
 reeference should be made to page 162, under ' Indian 
 reed.' 
 
164 
 
 INDIAN LAKE 
 
 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 frondosa, Ficus religiosa, 
 and i^ bengalensis, Schleichera trijuga, Shorea robusta, and 
 Zizyphus jujuba. The lac, though a secretion 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 sub- 
 stance, 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 spirits 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 
 painters 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.' 
 
COCHINEAL LAKES 
 
 165 
 
 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 much 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 
 when used as a dye for animal fibres belongs also to all the 
 lakes prepared from this substance : anyhow kermes pigments 
 are not met with in commerce at the present time. 
 
 Carmine and the Cochineal Lakes : Carmin — Laque 
 Cramoisie, or Crimson Lake — Purple Lake, etc. 
 
 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 ex- 
 tracted 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 employed 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 other impurities ; the finest varieties, how- 
 
1 66 
 
 COCHINEAL LAKES 
 
 ever, dissolve perfectly in strong liquor ammonise. The 
 liquor, which has deposited the carmine, gives up the re- 
 mainder of its colouring-matter to freshly-precipitated alu- 
 minium hydrates, or, after having been rendered alkaline by 
 potassium carbonate, to a solution of alum. Lakes are thus 
 formed. Lakes are also made by directly precipitating 
 cochineal extract with solutions of potassium carbonate 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 consequently weaker. Scarlet lake is 
 a mere mixture of crimson lake and vermilion. 
 
 Beautiful and rich as are the colours prepared from cochi- 
 neal, not one of them should ever find a place upon the 
 palette of the artist. They all become brownish, and ulti- 
 mately 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 1 2. 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 obliteration of every trace of 
 the original crimson from a deep wash of this pigment. A.11 
 the cochineal pigments become somewhat brownish during 
 the course of fading, but ultimately, when all the red has 
 disappeared, either 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 
 
BURNT C A AMINE 
 
 167 
 
 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 carmine and 
 indigo carmine are perfectly distinct examples, derived from 
 madder and indigo respectively. 
 
 It is not necessary to say more about the various cochi- 
 neal pigments, nor to point out their many falsifications, 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 pigment 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. Experiments in the latter medium 
 gave, after exposure to sunlight, the following residual inten- 
 sities out of ten : 
 
 Moist, after two years ... ... 1 
 
 Cake, after two years ... .. o 
 
 Moist, after five years ... ... 1 
 
 A sample of burnt carmine purchased of Messrs. Newman 
 about the year 1815 was found (as might have been antici- 
 pated) to have retained its colour in the cake perfectly 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. 
 
CHAPTER XVI 
 
 GREEN PIGMENTS 
 
 Terre Verte : Gree?i Earth — Terre de Verone — Griine 
 Erde — 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 glauco- 
 nite : 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 shown 
 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 : 
 

 TERRE VERTE 
 
 
 Water, given 
 
 off at ioo° C. 
 
 4-1 
 
 Water, given 
 
 off at a red heat 
 
 4"2 
 
 Ferric oxide 
 
 (Fe 2 3 ) 
 
 •• 20-3 
 
 Ferrous oxide (FeO) 
 
 
 2-6 
 
 Alumina 
 
 
 
 .. 17 
 
 Lime 
 
 
 
 IT 
 
 Magnesia 
 
 
 
 •• 5-6 
 
 Potash 
 
 
 
 .. 6-4 
 
 Soda 
 
 
 
 2-3 
 
 Silica 
 
 
 
 .. 52-0 
 
 169 
 
 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, particularly 
 as the iron in it is for the most part fully oxidised. 
 
 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 rainwater; it is then dried. Sometimes the selected 
 fragments are heated, and then quenched in very dilute 
 hydrochloric acid to remove ochre and other impurities ; 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- 
 
i7o 
 
 GREEN OXIDE OF CHROMIUM 
 
 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 course of time, owing partly to the 
 deepening of its own hue and partly to the increased trans- 
 lucency of the pigments 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. 
 
 Terre verte is rarely adulterated. A pure sample is not 
 affected when drenched with liquor ammonise, becoming 
 neither more bluish (presence of copper compounds), nor 
 more brownish (presence of Prussian blue). 
 
 Grekn Oxide of Chromium : Chromium Sesquioxide — 
 True Chrome Green — Opaque Oxide of Chromium — Vert 
 de Chrome — Grimes 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, Cr. 2 3 , varies in hue, in 
 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 treating 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. 
 
GREEN OXIDE OF CHROMIUM 
 
 17' 
 
 Ammonium bichromate gently heated, in small portions at a 
 time, yields a dull-coloured but a useful variety of this pig- 
 ment ; 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 pre- 
 paring 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 sesquioxide. The sulphur method yields at 
 once a good pigment, which needs nothing but a thorough 
 washing, first with very dilute sulphuric acid and then with 
 water, followed 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 occurs 
 in the form of a greyish-green powder of considerable 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- 
 
172 
 
 VIRIDIAN 
 
 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 preparations 
 generally contain some barium sulphate, often a considerable 
 quantity of gypsum, and, occasionally, alumina. 
 
 Viridian : Emerald Oxide of Chromium — ■ Vert Pannetier — 
 Vert de Guignet — Vert Emeraude — Mitthr's Green. 
 
 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 manu- 
 factured. 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 con- 
 stituent is often retained. Viridian is, however, essentially 
 a hydrated sesquioxide of chromium, having the formula 
 Cr 2 3 , 2 H 2 0. 
 
 It would be difficult to exaggerate the value of this addi- 
 tion 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 hydrogen, 
 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 perhaps the name by which this pigment is 
 
COBALT GREEN 
 
 17. 
 
 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 obtained. 
 Arnaudon's chrome green is of a somewhat opaque green 
 hue, rather like that of Schweinfurt ; it is a phosphate of 
 chromium. A similar product is Mathieu-Plessy's chrome 
 green; but under the name of 'chrome green' ('Griiner 
 Zinnober ') spurious pigments are constantly sold, the com- 
 monest of them consisting of mixtures of chrome yellow and 
 Prussian blue. They are worthless in comparison with 
 viridian. 
 
 Cobalt Grekn : RinmamJs Green — Vert de Cobalt — Vert 
 de Zinc — Kobalt Griin. 
 
 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 beauti- 
 ful green hue. This compound or mixture of the oxides of 
 zinc and cobalt may be prepared by : (1) Precipitating with 
 an alkaline carbonate a mixture of the nitrates of cobalt and 
 of zinc, and then strongly heating (after washing) the pre- 
 cipitate 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 
 
J 74 
 
 EMERALD GREEN 
 
 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 ex- 
 cellent deep sample contained 1 2 per cent, of cobalt oxide. 
 
 When properly prepared, cobalt green is a pigment of 
 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 pigments. 
 Cobalt green is, in fact, one of the too-rare pigments which 
 is at once chemically and artistically perfect. 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. 1 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 Aceto-Arsenite — Schweinfurt Green 
 — Vert Paul Veronese. 
 
 This pigment was discovered in 18 14 during the course of 
 experiments made with the object of preparing an improved 
 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 dissolved in acetic acid, 
 and added to a boiling aqueous solution of white arsenic : 
 
 * The cobalt green sold by Edouard, of Paris, is by far the best I 
 have examined. 
 
EMERALD GREEN 
 
 175 
 
 on continued ebullition a deposit of emerald green occurs. 
 Sometimes copper sulphate, 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 untarnished 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 cadmium 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 generally shows the pre- 
 sence 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 Emeraude is the name given to 
 viridian, the emerald oxide of chromium. 
 
176 
 
 SCHEELE'S GREEN 
 
 Scheele's Green: Cupric Arsenite — Swedish Green — 
 Mitds Green — Scheele's Griln. 
 
 This pigment, discovered in 1778, is an arsenite of copper 
 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, Mittis green, and Veronese green are 
 names which have been given to specially prepared varieties 
 of this cupric arsenite ; but there are very many other desig- 
 nations by which pigments of essentially the same composi- 
 tion 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 
 Greeti — Green Carbonate of Copper — Vert de Montague 
 
 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 
 American localities. The mines at Ekaterinburg and 
 
MALACHITE 
 
 177 
 
 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 CuCO.pCuH^CX,. It 
 contains, therefore, less of the copper carbonate than 
 azurite, or blue verditer. 
 
 Malachite requires no other treatment than careful grind- 
 ing to fit it for use as an artists' pigment. The raw material 
 must, however, be carefully selected, and all visible im- 
 purities, such as ochreous veins and deposits, and azurite, 
 completely removed. An artificial malachite has been 
 prepared, and is often substituted for the mineral ; but it is 
 inferior in colour and stability to the native form. 
 
 Malachite as an oil-paint has often proved to be perma- 
 nent, although it may seem to acquire a dull, brownish hue, 
 owing to the darkening and yellowing of the oil ; some- 
 times, 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 unprotected by any 
 hydrofuge, that it is quite inadmissible as a water-colour. 
 In old tempera paintings it is sometimes 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, when 
 the malachite dissolves, leaving the baryta white as a sedi- 
 ment. To detect an arsenical green, a small portion of the 
 sample should be mixed with powdered charcoal, and heated 
 
VERDIGRIS 
 
 in a long narrow test-tube ; 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 — Griinspan. 
 
 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 Grece ' — that is, verdigris — was 
 used by the ancient Romans as a pigment,, 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 hlackness of the shaded parts in many 
 Venetian and Spanish pictures of the sixteenth and seven- 
 teenth centuries has been attributed to the changes which 
 this pigment suffers in oil. The mediaeval writers on the 
 practice of painting endeavoured to show how the peculiar 
 liability of verdigris to change could be obviated by locking 
 it up in some hydrofuge substance as a resin or balsam. 
 Later authorities have recommended copaiba for this pur- 
 pose; but copal varnish and hard paraffin are more effective. 
 The large proportion of resinous matter employed by early 
 painters for the protection of verdigris frcm alteration, 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 
 

 VERDIGRIS 
 
 179 
 
 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 proportions of these 
 acetates. The most blue basic acetate contains 1 molecule 
 of copper acetate, and 1 of copper hydrate, with 5 mole- 
 cules 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 fermentation. 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 hydrogen 
 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. For these reasons its 
 employment in artistic painting ought to be abandoned. 
 
 Verdigris, if pure, dissolves perfectly in liquor ammonias, 
 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 sulphate 
 indicates the presence of copper sulphate. 
 
CHAPTER XVII 
 
 BLUE PIGMENTS 
 
 Ultramarine : Lapis Lazuli Blau — Lasurstein Blau — 
 Outremer — 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, and in 
 many other Siberian localities ; at Ditro, in Transylvania ; 
 in the Andes of Ovalla, 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 impuri- 
 ties, are heated in a crucible and quenched (etonne) in cold 
 water, or very weak vinegar. The material, thus disin- 
 
ULTRAMARINE 
 
 tegrated, is washed by decantation, and then dried and 
 carefully ground. The powder is then purified by elutria- 
 tion, 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 bee's-wax, and knead, beat, or macerate 
 the lump under very weak potash, or soda-lye — the alkaline 
 water carries off or withdraws the greater part of the pigT 
 ment, 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 procurable from the 
 same raw material by means of the above-described pro- 
 cesses, 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 pig- 
 ments are deposited from the earliest wash-waters. 
 
 Optically, the superb blue of native ultramarine approaches 
 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 specimens 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 transparency when used in oil, and 
 is then ot excellent working quality. 
 
 Ultramarine withstands the action of light, moisture and 
 sulphuretted hydrogen perfectly : it neither affects nor is 
 affected by any other pigments. 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, 
 
lS2 
 
 ARTIFICIAL ULTRAMARINE 
 
 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. 
 
 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 ultramarine 
 may be seen. If in some cases it has acquired a greenish or 
 dull hue in oil-paintings, 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 operations by means of which the 
 pigment is prepared. But when every allowance is made on 
 account of the troublesome and lengthy process of manu- 
 facture, the cost of ultramarine is unwarrantably exces- 
 sive. 
 
 Artificial Ultramarine : New Blue — French Biue — , 
 Permanent Blue — Gmeliiis Blue — Guimefs Blue. 
 
 In the year 1814 a blue colouration, subsequently proved 
 to be due to ultramarine, was noticed in the soda (black-ash) 
 furnaces of St. Gobain. About fourteen years afterwards a 
 method of making the same blue substance at will was 
 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 condi- 
 tions under which the above-named blue colouration 
 
ARTIFICIAL ULTRAMARINE 
 
 I8 3 
 
 occurred. By successive improvements in its manufacture 
 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 France. 
 
 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 calcina- 
 tion is sometimes required to develope the proper blue 
 colour. 
 
 In preparing artificial ultramarine for use as an artists' 
 pigment it must be very finely ground, and very thoroughly 
 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 be associated in a 
 picture. 
 
 The hue of artificial ultramarine is commonly of a less 
 pure quality than that of the natural pigment, verging some 
 what 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 
 
1 84 
 
 ARTIFICIAL ULTRAMARINE 
 
 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 ultra- 
 marine, generally change the hue, and always ultimately 
 decolourize the artificial product. Those kinds which have 
 a somewhat violet tinge resist the destructive action of the 
 above re-agents longer than the pure blue and greenish-blue 
 varieties. Neither sulphuretted hydrogen, 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 composi- 
 tion 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 ; 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 ultramarine, 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 ultramarine 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 ultramarines 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 perma- 
 
A R TIFICIA L ULTRA MA RINE 
 
 nent both in water and oils. When thin washes on paper 
 appear to lose strengih 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 disco'our emerald green, chrome 
 yellow, Naples yellow (true), or flake white, it probably con- 
 tains 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 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 when 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 then separated in a 
 gelatinous form. The sulphur separated as such may 
 amount to as much as ro per cent, of the weight of the 
 pigment taken, or it may be less than half a per cent. The 
 sulphur disengaged as sulphuretted hydrogen through the 
 action of an acid varies between half a per cent, and 6 per 
 cent. As these variations have no relation to the depth of 
 
i86 
 
 COBALT BLUE 
 
 colour in the several samples, it is evident that a great pro- 
 portion 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 'Heumann's' 
 are of fine quality. Large quantities of this pigment are 
 manufactured in Germany and France, smaller amounts in 
 Belgium and England. The green and lilac ultramarines of 
 commerce are permanent, but not artistically valuable, pig- 
 ments. 
 
 Cobalt : Cobalt Blue — Bleu dc Thhiard — Kobalt Blau. 
 
 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 Leithners or The'nard's blue, a cobalt phosphate 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 inti- 
 mate mixture of aluminium hydrate and cobalt oxide. A 
 better way consists in moistening freshly - precipitated 
 aluminium hydrate with a solution of cobalt nitrate, drying 
 and then strongly igniting the mass. It may likewise be 
 prepared by precipitating a solution of sodium aluminate 
 by means of cobalt chloride solution. Thenard's blue may 
 be prepared by mixing about 8 parts of aluminium hydrate 
 with r 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 
 
CCERULEUM 
 
 187 
 
 solution to a solution of alum containing a little cobalt 
 sulphate. In all the above methods, the complete freedom 
 of the materials used from iron and nickel 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 
 of them are practically permanent even in impure air, but ^ / 1 
 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. 
 
 Cceruleum : Ceeliu — Cerulian — Cerulean Blue — Coelin- 
 Blau — Bleu Celeste. 
 
 When oxide of tin is moistened with cobalt nitrate solution 
 and strongly heated, a greenish blue mass is obtained, 
 which, after powdering and washing, constitues one of the 
 varieties of the pigment known as cceruleum. There are 
 other ways of preparing this substance. One of these con- 
 sists in precipitating potassium stannatewith cobalt chloride, 
 collecting and washing the precipitate, and then mixing it 
 with some pure silica and heating it. A good specimen of 
 cceruleum contained in 100 parts : 497 tin binoxide, i8"6 
 cobalt oxide, and 317 silica. Some samples contain cal- 
 
i88 
 
 PRUSSIAN BLUE 
 
 cium 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 187), 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 pigment, with a 
 moderate tingeing power. Although some painters find it 
 useful, coeruleum 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 : TurnbuWs Blue — Antwerp Blue — Berlin 
 Blue — Prussiate of Iron — Chinese Blue — Saxon Blue — 
 Bleu de Berlin —Pariser-Blau. 
 
 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 com- 
 pounds 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 potas- 
 sium ferricyanide solution. The blue precipitate formed is 
 washed with distilled water until the wash-water begins to 
 acquire a blue tint. The composition of the pigment 
 thus prepared is, when dry, represented by the formula 
 K 2 Fe 2 (CN) 12 Fe 2 . It contains 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, 
 
TURNBULUS BLUE 
 
 189 
 
 while its solubility in water causes it to stain the paper on 
 which it is spread in water-colour painting. It should in- 
 variably 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 consists 
 in roasting a small portion of the dry powdered pigment in 
 a porcelain bason 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. 
 
 II. 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 solu- 
 tion 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 v (CN) ]S : it 
 will be seen that it contains no potassium. It always con-, 
 tains some combined water, which cannot be driven off by 
 heat without decomposition of the salt. This blue is more 
 permanent than No. I. 
 
 III. Turnbull's Blue. — The chief constituent of the original 
 Turnbull's blue (more properly, Gmelin's blue) closely re- 
 
190 
 
 PRUSSIAN BLUE 
 
 sembles ordinary soluble Prussian blue, and, like it, contains 
 potassium. But the potassium may be removed from it by 
 stannous chloride solution, a substance being produced 
 having the empirical formula Fe 5 (CN) 12 , but containing 
 some water. Or the same body may be made by precipi- 
 tating a solution of ferricyanic acid with a solution of ferrous 
 sulphate or ferrous chloride. This blue is of good colour, 
 but is more difficult to obtain pure than No. II., the other 
 insoluble Prussian blue. Exposed to light, all the forms of 
 TurnbulFs blue, pure and impure, have a more decided 
 tendency 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 described. It 
 is made by adding green vitriol (ferrous sulphate) solution to 
 a solution of yellow prussiate of potash (potassium ferrocya- 
 nide). 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 form is, moreover, 
 the only one which yields, when roasted, a perfectly satis- 
 factory '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. 
 
CYAN IN E 
 
 191 
 
 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 pig- 
 ment 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. 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 17 10 by a colour-maker 
 of Berlin, Diesbach by name. When, as is sometimes the 
 case, this pigment is found in water-colour paintings of the 
 seventeenth century, it is scarcely necessary to state that 
 its presence betrays the brush of the restorer or the forger. 
 
 Antwerp blue is a sort of Prussian blue lake, the pigment 
 consisting of a colourless base dyed with Prussian blue. 
 According to one method of preparation, a solution of 
 1 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. xAlumina 
 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 : LeitcKs Blue. 
 
 A mixture of Prussian blue and cobalt blue has been sold 
 under the name of cyanine. It would seem from some 
 
192 
 
 INDIGO 
 
 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 Prussian blue 
 in it is at once turned into rust by 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 components of his mixtures. In the 
 case of cyanine, it appears that the more permanent consti- 
 tuent, 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 light which has penetrated through the cobalt par- 
 ticles 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 observed 
 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 indiciim by Pliny ; later on the Byzantine 
 writers called it azorium Romanum. ' Indigo bagadel ' — 
 that is, indigo of Bagdad — is named as early as 1228 in the 
 Marseilles tariffs ; in the early English accounts relating to 
 painting works (1274) it is called ' indebas.' It was first 
 largely imported from India into Europe in the seventeenth 
 century 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 
 
INDIGO 
 
 *93 
 
 Indigofera tincforia, a leguminous shrub, probably of Indian, 
 or at least Asiatic, origin. The exports of indigo from India 
 in a single year amount to ^4,000,000 worth. 
 
 Indigo (C ]6 H 10 N 2 O 2 ) does not exist ready-formed in the 
 plants which yield it, but occurs in the form of a colourless 
 compound, or glucoside, 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 
 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 (C 16 H 12 N 2 2 ) 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. 
 
 13 
 
194 
 
 INDIGO 
 
 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 compounds. Much of 
 the mineral matter may be removed by digestion in hydro- 
 chloric 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 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 paragraph. 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 indigo as a water-colour when exposed to sun- 
 light : 
 
 Original intensity ... ... ... 10 
 
 After two years ... ... ... 1 
 
 After ten years ... ... ... o 
 
INDIGO 
 
 195 
 
 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 sun- 
 light 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 conspicuous 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 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 ex- 
 periments were made. A pale tint of indigo was spread 
 upon (1) 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 speci- 
 mens 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 hygroscropic 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 condition, 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. 
 
 13—2 
 
INDIGO 
 
 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. Pro- 
 vided 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 impos- 
 sible to assert that this result was not due to a smaller 
 amount of indigo having been present in this particular case, 
 but I believe it to have been due to this sample of Venetian 
 red having been a spurious 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 treatment 
 with acid and the other solvents, already named — although 
 a result of recent experiments, seems to have been ascer- 
 tained 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 the paste when dry 
 ground in oil. Another plan recommended (in a note, 
 dated 1642) by Feltz consists in grinding 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 
 
INDIGO 
 
 197 
 
 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. 
 
 x\lthough it is not possible to ascertain the exact rich- 
 ness 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 the application of a few 
 simple experiments. A good sample should appear homo- 
 geneous, and should float on water. Dried at ioo° 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 nitration through asbestos cloth, potassium car- 
 bonate 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. 
 
 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 completely 
 left the exposed parts. In many cases where indigo is sup- 
 posed 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 
 
198 SMALT 
 
 pictures and drawings it will be found that the unnatural 
 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. 
 
 Smalt : Royal Blue — Dumonfs Blue — Zaffre- 
 Smalte — Smalte. 
 
 -Bleu de 
 
 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 essenti- 
 ally 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 
 
CHESSYLITE 
 
 199 
 
 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 ; moreover, the 
 finer the state of division in which it exists, the more rapid 
 is the change. It will be found that even spring or dis- 
 tilled water is competent to start the decomposition 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 the smalt — 
 proof of the liberation of some of the alkaline constituent 
 (potash) of this blue glass. 
 
 Chessylite : Blue Verditer — Bice — Mountain Blue — 
 Azurite — Cendres Bleus — Bergblau. 
 
 This copper mineral differs from malachite in containing 
 less hydrate, or more carbonate of the metal, its composition 
 being represented by the formula 2CuCO.„ CuH 2 0. 2 . 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. 
 
 Many old pictures, especially those in tempera, afford 
 evidence of blue verditer having become green. With the 
 extensive range of more permanent blues at the command 
 of the modern artist, there is no need to retain this pigment 
 on the palette. 
 
CHAPTER XVIII 
 
 BROWN PIGMENTS 
 
 Raw Umber : Levant Umber — Terr e d'' Ombre — Umbraun — 
 Umbra — Kolnische Erde — Terra Ombra. 
 
 This earth is found in several localities ; the best variety 
 has come for some time past from Cyprus. A considerable 
 number of Cypriote specimens, of several nuances, some 
 excellent, were shown in the Colonial 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 manga- 
 nese (Mn 3 4 , or Mn0 2 ), 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. A 
 recent analysis of my own, made with a choice sample from 
 Cyprus, showed the following percentages : 
 
 Water, given off at 100° C. ... ... 4-8 
 
 Water, given off at a red heat* ... ... 8 - 8 
 
 Iron oxide (Fe^O^) ... ... ... ... 48*5 
 
 Manganese dioxide (Mn0 2 ) ... ... 19-0 
 
 Lime ... ... ... ... ... 1 '4 
 
 Magnesia ... ... ... ... ... 0*5 
 
 * Includes a little organic or bituminous matter. 
 
RAW UMBER 
 
 20 1 
 
 Alumina 
 
 Phosphoric acid (P2O5) 
 
 Silica 
 
 Carbonic acid, etc. ... 
 
 2'I 
 
 O-Q 
 137 
 
 °'3 
 
 This sample had the peculiar greenish hue so much prized 
 by artists. It should be stated that a part of the manganese 
 probably existed as Mn 3 4 . 
 
 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 pigment 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 pigments. 
 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 ' sub- 
 stances, which occasionally occur in the umbers from certain 
 localities. 
 
 Raw umber possesses a semi-opaque, citrine-brown colour ; 
 
RA W SIENNA 
 
 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 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, continuous 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 very 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 proportions, 
 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. 
 It is perfectly permanent, and exerts no action on stable 
 pigments. 
 
 Raw Sienna : Terre de Sienne — Siena-erde — Terra di 
 
 Siena. 
 This earth, which is found chiefly in Tuscany and the 
 Hartz, is a particularly rich variety of yellow ochre, and 
 

 BURNT SIENNA 203 
 
 contains a large proportion of a ferric hydrate. Mr. G. H. 
 Hurst (loc. cit.) gives three analyses of raw sienna. In these 
 the range in the percentages of the more important con- 
 stituents is as follows : 
 
 Hygroscopic water 
 Combined water* 
 Maganese dioxide 
 
 Iron oxide (Fe 2 3 ) 
 Silica 
 
 5-2 to 17-5 
 
 9 - o ,, i2'4 
 o"6 „ 1*5 
 
 45' 8 » 597 
 5'° » r 7'4 
 
 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 subsequently, 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 6o° C. to remove the 
 greater part of the accidental or hygroscopic moisture. 
 
 Raw sienna 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 without action on 
 other pigments, and is available for water-colour, oil, fresco, 
 and tempera painting. 
 
 Raw sienna is not subject to adulteration, but it is well to 
 be certain that the pigment has been well washed. 
 
 Burnt Sip:nna. 
 The roasting or calcination of raw sienna produces a very 
 great change in its hue as well as in the depth of its colour. 
 * Includes traces of organic matter. 
 
204 
 
 VANDYKE BROWN 
 
 The ferric hydrate of the raw earth becomes wholly con- 
 verted 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 pecu- 
 liarity in a much less marked degree. 
 
 Burnt sienna possesses a very beautiful, warm, reddish- 
 brown hue, which cannot be exactly imitated in translucency 
 and depth by mixtures of other pigments. It is permanent, 
 without action on other pigments, and not liable to adul- 
 teration. 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 quan- 
 tity of combined moisture. It consists mainly of the brown 
 hydrates and oxides of manganese and iron. When cal- 
 cined it loses its ruddy hue and becomes almost black — a 
 black with a slight brownish hue. 
 
 Caledonian brown, whether raw or burnt, is a permanent 
 and innocuous pigment, which is well adapted for oil and 
 tempera painting. 
 
 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 
 
VANDYKE BROWN 
 
 205 
 
 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 prolonged action of light, becoming 
 paler and redder in the course of time. The discrepancies 
 in the published statements 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. 
 
 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 bleaohed 
 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 practically permanent in oil, but even these 
 faded quite distinctly when exposed to strong light after 
 having been mixed with flake-white. 
 
2o6 
 
 CAPPAGH BROWN 
 
 Cappagh Brown : Euchrome — 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 considerable 
 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 Caledonian 
 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 following analysis 
 represents the composition in 100 parts of a characteristic 
 specimen of this pigment : 
 
 Water, given off at 1 00° C. ... ... 187 
 
 Water, given off at a red heat ... ... 11 -6 
 
 Ferric oxide (Fe. 2 :i ) ... ..- ... 34/4 
 
 Manganese dioxide (Mn0 2 ) ... ... 27-2 
 
 Alumina ... ... ••• ... ... 2 "6 
 
 Lime ... ••• ••• •■• •■• i'i 
 
 Magnesia ... ••• ••• ... ••• trace 
 
 Silica 4'6 
 
 Phosphoric acid (P 2 5 ) ••• ... ■•• 0-4 
 
 It is probable that a part of the manganese really exists in 
 the form of the red oxide (Mn 3 4 ). 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 6o° C. should not be exceeded. 
 
BISTRE 
 
 207 
 
 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 permanence has 
 scarcely been sufficiently tested. A rub of Cappagh brown 
 in oil, exposed to strong sunlight for one month, iost a little 
 of its yellow, assuming a somewhat ruddier hue ; the change, 
 however, was very slight, and did not appear to have 
 increased after continued exposure for another month. 
 
 Bistre : Bister — Brauner Lack — Russbraun. 
 
 Bistre is prepared from the tarry soot of certain woods, 
 especially from that of beech-wood, by the following process : 
 The soot is finely ground and sifted, and then the powder is 
 digested with successive portions of hot water until the latter 
 no longer acquires a brown or yellow tint ; the washed 
 material is then mixed 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 em- 
 ployed. 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. Pro- 
 fessor Ogden Rood, experimenting with a weak water-colour 
 wash of bistre, found that it lost 19 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 preparation is that made by extracting the 
 vegetable tars referred to above with water containing a little 
 ammonia, and then precipitating the deep-brown liquor with 
 a slight excess of acetic acid. 
 
208 
 
 ASPHALTUM 
 
 Asphaltum : Bitumen — Mineral Pitch — Antwerp Brow?i — 
 Mummy — Asphalt Braun. 
 
 Asphalt, asphaltum, or mineral pitch, has been long used 
 as a pigment. The best known is that from the Dead Sea 
 (Lacus asph.Jtites). Other abundant sources of this car- 
 bonaceous mineral occur in Trinidad ; Caxitambo and Be- 
 rengela, 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, charac- 
 ter, and proportion of its constituents. Essentially it con- 
 sists of a number of liquid, semi-solid and solid, colourless 
 hydrocarbons (related to the paraffins), associated 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, 
 
ASPHALTUM 
 
 209 
 
 and more particularly by associating it with a denser pig- 
 ment, 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. 
 
 ' Mummy,' as a pigment, is inferior to prepared, but 
 superior to raw, asphalt, inasmuch as it has been submitted 
 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 seven 
 years. It is perhaps scarcely necessary 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 hydro- 
 carbons previously alluded to, cedes to ammonia a consider- 
 able 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 addition 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. 
 
 14 
 
CHAPTER XIX 
 
 BLACK PIGMENTS 
 
 Indian Ink: Chinese Ink— Japanese Ink- 
 Chinesische Tusche. 
 
 -Encre de Chine- 
 
 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 indicum, Cannabis 
 sativa, and Dryajidria 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 earthenware 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 pre- 
 paration 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 excellent product may be obtained. The next step in 
 
INDIAN INK 
 
 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 dilu- 
 tion with water, or by admixture with opaque white pig- 
 ments. 
 
 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 are the 
 most esteemed; the pure black come next, and the brownish 
 or yellowish black last. 
 
 14 — 2 
 
INDIAN INK 
 
 I 
 
 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 cannot 
 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 pre- 
 paration 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 con- 
 tain as much. Japanese ink is generally inferior to 
 Chinese. 
 
 Chinese amateurs sometimes form collections of rare and 
 old kinds of Chinese ink, occasionally giving for sticks bear- 
 ing the marks of renowned makers not less than their weight 
 
LAMP BLACK 
 
 213 
 
 
 in gold. Such specimens are prized for their rarity, not 
 on account of any special merits as pigments which 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. 
 
 L amp-Black : Noir. de Lampe — Noir de Fumee — Noir de 
 Houille — Russ. 
 
 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 pro- 
 nounced 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. Some- 
 times small furnaces, 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 deposited 
 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 ; 
 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 excep- 
 tion 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. 
 
214 
 
 CHARCOAL BLACK 
 
 Numerous carbonaceous substances have been used as 
 black or brown-black pigments. Amongst these anthracite 
 and common bituminous coal may be named. Van Mander 
 and De Mayerne both mention forge or pit coal. 
 
 Charcoal-Black : Blue- Black — Vine-Black — Frankfort- 
 Black — Noir de Vigne. 
 
 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 con- 
 verted into paints. They are also hygroscopic, and there- 
 fore need to be dried before being ground in oil. 
 
 Amongst the best materials for producing these charcoal 
 or vegetable blacks may be named the hard shells or 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 imperfectly 
 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 intermediate in composition 
 between the original vegetable materials and the carbon, 
 
IVORY BLACK 
 
 215 
 
 which is the final product of their torrcfaction out of con- 
 tact with the air. And one peculiar property, possessed in 
 varying degrees by charcoal 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 decolourised, the 
 pigment being completely absorbed, although not really 
 destroyed. Animal charcoal (bone-black, ivory-black) exerts 
 a still more energetic action of this character 3 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. 
 
 Ivory Black : Noir d^Ivoire — Elfenbei?ischwartz. 
 
 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 painting 
 than with water colours. This decolourizing property 
 belongs also to the animal blacks obtained by charring 
 horn and bone shavings — products which are frequently 
 
2l6 
 
 GRAPHITE 
 
 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 cornu cerviniim, remains very intense. 
 
 Ivory and bone black are perfectly permanent black pig- 
 ments ; 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. 
 
 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 in reality 
 contains no lead, and is in no way related to that metal. 
 Graphite was found of good quality at Borrowdale in Cum- 
 berland, a locality which has been stated, probably errone- 
 ously, 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, how- 
 ever, 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 
 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 
 
SEPIA 
 
 217 
 
 fine powder, which is then ready for admixture with gum 
 water or, after drying, with oil. 
 
 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 
 is spread on a 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 adul- 
 terant. 
 
 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 commerce, partakes 
 of the character of a weak organic acid, and is soluble in 
 alkalies and precipitated by acids. In preparing the sub- 
 stance 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 decantation, 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 with dilute hydrochloric acid 
 previous to dissolving it. 
 
2lS 
 
 SEPIA 
 
 Sepia is of a redder or warmer brown hue than bistre, but 
 it is not so reddish as Vandyke brown. Of these three pig- 
 ments, 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 unalter- 
 able, from the consideration of the observed fact of the pig- 
 ment 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. 
 
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 im- 
 portant 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 : 
 
 f Natural : as ochre, terre verte, ultramarine. 
 Mineral Pigments. 1 . .. c . , ,. . .,. . ,. ,-, 
 
 1 Artificial : as aureohn, vindian, cobalt blue. 
 
 C Animal : as Indian yellow, carmine, sepia. 
 
 Organic Pigments, -j Vegetable : as gamboge, sap green, indigo. 
 
 t Artificial : as Prussian blue. 
 
 Such a classification brings into prominence one marked 
 distinction between the two groups, for, in accordance with 
 one's expectation, the mineral pigments are, as a rule, 
 characterized by a much higher degree of permanence than 
 
CLASSIFICATION OF PIGMENTS 
 
 those of organic origin. [The chemist looks upon all com- 
 pounds containing carbon, save the carbonates, as organic ; 
 but at the same time the distinction 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. There are 
 difficulties in carrying 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 : 
 
 E lements ; as graphite, lamp-black, gold. 
 Compounds ; as aureolin, viridian, vermilion. 
 Mixtures ; as yellow ochre, brown pink, rose madder. 
 
 After considerable expansion and some rearrangement, 
 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 inter- 
 action of pigments. The mixed and 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 classi- 
 fication, though convenient, has no pretension to scientific 
 exactness. I suggest the following eight groups : 
 
 Group I.— The Oxides. 
 
 Zinc white - - ZnO. 
 Green oxide of 
 
 chromium - Cr 2 O g . 
 Burnt umber - Oxides of Fe and 
 
 Mn. 
 Cobalt Green - CoO, n ZnO. 
 
 Coeiuleum - 
 Cobalt blue 
 Venetian red 
 Light red 
 Indian red 
 Burnt Sienna 
 
 CoO, n Sn0 2 . 
 CoO, n A1 2 3 . 
 
 hChiefly Fe 2 3 . 
 
CLASSIFICATION OF PIGMENTS 
 
 Group II. — The Sulphides. 
 
 Cadmium yellow CdS. 
 King's yellow - As 2 S 3 . 
 Vermilion - - HgS. 
 Uultramarine"~| ("Contain Si, Al, 
 Artificial l-J Na, O, and sul- 
 
 ultramarinej \_ phur. 
 
 Group III. — The Hydrates. 
 
 Yellow ochre - Fe 2 3 «H 2 0, etc. 
 
 ~ . f Con tain oxides 
 
 Raw sienna > I ... 
 
 ' f -J and hydrates of 
 Raw umber P , ,„• . 
 
 ^ FeandMn,etc. 
 
 Emerald oxide ) n ^ , H r> 
 , , [ Cr 2 3 , 2H 2 0. 
 
 ot chromium ) 
 
 Group IV. — The Carbonates. 
 
 Flake white - - 2PbC0 3 , PbH 2 2 . 
 
 Whitening - - CaCQ 3 . 
 
 Malachite - - CuC0 3 , CuH 2 2 . 
 
 Chessylite - - 2CuC0 3 ,CuH 2 2 
 
 Group V.— The Silicates. 
 
 Silicate of Fe, K, 
 
 Terre Verte 
 
 Mg. 
 
 Smalt j Silic ^ ° f C °' 
 
 ( and K. 
 
 Group VI. — Other Inorganic 
 Salts. 
 
 Baryta white - BaS0 4 . 
 Aureolin- - - K G Co 2 i2N0 2 . 
 Baryta yellow - BaCr0 4 . 
 Strontia yellow - SrCr0 4 . 
 Chrome yellow - PbCr0 4 . 
 Chrome red - - Pb 2 Cr0 5 . 
 Zinc Chrom ate - ZnCr0 4 . 
 
 Group VI. — Other Inorganic 
 
 Salts {continued). 
 Naples yellow Contains Pb, Sb, O. 
 
 Schweinfurt ) Contains Cu, As, O. 
 green J 
 
 Group VII. — Organic 
 Compounds. 
 Indian yellow. 
 Yellow lake. 
 Yellow madder. 
 Brown pink. 
 Rose madder. 
 Madder carmine. 
 Rubens' madder. 
 Madder red. 
 Purple madder. 
 Brown madder. 
 Carmine. 
 Crimson lake. 
 Scarlet lake. 
 Purple lake. 
 Indian lake. 
 Sap green. 
 Verdigris. 
 Emerald green. 
 Indigo. 
 Prussian blue. 
 Bitumen. 
 Bistre. 
 Sepia. 
 Vandyke brown. 
 
 Group VIII.— Elements. 
 Silver. 
 Gold. 
 
 Ivory Black ^ 
 Charcoal black 
 
 Lamp black )■ Contain carbon. 
 Indian ink 
 Graphite 
 
THE CARBONATES 
 
 One of the chief lessons to be learnt from this classifica- 
 tion 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 I., 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 II. neither give sulphur 
 to, or receive it from the other sulphides, for all 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. : The 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 II. : The 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 sometimes contain 
 free sulphur, or injurious sulphur compounds. 
 
 Group III. : The Hydrates. — The water present in 
 these 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 is 
 rare and slight. In the case of raw umber, the water present 
 acts rather in aiding the oxygen of the air, under the influ- 
 ence of sunlight, to oxidize some of the peaty or bituminous 
 matter sometimes present in this pigment. 
 
 Group IV. : The Carbonates. — Three out of the four 
 
THE ELEMENTS 
 
 223 
 
 carbonates included in this group are liable to suffer change 
 on account of the metal they contain (lead or copper) com- 
 bining with sulphur, and so forming a brown or black 
 sulphide. 
 
 Group V. : The Silicates. — These are generally inert 
 bodies, little prone to suffer or cause change. Some of the 
 ochreous earths contain silicates of iron, manganese, and 
 alumina, as well as the hydrates of the two former metals, 
 and so might be placed in this group. 
 
 Group VI. : Other Inorganic Salts. — A rather miscel- 
 laneous group. Some members, such as the chromates, 
 with lead antimoniate, tend to lose a' part of their oxygen, 
 which may serve to attack some of the organic pigments of 
 the next group with which they happen to be mingled ; 
 they themselves become greenish, or greyish at the same 
 time. Those members which contain lead may become 
 brown or black in the presence of sulphuretted hydrogen, 
 etc. Aureolin, a nitrite of cobalt and potassium, owing to 
 its nitrous constituent, acts upon indigo and some other 
 organic pigments. 
 
 Group VII. : 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 combined action of water and oxygen : 
 in oily and resinous media it is lessened, retarded, or even 
 prevented by the hydrofuge character of these vehicles. 
 
 Group VIII. : The Elements. — All the black pigments 
 in ordinary use consist of the element carbon more or less 
 pure, and are not subject to change : graphite is a form of 
 carbon absolutely unchangeable, and quite inert. Gold, if 
 
224 
 
 CLASSIFICATION OF PIGMENTS 
 
 nearly free from alloy, is unalterable, but silver readily 
 tarnishes by absorption of sulphur ; drawings in silver-point 
 are frequently found to have changed in hue through this 
 cause. 
 
 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 : 
 
 Vermilion. 
 
 Smalt. 
 
 King's yellow. 
 
 Strontia yellow ; aureolin. 
 
 Asphalt. 
 
 Molecular rearrangement 
 
 Subsidence... 
 
 Volatilization 
 
 Solution 
 
 Fusion 
 
 Oxidation ... 
 Reduction .., 
 Sulphuration 
 
 ... Carmine; Vandyke brown. 
 . . . Naples yellow ; chromates. 
 ... White lead; emerald green. 
 
 The effect of pulverization upon pigments may be men- 
 tioned in this connection. Generally, the more finely an 
 alterable pigment is ground, the more susceptible does it 
 become to chemical injury : its colour becomes at the same 
 time paler, and may even change in hue. Continued grind- 
 ing, beyond the degree necessary to develop the proper 
 colour, improves some pigments, but injures others. 
 
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 accord- 
 ance with their varying degrees of stability. Such data are 
 derived partly from the known chemical and physical con- 
 stitution 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 approxima- 
 tions. From some minute and often obscure cause differ- 
 ences of deportment, under exposure to hostile influences, 
 will occasionally be observed in the case of two specimens 
 of the same pigment having the same hue. And, further, 
 the grouping 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 
 
 15 
 
226 
 
 TABLES OF PIGMENTS 
 
 discussion. For when we leave the practically unalterable 
 mineral pigments, we have to deal with a number of prepa- 
 rations which fall by irregular and often barely recognisable 
 steps from the almost permanent to the hopelessly fugitive. 
 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 
 truly 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 
 
 Class II 
 
 White 
 
 Class III 
 
 
 Baryta white. 
 
 
 
 
 Zinc white. 
 
 
 
 
 Flake white. 
 
 Yellow 
 
 
 
 Yellow ochre. 
 
 Aureolin. 
 
 King's yellow. 
 
 
 Raw sienna. 
 
 Baryta yellow. 
 
 Yellow madder 
 
 '■ 
 
 Naples yellow. 
 
 Indian yellow. 
 
 Brown pink ; 
 
 yellow 
 
 Cadmium yellow. 
 
 Strontia yellow. 
 ^■Chrome yellow. 
 
 lake. 
 
 
 Cadmium orange. 
 
 Gamboge. 
 
 
 
 Zinc chromate. 
 
 
 
 Red 
 
 
 
 Vermilion. 
 
 Madder carmine. 
 
 Crimson lake. 
 
 
 Indian red. 
 
 Rubens madder. 
 
 Carmine and 
 
 burnt 
 
 Light red. 
 
 Rose madder. 
 
 carmine. 
 
 
 Venetian red. 
 
 Madder red. 
 
 Indian lake. 
 
 
 Red ochre. 
 
 Purple madder. 
 
 Scarlet lake. 
 Purple lake. 
 
 
TABLES OF PIGMENTS 
 
 227 
 
 Class I 
 
 Emerald oxide of chro- 
 mium. 
 
 Green oxide of chro- 
 mium. 
 
 Class II 
 Green 
 
 Cobalt green. 
 Emerald green. 
 Terre verte. 
 Malachite. 
 
 Class III 
 
 Verdigris. 
 
 Sap green. 
 
 'Green vermilion,' etc. 
 
 Ultramarine. 
 Artificial ultramarine. 
 Cobalt. 
 Coeruleum. 
 
 Burnt sienna. 
 
 Raw and burnt umber. 
 
 Canpagh brown. 
 
 Caledonian brown. 
 
 Verona brown. 
 
 Prussian brown. 
 
 Ivory-black. 
 
 Charcoal-black. 
 
 Lamp-black. 
 
 Graphite. 
 
 Blue 
 
 Smalt. 
 
 Prussian blue. 
 Antwerp blue. 
 
 Brown and Black 
 
 Madder brown. 
 Cologne earth. 
 Bitumen. 
 
 Vandyke brown A 
 {earthy). 
 
 Indigo. 
 Blue verditer. 
 Blue ochre. 
 
 Vandyke brown 
 (Intutninous). 
 
 B. 
 
 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. 
 
 15—2 
 
228 
 
 TABLES OF PIGMENTS 
 
 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 pig- 
 ments is still further reduced. 
 
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 im- 
 possible to exclude every pigment which is susceptible 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 finds it easy 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 mar- 
 vellous 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 enlargement of the palette will render 
 such mixing unnecessary. 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 transparent pigment opaque, but the reverse opera- 
 tion is impracticable. 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 
 possessed of transparency, or, at least, of translucency. 
 
230 
 
 SELECTED PALETTES 
 
 Thus he adds to his cadmium yellow, aureolin ; to his ver- 
 milion, madder carmine ; to his emerald green, viridian ; to 
 his cceruleum 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 different 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 retains 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 commixture 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 instructive 
 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 many of such 
 palettes lies in their inclusion of a few treacherous pigments, 
 such as asphaltum, and of a few evanescent pigments, such 
 
SELECTED PALETTES 231 
 
 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 refinement 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 compounds, 
 and by the use, in the same picture, of incompatible 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 pigments : 
 
 i 
 
 Flake white. 
 
 Yellow ochre. 
 
 Lake. 
 
 Ultramarine. 
 
 Black. 
 
 ii 
 
 Flake white. 
 
 Yellow ochre. 
 Orpiment. 
 
 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. 
 
 Asphaltum. 
 
 
 Paul Delaroche and H. Vernet employed these eleven 
 pigments : 
 
 Flake white. 
 
 Yellow ochre. Vermilion. Artificial ultra- 
 Naples yellow. Lake. marine. 
 Raw sienna. Brun rouge. 
 Burnt sienna. 
 
 Blue black. 
 Ivory black 
 
 W. Etty, 
 
 R.A., used ten pigments : 
 
 
 flake white. 
 
 Naples yellow. Vermilion. Terre verte. 
 Light red. 
 Indian red. 
 Lake. 
 
 Raw umber. 
 Burnt umber 
 Black. 
 
SELECTED PALETTES 
 
 Samuel Palmer employed in oil painting the following 
 pigments, eighteen to twenty in number : 
 
 Flake white. 
 
 Naples yellow. 
 Yellow ochre. 
 Raw sienna. 
 Aureolin. 
 Cadmium yellow. 
 
 Vermilion. 
 Venetian red. 
 Indian red. 
 Madder car- 
 mine, etc. 
 
 Terre verte. 
 Green oxide 
 
 chromium. 
 Emerald green. 
 
 Artificial ultra- 
 marine. 
 Antwerp blue. 
 Cobalt. 
 
 He added to these, as water colours, gamboge and Prussian 
 blue. 
 
 Thomas Wright, of Derby, employed fourteen pigments, 
 and it is to be presumed flake-white also : 
 
 Naples yellow. 
 
 Vermilion. 
 
 Cartnine. 
 
 Terraceum blue (?). 
 
 Ivory black 
 
 Brown pink. 
 
 Burnt ochre. 
 
 Lake- 
 
 Ultramarine. 
 
 
 
 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 employed by some 
 distinguished living artists. It should be added that in one 
 or two cases these painters have since somewhat altered 
 their selections of colours. The palettes quoted have been 
 chosen as representative of different types. 
 
 Mr. A. employs ten pigments : 
 
 Flake white. Naples yellow. Vermilion. 
 
 Yellow ochre. Venetian red. 
 
 Cadmium yellow. Pink madder. 
 Raw sienna. 
 
 Mr. B. twenty-three pigments : 
 
 Cobalt blue. 
 Antwerp blue. 
 
 Burnt sienna. 
 Raw umber. 
 
 Vandyke brown. 
 Ivory-black. 
 
 Zinc white. 
 
 Lemon yellow. 
 Cadmium, i, 2, 3. 
 Aureolin. 
 Yellow ochre. 
 Roman ochre. 
 
 Vermilion. 
 Light red. 
 Indian red. 
 Madder lake. 
 
 Oxide of chro- 
 mium. 
 
 Emerald oxide 
 chromium. 
 
 Cobalt green. 
 
 Ultramarine. 
 Artificial ultra- 
 marine. 
 Cobalt blue. 
 
 With, in addition, raw umber, burnt sienna, cappagh brown, Vandyke In-own, ivory 
 black. 
 
 Mr. C. ten pigments 
 
 White. 
 
 Yellow ochre. 
 Raw sienna. 
 
 Vermilion. 
 Rose madder. 
 Purple lake. 
 
 Cobalt blue. 
 
 Raw umber. 
 Vandyke brown. 
 Ivory black. 
 
 Mr. D. fifteen pigments in water-colour pictures : 
 
 Chinese white 
 
 Yellow ochre. 
 Raw sienna. 
 
 Vermilion. Cobalt. Burnt sienna. 
 
 Light red. Artificial ultra- Vandyke broivn 
 
 Venetian red. marine. Ivory-black. 
 
 Indian lake. Indigo. 
 
 Prussian blue. 
 
 Antwerp blue. 
 
SELECTED PALETTES 
 
 233 
 
 Mr. E. twenty-six pigments 
 
 Flake white. 
 
 Lemon yellow. 
 Cadmium yellow. 
 Gamboge. 
 Laque Robert. 
 Naples yellow. 
 Yellow ochre. 
 Raw sienna. 
 
 Orange ver- 
 milion. 
 
 M adder car- 
 mine. 
 
 Venetian red. 
 
 Indian red. 
 
 Indian lake. 
 
 Burnt lake. 
 
 Ultramarine. 
 Antwerp blue. 
 Cobalt blue. 
 Green oxide 
 
 chromium. 
 Emerald oxide 
 
 chromium. 
 Malachite. 
 
 Raw umber. 
 Burnt umber. 
 Burnt sienna. 
 Cologne earth. 
 Blue black. 
 Ivory-black. 
 
 Mr. E. has also used the two so-called yellotv madders. 
 
 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 selection is 
 offered. It is arranged in two sections, the second including 
 what may be called ' supplementary ' pigments : 
 
 Section I. 
 
 includes 
 
 12 pigments. 
 
 Section II. 
 
 includes 
 
 13 pigments 
 
 'Flake white. 
 
 Cadmium yellow. 
 
 Aureolin. 
 ,. Yellow ochre. 
 'Raw sienna. 
 
 Naples yellow. 
 
 Baryta yellow. 
 
 marine. 
 
 Vermilion. 
 Madder car 
 
 mine. 
 Light red. 
 
 Purple madder. Green oxide 
 Madderbrown. chromium. 
 
 Terre verte. 
 
 Malachite. 
 
 Emerald green. 
 
 Viridian. Raw umber. 
 
 Artificial ultra- Cappagh brown. 
 Ivory-black. 
 
 Cobalt. 
 Prussian blue, 
 
 (insol.). 
 Burnt sienna. 
 C aledonian 
 
 brown. 
 
 It will be remembered that emerald green cannot be 
 safely associated with cadmium yellow, and that there is no 
 reason why several other pigments should not be included 
 in Section II., beyond the desirability of limiting the 
 number of paints to those really required. Garance doree, 
 Rubens madder, 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 pos- 
 sible. 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 restricted pal- 
 ettes : 
 
234 
 
 RESTRICTED PALETTES 
 
 i. Flake-white, yellow ochre, light red, cobalt, ivory-black. 
 
 2. Flake-white, cadmium yellow, vermilion, ultramarine, 
 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, Cappagh 
 brown, ivory-black. 
 
 It is scarcely necessary to say that the capacity of No. 1 
 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 necessary to employ for this purpose will be a little 
 less luminous than the originals, since these hues will have 
 been produced by the increased absorption 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 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 brown, cappagh brown. Mr. Hamerton tested the 
 range of his restricted palette by imitating with its consti- 
 tuents many of the excluded pigments. I give some of his 
 results, as modified by my own experiments with my palette 
 No. 3. 
 
 Naples Yellow. — Imitated by flake-white, with cadmium 
 yellow and a trace of yellow ochre : exact. 
 
RESTRICTED PALETTES 
 
 235 
 
 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 carmine, 
 a little Cappagh brown : exact. 
 
 Lndian 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, arti- 
 ficial ultramarine : not so brilliant as the orginal. 
 
 Malachite. — White, cadmium yellow, yellow ochre, viridian, 
 ultramarine. 
 
 Terre Verte. — White, aureolin, viridian, ivory-black. 
 
 Cobalt Green. — Ultramarine, viridian, trace of flake-white. 
 
 Lndigo. — 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 himself 
 to our restricted palette of ten pigments (No. 3, page 234), 
 as experimental trials of its capacity are easily made. 
 
 So far thus 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 en- 
 
236 
 
 RESTRICTED PALETTES 
 
 during water colours. In the more extended list (page 233), 
 zinc-white must replace flake-white, while vermilion, purple 
 madder, brown madder, malachite, and emerald green 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 replacement of arti- 
 ficial vermilion by native cinnabar, and of Cappagh brown 
 by Mars brown, and of ivory-black by Indian ink. The 
 two palettes (A. and B.) will then finally assume the follow- 
 ing forms : 
 
 (A.) _ TZiiic white. 
 
 Section I. J Cadmium yellow. 
 
 includes j Aureolin. 
 13 pigments. I. Yellow ochre. 
 
 Section II. 
 
 includes 
 S pigments. 
 
 ':( 
 
 Raw sienna. 
 
 Light red. 
 Indian red. 
 Madder car- 
 mine. 
 
 Vermilion (cin- 
 nabar). 
 
 Viridian. 
 Artificial ultra- 
 marine. 
 Cobalt. 
 
 Prussian blue 
 (insol.). 
 
 Raw umber. 
 Burnt sienna. 
 Indian ink. 
 
 Mars brown. 
 Ivory-black. 
 
 Doubtless artists will especially miss from this palette five 
 pigments, namely, gamboge, rose madder, brown madder, 
 Vandyke brown, and indigo. But after the overwhelming 
 evidence adduced in Chapter XXVI. as to the want of per- 
 manence shown by these water-colour paints, one feels com- 
 pelled to exclude them. Our second and more restricted 
 palette (B.) is thus composed : 
 
 (B.) 
 
 Chinese 
 
 Yellow ochre. 
 
 Cinnabar. 
 
 Ultramarine. 
 
 Mars brown. 
 
 white. 
 
 Cadmium yellow. 
 Aureolin. 
 
 Madder car- 
 mine. 
 
 Viridian. 
 
 Indian ink. 
 
 Although it is obvious that with these limited palettes it 
 is impossible to produce exact imitations of every excluded 
 pigment, yet there are two considerations which must not 
 be forgotten in estimating the influence of this defect on 
 artistic painting. Foremost may be placed the fact that 
 pigments are rarely employed wholly unmodified by admix- 
 ture with others ; then it must be noted that the differences 
 between our imitations and the original pigments 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. 
 
l m 
 
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 employing these materials. 
 
 These methods are six in number, and may be thus de- 
 fined : 
 
 ***** VMdes 4*ri£f&me 
 
 i. Tempera - - Egg-yolk emulsion ; solution of gelatin ) ( Desiccation or 
 
 or albumen j \ coagulation. 
 
 2. Fuesco - - Lime-water, in both buon' fresco and 
 
 fresco secco Carbonation. 
 
 -5. Stereochromy Aqueous solutions of alkaline silicates - Formation of in- 
 soluble silicates. 
 _. „ i ^Oxidation, 
 
 4. Oil - Painting \ I Resinification, 
 
 and Spirit- >■ Oil, and solutions 01 resin, wax, paraffin X t? .• 
 
 ,-, I Evaporation, 
 
 fRESCO J [Solidification. 
 
 5. Water-Colour Aqueous solutions of gum, glycerin, 
 
 honey Desiccation. 
 
 6. Pastel, ^ 
 
 Charcoal, I N None> 
 
 Plumbago, 
 Silver-point ) 
 
 1. Tempera-painting, or paintingjn distemper, is generally 
 assumed to include two, if not three, methods of procedure, 
 in which different vehicles or media are employed. These 
 vehicles all contain a nitrogenous constituent ; but in one of 
 them — and that the most important — oil or fat is present in 
 addition. Tempera-grounds must be rigid, tenacious, and 
 
240 
 
 TEMPERA -PA INTING 
 
 firm ; they need not be dry, but if organic pigments are to 
 be used, they should not contain caustic-lime. Thus, a sur- 
 face 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 avail- 
 able 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 Hti7ius-paper turns blue or purple, while phenolphthalein- 
 pafier acquires a crimson hue. If these tests show the 
 absence of caustic-lime, the painting may be commenced, 
 otherwise the surface must be carbonated 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 compositions of which caustic-lime is not a com- 
 ponent. 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 neutralized by the cautious addition of a very few 
 drops of white vinegar — fig-tree sap or white wine were 
 formerly employed for the same purpose. Some artists 
 content themselves with diluting the egg-yolks with a little 
 
FRESCO -PA INTING 
 
 241 
 
 water ; others add a small proportion of white of egg, pre- 
 viously 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 em- 
 ployed in tempera-painting. The white of egg needs dilu- 
 tion 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 become partly insoluble and coagulated. 
 As the amount of oil in egg-yolk is twice as great (30 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 albuminoids of egg-yolk 
 has acted injuriously upon some of the pigments of the 
 picture ; but by excluding, as we now do, all paints contain- 
 ing 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, 
 sized, and varnished, the varnish being often made by dis- 
 solving 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. 
 
 2. In fresco-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 
 
 16 
 
242 
 
 FRESCO-PA INTING 
 
 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 
 carbonic 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 introduced by 
 means of lime-water itself, or even by baryta-water, which 
 contains sixty 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 pig- 
 ments 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 in every case. Silicate of lime as a binding material 
 is more permanent than the carbonate. 
 
 In fresco sccco the plaster is allowed to dry, and the 
 operation of painting may be continued at leisure. The 
 ground 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 process is far easier 
 of execution than .true fresco ; but the fixation of the pig- 
 
FRESCO-PA INTING 
 
 243 
 
 ments, though resulting from the same cause, is less com- 
 plete. 
 
 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 bind- 
 ing carbonate of lime is converted into the sulphate, break- 
 ing 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-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 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, for it enabled a greater rich- 
 ness 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 pig- 
 ment is thinly painted over a slab of plaster of Paris, and 
 
 16 — 2 
 
244 
 
 STEREOCHROMY 
 
 then half of it 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. 
 As lime in the caustic state acts strongly upon wood, it is 
 necessary to employ palettes of zinc or glazed earthenware ; 
 bone or ivory palette-knives are preferable to those of 
 steel. 
 
 3. In stereochromy, or water-glass painting, a process intro- 
 duced more than forty years ago, the fixative employed is an 
 alkaline silicate dissolved in water. From time to time 
 different experimenters have improved the 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 introduced. The constituents and pre- 
 paration of painting-grounds adapted for this process have 
 been discussed in Chapter IV. The pigments should be 
 treated, as recommended by Kuhlmann, with some of the 
 fixing liquid, and then reground ; in some cases they 
 require the 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 ammonias. The surface is shortly after- 
 wards washed repeatedly with hot distilled water ; and, if 
 
OIL-PAINTING 
 
 245 
 
 necessary, 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 
 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, ultramarine, 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 satu- 
 rating this paper with a solution of peroxide of hydrogen. 
 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 
 
246 
 
 OIL-PAINTING 
 
 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 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 convenient means of neutralizing the residual 
 alkalinity of a lime-plaster ground intended for oil or spirit- 
 fresco painting is afforded by linoleic acid.f This liquid 
 fatty acid is an article of commerce, moderate in price, and 
 easily obtainable. 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 this method of painting are not 
 miscible with water — are, in fact, hydrofuge materials repel- 
 
 * The hardest kind of paraffin is obtained from ozokerite. It is 
 known in commerce as ceresin. Some samples, the best for the present 
 purpose, require a temperature of over 8o° C. to melt them. 
 
 + By linoleic acid is here meant the mixture of fatty acids obtainable 
 from raw linseed oil. 
 
OIL-PAINTING 
 
 247 
 
 lent 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 com- 
 pletely 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 in- 
 soluble in water, may be dissolved 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 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 8 or 9 per cent. — such in- 
 crease in weight being accompanied by a considerable in- 
 crease 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 expansion • such ex- 
 pansion, owing to the viscosity of the oil, takes place mainly 
 in a direction at right angles to that of the surface of the 
 glass. 
 
 (fr) 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 
 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. 
 
 (r) Waxes and solid paraffins, when once deposited from 
 a solution by the escape of the solvent, neither expand nor 
 contract. 
 
> 4 s 
 
 OIL-PAINTING 
 
 
 (d) Most of the liquid solvents simply evaporate, leaving 
 no fixed residue due to their previous presence. But oil 
 of turpentine (spirits or essence of turpentine) generally 
 behaves differently. Some kinds of oil of turpentine differ 
 from the majority in this particular, but the remainder suffer 
 two simultaneous 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 con- 
 stituent in the structure of a picture, and its production 
 should be avoided either by employing a variety of turpen- 
 tine 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 completion, 
 the earlier and lower paintings should contain less 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 hardening, 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 
 
OIL-PAINTING 
 
 249 
 
 injury from external agencies. They repel and exclude 
 moisture, and, in a measure, oxygen — two of the chief agents 
 of chemical change. 
 
 It should be noted that different oil-paints contain very 
 different percentages of oil, ranging from about 12 per cent, 
 in flake-white to 67 per cent, in aureolin as commonly pre- 
 pared. This fact should be taken into account, as 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 percentages of oil present 
 in a number of the oil-paints in common use will be found 
 on page 45. Further information concerning such pigments 
 is given in Chapters XIII. to XIX. 
 
 In completing an oil-picture, the three operations of 
 '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 afterwards 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 protection to the sur- 
 face, and becomes a part of the picture itself. Under no 
 circumstances should any varnish be applied to the painting 
 
250 
 
 SPIRIT-FRESCO 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 minimum. A further advan- 
 tage 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 treatment to which the work may 
 afterwards be submitted. 
 
 The chemistry of Gam bier-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 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 condi- 
 tions. He desired to exclude linseed or other fixed drying 
 oils completely from the medium and other materials em- 
 ployed. With this end in view, he directed that the pig- 
 ments 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, so that 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 desicca- 
 tion of the resin. The wax present suffers no chemical 
 
WATER-COLOUR PAINTING 
 
 251 
 
 alteration, but merely solidifies. It should be added that 
 the painting-ground for this method of working is first pre- 
 pared 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. 
 
 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 laevulose 
 (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 preserv- 
 ing the pigments in working condition, and in counteracting 
 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 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 pig- 
 ments (artificial 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. 
 
PA STEL-PA INTING 
 
 Assuming the paper-ground to be of linen pulp, and free 
 from ' filling,' from bleaching substances, from antichlors, 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 ap- 
 plied to the surface 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 imprac- 
 ticable. The size in a water-colour drawing becomes 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 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. This 
 
SILVER-POINT DRAWING 
 
 result is further aided by the plan of working in" and ming- 
 ling 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 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. One method of fixing the coloured 
 particles in the finished drawing is to give the back of the 
 paper a coat of isinglass solution. This solution is made 
 with i^ ounce of the best Russian isinglass dissolved in 
 i quart of boiling distilled water. The liquid is filtered hot ; 
 when it is cold its own volume of proof spirit is added. In 
 plumbago (lead-pencil) and silver-point work the mechanical 
 adhesion of the coloured particles is naturally less imperfect, 
 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 prominence 
 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 
 
254 
 
 PASTEL-PAINTING 
 
 • ' 
 
 metal, but may advantageously contain a few per cents, of 
 metallic lead ; an alloy of 2 parts of lead with 1 part of tin 
 was sometimes 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. 
 
 Pastel or coloured chalk drawings frequently show a 
 higher degree of preservation, so far as certain hues are 
 concerned, than contemporary works executed in oil. One 
 can easily account for the pure and fresh air of old pastel 
 drawings, knowing that they have been carefully mounted 
 and framed, and that there has been no oil or resin to 
 yellow and darken the pigments. But how can the remark- 
 able state of preservation in which the 'carnations' are 
 found in so many examples be explained ? Has the 
 intimate commixture of chalk 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 
 chalks has been thoroughly studied. 
 
 
 
 ' 
 
 - ? 
 
 vv 
 
 k 
 
 <f© 
 
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 employed, the pig- 
 ments which can be identified, and the varnish which has 
 been applied to the surface, all these matters demand atten- 
 tion. The dates of the various works examined, the coun- 
 tries 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 sub- 
 ject requires not a brief chapter, but a whole volume. And 
 then our materials, though in some directions most abun- 
 dant, 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 im- 
 portant 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 Gallery, the 
 National Portrait Gallery, and the South Kensington Museum ; 
 
256 
 
 CHANGES IN PICTURES 
 
 and our selection will be confined to paintings in oil, tem- 
 pera, 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 consequent 
 upon this convexity need 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 conspicuous 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 histological 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 ob- 
 served in old pictures are connected with the medium, the 
 pigments, 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 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, 
 
OLD PAINTINGS 
 
 257 
 
 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 prominence, namely, vermilion and ultra- 
 marine ; 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 notice- 
 able 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 vegetable pigments in considerable 
 variety, became more marked as time went on. And during 
 the last century and the present the progress of synthetical 
 chemistry has 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 
 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, and 
 
 17 
 
258 
 
 ACTION OF WHITE LEAD 
 
 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 intro- 
 duction 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 work are those in which flake-white 
 has been used with considerable freedom. Here the con- 
 tinuity 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 considerable quantity of lead hydrate. The par- 
 ticles of this hydrate do not lie, as it were, side by side with 
 those of the chief constituent (the lead carbonate), but are 
 so 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 lead-soap. 
 
 This substance seems to be formed in part out of the 
 free fatty acids of the linseed oil, in part out of the glycerides 
 present therein. It combines in an unusual degree tough- 
 ness and hardness ; and it is to the production of this lead- 
 
ACTION OF WHITE LEAD 
 
 259 
 
 soap that I attribute the preservation of the continuity of 
 surface 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 ' saponifying ' the admixed oil to 
 anything like the extent that characterizes white lead. Now 
 there are modern preparations of white lead made chiefly by 
 precipitation and the ' wet way,' which produces a pigment 
 containing little or no lead hydrate. Some writers on pig- 
 ments advocate the use of these newer pigments. ' Why,' 
 say they, 'should you carefully exclude from your pictures 
 oils, and varnishes, and siccatives which contain lead in the 
 form of a lead-soap, and then introduce the very same sub- 
 stance 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 actuated by a desire, based on theoreti- 
 cal 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 
 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. 
 
 17— 2 
 
26o 
 
 ILLUMINATED MANUSCRIPTS 
 
 No discolouration 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 discolouration 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 pre- 
 vent 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 
 from individual pictures, it may be desirable to make a few 
 observations on some of the changes frequently observable 
 in old illuminated manuscripts and choral books. The 
 tarnishing of lead and copper pigments laid on without any 
 protection but that of gum is very frequently seen. The 
 darkening of vermilion is apparently capricious,* but this 
 molecular change has been explained when describing that 
 pigment. Ultramarine always stands out absolutely intact ; 
 sometimes it acquires extraordinary prominence by reason 
 of every other pigment on a page having altered. The red 
 cochineal, and kermes lakes have either gone or become 
 
 * An initial letter in vermilion, painted in the fifteenth century, and 
 perfectly unchanged, became black by one year's exposure to sunshine. 
 
OLD PAINTINGS 
 
 261 
 
 paler and brownish. Sometimes fruits painted in vermilion 
 have been shaded or dotted with a crimson lake, but the 
 latter has disappeared, leaving nothing but a slight gummy 
 appearance upon the scarlet ground. Blue flowers painted 
 in smalt and veined with indigo show nothing but traces 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-griin (of the seven- 
 teenth 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 pro- 
 duction. We begin with some works in the National 
 Gallery. 
 
 Rogier van derWeyden (1400 ?-i464). No. 664. Painted 
 on linen, which has received a very thin priming ; the pre- 
 servation of the work, although it has never been varnished, 
 is practically perfect. From certain peculiarities in the 
 touch, and from the minutely-wrought details of the woody 
 landscape, I conclude that the medium used could scarcely 
 have been the usual tempera containing egg-yolk, but was 
 rather a thin size. 
 
 Melozzo da Forli (1438-1494). No. 755. It is probable 
 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. 
 
 Jan van Eyck ( t 390 ?- 1440). No. 186. The green robe 
 in this famous oil picture shows distinct cracks, which differ 
 in kind and are larger in size than any others in the work. 
 The flesh tints are perfectly preserved as to texture. I 
 
262 
 
 OLD PAINTINGS 
 
 suspect verdigris has formed a constituent of the green paint 
 employed. 
 
 Tuscan School. 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. 
 
 Fra Giovanni Angelico (1387-1455). No. 663. The 
 translucent reds and purples in this work have faded some- 
 what ; the green, which appears to be malachite, has stood. 
 On the whole this exquisite work in tempera is remarkably 
 well-preserved. 
 
 Bennozzo Gozzoli (1420-1498). No. 591. The vermilion 
 in this tempera picture is preserved in startling brilliancy ; 
 the translucent reds have become rather faded and em- 
 browned. 
 
 Ridolfo del Ghirlandaio (1483-1561). No. 1,142. This 
 oil picture, originally painted on wood, but now transferred 
 to canvas, has been repaired and repainted in 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 pigments are closely 
 related chemically to one another, and are not likely to 
 react. 
 
 Michelangelo Buonarroti (1475-1564). No. 790. This 
 unfinished tempera picture illustrates the permanence of 
 terre verte and madder-lake. 
 
 Gheeraert David (i45o?-i523). No. 1,045. The fine 
 crimson glazings and madder-lake in this oil picture are in 
 perfect preservation. 
 
 Gregorio Schiavone (fl. 1470). No. 630. The madder 
 
OLD PAINTINGS 
 
 263 
 
 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, now in the author's 
 possession. 
 
 . In the National Gallery there are eleven portraits in wax- 
 pigments from the Hawara Cemetery in the Fayum, Egypt. 
 Seven of these show the use of the Tyrian or Murex purple, 
 and prove that it has lasted apparently unchanged for some 
 seventeen centuries. But it must be remembered that these 
 remarkable paintings (Nos. 1,260 to 1,270) have been pre- 
 served in darkness since they were executed by Greek artists 
 in the second century, or in the first half of the third. It 
 has been conjectured that a pink colour occurring in some 
 of these pictures was derived from madder. The other 
 pigments were yellow, and red and brown ochre, charcoal 
 black, a blue made from cupreous glass, and, possibly, red 
 lead. The pigments, incorporated with wax, were laid on, 
 in a fused condition, upon a distemper priming. 
 
 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. 534, 'Chichester,' the bright lake-reds 
 in the sky have become reduced to brown stains — anything 
 but luminous. In No. 560, the 'Approach to Venice,' 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. 
 
264 
 
 OLD PAINTINGS 
 
 We may now pass on to some instructive examples pre- 
 served in the National Portrait Gallery : 
 
 Marc Gheeraedts (1561-1635). No. 64. In this por- 
 trait, 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 (16 1 7-1 680). 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 pro- 
 bably painted about 1669. 
 
 William Hogarth (1 697-1 764). No. 289. This por- 
 trait of Hogarth, painted in 1758 by himself, affords some 
 information 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 Naples 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 blue verditer. The cap on the 
 artist's head has certainly faded in colour ; probably it was 
 painted with lake. 
 
 William Hoare, R.A. (1 706-1 792). No. 112. This por- 
 trait of Alexander Pope, in coloured crayons on grey paper, 
 shows the blues apparently intact. 
 
WATER-COLOUR DRAWINGS 
 
 26: 
 
 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 pro- 
 portion of white lead present has been large. 
 
 The remaining works to which attention is now called 
 are a few of the water-colour drawings shown in the South 
 Kensington Museum, 
 
 William Daniell, R.A. (1769-1837). In one of the water- 
 colours by this artist the blue and green elements have dis- 
 appeared, 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 (1775-1837). No. 1,358, 1874. In 
 this fruit and flower piece the indigo in the sky has gone, 
 while the yellow pigments and the red lakes have suffered 
 greatly ; the roses are blanched, and the purple grapes have 
 lost their crimson element. 
 
266 
 
 WATER-COLOUR DRAWINGS 
 
 John James Chalon, R.A. (1778-1854). No. 570. The 
 ' River Scene in Devonshire,' painted in 1808, shows the 
 shaded parts of the clouds pink, from the loss of indigo. 
 The hills are now too pale for the trees dotted upon them, 
 through the fading of sap-green and gamboge, which have 
 been used in painting the grass. The shadows under the 
 ripples of the water have greatly altered, from the change of 
 indigo and other pigments; they still show dirty stains and 
 elaborate brushwork. 
 
 Francis Danby, A.R.A. (1793-1861). No. 480. The 
 Prussian blue in the sky unchanged, but the pigments which 
 once modified its hue have fled. 
 
 John Varley (1 778-1842). 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 change of crimson 
 lake. 
 
 Samuel Prout (1783-1852). 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 har- 
 mony with the architectural features, some of the pigments 
 in which must have faded. These drawings should be com- 
 pared with others by the same artist which hang beside 
 them, and in which the blues of the sky, as well as some 
 of the pigments in other parts, have faded. Here it may be 
 convenient to remark upon the startling prominence 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 
 
WATER-COLOUR DRAWINGS 
 
 267 
 
 ultramarine and cobalt blue, the latter pigment being, of 
 course, of comparatively recent introduction. 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 hawthorn-blossom in 1,470, 
 1 869, has lost the faint rosy blush that was once visible in 
 some of the flowers. 
 
 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. 
 
I 
 
 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 ap- 
 proximate darkness, the lead-whites may tarnish, and the 
 oil and resins darken. Even with the most moderate illumi- 
 nation, however, the more fugitive pigments, 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 con- 
 structed 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 incande- 
 scence 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 pig- 
 ments. But the light by which pictures are to be seen is 
 
CONSERVATION OF PICTURES 
 
 269 
 
 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 con- 
 sequence, too great rigidity in the system of fixing adopted 
 should be avoided. Blocks of indiarubber (not vulcanized), 
 duly secured in the rebate, afford a convenient means of 
 obtaining the necessary freedom of movement, while pre- 
 venting 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 must be 
 taken that it is sufficiently dry not to deposit water upon the 
 picture. For the purpose of regulating the hygroscopic con- 
 
270 
 
 CONSERVATION OF PICTURES 
 
 dition of the atmosphere in a picture-gallery, the introduc- 
 tion 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 recog- 
 nised. A strip of drawing-paper, another of primed canvas, 
 and another of mahogany, all three being in a normal hygro- 
 scopic 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 they are attached remains prac- 
 tically true, the air may be regarded as in a satisfactory 
 hygroscopic condition. Three pairs of ordinary apothecaries' 
 scales (or spring-balances) suffice for the construction of this 
 apparatus, which should be protected by a glass case to which 
 the air has free access. This question of the due amount 
 of moisture in the air — neither in excess nor in defect — has 
 scarcely received the attention 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, suc- 
 ceeded 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 objec- 
 tions 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 back of pictures, especially of those 
 painted on canvas, is often forgotten, 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 
 
FRAMING AND MOUNTING PICTURES 
 
 271 
 
 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 the solution 
 of indiarubber used by book-binders, and this 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. To hermetically seal a 
 framed drawing, to the entire exclusion of all moisture and 
 all air, is not possible. That under such conditions nearly 
 every pigment would be unalterable has been long known. 
 We should add to these observations 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. 
 
272 
 
 PRESERVATION OF DRAWINGS 
 
 The plan of preserving the water-colour drawings of 
 Turner, devised by Professor Ruskin, may be mentioned 
 fitly here. It was described in a letter to the editor of the 
 Iwies (October 28th, 1856). The recommendation is to 
 enclose each work in a light wooden frame, under a glass, 
 the interior surface of which is prevented 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 keep- 
 ing of such works, in their unframed state, in portfolios. 
 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 reference to such 
 exposure in a letter to the Literary Gazette (November 13th, 
 1858), in which he says that ' the officers of both the Louvre 
 and of the British Museum, refuse to expose their best 
 drawings or missal-pages to light, in consequence of ascer- 
 tained 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 
 
PRESERVATION OF DRAWINGS 
 
 273 
 
 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 nurserymaids ; 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 waste-paper 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 
 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 statements 
 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 modifying the light that 
 illuminates our pictures as to remove from it certain par- 
 ticularly active beams, we might considerably augment the 
 list of permanent pigments. Experiments on a small scale 
 prove that several fluorescent substances, such as a solution 
 
 t8 
 
274 
 
 LIGHTING OF PICTURE GALLERIES 
 
 of quinine sulphate, while intercepting dangerous rays, do 
 not sensibly modify the colour of the light, and yet lessen 
 its chemical activity. Possibly a transparent screen of this 
 character will some day be used for our picture galleries. 
 But the further discussion of this subject will be found in 
 the next chapter, and to this I would refer my readers. 
 
 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 excluded. Gas, before 
 and after burning, is bad for pictures. The evil effects of 
 an occasional escape of unburnt gas are less to be dreaded 
 than those caused by the products of gaseous combustion. 
 These products are sulphuric 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 
 products 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. 
 
AIR IN PICTURE GALLERIES 
 
 275 
 
 With respect to the building itself in which pictures are to 
 be kept, our aim should be to secure as far as possible 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 eleva- 
 tion above the ground-level, and double walls enclosing an 
 air-space, are desirable, as conducing to uniformity of 
 temperature, and preventing the condensation 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 independent source. The place of 
 intake 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 off and 
 intercepted by passing the air through a layer of loosely 
 packed carded cotton — 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 distemper paint containing 
 white lead, this absorption of impurities goes on continually. 
 For these impurities are more readily absorbed by a pro- 
 perly-prepared distemper than by the changeable pigments 
 in the pictures. To secure this result the distemper should 
 
 18—2 
 
276 
 
 RESTORATION OF PICTURES 
 
 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 
 status quo ante. The operations involved should never be 
 undertaken by the inexperienced amateur. And picture- 
 restorers themselves are too often artists who have mis- 
 taken their profession, or who have been imperfectly trained. 
 Many possess no power or appreciation of accurate draughts- 
 manship. 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 surface. Then the pigments they use are too often 
 unsafe, and their vehicles unsatisfactory ; so both soon alter. 
 At the same time, the skill of some restorers in the matter 
 of mechanical repairs — parquetting, transferring, relining, etc. 
 — cannot be too highly extolled. 
 
 Several manuals of directions for restoring pictures have 
 been given to the world ; they are of very unequal value. 
 Some of these tell you nothing, for they are intended merely 
 to advertise the skill of the writers. Others advocate a 
 treatment which may be called heroic, giving you solvents, 
 not only for the discoloured varnish, but for glazings and 
 paints. In reality, no directions can replace experience and 
 skill. M. von Pettenkofer's method is one of the best 
 known, but it is very rarely applicable with safety and 
 
RESTORATION OF PICTURES 
 
 277 
 
 success. The object of this method is the renewal of the 
 transparency and continuity of the varnish by a process of 
 re-solution in situ. With this intention, the picture is 
 exposed in a closed shallow box to the action of the vapour 
 evolved from moderately strong spirits of wine. This vapour 
 dissolves the mastic on the surface of the picture, forming 
 once more a spirit-mastic varnish. This, on exposure to 
 the air, hardens, and leaves a shining coat of resin. But 
 this resin, being necessarily discoloured and sinking into the 
 cracks of the paint, makes them more prominent, while 
 there is great danger of its being unequally distributed over 
 the surface of the work. 
 
 When the varnish of an old picture is practically intact, 
 but the surface is begrimed with soot and dirt, it should not 
 be cleansed by the direct application of water, much less by 
 the use of a solution of soap ; but a loaf of household 
 bread, not more than a day old, should be taken, and its 
 crumb broken up into a tin canister furnished with a lid; 
 it is important that no pieces of crust, and no fragments of 
 crumb which have become hard by drying, should be intro- 
 duced. Then the crumbs should be shaken out, in portions 
 at a time, from the canister on to the varnished surface, and 
 rolled gently thereon by means of the fingers. By repeating 
 this operation until fresh crumbs no longer become dis- 
 coloured, it is often possible to improve the appearance of a 
 picture very greatly. In any case, it affords a useful pre- 
 liminary to the removal of the old varnish where such a 
 further step is imperatively required. Such removal is 
 effected by the mechanical process of chafing. A single 
 tear of pure mastic resin is ground or crushed to fine 
 powder, and placed upon some unimportant part of the 
 surface of the picture ; but the operation may be begun 
 without the aid of the mastic-powder. A gentle rotatory 
 
278 
 
 REMOVAL OF VARNISH 
 
 movement of the ends of the fingers soon reduces the old 
 varnish-layer to powder, which is then removed by means 
 of a soft badger-hair brush, or other suitable means. The 
 work should be performed in a good light, and great care 
 must be taken not to injure any tender glazings belonging 
 to the painting itself. To ascertain whether the removal of 
 the varnish has been carried far enough, the parts treated 
 may be moistened with distilled water applied on a plug of 
 carded cotton. When the operation is complete, and the 
 surface is quite dry, a new coat of mastic-varnish may be 
 applied, if possible in an artificially dried atmosphere. 
 Sometimes a little dragon's blood, or other warm-coloured 
 resin, is added to the mastic-varnish, in order to prevent the 
 cold and raw look which a picture which has lost its old 
 toned varnish frequently presents. An oil-painting in which 
 no megilp has been used, and which has received, a year 
 after completion, a thin 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 
 process just described. And, even under less favourable 
 conditions, it is the only method which can be recommended 
 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 conspicuously 
 evident on the surface. To these remarks on the chafing 
 process, we may add that it is sometimes advisable 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 
 
RESTORATION OF PICTURES 
 
 279 
 
 water. It is applied by means of plugs of carded cotton, 
 the action of the solvent being arrested, when necessary, by 
 instantly moistening the spot with spirits of turpentine on 
 another plug, 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 treatment 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 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 solvents are acetone, 
 benzene, chloroform, and solutions of caustic alkalies. Great 
 risk of injury attends their employment — indeed, the appli- 
 cation 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 neigh- 
 bouring parts of the picture ; oil-colours must be used. In 
 
2SO 
 
 RESTORATION OF PICTURES 
 
 any necessary replacements of lost colours in old oil-paint- 
 ings, 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 progress of the 
 work, by no means an easy thing to manage. When in any 
 kind of re-painting oil-paints are used, they should be mixed 
 stiffly with a very little copal-varnish and spirits 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. 
 
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 experi- 
 ments of another order. The study of old paintings often 
 furnishes us with results of some value, the results of unin- 
 tentional testings. But for the purpose of securing com- 
 plete 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 materials and conditions are wholly wanting ; 
 even the South Kensington report affords us no information 
 as to the composition of the pigments employed, nothing 
 
 * 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. 
 
282 
 
 TRIALS OF PIGMENTS 
 
 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 unprece- 
 dented, care was taken in order to determine the conditions, 
 physical and chemical, under which the pigments 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 pigments, 
 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 with- 
 out 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 concern- 
 ing the purity and genuineness of the pigments with which 
 the experiments have been made. I have not been 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 Captain Abney, 
 
TRIALS OF PIGMENTS 
 
 283 
 
 who have likewise furnished some particulars 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 concerning the nature 
 of many of the pigments he tried is too imperfect to be of 
 any use ; secondly, we are not acquainted with the condi- 
 tions 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 embrowning of the surface are general, 
 and though the names of the pigments employed are often 
 undecipherable or meaningless, yet something useful re- 
 mains. From the experiments made in 1772 we may gather 
 the following facts. The proper hues of several pigments 
 remain in a measure : orpiment. or king's yellow in crystals ; 
 yellow lake, with wax and drying oil ; gamboge, with lake 
 and Venice turpentine ; gamboge, with (Venice) turpentine : 
 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 
 discolourations. 
 
 M. J. Blockz, in his ' Peinture a l'Huile,' gives the 
 results of a number of experiments made by M. J. Dyck- 
 man. He condemns, for various reasons, not only asphalt, 
 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 unneces- 
 
284 
 
 Mi?. ANDREW'S EXPERIMENTS 
 
 sarily extended, not being justified, in all particulars, by 
 further and more careful experiments. 
 
 The experiments of Mr. F. W. Andrew, of the South 
 Kensington 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 III., 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, and orange chrome 
 showed dark patches. Further details must be given as to 
 the pigments which were affected. In the tabular state- 
 ments 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 employ- 
 ment of cake or moist 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. The 
 tintometer of Mr. J. W. Lovibond, of Salisbury, may be 
 employed with advantage in these estimations. 
 

 
 
 
 
 
 
 TRIALS OF 
 
 WATER-COLOURS 285 
 
 
 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. 
 
 
 - - 62 
 
 - 
 
 - - 10 
 
 [yellow- 
 
 M. 
 
 
 - - 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 
 
 - 
 
 - - 
 
 
 C. 
 
 Yellow madder 
 
 - - 28 
 
 - 
 
 - - 1 
 
 
 M. 
 
 Yellow madder 
 
 - - 28 
 
 - 
 
 - - 3 ■ " 
 
 Pinkish grey. 
 
 M. 
 
 Yellow madder 
 
 - - 62 
 
 - 
 
 - - 1 
 
 
 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 
 
 - 
 
 . . 1 . . 
 
 Pale buff. 
 
 M. 
 
 Vermilion - - 
 
 - - 62 
 
 - 
 
 . . — . . 
 
 Blackish. 
 
 M. 
 
 Vermilion - - 
 
 - - 82 
 
 - 
 
 . . — . . 
 
 Black. 
 
 M. 
 
 Carmine - - - 
 
 - - 28 
 
 - 
 
 - - - - 
 
 Pale grey. 
 
 M. 
 
 Crimson lake - 
 
 - - 28 
 
 - 
 
 . . - - 
 
 Greenish grey. 
 
 M. 
 
 Burnt carmine - 
 
 - - 28 
 
 - 
 
 . . 1 - . 
 
 »> 
 
 C. 
 
 Pink madder - 
 
 - - 28 
 
 - 
 
 - - 1 
 
 
 M. 
 
 Rose madder - 
 
 - - 28 
 
 - 
 
 " " 3 
 
 
 M. 
 
 Rose madder - 
 
 - - 62 
 
 
 . . 1 . . 
 
 Pinkish grey. 
 
 M. 
 
 Rose madder - 
 
 - - 82 
 
 - 
 
 . . 1 . . 
 
 " 
 
 M. 
 
 Madder carmine 
 
 - - 62 
 
 - 
 
 - - 2 
 
 
 M. 
 
 Madder carmine 
 
 - - 82 
 
 - 
 
 - - 
 
 
 M. 
 
 Purple madder - 
 
 - - 28 
 
 - 
 
 - - 4 - - 
 
 A pale wash. 
 
 M. 
 
 Purple madder - 
 
 - - 62 
 
 - 
 
 - - 7 
 
 
 M. 
 
 Purple madder - 
 
 - - 82 
 
 - 
 
 - - 2 
 
 
 C. 
 
 Brown madder - 
 
 - - 28 
 
 - 
 
 . . 1 . . 
 
 Warm grey. 
 
 M. 
 
 Brown madder - 
 
 - - 28 
 
 
 . . 1 . . 
 
 jj 
 
 M. 
 
 Brown madder - 
 
 - - 82 
 
 - 
 
 - - 
 
 
 C. 
 
 Indigo - - - 
 
 - - 28 
 
 - 
 
 - - 5 - - 
 
 Greenish grey. 
 
 M. 
 
 Indigo - - - 
 
 - - 62 
 
 - 
 
 - - 1 
 
 
 M. 
 
 Raw umber - - 
 
 - - 60 
 
 - 
 
 - - 9 - - 
 
 Rather yellower. 
 
 M. 
 
 Vandyke brown 
 
 - - 28 
 
 - 
 
 - ■ 7 
 
 
 M. 
 
 Vandyke brown 
 
 - - 60 
 
 - 
 
 - - 1 
 
 
 M. 
 
 Bone brown 
 
 - ■ &2 
 
 
 - - 8 
 
 
2S6 
 
 MADDER VERSUS COCHINEAL 
 
 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 : 
 
 Name of 
 Pigment 
 Rose madder - 
 
 2. Madder carmine 
 
 3. Madder carmine 
 
 1. 
 
 Madder red 
 Purple madder 
 
 Residual Depth 
 {Original^ 10) 
 - - 8 - - 
 
 6. Brown madder 
 
 Change of Hue, etc. 
 
 Slightly more purplish. 
 
 Almost unchanged. 
 
 Much more purplish. This sample 
 
 was from another source. 
 Less red, more purplish. 
 Duller, less red, more blue. 
 Less red, more yellow-brown. 
 
 In contrast to the above results with madder carmine, the 
 following experiment with the ordinary carmine (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, how- 
 ever, protected completely from all access of light. The 
 exposure of 100 hours sufficed to bleach the last breadth 
 
PROFESSOR ROOD'S EXPERIMENTS 
 
 287 
 
 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 2 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 re- 
 sults 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. 
 
 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 
 of Pigment 
 
 1. Chrome yellow ■ 
 
 2. Red lead 
 
 3. Naples yellow 
 
 4. Raw sienna - 
 
 5. Vermilion 
 
 6. Aureolin - - 
 
 7. Indian yellow 
 
 8. Antwerp blue 
 
 9. Emerald green 
 
 10. Rose madder 
 
 11. Sepia - - - 
 
 12. Prussian blue 
 
 Nature 
 of Change 
 Slightly greenish. 
 Less orange. 
 
 Slightly greenish 
 
 brown. 
 Fades, yellower. 
 Darkens, brownish. 
 Fades slightly. 
 Fades slightly. 
 Fades slightly. 
 Fades slightly. 
 Fades slightly, 
 
 purplish. 
 Fades slightly. 
 Fades somewhat. 
 
 Name 
 of Pigment 
 
 13. Hooker's green - 
 
 14. Gamboge - - - 
 
 15. Bistre ■ ■ ■ ■ 
 
 16. Brown madder - 
 
 17. Neutral tint - - 
 
 18. Vandyke brown - 
 
 19. Indigo- - - - 
 
 20. Brown pink - - 
 
 21. Violet carmine - 
 
 22. Yellow lake - - 
 
 23. Crimson lake 
 
 24. Carmine - - - 
 
 Nature 
 of Change 
 
 More bluish. 
 
 Fades, greyish. 
 
 Fades, greyish. 
 
 Fades. 
 
 Fades. 
 
 Fades, greyer. 
 
 Fades. 
 
 Fades greatly. 
 
 Fades greatly, 
 brownish. 
 
 Fades greatly, 
 brownish. 
 
 Fades out. 
 
 Fades out. 
 
288 
 
 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 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. 
 
 Professor W. N. Hartley's Experiments. — On September 
 4, 1886, Professor Hartley read, before the British Associa- 
 tion at Birmingham, a paper on 'The Fading of Water 
 Colours.' His trials as to the effect on pigments of a com- 
 paratively brief exposure to intermittent sunshine in pure air, 
 may be thus summarized. Washes on the best drawing- 
 paper were the subject of the experiment : 
 
 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 crim- 
 son tones to become very much lighter, the hue of the pig- 
 ment 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 becoming 
 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. 
 
PROFESSOR HARTLEY'S EXPERIMENTS 
 
 289 
 
 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' ex- 
 posure—somewhat more so, indeed, than was the case when 
 these pigments were freely exposed to the air. 
 
 All the results above noted are in practical accord with 
 those obtained by other observers. The exposure to inter- 
 mittent sunshine ' for six hours a day during fourteen days,' 
 does not produce a sensible effect upon vermilion and in- 
 digo. Had Professor Hartley extended his observations 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 ' (Brit. Assoc. 
 Report, 1886, p. 581) must, therefore, be modified into, 
 ' indigo appears to have suffered no change after fourteen 
 days' exposure to intermittent sunshine.' A similar alteration 
 is demanded with regard to the stability of vermilion. 
 
 Professor 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 cer- 
 tainly 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, 
 
 19 
 
290 
 
 PROFESSOR HARTLEY'S EXPERIMENTS 
 
 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 
 vacuous tube), the suspension of fading and alteration of 
 hue is still more marked and general. 
 
 It should be added here that Professor 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 been 
 associated. These blue pigments could have been nothing 
 other than Prussian blue, indigo, or natural ultramarine. 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 sul- 
 phates) to destroy its colour. The products 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 
 Professor Hartley's statement that the best drawing-papers 
 have an acid reaction. The results of numerous trials of all 
 kinds of drawing-papers, good and bad, have been already 
 given in Chapter I., and so a mere reference to the facts, 
 as derived from my own observations, must here suffice. I 
 
MR. W. SIMPSON'S EXPERIMENTS 291 
 
 find that these sized papers are generally perfectly neutral to 
 test-papers, and that inferior papers are more often slightly 
 alkaline than acid. 
 
 Mr. W. Simpson's Experiments. — Some washes of water- 
 colour, of thirty-one different kinds, were made upon cards 
 by Mr. W. Simpson. He so cut the cards as to divide each 
 coloured strip in half ; one section was preserved in dark- 
 ness, 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 Nature Name Nature 
 
 of Pigment of Change of Pigment of Change 
 
 Yellow ochre - - None. Madder lake - - More purplish. 
 
 Indian yellow - - Faded consider- | Purple madder - - Hue altered. 
 
 ably. , "Brown madder - - Loss of redness. 
 
 Lemon yellow - - None perceptible. Emerald green - - Slight. 
 
 ' Newman's perma- Cyanine blue - - Apparently none. 
 
 nent yellow ' - - None. ; ''Prussian blue - - None. 
 
 Cadmium yellow - Perhaps browner. ; French blue - - - Faded very slightly. 
 
 Chrome yellow - - Faded consider- ' Cobalt None. 
 
 ably. I Ultramarine - - - None. 
 
 Brown pink - - - Faded. ■ Indigo, rather deep Very pale grey. 
 
 *Vermilion - - - None. | Burnt sienna - - None. 
 
 Light red - - - - None. ! *Vandyke brown - None. 
 
 Indian red - - - None. "Sepia ----- Fadedveryslightly. 
 
 Crimson lake - - Gone. I *BLstre None. 
 
 Carmine - - - - Gone. ' 
 
 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 change- 
 able 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 explanation. The madder pigments seem 
 
 19 — -2 
 
292 
 
 TRIALS OF PIGMENTS 
 
 I 
 
 
 to have stood more than usually well, but they often exhibit 
 large differences 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 intermittent and capri- 
 cious sunshine of the Metropolis never fell on the trial cards 
 after ten a.m. 
 
 Mr. R. H. Soden-Smith, of the South Kensington Museum, 
 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 181 5 
 of Newman, in Soho Square. This set is peculiarly interest- 
 ing 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 
 present century. The cakes are : Indian yellow, raw sienna, 
 raw umber, burnt sienna, burnt umber, vermilion, carmine, 
 burnt carmine, pink 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 sun- 
 shine, 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 seventy-five years ago a degree of 
 permanence greater than that possessed by their representa- 
 tives of to-day. 
 
SOUTH KENSINGTON REPORT 
 
 293 
 
 By far the most important series of trials of water-colour 
 paints yet published is that to be found in the report by 
 Dr. Russell and Captain Abney to the Science and Art 
 Department (1888). The reporters endeavoured to give pre- 
 cision to their experiments and their conclusions by a careful 
 comparison of the effective radiation from different sources 
 of light. The first part of their report is in part occupied 
 by a 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 exposure 
 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 outside the Museum. 
 Part II. of the report contains the results of twelve sets of 
 experiments with various pigments. In all the series the 
 same paper (Whatman's) was used. In the paragraph re- 
 lating to this subject there is, however, one curious error, 
 and one obscure statement (page 27). It is quite impossible 
 that the paper used — its weight per ream is not given — 
 could have contained so little as nearly 1 grain of sizing 
 matter per square foot; 10 grains is a more probable quan- 
 tity. The next following sentences do not state the condition 
 of the papers which absorbed from a moist atmosphere from 
 12*07 t0 1 2 "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 
 
 (<) 
 
 
 t£ 
 
294 
 
 SOUTH KENSINGTON REPORT 
 
 
 exposed in tubes open at both ends, but having the upper 
 extremity 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 lasting from May, 1886, until March, 
 1888. The pigments are arranged in the order of insta- 
 bility, the most fugitive being placed first : 
 
 *Carmine. 
 *Crimson lake. 
 *Purple madder. 
 *Scarlet lake. 
 *Payne's grey. 
 *Naples yellow. 
 *OHve green. 
 *Indigo. 
 *Brown madder. 
 *Garnboge. 
 •Vandvke 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. 
 
 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 pre- 
 viously heated ; the specimens were then sealed up hermeti- 
 cally : as no moisture-absorbing material was enclosed with 
 
SOUTH KENSINGTON REPORT 
 
 295 
 
 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 Captain 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 
 wholly or partly of organic origin, while the seventh contains 
 an acetate. 
 
 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 pig- 
 ments 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 
 
296 
 
 SOUTH KENSINGTON REPORT 
 
 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 admixture 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 
 circumstances in which pictures are kept. The frame was 
 exposed from August 6, 1886, until May 6, 1888, to very 
 bright light, but not to sunshine. Gamboge, indigo, 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 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 under 
 varied conditions of exposure, we must refer our readers to 
 the report itself. It may, however, be remarked 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 elsewhere 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 distinguished 
 
SOUTH KENSINGTON REPORT 
 
 297 
 
 artists using water-colours. Forty-six painters replied to the 
 invitation of the Science and Art Department ; 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 17 out the 46 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 certain colours as to the stability 
 of which there is no question. The following tabular state- 
 ment gives the proportion of artists, per 100, who use the 
 eleven perishable 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 - - 
 
 - 11 - 
 
 - Faded to 7. 
 
 Vandyke brown - 
 
 - 74 - 
 
 Gone. 
 
 Sepia - - - - 
 
 - 65 - 
 
 - Faded to 8. 
 
 
 - 52 - 
 
 - Faded to 8. 
 
 w 
 
 1 represents the 
 lightest tint, 8 the 
 darkest. The washes 
 of pigment were fully 
 exposed for twenty- 
 two 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 
 
298 
 
 SOUTH KENSINGTON REPORT 
 
 I 
 
 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, 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 Captain 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 
 works 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 
 
 * In the preceding brief resume of certain parts of the South Ken- 
 sington 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, 1 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. 
 
EXPERIMENTS WITH OIL-PAINTS 
 
 299 
 
 been proved by the reporters themselves to suffer ' marked 
 deterioration ; by an exposure of twenty-two months only 
 to strong daylight without direct sunshine. Moreover, it 
 must not be forgotten that the fading of a single important 
 pigment in a water-colour drawing is ruinous to the whole 
 effect, destroying the balance of the chromatic scheme of 
 the artist more effectually than a slight, but equal, degrada- 
 tion of all the hues. 
 
 Amongst the series of trials of oil-paints made by the 
 author of this handbook, one set first arranged in 1880 may 
 be described here. Chance's colourless plate-glass was 
 employed as the painting-ground, so as to avoid all interfer- 
 ence 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 complete series was pre- 
 pared in duplicate — one for preservation 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 Dussel- 
 dorf). Specimens of each pigment were reserved for further 
 examination and analysis. Some of the chief results obtained 
 are given in the annexed table; some remarks on the changes 
 observed in some of the pigments which had been mixed 
 with flake white are added : 
 
 Pigment 
 
 Years of 
 
 Exposure 
 
 Residual Change of Hue, 
 Depth and Remarks 
 
 (Original^ 10) 
 
 Yellow ochre 
 
 ■ - 5 
 
 - 
 
 - - 10 - Browner ; more translucent 
 
 Auieolin 
 
 - - - 5 
 
 - 
 
 - - 9 - None. 
 
 Indian yellow 
 
 - - 5 
 
 
 - - 8 - Slightly hrownish. 
 
 Naples yellow 
 
 (true) - 5 
 
 
 - - 10 - None. 
 
LIGHT AND WATER-COLOURS 
 
 D - , Years of 
 
 Pigment „ , J 
 
 ° hxposure 
 
 Pale yellow madder - 2 - 
 
 Residual Change of Hue, 
 Depth and Remarks 
 
 (Original= 10) 
 
 - - 7 - Greyish salmon when mixed 
 with flake white. 
 
 Deep yellow madder 
 
 2 - 
 
 - - 6 - 
 
 Dirty pink when mixed with 
 flake white. 
 
 Laque Bran 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. 
 
 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 - - - 
 
 Indigo 
 
 Artificial ultramarine 
 
 5 - 
 5 - 
 
 5 - 
 
 - - 8-5- 
 
 - - 8 - 
 
 - - 10 - 
 
 Slightly greener. 
 Slightly greener. 
 None. 
 
 I devote the few pages remaining at my disposal to a 
 subject connected very intimately, not only with trials of 
 pigments, but also with the conservation of paintings. A 
 long and somewhat acrimonious discussion as to the effect 
 of light upon water-colour drawings was commenced by Mr. 
 (now Sir) J. C. Robinson by a letter which appeared in the 
 Times of March 11, 1886. The writer affirmed, with regard 
 to the collection of English water-colour drawings at the 
 South Kensington Museum, that, having ' been continuously 
 exhibited in the full daylight for twenty or thirty years past, 
 by the mere fact of such exposure all these drawings have 
 been more or less irrevocably injured, and that, in many 
 cases, the specimens are now, as it were, but the pale ghosts 
 of their former selves. These treasures, then, have sufficed 
 for the delectation of one generation only, and we ourselves 
 have practically used them up.' Mr. Robinson adds his 
 recommendation that all water-colour drawings which ought 
 
LIGHT AND WATER-COLOURS 
 
 3 QI 
 
 to be fully and freely shown to the public, should be so 
 shown only in the evening, and by the aid of the electric 
 light. 
 
 To this letter Sir J. D. Linton replied in the Times of 
 March 18th, traversing the statement with regard to the 
 condition of the South Kensington drawings, and affirming 
 that both the older tinted works, and those painted in ' pure 
 colour' are slightly lowered in tone, but in other respects 
 very little changed. Moreover, he cites one drawing by 
 Turner (' Wark worth Castle,' No. 547), and the drawings 
 by W. Havell, as ' absolutely richer and deeper in tone than 
 when they were first painted.' He adds that the modern 
 work, such as the ' Hawthorn Blossom ' and two other 
 drawings by William H. Hunt, is 'as brilliant' as on the 
 day when painted : he speaks similarly of the ' Nottingham ' 
 by De Wint, the ' Windsor Castle ' and ' Windermere,' by 
 David Cox, and of all the drawings by Cattermole. Sir J. 
 D. Linton considers that Mr. Robinson has fallen ' into the 
 common error of confusing the so-called fading of colour by 
 the action of light with the chemical changes chiefly caused 
 by the unfortunate use of injudicious colours, particularly of 
 Indian red, which in the skies of some of the drawings of 
 the masters has had a deleterious effect.' He concludes by 
 saying that he writes in order ' to combat the popular idea 
 that water-colours fade by the action of light.' 
 
 The third contribution to the discussion was furnished by 
 the author of the present volume (the Times, March 26). 
 In it examples of drawings illustrative of the fading of indigo, 
 and of the various cochineal pigments, were cited, while it 
 was pointed out that many of the South Kensington draw- 
 ings had changed for the worse long before their exhibition 
 in the museum. The effects of direct sunshine, of diffused 
 daylight, of gas and of hygroscopic moisture were named. 
 
LIGHT AND WATER-COLOURS 
 
 
 The use of a selected, restricted and perfectly safe, yet 
 adequate palette was recommended. Finally, the real cause 
 of the ' hot ' appearance of skies and clouds represented by 
 mixtures of indigo and iron-reds was explained. 
 
 Mr. Robinson returns to the charge (on March 26), ex- 
 panding and reiterating his first statements. Then Sir J. D. 
 Linton (April 3) once more combats Mr. Robinson's views, 
 conceding, however, that changes have taken place in some 
 of the earlier works by Girtin, Barret, De Wint, Havell, and 
 others from ' exposure to damp, smoke, and direct sunlight, 
 but chiefly from the use of Indian red,' these changes being 
 stated to have occurred prior to the acquisition of the 
 drawings by the museum. Sir J. D. Linton concludes by 
 denying that he had spoken of chemical changes caused by 
 the use of Indian red. [These, however, were his words, 
 see ante, p. 301.] 
 
 The communications which appeared in the Times of 
 April 3 and 14, from the pens of Mr. W. Severn, Mr. G. C. 
 Bentinck, an Artist, and Mr. Ruskin, do not demand notice 
 in this place. The present writer's second letter (April 14) 
 described the chief changes in washes of pigments as due to 
 the combined influence of moisture, oxygen and light, and 
 referred to several other related topics, which will be found 
 fully discussed in the present volume. Other contributions 
 to the controversy, by Mr. Frank Dillon, Mr. Ayscough 
 Fawkes, 'F.R.C.S.,' and by the two disputants who opened 
 the debate, will be found in the Times of April 14, 20, 28, 
 and June 11 and 14. 
 
 After a lull of some weeks the above-described discussion 
 was resumed in the Times of July 16. A letter from Mr. 
 Robinson appeared ; in this the protection from fading 
 afforded to crimson lake by a vacuum, or by the sifting of 
 solar rays by means of a screen of crimson glass were 
 
LIGHT AND WATER-COLOURS 
 
 30j 
 
 mentioned. The notorious and free use of this pigment by 
 many water-colour painters of the first half of this century 
 was commented on in connection with the observation that 
 three days' sunshine sufficed to take out all the colour from 
 a washed tint of this crimson lake. A letter from (the late) 
 Dr. Percy to Mr. Robinson, printed with the above-named 
 communication, states the important fact that while greys 
 made with indigo and Indian red have been preserved 
 unchanged for fifty-seven years in the dark, the indigo in the 
 same association has wholly disappeared in other instances 
 where drawings have been long exposed to solar light. Dr. 
 Percy drew attention to the curious purple tint which some 
 plate-glass containing manganese acquires by exposure to 
 sunlight, citing this change as evidence of chemical altera- 
 tion in a hard, solid and compact body. 
 
 On July 24 Colonel Donnelly announced the appointment 
 of a committee consisting of eight artists and the keeper of 
 the prints in the British Museum, to consider the question 
 of the action of light on paintings in water-colours. Mr. 
 Robinson criticised the composition of this committee in 
 the Times of July 28, and observed that measures had at 
 last been taken to shield the South Kensington water-colours 
 from the direct sunlight which was wont to impinge upon 
 them. Colonel Donnelly rejoined ' that the measures now r 
 taken to protect the pictures from the direct action of 
 sunlight are precisely the same as have been employed for 
 many years past.' Here I may interpose the remark, that 
 the constant use of the skylight blinds during sunshine, not 
 the existence of these protecting screens, had been called in 
 question. 
 
 Mr. Ruskin's strongly expressed views on the proper 
 method of securing water-colour drawings from the injurious 
 effects of light, and of other hostile influences, are quoted by 
 
3°4 
 
 LIGHT AND WATER-COLOURS 
 
 Mr. Robinson in his letter, published in The Times of 
 August 4. The passages cited are from the first volume of 
 'Arrows of the Chase,' pp. 129, 130, 149. The discussion 
 was continued in The Times of August 10, where letters by 
 Messrs. E. A. Goodall, F. Dillon, L. Fagan, J. C. Robinson, 
 and James Orrock, appeared. Again, on the nth, when 
 Colonel Donnelly once more denied Mr. Robinson's asser- 
 tions regarding the use made of the skylight blinds at 
 South Kensington. Again, on the 17th, by Mr. Robinson ; 
 on September 6, by Mr. Orrock; and, on the 13th, by 
 Mr. Robinson. These last three letters were mainly 
 devoted to the nature, treatment, and condition of draw- 
 ings belonging to Dr. Percy and Mr. Orrock. A valuable 
 communication from Mr. W. Simpson also appeared in 
 The Times of September 13, 1886, but, as it referred to 
 actual trials of pigments, its conclusions have been already 
 reported (page 291). 
 
 Other contributions to this discussion remain to be 
 noticed. These appeared in The Athenaeum, The Saturday 
 Review, The Nineteenth Century, and The Art Journal. 
 
 The Athenaum (June 12, 1886) is of opinion that a com- 
 mittee of painters drawn from the Royal Water-Colour 
 Society ' would not sanction such flagrantly absurd state- 
 ments as that because Egyptian distemper pictures exist of 
 any age, therefore all kinds of water-colour drawings are 
 permanent ; or, on the other hand, that because water- 
 colour drawings, after having been exposed to strong light 
 for lengthened periods of time, have more or less faded, 
 therefore the art cannot be relied on. Our experience 
 justifies the opinion that nine out of ten, if long exposed to 
 strong light, suffer more or less, some being completely 
 ruined, others scarcely affected at all. A few escape alto<- 
 gether, but these are of the nature of the Egyptian distem- 
 
LIGHT AND WATER-COLOURS 
 
 305 
 
 pers, and for very long periods may be trusted to defy the 
 sun himself. Broadly speaking, it is safest not continuously 
 to expose drawings to strong light ; but, on the whole, daily 
 experience declares that vast numbers of drawings have 
 been hung in rooms illuminated in the ordinary manner, 
 and have suffered in no considerable degree, or very little 
 indeed. The truth lies between the extremes of what has 
 been said concerning the drawings now at South Kensington. 
 A very few are practically intact ; the majority have suffered 
 by the way in which they are shown to the public, a way 
 which ensures the destruction of everything not executed in 
 the manner of the Egyptians.' 
 
 In an article on ' The Preservation of Water-Colours,' 
 which appeared in The Saturday Review of July 3, 1886, 
 the complex and varied nature of the changes generally 
 called ' fading ' is emphasized. The rigorous protection 
 from pure sunlight of water-colour drawings is urged, while 
 it is recommended that exposure to ordinary daylight 
 should be limited so far as may be possible. It is affirmed 
 that ' Mr. Robinson obviously and grotesquely overshoots 
 his mark when he asserts that " all " the drawings in the 
 South Kensington Museum have been "more or less irre- 
 parably injured." Sir James Linton writes still more wildly 
 when he avers that those collected in his exhibition "are 
 all in a perfect condition, brilliant, unfaded, beyond the 
 contradiction of even Mr. Church or Mr. Robinson. Mr. 
 Ruskin joins in the affray with his authoritative air and 
 his audacity of fence, and is, as usual, incisive and provo- 
 cative, felicitously right and preposterously wrong in a 
 breath.' 
 
 In connection with the above discussion I may refer to 
 an important paper which appeared (before its commence- 
 ment) in the Nineteenth Century for March, 1886. In it 
 
 20 
 
306 
 
 LIGHT AND WATER-COLOURS 
 
 Mr. W. G. Rawlinson, speaking of the early English water- 
 colourists, says, ' Time has dealt hardly with the majority of 
 their pictures, and few of even the more important drawings 
 that now come into the market but have faded more or less. 
 I do not hesitate to say that only those who have the good 
 fortune to know collections such as that of Dr. Percy and 
 the one in the Print Room of the British Museum (which 
 are habitually guarded from light and kept in portfolios) can 
 form an adequate idea of the delicacy, force, and beauty 
 of colour which were attained by the artists I have named, 
 and by others of their less known contemporaries. A large 
 proportion of the splendid Ellison and Townshend bequests 
 permanently exhibited at South Kensington have greatly 
 deteriorated, and we have only to look at several of Turner's 
 drawings in the present Exhibition ' (R. A., January, 1886), 
 ■ to see the havoc which undue exposure has made of them. 
 .... The avoidance of anything like direct sunlight is an 
 absolute necessity.' 
 
 In The Art Journal for August, 1886 (page 252), Mr. 
 Walter Armstrong makes the assertion that the author of 
 the present handbook ' declares practically that all water- 
 colour drawings begin to die away on exposure to ordinary 
 daylight.' I have endeavoured, without success, to obtain 
 from Mr. Armstrong a reference to any words of mine which 
 could bear such an interpretation. 
 
 The last communication on this subject which I mention 
 here is an article by Mr. Frank Dillon, in The Nineteenth 
 Century of August, 1886. It extends over nine pages, and 
 contains many data of importance. 
 
INDEX 
 
 
 PAGE 
 
 
 PAGE 
 
 Abney, Capt. W. ... 
 
 ... 293 
 
 Caledonian brown ... 
 
 . 204 
 
 Acetone 
 
 ... 80 
 
 Camphor 
 
 • 90 
 
 Albumen 
 
 ... 61 
 
 Canvas 
 
 . 26 
 
 Alcohol 
 
 ... 81 
 
 ,, preservation of 2 
 
 :8, 269 
 
 Alterable pigments .. 
 
 ... 226 
 
 ,, priming of ... 
 
 . 26 
 
 Amber 
 
 ... 48 
 
 Cappagh brown 
 
 . 206 
 
 ,, oil of... 
 
 ... 90 
 
 Carbon bisulphide ... 
 
 . 80 
 
 Andrew, Mr. F. W. .. 
 
 ... 284 
 
 Carbonate of lead ... 
 
 • 259 
 
 Anime 
 
 ... 52 
 
 Carbonates ... 
 
 . 221 
 
 Arsenic, sulphide of.. 
 
 ... 145 
 
 Carmine 
 
 • 165 
 
 Asbestos 
 
 18, 20 
 
 Cassel brown 
 
 . 205 
 
 Asphaltum ... 
 
 ... 208 
 
 Charing varnish 
 
 . 277 
 
 Aureolin 
 
 ... 131 
 
 Charcoal black 
 
 214 
 
 
 
 Chessylite 
 
 • 199 
 
 Baryta water 
 
 ... 76 
 
 Chloroform ... 
 
 . 81 
 
 ,, white 
 
 120 
 
 Chrome yellow 
 
 • 143 
 
 Benzene 
 
 ... 82 
 
 Chromium oxide 
 
 . 170 
 
 Bistre 
 
 . . , 207 
 
 Cinnabar 
 
 . 146 
 
 Bitumen 
 
 ... 208 
 
 Coagulation of albumen 
 
 . 61 
 
 Black-lead 
 
 ... 216 
 
 Cobalt blue ... 
 
 . 186 
 
 Black pigments 
 
 ... 210 
 
 „ green 
 
 ■ 173 
 
 Blockz, Mr. J. 
 
 ... 283 
 
 ,, yellow 
 
 • I3 1 
 
 Blue pigments 
 
 ... 180 
 
 Cochineal lakes 
 
 . 165 
 
 ,, verditer 
 
 ... 199 
 
 Cceruleum 
 
 . 187 
 
 Borate of lime 
 
 ... 96 
 
 Conservation of pictures . 
 
 . 268 
 
 „ manganese 
 
 ••• 95 
 
 Copal 
 
 . 28 
 
 „ zinc 
 
 ... 96 
 
 „ oil of... 
 
 ■ 9° 
 
 Brown pigments 
 
 . . . 200 
 
 „ oil varnish ... 
 
 . IOI 
 
 Burnt carmine 
 
 ... 167 
 
 „ pebble 
 
 • 5i 
 
 „ sienna... 
 
 ... 203 
 
 „ Sierra Leone 
 
 5i 
 
 „ umber... 
 
 . . . 202 
 
 „ spirit varnish 
 
 . 100 
 
 
 
 ,, West Indian ... 
 
 • 52 
 
 Cadmium, pale 
 
 ... 129 
 
 „ Zanzibar 
 
 • 52 
 
 yellow 
 
 ... 126 
 
 Cowdi resin ... 
 
 20 2 
 
 53 
 
3 o8 
 
 INDEX 
 
 
 
 PAGE 
 
 
 PAGE 
 
 Cremnitz white 
 
 .. 113 
 
 Lamp-black ... 
 
 ... 213 
 
 Crimson lake 
 
 •• 165 
 
 Lavender, oil of 
 
 ... 89 
 
 Cyanine 
 
 .. 191 
 
 Lead dryers ... 
 
 ••• 93 
 
 
 
 „ oxychloride 
 
 ... 117 
 
 Dammar 
 
 •• 53 
 
 „ sulphate 
 
 ... 117 
 
 Dextrin 
 
 .. 70 
 
 ,, white ... 
 
 ... in 
 
 Diluents 
 
 .. 78 
 
 Lemon yellow 
 
 ••• 133 
 
 Dipentene 
 
 .. 89 
 
 Light, action of 268, 274, 281-306 
 
 Dryers 
 
 78,93 
 
 ,, red 
 
 ••• 159 
 
 
 
 Lime, burnt ... 
 
 ... 15 
 
 Elements 
 
 .. 221 
 
 „ mild ... 
 
 15, 16 
 
 Elemi 
 
 ■• 54 
 
 ., putty 
 
 ... 16 
 
 Emerald green 
 
 .. 174 
 
 „ slaked 
 
 ... 15 
 
 Emulsions 
 
 .. 63 
 
 „ water .... 
 
 •■• 75 
 
 Ether 
 
 •■ 79 
 
 Limonene 
 
 ... 88 
 
 
 
 Linolein 
 
 ... 36 
 
 Flake white ... 
 
 in 
 
 Linoxine 
 
 ••• 37 
 
 ,, action of 
 
 .. 2^8 
 
 Linseed 
 
 ■•• 33 
 
 Fresco grounds 
 
 •■ 17 
 
 oil 
 
 ■•• 33 
 
 „ method 
 
 .. 214 
 
 ,, ,, siccative 
 
 ••• 37 
 
 
 
 „ „ testing 
 
 ... 40 
 
 Gamboge 
 
 •• 134 
 
 ,, white 
 
 •■• 33 
 
 Glue ... 
 
 .. 63 
 
 Lovibond's tintometer 
 
 281, 284 
 
 Glycerides 
 
 •• 3i 
 
 
 
 Glycerin 
 
 .. 70 
 
 Madder brown 
 
 155, 158 
 
 Graphite 
 
 .. 216 
 
 ,, lakes 
 
 ... 151 
 
 Green chrome 
 
 •• 173 
 
 Malachite 
 
 ... 176 
 
 ,, oxide of chromium 
 
 .. 170 
 
 Manganese, borate ... 
 
 ••• 95 
 
 Gum arabic ... 
 
 .. 66 
 
 ,, dryers . . 
 
 ... 94 
 
 „ British ... 
 
 .. 70 
 
 ,, _ oil 
 
 • •• 37 
 
 ,, Senegal 
 
 ■ 67 
 
 Manuscripts, illuminated 
 
 . . . 260 
 
 „ tragacanth 
 
 .. 66 
 
 Mars yellow 
 
 ... 138 
 
 
 
 Mastic 
 
 • •• 54 
 
 Hartley, Prof. W. N. 
 
 .. 283 
 
 ,, varnish 
 
 .:. 98 
 
 Hydrates 
 
 .. 221 
 
 Mediums 
 
 ... 105 
 
 
 
 Megilp 
 
 ... 106 
 
 Indian ink ... 
 
 .. 210 
 
 Mixed varnishes 
 
 ... IOI 
 
 „ lake ... 
 
 .. 164 
 
 
 
 ,. red 
 
 .. 161 
 
 Naples yellow 
 
 ••• 139 
 
 „ yellow 
 
 • ■ 136 
 
 National Gallery 
 
 ... 261 
 
 Indigo 
 
 .. 192 
 
 ,, Portrait Gallerj 
 
 . . . 264 
 
 Ink, Indian ... 
 
 .. 210 
 
 
 
 Intonaco 
 
 17 
 
 Oil, action of, on paints 
 
 ••• 43 
 
 Ivory black ... 
 
 .. 215 
 
 ,, extraction of 
 
 ... 32 
 
 
 
 ,, jn egg-yolk 
 
 63, 241 
 
 Kauri resin ... 
 
 •• 53 
 
 ,, in paints 
 
 ... 44 
 
 King's yellow 
 
 •■ 145 
 
 ,, linseed ... 
 
 •■• 33 
 
 
 
 ,, manganese 
 
 ••• 37 
 
 Lasvulose 
 
 .. 70 
 
 ,, nut 
 
 ... 42 
 

 INDEX 
 
 309 
 
 
 PAGE 
 
 
 PAGE 
 
 Oil painting ... 
 
 ... 245 
 
 Sandarac 
 
 • 54 
 
 >» poppy 
 
 ... 42 
 
 „ varnish ...• 
 
 100 
 
 ,, siccative 
 
 ••• 37 
 
 Scheele's green 
 
 . 176 
 
 ,, turpentine 
 
 ... 83 
 
 Selected palettes ... 229,233 
 
 ,, varnishes 
 
 ... 101 
 
 Sepia 
 
 . 217 
 
 Oils 
 
 ... 31 
 
 Silicates, alkaline ... 
 
 ■ 73 
 
 „ drying 
 
 ... 32 
 
 Silver-point method ... 
 
 • 253 
 
 Old pictures ... 
 
 •• 255 
 
 Simpson, Mr. W. 
 
 . 291 
 
 Organic compounds . . . 
 
 ... 221 
 
 Size ... 
 
 18,63 
 
 Oxides 
 
 ... 220 
 
 Slate 
 
 21 
 
 
 
 Smalt 
 
 . 198 
 
 Painters' materials ... 
 Painting methods 
 Panel 
 
 ,, preparation of 
 
 ,, preservation of 
 Paper ... 
 
 „ analysis of ... 
 
 ,, ash of 
 
 1 
 
 ... 239 
 
 22 
 
 ... 23 
 
 ... 24 
 
 7 
 8 
 
 9 
 
 Solvents 
 
 ,, of old varnish 
 South Kensington Museum 
 ,, ,, Repoi 
 Spike, oil of ... 
 Spirit-fresco grounds 
 „ medium 
 ,, method... 
 Starch 
 
 • 78 
 . 278 
 
 265 
 t 293 
 . 89 
 
 • 19 
 . 107 
 
 • 250 
 . 69 
 
 19 
 
 • 244 
 
 21 
 . 88 
 
 „ size in 
 
 „ testing 
 
 ,, water in 
 Pastel method 
 Permanent pigments 
 
 9, 12 
 
 10 
 
 8 
 
 ... 252 
 
 226, 227 
 
 Stereochrome grounds 
 Stereochromy 
 Stone... 
 Sylvestrene ... 
 
 Petroleum spirit 
 Piuri 
 
 ... 91 
 
 1^6 
 
 Tempera grounds 
 
 18, 25 
 
 Plaster 
 Poppy oil 
 Prussian blue 
 
 14 
 
 ... 42 
 ... 188 
 
 ,, method 
 Terpenes 
 Terra cotta ... 
 Terre verte ... 
 
 . 240 
 
 • 83 
 
 21 
 
 . 168 
 
 
 
 Toluene 
 
 . 82 
 
 Raw sienna ... 
 
 . . . 202 
 
 Turnbull's blue 
 
 . 189 
 
 ,, umber ... 
 
 . . . 200 
 
 Turpentine, oil of ... 
 
 • 83 
 
 Red ochre 
 
 ... 162 
 
 
 
 „ pigments 
 
 ... 146 
 
 Ultramarine ... 
 
 . 180 
 
 Resins 
 
 ... 47 
 
 „ artificial 
 
 . 182 
 
 ,, amber 
 
 ... 48 
 
 
 
 ,, anime 
 
 ... 52 
 
 Valenta's test for oils 
 
 41 
 
 ,, copal 
 
 ... 5° 
 
 Vanadium yellow 
 
 • 144 
 
 „ cowdi 
 
 ••• 53 
 
 Varnish, mastic 
 
 • 98 
 
 „ dammar 
 
 • •• 53 
 
 Varnishes 
 
 97 
 
 ,, mastic 
 
 • •• 54 
 
 Vellum 
 
 J 3 
 
 ,, sandarac 
 
 ... 54 
 
 Venetian red ... 
 
 . 160 
 
 Restoration of pictures 
 
 ... 276 
 
 Verdigris 
 
 . 178 
 
 Restricted palettes ... 
 
 231, 234 
 
 Vermilion 
 
 . 146 
 
 Reynolds, Sir J. 
 
 ... 283 
 
 ,, tested 
 
 • 149 
 
 Rood, Prof. 0. N. ... 
 
 ... 287 
 
 
 
 Rose madder 
 
 •• 155 
 
 Water 
 
 . 78 
 
 Russell, Dr. W.J. ... 
 
 ... 293 
 
 Water-colour method 
 
 • 251 
 
3i° 
 
 INDEX 
 
 Water glass ... 
 
 PAGE 
 
 ■•• 73 
 
 Wood 
 
 PAGE 
 
 22 
 
 Wax 
 
 ••• 55 
 
 „ spirit ... 
 
 .. 80 
 
 ,, bees' 
 
 ••• 55 
 
 
 
 , , Brazilian 
 ,, Chinese 
 ,, Japanese 
 
 ••• 57 
 ••• 57 
 ••• 57 
 
 Yellow king's 
 „ lake ... 
 ,, madder 
 
 .. 141 
 
 •• 145 
 141 
 
 ,, painting 
 ,, paraffin 
 
 White lead 
 
 ,, ,, action of, on oil 
 
 56. 263 
 ... 57 
 ... in 
 115,258 
 
 „ ochre 
 „ pigments 
 Yolk of egg :.. 
 
 • 123 
 .. 122 
 .. 61 
 
 ,, „ adulteration of 
 
 ... 113 
 
 
 
 ,, „ defects of,., 
 
 .. "5 
 
 Zinc, borate ... 
 
 .. 96 
 
 ,, ,, impurities in 
 
 ... 112 
 
 ,, sulphate 
 
 .. 96 
 
 » of egg 
 
 ... 61 
 
 ,, sulphide 
 
 .. 119 
 
 ,, pigments 
 
 ... in 
 
 „ white ... 
 
 .. 118 
 
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