A Discourse on the Chemistry of Artists' 1 Paints Vehicles and Varnishes Held at The Art Students League of New York and at the Pennsylvania Academy of Fine Arts, Philadelphia 1922-1923 By F. W. WEBER Technical Director of F. Weber Co. Manufacturing Artists’ Colormen Since 1854 Philadelphia, Pa. A DISCOURSE ON THE CHEMISTRY OF ARTISTS PAINTS, VEHICLES AND VARNISHES Held at The Art Students League of New York and at the Pennsylvania Academy of Fine Arts, Philadelphia 1922-1923 By F. W. WEBER Technical Director of F. Weber Co., Philadelphia, Pa., Manufacturing Artists Colormen Since 1854 The study of the composition and chemistry of Artists’ colors, vehicles and varnishes which today is of such importance, is unfor- tunately only too frequently neglected by the student and Artist. It is not necessary that the Artist become a color chemist, but a practical technical knowledge will greatly aid in assuring permanent and durable results, when the lack of same often proves of serious embarrassment, sometimes even during the Artist’s own lifetime. It is only within comparatively recent time that the manufacture of Artists’ colors began as an industry. Before this time the painter prepared his own products and no doubt welcomed the commercial- izing of this phase of his art. This severance of course was inevita- ble, due to the rapid progress of chemistry as a science, whereby an unlimited number of pigments, etc., began to elaborate the Artist’s selection. Today the student may choose from such a variety, that not to run into difficulties would almost be a miracle. The ideal way to relieve the Artist of most dangers would be to appoint a commission composed of Artists and technical men. I understand there are such commissions abroad, who publish the result of their decisions in pamphlet form for the Artist. In fact, I believe the time will eventually come when such a commission will be by national appointment, as a necessary means to preserve art. The object of such a commission would be: i. To carefully look into the quality of paints, vehicles, var- nishes and sundry products offered to the artist with which a lasting work of art is to be created. A guarantee of per- manence and durability, thereby eliminating any loss of vitality by the Artist in worrying over his materials. 2 2. To work toward the end of compelling all manufacturers to truthfully label all their products. To prevent such misrep- resentations as labeling inexpensive or dangerous substitutes with the names of the products they imitate. Establish na- tionally recognized nomenclature, to which all products must conform. 3. To consider technical questions affecting painting as a whole in all its phases and diffuse such knowledge among Artists. In absence of such a commission the Artist should not hesitate to put these questions directly up to the manufacturer. The future will unquestionably see the buyer of paintings de- manding to know the palette of the Artist. Both the art collector and art speculator cannot afford to be anything else but seriously interested in the durability and permanence of modern art creations. The Artist of the seventeenth and early eighteenth centuries was undoubtedly the most unfortunate. Chemistry about this time began to develop as a science, and during the ensuing years rapidly pro- duced an exceedingly large number of many brilliant, but unfor- tunately also many unsafe colors, which during their introduction were mostly offered very impure. The Artist welcomed the addition of such a variety to his palette and was necessarily forced to select by standards of brilliancy only. We also find that many colors appeared under several names, each manufacturer striving to have the pigment, or a modification of it, appear as a specialty of his own. For example, Prussian Blue, which was discovered by Diesbach in 1704, became known as Paris Blue, Berlin Blue, Bronze Blue, Min- eral Blue, Chinese Blue, Milori Blue, and lately also as American Blue. Even today many dangerous pigments are offered under fanciful, misleading names, which are meaningless and only too often cause the unsuspecting Artist to fall into serious difficulties. The ideal nomenclature of pigments would perhaps be, to express the chemical composition, which, however, would not be very practical when naming pigments of organic origin, these mostly being of very com- plex composition with correspondingly lengthy names. Pigments, in order to be classed as such, must be permanent to light, air, moisture, gases, chemically indifferent toward each other in mixtures and not suffer incalcuable alteration in hue in any technique. All durable pigments should also be insoluble in water 3 or alcohol. By being permanent to light is presupposed to mean that the pigment be absolutely permanent under ordinary diffused light, as also show complete stability when exposed to direct sunlight. The student generally supposes light to be the worst enemy of permanence, which usually, however, is not as serious as climate variances in temperature and atmospheric influences. Only seldom is a painting exposed to strong sunlight for any length of time, but impure air, gases and moisture come in constant contact with the majority of pictures even in some of our largest galleries. A great many of the old masterpieces owe their destruction to disintegration, caused by the constant condensation and evaporation of moisture on their surface, which, carried on over an indefinite period, together with the action of impure air, contaminated with sulphurous gases, etc., gradually brought about changes, which were impossible for light alone to have accomplished. At a later lecture the subject of cracking, fading, wrinkling, etc., and their prevention, will be inti- mately discussed. Pigments may be divided into two' classes : f Natural , such as the Ochres. Mineral j Artificial , such as the Cadmium Yellows, Cobalts, (. Vermilion, Emeraude Green. ( Vegetable , such as Madder Lakes, Gamboge, Indigo. ■Animal, .such as Sepia, Indian Yellow, Carmine. Artificial, such as Alizarin Lakes. The natural and artificial mineral pigments represent the most important group, as it is from this group that the most desirable pigments, are obtained. From the natural mineral group the Old Masters obtained most of their colors, but today the colorman selects a large number of his best products from the artificial mineral group. Of least importance to the Artist are the pigments of organic origin, among which the Madder Lakes, Indigo, Gamboge are perhaps the best from vegetable source. The many yellow lakes, such as Italian Pink, Dutch Pink, Brown Pink, etc., derived also from this source, are of little importance owing to their fugitive character to light and instability in mixtures with many metallic pigments such as the White Leads, Chrome Yellows, etc. Sepia, Indian Yellow, and Carmine are the most important of those from animal source. All three may be easily dispensed with ; especially do I wish to warn the Artist against the use of Carmine. This pigment, although of 4 such brilliance and individuality of hue, is very fugitive to light and readily decomposed in mixture with many metallic pigments, such as White Leads, Chrome Yellows, Yellow Ochres, etc. Being an expensive color, it may be easily replaced by the very desirable Alizarine Madder Lakes. The artificial organic pigments unquestionably furnish a large” number of pigments than all other groups. Since the accidental discovery of Mauve from aniline (a coal-tar derivative) in 1856 by the English chemist Perkins, which formed the starting point for the inconceivable number of dyes developed since then, most of the lake pigments produced with these dyestuffs unfortunately prove far too fugitive for use as Artists’ pigments. The exception in this in- stance being the very permanent Alizarine Lakes, derived from an- thracene, which is also a coal-tar derivative. I have found that many artists are of the opinion that the Alizarine Lakes are aniline colors. The fact that aniline and also anthracene are both derivatives of coal-tar should not lead the Artist to believe that the colors obtained from, these products are identical in their properties. The aniline derivatives such as Mauve, Magenta, etc., are not desirable owing to their instability and lack of perma- nence, but the Alizarine Lakes are chemically a different class of compounds and are very desirable, possessing high stability and permanence. We have spoken above of Lake colors and I think it may be of sufficient interest to describe such a product. The derivation of the name lake is said by Pliny in his Naturalis Historia , A. D. 77, to be from the lac, or coloring principal, of insect origin, used by the early Italian dyers. In conjunction with compounds of tin and aluminum the dye was precipitated and fixed indelibly on the fabric. During the process of dyeing some of the lac combines with some of the tin and aluminum to form an insoluble compound, forming a colored scum on top of the dye-vat. This substance, called by the Italian dyers lacca, was collected, dried and sold to Artists as a pigment. Soon the natural dyestuffs were found to yield variously colored lacca and methods were soon developed whereby the lakes were ob- tained direct and not as a residue or scum of the dye-vat. In fact, today the manufacture of lake colors ranks commercially as impor- tant as the dye industry. A lake pigment is not simply a mechanical mixture of a base with a dyestuff, as this product would “bleed” the dye in water. A 5 lake which has the dye fixed indelibly on a neutral base is only desir- able as a pigment. In practice the neutral base on which the dye- stuff is fixed, is usually Alumina, Clay, Barytes, or Paris White. The earlier lakes were obtained from natural coloring matters, such as lac, cochineal (carmine), Persian berries, Brazil wood, log- wood, etc., but today the artificial or synthetic dyestuffs have almost entirely supplanted the natural coloring extracts, yielding in- numerable brilliant colors, most of which are only of sufficient per- manence to be used by the Artist for commercial work, if at all. Many of these lake colors are often employed to give stronger color to pigments, but their addition yields but temporary brilliance. The Artist should be in a position to roughly detect at least the addition of harmful admixtures to his colors, as, for instance, the addition of fugitive dyes, or if colors, such as the Cadmium Yellows, have been adulterated with Chrome Yellows, or whether a pigment such as Cobalt, for which he pays a big price, be actually pure Cobalt and not a mixture or cheap substitute, or likewise if Whites be unadulterated with Chalk, Clay, Barytes, etc., and whether a White be Zinc, Lead, etc. The time has arrived when the Artist must know something of the composition of his materials. The new . products appearing yearly only tend to lead into difficulties, unless their use be accom- panied with the proper knowledge of their properties. Not only does the student or Artist owe it to himself, but the future generations will look back with gratitude when examples of various periods re- main durable throughout the ages. Why in this one profession should the study of the materials employed in the various techniques be so often thought of such little importance? We stand helplessly by and witness the gradual de- struction of many of the finest examples of the various periods simply because the respective Artists knew nothing of the dangers of using unstable pigments, oils, etc., or were victims of the alluring, brilliant, unsafe products during their introduction. We may ex- cuse the Artist of former times, but today there is no reason why the student should not reflect on the importance of preserving his work for the future. Sometimes the improper use of even durable materials has caused the Artist considerable trouble. With a few bottles of reagents tucked away in the studio, the Artist may at any time readily test any color in question, at least for harmful adulterations or impurities. I have a book now in press 6 (published by D. Van Nostrand Co., New York) in which many tests are given for all standard pigments, also much other information on pigments of interest and value to the Artist, student, collector and restorer, which I feel should fill a long-felt want. The Artist should have a small bottle each of Alcohol — Denatured Sodium Sulphide An acid — Hydrochloric , Nitric or Sulphuric Acid Ammonia Water or a weak solution of Caustic Lye. The alcohol may be denatured alcohol, as this serves the purpose for all practical needs. It is used to detect the presence of adultera- tion with dyes, which, if soluble in alcohol, will color the alcohol. A color when treated with alcohol or water which does not stain these liquids would indicate no water or alcohol soluble dyes being present. Some dyes require a few drops of ammonia water to the alcohol to draw them from the pigment. If the pigment be in dry powder form it need but be shaken in a small bottle, or better a test tube, together with a small quantity alcohol. Casually the color which the Artist examines is either an oil or water color. Only seldom do the oils or gums prevent reaction of the above-named reagents. More definite results are, however, obtained by using the pigment in powder form, that is free from oils, or gums, etc. Water colors are easily washed free of these gums. A small quantity of the color is placed in a small container to which sufficient water is added to make a dilute solution. After thorough shaking, upon leaving the pigment settle, the water should be poured off. It is important to note whether the water has become stained with color; this would indicate a partial solution of the pig- ment or the addition of water-soluble dyestuff to the pigment. Oil colors may be freed from oil or resins by washing in similar manner, using turpentine in place of water and then removing the turpentine by washing with alcohol. If the alcohol or turpentine becomes colored it would indicate adulteration with dyestuffs. Some pigments are in a very fine state of division and would require quite a time to settle, therefore much time may be saved by filtering the pigment from the turpentine or alcohol. In place of turpentine other solvents are often employed, such as benzol, toluol, xylol, ether, chloroform, acetone, amyl-acetate, carbon tetrachloride, benzine, etc., 7 etc. Certain colors, such as Prussian Blue, have such strong tinting strength that more than one filtration is required to remove the finely divided particles from the solvent, which otherwise may mislead the student to believe that the discoloration is caused by dyes. Our next reagent consists of a solution of about one ounce sodium sulphide in a pint of water. Sodium sulphide is an inexpen- sive chemical and is used principally to detect the presence of lead or copper in pigments. Such pigments as the White Leads, Flake White, Cremnitz White, the Chrome Yellows, Naples Yellows, Red Lead, Orange Mineral, Chrome Greens (containing Chrome Yel- lows), Verdigris, Malachite Green., Emerald Green, or any other pigments containing lead or copper, are rapidly turned black when a drop of sodium sulphite solution is applied to them. For instance, if any Cadmium Yellow becomes blackened by sodium sulphide, we immediately suspicion adulteration with Chrome Yellows, as the Cadmiums, when pure, should not become; blackened. Cadmium Orange and Cadmium Red may show adulteration with Red Lead or Chrome Orange if blackened; when pure both are not discolored by this reagent. Yellow Ochre should remain unaltered, likewise the genuine Vermilions, if pure, are not blackened by sodium sul- phide. Any of the green pigments turning black with this reagent would indicate either Chrome Yellows or Copper Greens to be present. Any color becoming discolored brown or black with sodium sulphide should not be used by the Artist desiring complete stability or durability. The reaction which takes place with this reagent shows exactly what will occur if a painting be hung where sulphur- ous gases come in contact with the unprotected pigment. Many Artists argue that in their experience the Chrome Yellows, Flake Whites or White Leads have not shown discoloration for a number of years and would no doubt continue to remain unchanged. This may be true in the case of the White Leads, but only under one condition, and that is, that the pigment be properly protected from impure air by an application of varnish or other means. White Leads are perfectly permanent to light and very desirable if prop- erly used. On the other hand, this can not be said of the Chrome Yellows, as we will learn when speaking later of these pigments. The same is also true of the Chrome Greens (not to be confused with the Oxide of Chromium Greens, such as Emeraude Green or Viridian, which are extremely stable pigments), Verdigris, Malachite Green, etc. 8 A bottle of any acid, such as hydrochloric acid, which I usually prefer, or sulphuric acid or nitric acid, is useful in testing certain colors. Cobalt Blue, Cerulean Blue, Emeraude Green, Viridian, Permalba, Vermilions, Prussian Blue, Cobalt Violets, all Blacks (ex- cept Ivory Black, which is partly soluble in acid), are indifferent to dilute acids and any change taking place would indicate the pigment to be impure or adulterated. A solution of a base, such as caustic lye or ammonia water, serves to determine purity and adulteration of pigments, which should remain unaffected by these alkalies. The pigment of which the Artist uses a larger amount than of any other, is White. The three principal Whites are the Lead Whites ( Flake and Cremnitz ) , Zinc White and Permalba. The Lead Whites (basic lead carbonates) were employed by the Egyptians. There is and always has been, much controversy on the use of these pigments in the Fine Arts. We only too often wrongly accuse Lead Whites of being unde- sirable pigments. It must be said in their favor that when used properly the Lead Whites are very durable and permanent pigments. The sensitiveness of the Lead Whites toward sulphur compounds and gases (which tend to convert the lead to black lead sulphide) makes the proper use of these Whites very important. Unfortu- nately the opacity of the Lead Whites has done much to make these pigments almost too popular. The Artist using Flake, Cremnitz or White Lead for underpainting, could not get a more desirable pig- ment for this purpose, as here the color is properly protected from impure air contaminated with sulphurous gases. But where these pigments are used and left exposed, it is only a matter of time, depending on how impure the atmosphere in which the painting is placed, that discoloration will occur. An; application of varnish will considerably protect and retard this reaction. White Leads also tend to reduce most organic pigments in mixtures and should not be employed together with impure Cadmium Yellows, Vermilions, Ultramarines, etc. The tinting value of the White Leads does not approach that of Zinc Whites or Permalba. White Lead is a cumu- lative poison. A simple test for White Lead is the black discolora- tion when treated with sodium sulphide. In most acids White Lead dissolves with strong effervescence. When strongly heated, it turns from yellow to red color. In these three latter respects it differs 9 from Zinc White, which dissolves without effervescence in acid and upon heating turns yellow; but upon cooling, again turns white. Nitric acid or acetic acid entirely dissolves White Lead; any insolu- ble residue would indicate admixture with such materials as clay, barytes, silica, etc. Caustic lyes also dissolve White Leads. White Leads in oil dry well, yielding an elastic and tough film. Owing to their sensitiveness to impure air White Leads are not practically adaptable to other painting techniques. A' very popular pigment is found in Zinc White , the use of which as a pigment dates from the latter part of the eighteenth century. Zinc White is the oxide of the metal zinc and like many other pigments was too severely criticized during the years follow- ing its introduction. The impure condition of these Zinc Whites did much to destroy the confidence which should be placed in this desirable pigment when pure. Today the American Zinc Whites! can not be excelled for their dependable purity and consequent sta- bility as a pigment. Pure Zinc Whites are very permanent under all ordinary conditions of painting. When ground in oil, they dry more slowly than the Lead Whites and yield a much harder film. In fact, it is to be advised against, painting Zinc Whites too impasto, the application tending to become horny and friable upon ageing. The tinting power of Zinc White is very high. Sodium sulphide so- lution does not discolor this pigment. I have introduced in recent years a pigment which bids fair to become one of the most desirable Whites for Artists’ use. This pigment, called Permalba , does not contain either lead or zinc and is unaffected by all ordinary chemical reagents, remaining unchanged under all conditions of painting. The high tinting value and excep- tional opacity, together with its stability and inertness toward all other pigments in mixtures, in all painting techniques, ranks Per- malba as an ideal Artists’ White. In oil, Permalba requires about the same time as Zinc White to dry, yielding a very flexible and durable film. Permalba has gone through a very thorough experi- mental stage, ranging over a number of years, and has been found to remain permanent under all conditions of painting. Its insolubility in acids and alkaline reagents which dissolve Whites of lead or zinc composition, readily distinguishes Permalba from these. The most important Red Pigments are the Alizarin Madder and Genuine Madder Lakes, Genuine Vermilions, Red Ochres and Red Iron Oxides. 10 The Alizarin Madder as also the genuine Madder Lakes derive their color from Alizarin, which today is prepared from; anthracene, a derivative of coal-tar. The ancients already obtained this product as an extract from the root of the madder plant, in which it is usually associated with the less permanent and more purple in hue Purpurin. The synthetic product is produced today, so that a very pure and dependable pigment is obtained, equal, and in some in- stances better, than the natural color extract. The Alizarine Mad- ders or modifications of these colors appear commercially as Alizarin Crimson, Alizarin Madder, Rose Madders, Madder Lakes, Pink Madder, Brown Madder, etc. The Alizarin Madders are insoluble in water or alcohol, which distinguishes them from most of the ordinary organic dyestuffs, which impart color to these liquids. The Alizarin Madders are best used as overglaze colors and mixture with Chrome Yellows, Lead Whites, Flake White, Yellow Ochre and Raw Earth Colors are best regarded as being of uncertain stability. Mixtures with dura- ble pigments such as the Cadmiums, Permalba, Burnt Ochres, Red Oxides, Emeraude Green, Cobalt Blue, Ultramarine, all Blacks, etc., show high stability. The Genuine Vermilions are compounds of the elements sul- phur and mercury (quick-silver), and were known and used 400 B. C. by the Egyptians and early Chinese. Pliny, A. D. 77, refers to them as minium, a name now given to Red Lead. In more modern times the Vermilions are offered often very impure, some- times containing an excess of sulphur, etc., and these impurities are principally responsible for the bad reputation the Vermilions re- ceive. When the Vermilions are pure, no discoloration should take place in mixture with pure Flake Whites. They are very durable in mixtures with other stable pigments and are not affected by im- pure air, sulphurous gases or sodium sulphide. A black discolora- tion would indicate admixture with Red Lead or Chrome Red or Orange upon treating Vermilions with the sodium sulphide solu- tion. Alcohol, water, weak acids or alkalies should not react with genuine Vermilions. When strongly heated, Vermilions sublime, leaving but a trace of residue. A large amount of residue would indicate adulteration with red lead, clay, barytes, etc. For some inexplicable reason some varieties of Vermilions darken somewhat on long exposure to direct sunlight, especially is this evident with impure Vermilions. Vermilions, when overpainted 11 with Alizarin Madder, have shown greater permanence under pro- longed exposure to direct sunlight than when used alone. The Red Iron Oxides and Red Ochres, such as Indian Red , Venetian Red, Light Red, etc., receive their color from the oxides of iron, principally ferric oxide. The natural and artificial ochres are practically alike fin properties, resisting dilute acids and alkalies and showing no discoloration with sodium sulphide solution. These pigments were used in all techniques, from early times. Most of the modern exceedingly brilliant Red Lakes appearing under many fanciful names, although of considerable value for com- mercial work, are not desirable for absolute permanency. The Artist had better acquaint himself with the durability of the pig- ment in question, from the manufacturer of the respective color when desiring to use such as the Geranium Lakes, Scarlet Lakes, Brilliant Lakes, etc. Carmine need not be discussed as it should not be employed, except for limited durability, as in commercial work. The most important yellow pigments are the Cadmium Y ellows, which are all compounds of the elements, cadmium and sulphur. When pure, these yellows, ranging from a pale yellow to deep orange, are permanent to light, not affected by sulphurous gases or compounds and are durable in mixtures with other dependable pig- ments. An exception of this, however, is found with Emerald Green and Cadmium Yellow in mixture. These two colors are not compatible and should never be used together. Chrome Yellows frequently are used to adulterate Cadmium Yellows, the detection of which is readily discovered by treating the color with sodium sulphide, when, if Chrome Yellows are present, the sample will turn brown or black. Pure Cadmium Yellows are not discolored by this reagent. In concentrated hydrochloric acid the Cadmium Yellows should be entirely soluble, leaving no residue. Chrome Yellows ranging in color from a pale yellow to deep orange are essentially compounds of lead chromate and, like all pig- ments containing lead, they are very sensitive to sulphurous gases and compounds. Not only are the Chrome Yellows blackened by sulphur, but under exposure to direct sunlight they invariably turn brownish ; especially is this evident when the pigment is not chemi- cally pure. Chrome Yellows are likewise not compatible in mixtures with most organic and lake colors. There are many Artists using Chrome Yellows who should first apply some of the simple tests for durability before placing undue reliance in their permanency. 12 Indian Yellow is a transparent color of good permanence and stability in mixture with most durable pigments. There are several Yellow Lake pigments, the coloring principal of which is derived from coal-tar, which are being accepted in place of the genuine Indian Yellow. These colors are also very permanent and especially useful as overglazing colors. The Lemon Yellows ( Barytes Yellow , Strontian Yellow, and Zinc Yellow ) are very useful, and when pure have proven to pos- sess considerable permanence. The further discussion of these pig- ments, as also the Cobalt Yellow, Naples Yellow, etc., must be taken up later. Of the green pigments, unquestionably the Transparent Oxide of Chromium, also known as Emeraude Green and Viridian, is the most desirable, possessing complete stability in all techniques and remaining durable together with other pigments in mixtures. Adul- terations are readily detected, as the pigment should remain un- affected upon treating with acids, or alkalies, or sodium sulphide. Any discoloration would indicate admixtures. Water or alcohol will extract any dyestuffs. Of equal durability is the Opaque Oxide of Chromium, which, although possessing identical chemical proper- ties as the transparent variety, does not possess the strength of color, being a mat, dull green. Emerald Green is a pigment which is practically permanent to light, but, being sensitive to sulphurous gases and compounds, must be properly protected from these to insure stability. With most durable pigments Emerald Green is stable in mixtures, the principal exception being with the Cadmium Yellows. When Emerald Green is used, it is advisable to use the pigment alone, as in mixtures it has but little tinting strength and any danger of incompatibility is then removed. The pigments which, like Emerald Green, contain copper, are, however, best avoided by the Artist. To this group belong such colors as Malachite Green, Verdigris, and the blue copper pigments. They are sensitive to sulphur and unstable in mixtures with other pigments. Another set of very durable green pigments are the Cobalt Greens. They are of weak tinting strength, but are exceedingly per- manent to light and air and with other colors in mixtures. Sodium sulphide solution does not blacken these greens. The green lake pigments do not form an important group, most of these being only successfully employed for commercial purposes. 13 Usually the Artist may prepare his own greens on the palette, using Cobalt Blue, Ultramarine or Prussian Blue with the Cadmiums, etc. The principal blue pigments are Cobalt Blue , Ultramarines and Prussian Blue. All of these colors are very permanent to light, in- soluble in water or alcohol (detection of dyes) and durable in mix- tures with other stable pigments. Cobalt distinguishes itself from the other two in being insoluble in acids and alkalies. Ultramarines ( New Blue , Permanent Blue, French Blue), are destroyed by acids. Prussian Blue resists dilute acids but is discolored by lyes, for this reason can not be used as a Fresco color. Sodium sulphide will not blacken these blues, discoloration would indicate adulteration with copper blues. The Cobalt Violets possess the strongest color of the durable violet-hue pigments. They are perfectly permanent to light, being also indifferent towards acids, alkalies and sodium sulphide. These properties readily distinguish it from the very fugitive aniline lake, Mauve. Mauve and Magenta are very strong colors but much too fugitive for Artists’ use. Violets and purples may be easily mixed on the palette, using Cobalt or Ultramarine with Alizarin Madder. The natural and artificial ochres and umbers are the most desir- able brown pigments. Yellow Ochre, Roman Ochre, Transparent Golden Ochre, Raw Sienna, and Razo Umber are natural earth pig- ments deriving their color from oxides and hydrates of iron. The artificial ochres are called Mars Yellozv, Mars Orange, Mars Red, etc. Both the native and artificial products are very durable in all techniques and may be successfully used in mixtures with other stable pigments. Mixtures of lake colors and organic pigments with the raw earth colors are best regarded as being of questionable sta- bility. When these raw earths are calcined, they take on a decided red hue and are then dependable in mixture with all other pigments, being equally permanent to light and air, as the raw earths. They resist alkalies and are only slowly acted upon by strong acids. Raw Sienna and Yellow Ochre are sometimes toned with Chrome Yellow, the detection of which is evident, if the pigment is blackened by sodium sulphide solution. Bitumen or Asphaltum should not be used by the Artist desiring permanency. The colors are of organic origin, composed of a va- riety of pitchy, tarry substances which partly decompose under expos- ure to direct sunlight. As oil colors, they are exceedingly slow dryers, and even after years they soften and “bleed” or diffuse A 14 through overlying layers of paint. Heavy applications readily cause cracking. Vandyke Brown , also being partly composed of bitumen- ous matter, is unsafe for durability, fading to a cold grey tone under exposure to direct sunlight and should be replaced by Burnt Umber with Ivory Black. All the black pigments ( Lamp Black , Blue Black , and Ivory Black ) are very permanent and durable colors, resisting both acids and alkalies. With all other pigments they are safe in admixtures. With exception of Ivory Black, they are all principally composed of carbon. Ivory Black contains a varying percentage of bone ash; is in consequence partly soluble in acids, but is a better dryer in oil than the Lamp Blacks. Oils, Varnishes, Siccatifs and Mediums. I have found many Artists who were exceedingly conscientious in their selection of durable pigments, displaying a complete lack of technical knowledge of the vehicles they employ. The vehicles and mediums used in the various techniques are just as essential for permanency and durability as are the pigments. Let us first consider the importance of the proper oils used in Oil Paintings. For the Artist, oils may be generally divided into three principal groups: i. Drying Oils : such as Linseed and Poppy Oil. I 2. Semi- or Slow-drying Oils : such as Sesame, Cottonseed Oil. 3. Non-drying Oils: such as Olive Oil, Castor Oil, Cocoanut | Oil. The oils obtained from the animal kingdom are not practically adaptable for use in the Fine Arts. Only few of the volatile mineral oils, the lighter fractions of petroleum, such as Benzine, Naphtha, Gasoline, Petroleum ether, and sometimes Coal Oil may be used, but then only when their use be thoroughly understood. They find wider application as solvents for resins, as also do the lighter fractions of coal-tar, such as benzol, coal-tar naphtha, toluol, xylol, etc. We must leave the discussion of oils, varnishes, etc., for a later time, as this subject is as comprehensive as the matter on pigments and must be taken up in detail as it is of much importance. We will therefore now mention only the most interesting facts. The two principal drying oils, we have said, were Linseed Oil 15 and Poppy Oil. By drying we mean that these oils absorb oxygen from the air, thereby becoming converted into a solid, tough, elastic, transparent mass. This form of drying may be contrasted to the manner in which such substances as turpentine and the lighter frac- tion of the mineral oils dry. These latter dry by evaporation. This may be readily illustrated by placing a small known quantity of lin- seel oil in an open container and an equal amount of turpentine in another open container. After several days it will be noticed upon weighing each container that that which contains the linseed oil will have increased in weight about io per cent., whereas that which con- tained the turpentine will be practically empty. Again, upon closely examining the oil, we will find the mass to have dried with a con- siderably wrinkled surface (usually to be seen also on old cans of heavy paint which have stood open for a prolonged time). The oils belonging to the semi- and non-drying group, distinguish themselves from the drying oils in that they do not absorb oxygen from the air in such a degree as the drying oils and during their drying become partly rancid and do not yield tough, elastic, durable, transparent films, as do the drying oils. Linseed and Poppy Oils have been in use for several centuries and have proven conclusively their importance as painting oils and the Artist who, without fur- ther inquiry, makes use of the non-drying oils such as olive oil, castor oil, cocoanut oil, etc., is doing himself and his work a great injustice. Why do so many Artists believe to make remarkable discov- eries by employing such oils with waxes, varnishes, and strong Sic- catifs, and, as I have known, some to use even vaseline with their colors ? I must postpone explanation why the use of improper oils has caused the destruction of many works of art, it requiring further explanation of the composition of these products in order to more clearly understand their properties. Linseed Oil and Poppy Oil differ somewhat in the time required to dry, Poppy Oil drying somewhat slower. Raw Linseed Oil con- tains a natural coloring matter which is somewhat objectionable to Artists, especially for delicate tints and for whites. These colors, when ground in Poppy Oil, do not show this yellow cast. When Linseed Oil is exposed to direct sunlight this coloring matter is bleached, but returns when the oil is again placed in the dark. Com- mercially, Linseed Oil is bleached by different methods and must be thoroughly washed free from the acid, etc., used in this process, 16 in order to be desirable for Artists’ use. I wish to particularly warn the Artist against the use of anything but the purest Linseed Oil or Poppy Oil, which have proven their merits so successfully in past years. Turpentine , which is obtained by redistillation of exudations of various pine trees, is a very thin, volatile, colorless liquid used gen- erally in conjunction with oils or as a solvent for resins. It is one of the most useful vehicles in oil painting. The early painters had already discovered that by boiling lin- seed oil together with finely divided lead or lead compounds, a prod- uct was obtained which dried more quickly than the raw oil. To- day many such compounds are made, some using lead, manganese, and in late years cobalt compounds, to produce Siccatifs which are very quick drying compounds. The use and abuse of Siccatifs re- quires lengthy explanation and cannot be discussed at this time. I do, however, wish to warn the Artist against their use, except for commercial work where durability and permanence is of secondary importance. It will usually be found the speed with which a paint film is forced to dry by their use consistently subtracts from the durability of the painting, not even to mention the possible develop- ment of cracks and rapid darkening ensuing from excess use. There are three resins which find widest application in the Fine Arts, they are Mastic , Damar, and Copal. The Mastic resin is soluble in turpentine, as is also the Damar. The Copals distinguish themselves from these in being practically insoluble in most ordinary solvents, requiring special treatment to yield varnishes of the highest durability. The usual method employed in preparing Copal Varnishes consists in heating the resin together with linseed oil and turpentine and frequently the addition of drying compounds give quicker dry- ing Copal Varnishes. Copal Varnishes yield upon drying the most durable protective films, but on account of the manner in which they resist all ordinary solvents, they are very tedious for the restorer to remove after ageing, thereby endangering the underneath painting. Mastic Varnish can readily be removed from aged paint- ings with ordinary solvents, such as turpentines, etc., as can also Damar Varnish, and should for this reason not be employed together with the painting oils while painting. Any questions which the Artist or student may desire to ask will be very welcome, as it is his only means of obtaining informa- tion which I feel may mean much to him later. F. W. WEBER. Form 481-OM323