mining the composition and compatibilities. In fact, it is to-day possible to synthesize some of the fugitive natural vegetable dyes, obtaining substitutes, which are permanent and more brilliant.

There are on the market to-day a great many unnecessary colors appearing under various fanciful names, many dangerous aniline or dye colors, titled with misleading or alluring names, which mean nothing, but serve only to attract the unsuspecting buyer. Admixtures, to obtain unusual hues, can just as readily and more safely be made by the artist himself, to meet his special requirements, than by the manufacturer who is ignorant of the character of colors used in conjunction with the admixture.

The artist to-day has not the time to make his own materials, as in the days of the old masters, whose palettes were limited to but a few colors, and whose vehicles and pigments were only accepted by them after long years of tedious study and observation.

We are prone to credit the old masters and ancients, especially those from the time of Pliny about 77 A.D., to the end of the sixteenth century, with much technical knowledge concerning the composition of the materials they used. As chemistry was practically unknown as a science before the seventeenth century, how could the painter, before this time, possess knowledge only possible to obtain in comparatively recent years? The fact of their using mostly permanent pigments was not directly due to any scientific knowledge of the composition of their products, but was chiefly a matter of careful selection from an exceedingly small number of pigments, oils and varnishes at their disposal. Their organic colors were few in number, the innumerable, brilliant, but mostly fugitive synthetic dye-stuffs known to-day, date only from 1856.

The artists living during the eighteenth and early nine

teenth century were unquestionably the most unfortunate. During these years chemistry was rapidly introducing new colors, many of which during their introduction were offered very impure and under misguiding and fanciful names. By doing this, the manufacturer thought to hide the identity of the color, and the artist was forced to select by standards of brilliancy only.

With the unlimited number of chemical and natural raw pigments, vehicles and sundry products offered today, it requires a wide and intimate knowledge of their composition in order to make a proper selection.

The purpose of this book is to educate the user, not in the use of his materials, but to bring to him, in a conversational and as interesting a manner as possible, the chemistry and technology of Artists Pigments.

PIGMENTS

The application and use of pigments in the manufacture of paints for artistic purposes is of great antiquity. In the earliest periods known we have evidences that prove conclusively that the ancients understood colormaking and the use of colors for ornamentation. During the late centuries great industrial progress has developed the manufacture and selection of natural and artificial pigments for paint use. In this book we will, of course, only consider chiefly those paint pigments pertaining to the fine arts. These pigments are, however, the same as used in all branches and phases of paint making, both for artistic decoration as well as for protective requirements, the various techniques depending essentially on the respective vehicles or methods of manipulation.

We distinguish pigments from paints in that the latter are prepared from the former by the addition of a vehicle or medium. Pigments differ from dyes, as color-giving agents, by the fact of their being insoluble and chemically compatible with the vehicle employed, whereas the dyes are usually soluble.

Pigments in order to be termed and used successfully as such, should meet the following qualifications; be reasonably, or better altogether, permanent under exposure to light and air, chemically indifferent to each other in admixture, and not react with the vehicles employed or suffer thereby incalculable alteration in hue.

The important facts to be considered, when selecting pigments, are:

I. The chemical composition and physical properties of the pigment.

II. Whether the pigment is absolutely safe and dependable, durable and permanent to light, atmosphere,

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gases, etc., reacts with other pigments or vehicles, and whether affected by these when in mixture. If only reasonably safe, or if not safe to use at all, why and in what instances, and what changes are likely to occur.

III. How the pigment is recognized chemically and physically. How detected from other pigments identical in optical appearance. Simple qualitative analysis, detection when adulterated or when in mixture with other pigments. Its chemical properties.

IV. Which pigments are natural or artificial products. V. In what manner obtained and prepared, if of natural origin. If artificial, how made and from what various substances.

VI. Is it an opaque or transparent color, and as an oil color, does it influence the drying of the oils?

VII. To which painting techniques:-oil, water-color, tempera, pastel, fresco, stereochromy, etc.-is the pigment adaptable. If unsafe in certain techniques, why? VIII. Does the pigment appear commercially under several names?

IX. Imitation pigments. How recognized and if the imitation has dangerous adulterants, how detected and which substitutes are best avoided.

Pigments when selected for the manufacture of artists' paints, require most careful inspection and testing of their chemical and physical properties. Permanency is perhaps the most important factor and the pigment should meet this qualification in its broadest interpretation; namely be permanent to light and air, in mixture with other pigments and vehicles and according to the technique in which it is applied, it should be water-proof, alkali-proof, acid resistant, gas-proof, lime-proof, etc.

Pigments are said to be gas-resisting when such gases most commonly met with, as Hydrogen Sulphide (H2S), Sulphurous Acid Gas, Chlorine and Carbonic Gas do not react with them. Sulphur, either in the form of a sul

phide or acid, is the one most commonly met with and the one which is the most important to guard against. This element is found in the gases coming from decaying or putrid animal and organic matter, marsh waters, or swamps and in coal gas. All the inert pigments, such as Permalba, Terra Alba, Asbestine, etc., along with Lithopone, Zinc and Sublimed Lead, Venetian and Indian Red, Ochre, Oxide of Chromium, all Blacks, all Blues excepting copper blues and all Brown earth pigments and Red Lakes which are free from lead, are practically gasproof.

Pigments are said to be acid-resisting when no change is evident through reaction with such mineral or organic acids, commonly met with, as Oleic, Acetic, Sulphurous and Sulphuric Acids. Oleic Acid is present in the vegetable oils, also Sulphurous and Sulphuric Acids but the two latter only if not entirely removed from chemically bleached or refined oils. Acetic Acid is present in lead pigments that have not been properly washed.

Strong acids, which will more or less attack all pigments, rarely come in contact with finished paintings and the above mentioned weaker acids are representative to use in determinations. The pigments listed above as gasresistant can also be accepted as acid-resistant.

Pigments are alkali-proof, if in the presence of ammonia or other alkalies they suffer no change, a test for which is to boil the pigment for ten minutes in a 10 percent solution of ammonia. All inert pigments with the exception of clays, whiting and Terra Alba (gypsum) which are slightly attacked, Venetian Red and Indian Red, Ochres, Oxide of Chromium, Siennas, Cobalt Blue, Permalba, Lamp Black and Ivory Black, etc., are practically alkali-proof.

Pigments that undergo no change after being mixed in lime water for twenty-four hours are practically limeproof. This quality is greatly in demand since the inno