The Manufacture of Oil Colors

Factory-Made

1. The artist-grade or professional oil color is understood to be made of the best materials available and processed by the best methods known to the particular manufacturer. The pigments are supposed to be carefully selected for chemical purity and for the particular shade of color that the manufacturer considers best for that pigment. The oils used as binders should be of the best quality available, free of impurities. They should dry well and yellow as little as possible. Stabilizers should be kept to the minimum, being used only to correct undesirable pigment characteristics. There should be the maximum amount of pigment in relation to binder, consistent with the production of good flexible color films, and it should be carefully ground to the optimum consistency for brushing quality, good dispersion in the binder, and correct particle size for a good paint-film structure. In some cases special grinding procedures are necessary to produce paints meeting these specifications.

2. The second grade of colors, known as student grade, is less expensive than artists' colors. In most cases their raw materials and production techniques are less refined and more typical of mass-production methods than should be the case with the artist-grade colors. Sometimes the pigments may be slightly below the absolute top grade in chemical purity, strength, or color character. In other instances stabilizers may be employed somewhat more liberally than in the corresponding artist's color, and the oils may be less refined and purified. Less pains may be taken to maintain the maximum ratio of pigment to binding oil, and grinding operations may be briefer and less meticulous. Many of the expensive pigments in the artist-grade color lists are replaced in the student grade by mixtures of cheaper pigments which approximate, more or less, the hue of the original color. Thus one often finds in the student grade a mixture of ultramarine instead of cobalt blue, or mixtures of phthalocyanine blue instead of cerulean blue. Similarly cadmium lithopones and azo colors are sometimes substituted for cadmium sulfides. Because of the better quality of oils and smaller amounts of stabilizer employed in the artists' colors, one expects them to retain their tone with less yellowing than is the case with students' colors. The artist-grade colors should have a markedly higher tinting strength in mixtures, and it should be possible to intermix them more freely. It can be stated, however, that many brands of students' colors, particularly those manufactured in America, are of remarkably good quality, considering their price, and give very good value.

Some color manufacturers grind their more expensive artist-grade white paints in poppyseed oil or safflower oil. Such whites appear brighter and less yellowish than those ground in linseed oil. It should be noted that these poppyseed oil paints will not dry as rapidly as linseed oil whites made of the same pigments, nor will their films be as tough and flexible. White paints ground in poppyseed oil should not be used for underpainting or for priming canvas.

In recent years many manufacturers have offered quick-drying whites, sometimes called underpainting whites, which are thinned and handled like oil colors, although they dry much more rapidly. The specific ingredients that give these paints their setting qualities are not usually indicated on the label or in the catalogue. In general, it may be assumed that, in respect to ultimate durability, they are not an improvement over standard artist-grade flake white or titanium white oil color. However, they are a great convenience when a rapid-drying underpainting is desired. I advise artists to test samples of any brand they employ habitually since great differences in color stability exist between brands, at least in those samples that I have observed during the last twenty years. In two years, samples of one widely advertised underpainting white developed the tone of a well-made Naples yellow, while other brands remained as white as an excellent flake white. [pp. 64-65]

Labeling Procedures
For reasons stated previously it would be to the advantage of the artist if all tubes of factory-made colors carried on the label specific statements indicating:

A. The chemical name of the pigment as well as the standard name.

B. The oil used as a binder and its processing, if any. C. The chemical name of the stabilizers used and the amount used in terms of the percentage of the total volume of the tube's contents. Such a label might read as follows:

Viridian Green--hydrous chromic oxide in refined linseed oil, aluminum stearate 2 percent by volume.

Obviously such labeling would not tell artists everything that they need to know. The quality of pigment, the purity of the oil, and the care taken in grinding and tubing techniques would still be unknown factors affecting the permanence of the product. However, artists would at least be sure that the pigment had not been adulterated with an impermanent green, such as chrome green; that other oils, such as safflower oil or poppy-seed oil, had not been substituted for linseed oil; and that the tube did not contain excessive percentages of fillers.

Suggestions for standard names for artists' colors and the identification of each color name by a specified chemical composition are contained in the Commercial Standard CS-98-62, published by the U.S. Department of Commerce. Manufactaurers who state on their labels that their oil paint conforms to CS-98-62 guarantee that the names and chemical composition of their pigments agree with those of the Standard, that their vehicles are pure linseed or poppyseed oil with no more than the permitted percentages of driers added, and that the brushing quality, tinting strength, percentages of extenders, and drying rates of their paints meet the requirements of the Standard. [pp. 65-66]