Purity

On the other hand, a pigment is not necessarily a single chemically [p. 27] pure compound, and the name or chemical formula of a pigment does not always mean that the principal substance of which it is composed is its sole ingredient. Frequently small amounts of modifying ingredients are necessary to develop the full perfection of a color; these are permanent in themselves, are recognized components of the pigment as known under its specific name, and are not considered impurities.

There are a few exceptions to the rule that all pigments must be concentrated, full-strength examples of their types. Prussian blue, phthalocyanine blue, phthalocyanine green, and some of the other synthetic organic pigments are occasionally improved by the addition of various amounts of inert pigment. The cadmium-barium colors and titaniam-barium white, which contain relatively large amounts of barium sulphate, are acceptable pigments, although the same types are also obtainable and may be used in their concentrated, full-strength forms. The inert ingredients, in these instances, may be produced or formed during manufacture, as an integral part of the pigment or often as a substance added to or mixed with the finished color. Some pigments give dull or inferior results when used full strength in gouache paints and are brightened and improved in paint quality when the correct amount of inert pigment is mixed with them.

Emphasis is always placed on the purity, brilliance, and strength of the color characteristics of a pigment. This does not mean that one must paint all pictures in an intense, clean, brilliant key, but such qualities are necessary because it is not possible to use color in painting to its fullest complete range and in complete manipulative control unless one has full command of all potential color values and qualities. The pigments provide a tool or means of expressing the all-important element of color in painting, and as such must be of the best available grade, just as brushes, carving tools, and other implements must be. The artist who paints in a free, spontaneous, or loose manner demands the same high-quality brushes as the one who does more precise, meticulous work, and the sculptor who carves rough and direct forms requires the same keen implements as the one who produces smooth, polished work. Likewise, when painters work in dull or low color keys, they need the same clean lines as when they paint brighter pictures; in the blending and mixing of hues and tones to produce somber results, purity and clarity of color characteristics play as important a role as they do when bright color effects are desired. [pp. 27-29] [The dry powdered pigments, from which artists' paints are made, must conform to several requirements in order to be acceptable for use in painting.]