substance that imparts color to other materials. In paint, the pigment is a powdered substance which, when mixed in the liquid vehicle, imparts color to a painted surface. The pigments used in paints are nearly all metallic compounds, but organic compounds are also used (see lake). Most black pigments are organic, e.g., bone black (animal black or charcoal) and lampblack. Some of the metallic pigments occur naturally. The brilliant and beautiful coloring of the rock and soil in some parts of the United States, especially in the Grand Canyon of the Colorado River, the Painted Desert of Arizona, and Bryce and Zion canyons of Utah, is largely produced by such compounds, chiefly oxides. Yellow ocher, sienna, and umber are oxides of iron. Litharge is a yellow oxide of lead. Red lead is also an oxide of this metal. Lead chromate, or chrome yellow, is an important yellow pigment. White lead, or basic lead carbonate, is a pigment long in use; it is rendered more durable by mixture with zinc oxide. Cadmium yellow is a sulfide of cadmium. Ultramarine is an important blue pigment, as is Prussian blue (ferric ferrocyanide). Green pigment is produced by mixing Prussian blue and chrome yellow. Vermilion (mercuric sulfide) is red. Pigments occur in plant and animal bodies. The bright colors of plants, for example, are the result of the presence of such substances as chlorophyll (green) and xanthophyll (yellow), both of which are also found in some animals. Among others are carotene, the yellow of carrots and certain other vegetables, and anthocyanin, which imparts blue, red, and purple to flowers. Blood receives its color from the hemoglobin in the red corpuscles. Coloration of human skin is caused by the presence of pigments (see pigmentation).
Summary Article: pigment
From The Columbia Encyclopedia