Pigment

(pig'-ment). In biology, a pigment is any organic coloring-matter in the ti ues of plants or animals, e.g., the coloring matter occurring in the iris, retina, hair, and in the rete mucosum of the skin. It may be of mimetic value, or concerned in a imilation and metabolism, or in respiration. P., Color, and Dye-stuff; a pigment is any substance that is employed in the arts for the purpose of imparting color to bodies. The term is properly restricted to the dry coloring-matter, which when mixed with a vehicle becomes a.paint. O. N. Witt a umes the presence of certain characteristic groups chromophorous groups in all dyestuffs, which, by introduction into colorle bodies, give rise to the basis structure of dyestuffs chromogen ous groups. When these chromogen ous groups are joined to salt-forming groups, such as hydroxyl or amidogen, dyestuffs are formed. Color is applied to any hue, especially a pure tint, other than black or white. A dye-stuff is any dyewood, lichen, powder, or dyecake used in dyeing and staining dre -materials. A fast color is one which resists the weather, light, soap-lye, dilute alkalies, and very dilute acids; a fugitive color is one which is di ipated under similar circumstances. A substantive coloring-matter is one which pa es into an insoluble state upon the fiber without the intervention of a mordant; examples, all the mineral coloring matters, indigo, turmeric, annatto, safflower, and most of the coal-tar colors. An adjective coloring-matter is one which requires a mordant or mediating agent in order to become insoluble upon the fiber. A mordant is a substance which has an affinity for or which can at least penetrate the ti ue to be colored, and which po e es also the property of combining with the coloring-matter employed, and of forming with it an insoluble compound within or about the fibers. Mordants may be iron salts (copperas, ferrous acetate, iron pyro lignite, ferric sulphate, and nitrates), nickel, chromium (chromium sulphate, fluorid, chlorate, pota ium di-cnromate and chromate), tin, manganese, lead, copper (nitrate), antimony (tartar emetic), or tannin. Raising is the proce or method of intensifying colors by means of mordants.