PIGMENTS AND PAINT.
Pigments (Fs., Pigments; GER., Furben).—The term " pigments" is applied to those colouring matters which are mixed in a powdery form with oil or other vehicle for the purpose of painting. They differ in this respect from the dyestuffs (see Coal-tar Products, pp. 641-684, and Dyestuffs, pp. 854-869). Their preparation for use and their application are described hereafter in the section on Paint (see pp. 1552-1556) ; the present article embraces only their origin and production. A very large proportiun of the pigments are derived from the mineral kingdom. Organic colouring matters for use as pigments are mostly made in the form of " lakes," by one of the three following methods :—(a) To a filtered solution of the colouring matter, is added a solu tion of alum ; the whole is agitated, and the colour is precipitated by a solution of carbonate of potash. (b) A solution of the colouring matter is made in a weak alkaline lye, and precipitated by
adding a solution of alum. (c) Receutly-precipitated alumina is agitated with a solution of the colouring matter as before, until the liquid is nearly decolorized, or the alumina assumes a suffi ciently deep tint. The first method is generally adopted for acidulous solutions of colouring matter, or those injured by alkalies ; the second, for- those not injured by alkalies ; the third, for those whose affinity for gelatinous alumina enables them to combine with it by mere agitation. (See Alumina, p. 333.) It will be convenient to describe pigments under the heads of the chief colours, in alphabetic order—blacks, blues, greens, reds, whites, and yellows.
BLACKS.—See &tide Blacks, pp. 452-456.