Bronze.—Manganese chloride followed by caustic soda.
Soluble Colours.
(A) Natural Dyes. These colouring matters are now seldom used.
Yellow and Brown.—The vegetable extracts, such as fustic, quercitron, cutch, turmeric, have practically all been replaced by aniline colours.
Red.—Madder (Turkey red), Brazilwood, cochineal (a dye obtained from dried cochineal insects). Safflower.
Black.—Logwood, used in conjunction with an iron salt. Cutch, used with an iron salt.
(B) Coal Tar Dyes. The dyeing and colouring of paper pulp by means of the artificial organic substances has become a matter of daily routine, the expensive natural dyes and the ordinary pigments having been almost completely superseded. The numerous colouring matters available may be classified either by reference to their chemical constitution or simply on general lines, having regard to certain broad distinctions.
If the latter classification is taken, then the dyes familiar to the paper-maker may be divided into—
(a) Acid dyes, so called because the full effect of the colouring matter is best obtained in a bath showing an acid reaction.