Indigoid Dyes

a group of vat dyes closely resembling indigo in structure and used to dye cellulose and protein fibers as well as for cotton printing. These dyes cover a broad range of the color spectrum, from orange to black. Their resistance to light and water are rather high but inferior to that of polycyclic dyes. Indigo and thioindigo are characteristic indigoid dyes. The range of indigoid dyes was considerably extended at the beginning of the 20th century. Subsequently some of them were replaced by other classes of dyes; 15-20 indigoid dyes are still used. The manufacture of indigoid dyes is a complex, multistage process. The starting compounds are various derivatives of aniline, naphthalene, and other substances.