A dye containing sulphur and soluble in a 0.25–0.50% sodium sulphide solution, and used to dye cotton; the dyes are manufactured from aromatic polyamines or hydroxy amines; the amine group is primary, secondary, or tertiary, or may be an equivalent nitro, nitroso, or imino group; an example is the dye sulphur blue. Also known as sulphur dye.