Direct dyes
Sulphur dye is a water-insoluble dye, containing sulphur both as an integral part of the chromophore and in attached polysulphide chains, normally applied in the alkaline soluble reduced (Ieuco) form from a sodium sulphide solution and subsequently oxidized to the insoluble form in the fibre.
The first sulphur dye was discovered in France in 1873, and further work done by Raymond Videl enabled the manufacture of 'Videl black". Its outstanding fastness to light, washing and boiling far surpassed any cotton black known at that time. The general disadvantage of the Sulphur dyes that they produce dull shades and lack a red. The main advantage lays in their cheapness, ease of application and good wash-fastness. In their normal state Sulphur dyes are insoluble in water but are readily soluble in the solution of Sodium Sulphide. In this form they have high affinity to the all cellulose fibres.
The use of Sulphur dyes is restricted to dull brown, Khaki and Navy shades, where a good wash but not boil-fastness is required. Most Khaki and Navy overalls are dyed with Sulphur dyes. An outstanding member of this family is Sulphur black. It dyes all cellulose fibres, but particularly linen and jute, to a lustrous and deep black with excellent wash and light fastness. Sulphur dyes are dyed from a dye bath containing Sodium Sulphide and common or Glaubers Salt, and are oxidized by airing or with some oxidizing agents (Sodium Bichromate or Hydrogen Peroxide) in a fresh bath.
The sulphur dyes contain sulphur in one form or another. Nearly all colors except reds have been produced in this chemical group. The sulphur blacks, blues, and browns are among the fastest produced. They are used only in cotton and other vegetable fabrics and are fast to light, washing, and acids, or perspiration. Sulphur colors are excellent for dyeing cotton hosiery and other knit goods in dark colors or blacks. Some of them require some after-treatment to fix them permanently in the fiber.