Sulphur dyes are the most commonly used dyes manufactured for cotton in terms of volume. They are cheap, generally have good wash-fastness and are easy to apply. The dyes are absorbed by cotton from a bath containing sodium sulfide or sodium hydrosulfite and are made insoluble within the fiber by oxidation. During this process these dyes form complex larger molecules which is the basis of their good wash-fastness.
These dyes have good all round fastness except to chlorine. Due to the highly polluting nature of the dye-bath effluent, slowly sulfur dyes are being phased out. Sulfur dyes are primarily used for dark colors such as blacks, browns, and dark blues. The deep indigo blues of denim blue jeans are a product of sulfur dyes.
This oxidation can be done in air or by using oxidizing agents like hydrogen peroxide or sodium bromate in a mildly acidic solution. Now as the dye has become water insoluble in fiber so it will not bleed in water when washed and will not stain other clothes. However the dye may have poor fastness to rubbing, that is the dye from the fiber may come out gradually if the fabric is rubbed against. Also the fastness to hypochlorite bleach is poor because hypochlorite breaks the color imparting group in the dye and hence the colored part becomes colorless
Gayatri Dyes & Chemicals brings its customer all the series of Sulphur Dyes:-