Sulphur dyes are low-cost dyes for cotton, used mainly for deep black, navy and khaki, especially in large volumes and low-priced goods. They are applied in a reduced state and then oxidised inside the fibre. The result is a deep black at a lower cost than reactive dyes.
The drawbacks: the shades are flatter, the colour range is limited, and over time the fibre can weaken if residual sulphur is not properly neutralised. For this reason some buyers avoid them for premium garments. If in doubt, ask the supplier which dye class was used.
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