Sulfur dyes are applied on cotton to produce deep shades at low cost; they provide excellent color fastness, except against chlorinating agents. Sodium sulfide used as a reducing and solubilizing agent in this dyeing process is highly toxic and produces unhygienic hydrogen sulfide. In this study, alkaline protease was used in place of sodium sulfide to see if the latter could be substituted with the former, because of its hydrolytic and reducing nature in an alkaline bath. The study revealed that alkaline protease was quite effective in this regard and capable of substituting sodium sulfide with comparable dye strength of dyed cotton along with promising color fastness.

Sulfur dyes are water insoluble and require reduction as well as solubilization before application. These dyes are used for dyeing cotton with heavy shades, primarily because of good light and wash fastness at low cost. Sodium sulfide used for reduction is highly toxic, releasing sulfur products in drained out liquor, including hydrogen sulfide gas. Enzymes capable of reducing sulfur dyes were studied to replace sodium sulfide in dyebath formulations. It was found that a few enzymes viz. protease, pectinase, lipase, and catalase can effectively reduce all sulfur dyes. Dyebath potential, color strength (K/S), reduction bath stability, and colorfastness of dyeing were comparable among the reducing systems, thus demonstrating the feasibility of enzymatic cotton dyeing with sulfur dyes.