Page "Dye" Paragraph 13

Direct or substantive dyeing is normally carried out in a neutral or slightly alkaline dyebath, at or near boiling point, with the addition of either sodium chloride ( NaCl ) or sodium sulfate ( Na < sub > 2 </ sub > SO < sub > 4 </ sub >) or sodium carbonate ( Na < sub > 2 </ sub > CO < sub > 3 </ sub >).

Direct dyes are used on cotton, paper, leather, wool, silk and nylon.

They are also used as pH indicators and as biological stains.