The dye used in textiles at low pH levels is acid dyes. It’s mainly for the dyeing of wool, not cotton textiles. As food colourants and in the medical industry some acids dyes can also be applied to stains on organelles.

 Acid dyes are anionic and soluble in water, so they’re basically put into the acid bath. These dyes have an acidic group, e.g. SO3H and COOH, which are applied to wool, silk and nylon when the ionic bond between the protonated -NH2 fiber band and the Acid Group of Dyes is formed. Overall wash fastness is poor although lightfastness is quite good. Due to the opposing electrical nature of dyes and fibers, acid dyes attack these fibers more quickly and absorb them faster; larger concentrations of electrolyte are added to slow dye uptake and provide leveled hues. Temperature aids in replacing the negative portion of acid with anionic dye molecules after acid creates cation on fiber.