Acid dyes

Acid dyes are water-soluble anionic dyes, containing one or more sulfonic acid substituent or other acidic groups.
Acid dyes are applied from acidic dye baths to nylon, silk, wool, and modified acrylics. They are also used to some extent for paper, leather, ink-jet printing, food, and cosmetics.

The sodium salts of organic acids used in the dyeing of silks and wool. They are so called because they are applied from a bath acidified with dilute sulfuric or ethanoic acid.