The acid dye class is a water-soluble class of dyes with anionic properties. The textile acid dyes are effective for protein fibers such as silk, wool, nylon, and modified acrylics. Acid dyes fix to the fibers by hydrogen bonding, Vander Waals forces, and ionic linkages.

Properties of Acid Dyes

Acid dyes are usually sodium salts of sulphonic acids, or less frequently of carboxylic acids, and are therefore anionic in aqueous solution.

They have substantivity towards protein and polyamide fibers.

These dyes are suitable for wool, silk, polyamide, and modified acrylics.

These dyes have no affinity for cotton cellulose, hence not suitable for cellulosic fibers.

They are highly water-soluble.

Acid dyes have molecular weights in the range 300–1000 g mol-1.

They create ionic bonds with fiber, hydrogen bond and Vander Waals force of attraction also contribute.

The dye anion is the active colored component in these dyes.

Overall wash fastness of acid dye is poor, though lightfastness is quite good.