ACID DYES These dyes comprise a large number of dyes used for the dyeing of wool, silk and nylon. They vary considerably in their basic chemical structure, but have one common feature - they dye from an acid dye bath. All acid dyes can be grouped in three broad sub groups:

a. Level dyeing acid dyes. These dyes produce bright dyeing. The main feature is their good leveling properties. They are dyed from a dye bath containing strong acids (Sulphuric or Formic acid). These dyes exhibit low wash and light fastness.

b. Acid milling dyes. Selected because of their high and light fastness and are extensively used for dyeing woolen fabrics that are subsequently milled. These dyes require great care in application because uneven dyeings are difficult or impossible to rectify. The dye bath requires the presence of weak acid (acetic acid) or acid releasing salts (ammonium sulphate or ammonium acetate) from which acid is liberated during dyeing.

c. Pre-metalized dyes These dyes represent an extension of mordant dyes. The metal component being already incorporated in the dye during manufacturing process. Very good light fastness even in pale shades

USE: The family of acid dyes is very large and diverse, varying widely in their methods of dyeing, application and end use of the dyed fabric. A choice of dyes should be made considering sometimes-incompatible factors: - level dyeing, fastness, brightness and ease of application. Care must be taken to use the appropriate method as prescribed for a given dye. A number of acid dyes are also used to dye nylon.