1. Acid Dyes 
• These dyes comprise a large number of dyes used for the dyeing of wool, silk & 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 3 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 & light fastness.

b. Acid milling dyes
:• Selected because of their high & light fastness & 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 
• The family of acid dyes is very large & diverse, varying widely in their methods of dyeing, application & end use of the dyed fabric. 
• A choice of dyes should be made considering sometimes-incompatible factors: - level dyeing, fastness, brightness & 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. 


2. Metal Complex Dyes
• Relatively difficult to Mainly used complex apply; expensive; complete colour range but duller shade than acid dyes; good fastness due to high molecular size & metal complex structure.)


3. Chrome Dyes
• Complicated application; expensive; complete color range but very dull shade;  good all round fastness. Mainly used for wool products especially for the end use of carpet.