Vat Dyes are an ancient class of Dyes, based on the natural dye, indigo, which is now produced synthetically. Vat dyeing is a process that refers to dyeing that takes place in a Bucket or Vat. Cotton can Dyed with Vat Dyes. Although almost all dyeing can be done in a Vat, the term Vat Dye is used to describe a chemical class of dyes that are applied to Cellulosic Fibre (i.e. Cotton) using a redox reaction as described below. Because of the use of Caustic Soda, and the very high ph of the dye bath in the dyeing process, wool cannot be dyed using Vat Dyestuffs.
The vat dyes have high color fastness, which is uncommon in other dye classes. On the other hand, vat dyes tend to have poor rubbing fastness, but this can be mitigated with special treatments to the fabric