The name of “Vat” colorant come from the large wooden recipient/vessel, which was used when dye reduction and dissolving, was first performed.
- General properties of vat coloring agents are:
- Insoluble in water
- Applicable for cellulosic fibers
- Wide shades of different colors can be produces, especially, for green and blue colors
- The class of vat dyes has most light fastness than other colorants. However, all dyes in Vat class have different light fastness properties. Highest light fastness rating of such colorants is 7 and lowest is 5 on the scale of 8. Rating 5 is better than light fastness of many other dyes.
- Wash fastness rating of such coloring agents is 4-5.
- During dying process, coloring agent is passed through reduction phase in which they are converted into water-soluble leuco-derivatives.
Classification of Vat Dyes:
Based on application conditions, such coloring agents can be classified as follows:
- IN (Bayer classification) or CI (Ciba classification) dyes (Hot)
- IW or CII dyes (Warm)
- IK or CIII dyes (Cold)
- IN special dyes
Based upon chemistry, this colorant can be classified into Indigo derivatives and Anthraquinone derivatives.