Classification of colorants

The Colour Index International, produced by the Society of Dyers and Colourists, in Bradford, is a comprehensive list of known commercial dyes and pigments and is updated regularly. Each colorant is given a Colour Index (C.I.) Name and Number.  For example:

All the colorants in the list have been classified by their chemical structure and by their method of application.

Classification of colorants by their chemical structure

The Colour Index assigns dyes of known structure to one of 25 structural classes according to chemical type.  Amongst the most important are:

a) azo dyes
b) anthraquinone dyes
c) phthalocyanines