The Colour Index is a reference database of dyes and pigments, published by the Society of Dyers and Colourists with the American Association of Textile Chemists and Colorists. It gives each colourant a generic name and, where the chemical structure is disclosed, a constitution number.
Buyers and suppliers use these names as a common language. A buyer can ask for C.I. Pigment Blue 15:3 and every maker knows what chemistry is meant.
Trade names change from maker to maker, and many Indian plants sell the same dye under their own house names. The CI name lets you compare like with like across suppliers, which is the first step in any fair quote comparison.
The two parts
- The C.I. generic name gives the application class, the hue and a number, such as C.I. Reactive Black 5, C.I. Disperse Blue 79 or C.I. Pigment Green 7.
- The C.I. constitution number is usually a five-digit number tied to the chemical structure, such as 74160 for copper phthalocyanine blue.
- Some dyes have a generic name but no constitution number, because the maker has not disclosed the structure.
- Pigment names can carry a suffix after a colon, such as 15:3, that marks a crystal form or salt.
What the CI name does not tell you
A CI name identifies the main colouring molecule. It does not tell you strength, shade, particle size, purity, salt content, physical form or which additives are present. Two products sold as C.I. Reactive Red 195 can differ in strength by a wide margin and in shade enough to fail a match.
Many commercial dyes are also mixtures of several CI dyes, blended to hit a target shade. The label may name only the main one. Ask the supplier to declare every CI component in a mixture, so you can check each against restricted lists.
Some suppliers also sell a product under a CI name it does not fully match, for example a close shade built from cheaper components. A lab test against a known reference can show this. That is one reason to buy against a sample, not against a name alone.
How to use CI numbers in buying
- Quote the full CI name in your enquiry and contract, including any suffix.
- Ask for the CAS number as well, since regulators and safety data sheets use CAS numbers rather than CI names.
- Check each CI name against your customer's restricted substance list and the ZDHC MRSL. See whether Indian dyes comply with the ZDHC MRSL.
- Still set strength and shade against your own standard sample, as explained in how to measure dye strength.
Next step
We match your CI list to manufacturers in Gujarat, check their documents and compare samples against your standard. To begin, book a free sourcing review.