Colour Index
Description
Initially published in 1924 by the Society of Dyers and Colourists in England, this widely acclaimed system enabled each commercial colorant to be assigned a name and number according to its composition, chemical class and shade. Two formats, the Colour Index™ Generic Names (CIGN) and Colour Index™Constitution Numbers (CICN), are used for each colorant. For example, cobalt yellow is CI Pigment Yellow 40 and CI Number 77357.
Any manufacturer of a dye, or pigment can register their product. To date, over 27,000 individual products have been registered under 13,000 Colour Index references. Each product name is listed the manufacturer, physical form, principal usages and comments supplied by the manufacturer to guide prospective customers. The C.I. Generic Name defines the essential colorant only. Commercial products listed under the same C.I. Generic Name may not have identical application, fastness or ecological properties; check with the supplier concerned. The Colour Index generic name relates to the application of the colorant; for example, P stands for pigment, along with a description of the hue, such as Y for yellow or R for red followed by a sequential number. Examples include:
- Cobalt yellow (as above): CI Pigment Yellow 40, or PY40
- Hansa Yellow G: PY1
- Orthonitroaniline Orange: PO2.
The Colour Index Constitution Number indicates the chemical classification of the pigment or dye, as series of numbers have been assigned to particular colorants that are chemically related. For example:
| Chemical Category | CI Number range | Chemical Category | CI Number range | |
|---|---|---|---|---|
| Nitroso | 10000–10299 | Quinoline | 47000–47999 | |
| Nitro | 10300–10999 | Thiazole | 49000–49399 | |
| Monoazo | 11000–19999 | Azine | 50000–50999 | |
| Disazo | 20000–29999 | Oxazine | 51000–51999 | |
| Trisazo | 30000–34999 | Thiazine | 52000–52999 | |
| Polyazo | 35000–36999 | Anthraquinone | 58000–72999 | |
| Diarylmethane | 41000–41999 | Indigoid | 73000–73999 | |
| Triarylmethane | 42000–44999 | Phthalocyanine | 74000–74999 | |
| Xanthene | 45000-45999 | Natural | 75000–75999 | |
| Acridine | 46000-46999 | Inorganic | 77000-77999 |
Commercial colorant tradenames on tubes, bottles and cans of colorants can be arbitrary or vague, but current ASTM protocols in the U.S. require that all containers as well as their technical sheets provide the precise identify of the colorant. This is usually done by listing its CIGN.
For dye analysis results listed by their Colour Index names, please see Colour Index list in the Dye Analysis collection
Synonyms and Related Terms
CI; Color Index; index de couleur (Fr.);
Resources and Citations
- Wiley Online Library: Chemical constitutions in the Colour Index™: A century of colourant classification 23 March 2025
- Colour Index Generic Name: Definition Published online by Society of Dyers and Colourists and American Association of Textile Chemists and Colorists.
- Society of Dyers and Colourists, Colour Index, 3d ed. (Bradford, England, 1971),
- Ruth Johnston-Feller, "Standard Specifications of Pigment Composition and Color," in Artists' Pigments: A Handbook of Their History and Characteristics, ed. Robert L. Feller, vol. I (Washington, 1986, 299-300.
- D. Tamburini, F. Sabatini, S. Berbers, M.R. van Bommel, I. Degano, 'An Introduction and Recent Advances in the Analytical Study of Early Synthetic Dyes and Organic Pigments in Cultural Heritage', Heritage 7(4) 2024. link