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Definition of a Colour Index™ Generic Name

A C.I. Generic Name describes a commercial product by its recognised usage class, its hue and a serial number (which simply reflects the chronological order in which related colorant types have been registered with the Colour Index), e.g. C.I. Acid Blue 52, C.I. Direct Red 122, C.I. Pigment Yellow 176 and C.I. Solvent Black 34.

This definition enables a particular commercial product to be classified along with other products whose essential colorant is of the same chemical constitution and in which that essential colorant results from a single chemical reaction or a series of reactions. The definition also includes multi-constituent substance or ‘products by process’ [see e.g. Regulation (EC) No 1907/200 REACH and related RIPS]. It is intended to exclude products obtained simply by physical admixture of essential colorants.

In some cases, the same essential colorant is present in more than one application category. Typically, a disperse dye can often be applied as a solvent dye, and a vat dye can sometimes be used as a pigment.

However, it cannot be guaranteed that the essential colorant of each and every C.I. Generic Name results from a single chemical reaction or series of reactions and that there are no physical admixtures. The Colour Index is a living document and has had to adapt to advances in analytical techniques and the additional information now requested from registrants. Consequently, that which was acceptable historically is now viewed more critically.

Many commercial products contain, as well as the substance responsible for the colour, quantities of other chemicals (generally referred to as additives) designed to improve the application properties of the product, such as the dispersibility, flow and flocculation resistance of pigments; dyes often contain significant amounts of diluents. In all cases, the essential colorant is the portion of the material responsible for the colour and excludes any additives.

Colorants listed under a C.I. Generic Name whose serial number contains a colon differ slightly from those listed under the parent C.I. Generic Name. This slight difference is usually chemical but may be due to different crystal modifications in the case of certain pigments.

Historically, a colon number was added to the serial number of a particular C.I. Generic Name when a new product was reported by a manufacturer as being similar to the original. ‘Similar to’ can generally be interpreted as meaning slightly different chemically. This imprecise definition gave manufacturers the opportunity to request new C.I. Generic Names for products that should have been given colon numbers. Conversely, subsequent disclosures revealed that certain products that had been given colon numbers should really have been allocated new generic names. The system has, nevertheless, been continued where it was considered helpful to users to group certain colorants together in this way.