Chemical constitutions in the <scp><i>Colour Index</i></scp>™: A century of colourant classification

Abstract This article details how the Colour Index ™ (CI) system categorises and unambiguously labels commercial dyes and pigments based upon their chemical constitutions. It outlines the current process by which colourants that are new to the market find a place within CI and acquire generic identifiers. The contents of this paper will enable both experienced users of CI and those who are unfamiliar with the resource to gain not only a detailed understanding of its classification system, but also a deeper appreciation of what colourant designations signify and how they are correctly utilised.