Dye refers to a class of substances allowing other substances (such as fiber and its main products, etc.) to obtain certain colors with mainly being organics. The ancient paint is extracted from plants and animals. China is one of the first countries in the world which began use natural dyes. At 4000 years ago, people in china had already known how to do silkworm breeding and reeling and dye to various colors. Indigo, Alizarin, gall and carmine are among the earliest applied natural dyes in ancient China. However, there is only 100 years of history for modern industrial production of organic dyes. The first synthetic dye, mauveine, was synthesized in 1856, by the British chemist Perkin for wool and silk dyeing. In 1901, a German chemist invented the Vat Blue (called Indanthrone blue) which becomes a solid cotton dye. In 1956, active dyes had appeared. Since the 1960s, with the emergence of a large number of synthetic fibers, the development of various types of dyes is greatly boosted and until now dyes with practical applications has reached 1000 or more and has almost replaced all natural dyes. According to the structure of the dyes, it can be divided into dye azo dyes, carbonyl dyes, reactive dyes, aromatic dyes and phthalocyanine dyes; based on the application, it can be divided into acidic dyes, direct dyes, solvent dyes, vat dyes and disperse dyes and the like.

The solvent dye refers to dye being insoluble in water but soluble in an organic solvent. Based on the types of the solvents, it can be divided into: (1) A series. It can be dissolved in alcohol dye with bright color and is generally used for dyeing alcohol. (2) O series. It can be dissolved in an organic solvent and grease and is mainly used for the coloring of fats and oils. (3) W series. Used for the specific dyes for wax coloring.