Sulfur dye, a class of dye containing sulfur, has more complex molecular structure. Sulfur dye is generally heated sulfur or sodium sulfide together with certain aromatic amines, amino phenols and other organic compounds, namely vulcanization. Most sulfur dyes are insoluble in water. In dyeing, sulfur dye needs to be dissolved in a sodium sulfide solution or alkaline hydrosulfite solution to reduce to its hidden color, and then absorbed and oxidized by fiber to show color. According to the desired dyeing conditions, sulfur dye can be divided into sulfur dye and sulfide vat dye. The former use sodium sulfide as reducing agent; the latter hydrosulfite as reducing agent, and its fastness and properties is between sulfur dye and sulfide vat dye, so that it is a higher sulfur dye.
In 1873, the initial sulfur dye is made out from melting sodium by Groissant. In 1918, sulfur dye began to be produced in our country, mainly used for plant fiber dyeing. Sulfur dye is characterized by containing a sulfur atom in the molecule, becoming into water-soluble hydrocolloid after the reaction with a reducing agent such as sodium sulfide, dyeing the fibers, and then the dye turns insoluble through the air oxidation. The sulfur dye is not very bright, but generally washable and light fast, enables the fiber brittle. There is also soluble sulfur, which is soluble in water, and more convenient to use. The sulfur dye is a mixture generating from every reaction stage. In 1950, the continuous dyeing method of fine particles of sulfur appeared, but it occurred unsalable after the 1950s, because of the successive appearance of reactive dyes and advanced direct dyes, lightfastness direct dye especially. Still, owe to its budget and other factors, it is still in use.
Sulfur dyes is more popular with rural customers for its relatively simple manufacturing process and low cost, also, it is washable, light fast, not bright shade therefore can be dyed dark, adapted plant fibers and stained. In addition to color is not bright, the dye chromatography insufficiency, lacking of good red and purple, and low color strength, larger dosage, therefore sulfur dyes is limited in application, but so far it still is the largest output and applied widely dyes in China.