The first dyes were extracted from nature mostly plants. Their usage is going on in India for centuries. The first synthetic dye was made by William Perkin also called organic dyes these chemicals have been made into wide variety of colors since then. The basic function of these chemicals is to impart color to the substrate. Both natural and synthetic dyes perform this function. The pigments differ much from these organic substances and do not impart color to the substrate.
The organic dyes have totally replaced natural ones as they are economical and display wide array of colors. There are many types of these color imparting substances and they differ not only in color but the type of process they can be subjected to. Some of the types are: acid, basic, direct, reactive and sulfur dyes. The function and action differs a lot, hence some may be used to color food others for or clothing and some for hair. Actually the list is quite large and more development is taking place in the chemical industry.
These chemicals are subjected to may tests and regulation during and after manufacture. Food coloring agents have to be safe for human consumption and hence are tested vigorously for carcinogenicity and toxicity. Some coloring chemical used on fibers may cause allergies hence they are not used.
Acid, reactive and cold ones are most used on clothing fibers. Each is used in different substrate like cotton, silk, wool and nylon. Direct ones are used on leather besides fibers. Denim is colored by Vat dye that imparts characteristic color to jeans which we commonly wear. Some of these coloring agents function in presence of another agent and are mostly used in imparting special effects to fibers like cotton. Lot of specialization has taken place in case of manufacture with progress in technology. The manufacturing is a complex process with usage of intermediates, differing methods and technology.
The manufacturing units are spread all over the globe but major producers are in the developed countries. The consumption of coloring chemicals is continuously on the rise. Though useful some of the dyes are health hazards and can be used in limited quantities only.