• Using dye to color fabrics goes back thousands of yearsDye image by vertellis from Fotolia.com
  
  Throughout recorded history, people have used dyes to color fabrics. Paintings and writings from ancient times describe how fabrics were colored and used to make clothing. Most early dyes were made from natural sources, such as the herb madder, which provided red pigment, and indigo, that came from plant extracts and produced blue shades. Several modern types of dye are now used to color both natural and synthetic fibers.
  
  

Acid Dye

• Acid dyes often are used to color such natural fibers as silk, cashmere and wool. They are also used to color nylon fabrics. While some of them can be toxic, others are so safe that they are used in food coloring. Acid dyes are applied in the form of an acidic solution, in which the acid component typically is provided by harmless and natural vinegar or citrus. Acid dyes are effective because they contain molecules known as anionic molecules, which are attracted to corresponding cationic molecules in the fiber.
  
  

Disperse Dye

• Disperse dyes are used to color synthetic fabrics such as polyester. These dyes do not dissolve easily in water, but the molecules in the dye disperse easily and find gaps in the structure of the polymer being colored. High pressure, and temperatures of 266 degrees Farenheit, are used in the dyeing process to loosen the structure of the polymer, allowing the dye molecules to find gaps.
  
  

Reactive Dye

• Fiber reactive dyes are used to color cellulose fibers such as hemp, linen and cotton, although some fiber reactive dyes are being created specifically to work with wool and silk. These dyes give strong, bright results and the color is considered to be colorfast, meaning that it will not fade or wash out easily. This is because the dye molecules form a covalent bond with the cellulose molecules in the fiber. This means that a dye molecule bonds with a cellulose molecule in such a way that they form a single, colored molecule.