Bleach is any substance that lightens, brightens, or removes the color from a material. Manufacturers bleach textiles, paper, and other materials to whiten them or to prepare them to be dyed. Homemakers use laundry bleach to brighten clothes. People also use some bleaches as disinfectants. There are two main kinds of bleaches, chemical and optical.
Chemical bleaches act on the molecules that give a material its color. The bleaches make materials colorless or nearly colorless. The most widely used chemical bleaches include chlorine bleaches and oxygen bleaches. Many household and industrial bleaches are chlorine bleaches, which remove the color from most textiles, wood pulp, pottery, and other materials. Oxygen bleaches are milder than chlorine ones. People use hydrogen peroxide and other oxygen bleaches to lighten hair and to brighten colored fabrics and other materials that might be harmed by chlorine bleaches (see Hydrogen peroxide).
Other chemical bleaches include certain sulfur compounds. These compounds are used to bleach some wools, silks, and various types of manufactured fibers.
Optical bleaches mask yellow discoloration in a material. These bleaches, commonly called fabric brighteners, absorb ultraviolet light and change it to blue light. The combination of the blue light and the yellow discoloration produces white light that makes the material seem brighter (see Color (Mixing colored lights)). Several laundry detergents contain optical bleaches to mask discolorations that are hard to remove.
Many ancient peoples bleached textiles. They treated the cloth with smoke from burning sulfur or with bleaches they made from various plants or plant ashes. Then they spread the treated cloth on the ground to whiten in the sun. Similar bleaching methods were used until the 1700’s, when manufactured bleaches were developed. Today, textile factories use a variety of methods, depending on the kind of cloth. In most cases, the cloth is washed, soaked in a bleaching solution, then soaked in various chemicals to reduce any harmful effects from the bleach. Finally, the cloth is rewashed, thoroughly rinsed, and dried.
