If you want to drastically lighten the color of your hair, permanent dyes are usually not sufficient. Instead you will need to first bleach your hair, and then color it. This two-step procedure is commonly referred to as the “double process”. With ordinary oxidation tints, the hydrogen peroxide in the developer serves as a bleaching agent. However, when you wish more dramatic lightening such as changing black or dark brown hair to flaxen blond, the amount of bleaching in a permanent tint would be inadequate. In this case a separate bleaching step is required to “strip” your hair of its natural color. Bleaching agent contain 6 percent hydrogen peroxide and an “accelerator” substance, usually a persulfate, to boost the bleaching reaction. They frequently contain ammonia, which is needed to ensure adequate bleaching.
After bleaching, a toner dye is used to achieve the right shade. The bleaching makes your hair reddish and straw like; toners provide the finishing touch. Toners may either be semi-permanent or permanent dye products. Frosting, tipping, streaking, or painting are merely variations of the double process in which only portions of your hair, rather than all of it, are bleached and toned.
Bleaching damages hair. Unfortunately, the peroxide bleaching step, which is essential, is in fact an attack on the hair proteins and causes your hair to be dry, brittle, and straw like. As a result, bleached hair is more fragile than natural hair and requires after-shampoo conditioners to give it body and manageability. To minimize further damage, bleached hair should be manipulated very carefully and as little as possible; this means brushing, combing, or blow-drying very gently. In general, don’t retint your hair more than once every four to six weeks, since this can result in further hair damage. Above all, carefully consider making any drastic changes in your hair color; the more drastic the change, the more damage is likely to be done.