These you have no doubt heard about—they are supposed to be the magical cure for graying hair and are often called color restorers. They deposit metallic dyes and salts of various metals such as manganese, cobalt, silver, and copper on your hair shaft, which gradually darkens the hair. But hair dyed this way does not permanent-wave well, nor is itscondition very good, as this kind of dye tends to make the hair look a dull, flat color. Metallic dyes have to be removed completely, with the use of a special preparation, several days before waving or tinting with a permanent colorant. Because of their many disadvantages, I think they are best avoided.
Hair bleaching is done with hydrogen peroxide, which affects the hair shaft both physically and chemically. Combined with an alkaline compound such as ammonia, it opens the imbrications of the cuticle so that it can penetrate the hair shaft, and then inside the cortex it chemically oxidizes the melanin pigments, fading their color, thus bleaching out the hair in the process. There are products on the market that are simple bleachers—they are called lighteners, and they consist of peroxide together with ammonia. Sometimes a “drabber” is added in order to remove the red highlights that come from bleaching darker hair. Bleaching forms an important part of the other permanent tints, which also rely on oxidation processes to work. (more…)
