Chapter 4 119 There are a wide range of products on the market that use all these processes. Table 1 highlights the main product types currently available and their coloring mechanisms. These products are also distinguished by the transformation that the consumer will notice and the permanency of the change. Table 1 Hair Color Products Hair Color Products Technology Level of Lastingness Temporary Dye Addition Wash out (with 1-2 washes) Semi-permanent Dye Addition Wash out (with 6-8 washes) Demi-permanent Dye Addition Wash out (with up to 24 washes) Permanent Lightening + Dye Addition Permanent (grows out) Bleach Lightening Permanent (grows out) Any process that involves lightening of the underlying color of the melanin will result in a color change to the existing hair that will be permanent until new hair grows. New growth will, of course, have the natural hair color and so the roots will be evident. The lightening mechanism for a permanent coloring product is different from that of a bleach product. The permanent product typically uses alkaline hydrogen peroxide at pH 10 and the bleach product uses the combination of hydrogen peroxide and persulfate salts at pH 10. The level of lightening achievable is also very different: Bleaches can deliver a much higher level of lightening than permanent coloring products. The dyes used in the various products are also different. The permanent and demi-permanent products use oxidative dyes. In these products, uncolored dye precursors are mixed immediately before coloring with hydrogen peroxide to activate a chemical process— oxidative condensation—which forms the colored dye molecules. The rate of dye formation is controlled so a significant amount of the smaller dye precursors can penetrate into the hair, where they then react to form the larger dyes inside the hair. They are now “trapped” and will stay in the hair for many repeat washes or until the hair is cut. The semi-permanent and temporary dyes use direct dyes larger,
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