There are three basic categories of hair colors, depending on the duration of the effect produced: temporary, demi-permanent and permanent. Temporary hair colors modify the color of the hair temporarily and are readily removed by washing. These products contain “direct” dyes – these color molecules are unable to penetrate the hair fiber so they settle on the hair’s surface. They will be washed away after a few shampoos.
Demi-permanent hair colors are made of color molecules that are able to penetrate the hair. These colors settle on and within the scales of the cuticle, becoming established around the cortex without modifying the hair’s natural melanin. However, since these molecules are also not bound to the hair protein, the color gradually fades with washing. The color normally stays in for about 2 months.
Oxidation hair colors are easy to recognize. They require at least two components which have to be mixed together immediately prior to use. Oxidative hair colors change the natural hair pigments and give the hair – depending on the formulation – either “tone-on-tone” color (also referred to as “demi-permanent”) or “permanent”, lasting color. Permanent colors cannot be washed out and are the way to permanently change hair color. They produce an effect that is resistant to washing and are chosen to provide long term color changes, as well as excellent coverage of “grey” hair.
The two components that are mixed are an alkaline agent (the ‘color’) and a bottle that contains hydrogen peroxide (the ‘developer’).
How do Permanent Oxidation Hair Colors Work?
The effect of each oxidative dye is based on the following components: an alkalizing agent – usually ammonia – and oxidative coloring agents. The alkaline agent has the effect of opening the outer hair layer so that coloring and oxidizing agents can penetrate into the hair shaft more easily. The starting materials for developing the new color are called color precursors which are very small, colorless molecules that only develop their own color nuance once inside the hair. The process is similar to developing a photo in that there must be a chemical reaction for the image, in this case the color, to appear.
The oxidizing agent – usually hydrogen peroxide – is mixed with the color prior to application. The oxygen is released by the reaction between the alkaline agent and the oxidizing product. It triggers the actual color-changing reaction. Large, colored molecules are formed within the hair’s cortex which are resistant to being washed out of the hair. Simultaneously, the oxygen released will lighten the natural melanin pigment in the hair so that the new color can be seen, effectively replacing the hair’s natural color.
Demi-permanent colors also include an oxidation step (for example, mixing with peroxide) but do not provide a marked lightening of the hair’s natural melanin pigment. Demi-permanents traditionally enhance or deepen the natural hair color, or may be used to alter the tone of the natural color. http://www.ultraimports.com.au/terms.php
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