When natural hair color is altered chemically ALKALI in the color mixture causes the hair to swell and the cuticle to open, expediting the penetration of color molecules into the hair fiber. This is why alkaline colors are more effective in coloring resistant gray hair
The act of peroxide/alkali mixture begins the process of decolorizing the melanin and continues as long as there is a sufficient amount of active peroxide and alkali to affect the change.
What happens next depends on the nature of the actual dyes used for coloring.
Direct dyes staying the hair fiber but are easily removed by shampooing, especially if the hair is extremely porous as a result of weathering or damage. Even in coarser, more resistant gray hair, direct dyes fade quickly.
Oxidation Dyes penetrate the hair shaft and are oxidized into undue dye molecules that are, in effect, “trapped” inside the hair fiber because they are too large to escape easily. They are truly permanent and can not be readily removed by shampooing. The alkali and peroxide gradually calm and active and the coloring process slows to a halt. Hair is shampooed and conditioned to restore normal pH.
The ideal permanent color system would use oxidation dyes exclusively, without direct dyes. It would carefully select these colorings for efficient coverage and lasting durability. And it would include natural or naturally derived conditioning agents in its formulation to protect hair or and help and parts shine during and after the chemical process.
Haircolor has 3 parts to it:
A coupler is a molecule that doesn’t have color itself, but when combined with other molecules, creates a color.
Para-Phenylenediamine: This tint molecule produces darker shades of color, basically browns and blacks.
To dyes such as those listed above are couplers/modifiers such as Resorcinal, which create new colors when combined. The finished dyes attach to the salt bonds of the hair, leaving the sulfur bonds free for other services like perming.
DEVELOPERS: or generators that cause the process of oxidation to take place, lightening the natural melanin and depositing the artificial pigments.