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Metallic dyes

Metallic dyes

Postby chris the limey » 22 Oct 2010 02:33 pm

These work by depositing metal salts in the hair cortex and on the hair cuticle, which dulls the hair. There are three main types:
1 Sulphide dyes here the hair is first coated in sodium sulphide and then with a
metallic salt.
2 Reduction dyes here a metal salt is converted to just the metal by a reducing
agent, e.g. pyragallol. The minute particles of metal are deposited in and on the
hair, thus colouring it.
3 'Hair colour restorers' these are not usually used in the salon but can be bought by the public from chemists. The idea is to tint the hair in order to darken unpigmented white hair. They contain lead acetate and sodium thiosulphate which react very slowly together and darken the hair by depositing lead sulphide in the cortex and on the cuticle.

Disadvantages of Metallic Dyes
• They dull the hair.
• They can colour the skin as well as the hair.
• Some metals used in metallic dyes react with hydrogen peroxide. Therefore the hair cannot be permed, bleached or tinted.

Incompatibility test
Always test hair for the presence of any metallic salts before perming, tinting or bleaching the hair if there is any uncertainty as to what the client has had on their hair. This test is known as an incompatibility test.

To carry out the test:
1 Take a small cutting of the hair from the crown area or the front (if the client has been tinting their own hair this will have the highest concentration of tint present).
2 Mix a simple bleach, which is a mixture of hydrogen peroxide and ammonia.
3 Immerse the cutting in the simple bleach.
4 If incompatible chemicals are present on the hair a reaction will occur.
5 Bubbles of gas (oxygen) being given off can be observed. Steam rises and heat is given off. The hair elasticity is increased and breakage occurs until the hair is completely destroyed.
chris the limey
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