Colouring - Decolouring the Hair
Colouring ('tinting' or 'dyeing') is the physical / chemical process of adding colour to hair-shafts in one of the following forms:
Inorganic dyes: includes hair colour restorers.
Sulphide and Reduction dyes based on metallic salts (lead copper silver and iron). These dyes produce permanent colour changes. Permanent waving the hair may be contraindicated because the combination of chemicals thus introduced may lead to rapid hair-shaft destruction at scalp level.
Synthetic organic dyes are based on coal tar products - they include: Temporary dyes such as Cationic dyes (e.g. Methyl violet) and Anionic dyes (or Azo dyes as in water based rinses). These dyes will wash out of hair. Semi-permanent dyes: mixtures of nitro dyes and anthraquinones produce red yellow and blue colorings which wash out of hair after 6-8 shampoos.
Permanent oxidation dyes known as 'para' dyes require an oxidising agent e.g. hydrogen peroxide to function. These dyes include: • para-phenylenediamine (black) • para-toluenediamine (brown) • ortho-phenylenediamine (Brown) • para-aminophenol (reddish brown) • ortho-aminophenol (light brown). These dyes require allergic reaction tests over the 48 hour period immediately prior to the intended application irrespective of uneventful history. Moderate to severe allergic reaction dermatitis (even toxaemia) may result from injudicious applications. Colours may fade with strong sunlight. Hair shafts so treated will require special care when subjected to permanent wave processing. The process may change the feel of hair. Tinted hair shafts may be more vulnerable to breakage.
Quasi-permanent dyes are a mixture of semi-permanent and permanent oxidation dyes. The semi-permanent ingredient will wash out. Allergy testing is necessary in the author's opinion.
The scalp should first be carefully inspected for signs of infection cuts or abrasions or any pre-existing skin condition or acknowledged sensitivity. The full length of hair shafts should be closely inspected and tests conducted on randomly selected full length tails to reveal compatibility with the intended chemical procedure colour achievability and skin reactivity. Other tests should include porosity and elasticity in the dry and wet state.
These procedures should only be conducted by highly skilled and experienced operators. Where obvious scalp or hair abnormality exists additional caution is required. If in doubt procedures should not be conducted.
De-colouring ('bleaching' or 'high-lift tinting') is the process of lightening the natural colour pigment of hair either using a bleach (an alkali powder + hydrogen peroxide) or an oxidation dye + hydrogen peroxide. In the latter instance allergic reaction tests 48 hours in advance apply.
Visual examination of scalp and hair together with porosity, elasticity and compatibility testing should also be conducted, and patch testing the concentration of oxidant immediately prior to the application (reactivity to any concentration of hydrogen peroxide may vary by the hour). Any abnormality should be a reason to abort the procedure. The use of high concentration hydrogen peroxide should be avoided in procedures where scalp exposure is inevitable/possible.
Any area of pre-existing de-colouration should be cautiously approached in order to avoid saturation at any point of overlap.
Highlighting (with powerful bleaching reagents) should be conducted with great care to avoid leakage onto adjoining scalp, or the more serious potential risk of a blow-out of super-hot oxygen caused by the exothermal decomposition of the hydrogen peroxide within the semi-sealed foil parcels in which the bleaching process is being conducted.
Chemical hairdressing procedures may initiate inflammatory skin reactions :
• Irritant contact dermatitis may be the response to primary irritants (chemicals used routinely in salons e.g. relaxing, permanent waving chemicals and hydrogen peroxide). Symptoms may include pruritis, blistering and crusting.
• Allergic contact dermatitis follows sensitisation to a complete allergen. Oxidation hair-dyes are incomplete allergens which have the ability to pass through the skin and amalgamate with proteins forming a complete allergen. The symptoms may be serious and include pruritis and oedema - the reaction can be localised but the whole body may be inculcated. Allergic reaction testing prior to each exposure is therefore essential.
HYDROGEN PEROXIDE strength measured as a percentage or 'volumes' of available active oxygen per unit volume.
This is a dangerous substance and must always be used with care. Great temperatures may be rapidly reached during its exothermic decomposition.
1 unit of 3% hydrogen peroxide liberates 10 times its volume in oxygen.
1 unit of 6% hydrogen peroxide liberates 20 times its volume in oxygen.
1 unit of 9% hydrogen peroxide liberates 30 times its volume in oxygen.
1 unit of 12% hydrogen peroxide liberates 40 times its volume in oxygen.
OVER-PROCESSING - hair-shaft damage (ranging from debilitation to severance) associated with exposure to colouring, de-colouring and other chemical procedures during which one or more of the following factors may apply:
• injudicious choice of oxidant.
• Excessive or over-exposure of hair to oxidants.
• Exposing non-virgin (previously chemically treated) hair to further chemical procedures.
© 2013 Barry Stevens PhD FTTS