Bleaching, is one of the older, unchanging and simplest method of altering the hair’s natural colour and involves decolouring either part of, or all of the hair’s natural melanin. It is also still to date the most effective way to lighten artificial hair colours. The bleaching process progressively lightens until finally white or blonde shades are produced. Although there are a several different chemistries for ‘bleaching’, this blog will cover the chemistry used for bleaching hair that involves an alkaline solution of hydrogen peroxide.
Hair Bleach
Hair bleaches consist of solutions up to 12% hydrogen peroxide (H2O2). Although stored in an acid solution they become most active at a high alkaline pH. Immediately prior to use the H2O2 is mixed with an alkali to give a final pH around 10-11. Don’t be fooled by manufacturers who use ‘peroxide-free’ labels as a way to promote their products as ‘hair-friendly’. Although these mixtures do not contain peroxide, they will contain another oxidizing agent to create the effect which will have the same damaging profile on the hair.
Bleaches are more traditionally found in powders of different colours, commonly blue and white, the colour of the powder will have no impact on the finished result. Bleach is also available in crème, paste, gel and oil varieties. It is a matter of performance, preference, cost and also situation; example some on-scalp marketed products contain cooling ingredients to help manage the smarting sensation that some can feel on their scalp, please note they do not reduce irritation, but if you have a sensitive scalp they can help to make the process more comfortable. H2O2 by itself would be too slow to achieve the desired blondes of today and ingredients such as ammonium and potassium persulfate are added to boost performance. Bleaches also contain thickeners to improve the rheology (spreading and stickiness) and consistency of the finished product, after all we need to be precise when placing it onto the hair.
Ammonia is the preferred alkaliser, normally supplied by ammonium salts, an essential part of the formulation since less bleaching occurs in other amines or alkaline agents. Simply the bleaching effect decreases with decreasing pH. The pH is regulated throughout the bleaching process by metasilicates, which allows us to work with lower H2O2 for longer development times giving more time for effective lightening of the natural melanin; low and slow wins the race to be blonde.
The Bleaching Action
H2O2 works by breaking the disulfide bonds of cystyl residues in the fiber. During normal bleaching, 15-25 percent of the bonds might be broken, during more intense bleaching when taking hair from a dark natural base up to a very pale blonde up to 45 percent of these bonds might be broken. This is where the category of ‘plexes’ work in fixing these broken bonds.
Once the bleach mass comes in contact with the hair, the alkaline pH swells the hair to allow the bleach to travel throughout the hair lightening everything it comes in contact with. Very bleached hair takes on a yellow tone, because keratin (the protein your hair is made of) is naturally a pale yellow. Some bleaches do come with anti-yellow or direct-acting dyes that can deposit colour while the hair is being bleached. But to achieve that ‘platinum blonde’ look, hair will need to be coloured or toned as well as bleached over a multi-step process. It’s impossible to make your hair a lighter shade without the help of a bleaching agent – all of which are called ‘oxidizing agents’.
Black hair before and after beaching.
Radicals can be formed in the bleach if in contact with metals such as iron and copper, this can be observed by excessive swelling of the product or heat being generated. Fortunately, bleaches contain certain chelants that can inhibit or reduce the effect as there are trace metals found in all hair.
Note; working with foil will also increase free-radical activity, this is known and understood and managed through technique (careful placement and smaller quantities of product) and working with lower H2O2.
Shutting down the chemistry
Once the require lift has been achieved the bleach is removed with water and a mild shampoo. Then working with a post-bleach treatment that contains anti-oxidants to stop any residual chemistry.
Next time I will have a look at Bleach; the Art Form.
Caroline
