Red colored hair see under a videomicroscope

Colouring the hair has now become totally commonplace. The ease with which colouring products can now be applied and the constant association of beauty and hair health means we no longer have to think about the complex processes behind this journey into the world of color.

But before we explore the world of colors any further, we must make a distinction between three regions: the region of permanent colouring, that of semi-permanent colouring and that of temporary colouring. As the name indicates, permanent colouring is not removed by shampooing, and its action lasts until what is incorrectly called the hair 'roots' grow again.
'Traditional' permanent colouring enables a lighter color to be applied, one in the same tone, a darker color or highlights. It is also capable of colouring totally white hair.
Permanent "matching tone" colouring adds color in the original shade or makes it slightly darker. It is used to add highlights or to color hair including up to 50% white hairs provided they are well distributed. As for semi-permanent colouring, this gradually fades away with each shampoo. It is used to color in the natural tone or a little darker, in order to add highlights or color hair which has up to 30% of evenly distributed white hair.

Finally, temporary colouring provides a slight modification of the natural color and adds highlights until the next shampoo.

  A strange world

Crystals of colorants

If we now venture a little further into the world of permanent colouring, we are liable to have quite a surprise - because color seems to be totally absent! We find ourselves in a landscape of white powders and colourless liquids. Instead of a multiplicity of pigments, we come across color precursors which only become coloured when they react with oxygen.

For oxygen in fact triggers many results. As it lightens hair naturally, in particular when associated with water and sunlight, it also activates the molecules making up the precursors so that they gradually color until they reach the required shade. This is referred to as oxidation colouring .
In the process of "traditional" permanent colouring, these two functions are furthermore associated. The oxygen released by the reaction between an alkaline agent such as ammonia and the oxidising product based on hydrogen peroxide will simultaneously lighten the melanin in the hair and act on the precursors to develop the colorants.
However, precursor molecules are very large and would be unable to penetrate the cuticle in its normal state. Use therefore has to be made of the hair's permeability.

The hair is capable of absorbing large quantities of liquid, quantities which increase as the liquid's alkalinity rises. This causes the fibre to swell and separate the scales of the cuticle, producing gaps through which the precursors can pass. When these have developed the desired color, depending on the molecule and the time it is allowed to act, the use of an appropriate shampoo or cream closes up the cuticle's scales. The color is thus imprisoned and protected by the cuticle just like the natural melanin pigments,so that the coloration will be retained for a long period. As the hair grows from its root, the original color will gradually appear at the visible base of the hair, and become more apparent as it grows.

In the case of semi-permanent colouring, the problems appear simpler, in as much as the colorants are directly applied and do not rely on oxidation for them to be formed. These colorants settle on the scales of the cuticle and become established around the cortex without modifying the hair's natural melanin .
But there is a problem concerning the medium, or the vehicle which will enable these colorants to act on the hair with maximum efficiency as well as protecting it, caring for it and beautifying it. The ideal formulation of this product can only take place when a perfect balance between the medium and colorant is achieved. Any deficiency in this balance will immediately be reflected in the color itself.

Finally, temporary colouring, even if it has to be eliminated at the first shampoo, must also scrupulously respect the hair. In this case, only the cuticle is concerned, since the colorants settle on its surface. But as the cuticle is the only protection for the body of the hair, it must receive special attention.

  The long history of coloration

In our day, coloration is controlled by extremely subtle and fine-tuned chemistry. However, human beings have apparently wanted to color their hair since ancient times. As a result of the analysis carried out on the hair of Rameses II. We know that the use of henna was already very fashionable in the Egypt of the Pharaohs, and it is still in common use today.
The Greeks and Romans used other vegetable extracts derived from walnuts and elderberries, for example.
They also used minerals and metals such as lead, mercury or copper, and even animal matter in the form of burnt ant's eggs!

It wasn't until the 19th century that substances until then used for the dying of wool began to be used for colouring human hair. And then in the 20th century, the first specific hair dyes were introduced (Lien 6.1). Initially designed to hide white hair, they have undergone continual development since then, so that they now offer a range even more extensive than that of natural color.

  A modern art

But we have come a long way from simply covering up the hair with color. Whether you want to radically change your color, add highlights or hide white hair, it is the natural appearance which counts above all and the fact that hair is coloured should no longer be perceptible. This is why modern color is made up of so many subtle shades and offers such an infinite range of highlights.To achieve this, the basic colors have to be associated with couplers that modify this foundation by introducing a subtle play of highlights.

So that ultimately, it is not uncommon for the desired color to be the result of a mixture of some 10 or more different colorants. This association of basic colors and couplers enables a variety of blues, oranges, yellows, reds, violets and reds to be created within the hair to play in harmony, neutralising or emphasising each other, so that the end result is perceived as a living, vibrant and authentic color.

  The way forward

Modelisation of 5,6 dihydroxyindole

The strange and subtle chemistry of coloration is constantly evolving, and the desire to re-pigment white hair as naturally as possible has given birth to a radical new approach: biomimetics . This is by no means a misnomer since it actually does imitate a natural biological process, that of the final stage involved in creating melanin within the melanocytes.
In fact, nature develops its own precursors within the melanocytes, which in turn generate coloured pigments. To-date, only eumelanin , the pigment which varies from reddish brown to dark black has given up its secret. Its pre-cursor is 5.6 dihydroxyindole, a very simple word if you compare with the complex work - and courageous determination - of those researchers who needed 30 years to identify, isolate, purify, synthesise and stabilise it, so as to finally introduce it into a cosmetic medium that can be applied to the hair.

Once it comes into contact with the hair again, this precursor does not act immediately, as is the case with traditional precursors. Reacting with the oxygen in the air, it oxidises slowly darkening with each application, until it has restored the hair to its original color.

It was a long, difficult and challenging adventure. But it was certainly worth it since, with the introduction of biomimetics, a whole new type of chemistry has come into being.
The use of precursors identical to those found in nature broadens the scope of possible colors, which may yet be extended even further by this type of recomposed natural pigments.




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