Hair colouring, in one specific method as described by the provided reference, involves specially designed molecules interacting within the hair shaft to deposit colour. This process is distinct because it does not rely on ammonia to alter the hair's natural pigment.
The Colouring Process Explained
Understanding how this particular type of hair colouring works involves looking at the structure of the hair itself. Each strand is made up of several layers, including the outer cuticle and the inner cortex.
Here's a breakdown of the steps involved in this ammonia-free method:
- Penetration: Tiny pre-color molecules found in the colouring product are small enough to penetrate the cuticle (the hair's protective outer layer).
- Entry into the Cortex: These molecules then make their way into the hair's inner core, known as the cortex. The cortex is where the hair's natural pigment (melanin) resides.
- Molecule Partnership: Once inside the cortex, the pre-color molecules partner with each other or with other components in the product.
- Colour Molecule Creation: This partnership leads to the creation of medium-sized color molecules. This reaction typically involves an oxidizer (like hydrogen peroxide) present in the developer, even though ammonia is absent.
- Colour Deposit: These newly formed colour molecules are now deposited within the cortex, providing the desired shade.
Why This Method Lasts
A key characteristic of this process, as highlighted in the reference, is that the resulting colour molecules are larger than the initial pre-color molecules. Their larger size means they take longer to wash out compared to temporary colours that just coat the hair surface.
Limitations of This Process
The reference specifically notes that these products do not contain ammonia. Ammonia is typically used in permanent hair colour to swell the cuticle and help remove natural pigment, allowing for lighter colours or significant shade changes. Because ammonia is absent in this method, the natural pigment can't be lightened. This means this type of colouring is best suited for:
- Depositing a darker shade.
- Changing the tone of the current colour.
- Covering grey hair without lifting the base colour.
It cannot be used to make dark hair significantly lighter.
Comparing Colouring Methods
While the reference describes a method using pre-color molecules and no ammonia, other hair colouring techniques exist, including permanent colour (which typically uses ammonia and hydrogen peroxide to lift pigment and deposit new colour) and temporary colour (which coats the hair surface and washes out easily).
- This Method (Semi/Demi-Permanent without Ammonia): Molecules penetrate cuticle, form larger molecules in cortex, adds colour, does not lighten.
- Permanent Colour: Swells cuticle (often with ammonia), removes natural pigment, deposits new pigment deep in cortex, can lighten.
- Temporary Colour: Coats hair surface, does not penetrate cortex, washes out quickly, does not lighten.
Understanding the process described in the reference provides insight into how certain types of longer-lasting, yet non-lightening, hair colours achieve their results by working within the hair's structure without relying on ammonia to alter the natural base.
