Oxidising hair dyes are still today the most popular form of hair colouring either Professionally or in Retail, you only have to walk into the hair colouring section of any outlet to witness the volume of choice. Their popularity is down to the reliability, effectiveness and resistance to shampooing and other external factors, such as drying, friction and light. Oxidative hair colour is a very large category, often it is mistaken as only permanent hair colour but it covers more; any colouring product that requires an oxidant to initiate the chemistry and that includes demi-permanents, semi-permanents that require mixing with a developer, powder colours that are mixed with water and some foam and cream colours that take a few days to appear (air-oxidising)
These colouring products contain very small separate molecules that can penetrate the hair and through the oxidation process join to become larger compounds that become trapped as they are now too large to come out of the hair the way they went in. With oxidative permanent colours you can achieve a wide variety of results from coverage of white hair, darkening, changing the tone, adding vibrancy or lightening the hair. The milder demi-permanents can blend white hair, impart tone and with some quasi versions (that include ammonia) create a little lift. Although they share some chemistry their actions on the hair is different, a bit like comparing regular coffee to decaffeinated.
How does it work
Now I get a bit geeky… unlike complete colours such as direct-dyes the components of an oxidising colour need to be kept separate and only mixed prior to application. There are three main elements:
- Dyestuff: typically, these are packaged in a tube, bottle or sealed sachet. They can also be found in plastic tubes and aerosol cans depending on the functionality e.g. air-oxidising. Dyestuff are often referred to as intermediates, because most of them are uncoloured and only create the coloured compounds through oxidation. The colour is formed when a dye precursor (or primary intermediate), reacts with the modifier (coupler). Each pair form a unique aspect of the final colour, like a lot of pixels coming together to create a picture. A brown hair colour is not just one molecule it tends to be a balanced combination of yellow, green, violet and red (these are different based on the brand), this also explains why browns by different brands not only look different, but can fade differently too. If one of the colour compounds is sensitive to UV desegregation e.g. violet then its opposite will become predominant i.e. brassy or yellow.
Did you know; that each manufacturer copyrights their shades, so each one needs to formulate their own unique version of brown, blonde red etc.
2. Alkaline, normally in with the dyestuff; the pH needs to be adjusted on the hair and in the hair to create the right environment for the chemistry to work; alkaline ranges are between pH 9-11 depending on the type of colour i.e demi-permanent or permanent. You will hear/read ingredients such as ammonia, MEA (monoethanolamine) and sodium hydroxide in use, the latter is less common. There is much debate on which is best and (personal option alert) there is a place for them all and each one has its own benefits and challenges. The role of the alkaline is to allow the dye molecules to penetrate into the hair’s cortex, after all the hair is naturally acidic (pH 5-6), tightly closed and not the right environment for oxidative hair colouring to take place. Ammonia effectively enables the lightening of the hair’s natural melanin allowing for greater lift and vibrancy in colours whereas MEA does not oxidise the melanin which makes it particular good when colouring on a similar depth and where more subtle tones are desired.
Figure 3: Need to have a molecule in there for a science blog Hydrogen Peroxide H2O2. 
Figure 4 Cross section of an oxidising permanent red dye
3. Oxidant H202, generally kept separate as this is the initiator of the other two components. There are two types of oxidants used: hydrogen peroxide, when the vehicle is water, and sodium persulfate, when it is a powder. The peroxides are very unstable, requiring the use of stabilisers such as sodium stannate and the pentasodium pentetate. Available in liquid and more stable cream-like solution in a wide variety of strengths called percentages (e.g. 6% or 12%) or volumes (e.g. 20vol or 40vol). The higher the percentage/volume the greater the energy in the mix, needed for vibrant and lightening colours whereas the lower percentages/volume means less energy for darkening and softer effects. The oxidant starts the chemical reaction, lightens the natural melanin and results in a colourful complex with a high molar mass that prevents it sneaking out of the hair.
So why should I care?
- Get it on the hair quickly, once mixed the chemistry gets to work immediately and will keep on working till it runs out of energy. Part of the reaction will happen in the bowl/bottle, in the cuticles, (but they will be removed during the first washes) and as desired within the cortex of the hair. The process is not linear, it is happening all together; so, mix the product freshly before you apply and get it onto the hair as quickly as possible.
- Put the colour where you need and want it; OK, I know it sounds obvious but I have often witnessed not sufficient product applied, chemistry is not that smart, it will only work where you put it and if you spread it too thin, then your result will also be thin and empty looking.
- Don’t mix different brands together as they all have different formulas, dyestuff concentrations and combinations; a combination that produces a brown in one range can be used to create a pink in another. See figure 1 combinations.
- Do mix with purpose different shades together from the same brand to create wonderful unique shades, avoid too many different ‘bits’ of dyestuff, this will only create a dull flat result. Colour circle theory shows us that complementary (neutralising) colours equals grey, brown or black. If you have ever witness an artist, a child or yourself paint, think about the water used to clean the paint brushes, yes muddy and flat, the same can happen with overly complex mixes. TIP many manufactures create pure tones or super mixes that can be added into the colour, these are a great way to create bespoke looks.
Whether you want cover those white hairs, enhance what nature gave you or just make a statement it is likely the colouring product you will be using will be oxidising.
Caroline
