Base and Coupler The oxidation dye pair is divided into Base and a Coupler. The condensed Base Coupler pair is coloured. This is because the electron clouds on the molecules effectively combines and gets delocalised in new molecular setup. The intense colour is the result of an intense interaction between light and a delocalised electron cloud. The Base (ortho-or para-derivatives) yields the deep shades and becomes the basis of the colouring formulation. While the Couplers if taken separately yields colouring through oxidation that is only feeble.

Oxidation dyes are primarily aromatic compounds, that belongs to three major chemical families given here under:

• Diamines
• Aminophenols (amino naphthols)
• Phenols or naphthols

Oxidation dyes are generally colourless, and are typically a low molecular weight product. Primarily its usage lies as a very popular colourant material. It forms the basis of the hair dyes. This is because the oxidation dyes has the property to cover up grey and achieve long lasting results. They give a wide array of colour range that includes colour enhancement, grey control and fashion colours. In the context of hair dyes, Oxidation dyes have been found just right for permanent and demi-permanent or semi-permanent applications.

Oxidation dyes falls under two categories, namely oxidation base (primary intermediate) and coupler (secondary intermediate). For generating colour using these types, it is essential to use at least one type of each and mix it with a perfect oxidant under alkaline conditions. This would ensure the best results. Oxidation dyes often depends on a solution of dye intermediates like p-phenylenediamine for achieving the perfect colours. Another important ingredient is hydrogen peroxide. Typically a higher volume of peroxide in the dye has been seen to give a lighter and faster result.

To formulate a high quality oxidation dye product with optimum results, the following points need to be taken care of:

• A thorough understanding of the oxidative condensation process.
• For hair dyes, considerable experience with a fair number of practical trials. This should take into account various kinds of hair type.
• A delicate balance among:
  • Bleaching strength
  • Nature of the dye precursors
  • Quantity of ammonium used

The draw back of the Oxidation type of hair dye, is it's supposedly harmful effects on the hair structure. Which results in the need for using another product to repair damages as a result of high alkalinity and strong oxidizing agents.