The technical terms any DIY or salon colourist should know


From the french for ‘sweep’ this is an old hair-colour technique that has recently regained popularity. In involves hand-painting colour without the use of foils for a mutli-tonal look.


Base Colour

This is the foundation colour - usually permanent and containing PPD - applied to the hair before other colour options are applied on top. Base colour gives a uniform appearance to the hair.


Double Process

This is when two hair colouring techniques are applied to the hair in sequence - for instance bleaching followed by the application of a new colour.



Foiling is a technique used to keep different areas of the hair apart and is often used for highlights. Sections of hair are painted and then wrapped in foil to keep them separate from unpainted sections. For more on this technique in relation to PPD allergy, see PPD Myths and Misconceptions.



Ombré is the transition from one shade to another, with the hair generally darker at the roots and lighter at the tip. It’s the look achieved by balayage.


Crazy Colour / Direct Dye

Bright or pastel shades of hair colourant, usually applied to bleached hair via semi-permanent and temporary dyes, to achieve an overall hue such as pink, silver or lilac. Frequently available without PPD and PTD, and so make a viable alternative to traditional toners on lightened hair.


Single Process

This is a one-step procedure that gives an all over colour with a single treatment, via semi permanent or permanent dye.



Ammonia is a compound of nitrogen and hydrogen. It’s used in permanent hair dye to change the hair’s pH value, which opens the cuticle and allows dye molecules to lodge in the cortex of the hair. In ammonia-free dyes, another alkaline substance is used in its place.


Hydrogen Peroxide

In a dilute form, hydrogen peroxide has two roles in colouring hair. First, it strips the hair of its existing colour, readying it for a new shade. Second, it triggers the oxidisation of PPD, which begins the dyeing process on the hair shaft.



This is an ingredient in hair dyes which works with other chemicals to create a permanent colour effect. It’s also used to treat dermatological conditions. However, in higher doses it is toxic, can disrupt the nervous system and cause thyroid dysfunction. It can irritate the skin and according to the World Health Organisation can cause sensitization, meaning that repeated use can lead eventually lead to an allergic reaction. 



With the exception of certain brands of henna, there is currently no such thing as a completely organic hair dye. Products described as organic may consist primarily of organic ingredients, but rely on a a degree of synthetic chemicals to work effectively.



Highlights are areas of the hair that have been lightened with the application of dye or bleach. These may be full highlights, which means areas have been lightened throughout the whole head of hair, or partial highlights, where the top layer or the area around the face is treated in order to give the appearance of volume.



Much like highlights, lowlights are specific areas of the hair which are coloured differently to the base layer. In the case of lowlights, though, these sections are coloured darker than the base layer to give the impression of depth and shadow.



Coverage is simply a measure of how effectively a given hair dye can colour grey hair. Only permanent hair dye, containing PPD or PTD, can cover 100% of greys. Semi permanent colours have less coverage, but can blend away greys on some hair. Temporary colours have no coverage, as they do not penetrate the hair shaft, only coat it.


Glaze and Gloss

A gloss is a semi-permanent liquid solution which lasts around two to four weeks, adds shine and adjusts the tone of the hair. A glaze, which is often clear, has similar effects but, unlike a gloss which partially penetrates the hair cuticle, a glaze simply coats it and so is more temporary. ‘Glaze’ was initially used to describe a product which added shine and semi-permanent colour, while a gloss only added shine - but now the two terms are often interchanged at will.



The developer is the element of a hair dye - usually hydrogen peroxide - which reacts with the other components, oxidising the dye to start the process of colourisation.



A (usually ammonia based) liquid applied after bleaching to alter or manipulate the tone of lightened or highlighted hair. For example, a toner is used to turn a brassy yellow blonde into a cooler, ashier tone. Most classic toners contain PPD, but in recent years, as the trend for swapping bleached hair colour regularly (pink one week, silver the next, for example) has become more popular, many consumers have turned to temporary direct dyes or tinted shampoos, using them in place of classic toner. Many salon colourists will also use semi-permanent colourants in place of toner. These may or may not contain PPD, so it’s important to ask and as always, obtain a skin test at least 48 hours before an appointment.