Hair dying generally falls into one of four categories: bleaching/lightening, temporary, semi-permanent and permanent. A patch test should be carried out before any dye application takes place to determine if there are any allergies to that particular product.
Bleaching/lightening
Bleaching, also know as hair lightening, is a chemical process and usually the first stage in permanent and semi-permanent colouring. A bleach, usually peroxide, is used to penetrate the hair by diffusion and break up the melanin within, resulting in a lightening of the hair fibre.
Temporary hair colour
The pigment molecules in temporary hair colorants are larger than those in permanent solutions, preventing them from penetrating the cuticle layer of the hair fibres. This leads to only a coating layer which can be removed by simply shampooing. Temporary hair colouring is often used as part of Halloween costume and make-up effects or by people who want a change of style for the weekend but can’t change their hair colour permanently for various reasons including school and work. Temporary hair colour is available in various product forms including rinses, shampoos, gels, sprays, and others. This type of hair colour is typically used to give brighter, more vibrant shades or colours such as orange or red that may not be possible to achieve with semi-permanent or permanent hair colour.
Semi permanent
Semi permanent colorants have smaller molecules than temporary colorants and are able to penetrate the cuticle layer of the hair fibres. This means that that it can last much longer than temporary hair colours and can stay in the hair for anywhere between 8 – 14 washes.
Permanent
Permanent hair dye is mixed with developer and will remain within the hair until new hair growth occurs. Although this type of hair colouring is called ‘permanent’ some fading may occur over time with washing and repeated colouring sessions may be required to maintain a desired level of vibrancy in the colour. This type of colouring is often used to match, lighten, and cover grey hair.
Highlighting
Highlighting can range from temporary to permanent, using the techniques listed above and a special application process. The techniques required to apply highlighting can be difficult for an individual to perform upon him/herself and should mostly be performed by a professional with experience in this area. One can create looks that range from subtle highlights acquired during a day at the beach, to more dramatic looks, such as bold, chunky highlights
Special fx
Special effects include highlighting and also more unusual hair colours such as green or fuchsia. These more exotic dyes typically contain only tint, and have no developer. These are typically sold in alternative type stores, but are rarely available at commercial hair dressers. Many colours are available and it is also possible to find UV reactive shades. Individuals with darker hair are advised to use a bleaching kit prior to tint application for the full effect of the colour. Some people with fair hair may also benefit from bleaching prior to use as well as the yellow undertones of blonde hair can make blue dye look green. It should be noted that these types of dyes are not permanent and tend to bleed into surround fabrics such as bedding.
