Types of Hair Coloring
The four most common classifications are 'temporary', 'semi-permanent', 'demi-permanent' (sometimes called 'deposit only') and "permanent".
Temporary hair color
Temporary hair color is available as rinses, shampoos, gels, sprays, and foams among others. This type of hair color is typically brighter and more vibrant than semi-permanent and permanent hair color. Temporary color is most often used to color hair for special occasions and is often used in unusual shades for events, parties and Halloween.
The pigment molecules in temporary hair color are large and cannot penetrate the cuticle layer. Instead, the color particles remain adsorbed (closely adherent) to the hair shaft and are easily removed with a single shampooing.
However, even temporary hair color can persist if the user's hair is excessively dry or damaged, allowing for migration of the pigments to the interior of the hair shaft.
Semi-permanent hair color
Semi-permanent hair dye has smaller molecules than temporary dyes, and is therefore able to partially penetrate the hair shaft. For this reason, the color will survive repeated washing, typically 4-5 shampoos. Semi-permanents contain no, or very low levels of developer, peroxide or ammonia, and are therefore safer for damaged or fragile hair. However, semi-permanents may still contain the toxic compound P-Phenylenediamine or other such ingredients.
The final color of each strand of hair will depend on its original color and porosity, so there will be subtle variations in shade across the whole head. This gives a more natural result than the solid, allover color of a permanent dye. However, it also means that gray or white hairs will not dye to the same shade as the rest of the hair. If there are only a few gray/white hairs, the effect will usually be enough for them to blend in, but as the gray spreads, there will come a point where it will not be disguised as well..
In this case, the move to permanent color can sometimes be delayed by using the semi-permanent as a base and adding highlights.
Semi-permanent color cannot lighten the hair.
Demi-Permanent hair color
Demi-permanent hair color is, in fact, permanent hair color that contains an alkaline agent other than ammonia (e.g., ethanolamine, sodium carbonate) and, while always employed with a developer, the concentration of hydrogen peroxide in that developer may be lower than used with a permanent hair color. Since the alkaline agents employed in dem-perms are less effective in removing the natural pigment of hair than ammonia these product provide little to no lightening of hair's color during dyeing. As the result, they cannot color hair to a lighter shade than it was before dyeing and are less damaging to hair than their permanent counterpart.
Demi-permanents are much more effective at covering gray hair than semi-permanents, but less so than permanents.
Demi-permanents have several advantages as compared with permanent color. Because there is essentially no lifting (i.e., removal) of natural hair color, the final color is less uniform/homogeneous than a permanent and therefore more natural looking; they are gentler on hair and therefore safer, especially for damaged hair; and they wash out over time (typically 20 to 28 shampoos), so root regrowth is less noticeable and if a change of color is desired, it is easier to achieve.
However, demi-permanent hair colors must be used with caution because they are, in essence, permanent color and the darker shades in particular may persist longer than indicated on the packet.
All "permanent" haircolor products and lighteners contain a developer, or oxidizing agent, and an alkalizing agent ammonia.
When the tint containing the alkalizing ingredient is combined with the developer (usually hydrogen peroxide), the peroxide becomes alkaline and diffuses through the hair fiber, entering the cortex, where the melanin is located. Lightening occurs when the peroxide breaks up the melanin and replaces it with new color.
The ammonia opens the cuticle of the hair to allow the color pigments to penetrate deep into the hair shaft.
Permanent color is truly permanent and will not wash out, although it may fade. New hair regrowth will obviously be in the hair's natural color, meaning that regular monthly or six-weekly coloring will be essential for as long as the hair color is maintained.
Permanent haircolor is the only way to dye dark hair into a lighter shade, and it must be done in two parts: First, the hair is bleached, then color is applied.
The only way to get rid of permanent color is to undergo a stripping process (which is not possible with all colors and can damage the hair) or color it back to its natural color (which can be difficult if the color change has been extreme).
Hair lighteners and bleaches
"Hair lightening," referred to as "bleaching" or "decolorizing," is a chemical process involving the diffusion of the natural color pigment or artificial color from the hair plus the raising of the cuticle making the hair more porous.
Hair color was traditionally applied to the hair as one overall color. The modern trend is to use several colors to produce streaks or gradations, either on top of the natural color or on top of a single base color. These are referred to as:
- Highlighting, where sections of hair are treated with lighteners, usually to create blond streaks.
- Lowlighting, where sections of hair are treated with darker hair color.
These can be applied by the following methods:
- Foils, where pieces of foil or plastic film are used to separate off the hair to be colored; especially when applying more than one color.
- Cap, when a plastic cap is placed tight on the head and strands are pulled through with a hook.
- Balayage, where hair color is painted directly onto sections of the hair with no foils used to keep the color contained.
All application techniques can be used with any type of color. For highlights, the hair will usually have to be bleached before coloring.
Exotic Hair Colorants
A minority of hair coloring products are designed to create hair colors not typically found in nature. These are available in almost any color imaginable, including green or fuchsia.
These dyes are typically sold in punk-themed stores (such as comic book and music stores), with brand names like "Beyond The Zone", "Splat", "Clairol Jazzing", "Manic Panic", "Special Effects", "Punky Colour". A permanent alternative in some colors (such as bold infa-red reds and dark, inky purples and blues) is available in the U.S. under "Paul Mitchel: Inkworks" and "Chi: InfaReds". Some exotic color shades are blacklight reactive, to show up under nightclub lighting.
The chemical formulae of exotic colored dyes typically contain only tint, and have no developer. This means that they will only create the bright color of the packet if they are applied to light blond hair. People with darker hair (medium brown to black) will need to use a bleaching kit prior to tint application. Some people with fair hair may benefit from prior bleaching as well. Gold, yellow and orange undertones in hair that hasn't been lightened enough can adversely affect results, especially with pinks, blues, and greens.