Hair coloring
Hair coloring, or hair dyeing, is the practice of changing the color of the hair on humans' heads. The main reasons for this are cosmetic: to cover gray or white hair, to alter hair to create a specific look, to change a color to suit preference or to restore the original hair color after it has been discolored by hairdressing processes or sun bleaching.
Hair coloring can be done professionally by a hairdresser or independently at home. Hair coloring is very popular, with 50-80% of women in the United States, Europe, and Japan having reported using hair dye. At-home coloring in the United States reached sales of $1.9 billion in 2011 and were expected to rise to $2.2 billion by 2016.
History
The dyeing of hair is an ancient art that involves treatment of the hair with various chemical compounds. Assyrian herbals dating back to contain some of the oldest recipes for cosmetic preparations known, including hair dye. The ancient Egyptian Ebers Papyrus,, has recipes for dyeing gray hair and eyebrows. Assyrian clay tablets dated to the 7th century BCE mention using the gall of a black ox, cypress oil, licorice, and honey to turn gray hair black. In ancient times, the dyes were frequently obtained from plants. Some of the most well known are henna, indigo dye, Cassia obovata, senna, turmeric, and amla. Others include katam, black walnut hulls, red ochre, and leeks.Diodorus Siculus, a Greek historian, described in detail how Celtic people dyed their hair blonde: "Their aspect is terrifying. They are very tall in stature, with rippling muscles under clear white skin. Their hair is blond, but not naturally so: they bleach it, to this day, artificially, washing it in lime and combing it back from their foreheads. They look like wood-demons, their hair thick and shaggy like a horse's mane. Some of them are clean-shaven, but others — especially those of high rank — shave their cheeks but leave a moustache that covers the whole mouth."
Hair coloring recipes were common in the medieval period and Renaissance. Trotula's De ornatu mulierum, from the 12th century, has multiple recipes for bleaching and coloring hair. In the 1661 book Eighteen Books of the Secrets of Art & Nature, various methods of coloring hair black, gold, green, red, yellow, and white are explained. In 1856, English chemist William Henry Perkin accidentally discovered the first synthetic dye, mauveine, while attempting to synthesize quinine, a treatment for malaria. His discovery marked the beginning of the synthetic dye industry and laid the groundwork for later innovations in hair dye chemistry. The development of synthetic dyes for hair is traced to the 1860s discovery of the reactivity of para-phenylenediamine with air. Eugène Schueller, the founder of L'Oréal, is recognized for creating the first synthetic hair dye in 1907. In 1947 the German cosmetics firm Schwarzkopf launched the first home color product, "Poly Color". Hair dyeing is now a multibillion-dollar industry that involves the use of both plant-derived and synthetic dyes.
Application techniques
All coloring techniques can be used with any type of color. For lightening, the hair has to be bleached.Off-scalp
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. These are referred to as:- Highlighting, where sections of hair are treated with lighteners
- Lowlighting, where sections of hair are treated with darker hair colors
- Splashlighting, a horizontal band of bleached hair from ear to ear
These are off-the-scalp techniques, and can be applied by the following methods:
- Foiling, where pieces of foil or plastic film are used to separate the hair to be colored. Employed especially when more than one color is to be applied, this method ensures that only the desired hair strands are colored, and the rest spared.
- Cap, when a plastic cap is placed tightly on the head and strands are pulled through with a hook, a method infrequently practiced other than for applying highlights to short hair.
- Balayage, where hair color is painted directly onto sections of the hair with no foils used to keep the color contained, a method growing in popularity due to its observed effect of appearing more natural. The difference between balayage and ombré is that a balayage requires more precise hand-painting sections of hair and typically costs more.
- Baby lights, very thin highlights that are created by using a fine color technique, baby light results are very natural and subtle.
- Dipping or tip dyeing, where tips of the hair are dipped directly into dye.
On-scalp
- All-over color, where the person wants all of their hair to be a different solid color
- Root touch-up, where color is applied only to the most recent section of re-growth, usually the first inch of hair nearest the scalp. Root touch-ups are repeated every 4 to 6 weeks as the natural color grows in and becomes apparent. People who color their hair to disguise gray often have root touch-ups.
- Block coloring, where the person wants two or more colors applied to their hair, resulting in dimension and contrast
Synthetic dyes
Permanent synthetic dyes
Permanent hair color generally contains ammonia and must be mixed with a developer or oxidizing agent in order to permanently change hair color. Ammonia is used in permanent hair color to open the cuticle layer so that the developer and colorants together can penetrate into the cortex. The developer, or oxidizing agent, comes in various volumes. The higher the developer volume, the higher the "lift" will be of a person's natural hair pigment. Someone with dark hair wishing to achieve two or three shades lighter may need a higher developer whereas someone with lighter hair wishing to achieve darker hair will not need one as high. Timing may vary with permanent hair coloring but is typically 30 minutes or 45 minutes for those wishing to achieve maximum color change.Demi-permanent synthetic dyes
is hair coloring that contains an alkaline agent other than ammonia, 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. These products provide almost no lightening of hair's color during dyeing, since the alkaline agents employed in demi-permanent colors are less effective in removing the natural pigment of hair than ammonia. 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 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, so root regrowth is less noticeable and if a change of color is desired, it is easier to achieve. Demi-permanent hair colors are not permanent but the darker shades in particular may persist longer than indicated on the packet.
Semi-permanent synthetic dyes
permanent hair coloring cannot lighten the hair either. Because it involves no developer or ammonia, it is thus less damaging to hair strands than their demi-permanent counterpart.There will be subtle variations in shade across the entire head, because of hair's color and porosity along the length of a hair strand. The final color of each strand of hair will depend on its original color and porosity. This variation gives a more natural looking result than the solid all over color of a permanent. Because gray or white hairs have a different starting color than other hair, they will not appear as the same shade as the rest of the hair when treated with semi-permanent color. If there are only minimal grey/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 demi-permanent as a base can be used sometimes adding highlights, to delay permanent coloring.
Semi-permanent hair color uses compounds of lower molecular weight than are found in temporary hair color dyes. These dyes are only able to wedge under the cuticle layer of the hair shaft only. For this reason, the color will survive limited washing, typically 4–8 shampoos.
Semi-permanents may still contain the suspected carcinogen p-phenylenediamine or other related colorant carcinogens. The U.S. Environmental Protection Agency reported chronic exposure to PPD in the diet of rats and mice depressed body weight of the animals, with no other clinical signs of toxicity observed in several studies.
Temporary color
Temporary hair color is available in various forms including rinses, shampoos, gels, sprays, and foams. Temporary hair color is typically brighter and more vibrant than semi-permanent and permanent hair color. It is most often used to color hair for special occasions such as Christmas and Halloween costume parties.The pigments in temporary hair color cannot penetrate the cuticle layer of the hair. The color particles remain adsorbed to the surface of the hair shaft and are easily removed with a single shampooing. Temporary hair color can persist on hair that is excessively dry or damaged in a way that allows for migration of the pigment to the interior of the hair shaft.
Some plants can be used for temporary coloring, too, e.g. beet juice.