Dying to Know the Truth About Oxidative Dyes?

Most dyes are direct dyes, meaning that they have affinity to the surface on which they are being applied such as cloth, skin, hair or paper. The color of the dye solution also indicates the final color of the substrate. 
   
This is not true with oxidation dyes that furnish very stable hair coloring shades. These dyes or intermediates have no affinity for hair, and as the name indicates, must be oxidized in order to provide color. The commercial product has the dye mix in one container, and the oxidizing agent in the other bottle. When mixing liquids, the oxidizer is always 20 volume or 6% hydrogen peroxide. In the past, I have seen a powdered one package product containing both oxidation dyes and the oxidizer which is mixed with water to activate. In this case, the oxidizing agent could be sodium perborate.
   

The most important oxidation dye is p-phenylenediamine (PPD). It was discovered about 150 years ago and was used for fur dyeing before it became a hair coloring dye in the 20th century. PPD and its salts are soluble in water, alcohol and water-alcohol mixtures. It is easily oxidized to form an intermediate which is readily polymerized or condensed with couplers to yield different colors.
   
PPD is a skin irritant; therefore, in the U.S., a preliminary patch test is necessary. A few drops of the hair color is mixed with an equal amount of the developer and applied to the skin inside the bend of the elbow or behind the ear and left undisturbed for 24 hours. If there is no irritation, the product is usable.

A Range of Shades

PPD is used with many intermediates to form various shades. The table below lists some of them with the resultant shade. PPD can be used with these ingredients to make any color (Table I). This dying procedure works best at an alkaline pH, probably because of the hair swelling effect.

Ammonium hydroxide, rather than a fixed alkali, is preferred to raise the pH to 9.2-9.5 because it is volatile and will not leave residue in the hair while processing. Dye solutions contain thickeners/emulsifiers, conditioners, solvents, an antioxidant and chelating agent so that the peroxide, when added, is not dissipated too fast. Here’s a dye base formula:

Dye Base

Ingredients    %Wt.
Water    q.s. to 100
Dye mixture    q.s.
Sodium sulfite      0.1
Trisodium EDTA      0.5
Nonyl phenol ethylene     15.0
    oxide condensate
SD Alcohol 40    20.0
Oleic acid      9.0
Oleyl alcohol    15.0
Ammonium hydroxide (28%)    5.0
Perfume    q.s.

Procedure:

Heat first five ingredients to dissolve the dyes. In a separate container, mix the next three items in the alcohol. When clear, add to tank. Cool to 40°C and add last two items. 

Formulating oxidation dyes is more art than science. The resulting color can be affected by different ingredients in the base and the purity of the dyes themselves. Sometimes a less pure intermediate will furnish a more satisfactory color result. An experienced chemist is able to determine which dye will work best in a particular base or shade.

About the Author
Harvey Fishman has a consulting firm at 34 Chicasaw Drive, Oakland, NJ 07436, hrfishman@msn.com, specializing in cosmetic formulations and new product ideas, offering tested finished products. He has more than 30 years of experience and has been director of research at Bonat, Nestlé LeMur and Turner Hall. He welcomes descriptive literature from suppliers and bench chemists and others in the field.