Cosmetic color additives fall into one of two broad categories: dyes or pigments.
Dyes – Dyes are those color additives that are soluble in the medium in which they are used.
Pigments – Pigments are those color additives that are not soluble in the medium in which they are used. Pigments are further classified as organic or inorganic pigments.
As a general rule in cosmetic products, the term solubility relates to water solubility, keeping in mind that most water soluble dyes are also soluble in ethanol. The majority of the color additives used in toiletries are dyes while the majority of those used in decorative cosmetics are pigments. Both dyes and pigments can either be natural or synthetic.
Synthetic colorants normally exhibit brighter, more intense colors than natural ones. The synthetic inorganic ones normally exhibit better stability properties to chemical and physical interactions.
Organic pigments fall into three classes. The classes are based on the colorants individual chemistry with respect to insolubility.
- Lakes – Lakes are pigments made by absorbing a water soluble dye onto an insoluble, inorganic substrate. There is no chemical bond between the dye and the substrate. The dye simply takes on the insoluble nature of the substrate. Typical substrates are aluminum hydrate and aluminum benzoate.
- Toners – Toners are pigments that are produced by precipitating a water soluble dye as a metal salt. Typical metals used for the precipitation include sodium, calcium, barium and strontium. Toners are capable of complete insolubility without the aid of a substrate. Most toners are diluted with an inert substance to reduce their intensity, improve their dispersibility or change their transparency. Materials commonly used for this purpose are barium sulfate, talc and rosin.
- True Pigments – True pigments are those colorants which are insoluble based on their chemical structure and constituent groups. They typically do not contain the normal substituent groups that promote water solubility such as sulfonic acid and carboxylic acid groups. The true pigments are normally used without any diluents.