Color additives fall into one of two broad categories: dyes and pigments.
Dyesare those color additives that are fully soluble in the medium in which
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Table 1.2 Dyes and pigments.
Dyes Pigments
Soluble Insoluble
Color is transparent Color films are opaque
Dissolved to impart color Color imparted through dispersion Pure dye content>90% Pure dye content 10–50%
Not particulate in use Crystalline in use
they are used, whilepigmentsare those that are insoluble in the medium in which they are used. As a general rule in cosmetic product development, the term “solubility” relates to water solubility, or an additive’s ability to dissolve into water, as opposed to oil or another base medium. In addition to solubility, the other major difference between the two types of colorants is that dyes are transparent and pigments are opaque. The majority of the color additives used in toiletries are dyes, whereas the majority of those used in decorative cosmetics are pigments. The reason for this is that most col- ored toiletry products, such as shampoos, mouthwashes, gel deodorants, and clear toothpastes, are transparent and therefore require the transparency of dyes in order to exhibit their color. Color cosmetics, on the other hand, are designed to cover the skin, so they benefit from the opacity exhibited by pigments.
Both dyes and pigments can either be natural or synthetic, and both find use in cosmetic products. The synthetic colorants normally exhibit brighter, more intense color than the natural ones, and generally better stability with respect to chemical and physical interactions. Table 1.2 shows the complete list of property differences between dyes and pigments.
Pigments are divided into two broad categories: organic and inorganic, both types being used in cosmetic products. The organic pigments are, generally speaking, brighter and more intense than the inorganic ones.
On the other hand, the inorganic pigments exhibit better stability than the organic ones.
Organic pigments fall into three classes, based on the colorants’ individ- ual chemistry with respect to insolubility, as follows:
Lakes:Pigments made by absorbing a water-soluble dye on to an insolu- ble, inorganic substrate. There is no chemical bond between the dye and the substrate; the dye simply takes on the insoluble nature of the substrate, thereby creating a pigment. Typical substrates are aluminum hydrate and aluminum benzoate. Based on the absorptive powers of the substrate,
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N NaO3 S
N
OH NH2
SO3 Na
Figure 1.9 D&C Red 33.
H3C N N
HO COONa
SO3 Na
Figure 1.10 D&C Red 6.
dye contents, defined as the amount of dye in the lake, range from 12 to 40%. Figure 1.9 shows the chemical structure of a typical dye used to form a lake, in this case D&C Red 33. As the reader may see, the structure contains two sulfonic acid (SO3) groups, which renders the material quite water-soluble.
Toners:Pigments produced by precipitating a water-soluble dye as a metal salt. Typical metals used for the precipitation include sodium, calcium, bar- ium, and strontium. Toners are capable of complete insolubility without the aid of a substrate. In actual practice in the cosmetic industry, most ton- ers 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. Figure 1.10 shows the structure of a toner. It contains both a sulfonic acid (SO3) group and a car- boxylic acid (COOH) group, which are hydrophilic and polar; therefore, as an acid dye, the toner is water-soluble.
True Pigments:Those colorants that are insoluble based on their chem- ical structure and constituent groups. They typically do not contain the normal substituent groups that promote water solubility, including sul- fonic acid (SO3) and carboxylic acid (COOH) groups. The true pigments are normally used without any diluents. A typical structure of a true pigment is shown in Figure 1.11.
All of the color additives described here find use in cosmetic products.
Choosing the appropriate one for use in a given formulation is done based
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O2N N N
HO CI
Figure 1.11 D&C Red 36.
Table 1.3 Organic pigment chemical classes.
Color additive Chemical class
Carmine Lake
FD&C Red No. 40 Al Lake Lake
D&C Red No. 6 Toner
D&C Red No. 6 Ba Lake Toner
D&C Red No. 7 Ca Lake Toner
D&C Red No. 21 Al Lake Lake
D&C Red No. 22 Al Lake Lake
D&C Red No. 27 Al Lake Lake
D&C Red No. 28 Al Lake Lake
D&C Red No. 30 Al Lake True pigment
D&C Red No. 33 Zr Lake Lake
D&C Red No. 33 Al Lake Lake
D&C Red No. 34 Ca Lake Toner
D&C Red No. 36 True pigment
D&C Orange No. 5 Al Lake Lake
FD&C Yellow No. 5 Al Lake Lake
FD&C Yellow No. 6 Al Lake Lake
FD&C Yellow No. 10 Al Lake Lake
FD&C Blue No. 1 Al Lake Lake
D&C Black No. 2 True pigment
D&C Black No. 3 True pigment
D&C Violet No. 2 True pigment
on several factors, or properties, which singularly or in combination offer various benefits and detriments depending on the intended usage. Due to the variations in terms of color and physical properties of the organic pig- ments, it is essential for the formulator to know which type each is before working with it. Table 1.3 identifies the commonly used organic pigments by chemical class.
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