Specialty pigments tend not to be used in large volumes due to regulatory restrictions, handling and compatibility issues, cost or simply because their effects are only needed in certain instances. Despite their limited use, these pigments bring unique effects to personal care products, thus they are an important class of color additives for the decorative cosmetic industry. Following is a review of their properties and benefits.
In contrast to pigments composed of iron oxide and/or titanium dioxide-coated natural and synthetic micas, metallic specialty pigments are truly metallic—essentially, the pure metals aluminum, copper and bronze. Their mechanism of color display is different from absorption and effect pigments. Absorption colors operate by selectively absorbing, reflecting, refracting and transmitting light, as shown in Figure 1. Here, arrows show incident light being reflected at both specular and diffuse angles, and being transmitted through the crystal. In contrast, metallic pigments produce color by reflecting the entire wavelength range of incident light, producing a bright metallic look similar to jewelry. Figure 2 demonstrates this mechanism, where the flat, platelike particles are the metallic pigment and the arrows are incoming reflected light, most of which is at the specular angle.