Three Color Effects From Interference Pigments

Abstract

Pearlescent and interference pigments are incorporated in plastics; coated on substrates;used in printing inks, in cosmetics, and used extensively in automotive paints. Although pearlescent pigments encompass the natural pearl essence derived from the fish and the various crystal forms of bismuth oxychloride, it is the coatings of titanium dioxide and iron oxide on mica that have gained the most acceptance and are the most commercially successful. The coatings of titanium dioxide on mica and their derivatives are the subjects of this chapter. The optical properties of pearlescent and interference pigments were examined and compared to absorption colorants. The reflection from pearlescent and interference pigments is specular. The reflection from absorption pigments is scattered and diffuse. Because of this difference, interesting color effects are observed when the two are mixed. When absorption colorants are directly precipitated on interference pigments, combination pigments are formed. Three distinct colors can be observed depending on the colorants and the angle of observation. At the specular angle, the reflection color from the interference pigment is observed. At the diffuse angle or angles away from the specular, the absorption colorant is seen. A third color can be seen by transmission that can be entirely different from the reflection color or the absorption color. The absorption colorant mixes with the transmission color of the interference pigment to form a new third color, an enhancement of the absorption color, or a neutralization of color depending on the colors and how they mix.