Pearlescent pigments work based on the following phenomenon: behind their attractive shimmer is the simple process of refraction. At boundary layers, such as between air and glass, white light is broken up and divided into its components – the colors of the rainbow. The greater the difference between the refractive indexes of the adjacent materials, the stronger the refraction. Depending on the angle at which the light hits the boundary layer, it may be completely reflected or passed through unchanged.
A key feature of the classic pearlescent pigments is the difference in color between the share of the incoming light which is reflected by the pigment and the share of light completely passing through. The color of the transmitted light is complementary to the color of the reflected light. For example, a red reflection color goes with a green transmission color, while yellow and blue form another pair of reflected and transmitted light.
A piece of nature at its core: mineral mica
Mineral mica is a natural inorganic pigment. The mineral is the starting material for some of Merck's effect pigments. After extraction, it is cleaned, ground and then coated with one or more metal oxides in a precipitation process. The result: a layer-substrate pigment which interacts in a specific way with light called interference. The result is a specific interference color, depending on the thickness of the metal oxide. A wide variety of effects can be achieved, from matte shimmer similar to that of pearl or mother of pearl to interference looks with significant shimmer in all colors of the rainbow.
Innovative substrates for novel effects
The combination of the substrate and coating is key to the look of every effect pigment. A transparent substrate is an important pre-condition for the perfect interaction between the light and the pigment. Natural mica was just the start – today it is possible to produce transparent substrates with similar properties artificially. By coating them with metal oxides, completely new effects can be achieved, far beyond the options offered by natural mica. The innovative substrates include synthetically produced aluminum oxide (Al2O3) platelets, silicon dioxide (SiO2) platelets and glass platelets made from calcium aluminum borosilicate.