Intense Pigment
The inspiration for pearl effect pigments comes from various natural phenomena in the world, such as seashells, pearls, butterflies, soap bubbles, insect eyes, and minerals. The development of color pigments with a pearl effect can be traced back to early stages when they were derived from fish scales, bismuth oxychloride, and basic lead carbonate. However, due to cost control and environmental concerns, only bismuth oxychloride remains in the market today. The widely used pearl effect pigments now mimic the multilayer structures found in those early pigments. Unlike bismuth oxychloride, which exhibits a pearl effect through a single crystal structure, modern pearl effect pigments utilize a basic structure of metal oxide coating on a substrate.
Different pearl effects and textures can be achieved by coating different substrates with metal oxides, such as titanium dioxide or iron oxide. Pearl effect pigments based on the interference principle are often referred to as interference-type pearl pigments. The interference colors in these pigments are generated through the interference effect of light.
The principle behind the formation of interference colors in pearl effect pigments involves the calculation of contrasting refractive indices, such as high refractive index of the metal oxide coating and low refractive index of the substrate. Effective interference colors are produced when the peaks of reflected and refracted light waves coincide, or when their wavelengths differ by a multiple of λ (lambda).
On the other hand, no interference colors are generated when the peaks of reflected and refracted light waves coincide with the troughs, or when their wavelengths differ by (n + ½) λ (lambda). The color effect of the interference colors is determined by the thickness of the coating. As shown in the figure below, with increasing coating thickness, the color of the pearl pigment changes from white to interference gold, interference red, interference blue, and interference green.
For colored interference pearl pigments, some users refer to them as iridescent pearl pigments. The powder of interference pearl pigments appears white, and their true color effect can only be seen when applied. When applied on a black background or mixed with black pigments, the colored interference pearl pigments display a pure color effect. For example, interference gold exhibits a pure gold color effect when applied on a black background.
