The effect of pearlescent pigments

Pearlescent pigmentThe effect of

　　The color of general pigments is derived from the selective absorption (or reflection) of light at specific wavelengths, while the luster of pearlescent pigments comes from the interference of light.

　　If an object reflects all the illuminated white light, it appears white; if part is reflected and part is absorbed, it is gray; when almost all is absorbed, it appears black. If an object appears red, it is because in the incident white light, only the wavelength of red light is reflected, and the rest of the color light is all absorbed. When general pigments are added to the colorants of plastics, coatings, and inks, the combined effects of absorption, diffusion, and penetration of light by the pigments show different effects such as the color, luster, or transparency of the object. Pearlescent pigmentColor-changing pigment,Fluorescent pigment

　　The pearl luster effect produced by the interference of light can be understood from the example of oil floating on water. The occurrence of this rainbow-like color is due to the interference and enhancement of visible light reflected simultaneously from the air/oil interface at the top of the film and the oil/water interface at the bottom.

　　Thepearlluster of pearlescent pigments comes from the titanium dioxide layer deposited on mica flakes and with strictly controlled film thickness. When light shines on the flakes of pearlescent pigments, there are many paths. Some light passes through the air or interfaces with low refractive index near the pearlescent pigment (such as the resin of the coating film), and when the light hits the surface of the titanium dioxide layer, it is reflected, because titanium dioxide has a high refractive index and the refractive index at the interface between the resin and titanium dioxide is different. Some of the light passes through the titanium dioxide layer and is reflected again at the interface between the titanium dioxide layer and mica. Through multiple reflections and refractions like this, thepearlluster can be produced.

　　The resulting color depends on whether the light reflected from the two different interfaces reinforces or interferes with each other. Changes in the thickness of the titanium dioxide film will cause changes in the color light. The optical thickness (the product of geometric thickness and refractive index) of the transparent film is a prerequisite for the occurrence of light interference. Because the interference color changes with the light and the angle of observation, the iridescence appears.

　　The optical properties of pearlescent pigments are different from those of general pigments. It has regular multiple reflections and refractions. Therefore, when the surfaces of pearlescent pigment particles are arranged in parallel, more beautiful effects can be displayed.