Kaolin clay is one of the most abundant minerals and common constituents of the earth's crust. Clay occurs in many different forms, but kaolin or china clay is the purest and most versatile. Kaolin clays are commonly used in paints, paper, plastics, rubber, ink, pigments, fiber glass, cosmetics, cement & concrete, adhesive & sealants, cable & wire due to their hardness, opacity, abrasion resistance, high brightness, particle size, promote flattening, easy dispersion, high aspect ratio, tint strength, good exterior durability, structure, ability to extend titanium dioxide and their relatively low cost.
Calcined kaolin “structure” is like a house of cards. Air voids within the calcined kaolin contribute to opacity because the index of refraction of air is different from that of kaolin. The opacity derived from structured pigments is due to light scattering, allowing the light to refract and be reflected back to the viewer. The human eye then views the object as “white.” The same opacifying effect takes place when you see the white foam bubble. The small bubbles have many air-liquid interfaces which scatter the light