White Hiding and Extender Pigments: Unit 7 (Federation of Societies for Paint Technology)

A pigment may be defined as a finely powdered solid essentially insoluble in the medium in which it is dispersed. It is white if it highly reflects all visible wavelengths of light diffusely and non-selectively. The more completely it reflects the light, the brighter it is said to be. One important distinction between extender and prime (high hiding) pigments is their relative indices of refraction; those of extenders being relatively low (1.5 to 1.7). The Relationship of refractive index to opacity will be discussed more fully in later.