Inorganic Pigments: Bases for Colored,Uncolored, and Transparent Products

Colored and uncolored inorganic pigments have been obtained since prehistoric times from natural minerals, at first empirically, then by specially developed methods. Since the beginning of the 18th century they have also gradually come to be studied scientifically, and today such research makes use of the latest techniques of solid-state physics and chemistry. On the basis of our knowledge of technically and aesthetically important properties, it has been possible in the last seventy years to make synthetic pigments superior to the natural ones, to increase production drastically while maintaining the pigment properties unchanged or improving them, and to broaden the range by the addition of new synthetic pigments. Nowadays it is in principle possible to write down a specification for many fields of application, taking into account aesthetic, technical, economic, and ecological aspects, and to make the corresponding inorganic pigment in adequate amounts. In what follows I shall discuss the dependence of the scattering and absorption constants of pigments on the refractive index, the wavelength of the light and the particle size, the properties of pigmented systems that depend on the particle geometry, and also some of the optical characteristics determined by the arrangement of the atoms in the crystal lattice.