Thin opaque films such as paint, paper, paper coatings, vitreous enamels, and printing inks, are widely used. Such films usually are composed of finely divided materials dispersed in a relatively transparent medium of considerably different refractive index. The optical properties of these thin films, particularly for white or light colors, have been carefully studied. These important properties are color, opacity to transmitted light, and hiding power or ability to obscure an underlying contrast.