The refractive indices of polymer film formers, pigments and additives used in tablet film coating: their significance and practical application.

The refractive indices of both the polymer film formers and additives are a fundamental factor in defining the appearance of the subsequent film coatings. The refractive indices of the polymer film formers are all in the region of 1.5 but those of pigments and additives vary between 1.5-3.2. Most pigments and additives are also anisotropic, i.e. they possess different refractive indices depending on their orientation. These observations have implications in the use of pigments and additives for the production of both opaque films with good hiding power and film-coated tablets with highlighted intagliations.