Light diffusion
Color and visual appearance. Transparent, translucent, opaque

We have briefly described transparency and translucency by varying only the absorption of light by a homogeneous, non-scattering material. This makes it possible to describe said material using the unique notion of a complex refractive index or, more generally, a complex dielectric tensor with at most 6 distinct components. Viewed on an atomic or molecular scale, the interaction with light is called scattering, and this term is to be considered as the most global, incorporating all interaction mechanisms, whether surface or volume-based.