Scattering in solids

This page is about scattering-coloured solids. The header picture is an owl made of glass including a metallic vapour. This is a splendid Rayleigh scatterer and, with suitably arranged illumination, can reproduce the full range of twilight sky colours. A similar range of phenomena could be seen in an old astronomical 74 inch glass mirror blank mounted in the grounds of Herstmonceux Castle in Sussex, England when it was the home of the Royal Greenwhich Observatory.

The sketch shows how shadows can be used to produce the whole spectrum of twilight colours (Fosbury 1984). Rayleigh scattering has a strong dependence on colour - the cross-section varies as 1/(wavelength)^4 - and so a single scattering process produces very blue hues. This is the reason for the deep blue of the zenith sky seen from a mountain or an aircraft. If, however, this blue light passes through a scattering medium which is in shadow, ie, no blue light is added to the beam, the light becomes redder as the pathlength in the shadow increases and the blue light gets scattered out of the beam. This causes the range of twilight sky colours as explained in the pages on the sky .

Scattering is an important source of blue colours in animals and various types of solid and semi-solid matrix containing suitably small scattering centres are found. An example is the graded blue colour on the wing feathers of a jay.