Colour

Abstract

Before examining the various ways in which colour can be produced in gemstones we should understand that the colour of any object resides in the white light in which we view it. When all the wavelengths which combine to give white light are present the object will appear colourless; when by the operation of colour-causing mechanisms some of the wavelengths making up white light are absorbed, the unabsorbed wavelengths combine to give the object a residual colour. What the colour actually is depends on which wavelengths have been absorbed. This refers to body-colour and not to play of colour, interference or dispersion, all of which give areas of all the spectrum colours. A number of optical mechanisms can give rise to the colour of a gemstone, including dispersion, interference, diffraction and scattering (which may give other optical phenomena too).