Artificial Colouration in Diamond

 Artificial Colouration

The artificial colouration of diamond is a hot topic today!

 

History

The production of a green colour in diamond   by   bombardment with radioactive particles from radium compounds has been known since early in the twentieth century. Owing to the expense of the method and the ease with which such artificial colouration can be detected – for the stones themselves become radioactive from the treatment – ‘radium-greened’ diamonds are not commonly encountered. Other methods of colouring diamonds by particle bombardment, using high-voltage particle accelera- tors, have led to the sale of artificially coloured diamonds.

Cyclotrons using protons (a particle in the nucleus of all atoms) and deuterons (the nucleus of the heavy hydrogen atom) produce in diamond a green colour, provided the heat generated by the impact of the particles is dissipated (usually by the use of a jet of liquid helium), otherwise a brown colour is produced. In any case a brown or yellow colour may be produced by subsequently heating the greened stones at a controlled temperature.

A similar type of colouration has been produced by using neutrons (uncharged particles in the nucleus of most atoms) generated in an atomic reactor (atomic pile), and such artificial colouration of diamond is now carried out commercially both in Great Britain and in the USA. The diamonds leave the reactor a pale green in colour which can be altered to brown or yellow by subsequent heating under controlled conditions. Unlike cyclotroned diamonds in which the colour is little more than skin deep, these diamonds are coloured throughout. Electrons can produce a light green or an aquamarine-blue colour in diamonds.

A type of colour alteration sometimes practised, usually for fraudulent purposes, is to paint the rear facets of off-coloured yellowish diamonds in order to make them appear whiter. Scientifically it is well known that when two complementary colours mingle white is produced; it is this effect which is used in the whitening of diamonds. Experiments are not usually carried out on the finest diamonds – Cape stones are usually chosen – because something might go wrong!