Fancy-colored diamonds are among the most highly gemstones, but care needs to be taken to ensure that the visible color is the result of natural process and not artificial treatments. One of those is irradiation, and it refers to a process by which the color of diamonds are changed through high-energy electron saturation.
This is not a new technology. Scientists began irradiating diamonds more a century ago, after the English chemist, Sir William Crookes, discovered in 1904 that a diamond’s color could be changed after being exposed to radium salts in 1904. In these experiments the color changes were confined to thin zones near the surface of the stones, and diamonds were rendered radioactive.
Today, only a very small percentage of all natural diamonds are irradiated. Because of the risk of damage, most of the stones subjected to this treatment are typically under 10 carats. Depending on the type of radiation used, the color may be restricted to the surface, or it may penetrate the whole stone.
Several irradiation alternatives are available today, with the most commonly used being neutron bombardment in a nuclear reactor. This results in stones of green to black colors, but if they are then heated to between 500 and 900 degrees Celsius, orange, yellow, brown, or pink colors are obtained.
Electron bombardment using Van de Graaff generators produces a blue, blue-green, or green color, and these stones, if heated to temperature from 500 to 1200 degrees Celsius, can result in orange, yellow, brown and pink fancy colors.
Less commonly used methods include proton and neutron bombardment via cyclotrons and gamma ray treatments.
Irradiated diamonds are relatively easily detected in a properly equipped gem lab, by testing the absorption spectrum, using the UV-Vis spectrophotometer, and photoluminescence, using the Raman spectroscope at the temperature of liquid nitrogen.