Color Enhanced Diamonds
Generally there are three major methods to artificially alter the color of a diamond:
- irradiation with high-energy subatomic particles;
- the application of thin films or coatings;
- and the combined application of high pressure and high temperature (HPHT).
The first two methods can only modify color, usually to turn an off-color stone into a more desirable fancy-colored stone. Because some irradiation methods produce only a thin “skin” of color, they are applied to diamonds that are already cut and polished.
Conversely, HPHT treatment is used to modify and remove color from either rough or cut diamonds—but only certain diamonds are treatable in this manner. Irradiation and HPHT treatments are usually permanent insofar as they will not be reversed under normal conditions of jewelry use, whereas thin films are impermanent.
Presently diamonds are safely irradiated in four ways:
- proton and deuteron bombardment via cyclotrons;
- gamma ray bombardment via exposure to cobalt-60;
- neutron bombardment via the piles of nuclear reactors;
- and electron bombardment via Van de Graaff generators.
These high-energy particles physically alter the diamond’s crystal lattice, knocking carbon atoms out of place and producing color centers. Irradiated diamonds are all some shade of green, black, or blue after treatment, but most are annealed to further modify their color into bright shades of yellow, orange, brown, or pink.
The annealing process increases the mobility of individual carbon atoms, allowing some of the lattice defects created during irradiation to be corrected. The final color is dependent on the diamond’s composition and the temperature and length of annealing.