A number of firms sell treated black diamonds, including Chromagem, Lotus, and Israel’s First Diamond Group Ltd. Treated blacks are easier to find, cut, and match, and they take a better polish because the stones are not highly knotted or too heavily included. Prices for natural and treated blacks are comparable in melee sizes.

At present, there are three treatments:

Neutron irradiation. It’s apparently banned in the United States, but neutron-irradiated diamonds do enter the country, and while the chance that they’re radioactive is remote, all black diamonds should be tested for residual radioactivity.

Dror Yehuda of New York’s Yehuda Diamond Co. cites a way to detect irradiation. He says irradiated diamonds appear very, very dark green, and that if you look through a small transparent area with a strong fiber-optic light, you should see a green tint. Natural black diamonds look completely black.

High-energy electron processing. That’s what Lotus calls its process, which takes three to four months. Chromagem has a similar process, which it calls “high-energy particle processing.” According to Chromagem manager Marcus Fuchs, no neutrons are involved. Fuchs also claims that Chromagem’s results show no brownish or greenish color, and he says the stones can be recut without loss of color.

High-energy electrodynamic processes. John Haynes of Heath, Ohio-based InColor Enhanced Diamonds, the company that uses the process, says it “activates color centers in the atomic lattice.” (See “New Color Treatment for Diamonds,” JCK, June 2000, p. 82.) But GIA believes the process exposes diamonds to “some type of ionizing radiation.” According to Haynes, the diamond lattice is transformed into amorphous diamond from the surface down to about 250,000 atoms deep. Because it’s a surface treatment, repolishing the diamond can remove the color.