New HTHP Diamond Enhancement Revealed

December 2, 1999

New HTHP Diamond Enhancement Revealed

European Gemological Laboratory, New York City, on Wednesday announced a new high-temperature, high-pressure process it says can transform brownish diamonds to vivid fancy green and vivid fancy yellow without using irradiation.

Because natural green diamonds show radiation lines, the gemological theory always has been they are irradiated in the earth, so treated green diamonds generally are irradiated to replicate the process. This new revelation adds a dramatic new chapter to the rapidly unfolding history of diamond enhancements, particularly following the unveiling earlier this year of GE/POL, a treatment that improves the color grade of some colorless diamonds through HTHP.

Novatek of Provo, UT, a manufacturer of industrial diamonds known for its advancements in diamond synthesis, discovered the color-change process by accident. While doing color-change research for a client about six months ago, technicians "went too hot and burned up some diamonds," says Novatek's David Hall. They polished off the burned surface and found a green diamond underneath, then "spent several months trying to repeat the process," he says. As the company began to perfect the process, it adopted the name NovaDiamond Inc. to promote the product.

NovaDiamond's client later submitted several green diamonds to EGL for an origin-of-color report. "The diamonds were quite unusual for a variety of reasons and showed none of the lines associated with radiation treatment," says Branko Deljanin, EGL's director of gem identification and research. Deljanin contacted color-center diamond expert Dr. Alan Collins, who suggested the diamonds showed HTHP characteristics. The findings led researchers back to Novatek, which confirmed their suspicions.

One unusual feature of the green diamonds is very strong fluorescence with no zoning. "Whereas natural [greens] often exhibit fluorescence along graining lines, the treated stones have a very uniform fluorescence," Deljanin says. Though NovaDiamond achieved fancy yellow also, most of the diamonds are green and yellow-green. The green ones are uniform in color throughout, while irradiated and some natural green diamonds have only a thin layer of green. The color also is more vibrant than irradiated green diamonds, EGL researchers say.

Interestingly, similar findings from studies of green diamonds submitted to the Gemological Institute of America's Gem Trade Lab a few years ago were published in the Summer 1997 issue of Gems & Gemology. The diamonds showed characteristics similar to those treated by NovaDiamond's process, including strong green luminescence to visible light. The report suggests experiments with treatments of this kind took place in the past.

How the Process Works
NovaDiamond granted Deljanin and EGL's Gregory Sherman unprecedented access to its facilities to document the enhancement process and report the findings to the trade. The EGL researchers treated their own diamond samples. "In less than 30 minutes, we witnessed the transformation of 10 unattractive brown diamonds into very appealing green-yellow ones," Sherman says.

NovaDiamond uses mostly Type Ib natural brown diamond crystals from the Argyle mine in Australia, as well as light yellow and white. (Diamonds used in the GE/POL process are mostly Type IIA.) The crystals are embedded in powdered graphite and magnesium oxide and compressed to form a capsule, which is inserted in a pyrophyllite tube and a surrounding coat of soapstone. Metal thermocouples are placed on either end. Three factors – heat, pressure and time – control the outcome.

The capsule is placed in a specially designed prismatic press. Electric current passes through each side of the capsule to produce heat of about 2000°C. This is a much higher temperature than that used to manufacture synthetic diamonds. Meanwhile, six hydraulic arms apply pressure of about 60 kilobars. Temperature and pressure can vary depending on the desired outcome. Time can vary also, from minutes to several days. Afterward, the capsule is extracted and the diamond is removed from the capsule. "The temperatures are made to go up and down very quickly in a very controlled environment," Deljanin explains.

EGL researchers say they are very encouraged by NovaDiamond's desire to disclose everything about the enhancement and plan more sophisticated analysis in the coming months.

NovaDiamond plans to concentrate on yellow-green. Though Hall says the diamonds are easily identifiable because of their high fluorescence, NovaDiamond will certify, serialize and laser inscribe them with identifying marks.

Hall says he expects the diamonds to retail at 25% to 50% higher than a white diamond of similar quality. He plans to sell the diamonds to consumers on a new Web site,, but also will market to retailers using a site protected by a TradeLock™ password at Retailers will be able to offer the diamonds to consumers at a lower price than NovaDiamond's consumer Web site, Hall says. He plans to make a formal announcement during the Tucson gem fairs in February.

- by Robert Weldon, G.G., and Stacey King