Professional Jeweler Archive: Born-Again Diamonds

February 2000


Born-Again Diamonds

Heat, pressure and time give birth to a natural diamond. Man’s ingenuity has found a way to re-create these conditions to control diamond colors

The European Gemological Laboratory, New York City, revealed details of a high-temperature, high-pressure process it says can transform brownish diamonds to vivid fancy greens and yellows without irradiation.

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 [partially] burned up some diamonds,” says David Hall, Novatek president. Technicians polished off the burned surface and found a green diamond underneath, he says, then spent several months trying to repeat the process. As the company perfected the process, it adopted the name NovaDiamond Inc. to promote the product.

High Temperature/High Pressure Detected

NovaDiamond’s client submitted several green diamonds to EGL for origin-of-color reports. “The diamonds were quite unusual, showing none of the lines associated with radiation treatment,” says Branko Deljanin, EGL’s director of gem identification and research. Because natural green diamonds show radiation lines, the gemological theory always has been they are irradiated in the earth. As a result, treated green diamonds generally are irradiated to replicate the process.

Deljanin contacted Dr. Alan Collins, a color-center diamond expert in Great Britain, who suggested the diamonds showed high-temperature/high-pressure characteristics. This led researchers back to Novatek, which confirmed their suspicions. The revelation adds to the rapidly unfolding history of diamond enhancements, particularly following the unveiling last year of GE/POL, a treatment that improves the color grade of colorless diamonds through high temperature and high pressure. The GE/POL treatment was the first known time that a high-temperature/high-pressure process was found to alter color in non-nitrogen (Type IIb) diamonds.

NovaDiamond’s treated diamonds are different because they are mostly Type Ib nitrogen-bearing diamonds, which have long been known to react to heat. NovaDiamond says its aim is to produce fancy colors, not colorless diamonds.

Identifying Marks

NovaDiamond’s treated green diamonds demonstrated strong fluorescence without zoning. “Natural [greens] often exhibit fluorescence with zoning along graining lines,” Deljanin says. Though NovaDiamond achieved fancy yellow also, most of the diamonds are green or yellow-green. The greens are uniform in color 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.

Non-irradiated green diamonds have shown up in a lab before – experiments with high-temperature/high-pressure treatment date back several decades, though now the focus is on perfecting processes and achieving repeatable results. Findings similar to EGL’s were reported in the Summer 1997 issue of Gems & Gemology, the quarterly journal of the Gemological Institute of America, after several greenish diamonds were submitted to GIA’s Gem Trade Lab. Those diamonds apparently show characteristics similar to ones treated by NovaDiamond’s process, including a greenish glow, called luminescence, as they react to visible light.

How the Process Works

NovaDiamond granted EGL’s Deljanin and Gregory Sherman unprecedented access to its facilities to document the enhancement process and report its findings to the trade. EGL says NovaDiamond uses primarily natural brown diamond crystals. The crystals are embedded in powdered graphite and magnesium oxide and compressed to form a capsule. The capsules are inserted in a pyrophyllite and soapstone casing sealed with metal thermocouples at both ends. Three factors – heat, pressure and time – control the outcome.

The capsule is placed in a specially designed prismatic press. Electric current passes through the metal thermocouples to produce heat of about 2000°C. This is a much higher temperature than that used to manufacture synthetic diamonds. During the heating phase, hydraulic arms apply pressure of about 60 kilobars. Temperature, pressure and time vary depending on the desired outcome. “The temperatures rise and fall quickly in a very controlled environment,” EGL’s Deljanin says.

NovaDiamond first experimented with treating cut and polished diamonds, but Hall says researchers found it easier to subject rough to the high-temperature/high-pressure treatment and do the cutting afterward.

EGL says it’s encouraged by NovaDiamond’s desire to disclose everything about the enhancement. EGL plans a more sophisticated study in the future.


NovaDiamond plans to concentrate on producing yellow-green diamonds. 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 expects the diamonds to retail 25% to 50% higher than a colorless diamond of similar quality. He plans to sell the diamonds to consumers through a new Web site, The site’s technology will allow high-resolution diamond photos to load quickly on consumers’ computers. “So many people now want to go on-line to buy their diamonds, and we found we’d be missing a big part of the market if we didn’t give them a way to buy direct,” he says.

However, NovaDiamond will give consumers an incentive to buy in retail stores too. The company will send CD-ROMs to jewelers and prepare in-store displays to market to consumers. Then retailers can buy the diamonds from a trade-only site protected by a TradeLock™ password at “Retailers can buy it at a discount, set it and resell it to consumers for less than the price on our consumer Web site,” he says. NovaDiamond will introduce the diamonds during the Tucson gem shows.

– by Robert Weldon, G.G., & Stacey King

Diamonds like the brown crystal (to the left in the photo above) are placed in powdered graphite and magnesium oxide in a pyrophyllite and soapstone capsule (right) to be heated and then placed in a diamond press. Depending on temperature, pressure and length of treatment, diamonds are changed to varying shades of green and yellow. Samples courtesy of EGL, New York City.
This insert shows two halves of the same diamond. At left, one half without any treatment. At right, the other half fluorescing after being treated by high temperature and high pressure.

The multimillion-dollar computer-controlled diamond press, shown with EGL’s Branko Deljanin (left) and NovaDiamond President David Hall, transforms brownish diamonds to yellow and green with a high-temperature/ high-pressure process. A press of this caliber may cost up to $20,000 a day to operate.
Upon completion of the treatment, and after the capsule has cooled, the diamonds are reborn by being broken out of the capsule.

Copyright © 2001 by Bond Communications