Identifying CVD Synthetic Diamond

Gary Roskin -- JCK Online, 11/1/2003 2:00:00 AM

The Gemological Institute of America (GIA) reports that four Apollo rough crystals and four Apollo faceted diamonds were submitted to GIA's Gem Trade Lab (GTL) for identification and research. The European Gemological Laboratory (EGL) and gemologist Antoinette Matlins also have studied similar Apollo CVD diamonds.

The labs say identification of the new CVD material is fairly straightforward, but whether or not the average retailer/gemologist can do it remains uncertain.

GIA GTL reports, "Characteristic strain patterns were observed [under the microscope], which were different from those seen in natural diamonds." The lab also writes, "The CVD synthetic diamonds displayed strong red fluorescence while exposed to high-energy UV radiation in the De Beers DiamondView." The DiamondView was designed to detect synthetic diamond.

Observations by EGL USA include seeing clouds of white particles in one plane. EGL's Branko Deljanin says these inclusions can show up in natural diamonds as well but tend to be more dispersed. He also notes that retail jewelers studying CVD diamond under shortwave ultraviolet light may see yellow-green fluorescence that is one or two degrees stronger than under long-wave UV.

Using special spectroscopy instrumentation, GIA noted that CVD diamond has "a relatively strong photoluminescence emission at 737 nm due to trace impurities of silicon." Silicon is not found in natural diamond.

Both laboratories state that jewelers who see inclusions or fluorescence similar to those described here should send the diamond to a professional lab for further study. As with HPHT, Deljanin says, identification of CVD diamond requires advanced instrumentation to conclusively identify the high-quality single- crystal CVD diamond.

Matlins takes a different view. "It's an easy identification, if you do the right tests with proper techniques," she says. She recommends the following steps:

1. Use a "dual" electronic diamond tester—one that tests for thermal conductivity and electrical conductivity—to make sure the stone you're examining is a diamond.

2. Check to see if the diamond is Type II—the colorless synthetic diamonds produced by Apollo are all Type II. If it's Type I, it isn't synthetic. "As a pre-screener, use the SSEF (Swiss Gem Lab) Diamond-Type Spotter and eliminate any doubt," says Matlins. The Type Spotter shows whether the diamond is transparent to shortwave ultraviolet. If you hold the SWUV light over a Type II diamond, the SWUV will pass through the stone and cause the platform of the Spotter to fluoresce green. "If there's no green reaction, you do not have to worry," says Matlins. "It's not a synthetic colorless/near-colorless CVD diamond."

If you see the green, then you have a Type II diamond. Look for evidence that it's a natural Type II diamond, a CVD synthetic, an HPHT-treated diamond, or a CVD diamond that also has been HPHT enhanced.

3. Check fluorescence using a modified technique. If the stone is a Type II diamond, examine the stone with an ultraviolet lamp that provides long-wave and shortwave emission. Note the reaction under each wavelength. To use the ultraviolet lamp to determine whether the stone is a natural or synthetic diamond, do the following:

View the diamond on a black background. If possible, place the stone in a table-down position.
Hold the lamp as close to the diamond as possible.
Be sure the room is completely dark. The stone must be viewed in total darkness to see the reaction.
Note the reaction to long wave; repeat using shortwave.

To determine if a stone is a CVD synthetic, Matlins goes right to the UV unit. Quick test: If it fluoresces blue, it's not synthetic. "Natural diamonds can fluoresce almost any color, but the most common fluorescent colors seen are blue, yellow, and white. However, blue fluorescence is positive confirmation of natural diamond—only natural diamonds fluoresce blue."

When natural colorless diamonds exhibit fluorescence, the reaction is typically strongest under long-wave UV, becoming weaker when viewed under shortwave. Synthetic diamonds typically show the reverse reaction, showing the strongest reaction under shortwave.

In the case of the new synthetic colorless/near colorless CVD diamonds, the fluorescent reaction to the above technique is distinctive: A very dark brownish-red fluorescence under long-wave UV, becoming slightly stronger under shortwave, or dark red under long-wave, which changes to moderately strong yellowish/greenish under shortwave, is positive confirmation of synthetic diamond. In some cases, the reaction will be weak-to-moderate greenish/yellowish under long-wave, becoming much stronger under shortwave. This also indicates synthetic. A small number have exhibited phosphorescence under shortwave, which is positive confirmation of synthetic.

If the diamond's fluorescence indicates the stone is synthetic, no further steps are necessary. However, when looking at any Type II diamond, if there is no fluorescence under either wavelength, or if the fluorescence indicates natural diamond, submit the diamond to a major laboratory to determine whether the color is natural or the result of HPHT treatment.

Matlins worries that the retail trade won't take this seriously. "The trade has been so insistent that the colorless stones would not be affected by this that jewelers are going to continue using their diamond testers and think that they're covered."

Apollo Diamond's Robert Linares says the company is cooperating with the jewelry industry to ensure detection and full disclosure. "We will have full disclosure on rough material, and cut diamonds will be laser engraved and accompanied by a certificate," he promises.