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GIA Explains Synthetic Identification Processes at DMIA Meeting

Jun 19, 2012 12:41 PM   By Ricci Dipshan
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RAPAPORT... The Diamond Manufacturers & Importers Association of America (DMIA) held their general membership meeting on June 18 in New York, and hosted the Gemological Institute of America (GIA) to share  the latest measures in detecting synthetic diamonds.  GIA's   Tom Moses, the senior vice president of GIA Laboratory and Research, and Wuyi Wang, the director of research and development for GIA New York, were featured speakers.

GIA’s main purpose at the meting was to “give everyone a brief update on synthetic diamonds,” said Moses, adding that “we have had events like those in the last couple of weeks that makes us all aware about how important identification is.  So the important thing is to have a real respect of the process and a voice of confidence that we as an industry can really identify these synthetic stones.”

Moses explained the types of processes were used to create synthetic diamonds, Chemical Vapor Deposition (CVD) and high-pressure-high temperature (HPHT).  While difficult,  “there isn’t a significant breakthrough that has made the creation of synthetic diamonds easy — CVD and HPHT still are the only two ways.”

“A lot of people think of CVD as a new method of diamond growth, but the first synthetic diamonds were CVD,” Moses continued.  “Indeed the first recognized synthetic diamond was made in 1952 by Union Carbide Corporation through CVD.”

The benefits of CVD, explained Moses, was that it did not require high pressure in the process, and that more than one crystal could be grown at a time. The process, however, as a few drawbacks as well — it is extremely difficult to grow CVD diamonds with depth, especially more than 3mm thick.    The CVD process is also a slow one, as the average growth rate per hour is around 100 microns.  Though this process can be sped up, it results in lower-quality, and a brownish color, which is a characteristic of most CVD diamonds.

Despite these drawbacks, there have been many high-quality stones made through the CVD process in recent years.  In 2006, Apollo Diamonds grew near colorless diamonds, while in 2011 Gemesis created diamonds up to 0.9 carats that ranged from IF to VS qualities.  The largest near colorless CVD stone ever made was documented in 2010 to be around 1.05 carats.

“This is not something that we can stop,” said Moses, advising that synthetic diamonds were occupying a parallel market to the natural stone market.  “We cannot be intimidated by them, so we have to coexist with them.”  

While “gemologically its becoming more and more difficult to identify CVD diamonds,” declared Moses, “there are many ways in which to distinguish a real stone from a lab-created one.”

CVD diamonds, for example, have irregular black inclusions and dispositions of non-diamond carbon in them.  They also have a red orange fluoresce under an Ultra Violet (U.V.) light.  Labs can also spot CVD-type growth in a diamond under a U.V. light—a characteristic that a CVD diamond will have no matter what treatments its undergoes. 

Almost all of these identification methods, however, require lab-grade equipment and expertise.  “There are non-lab devices, some better than others, that will give you an indication that you should test more, but no device will tell you outright” said Moses. “It is becoming a ‘refer to a gem lab’ situation more and more.”

Turning to  HPHT, Moses noted that while this method can create diamonds of all colors and sizes, the stones  are more easily identifiable.  And while the largest HPHT stone ever made was 4.09 carats, HPHT stones are usually 0.4 to 0.6 carats in size. 

“These stones are a bit easier to identify, and as time goes by, we might even see less of these made,” said Moses, adding that CVD was the preferred process, though HPHT is still popular with many companies.

Because the HPHT process requires metal catalysts to speed up production of stones, many HPHT stones have recognizable metal inclusions that distinguish them from natural ones.  “A very good identification tool is a magnet — if you can pick the stone up with a magnet, it’s an HPHT synthetic,” explained Moses.

Other ways of identification include noticing with lab-grade equipment, specifically high energy U.V. source equipment, whether or not the stone has specific graining patterns and color zoning that is different from natural stones. 
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