Detection, corundum diamond cut focus of GIA GenFest Basel

Detection of synthetic diamonds is no longer a concern for the jewelry industry. That was a key good-news message presented by Dr. James Shigley, director of research for the Gemological Institute of America, during GIA’s GemFest Basel, part of the BaselWorld 2005 trade fair.

Synthetic diamonds first became a concern in 1970, when General Electric launched its first attempt at them, but the issue has come to the fore again in the past few years with the advent of several new producers and an article touted synthetics on the cover of Wired magazine.

But there is no known commercial production of colorless synthetics, said Shigley. Furthermore, synthetic diamonds have a unique crystal morphology due to how they’re grown in a laboratory. Their growth process produces a distinct color zoning feature that gives the stones identifying characteristic. They also have a distinct graining pattern and sometimes have metallic inclusions left from the flux used in the growing process.

In addition, diamonds produced by carbon vapor deposition don’t pose a threat to the market, he said. To date, all specimens GIA has seen from CVD producer Apollo were under a carat, and the process produces light brown stones, requiring further (HPHT) treatment to lighten them.

There may in the future be a joining of the two methods, whereby a CVD diamond is grown on a synthetic diamond substrate, but these stones would also be detectable, Shigley said. A greater concern is continued HPHT treatment of natural stones. The treatment used to be confined to Type II diamonds, but has now been expanded to Type I diamonds, the type that comprises 95% of the diamond market. With more people doing it, he said GIA is continually updating its research to keep up.

Shane McClure, GIA’s West Coast director of identification services, reviewed the current status of beryllium diffusion treatments of corundum but, more importantly, discussed a new fracture-filling treatment first seen late last year in some rubies from Madagascar. Since then, many of these stones have come into the market.

Opaque to translucent, highly fractured rubies are being infused with leaded glass, which has a very high refractive index and blends into the stone to make the inclusions less visible and the stone more saleable. Under magnification, one can see huge networks of fractures in these stones. The treatment is reasonably durable against normal processes like mounting and re-tipping, but when exposed to a caustic solution such as that used for pickling, it can remove or harm the glass filling.

GIA president Bill Boyajian wrapped up GemFest with a discussion of more elements of GIA’s forthcoming diamond cut grade. GIA’s system focuses on the interrelation of proportions to one another, not on any one set of specific proportions. This, says Boyajian, allows cutters to cater to different market tastes without penalizing a market by implying its preferred cut is a lesser cut.

What makes GIA’s system different from other cut grading systems is that appearance values are determined both by computer and by observation, and within each grade there are multiple sets of proportions that will yield top results, he said.

Boyajian also announced the nomenclature to be used to describe cut: Excellent, Very Good, Good, Fair, and Poor. He said GIA expects the bulk of stones submitted for grading will fall into the top three categories, but that the bottom two may be needed from time to time. The cut grading system will apply only to round brilliants, D to Z color, flawless to I3. It will not apply to modified round brilliants or to fancy cuts or colors.

GIA is creating software to assist dealers, manufacturers, cutters, retailers, and appraisers with the system. A key part of its process is to view the diamond in a controlled environment; e.g. in a light box, which has been developed and will be available from GIA’s Gem Insruments division.