RAPAPORT...  The following article was condensed from a longer, more technical report in GIA’s Gems & Gemology on the same topic.

Nearly five years after their well-publicized debut, synthetic diamonds produced by Apollo Diamond Inc. using chemical vapor deposition (CVD) have entered the commercial jewelry market in very limited quantities. The good news, according to the lead article in the Winter 2007 issue of Gems & Gemology, is that these synthetics can be identified by gemological tests and the advanced diamond-testing equipment used by the major labs.

GIA researchers Dr. Wuyi Wang, Matthew Hall, Kyaw Soe Moe, and Thomas Moses, as well as Apollo senior scientist Joshua Tower, detailed their examination of 43 CVD synthetic diamonds produced by Apollo Diamond during 2006 and 2007. These lab-grown stones were the latest generation of products manufactured by the Boston-based company, which in 2007 began marketing goods through a local retailer in a test program.

Unlike high-pressure, high-temperature (HPHT) diamond synthesis, which replicates some of the conditions of natural diamond formation, the CVD process involves mixing gases (typically methane and hydrogen) in a vacuum chamber. When heat is applied inside the chamber, chemical reactions of the gas mixture deposit synthetic diamond onto a diamond substrate. 

The CVD synthetic diamonds examined for the study weighed between 0.14 and 0.71 cts. (pictured.) The near-colorless goods ranged from E to M on the GIA color scale. Fourteen were fancy colors—11 orange to pink and three dark brown. The samples covered the clarity scale from VVS to I, though the majority were in the VS range.

The current set featured much more attractive colors than the samples G&G reported on in 2003, with the colorless and orange-to-pink material representing the material now hitting the market. The samples also showed improved clarity; however, some had small fractures that, unlike what is typically seen in natural diamonds, had no relationship to any inclusions within the stones.

The study explains that it is still a major challenge to grow gem-quality CVD synthetics rapidly to the point where well-proportioned round brilliant cuts can be fashioned from the flat, tabular crystals that typically result. Although other studies have found that “doping” the process with nitrogen (the source of yellow color in natural diamonds) speeds up growth, some of the Apollo specimens were type IIa—meaning that no nitrogen or boron (the cause of blue color), or only very trace amounts, could be detected.

Exposing the samples to short- and long-wave ultraviolet (UV) lamps revealed a close relationship between fluorescence and bodycolor. Of the 29 near-colorless polished specimens, only eight displayed very weak orange fluorescence. However, all of the eleven orange-to-pink goods showed very weak to moderate orange fluorescence, while the dark brown items showed no fluorescence.

In the (Diamond Trading Company) DTC DiamondView instrument, most of the near-colorless CVD synthetic diamonds showed strong pinkish orange fluorescence, while fancy-color goods in the orange-to-pink group displayed a strong reddish orange fluorescence.

All of the samples carried Apollo’s laser inscription on their girdle. In earlier reports, the company had pledged to cooperate with the jewelry industry by marking all of its products.

The new Apollo products showed a number of unusual characteristics, such as internal graining with fuzzy boundaries (though three samples had well-defined graining); complex fluorescence zoning, and a number of distinctive spectroscopic features. However, not all samples showed these characteristics to the same degree. This means that gemologists must employ a combination of tests to consistently identify CVD synthetic diamonds. Note that some of the characteristics used to identify HPHT synthetics, particularly the distinctive octagonal “stop sign” growth pattern, are not present in CVD products.

Given the marked improvement in the quality of these synthetics, it is likely that they will continue to evolve, thus creating the need to study them on an ongoing basis.

© Gemological Institute of America. All Rights Reserved, March 2008