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New Test for Small Synthetic Diamonds
Jewelry Scene

According to Gems & Gemology, many pieces of jewelry set with small yellow diamonds are set with synthetic diamonds.

In a study published in the fall 2008 issue, “Identification of Melee-Size Synthetic Yellow Diamonds in Jewelry,” by Hiroshi Kitawaki, Ahmadjan Abduriyim, and Makoto Okano of the Gemmological Association of All Japan-Zenhokyo Laboratory in Tokyo, one out of ten small yellow diamonds they tested were synthetic. Half the jewelry they tested set with small yellow diamonds contained at least one synthetic diamond.

“Given the current availability of synthetic diamonds and the fact that melee-size (especially those smaller than 0.05 carat) stones are more difficult to test, it should not come as a surprise that such small synthetic yellow diamonds have started to become mixed with natural diamonds, both in parcels of loose stones and in manufactured jewelry,” the authors said in the article. “Although synthetic diamonds still represent only a very small part of the gem market, they receive a great deal of attention within and outside the industry, so correct identification is of great importance.”

The authors of the article developed a new testing method to distinguish between natural and synthetic yellow diamonds as small as 0.001 carat without removing them from the mounting.

Infrared microspectroscopy, in combination with cathodoluminescence imaging, allowed for the rapid and accurate separation of melee-size natural and synthetic diamonds based on their characteristic mid-infrared absorption spectra and growth structures, respectively. With these techniques, the GAAJ-Zenhokyo Laboratory in Tokyo determined that approximately 10 percent of loose—and dozens of mounted—yellow melee diamonds submitted over a four month period were synthetic.

“Since many jewelers do not want to go to the trouble and expense of testing melee diamonds, there has long been the possibility that synthetics were being mixed with natural melee,” says G&G editor-in-chief Alice Keller. “GAAJ not only devised a quick and efficient approach to separating natural from synthetic yellow melee, but they also determined that a significant portion of the small loose and mounted goods that came through their lab over a four month period were in fact synthetic.”

natural yellow diamond ring
Loose synthetic diamonds from Chatham Created Gems illustrate some of the yellows produced by HPHT growth. Many are similar in hue and intensity to the natural yellow diamonds in this ring by Alan Friedman. The loose synthetics weigh 0.05-0.30 carats. The fancy intense yellow center diamond in the ring is 1.09 carat, and the 93 yellow melee weigh a total of 1.12 carats.
Photo by Robert Weldon, courtesy of GIA.