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Lab Spots Stone with CVD Coating
Dec 7, 2017 3:45 AM
By Rapaport News
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RAPAPORT... A Chinese gemological laboratory has identified a
well-concealed synthetic-diamond coating that bolstered the size of a small natural
stone. 
While the lower part of the stone was a colorless, natural
diamond, the upper section, including the crown and the top of the pavilion,
contained a layer of diamond created using chemical vapor deposition (CVD).
Although CVD coatings have been present in the industry for
many years, “CVD overgrowth, which significantly influences the weight and size
of the diamond, is still rarely reported up to now,” the Beijing-based National
Gemstone Testing Center (NGTC), which detected the stone, said in a recent
statement.
While the Gemological Institute of America (GIA) earlier
this year identified an overgrowth on a natural diamond that tinted it blue,
the layer that the NGTC discovered is more concerning for the trade, the
Chinese group explained.
The coating over the brilliant-cut, 0.11-carat,
near-colorless diamond was hard to detect, with no features betraying its
existence visible using a microscope, the NGTC said. The layer it found was
thicker, perhaps indicating an improvement in growth technique and, unlike in
the GIA case, there were no blemishes on the stone resembling needle marks.
NGTC gemologists were able to identify the overgrowth with
spectroscopic analysis, as well as images taken using DiamondView technology.
The lab could not say how much weight the coating added to the
diamond.
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Tags:
chemical vapor deposition, cvd, DiamondView, Gemological Institute of America, GIA, laboratory, National Gemstone Testing Center, NGTC, overgrowth, Rapaport News, synthetic-diamond
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