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GradingMay 22, 2019
GIA Spots Second Natural Diamond with Lab-Grown Layer
The stone is 0.64 carats and graded as a fancy grayish-greenish blue.
Gemological Institute of America researchers said the gray and blue components from the lab-grown layer of this diamond combined with the yellow from the natural substrate to create the color, fancy grayish-greenish blue. (Photo credit: Robison McMurtry)
Carlsbad, Calif.—GIA researchers recently spotted a second natural diamond with a lab-grown layer that added weight and improved the color, and warned that it could mean the trade will see more of these kind of composites.
According to an article by Troy Ardon and Garrett McElhenny in the spring 2019 edition of “Gems & Gemology,” the presence of both boron- and nitrogen-related defects—which are rarely seen together in natural diamonds—tipped them off there was something unusual about the stone.
The DiamondView fluorescence image of the diamond—a 0.64-carat fancy grayish-greenish blue cushion modified brilliant—showed a blue hue caused by the “cape” peak (nitrogen defect) and natural growth features.
The crown image, however, revealed a greenish-blue color common to boron-bearing diamonds and the dislocation patterns typically seen in diamonds grown using the chemical-vapor deposition (CVD) process.
In addition, a side view shows a distinct layer between the natural substrate and the CVD-grown portion of the stone. 
“These two distinct fluorescence patterns—the greenish-blue from the CVD layer and the darker blue from the naturally grown layer—prove that a layer of CVD synthetic diamond was grown on a natural substrate,” the article states.
A similar diamond, a 0.33-carat fancy blue that was also Type IIb with a CVD layer, was submitted to GIA in May 2017.
The CVD layer on this latest diamond is substantially thicker, 200 microns (approximately the thickness of two strands of human hairs) vs. 80 microns on the 0.33-carat diamond evaluated two years ago, and GIA noted that seeing a second example of this same type of composite could signal a new type of product entering the market.
The lab would not say if both diamonds came from the same client.
GIA also declined to comment on how the stones were submitted—as natural diamonds, or as natural/lab-grown composites—but did note that clients submitting goods are required to disclose all known treatments as well as whether a stone is natural or man-made.
To see more from the spring 2019 edition of “Gems & Gemology,” the Gemological Institute of America’s quarterly research journal, visit GIA.edu.
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