An article in GIA’s  latest issue of Gems & Gemology, in its Lab Notes section, will be of great interest, and no doubt some concern,  for those striving to ensure that the identities  and value chains of natural diamonds and lab-grown diamonds  are kept separate. The findings raise a new spectre – forget mixing the two kinds of diamonds in a single parcel; now, the two can be “mixed” in a single stone! And this is not the first stone to be so tested.

Troy Ardon and Garrett McElhenny have gone into a  detailed analysis of a 0.64 ct Fancy grayish greenish blue cushion modified brilliant, which, the article says, was “found to be a composite of synthetically grown and natural diamond”.

“During testing, the infrared spectrum showed both strong absorption of nitrogen and the absorption of uncompensated boron, features characteristic of type Ia and type IIb diamonds, respectively,” the authors note. “The UV-Vis-NIR spectrum showed “cape” peaks, which are nitrogen-related defects, but also a sloping absorption into the red portion of the spectrum caused by uncompensated boron. It is very unusual for boron- and nitrogen-related defects to be seen together in natural diamonds, though an example has been seen before (Spring 2009 Lab Notes, pp. 55–57).”

The authors add: “The DiamondView fluorescence image taken on the pavilion showed a blue hue, caused by luminescence from the N3 defect, and natural growth features. The image taken on the crown showed a greenish blue color common to boron-bearing diamonds and the dislocation patterns characteristic of CVD-grown diamonds. In the image taken from the side, a layer can be seen between the natural substrate and the CVD-grown addition. 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.”

Further experiments enabled the researchers to calculate an approximate layer weight of 0.10 ct and a thickness of approximately 200 microns of the CVD part of the stone.

But it appears that this is not something entirely new. The article notes: “A similar diamond previously reported was also a type IIb CVD layer grown on a natural Ia substrate (Summer 2017 Lab Notes, pp. 237–239). That composite was Fancy blue, weighed 0.33 ct, and had a CVD layer that was 80 microns thick.”

Also, as a result of further testing  of  the current gem under discussion, it was found that the Fancy colour of the diamond was derived as a result of the addition of the CVD layer. “The resulting colour was likely the main motivation for growing the CVD layer on top of the natural diamond, though the extra weight gained could also be a factor,” the authors said. They also observed, based on various tests, that that “it was a thick CVD layer and not a coating of CVD overgrowth”.

“With the second of these composites seen at GIA, this could be a new type of product entering the market,” the article concludes. “Earth-grown diamonds with synthetic diamond grown on the surface require extra scrutiny due to the presence of natural-looking features, both spectroscopic and gemmological. Careful inspection still reveals the presence of synthetic indicators, which expose the true nature of the diamond.”

Pic Cap: Face-up image of the natural diamond with CVD synthetic diamond overgrowth. The blue color is due to the boron-doped CVD layer. Photo by Robison McMurtry.

Pic Courtesy: GIA