Fraudsters forged a Gemological Institute of America (GIA) inscription on a synthetic diamond to make it appear that the stone was the true bearer of a natural-diamond grading report, the institute said.

The engraving on the polished diamond’s girdle contained a genuine GIA report number for a mined diamond the institute had graded in 2015, the laboratory explained. However, while the “real” diamond with that code was a round brilliant-cut, 1.74-carat, D-color, VVS1-clarity stone, gemologists at the GIA’s lab in Carlsbad, California, found the submitted diamond to be 1.76 carats, with F color and VS1 clarity.

The graders referred the stone for additional testing, which confirmed it as a synthetic diamond created through High Pressure-High Temperature (HPHT). The growth structure and phosphorescence — or light emission — visible via DiamondView technology betrayed this fact.

The discrepancies between the stone and the 2015 report gave the gemologists a good indication that the diamond they were looking at was not the same one. In addition, a test using Fourier-transform infrared spectroscopy (FTIR) revealed it was type IIb, while the stone the original report described was type Ia.

Even the attempt at forging the number did not get past the lab staff: Careful examination revealed the font was different from the GIA’s usual one, confirming it was a fake.

The person who submitted the stone had probably noticed the inconsistencies with the GIA grading report and sent it to the lab for an updated report, senior research scientist Christopher Breeding and senior staff gemologist Troy Ardon wrote in the lab note.

“Rarely do we encounter the type of blatant fraud described here,” the authors explained, urging traders to send suspicious-looking diamonds to a gemological laboratory for verification.

“It is important for the industry and public to exercise caution, because these types of misleading practices do occur,” they warned.