The Gemological Institute of America (GIA) has recently received “a number of” lab-grown or treated stones carrying natural-diamond reports and fake inscriptions, the organization warned.

Clients submitted the stones for updated reports or verification services, but the grading documents that came with the goods did not match the stones, the GIA explained Tuesday. The weights and grading scores of the lab-grown and treated diamonds were close but not identical to the original stones that appeared on the reports, and they all featured the corresponding natural-diamond report numbers in the form of counterfeit girdle inscriptions.

In one example, a stone submitted was a 1.51212-carat, D-color, VVS2-clarity, type IIa, lab-grown diamond with a cut grade of “very good.” However, the accompanying report — for which the client was seeking an update — was for a 1.50362-carat, VVS2, E, type I natural diamond with “excellent” cut.

In line with its policy, the GIA overwrote all the fraudulent inscriptions with X’s to obscure them, it added. The organization also issued new reports with the accurate details, and engraved the correct report number onto the girdle, and, where relevant, the phrase “laboratory-grown.” In these cases, it also considers informing the client that submitted the stone, law enforcement, and the public, the GIA noted.

Last month, the institute revealed that it had spotted three synthetic moissanites that clients had submitted with forged girdle inscriptions that disguised them as natural diamonds. The cases at its Johannesburg laboratory were the first times the GIA had discovered fake inscriptions on diamond simulants.