Large flame-fusion synthetic rubies are being disguised as naturals by intentionally cracking them and healing the fractures using flux. A GIA news release says these gems are being offered as “heat-treated natural rubies.”

“Basically, it’s the same material that we used to see a lot more of a number of years ago, maybe 15 years ago, or more,” says Shane McClure, director of gem identification at the Gemological Institute of America’s Gem Trade Laboratory in Carlsbad, Calif. “I tend to think that it’s new because we’re now seeing big stones. And a lot of them, which we never used to see.” GIA says sizes up to 52 cts. have been submitted.

Previously, the lab saw mostly 1, 2, and 3 ct. stones. “I don’t recall personally ever seeing a 20-carat [flux-healed flame-fusion synthetic ruby] back then,” says McClure.

Most suppliers said the synthetics were coming from Bangkok, Thailand. “It’s not a difficult identification,” says McClure, “not if you are looking for it. If you’re not looking for it, then you could easily let it go.”