In a major breakthrough study performed by Gübelin Gem Lab in Lucerne, Switzerland, and its research colleagues, the 18O and 16O isotopes of heated and unheated rubies and sapphires from 106 deposits worldwide were found to be unique, which makes them useful in determining origin.
One especially important discovery is that heated corundum specimens from a particular region have the exact same oxygen isotopic composition as unheated material from the same region. That provides another way to determine origin of heat-treated gems. Having a backup method is significant because traditional identification techniques use microscopic examination of inclusions, but inclusions are rendered indistinguishable after most heat treatments.
But don’t throw away your microscope yet: The new process doesn’t solve all the challenges inherent in identifying origin. “For example, not all localities have unique oxygen ratios,” says GGL director Daniel Nyfeler.
Nevertheless, GGL has concluded that “combined with traditional gemology techniques, oxygen isotope analysis will contribute toward defining the origin of some commercial high-value blue sapphires, especially from Kashmir.”