January 21, 2002
Corundum Diffusion Treatment Includes Rubies
The American Gem Trade Association's Gemological Testing Center, New York City, reports it's finding rubies treated with a high-temperature diffusion process to change the surface color to orange. The lab says the treatment appears to be similar to one reported earlier this year that is used to change pink sapphires to a more desirable pink/orange that mimics the hue of padparadscha sapphires ("Padparadscha Treatment Surfaces").
"We have in our lab several red stones that qualify as rubies," says Ken Scarratt, the labs director. "Immersed in a methylene iodide solution and viewed against diffused lighting, these samples exhibit a distinct orange rim along the three-dimensional outline of the stones. The rubies are treated with a high-temperature diffusion process that changes the surface color to orange. Scarratt says the treatment appears to be taking place on rubies that were originally very dark toned. "The diffusion appears to lighten and brighten the red color," he says.
Scarratt suspects the rubies are subjected to extremely high temperatures and that an unconfirmed element is diffused into the gemstone's surface layer. Some scientists believe a magnesium compound, coupled with very high temperature treatments may be responsible for the orange surface layer.
The rubies, like the sapphires detected earlier, come from a variety of sources. But the treatment takes place in Thailand, a gem-cutting center. Scarratt and other gem labs say the treatment is alarming because of the quantity of gem material (mostly sapphires) that appears to be involved, and because the stones are often sold without proper disclosure. Gems from 1.0 carat to over 5.0 carats are being encountered. Rubies and sapphires are varieties of the gem species corundum. Red corundum is described as ruby. Sapphires can be almost any color except red.
by Robert Weldon, G.G.