AGA Panel Scratches the Surface of Coated Diamonds

Colored diamonds are hot, but natural fancy-color diamonds are rare—and pricey. Hence, several types of enhanced color diamonds are appearing in the market.

One enhancement that’s arousing the color diamond market is being referred to as an “infusion technique.” The term infusion suggests that the resulting color has penetrated the stone’s sur-face, but at a recent seminar in Las Vegas, John Koivula, chief gemologist at the Gemological Institute of America, and Chris Smith, vice president of American Gem Laboratories, explained that “infusion-treated” diamonds were actually coated diamonds. They also said the enhancement isn’t permanent.

“The number of such stones in the market is increasing, in virtually every color—including shades of yellow, pink, and blue that look just like natural stones—and in every shape and size, including melee,” reported Richard Drucker, publisher of The GemGuide and vice president of the Accredited Gemologists Association, which sponsored the seminar.

“And, given the range in sizes and colors, it’s a potential nightmare for jewelers, designers, and manufacturers, unless there is a way to quickly and easily spot them,” warned author and consumer advocate Antoinette Matlins.

“By taking a carbide scriber—a simple tool that looks like a pen—and dragging its carbide point across one of the facets, the point will scratch through the coating,” Matlins explained. “It won’t scratch the diamond, just the coating, which can be seen immediately with the loupe.”

To test this observation, each participant at the conference was given a carbide scriber to use on diamonds provided by Serenity Technology, Temecula, Calif. In 100 percent of cases where a diamond had been surface coated, the carbide scriber revealed it.

Smith and Koivula also pointed out that coating techniques have been used for over 50 years, typically to make diamonds appear whiter; the technique could improve color by 6 or 7 grades.

Matlins noted that carbide scribers are available from AGA for $20, which includes two carbide points (fine and standard). Visit or call (619) 501-5444.

GIA’s spring issue of Gems & Gemology includes the feature story, “Serenity Coated Colored Diamonds: Detection and Durability,” which explains how diamond coating can be detected using magnification and overhead illumination, as well as by scratching.