Leslie & Co. has introduced another color—Royal Red—into its inventory of diffusion-treated stones. The San Diego company introduced the first diffusion-treated topaz back in 1998, a green color now called Evergreen. The company has since produced four other colors: Glacier Blue, Teal, Champagne, and Bali Bi-Color (green and blue). Royal Red and Bali Bi-Color will be introduced at this year’s Tucson gem and mineral shows. According to Leslie, these diffusion-treated topazes can withstand normal wear and tear, bench repair techniques, and ultrasonic cleaning.

Topaz has a long history with a variety of treatments. Most of what you see in supplier cases has been irradiated blue, and, depending on the tone and saturation of the treatment, stones may be labeled sky blue, Swiss blue, or London blue. Very pale to light blue can be a natural color and is usually available with documentation through professional gem and mineral experts.

A treatment called Aqua Aura, which first appeared in the early 1990s, begins with a colorless (often called “white”) topaz (or rock crystal quartz), which is then coated with pure gold. The gold adheres through an electronic bonding and gives the gem a blue and iridescent appearance.

Randy Gillis, president of Precious Designs Inc., Charlotte, N.C., is promoting a topaz treatment called titanium vapor deposition. The titanium gives topaz a rainbow appearance, with strong accents of purplish-red and green, rather than the blue overtone of the gold-coated Aqua Aura. Gillis markets the material as “Mystic Fire topaz.”

“It’s colorless Brazilian topaz, cut in Thailand and then treated in the United States,” says Gillis, who notes that Mystic Fire can be treated like regular topaz except for one consideration: If you buff the stone, the coating will come off.