Andy Lucas Recaps Main G&G Articles from 2003

By Mauricio Minotta

Andy Lucas, product manager, Gemology, provided an over-view of the main articles published in Gems & Gemology in 2003 as part of a series of free seminars hosted by GIA in Tucson.

Titled “G&G Recap,” the lecture covered topics that included gem treatments, lighting techniques for photomicrography, lattice diffusion-treated sapphires and a brief look at chemical vapor deposition (CVD) synthetic diamonds being developed by Boston-based Apollo Diamonds, Inc.

His comprehensive description of G&G’s Gem Treatment Chart covered bleaching of pearls, dyeing of jade, lattice diffusion of corundum, and the various treatments to diamond, including irradiation. 

Jadeite treatments, for example, can run the gamut of sophistication – from simply rubbing some wax on the surface to improve luster, to using advanced chemical reactions to get desired effects, Lucas said.

A portion of the lecture also focused on diamond treatments represented on the chart. As explained in the G&G article, Lucas said observing a fracture-filled diamond under dark field illumination and rocking it back and forth would cause a colored flash effect – a clear sign of its treatment.

He also briefly covered high pressure/high temperature (HPHT) treatment, which is done mostly on type IIa, and in some cases type Ia diamonds, to improve their color. Detection is very challenging, and usually can be done only in a laboratory.

“Some of the treatments are easy to detect. Others require advanced testing,” Lucas said. “But it’s important to be aware of what treatments are possible. If you know which ones you can detect, you’ll be in good shape.”

Another important treatment, the subject of a major article in the Summer 2003 issue, was the lattice diffusion of corundum. Lucas showed several slides to demonstrate examples of lattice-diffusion treatment during which treaters subject corundum to very high temperatures before introducing other elements to enhance the stone’s color. But the extent of color penetration varies, he said.

“I’ve seen some of the yellow to padparadscha colors that have gone all the way through the stones and others that is limited to just below the surface,” Lucas said. “So it can vary greatly.”

He also showed color concentrations along facet junctions and zoning related to the stones’ outline while being observed under immersion. Other examples of lattice diffusion showed signs of natural inclusions that have been distorted as a result of the treatment.

“The heat alters the inclusions. Whitish clouds are the result of inclusions being burned, such as rutile needles that have dissolved to look like intersecting dots,” Lucas said. “All are indications that corundum has been subjected to high temperature.

“There’s nothing wrong with this material or this treatment just as long as there is proper disclosure all the way down the line at each transaction.”