Shigley Provides Updates on Cut, Synthetics

By Mauricio Minotta

Dr. James Shigley, director of GIA Research, presented the Institute’s latest findings on developments affecting the gem and jewelry industry, including an update on its diamond cut project, in Tucson Feb. 7.

The lecture covered a brief history of the ongoing study of cut by GIA Research, which first looked at a round-brilliant diamond’s brilliance and fire in relation to that diamond’s proportions.

Shigley explained that more than 70,000 observation tests over the last two years had been conducted with members of the industry and the public that ultimately supported findings on diamond appearance reached with computer modeling and mathematical calculations.

GIA researchers are in the final stages of the phase that studies how proportions of a round brilliant are related to scintillation. Once that phase is completed, Shigley said the project results will be the basis for a diamond cut grading system for colorless round brilliant diamonds.

Shigley’s lecture also touched on synthetic diamonds and gem treatments that have gradually become more prevalent in the industry over the last few years. He briefly explained the process of chemical vapor deposition (CVD) used to produce small synthetic diamonds, which are grown in high temperature, but low pressure environments to produce thin wafers.

High pressure/high temperature (HPHT) annealing tests done by GIA on a small sample of CVD-grown diamonds to attempt to change their color drew mixed results, Shigley said.

One sample turned black, a second showed no change, while a third turned more colorless. To date, researchers are uncertain of reasons for these differences in the material’s reaction.

Relatively new to the industry, CVD-grown diamonds could be in their infancy in terms of the availability of the material.

“I think we are going to continue to see diamonds grown this way in the future,” Shigley said. “However, based on samples examined to date, we are able to identify CVD-grown diamonds in the lab.”

He also reported on new characteristics associated with internal laser drilling treatment of diamonds that have been seen recently by GIA. As technology develops, so does the extent of visible damage this treatment leaves behind.

Instead of straight channeling from the inclusion to the diamond’s surface, researchers have observed different kinds of patterns of lines near or within an inclusion or fracture that they believe is damage caused as the laser is moved back and forth within the stone, he said.

“The pattern of laser drilling has been changing, perhaps to change the treatment’s appearance,” Shigley said. “This may not be a deliberate act, but may also be an accidental result of the treatment process.”

A new form of treatment to blue sapphire is among the latest identification challenges seen by GIA, Shigley said. Unlike beryllium diffusion-treated corundum, which displays color zoning related to a stone’s outline as seen under immersion, this treatment shows dark blue central color concentrations with curved irregular edges surrounded by a light-blue to near-colorless zone. The pale outer zone varies in depth and, in this case, does not conform to the stone’s outline.

GIA researchers traveled to Sri Lanka to visit a center where this new treatment is being conducted, but a conclusion to exactly how it is being carried out has not been reached, to date.