Tucson 2015: Gemologists Share the Latest Research Activities
March 25, 2015
He began with a summary of GIA’s major research efforts: to collect and characterize new gem materials to support GIA’s gem identification capabilities; to conduct experiments to determine new methods for identifying treated diamond; to develop standards for calibrating instruments across GIA’s gem identification and grading laboratories; and to examine the appearance of the major categories of fancy-shape diamonds.
One of the most important activities is to build GIA’s gem database by cataloging information from gems submitted to GIA for testing and those collected by GIA field gemology teams at the source in locations around the world. GIA has routinely conducted field expeditions – nearly 60 trips to 16 countries in the last five years – to collect material. Last year, researchers traveled to Brazil, Cambodia, Madagascar, Malawi, Mozambique, Myanmar, Sri Lanka, Thailand, Vietnam and Zambia.
“Travelling to these countries and collecting gem specimens directly at the source – seeing them come from the earth – ensures they have not been treated and are not synthetic,” Shigley said. Knowing without question where a gem was sourced and understanding its distinctive characteristics also helps researchers make country-of-origin determinations, he said.
Researchers archive the rough specimens they collect, characterize them using specialized instrumentation, then record the results in a database shared with all GIA laboratories.
Shigley said one of the biggest challenges is how to identify gem treatments. In a recent study, researchers collected data on unheated (brown) zoisite, and then heated the gems to known temperatures to examine differences in color and spectra after the treatment. The heated gems turned a dark blue and purple color – a variety of zoisite known as tanzanite. Researchers examined the visible spectra and inclusions then compared this information to the data from the same stone before it was heated.
These experiments determined that visible spectra are inconclusive in determining whether a tanzanite has been heat treated or not; the absence of three pleochroic colors may suggest that a tanzanite is unheated, but it can be difficult to observe all three colors in a cut stone; and unaltered fluid inclusions are perhaps the best indication that a stone has not been heat treated, while ruptured fluid inclusions are an indication of heat treatment.
Shigley explained the importance of accurate and efficient instruments in gemological research and the GIA laboratory. Instrumentation at all GIA lab locations are regularly monitored and calibrated to ensure consistent measurements. He mentioned the GIA DiamondCheck, a device introduced in early 2014 that differentiates natural diamonds from those that are potentially synthetic or color-treated, as an example. GIA, working with the World Federation of Diamond Bourses (WFDB), has made the DiamondCheck available on a lease basis at no cost to 20 diamond bourses and industry organizations around the world.
Shigley also reviewed the progress on a cut evaluation system for fancy-shape diamonds. GIA introduced the cut grading system for standard round brilliant diamonds (in the D-to-Z color scale and the Flawless-to-I3 clarity range) in 2006. Since then, the research team has investigated the cut and appearance for the most common fancy-shape diamonds. Researchers interviewed more than 440 experts from different backgrounds in Antwerp, Hong Kong, Mumbai, New York, Tel Aviv and Tucson in 2014. Participants were asked to examine fancy-shape diamonds and record what they saw to help determine industry preferences for certain aspects of diamond appearance.
A GIA laboratory team continues to evaluate client-submitted stones on a daily basis, noting results in a database that contains more than 9,000 observed fancy-shape diamonds. While no decision has been made to offer a cut grade for these diamonds, some basic concepts for an evaluation system are beginning to be uncovered.
Shigley asked Dr. Christopher M. Breeding, a research scientist at GIA in Carlsbad, to share research updates on diamond fluorescence, and synthetic and irradiated diamonds.
Approximately 35% of diamonds on the D-to-Z color grade scale exhibit fluorescence under long-wave ultraviolet (UV) light, Breeding said. Blue is the most common color, followed by yellow. Of the diamonds that fluoresce, 38% are faint and 62% display medium or strong fluorescence. For the majority of diamonds, the strength of fluorescence does not have an effect on appearance except in rare instances of very strong blue fluorescence. Fluorescence is recorded on a GIA Diamond Grading Report as an identification feature.
There are several UV sources that can be used to detect long-wave fluorescence, including hobbyist UV lamps, mercury UV lamps and LED UV loupes. Variations in wavelength in lamp output can affect the observed fluorescence by shifting the fluorescence color. Breeding said GIA is developing a new long-wave LED UV source with no side-bands, a longer operating life, no glass filter and more consistent illumination conditions between units. This new, compact and light-weight source will help standardize the way fluorescence is observed to ensure accuracy and improve consistency.
Breeding also discussed synthetic diamonds, which have become more prevalent and available in recent years. Companies that create colorless HPHT (high pressure, high temperature) and CVD (chemical vapor deposition) synthetic diamonds have produced relatively large diamonds with good color and clarity, he said. The full results of one of the studies – HPHT diamonds from the AOTC Group – were published in the Spring 2014 issue of Gems & Gemology (G&G).
Next, Breeding shared new research on irradiation color treatments, which he said can be challenging to identify because natural radiation in diamond produces a similar green coloration as when one is treated. In recent years, naturally irradiated, light-colored diamonds have been treated to create slightly more intense colors. Research on diamond color treatments remains an ongoing process, but GIA is constantly exploring new ways to ensure that these treatments can be identified.
Shigley closed by stressing that all of GIA’s research efforts – from field expeditions to experiments – serve to protect those who buy or sell gems. The information gained from research ensures GIA’s grading and identification reports are accurate and complete, and is also shared through education, G&G and GIA’s website.
Dr. James Shigley, left, and Dr. Christopher M. Breeding. Photos by Kevin Schumacher/GIA
