The following article appears courtesy of GIA’s Gems & Gemology eBrief
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Synthetic diamonds grown by chemical vapor deposition (CVD) have seen significant advances over the last decade, reaching the mainstream jewelry market in larger sizes and better qualities. Meanwhile, new processes have dramatically improved the color of these products.
But an article in the new Spring 2010 issue of Gems & Gemology shows that some CVD synthetics undergo temporary color changes in response to UV radiation or heat. In the study, De Beers DTC researcher Dr. Rizwan Khan and coauthors examined a group of untreated Element Six lab-grown diamonds. The samples became darker (from Fancy to Fancy Deep brown in one case) when exposed to UV radiation, a routine part of gemological testing. Heating them to 450°C, a temperature exceeded in some jewelry repair procedures, lightened the color (from J to E in another case).
“Although the CVD-grown diamonds did revert to their stable color over time when exposed to light, the color alterations could have important implications for grading if the gems were placed in the dark immediately after the exposure,” said Alice Keller, editor-in-chief of G&G.
In another major article from the Spring issue, Dr. Wuyi Wang and coauthors look at a new generation of strongly colored pink CVD synthetics from Boston-based Apollo Diamond Inc. The study describes the characteristics of these Fancy Intense to Fancy Deep pink lab-grown stones, as well as the gemological and spectroscopic criteria for identifying them.
The Spring issue also includes articles on the possible existence of “sister” stones of the Hope diamond, the use of confocal micro-Raman spectroscopy to identify natural and synthetic emeralds (and emeralds from specific localities), and rare brownish orange bastnäsite-(Ce) and parisite-(Ce) from Malawi.
The G&G Lab Notes section features the latest discoveries from the GIA Laboratory, including natural pink diamonds colored by multiple treatment processes, a large HPHT-treated type IIb blue diamond, and unusually transparent treated jadeite. The Gem News International section covers the 2010 Tucson gem shows, including “soufflé” freshwater cultured pearls, and reports on tsavorite mining in northern Tanzania and treated-color pink CVD-grown synthetic diamond melee.
Two special Spring issue features are this year’s Dr. Edward J. Gübelin Most Valuable Article Award winners and the G&G Challenge, a multiple-choice quiz based on articles from the 2009 issues. Subscribers who score 75 percent or better on the G&G Challenge receive a GIA Letter of Completion; those who score 100 percent also get recognition in an upcoming issue.
Copies of the Spring 2010 issue (print and PDF) can be ordered from the GIA Store. To purchase PDF versions of specific articles or sections, visit Gems & Gemology Online. To subscribe to G&G, visit the GIA Store or contact Circulation Coordinator Martha Rivera at firstname.lastname@example.org or call toll-free (800) 421-7250, ext. 7142. From outside the U.S. and Canada, call (760) 603-4000, ext. 7142.