From Gems & Gemology: Winter Issue Features D-to-Z Color Grading, Winza Rubies, and the Wittelsbach Blue

CARLSBAD, Calif. – Jan. 26, 2009 – The Winter 2008 issue of the Gemological Institute of America’s (GIA) Gems & Gemology (G&G), which mailed Jan. 16, examines the color grading of colorless to near-colorless diamonds, a new source of ruby and sapphire, and one of the most famous blue diamonds ever fashioned.

The lead article is “Color Grading ‘D-to-Z’ Diamonds at the GIA Laboratory.” Co-authors John King, Ron Geurts, Al Gilbertson, and James Shigley review the history of the GIA Laboratory’s system for color grading colorless to light yellow polished diamonds. They also detail the lab’s grading procedures and special considerations such as selecting master color comparison diamonds (“master stones”) and the impact of advanced instrumentation.

“GIA’s D-to-Z color grading scale has become universally accepted over the past 50 years,” said G&G Editor-in-Chief Alice Keller. “But GIA’s color grading system requires standardized viewing conditions, calibrated references, and consistent procedures, which is why this article is a must-read for anyone involved in the evaluation of diamonds.”

Next is “Rubies and Sapphires from Winza, Central Tanzania,” by Dietmar Schwarz and co-authors. The article describes the mining and geology of the deposit and provides a detailed gemological characterization of this new corundum, which began to arrive on the market in early 2008.

Rounding out the feature articles is a look at the famed Wittelsbach Blue diamond, which was recently sold at auction for a record price of just over $24 million. Authors Rudolf Dröschel, Jürgen Evers, and Hans Ottomeyer chronicle the colorful history of the 35.56 carat gem and present the results of known gemological investigations.

The Lab Notes section features the latest discoveries from the GIA Laboratory: a Fancy Dark brown-yellow zoned type IIa/IIb diamond, an HPHT-treated CVD-grown synthetic diamond submitted for Dossier grading, quartz with secondary covellite dendrites, and experimentally induced copper contamination of tourmaline. Among the Gem News International highlights are reports on andesine from Tibet and Inner Mongolia, dyed chalcedony resembling chrysocolla, and purplish blue synthetic quartz.

You can read the Winter 2008 issue now. Just visit gia.metapress.com and click on “Journal Issues” or the G&G cover to buy a PDF version. For an online or print subscription, visit www.gia.edu/gemsandgemology or call toll-free (800) 421-7250, ext. 7142. Outside the U.S. and Canada, call (760) 603-4000, ext. 7142.