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Winter 1998, Volume 34, Issue 4

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Characterizing Natural-Color Type IIb Blue Diamonds
John M. King, Thomas M. Moses, James E. Shigley, Christopher M. Welbourn, Simon C. Lawson, and Martin Cooper


blue diamondsAlthough rarely encountered, blue diamonds are among the most famous, and most distinctive, of fine gemstones. To better understand these unique gems, more than 400 were studied at the GIA Gem Trade Laboratory over several years to reveal additional information about the relationships between their color, clarity, and other gemological properties. The overwhelming majority of natural-color blue diamonds are type IIb. The color appearance varies widely from light to dark, but there is a limited range of color saturation. As a result, color appearance shifts between neighboring GIA GTL color grades can be subtle. Of the blue diamonds examined at GIA GTL, few had any solid inclusions. Nevertheless, internal features such as graining and color zoning can make the cutting and polishing of these diamonds a challenge.

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