Platinum, emerald and diamond ring. Photo Sotheby's

The cushion-shaped emerald weighing approximately 12.60 carats, flanked by half-moon-shaped diamonds weighing .98 and .94 carat, size 6¼. ESTIMATE 575,000-675,000 USD. Lot Sold: 746,500 USD

Accompanied by:

AGL report no. CS 45256 stating that the emerald is of 'Classic' Colombian origin, clarity enhancement: none.

SSEF report no. 58337 stating that the emerald is of Colombian origin, no indications of clarity modification.

GIA Diamond Dossier report no. 2115949779 stating that the .98 diamond is F color, VS1 clarity.

GIA report no. 2115949778 stating that the .94 carat diamond is E color, VS1 clarity

Together with a letter from the AGL stating that 'In this particular case, the combination of size, origin and quality elements for the emerald described in AGL report no. CS 45256 signifies a gem worthy of distinction.

This 12.60 carat emerald has received the highest origin determination issued by AGL: 'Classic' Colombia. Of particular note, this emerald has not been clarity enhanced to improve its appearance. In addition, this gemstone exhibits a very fine, saturated, slightly bluish green color that is reminiscent of high-quality emeralds from the Muzo mining area. In addition, it has been fashioned into a cushion-shaped mixed cut, which presents the intrinsic quality and color of this gem to its fullest. Top-quality Colombian emeralds of 12 carats are very rare. This combination of quality factors, absence of clarity enhancement, size and origin determination represents a particularly fine example of a Colombian emerald.'

Sotheby's. Magnificent Jewels. New York | 07 Dec 2011 www.sothebys.com