The former Cowdray collection of grey pearls is another great example.
The natural saltwater grey pearl is a rarity. It is formed by the accumulation of successive layers of nacre that can create various shapes. Unlike gemstones, it is not cut. The assembly of a large quantity of perfect pieces of homogeneous hue and luster seems to be impossible now.
The Cowdray necklace, auctioned by Sotheby's in London in 1937 as a necklace of 43 pearls totaling approximately 882 grains, is a set with no known equivalent. It was sold for £ 2,17M including premium by Christie's on June 13, 2012. It was then made up of 38 pearls.
This necklace was recently enhanced by the integration of four more pearls of the same quality of which two had been in the original necklace, for a new total of 42 round pearls graduated between 12.9 and 6.6 mm. The necklace comes with a pair of diamond earclips centered by a button shaped pearl. This suite is estimated HK $ 35M for sale by Sotheby's in Hong Kong on October 7, lot 1870.
A pearl of same nature but of phenomenal size, button shaped 21.2 x 21.1 x 12.0 mm, assembled on a brooch in a surrounding of diamonds, was sold for $ 1,87M including premium by Sotheby's on December 5, 2012.
Note that the jewelry auctions earlier this year have shown a growing interest from the buyers for cultured pearls, which allows to predict a result of high level for the natural Cowdray pearls.
I invite you to watch the video shared by Sotheby's :