Natural pearl, cultured pearl and diamond necklace, late 19th century, composite. Estimation  3,500 — 5,500 GBP. Photo Sotheby's.

Of negligée design, set with two natural pearls within surrounds of cushion-shaped diamonds, to a surmount set with a cultured pearl and similarly-cut diamonds, to a fine link chain, length approximately 420mm.  

Accompanied by CISGEM report no. 84349, stating that the two smaller pearls were found to be natural, saltwater.

Sotheby's. Fine Jewels, Londres, 18 mars 2015, 10:30 AM