The remarkable stone was previously unknown, having passed privately through the royal families of Europe for the last 300 years. According to Sotheby’s it was originally given to Elisabeth Farnese, daughter of the Duke of Parma, in 1715 when she married Philip V of Spain. Based on the timing the stone is assumed to be from the Golconda diamond mines of India, the same area the famed Hope Diamond is also believed to be from. Like all natural Blue Diamonds, the unique color is caused by trace boron atoms within the carbon structure of the diamond.
A recent GIA report done on the stone determined the exact color, Fancy Dark Grey-Blue, with an SI1 clarity. Based on the report it looks like the clarity characteristics are due to surface/edge damage on the stone. A polishing of the stone might remove a lot of that damage and help the stone achieve a higher clarity grade.