The Polar Star

(via Diamond Cuts in Historic Jewelry:1381-1910) Herbert Tillander writes:

The historic Polar Star diamond was so named because of the double star-like arrangement of its interlocking culet faces, which can be clearly seen through its large table facet. Although fairly small, it has been one of the world’s most famous diamonds since it was acquired by Joseph Bonaparte in about 1806. It belonged to the Russian ducal family of Youssoupoff for more than a hundred years before passing to Henry Deterging and his Russian-born wife, Lydia. It made world headlines in 1980, when it was auctioned and sold at a record price per carat to a buyer from Sri Lanka.

The fame of The Polar Star is due to three factors: its unsurpassed brilliance, the precision of its cut (it can be balanced on its tiny culet) and its limpidity. According to the late Hans Nadelhoffer of Christie’s in Geneva, who auctioned the stone, the rough was found in the bed of the Krishna river, India, at the end of the eighteenth century. Nadelhoffer also suggests that it was fashioned in Amsterdam, but since London was at that time the world center for precision cutting it seems more likely that it was there that it was given its exquisite faceting.

The Gubelin Laboratory in Switzerland has given a very detailed report on this diamond. It weighs 41.28 ct (41.285), which is considerably less than a Brilliant of this size with classic 45° proportions would normally weigh. In fact, it is equal in size to a classic well-made Brilliant of 52.5 ct. The reason for this surprising lightness is the flatness of the crown with its large table. The clarity of the gem has suffered over the years from careless handling. The girdle is slightly abraded and there are other small scratches, but the loss of weight that would be involved in restoring it to its original flawless condition would be negligible. Its color is of the second highest grade, E (River), with a trace of pink. A distinct blue fluorescence was noticed under ultraviolet light (UV 365), and spectrophotometry revealed that the diamond was of extremely rare type known as IIa. It is virtually impossible to assess how far the exceptionally attractive light effects are due to the trace element boron in type Iia diamonds, and how far they are due to the unusual faceting of the pavilion.

Measured dimensions and approximate median proportions:
Diameter: 21.77 – 20.63mm – 100%
Table: 14.5 – 14.2mm – 67%
Crown: >12.2mm – 29.3° - 40.8° - 12.5% - 37°
Pavilion: > 12.2mm – 41.2° - 48° - 45% - 45°
Culet: 2.20 – 2mm – 10%