The Grand Sancy

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

The Grand Sancy (sometimes known simply as the Sancy and documented in June 1586) was bought by the Banque de France and the Musées de France from the 4th Viscount Astor in 1977 and is now on display in the Galerie d’Apollon of the Musée du Louvre, Paris. According to Cletscher, the rough Grand Sancy was acquired in Constantinople and fashioned in Paris. In its lifetime it has been part first of the English and then of the French Crown Jewels.

The outline and faceting of the stone: At its pointed end it looks very like a Rose Cut, which probably explains why it has so often wrongly been described as a Double Rose. But between the table and the blunt end the faceting is of a totally different design.

The central facet, the table, has always been thought to be pentagonal, but under a magnifying glass one can see that the narrow end does not, in fact, terminate in a point but has three edges, and that three of the five triangular facets which appear to meet at the point have had their apexes removed and join the table at these upper edges. This means that instead of being a pentagonal kite, as it appears to the naked eye, the table is actually eight-sided. The pavilion is faceted in more or less the same design as the crown, except that the culet, which is the same size as the table, is genuinely pentagonal. The gem is ‘convexo-convex’ (i.e the two sides are rounded) and the two convex surfaces meet at the girdle. It was not possible to study the girdle itself as this was hidden in the setting when I had it in my hands. The dimensions are:

Height: 25.7mm
Width: 20.6mm
Thickness: 14.3mm
Weight: 55.23 ct (according to Sancy himself, 60 ct including te setting of about 1.3 grams)

Through the pointed end, a distinct flaw and several abraded facet edges are visible, even in photographs.