Ofterdingen and Kropotkin

In 1673, Louis had his Flemish jeweller, Sieur Pitau, undertake the risky task of cleaving then cutting the Tavernier violet down to 67.125 carats, very nearly halving it in size, but doubling its value to 400,000 livres (1691). The cleavings soon vanished, but may have reappeared briefly in the nineteenth century as the so-called Pirie and Brunswick blue diamonds, both of which have since gone to ground. The Tavernier violet stayed with the French crown jewels, and eighty years later, it was mounted...into King Louis XV's elaborate, gem-encrusted badge of the Toison d'or, the Order of the Golden Fleece. [...]

In June 1791 the Toison d'or was confiscated, along with the rest of the French crown jewels, and stored temporarily at the Garde Meuble in Paris. Thence, following a break-in fifteen months later, the jewel was stolen. It may have been an inside job. Old gossip attributes to Georges-Jacques Danton the decision to break the Hope Diamond out of its setting, then use it to bribe the Duke of Brunswick, commander of the Prussian and Austrian armies, into retreating from Valmy, where untested revolutionary forces, outnumbered two to one, were preparing to resist invasion, the purpose of which was to rescue the Royal Family. The Prussian and Austrian manoeuvre, apparently otherwise inexplicable, provided the new Government in Paris with much-needed breathing space, and indeed the monarchy was abolished the day after it, on Sep 22, 1792.