11 September 1792: The French Blue diamond is stolen

Precious jewels often seem to cast a spell over people. But depending on whom you asked, this was quite literally so of the famous French Blue. A spectacular gem that belonged to the kings of France, the 112-carat diamond shines a lustrous deep-blue. But held under ultraviolet light, it glows a sinister red evidence to some that the diamond was cursed.

The Bijou du Roi – the King's jewel, as it was also known – was plucked from the eye-socket of a statue that stood in a far-flung Hindu temple. That's if you believe the Victorian newspapers. In all likelihood, the diamond came from the Kollur mine in southern India – the same mine that produced the Koh-i-Noor in the British Crown jewels.

A 17th century French merchant and adventurer named Jean-Baptiste Tavernier bought the diamond and sold it to the Sun King, Louis XIV, around 1668. The French king had the diamond cut by the royal jeweller and it became known as The Blue Diamond of the Crown, or the French Blue for short.

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The diamond was set into a pendant for the illustrious Order of the Golden Fleece, and in time, the pendant came down to Louis XVI and his Austrian queen, Marie Antoinette. Then the French Revolution erupted.The king and queen were locked up, and on 11 September 1792, a mob ransacked and stole the French crown jewels. Louis XVI and Marie Antoinette met their end on the scaffold, and the French Blue disappeared without a trace.

That is until 20 years later. A suspiciously similar, albeit smaller, diamond popped up in 1812, in the possession of a London merchant. That diamond passed into the hands of King George IV for a short time, and then on through a succession of private dealers and family inheritances.

Today, the diamond is known as the Hope Diamond after one of its owners in the 1830s. You can go and see it at the Smithsonian in Washington, DC. In 2005, scientists were able to confirm that the Hope Diamond had been cut from the French Blue.

So, what's it worth? Well, the Smithsonian is coy – no surprises there. "How do you put a value on history", it shrugs. And as for the curse, the museum's still waiting on that one.