The Brunswick Blue Diamond

One of the more mysterious diamonds in history, the story of the Brunswick Blue is an intriguing one, with unusual gaps in the story and tantalising links to one of the most famous diamonds in the world!

The backstory begins with the French Blue, a 115 carat rough diamond of a most wonderful metallic-blue shade. It was bought by the legendary diamond merchant Jean-Baptiste Tavernier in the mid-1600s.

Tavernier bought the stone near Golconda, the mine from which sprang many of the most famous diamonds ever, including the Koh-i-Noor, the Idol’s Eye and the Regent. The stone eventually found its way to the King of France. It was sold in a lot with over 1000 other diamonds, for a price equivalent to 147 kilograms of pure gold – close to 6 million dollars today!). He had it cut by a man called Jean Pitau, such that when viewed through the top one could see seven rays emanating from a central “sun”, echoing the Sun King’s splendour – “At the diamond’s dazzling heart was a sun with seven facets – the sun being Louis’ emblem, and seven being a number rich in meaning in biblical cosmology, indicating divinity and spirituality.” This recutting cost almost half a million dollars, and lowered the weight to 69 carats, a total loss of 46 carats. This percentage of weight loss is normal for diamond cutting, and typically the dust and fragments are cut into smaller diamonds if possible, or the dust recycled for use on polishing wheels.

The French Blue stayed in the Royal Collection, until it was stolen from the Garde Meuble de la Couronne in 1792. Although many of the gems taken were later recovered, the French Blue diamond disappeared forever.

For many years it was speculated that the French Blue was recut into the diamond we now know as the Hope Diamond. This was initially based on the circumstantial evidence of the timeline of the Hope’s appearance in 1812, and the similar shades of blue. In 2007, this theory was confirmed when a previously unknown cast of the French Blue was discovered in the archives of the French Museum of Natural History, allowing precise comparison of the two to be made, and giving us certainty as to the origins of the Hope.

However, the Hope Diamond weighs only 45 carats! So, the question was asked as to what happened to the other 24 carats?

This is where the Brunswick Blue comes into the picture. A blue diamond of unknown origin and weight, it was first known of when it was sold in 1873 as part of the estate of the late Duke of Brunswick. Valued at half a million dollars, it was clearly an important gem.

The Duke had suffered from a paranoia that his valuable gem collection might be stolen. (Given the theft of the Royal Jewels in 1792 it was perhaps a valid fear). He converted his home in Paris into a fortress, with a high external wall rigged with spikes and bells, a bedroom with only one tiny window and a safe hidden behind the Duke’s bed. The Duke never slept anywhere else, not even for one night. Should an intruder manage to get into the grounds, into the house, into the bedroom and past the Duke, there was an elaborate mechanism attached to the safe door, whereby opening it without correct procedures would discharge four guns pointed at the would-be thief! He also slept with twelve revolvers within arm’s reach!!

In no small part because of these precautions, the Duke’s diamonds remained with him, and were never stolen!

After his death in 1873, some of his collection was sold off. One magnificent stone, the 30 carat Brunswick Yellow diamond, was bought by Tiffany’s. Another stone was this mysterious dark blue drop-shaped diamond, whose weight is still unknown. Given the similar colour of the Brunswick Blue to the Hope, and knowing the history of the French Blue, the possibility was immediately raised that both smaller stones were once part of the French Blue. A London diamond dealer, Edwin Streeter, wrote a contemporary account of the diamond, concluding that it must have come from the French Blue, based on its “identical colour and quality”. However, in a later edition of his book “Precious Stones and Gems”, Streeter claims that the French Blue was cut into three, and not two, pieces. He further claimed to have bought the smallest of these three pieces, a one carat blue diamond. He also revised the weight downwards to 6 or 7 carats, to account for the existence of this third fragment.

This may have been wishful thinking on Streeter’s part, as recent research by the Smithsonian (custodians of the Hope Diamond) makes it clear that no other diamond was cut from the French Blue. This still leaves the possibility that the Brunswick Blue was cut from the 115 carat rough diamond in 1673. If we take Streeter’s second estimate of weight, 6 to 7 carats, then it is very possible that a single piece of that size could have been cleaved off from the original cutting.  The waters are muddied by a 7.6 carat diamond that was once in the Russian Crown Jewels, and has been in a Russian museum continually since 1827, and a 2.25 carat diamond in the V&A Museum in London since 1869. Neither can be the Brunswick, and both are of the correct colour to possibly be from the same piece of rough. However, records from that time are sparse, so unless we turn up Pitau’s records or the Brunswick Blue re-emerges it seems that the mystery will continue.

Read more about the Hope Diamond and its notorious curse here:

The featured image of the only known sketch of the Brunswick Blue diamond is open source, from You may copy it, give it away or re-use it under the terms of the Project Gutenberg License included with this eBook or online at