Smithsonian National Museum of Natural History


Department of Mineral Sciences

"Two new discoveries concerning the "diamant bleu de la Couronne" ("French Blue" diamond) at the Muséum national d'Histoire naturelle in Paris"

Within the mineral collection of the Muséum national d'Histoire naturelle in Paris, we found a previously unknown lead model of the "French Blue" diamond, the third mythic blue diamond of the French Crown Jewels. Until 2008, this diamond was known only from two inaccurate drawings of the emblem of the Golden Fleece of king Louis XV of France (dated 1749 and 1889). This diamond was unfortunately stolen in 1792 during the French Revolution. Then, the diamond is believed to have been recut into the "Hope" diamond, which appeared in 1812 in London. To prove this, 3D models of both models are required to verify this assertion as the French blue diamond was modeled from the 1889 drawing.

Accordingly, the analysis of the lead model reveals major differences in the cut that are missing in the 1749 and 1889 drawings. Using the latest laser scanning and 3D CAD rendering technologies, the diamond was numerically reconstructed. A number of new features in common have been discovered among the French Blue and the Hope diamond. Based on this, we also virtually reconstructed the emblem of the Golden Fleece of king Louis XV of France, the masterpiece of the French Crown Jewels (see picture).

Finally, the label for this model, donated by Charles Achard, the highest authority in Paris about gems at this time, seems to mention that Henry Philip Hope possessed the "French Blue" diamond intact, i.e., before it was secretly re-cut into what will later become the "Hope" diamond. Francillon and Eliason possibly served to hide the effective identity of the owner. This scenario appear in better agreement with the French-English scenario of the robbery (involving Cadet Guillot Lordonner), partially well documented by the French Revolution archives.