By                                                                Joseph Stromberg                       

Every day, thousands of visitors to the Smithsonian Natural History Museum crowd around a glass case on the  second floor to gaze at the Hope Diamond, one of the world’s most famous jewels. It’s  been the subject of dozens of books, documentaries and scientific inquiries, partly due  to persisting legends that it’s cursed. Despite all this attention, though, it  seems that the inch-wide, 45.52-carat diamond still conceals secrets waiting to  be uncovered.

One of these secrets was recently discovered by François Farges, a professor of mineralogy at the National d’Histoire  Naturelle in Paris, and Jeffrey Post, the Smithsonian museum’s curator of  minerals. Using computer modeling, a recently-rediscovered 17th century lead  replica and scientific analysis, they’ve determined that back when the Hope  was known as the “French Blue” and part of the personal collection of  King Louis XIV of France, during the late 17th century, it was  likely placed on a gold background and specially cut to produce an effect  reminiscent of a sun at its center. Only after it was stolen in 1792, during the  French Revolution—and before it resurfaced in Britain in 1812—was it recut  to the familiar, smaller shape we know today.

Their new discovery, described in an article published in the month’s Rocks  and Minerals magazine, stems from Farges’ 2009 discovery of a lead replica of the French Blue in  the National d’Histoire Naturelle mineral collections, which provided the  exact dimensions of King Louis XIV’s French Blue for the first  time. Both Post and Farges are mineral scientists, and  much of their other work on the Hope is concerned with the science behind its distinctive hue, but they’ve also  used the tools of science to investigate the gem’s complex provenance.

And the history of the diamond is a complex one: It was bought somewhere in  India in a  rougher, less finely-cut shape by Jean-Baptiste Tavernier, a French merchant, and brought to  France in 1668. “Unfortunately, Tavernier wrote some really wonderful journals  about the trip, but nowhere in them did he say anything about where he actually  bought the diamond,” Post says. It’s believed that the stone was plucked from  the Kollur  Mine, in what’s now the southern state of Andhra Pradesh, but no one knows  for sure.

From there, it became part of the French crown jewels, and was cut by Jean  Pittan, one of King Louis XIV’s court jewelers, sometime between 1669 and  1672, eventually becoming known as the French Blue. That the Hope and the French  Blue were the same stone was suggested by diamond experts as far back as  1858, but only proved definitively in 2009, when Farges unearthed the lead  replica at the Paris museum. At the time, jewelers made metal replicas for  extremely precious stones and used them as placeholders when designing  settings.

“They didn’t even know they had it. It was in their collection, but filed  under lead specimens,” Post says. Drawings and descriptions of the French Blue  had previously suggested it could have been recut to produce the Hope, but  the exact physical dimensions provided by the lead  replica allowed Farges to collect digital 3D measurements that  would prove it. When they compared these measurements to those of the Hope,  “it fit into the French Blue perfectly—you could see exactly how the French  Blue was cut to form the Hope,” says Post.

The replica, though, also raised a question: Why was the French Blue cut into  such an uncommon shape?

Nowadays, when jewelers cut diamonds, they use sharp angles on the back  of the stone—always higher than 23 degrees, the critical angle of diamond, so that light that enters  the gem reflects inside it several times. The ubiquitous brilliant cut, for instance, is designed to maximize the  number of reflections that light entering the diamond encounters, thus  maximizing the distance that light travels within the diamond. This  heightens the brilliance for the viewer.

But the back of the French Blue had low angles and even an  entirely flat culet on its back, allowing some light to travel through and  straight out the back of the stone. Compared to the rest of the stone, the  material right in front of the culet at the gem’s center would have  appeared relatively clear and colorless, almost like looking through a glass  window.

Farges and Post’s intriguing explanation: that the  jeweler intended for the center of the stone to serve as a window.  Along with the flat culet, the French Blue had a series of star-shaped facets  that were also below the critical angle, which would have caused the region in  front of them to also appear relatively clear.

A 1691 inventory of the French Crown Jewels notes that the gem was “set into  gold and mounted on a stick.” If placed in front of a gold sheet, they realized,  these unique cuts would have caused a dazzling golden sun to appear at the  center of the deep blue stone.

Farges and Post have used computer modeling to produce an image that  simulates exactly how this would have appeared, shown above. “King Louis XIV was  the ‘Sun King,’ and so this would have been an emblem representing his power,”  Post says. “His colors were blue and gold, and so to have a blue diamond with a  gold sun in the center—that’d be something that no one else has, something that  would almost seem divine.”

The researchers are planning on comissioning a cubic zirconia replica, cut and colored to match the French  Blue, which would demonstrate this effect and could someday be put on display  with the Hope to illustrate the stone’s transformation and history. They’re also  scrutinizing archives of Louis XIV’s jewelers from that era to look  for conclusive evidence that this design was intentional.

One thing they know for sure is that the sun effect was eradicated around  1749, when the Sun King’s great-grandson, King Louis XV, ordered the stone to be  lifted from its mounting and incorporated into an elaborate emblem. During  the French Revolution, it was stolen along with the rest of the Crown Jewels,  and although most of the other gems were recovered by  French officials, the famous French Blue disappeared. The slightly smaller Hope  Diamond—which we now know was cut from the French Blue—was first documented as  being in London in 1812, and became well known when it showed up in the  collection catalogue of banker Henry Philip Hope in 1839.

More than a half century after it was donated to the Smithsonian in  1958, the Hope is still one of the Natural History Museum’s most-visited and  well-known artifacts. “It speaks to the remarkable power of a gemstone. It  has generated so much research, interest and curiosity, and it’s focused  people on a history that might otherwise go untold,” Post says. “All due to a  gem one inch in diameter.”

Louis XIV of France depicted as the Sun

Louis XIV apparently chose the sun as his emblem after dancing the “sun” in the Ballet de la Nuit. Throughout Versailles, decoration images of Apollo (laurel, lyre, tripod) with the king’s portraits and emblems (the double LL, the royal crown, the sceptre and hand of justice). The Apollo Salon is the main room of the Grand Apartment because it was originally the monarch’s state chamber. The path of the sun is also traced in the layout of the gardens.