A team of scientists from the Gemological Institute of America (GIA), collaborating with their colleagues from the Smithsonian National Museum of Natural History Department of Mineral Sciences and the curator from the Paris School of Mines, recently examined the Winston Red diamond – a very rare 2.33-carat red diamond which is now on display at the Smithsonian’s National Museum of Natural History in Washington, D.C. The Winston Red diamond is the fifth-largest diamond with an exceptionally pure red colour known to exist and the only such red diamond on public exhibit.

“The Winston Red diamond is one of the most exquisite gems on earth, from its unparalleled deep-red colour to its rich history,” said Susan Jacques, GIA president and CEO. “Natural fancy-coloured diamonds are very scarce, and red diamonds are exceedingly rare treasures of Mother Nature. Just two dozen pure red diamonds over one carat exist in the public record. Evaluating this spectacular gem is a scientific milestone for GIA and builds upon our expansive expertise in fancy-coloured diamonds.”

It’s fascinating to understand just how rare red diamonds are. Out of all the colored diamonds the GIA has examined, only a tiny fraction are red, and even fewer achieve the ‘Fancy red’ grade like the Winston Red.

Through careful analysis using advanced instrumentation and drawing on decades of research, experience and historical records, GIA scientists and their collaborators were able to determine the cause of the diamond’s rare colour and its possible geographic origin, which is most likely Brazil or Venezuela, based on its mineralogical characteristics and history.