That’s no ruby. It’s an extremely rare red diamond.

6 3 minutes read

While it may look like a blazing red ruby, the 2.33-carat Winston Red Diamond is just that—a diamond. One of the rarest diamonds in the world, the Winston Red Diamond is on display at the Smithsonian National Museum of Natural History in Washington DC–right near the more famous Hope Diamond.

To learn more about this exceedingly rare Fancy Red diamond, Smithsonian gem and mineral curator Gabriela Farfan and colleagues spent two years researching its history and tracing its geological past. The team officially categorized the diamond and also narrowed down its potential country of origin as Venezuela or Brazil. The findings are detailed in a study published June 6 in the journal Gems & Gemology.

a red diamond — *The science and history of the Winston Red Diamond is detailed in a new study. CREDIT: Photo by Robert Weldon, courtesy of Ronald Winston.*

History of the Winston Red

Ronald Winston, son of famed American jeweler Harry Winston, donated the roughly 8 millimeter in diameter diamond to the Smithsonian in 2023. It is the fifth-largest confirmed red diamond in the world. Based on its old mine brilliant cut, gemologists believe that it was likely mined before the middle of the 20th century. This older style of cutting diamonds predates the more modern brilliant cuts seen today.

Gemologists estimate that one in every 25 million diamonds is fancy red. According to the Smithsonian, this specific red diamond’s documented history begins in 1938, when it belonged to the Cartier Family. The Cartiers then sold it to the Maharaja of Jamnagar India sometime before the 1980s. Winston purchased the stone from the Maharaja in the late 1980s and the diamond once adorned a ring worn by actress Brooke Shields in 1989.

At 2.23 carats, it is smaller than the largest confirmed fancy red diamond. The Moussaieff Red clocks in at 5.11 carats and has been displayed in museums around the world. On April 1,the Winston Red Diamond officially went on display at the National Museum of Natural History in Washington DC.

How red and pink diamonds get their color

Scientifically describing and detailing the Winston Red’s color and history was one of the major goals of this new study. Red diamonds are exceedingly rare, which makes studying them equally difficult.

A diamond’s color is largely determined by its chemical make-up. For example, a traditional white diamond is mostly composed of carbon. Small amounts of nitrogen will give a diamond a more yellow hue. If those nitrogen atoms have enough time–several millions of years–to aggregate in groups, the diamond will appear more brown. After even more years, if the nitrogen atoms form in groups of three surrounding a missing carbon atom, it will turn a yellow color. If the element boron replaces carbon, it produces a blue hue.

a round orange diamond, square pink diamond, oval yellow diamond, round green diamond, round blue diamond, and large round red diamond in a line — Forty colorful diamonds ranging in size from 0.4 to 9.49 carats are on display at the National Museum of Natural History beside the Winston Red Diamond. CREDIT: Photos by Robert Weldon, arranged by Gabriela Farfan, courtesy of Ronald Winston.

Red and pink diamonds don’t owe their color to chemistry. The extreme pressures and temperatures deep within the Earth can lead to plastic deformation within the rock. During plastic deformation, the atomic bonds in the diamond break and re-form along imperfections called dislocations. These deformations will change the diamond’s atomic structure and affect how the light interacts with the stone. It’s this deflection that gives it its rosy hue. Pink diamonds get their color in a similar way, since the color red is a more saturated pink.

The Winston Red is also considered a Fancy Red diamond, meaning its color is pure red. It does not have any other modifying hues like purple, brown, or orange. Only 0.04 percent of fancy colored diamonds have this Fancy red color grade. The chances of finding a Fancy red diamond like the Winston Red is about one in 25 million diamonds.

[ Related: The mystery behind pink diamonds just got some more clarity. ]

To learn more, the team used several techniques including photoluminescence, spectroscopy, and cathodoluminescence to study the precious stone. These analyses confirmed the presence of plastic deformation bands and a pattern that officially classifies it as a type IaAB (A. The diamond underwent significant pressure and temperature conditions when it was forming. They also found that the Winston Red gets its pure crimson color because it had a careful balance of the right pressure and temperature during its formation.

Based on its mineralogical characteristics and mid-20th century cut, the team believes that it likely originated in Venezuela or Brazil. However, its precise place of origin is still unknown.