https://www.gia.edu/gems-gemology/spring-2025-winston-red-diamond

Figure 1. The 2.33 ct Winston Red diamond, displaying a vibrant Fancy red color. The old mine brilliant-cut stone measures approximately 8 mm in diameter. Photo by Robert Weldon; courtesy of Ronald Winston.

Feature Gems & Gemology, Spring 2025, Vol. 61, No. 1

A Study of the Winston Red: The Smithsonian’s New Fancy Red Diamond

Gabriela A. Farfan, Ulrika F.S. D’Haenens-Johansson, Stephanie Persaud, Eloïse Gaillou, Russell C. Feather II, W. Henry Towbin, and Daniel C. Jones

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Figure 1. The 2.33 ct Winston Red diamond, displaying a vibrant Fancy red color. The old mine brilliant-cut stone measures approximately 8 mm in diameter. Photo by Robert Weldon; courtesy of Ronald Winston.ABSTRACT

Figure 2. GIA Natural Colored Diamond Report for the Winston Red.

Figure 3. The Winston Red diamond (center, 2.33 ct), alongside the much darker “red-brown” DeYoung Red (left, 5.03 ct) and the DeYoung Pink diamonds (right, 2.82 ct). All three stones are currently on public exhibit at the Smithsonian NMNH. Photo by Gabriela Farfan.

Red diamonds are among the rarest gems on Earth, especially Fancy red diamonds that are pure red and unmodified by brown, orange, or purple. At 2.33 ct, the Winston Red diamond is the fifth-largest Fancy red diamond known to exist and the only Fancy red diamond on public exhibit. On April 1, 2025, it was unveiled in a new exhibit at the Smithsonian National Museum of Natural History in Washington, DC. This is the first scientific and historical study conducted on this noteworthy stone. Optical observation along with spectroscopic, cathodoluminescence, and photoluminescence analyses confirmed the presence of plastic deformation bands and dislocation network patterns that classify the Winston Red as a type IaAB (A

The 2.33 ct Winston Red diamond (figure 1) is on the verge of becoming one of the most famous fancy-color diamonds in the world. Currently the largest pure red diamond on public display, it is the fifth-largest red diamond with the coveted Fancy red GIA color grade. As part of one of the most significant donations to the National Gem Collection in the last decade, this diamond is the “cherry on top” of a world-class collection of fancy-color diamonds that went on display in an exhibit titled “The Winston Red Diamond and the Winston Fancy Color Diamond Collection” at the Smithsonian National Museum of Natural History (NMNH) on April 1, 2025.

Figure 2. GIA Natural Colored Diamond Report for the Winston Red.

Formerly referred to as the “Raj Red,” the Winston Red is an old mine brilliant-cut diamond measuring approximately 8 mm in diameter with a very large culet and an extremely thin bruted girdle (again, see figure 1). The red color distribution is described as even, and the clarity is graded I₂ due to a combination of inclusions, chips around the girdle, and a particularly large but shallow feather that runs perpendicular to the table, as illustrated in the natural colored diamond report issued by GIA in 2023 (figure 2). Yet the color makes the Winston Red truly remarkable and one of the most beautiful red diamonds in the world.

In this study, scientists from the Smithsonian NMNH Department of Mineral Sciences teamed up with GIA and the curator from the Paris School of Mines to examine this rare diamond. This provided a unique opportunity to showcase the science behind the beautiful red color, interrogate the geological nature of its uncommon occurrence, and reveal the rich history of the stone before going on display at the Smithsonian. This investigation also highlights the threefold mission of natural history museums: to display awe-inspiring specimens, preserve natural history for future generations, and uncover new knowledge through scientific examination. Every specimen is useful for study—especially those that are extraordinary and historically valuable, such as the Winston Red diamond.

Comparison to Other Red Diamonds. Unmodified Fancy red diamonds are among the rarest objects of natural history on the planet; only 24 stones over one carat exist in the public record, as identified in auction catalogs and news articles by this study (table 1). Beyond those listed in table 1, there are additional privately owned stones that have passed through GIA and other gemological laboratories but are excluded from these detailed tables as they are not public knowledge. The Winston Red is notable for being the fifth-largest unmodified Fancy red diamond among all the Fancy reds graded by GIA, and the second-largest Fancy red diamond that is in the public record, as listed in table 1. It is also the largest Fancy red diamond on public display now that it is officially part of the National Gem and Mineral Collection. The immense value of diamonds with the coveted Fancy red color grade is exemplified by the 2024 sale of the 1.56 ct, I₂ clarity Argyle Phoenix, which simultaneously commanded the highest price ($4.2 million) and price per carat ($2.7 million/ct) for a Fancy red diamond to date.

Figure 3. The Winston Red diamond (center, 2.33 ct), alongside the much darker “red-brown” DeYoung Red (left, 5.03 ct) and the DeYoung Pink diamonds (right, 2.82 ct). All three stones are currently on public exhibit at the Smithsonian NMNH. Photo by Gabriela Farfan.

More than 20 years ago, the largest confirmed Fancy red diamond, the 5.11 ct Moussaieff Red, was on loan for the temporary “Splendor of Diamonds” exhibit at the Smithsonian NMNH in 2003 (King and Shigley, 2003). Since then, the only red-hued diamond exhibited at the Smithsonian has been the 5.03 ct DeYoung Red, with a darker, “red-brown” color (table 2; Shigley and Fritsch, 1993). Notably, in GIA’s color grading system, a diamond is not considered a red diamond unless the final word in the color description is red. Hence some historically “red” diamonds listed in table 2 may include stones that were not predominantly red, such as the DeYoung Red. The stark differences in hue and saturation between the Winston Red and the DeYoung Red are visible when they are placed side by side (figure 3).

In 1987, GIA examined the Winston Red and issued a gem identification report describing it as a “brownish-orange-red” diamond. The fancy-color grading system has since been refined and standardized with controlled viewing and lighting environments, expanded terminology, and color comparators such as colored diamond master stones and Munsell color chips (King et al., 1994). King et al. (2002) highlight the particular challenge of color grading predominantly red diamonds. Their scarcity left few historic points of reference, resulting in a range of opinions regarding what a “red” diamond should look like. A Fancy red diamond has a unique appearance compared to other red gemstones. The GIA Natural Colored Diamond Report issued in 2023, with modern color grading, determined that the Winston Red is Fancy red (again, see figure 2).

Natural, untreated diamonds that have been described by GIA as having a predominantly red hue are exceedingly rare (e.g., Kane, 1987; King et al., 2002, 2014; King and Shigley, 2003; Eaton-Magaña et al., 2018). Analysis of more than a million natural fancy-color diamonds submitted to GIA for laboratory services (i.e., excluding D-to-Z color diamonds) reveals that predominantly red diamonds account for only approximately 0.07% of the stones. Among these red diamonds, those graded Fancy red account for 56.9% (i.e., 0.04% of all fancy-color diamonds), with the remainder modified by purple (39.5%), orange (2.0%), or brown (1.6%). King et al. (2002) describe and illustrate the differences between the Fancy Deep pink, Fancy Vivid pink, and Fancy red color grades, noting the distinctive tone and saturation associated with Fancy red diamonds. The narrow ranges of tone and saturation for diamonds described as red also mean that they can receive only one fancy grade: Fancy. The only other colors that warrant this approach are Fancy black and Fancy white diamonds.

The geological processes involved in creating red color in diamonds are extreme (discussed later) and may contribute to the small sizes and lower clarity grades that most red diamonds have received from GIA (see appendix 1). The vast majority of Fancy red (i.e., unmodified) diamonds are small, with only 4% larger than two carats, the largest being the 5.11 ct Moussaieff Red. Over 75% of Fancy red diamonds have received clarity grades of SI₁ to I₂, and approximately 30% have I₁ or I₂ clarity grades. In order of incidence, the most common clarity features were feathers, crystal inclusions, and natural surfaces. For most buyers, lower clarity in Fancy red diamonds is of little concern compared to the coveted red color (King et al., 2014). Typically, the shapes and cutting styles for Fancy red diamonds were chosen to maximize weight and enhance face-up color, with less than 4% of diamonds being cut into round shapes. The three most common shapes were rectangular (50%), square (16%), and oval (12%). Popular cutting styles were modified brilliants, most notably the cut-cornered rectangular and square modified brilliants, referred to as “radiant cut” in the trade.

The Winston Red ranks 12th in size among the larger confirmed “red” diamonds of the world, according to public records (table 2). The largest confirmed historically “red” diamonds are the Moussaieff Red (5.11 ct trilliant cut), followed by the Kazanjian Red (5.05 ct square cut), and the DeYoung Red (5.03 ct round brilliant cut). Still, accounts of six even larger reddish diamonds (18, 10.26, 8.00, 7.44, 6.00, and 5.71 ct) have been listed in previous studies as recorded in the Gem Catalogue of the Duke of Brunswick-Luneburg in 1860 and others (Kunz, 1926; Gill, 1978; Shigley and Fritsch, 1993; Wilson, 2014). It is important to note that although table 2 encompasses diamonds historically regarded as red, most lack a formal color grade. Other than the Moussaieff Red and Winston Red, none of the significant red diamonds in table 2 have received the Fancy red color grade (indicating pure, unmodified red) that follows today’s standards, and most are red with modifying colors (e.g., Fancy purplish red) or have not been graded by GIA. Some, such as the DeYoung Red, are described as red-brown and other colors that would not qualify as red today because the final word in the color description is not “red” (e.g., brownish red).

Categorizing Pink and Red Diamonds. It is well established that red diamonds acquire their color through the same mechanisms as pink diamonds (red is a more saturated pink color), relating to crystal deformation (King et al., 2002; Eaton-Magaña et al., 2018). In this article, we will discuss red and pink diamonds interchangeably. Here, we explore the literature on causes of color in pink and red diamonds to compare to the Winston Red and provide clues about its color origin, geological formation, and even geographic origin.

Although diamond is considered a hard, brittle material, it can deform plastically under applied pressures at high temperatures (Smith, 2023). Plastic deformation of diamond involves the generation of dislocations and their movement, generally resulting in slip along octahedral {111} planes in <110> directions (Evans and Wild, 1965). Diamond crystal distortion can also lead to an abrupt and localized change in the lattice orientation, resulting in mechanical twinning (Titkov et al., 2012). Following plastic deformation, natural annealing processes can also lead to dislocations reorganizing into lower-energy arrangements, notably the polygonized dislocation networks with cellular appearances observed in deformed low-nitrogen diamonds (e.g., Sumida and Lang, 1981; Kanda et al., 2005; Fisher, 2009; Laidlaw et al., 2021). Pink diamonds are often separated into groups that consider the nitrogen content as defined by the diamond type classification system (described by Breeding and Shigley, 2009), as well as the distribution of the pink color. This naming convention was originally developed by Gaillou et al. (2010, 2012) and expanded by Eaton-Magaña et al. (2020). Briefly, Group 1 pink diamonds are defined as those containing low concentrations of aggregated nitrogen, with B-centers (N₄V⁰) dominating over A-centers (nitrogen pairs) (type IaAHISTORY OF THE WINSTON RED METHODS RESULTS AND DISCUSSION CONCLUSIONS

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A Study of the Winston Red: The Smithsonian’s New Fancy Red Diamond