Editor’s Note
This article details the unveiling and first scientific study of the Winston Red, a 2.33-carat Fancy red diamond now on public exhibit at the Smithsonian. As the fifth-largest known diamond of its rare type, it represents a unique opportunity for both public viewing and scientific inquiry.
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 (N3, ZPL at 503.2 nm) Group 1 “pink” diamond and indicate that it underwent significant pressure and temperature conditions.
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).
The Winston Red owes its pure crimson color to a careful balance of absorption features: the 550 nm band associated with plastic deformation as well as the nitrogen-related N3 (N3, ZPL at 503.2 nm) centers (e.g., Green et al., 2022). This gives rise to a transmission window in the red part of the visible spectrum, producing the diamond’s characteristic color.
The 550 nm absorption band is responsible for the pink color in over 99% of natural pink-hued diamonds, as well as all natural red diamonds that have been graded at GIA (Eaton-Magaña et al., 2018, 2020; also confirmed by the current authors). The absorption intensity of the 550 nm band, as well as the diamond’s size and cut, determine the color saturation and whether it will be predominantly pink or red (King et al., 2002; Eaton-Magaña et al., 2018). The subtle balance of the 550 nm band and the N3, H4, and H3 absorption features are responsible for the Winston Red’s pure unmodified red color.
Although this 550 nm band has been associated with plastic deformation, the defect structure has not yet been determined (e.g., Orlov, 1977; Collins, 1982; Gaillou et al., 2010; Howell et al., 2015; Eaton-Magaña et al., 2018, 2020). The band is observed in both pink type Ia (Groups 1 and 2) and type IIa (Group 3) diamonds, suggesting that nitrogen content is not directly linked to the pink color centers. However, this does not rule out that the presence of nitrogen may still be indirectly involved in pink color formation.
In pink diamonds, the 550 nm band is typically observed along with a band at 390 nm (e.g., Eaton-Magaña et al., 2018); however, its presence could not be confirmed for the Winston Red diamond because the collected spectrum did not extend below 400 nm. Peaks at 609 and 600 nm, associated with the “609 nm system” first defined by Fritsch et al. (2007), are weakly observed, overlapping with the low energy tail of the broad 550 nm band.
Due to their extreme rarity, few Fancy red diamond UV-Vis-NIR absorption spectra have been published (Shigley and Fritsch, 1993; Eaton-Magaña et al., 2018); these reports also show intense absorption in the 550 nm band, coupled with comparatively weak absorption from N3, H4, and H3 centers, consistent with the Winston Red diamond.
Other notable features are the 535.8, 654.9, 660.8, and 710 nm peaks. The former is commonly seen in diamonds with B-centers and may be interstitial-related (Laidlaw et al., 2021), consistent with the Winston Red’s diamond type. A weak strain-broadened GR1 (neutral vacancy, V0) (Eaton-Magaña et al., 2020). The 490.7 nm defect is thought to be nitrogen-related and a product of plastic deformation (Collins and Woods, 1982).
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 (N3, ZPL at 503.2 nm). Microscopic observations show pink color throughout the stones, with wavy lamellae or graining. Detailed analyses through luminescence imaging techniques reveal cellular dislocation patterns, typical of plastically deformed diamonds with low nitrogen. In contrast, Group 2 pink diamonds are type IaA with higher nitrogen content and color concentrated in parallel lamellae.
In at least one instance, two directions of the banding converge to create a hollow Rose channel that appears to be associated with an unidentified inclusion (figure 9, A and B). In pink diamonds, Rose channels are due to plastic deformation and are the consequence of the intersection of two directions of mechanical microtwinning (Schoor et al., 2016).