Photos © Christie’s
Cut diamonds above 100 carats are always unique gems, especially if one considers the loss of weight during the cutting process, typically over 50%, meaning that a 100 carat cut diamond might have had over 200 carats in the rough.
To plan the cut of a rough crystal to properly shape it into a cut gem with an average diameter or length over 28 mm, depending on the cutting style and proportions, is critical to achieve those carat sizes, preferably with the best optical performance possible as far as light return, scintillation and fire is concerned.
In the case of a coloured diamond, an extra challenge is to plan the cut to achieve an optimal colour performance in the face-up position that will be critical in the attribution of a Fancy grade in a laboratory report.
In the photo, a 107.46 carat cushion-shape Fancy yellow diamond, VS2 clarity, apparently a retouched old cut with a noticeable culet, extremely thin areas on the girdle and short lower girdle facets in the pavillion, measuring 27.39 x 27.12 x 20.14 mm, in fact a rather deep stone, set in a gold and brooch Graff, that was displayed at Christie’s Geneva in 2020.
An example of a large coloured uncut, or rough, stone is the 253.70 ct Oppenheimer diamond found in 1964 at the Dutoitspan mine in South Africa, now at the Smithsonian National Museum of Natural History.
Photos © Smithsonian Institution
If it could result in a 100+ carat cut diamond with a Fancy colour, we’ll never know for sure as this is a very rare mineral specimen on a public display that has been serving the public in Earth Sciences and Gemmology education for decades.
Photos © Christie’s and Smithsonian Institution
Guest articles by Rui Galopim de Carvalho:
https://gem-spectrum.com/category/rui-galopim-de-carvalho
About the author:
Rui Galopim de Carvalho is a renowned independent Gem Education Consultant, author, luxury industry training expert and popular international lecturer on gemmology and on the history of gem materials. During his 30 year experience as a gemmologist, Rui has studied important collections in both public and private museums, notably the Portuguese Crown Jewels.
Founder of the popular Home Gemmology webinar series launched during the COVID-19 lockdown, Rui has a long history as a gemmology communicator, notably on social media where he is a popular figure.
Rui Galopim de Carvalho can be reached through his website:
