Lot 513. 'The Blue Moon'. An exceptional 12.03 carats Fancy Vivid Blue diamond ring. Estimate 34,200,000 — 53,700,000 CHF. Lot sold 48,634,000 CHF. WORLD AUCTION RECORD PRICE-PER-CARAT FOR A DIAMOND OR GEMSTONE. Photo Sotheby's 2015

The cushion-shaped fancy vivid blue diamond weighing 12.03 carats, mounted as a ring, size 471/2. 

Accompanied by GIA report no. 1162555606, stating that the diamond is Fancy Vivid Blue, Natural Colour, Internally Flawless, together with a Type IIb classification letter. The GIA report additionally accompanied by a separate monograph expressing the rarity and the characteristics of the stone. 

Exhibition: Natural History Museum of Los Angeles County, 13 September 2014 – 6 January 2015.

Bibliography: Cf.: Eloïse Gaillou and alii, “Study of the Blue Moon Diamond”, in Gems and Gemology, Winter 2014, vol. 50, n°4.

Cf.: GIA monograph.

Notes: “Blue diamonds shine among nature’s most rare and valuable gems. For centuries, their unique sparkle and intriguing form have captivated gemmologists, historians, and spectators worldwide. Though any diamond with natural blue colouration is a rare discovery, some are so exceptional that they emerge only once in a lifetime. The Blue Moon Diamond, a 12.03 carat gem of Fancy Vivid Blue colour and Internally Flawless clarity, is one of those remarkable occurrences”.

Introduction of the GIA monograph

Image courtesy of the Gemological Istitute of America

“Fancy Vivid blue diamonds are extremely rare and the Blue Moon is no exception. It is an historic stone that is one of the rarest gems with this colour and in this size to be found in recent history. After seeing the stone’s colour and understanding its significance, it was fitting to name it the Blue Moon Diamond as not only its shape is reminiscent of a full moon, but the metaphor for the expression is exactly what one could say about the occurrence and existence of such a gemstone”.

Suzette Gomes, CEO of Cora International

Image courtesy of the Gemological Istitute of America

Mining

“Thomas Cullinan discovered the Cullinan mine in 1902, which at that time was named the Premier mine. Established on the second largest kimberlite pipe by inherent value, the Premier mine gained immediate prominence as a quality producer of large colourless diamonds and also rare blue diamonds. Annual production from the Premier mine was the largest in the world for the mine’s first decade of operation. Perhaps one of the greatest finds in the mine’s history is the Cullinan diamond. The Cullinan diamond is the largest colourless diamond ever discovered with a weight of 3,106 carats which has since been cut and polished into nine major stones, including 96 minor stones. Two of them currently reside within the Crown Jewels of the United Kingdom”.

Excerpt from the Natural History Museum of Los Angeles website 

Furthermore the Cullinan I weighing 530.20 carats and the Cullinan II weighing 317.40 carats which are set in the Royal sceptre and the Imperial State Crown of the United Kindgom, the Cullinan mine is also the source of two other important blue diamonds: the Smithsonian Institution’s Blue Heart, a 30.62 ct Fancy Deep blue gem discovered in 1908, and the 27.64 ct Fancy Vivid blue Heart of Eternity, unveiled by Steinmetz in 2000. 

If “some of the earliest and most historical blue diamonds, such as the Hope and Idol’s Eye, are believed to have originated in the ancient mines of India, in more recent times, the only mine to produce blues with any regularity is the Cullinan mine in South Africa. However, that supply has diminished over the past decade; when in full production, less than 0.1% of diamonds sourced showed any evidence of blue colour. The Blue Moon Diamond is a shining member of that miniscule percentage. Reportedly unearthed from the Cullinan mine in January 2014 as a 29.62 carat rough crystal, the diamond is one of few to have been tracked precisely from the mine to the hands of its cutter”.

Excerpt from the GIA monograph

The historic Cullinan mine, South Africa, the only reliable source of blue diamonds in the world. Courtesy of Petra Diamonds Limited.

Manufacturing

The rough diamond was purchased at a tender by Cora International from Petra Diamonds, owner of the Cullinan mine. “Nature granted the Blue Moon Diamond with the gifts of stunning colour and form. However, it is the responsibility of man to capitalize on these qualities and bring the diamond’s innermost beauty to full display. The art of cutting allowed for the Blue Moon Diamond’s natural beauty to reach its optimum potential”.

Excerpt from the GIA monograph

Greg Stephenson, Diamond Marketing Manager for Petra Diamonds, recalls the moment he first saw the exceptional rough diamond: “I opened the canister in which it was shipped and it fell on to my work pad. I sat there for about a minute just looking at it on my white pad - no light, no loupe - just awe-struck. The colour, the tone, the saturation… magnificent. It was as though it had been dropped in a bottle of old blue ink - extraordinary saturation with no hint of zoning and definitely no modifying colours. It was, without a shadow of a doubt, the most beautiful rough diamond I have ever seen.”

The rough diamond weighing 29.62 carats. Image courtesy of the Gemological Institute of America.

The rough diamond weighing 29.62 carats. Image courtesy of the Gemological Institute of America. The ‘Blue Moon’ weighing 12.03 carats.

Colour 

After several months of careful and precise cutting process, the gem could reveal its potential and magnificent beauty. The colour is the most important quality for a fancy coloured diamond.

“Diamonds obtain their colour from so-called “colour centres”. They are single or multiple non-carbon atoms that replace carbon in the structure of the diamond, causing a disturbance in the structure and sometimes giving rise to the colour. The distinctive blue colour in diamonds is attributed to trace amounts of the element boron in the crystal structure. Minute traces of boron are required to create the colouration. Less than one boron atom per million carbon atoms is sufficient to produce the blue colouration”.

Excerpt from the Natural History Museum website

“Likely to have never before been seen within such a large diamond, or any gemstone, [the hue of the Blue Moon diamond] could be indescribable to even the most experienced diamantaire or colour theorist; some, however, liken it to the ocean... The colour within the Blue Moon Diamond was so remarkable that it received the grade of Fancy Vivid. In blue diamonds, Fancy Vivid specifically describes those that are medium to dark in tone and strong to very strong in saturation. In a past  GIA study of 462 blue diamonds, only 1% were Fancy Vivid”.

Excerpt from the GIA monograph 

Image courtesy of the Gemological Istitute of America

Study 

The stone is so exceptional that scientists from the Smithsonian Institution and the National Gem and Mineral Collection carried out extensive research on the stone, exploring its physical properties and exceptional characteristics. They were able to study the diamond ahead of its being exhibited earlier this year in the Gem Vault of the Natural History Museum of Los Angeles County. 

“The Natural History Museum of Los Angeles (NHM) has unveiled one of the rarest stones, a 12-carat Fancy Vivid blue diamond, which is internally flawless. The Blue Moon Diamond was housed in a special, temporary exhibition in the Gem Vault from September 13, 2014 until January 6, 2015”.

Excerpt from the Natural History Museum website

Phosphorescence 

“The Blue Moon did not show any obvious fluorescence (…). It did show phosphorescence, in the form of an intense orange-red glow after exposure to UV light. The phosphorescence was most intense after exposure to short-wave UV light and remained visible to dark-sensitized eyes up to 20 seconds”.

Eloïse Gaillou and alii, “Study of the Blue Moon Diamond”, in Gems and Gemology

“The phosphorescence spectra which showed a red colour component (particularly in early decay time) is a characteristic of rare and exceptionally pure blue diamonds”.

Excerpt from the GIA monograph

“We are aware of only one other type IIb diamond from the Cullinan mine with orange-red phosphorescence. Type IIb diamonds with orange-red phosphorescence more commonly originated in India or Venezuela (…). The Blue Moon underscores the fact that the phosphorescence behaviour of type IIb diamonds is not tied to a specific geographical source”.

Eloïse Gaillou and alii, op. cit.

Sotheby's. Magnificent Jewels and Noble Jewels, Genève, 11 nov. 2015, 10:00 AM