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

“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


“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”.

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”.



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”.

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”.



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.”

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”.


“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”.

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”.

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”.


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


“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”.

Into the Blue

Geneva - Once in a blue moon, the earth sends forth a coloured diamond. Intense and intriguing, the stone may be yellow, pink, orange or violet, yet its fiery brilliance and exquisite colour – the most powerful emotional triggers in a gem – always come together with dramatic effect. Among these coveted stones (there is one for every 10,000 gem-quality white diamonds found), the blue diamond is considered the rarest, most captivating and most enigmatic treasure.

A fabulous fluke of nature, a blue diamond is produced by the random presence of the atomic lattice-bound trace element boron within the stone’s carbon structure during its formation deep in the earth’s core. The earliest known blue diamond came from the legendary Kollur mine in the Golconda, a region of India that produced such famous examples as the Idol’s Eye (15^th century) and the Hope Diamond (17^th century), perhaps the most fabled gemstone on the planet. Later, in the early 18^th century, blue diamonds were occasionally found in Brazil. But today the Premier Mine at Cullinan, some 40 kilometres east of Pretoria, South Africa, is the only one known to yield blue diamonds with any regularity. However, discoveries are still sporadic and always astonishing occurrences. Indeed, since the mine was acquired by Jersey-based Petra Diamonds in 2008, out of the eighteen million tonnes mined and five million carats recovered, only five world-class blue diamonds have emerged from Cullinan, or less than 0.1 per cent of the mine’s annual yield.


All of that changed in January 2014 with the appearance of a 29.62-carat rough blue diamond crystal. Following much press excitement, the diamond was purchased by Cora International, one of the world’s leading firms specialising in cutting large important diamonds. Cora’s experts spent approximately six months deliberating, planning and painstakingly cutting the rough into a magnificent cushion-cut 12.03-carat diamond of perfect proportions. In its detailed monograph, the Gemological Institute of America (GIA) classified the diamond as “fancy vivid blue” and “internally flawless,” hailing it as a “rare wonder.” A pinnacle of perfection with top classifications, the stone was named the Blue Moon and garnered much attention when it went on view at the Natural History Museum of Los Angeles County in August 2014. But when the exhibition closed this past January, the Blue Moon retreated to a vault.


One of the largest known fancy vivid blue diamonds, the Blue Moon is now re-emerging as the dazzling centrepiece of Sotheby’s November sale of Magnificent Jewels and Noble Jewels in Geneva. The last time a vivid blue diamond was polished from the rough was in 2009, when the 7.03-carat Star of Josephine, from the same Cullinan mine as the Blue Moon, fetched $9.5 million at Sotheby’s Geneva, then a record price per carat for any diamond.

The Blue Moon will be collectors’ ultimate object of desire, as well as one of tomorrow’s historic diamonds. For David Bennett, Sotheby’s Worldwide Chairman for Jewellery, the Blue Moon represents “the most mysterious and romantic” of coloured diamonds, its deep blue giving it a hypnotic magnetism. Almost other-worldly, unknowable and absolute, this spectacular specimen is simply awe-inspiring.

Beyond exceptional colour, brilliance and clarity, the Blue Moon, classified as a type IIb diamond, radiates with a captivating inner life. According to the GIA, type IIb diamonds are electrically conductive and known to phosphoresce, usually turning dark blue or green under ultraviolet light. Remarkably, the Blue Moon phosphoresces red, which infuses it with a flaming passion, another extraordinary quality.

Maximising these natural gifts, the Blue Moon also demonstrates diamond cutting’s new levels of excellence and expertise. The world’s elite diamond cutters have the ability to see into the heart of a stone, unveiling its secrets while understanding its intricate structure. Cutting and polishing a coloured diamond of immense value requires exceptional intuition, skill and experience, not to mention diamantine nerves, which the Blue Moon’s realisation embodies to the highest degree. Its exquisite cutting is clearly the result of a true art form, a blend of art and science, of the superrational with the hyper-instinctive. It should be noted that blue diamonds pose very specific challenges to gem cutters. Unlike white diamonds, type IIb blue diamonds are rarely symmetrical in structure; their internal angles are often likened to the knots in a piece of wood, making the cutter’s work all the more perilous. In addition, such stones often reveal uneven colour distribution, known as colour zoning, another parameter for the cutter to consider. One miscalculation, one slip, can mean the colour disappears entirely.

But while a blue diamond may present the greatest challenge for the diamond cutter, technical advances and increased understanding of coloured diamonds have also enabled experts to deepen precious stones’ intensity and illuminate their hues more than ever before. That much is evident in the Blue Moon’s cushion brilliant cut: its softness and noble lines not only celebrate the stone’s other-worldliness, but also enhance its tone and saturation, transforming our perception of the coloured diamond from mineralogical curiosity to refined work of art – impossibly rare, limited only by nature and discovered only once in a blue moon.