Petra Diamonds
Petra Diamonds is a leading supplier of rough diamonds. A number of acquisitions have established Petra as one of the world�s largest independent diamond groups by resources, with a total resource base of 262 million carats.
Cutting and polishing
The process of transforming a rough diamond into a polished gemstone is both an art and a science. A well-cut diamond reflects light within itself, from one facet to another, as well as through the top of the diamond, bringing out its spectral brilliance.
The cutting and polishing of a diamond crystal always results in a dramatic loss of weight; rarely is it less than 50%. Sometimes the cutters compromise and accept lesser proportions and symmetry in order to avoid inclusions or to preserve the carat rating.
After a stone has been cut, it is then polished and classified again, this time by its cut, colour, clarity and carat weight, characteristics known as ‘the four Cs’. It is then sold via one of the registered diamond exchanges (also known as; bourses’) located around the world or directly to wholesalers or diamond jewellery manufacturers.
Pink diamonds
Pink diamonds are known to occur in only a few mines throughout the world, and none of these have ever proved to be a steady commercial source for gem-quality pinks. It is this scarcity, coupled with their beauty, that has made them a highly desirable in the international jewellery market. Celebrities such as Jennifer Lopez, who sported a 6.1 carat pink diamond engagement ring in 2002, have helped to spread their appeal yet further.
The alluvial deposits in southern India produced a limited amount of pinks during the active mining years of the 17th century. The many alluvial deposits throughout Brazil have also been a notable but infrequent source of pinks. Currently the Argyle mine (Rio Tinto) in Australia is the world’s most significant source of pinks, though several Russian and African deposits, including the Williamson mine in Tanzania (owned by Petra Diamonds), are also known sources. Williamson is the source of the famous Williamson Pink, a 54.5 carat rough diamond which was recovered in 1947. It was polished to form a round ‘brilliant’ cut of 23.6 carats, and was presented to the then Princess Elizabeth as the centre piece of a floral brooch for her forthcoming wedding to Prince Phillip. Pinks have also been recovered at Petra�s Koffiefontein mine in South Africa.
The Darya-i-nur-”Sea of Light”, “River of Light” or “Ocean of Light “diamond is the largest pink diamond and one of the largest and oldest diamonds in the world. Weighing 182 carats its colour, pale pink, is one of the rarest to be found in diamonds. The Darya-i-nur presently forms part of the Iranian Crown Jewels.
Red Diamonds
Reds are undoubtedly the rarest of coloured diamonds. Less than 20 stones have so far ever been certified as a red diamond, most of them weighing less than half a carat. These diamonds are a collector’s item and every year prices reach new records. Prices per carat have so far ranged from about US$800,000 to US$1.9 million which makes red diamonds one of the most concentrated forms of wealth. Furthermore, they have never significantly lost value because supply has never come close to exceeding demand.
Red diamonds have the same properties as pink diamonds; the term ‘red’ refers to a dark or intense pink. Therefore the only colour grade for a red is ‘fancy’ as it falls in the pink category when being any lighter. They have been found in Brazil, South Africa, Borneo, India, Venezuela and Australia.
The most famous of these coloured stones is the Moussaieff Red Diamond. It is the largest red diamond ever to be graded by the GIA. The Moussaieff Red is reported to have been found by a Brazilian farmer in the mid-1990’s as a rough of approximately 13 carats. The diamond was purchased and cut by the William Goldberg Diamond Corp. where it went by its original name the Red Shield. The now 5.11 carat gem is currently owned by Moussaieff Jewellers Ltd.
Common names for red diamonds include blood red, ruby, magenta, raspberry, rose, strawberry, cherry, tomato etc. Red diamond rough is mined in Australia, Brazil and South Africa.
Coloured diamonds
Hope blue diamond
While coloured diamonds have been known and admired for centuries, their phenomenal growth in widespread popularity is a relatively recent phenomenon. In the not so distant past only large historic diamonds such as the Hope blue or the Dresden green commanded much attention, even within the gem and jewellery community. A major turning point came during the late 1970’s when the Argyle mine (Rio Tinto) in Western Australia was discovered, a prolific source of brown (“champagne”) and yellow diamonds, as well as some pinks and greens. New availability of coloured diamonds meant that they became more accessible to the greater public and Australian marketing transformed the previous mindset that colourless diamonds are most desirable.
Hancock Red
More attention was brought to these precious stones in 1987 when Christies auctioned the Hancock Red, a 0.95 carat red diamond, in New York. It was sold for $880,000, the record price per carat for any gem ever sold at auction at that time. However currently the record for the most expensive diamond ever sold belongs to a 3.73 carat blue diamond sold at auction to Lawrence Graff in May 2008, at US$1.3 million per carat.
According to Daniel Prince, a bespoke London jeweller, ‘No other jewel combines the rarity, beauty and sex appeal of a coloured diamond’. Coloured diamonds are indeed exceedingly rare. For every 100,000 D-flawless diamonds, there is perhaps one coloured diamond, and it is probably not flawless. The beauty and the rarity of these coloured diamonds have generated unprecedented desire and incomparable prices.
A diamond gets its colour from minute amounts of trace elements, such as nitrogen, boron, graphite and hydrogen, which interact with the carbon atoms that make up the stone, or via exposure to natural radiation. Each element contains its own hues. Nitrogen will result in a yellow or orange stone, which, with additional amounts, becomes deeper in colour. Sub microscopic inclusions, such as graphite, block all transmissions of light, resulting in a black diamond. Boron produces blue and uranium develops green. Hydrogen creates pink, purple and red. According to Fran�ois Curiel, jewellery expert and chairman of Christie’s Europe, “Rarely do imperfections add value. In the case of coloured diamonds, it is ironic that the beauty and rarity of these gems comes from an impurity. While a perfect colourless diamond now trades at $100,000 per carat, the benchmark for the best colour diamonds has surpassed $1 million a carat and continues to rise.”
Colour is the most important factor in determining the value of a gemstone, this being determined by its hue, tone, saturation and distribution. Hue is the term used for the actual colour of the spectrum: red, orange, yellow, green, blue, indigo or violet. The more pure a gemstone’s hue, the more valuable it is. Because gemstones are composed of many naturally occurring elements, they typically emit one dominant colour and one or more underlying colours. Tone represents how light or dark a stone appears depending on how much brown, black, grey or white is present. Saturation describes strength of colour in terms of degrees of intensity- the more colour saturated a gemstone is, the more valuable it becomes. Distribution is how evenly the colour spreads out across the body of the gemstone.
Coloured diamonds are graded by the terms Fancy, Fancy Deep and Fancy Vivid, in ascending order of desirability. Fancy Deep describes stones of medium to dark tone and moderate to strong saturation while Fancy Vivid is a deep colour with no infiltration of other colours. According to Thomas Burstein, “The main concern for collectors is that the diamond shows its colour; it has to be evenly dispersed.”
Each coloured diamond is different not only because of its natural colour but also because it is shaped and finely polished. The cutting of coloured diamonds is significantly important, performed by highly skilled craftsmen who combine their technical knowledge with a deep appreciation for beauty and colour.
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