Thinking of a diamond, the first thing that comes to mind is a beautiful, sparking colourless gemstone. However, it is not generally known that diamonds exist in almost all the colours of the rainbow. These diamonds, known as fancy coloured diamonds or more simply fancies, are extremely rare and it is estimated that only one in ten thousand diamonds mined can be defined as such, which explains why, in the past, they were the prerogative of Kings and Emperors and are now, following opening of the Chinese and Indian markets, highly coveted.

Within the niche of coloured diamonds, fancy yellows, once known as canary yellows, are the most common and it is estimated that they account for up to 60% of all coloured diamonds, generally mined in South Africa. Their cognac and chocolate variants are highly appreciated. Fancy yellows are of intense colour and should not be confused with “yellow” diamonds which are at the bottom of the colour grading scale and therefore the lowest in value. Their yellow colour is due to the inclusion of nitrogen impurities that absorb blue light.

Green diamonds are very rare and their colour is due to slight traces of natural radioactivity, while the colour of blue diamonds is determined by the presence of boron in the crystal. Red diamonds are the rarest of all coloured diamonds and only a few specimens exist, almost all weighing less than a carat. Their colour, whose genesis is not yet perfectly known, is probably due to structural abnormalities of the stone and is concentrated in lamellae that gemmologists call “pink graining”. Pink diamonds, associated with the Argyle mine in Northwest Australia, are close relatives of red diamonds and are considered to be amongst the most beautiful gemstones. The extremely rare “chameleon” diamonds that change hue if exposed to heat represent a special case in the category of fancies.
All coloured diamonds are graded according to hue and saturation, divided into categories ranging from the lightest to the most intense and valuable. Cut is also extremely important in coloured diamonds. Due to their particular characteristics, rough fancy diamonds require expert, specialised cutters able to exalt their colour, which is not evenly distributed in the crystals, often resorting to shaped or fantasy cuts. Lastly, the determination of the purity of coloured diamonds does not affect their value as in the case of their colourless counterparts; their price is determined by their hue and colour intensity. At this point, we may ask: How about black diamonds? What is a black diamond? Which category do they belong to? Black diamonds, which first appeared on the market in the mid-1990s and soon became very fashionable, represent a special case and, of all diamonds, have the lowest value. Their “black” colour is created by the presence of numerous small inclusions of graphite that make them very difficult to polish. To cater to high market demand, many black diamonds traded on the market have been obtained by irradiating inferior quality diamonds. It is not easy to distinguish between natural and irradiated black diamonds but the low price of both does not generate major variations in the market.

In the case of coloured diamonds, considerable attention is required to determine whether a coloured diamond is natural or has been treated to obtain an artificial colour. The first experiments to modify or enhance colour adopting irradiation treatments were carried out in France and England in 1904. Today, irradiation and/or heating may be used to obtain the colour of inferior quality diamonds. Most of the coloured diamonds sold today belong to this second category which caters to the massive demand for coloured stones which cannot be met due to the scarcity and high cost of naturally occurring diamonds. In fact, the price of a treated diamond may be up to thirty times lower than that of a naturally occurring diamond. To determine the natural colour and intensity of diamonds of high carat weight or particular colour, it is essential to refer to the Gemological Institute of America (GIA), the most high prestige gemmological laboratory in the field of diamonds. Aste Bolaffi is proud to present a rare and fascinating 7.44 carat Very Light Pink round-shaped diamond that is sure to attract the interest of international purchasers and collectors at its next Jewellery auction in September. The starting price will be 150 thousand euros.

BY Maria Carla Manenti