1.

Colours and Shades

Henry Kissinger once famously said, "A diamond is a chunk of coal that did well under pressure" and while this might not strictly be true it is known that a unique combination of heat and pressure is required to form this most sought after gemstone. When it comes to coloured diamonds however – which can be found in the mines of Russia, Canada, Botswana, Angola, Namibia and South Africa among others – a few other elements are needed which alter the atomic structure of the diamond and the way it absorbs and reflects light, which in turn produces these spectacular colours.

Red and Pink Diamonds

Red is the rarest colour of diamond, and very few of them exist in the world, which results in the highest value per carat. They are rarely found in large sizes and will usually amount to less than one carat. The hue is thought to be a deepening of the process needed to create the more common pink diamond, which involves a ‘plastic deformation’ or distortion in the crystal lattice structure of the carbon during formation. This causes some atoms to be displaced, resulting in various shades of pink and red which are highly sought after.

Blue Diamonds

When the chemical element of boron is present in the diamond’s atomic structure during its formation, blue diamonds are created. Blue diamonds are more commonly found than red and can range from a pale grey or a sunny sky blue to a deep ocean blue, with the more boron-heavy saturated blue being more difficult to find than a pale blue type.

Green Diamonds

The green hues often found in natural diamonds are the result of the presence of radiation in the ground during the formation of the gem, perhaps through proximity to a mineral rich in uranium which would penetrate to the core of the stone.

Yellow and Brown Diamonds

The yellow shade found in fancy coloured diamonds is due to the presence of nitrogen in the rock which can produce anything from a pastel lemon colour to a bright canary hue. Occasionally this can also produce an amber or brown tint.

Orange Diamonds

Pure orange diamonds—as opposed to citrus or amber shades—are some of the hardest to find and the most sought after on the market. The orange shade is thought to come from the presence of nitrogen but they have never been fully studied and the secret of their intense shade remains to be discovered.

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2.

Grading System

The grading system for coloured diamonds may seem overwhelming to collectors at first, so it’s always best to contact a specialist if there are any doubts. The system works by grading the stones from the palest shades to the most vivid, based on the strength of colour in the stone. Generally speaking, the stronger the colour, the rarer and more valuable the stone. The terms of grading can be confusing but, effectively, they vary from Faint (the closest to a colourless diamond) through to Very Light, Light, Fancy Light and Fancy to Fancy Intense, Fancy Vivid, Fancy Dark and Fancy Deep which indicates  the strongest saturation of colour and tone and is the rarest and most desirable grade. Before buying, collectors should ensure a diamond is accompanied by a certificate from the Gemological Institute of America (GIA) which will specify the colour grading of a stone.

It is also important to know that sometimes a diamond may be described as ‘fancy pinkish brown’ or ‘fancy orangey pink’ but it is the second part of this description that points to the main colour. An expert will examine the diamond to see what proportion is given to the other colour and this will determine its value. Again, rarity plays a major part in this. A pure pink colour is more desirable than an orange/pink or a purple/pink because it is less commonly found.

3.

Cut and Clarity

A diamond can be cut in many different shapes but some are more valuable than others. The most sought after cut is round, giving the stone the most facets, and therefore requiring precise craftsmanship. Other popular shapes include the pear, the princess cut (a rectangular shape that is known for its brilliance), the oval cut and the cushion cut, which is a square with rounded edges.

Before buying, collectors should also be aware of the clarity grade of a coloured diamond. This is measured on another scale that notes any imperfections within the stone. This ranges from ‘included’ (graded as I1–I3) which will have visible blemishes, to ‘slightly included’ (SI1–SI3), where the blemishes are existent but not as noticeable, to ‘very slightly included’ (VS1, VS2) and ‘very very slightly included’ (VVS1, VVS2) where the marks are almost unnoticeable, and finally to ‘internally flawless’ (IF) and ‘flawless’ (FL), categories which command the highest prices at auction.

4.

The Mania for Coloured Diamonds

Over the last 50 years the demand for coloured diamonds has increased significantly as collectors become more aware of the rarity of these gems through important collections or collectors. Queen Elizabeth II, for example, was given the famous ‘Williamson Pink’, a 23.60 carat flawless round brilliant-cut, gifted to her on the occasion of her marriage in 1947 by John Williamson, the owner of the mine in Tanzania where the rough was discovered.

Other royal fans of coloured diamonds include Queen Maxima of the Netherlands who wore the famous Stuart tiara – which holds a 39 carat pale blue diamond dating back to the 17th century at its centre – for her first official visit to the UK. These captivating gemstones are also popular among celebrities such as Victoria Beckham, Penelope Cruz and Adele, who have sparked a trend for coloured diamond rings among younger generations.

The industry has also played a part in elevating the status of coloured diamonds among collectors. Tiffany & Co. incorporated coloured diamonds into their designs in the early 20th century, long before they became ultra fashionable, and today Graff Diamonds and Moussaeiff, who were both early advocates of selling coloured diamonds, continue to be major players in the market. Additionally, in the 1980s, the Argyle mine in Australia began promoting brown-hued diamonds with names such as ‘Champagne’ or ‘Cognac’ which made them more appealing to collectors.

5.

On The Market

The market for coloured diamonds continues to be exceptionally strong. Prices have been steadily increasing over the past decade and demand is expected to continue to grow for rare examples. The appeal of these gems is universal and recent years have seen major collectors emerging, especially in Asia, as clients all over the world compete to own a unique and rare item – if they were as common as white diamonds these coloured stones would not have nearly the same cachet or appeal.

Estimates vary according to the rarity, size and clarity of the gem. In 2013, Bonhams sold an extremely rare Fancy Deep Blue diamond, weighing 5.30 carats in a Bulgari ‘Trombino’ ring for £6.2 million – a record breaking USD 1.8 million per carat and in 2018, £2.2million was achieved for a 5.03 carats Fancy Pink diamond, setting a new world record price per carat of USD 583,551.