Fancy colour diamonds

I first became aware of fancy-coloured diamonds in the 1980s. A friend who worked as a stone dealer showed me various shades; I was so taken with them that I bought them all.

Back then, they weren’t well known by the public, but I thought they were beautiful; I had various shades of pink and yellow, ranging in size from small 1.5mm to over a carat.  I wouldn’t be able to afford to buy them today!


In recent times, they have become much better known and well regarded; the most expensive gem ever auctioned is The Pink Star diamond, 59.6 carats natural pink, sold for £57.1 million at Sotheby’s in Hong Kong on March 29  , 2017. The Pink Star was mined by De Beers in an unspecified location in Africa in 1999. Originally 132.5 carats as a rough diamond, Sotheby’s says it was meticulously cut and polished over two years

Diamonds in the normal colour range are colourless to light yellow and are described using a D-to-Z colour-grading scale.  Rare specimens come in every spectrum colour, including yellow and brown, most rarely, blue, green, pink and red.

Only one in 10,000 diamonds has a fancy colour.

Unlike their colourless counterparts, fancy colour diamonds don’t lose value as their colour intensifies. In fact, their value tends to rise with the strength and purity of their hue. This makes large, vivid fancy colour diamonds not just rare, but also potentially lucrative investments. However, it’s important to note that many fancy diamond colours are muted rather than pure and strong.

As with most things, rarity equals value ( not always beauty!). With diamonds in the normal range, value is based on the absence of colour because colourless diamonds are the rarest. With fancy-coloured diamonds—the ones outside the normal colour range—the rarest and most valuable colours are intense pinks, blues, and greens. In all cases, even very slight colour differences can significantly impact value.

Unlike fancy yellows and browns, diamonds with a noticeable hint of any other hue are considerably rarer. Even in light tones and weak saturation, as long as they show colour in the face-up position, they qualify as fancy colours. Red, green and blue diamonds with medium to dark tones and moderate saturations are rare.


Red diamonds are so rare that only a handful are known to exist. Unlike other colours, the red or pink tone is due to structure deformity rather than impurities. Generally, pink and red diamonds are pure carbon.

Diamonds with red or reddish colours are scarce and highly valued. Pure pinks are the most popular and incredibly expensive. I really like the pink champagne tone. It’s a more sophisticated colour, much more affordable, and looks stunning when combined with rose gold and white diamonds. 

Blue diamonds are scarce. They generally have a slight hint of grey, so they’re rarely as highly saturated as blue sapphires. Boron impurities cause their colour—the more boron, the deeper the blue. Less than one boron atom per million of carbon atoms can give a diamond a blue colour. 

The De Beers Cullinan Blue, a true marvel, holds the title of the largest blue diamond ever to be auctioned. This extraordinary gem, weighing 15.10ct, fetched a staggering price of just under £46M at Sotheby’s Hong Kong on April 27th this year. Surpassing its £38m estimate, it fell just short of Oppenheimer Blue’s £46.4m record, further testament to its exceptional value.

The step-cut fancy vivid blue diamond weighs 15.10ct. Accompanied by GIA report no. 2223179803 stating that the diamond is Fancy Vivid Blue, Internally Flawless; also accompanied by a diamond type classification letter stating that the diamond is determined to be a Type IIb diamond. Type IIb diamonds are scarce in nature (less than half of one per cent). Today, the most significant source is limited to the Cullinan mine in South Africa. Among famous gem diamonds, the 70.21-carat Idol’s Eye and the 45.52-carat Hope are examples of Type IIb.

Green diamonds get their colour when radiation displaces carbon atoms from their normal positions in the crystal structure. This can happen naturally when diamond deposits lie near radioactive rocks or artificially as a result of treatment by irradiation. Fancy green diamonds are typically light in tone and low in saturation. Often, the colour appears muted, with a greyish or brownish cast. The hue is generally yellowish green. In most green diamonds, the hue is confined to the surface and rarely extends through the entire stone.

Brown is the most common fancy diamond colour and the earliest to be used in jewellery. Second-century Romans set brown diamonds in rings. In modern times, however, they took some time to become popular.

Brown diamonds were not typically considered for jewellery until the 1980s, when they began to appear in the production of the Argyle mines. Nitrogen, nickel impurities, and crystal deformation can cause the brown tone.

Our queen is not the sole royal to possess a rare diamond collection. The Golden Jubilee Diamond, a 545.67-carat brown diamond, stands as a testament to the grandeur and historical significance of these gems. It is the largest cut and faceted diamond in the world, a part of the Thai Crown Jewels, and outweighs the Cullinan I by an impressive 15.37 carats. 

Yellow is diamond’s second most common fancy colour. Yellow diamonds are sometimes marketed as “canary”. While this isn’t a proper grading term, it’s commonly used in the trade to describe fancy yellow diamonds. Nitrogen causes the yellow; the more nitrogen, the stronger the colour.  I have some beautiful, strong canary diamonds, but I also think some paler lemon colours can be very pretty. Also, the stronger golden tone works well in Platinum.

Until the late 1990s, there was not much demand for black diamonds. Their colour is caused by large quantities or clouds of minute mineral inclusions such as graphite, pyrite, or hematite. I like to use them as strings to put a pendant on; the sparkle they produce is stunning. They look beautiful as a contrast with orange sapphires.

Colour is the dominant value factor in fancy-coloured diamonds. Even diamonds with numerous inclusions that result in a low clarity grade are prized by connoisseurs if they display attractive face-up colour. Of course, inclusions threatening the gem’s durability can significantly lower a fancy colour diamond’s value. Fancy colour diamonds can exhibit colour graining, which is considered an inclusion.

treated diamonds

With anything of value, someone is always trying to cut corners. Diamonds involve what we call treatments. As a consumer, you will regularly encounter gems that have been treated to change their appearance in the marketplace.

Because these treatments are only sometimes apparent to the unpractised eye and are sometimes difficult to distinguish even by experts, it is necessary and legally required for anyone selling a gem to disclose any treatment procedure a gem may have received. Non-disclosure of this treatment could cause a person to believe that a particular gemstone was naturally higher quality and, therefore, more valuable than it is. One added challenge is that treatments can be permanent, long-lasting or short-lived under everyday jewellery use. Treated gems may require special care by their owner.

The most commonly encountered treatment of diamonds is irradiation. Neutron and electron radiation are the most common forms of artificial irradiation, and it is possible to induce black, green, blue, deep yellow, orange, pink, and red diamonds (often combined with a secondary step of heating to achieve certain colours).

Heating diamonds at high pressures and high temperatures (HPHT) is a transformative process that can remove or lessen their coloration, turning the gem into a mesmerizing colorless beauty. This method also has the potential to completely change the color of a diamond, as other types of diamond may be transformed from brown to yellow, orangey yellow and yellowish green, or blue colors, demonstrating the versatility and power of HPHT treatment.

Thin-film coatings are sometimes used to change the colour of diamonds. Crude yet effective coatings can also include permanent ink markers along the girdle surface of a diamond, affecting its face-up appearance by the colour of the ink used. More modern coating methods use thin films of metal oxide.


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