What do you think of when you hear the word diamond? Something sparkly, for sure, but what about the colour? For most of us diamonds are clear, almost white stones. But did you know that they also come in browns, blues and reds? In fact, diamonds can come in almost every colour imaginable. Known as ‘fancy’ diamonds, each stone possesses a unique chemical composition that determines not only its colour, but also its value, rarity and desirability.

Fancy coloured diamonds have been prized throughout history for their rarity, though their popularity has grown significantly over the past few decades, thanks in part to the Argyle mine, located in the far north of western Australia which, in the 1980s, began marketing its brown diamonds under the trade names of ‘Champagne’ and ‘Cognac’. Today, it produces more than 90% of the world’s supply of pink and red diamonds.

How are fancy coloured diamonds formed?

Fancy coloured diamonds contain impurities or structural defects within their chemical composition. These are caused by the conditions that were present during the crystallisation process when the diamond first formed. They are also the result of billions of years of exposure to heat, natural radiation, or the saturation of natural elements. Different impurities and conditions result in different hues, as well as different intensities of those hues.

Yellow, brown and orange diamonds

Nitrogen impurities in the carbon crystal structure give diamonds a yellow, orange or brown hue, since they absorb the blue range of the colour spectrum. Yellows and browns are the most common fancy coloured diamonds.

Blue and grey diamonds

Blue diamonds get their colour from boron, a rare element in the Earth’s crust, which absorbs the red, yellow and green areas of the colour spectrum. Many blue diamonds are modified with a grey secondary tone, or an uneven saturation, making natural, highly saturated blue diamonds extremely rare.

Green diamonds

Green diamonds absorb natural radiation just as they are about to leave the Earth’s crust, causing them to absorb red and yellow light and reflect a green hue.

Purple diamonds

Though not proven, it is believed that the presence of hydrogen may be partly responsible for a purple or violet hue.

Red and pink diamonds

As with purple diamonds, the exact cause of the colour in pink and red diamonds is unknown, but it is believed to be due to ‘plastic deformation’, which causes structural defects to the crystal lattice. Red is the rarest diamond colour, though not necessarily the most valued.

Black diamonds

While an increasingly popular colour choice, natural black diamonds are some of the rarest diamonds in the world, which means most black diamonds have actually been treated to enhance the colour. The natural stones get their colour from the accumulation and even distribution of dark inclusions, and unlike their colourless cousins they absorb, rather than reflect and refract the light.

How are fancy coloured diamonds graded?

Colourless diamonds are described using the industry’s D-to-Z colour-grading system. However, fancy coloured diamonds exhibit colour beyond the Z range. Consequently, they follow their own colour grading scale: ‘fancy light’, ‘fancy’, ‘fancy intense’ and ‘fancy vivid’.

While colourless diamonds usually decrease in value as the colour becomes stronger, the opposite is generally true of fancy diamonds – the purer and more vivid the colour, the higher the value. Large, vivid fancy coloured diamonds are extremely rare and highly valuable.

Colour-treated diamonds

With the increase in popularity of fancy coloured diamonds, the market for colour-treated diamonds has evolved enormously in recent years. So much so that most coloured diamonds in the marketplace are, in fact, treated by irradiation or temperature in order to produce the desired colour.

These are regular, natural diamonds – not lab-grown diamonds – that have had their natural colour enhanced or altered following the same process that occurs naturally in the Earth’s crust – only far faster.

When buying a fancy coloured diamond, be sure to find out if you are buying a natural or colour treated diamond, since this will affect the value and cost of your gem.

Famous fancy coloured diamonds

One of the most famous fancy coloured diamonds is the Hope Diamond – a 45.52-carat stone with a deep blue colour. It is one of the most sought-after gemstones in the world and official records can trace its ownership back almost four centuries.

Other famous fancy diamonds include the Tiffany diamond – a 128.54-carat canary yellow diamond that was mined in 1877 in South Africa – and the Dresden Green, a 41-carat natural apple-green diamond that is believed to originate from India and first shows up in records in 1722.

The most famous fancy red diamond is the Moussaieff Red, originally from Brazil and mined in the 1990s. In its rough, original form it measured 13.9 carats, although it has since been cut down to 5.11 carats.

For more fascinating facts about fancy coloured diamonds, take a look at our infographic below.

Diamond Rock Champagne and chocolates infographic

If you’re thinking about proposing to your partner and are looking for a ring with a difference, then take a look at our fancy colour engagement rings page or contact us for more advice on selecting the perfect piece.