How Diamonds Get Their Colour

By Sotheby's
D iamonds occur in an array of colours – from pure whites and soft pinks and blues to brilliant hues of purple and red. No matter the colour, each diamond possesses a unique composition of chemical elements that have the power to dictate rarity, value and desirability. Read on to discover exceptional diamonds from the upcoming Magnificent Jewels and Noble Jewels auction in Geneva and learn how nature creates the world's most radiant gems.

White Diamonds

Diamond ring, round brilliant-cut diamond weighing 36.57 carats, D colour, VVS1, excellent polish and symmetry. Estimate: CHF 4,500,000–5,500,000 / $4,500,000–5,500,000

White diamonds are the most common, falling into the largest colour spectrum on the Diamond Grading Scale, which begins with “D” colour, meaning totally colourless, and ending with “Z” colour, which is pale yellow or brown. The variable in this spectrum is the element Nitrogen – a D colour diamond has no nitrogen (or only a microscopic amount) nor any other element present. The larger the amount of nitrogen present the more the colour increases, thus moving the diamond along the colour spectrum. The vast majority of white diamonds mined today have a large content of Nitrogen, which classifies them towards the lower end of the colour scale. Diamonds that fall within the D-F colour range are rare and therefore more will command a higher price than those towards the end of the spectrum.   

Yellow Diamonds

Coloured diamonds contain impurities or structural defects within the chemical composition. In the case of yellow diamonds, nitrogen is incorporated into their carbon crystal structure. These nitrogen impurities give a diamond its yellow colour as they modify light and absorb the blue part of the visible spectrum. When there is a large amount of nitrogen present within the stone the diamond ceases to become a M-Z coloured diamond and becomes a fancy coloured diamond. All fancy coloured diamonds follow the same colour grading scale: Fancy Light, Fancy, Fancy Intense, and Fancy Vivid. As the colour concentration increases within the stone, so does its value.   

Pair of fancy yellow diamond earrings, Cartier. Estimate: CHF 50,000–70,000 / $50,000–70,000

Blue Diamonds

Blue diamonds are caused by Boron, a rare element in the Earth’s crust.

Many are modified with a grey secondary tone, or an uneven saturation with areas of colourless windowing, making natural blue diamonds with exceptional saturation and brilliance extremely rare.

Fancy intense blue diamond ring, weighing 1.01 carats, VS1 clarity Tiffany & Co. Estimate: CHF 150,0000–250,000 / $150,0000–250,000

Pink, Red & Other Coloured Diamonds

What makes a pink or red diamond? As yet we have no definitive answer. Whilst it is known that there is no impurity causing the colour, it is believed but not yet proved that it is due to a mutation in the crystal lattice that alters the stone’s molecular structure.

Fancy Purplish Pink Diamond Ring. Estimate: CHF 1,100,000–1,800,000 $1,100,000–1,800,000

Other colours, such as green, purple and orange, occur from natural radiation and other common elements within the Earth. Coloured diamonds are truly an anomaly of nature.

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