Recent record-breaking sales at prestigious auction houses Sotheby’s and Christie’s have intensified public interest in coloured diamonds. Favourites include a 5.30-carat, cushion-shaped deep-blue diamond from Bulgari, a 34.65-carat intense-pink diamond called “Princie” and a stunning 14.82-carat pear-shaped diamond named “The Orange”.
White diamonds fluctuate in price but fine-quality coloured diamonds are virtually investment proof, never decreasing in value. Red, pink, orange, blue and green diamonds have quadrupled in value over the last decade, while yellows have tripled. Champagne (brown) are the most affordable, often costing less than white diamonds.
For gemstone enthusiasts, the fascination with coloured diamonds begins well before they reach fine jewellery boutiques. Diamonds are formed deep within the earth’s mantle in a hot, carbon-containing silicate solution under high pressure. They are then catapulted towards the earth’s surface by lava at speeds of up to 100 km per hour.
The formation of white diamond is common enough, but the conditions and mechanisms required to produce a coloured diamond are more complex, involving impurities, colour centres and plastic deformation.
Most diamonds contain nitrogen as an impurity but the way it’s integrated into the crystal lattice can result in different colours. For example, nitrogen atoms are singly substituted for carbon atoms to produce fancy yellow to orange diamonds. Blue to violet diamonds may contain hydrogen as an impurity – as seen in Australian Argyle production – or may contain boron, like the famous 45.52-carat greyish-blue diamond “The Hope”.
The exact cause of pink to red colour in diamond is still a mystery to scientists but may be related to plastic deformation.
For less expensive alternatives to natural fancy-coloured diamonds, consider treatments, synthetics and imitations. A lower quality diamond may be subjected to single or multi-step treatments to simulate a fancy colour. Heat treatment or irradiation are commonly used to produce black diamond and a combination of these techniques can result in green or blue colours.
A very simple treatment is the application of a pink coating to the pavilion facets of a diamond to give the appearance of pink diamond. This coating may range from a vacuum-sputtered film to a crude dab of pink nail varnish.
Synthetic or laboratory-grown diamonds are now commercially produced using carbon vapour deposition (CVD) or high pressure high temperature (HPHT) techniques, and may be subjected to post-growth treatments to further enhance colour. Resulting hues include pink, blue, yellow, orange, grey, brown and even colourless.
Common coloured diamond imitations include cubic zirconia, glass, synthetic moissanite, synthetic garnets and diamond-coated cubic zirconia.
Whether blushing pinks, rosy reds or ocean blues, demand for these rare and intriguing gemstones will continue to soar, outpacing supply and setting new world records.