Most of the diamonds you see are colourless – these are graded D to Z with the best grade being D. However coloured diamonds are now becoming very popular, as seen in the recent Sotheby auction where pink and blue diamonds reached more than their predicted sale prices.
The rarer blue diamonds are caused by boron impurities, but some blue diamonds have been treated to make the blue darker.
Pink and Violet diamonds
They are caused by a combination of pressure and heat, causing internal lattice distortion, reflecting a pink hue.
These can be found with natural irradiation but have more often been treated.
These are one of the more affordable colours and are otherwise called chocolate, champagne or cognac diamonds. Brown diamonds were first popular as jewellery in Roman times. The brown colour is caused by small amounts of hydrogen and nickel which were incorporated into the diamond when it was formed millions of years ago.