Natural coloured diamonds are some of the rarest and most beautiful diamonds that you can imagine. Mined at a number of varieties across the world, including South Africa and Australia, coloured diamonds are prized by collectors and are sold for 10’s of thousands of dollars per carat. Coloured diamonds are increasing in popularity and as such, more and more purchasers are looking to invest in coloured diamonds. However, there are a number of points to bear in mind when investigating and purchasing diamonds of colour.
First and foremost, a buyer needs to know whether the colour in the diamond is natural, or enhanced. This is not to be confused with whether the diamond is a natural diamond or a synthetic diamond, but where the colour in the diamond actually comes from. What do we mean by this? A diamond with a naturally occurring colour, say yellow or blue, is a result of chemical impurities in the diamond (nitrogen for yellow, boron for blue) that were incorporated as the diamond grew in the earth’s mantle. The colour is intrinsic in the diamond, it is the colour it always was. Because naturally coloured diamonds are so rare, so expensive and now, so popular, a variety of laboratory techniques have been developed to alter, induce and enhance the natural colour of a diamond.
These laboratory techniques can artificially increase the value of a diamond and, despite diamond dealers being legislated by government authorities to report any laboratory treatments to clients, this does not always happen. An unscrupulous dealer could sell a laboratory treated yellow diamond as a natural yellow diamond and receive a higher purchase price from the unsuspecting client.
So, what are the laboratory treatments and the enhancements that you should be aware of?
Irradiation of diamonds and high pressure – high temperature (HPHT) treatments are some of the more common processes that diamonds may be subjected to, to improve colour and enhance perceived value. By subjecting brown diamonds to HPHT treatments, the colour of the diamond can be changed to a more desirable colour of yellow or green. Lighter brown diamonds or grey-tinted diamonds can be turned almost colourless, immediately improving their perceived value according to the diamond D-Z colour scale.
HPHT treatments are traditionally permanent, meaning that the diamond colour will not return to its original, natural colour. Irradiation of diamonds in a natural setting (such as the earth’s crust or mantle) leads to very rare green diamonds. Similarly, by irradiating a diamond in a laboratory, one can produce a green or blue-green diamond and, upon further treatment, even orange or pink stones. Many black diamonds are also the result of laboratory irradiation.
It is not easy to identify whether a diamond is natural or synthetic (laboratory-grown) but it is more difficult to identify whether the colour in a diamond is natural or laboratory-induced. Certification laboratories such as the GIA possess the necessary equipment to investigate the colour in diamonds and any questionable diamonds should be submitted to the GIA for investigation and proper certification.
If you are in the market for coloured diamonds, be aware of the laboratory treatments and make sure that your retailer knows the origin of the colour, the origin of the diamonds and can provide you with the necessary certification for the stones you are buying.