Treated coloured diamonds for jewellery designs
Treated coloured diamonds are natural diamonds that have been modified to enhance or alter their colour.
Natural diamonds aren’t always pure white, in fact diamonds can be found in many different shades from ivory, cream, beige, brown, right down to black and also in may ‘fancy’ colours such as pink, red, purple, blue, green, yellow, orange and brown. But these ‘fancy’ colours are far rarer than their white counterparts and far more expensive too! In general the more saturated the fancy colour, the higher the price. Many intensely coloured natural diamonds have sold at auction for several million dollars per carat!
What if us mere mortals want to enjoy the beauty of ‘fancy’ coloured diamonds?
White diamonds can be treated so that they change colour permanently. There are a couple of methods that can be used:
Irradiation: This method involves exposing the diamond to a high-energy source, such as nuclear radiation, to alter the diamond's atomic structure and permanently change the colour of the diamond. Both the intensity and type of irradiation used can affect the colour of the diamond, also the presence of any impurities or defects in the diamond will determine the final colour it changes to. For example, a diamond that contains nitrogen impurities may turn green when irradiated but a diamond that contains boron impurities may turn blue. Scientists have to use specialised equipment and techniques, such as spectroscopy to determine the chemical composition of any impurities. That gives them an idea of what colour a diamond might end up after irradiation.
High pressure high temperature (HPHT): This method involves applying high pressure and high temperature to the diamond in order to create or enhance colour depending again on the impurities present in the natural stone.
What diamonds do they treat?
A top grade white diamond that scores highly in the 4Cs for pure Colour and Clarity will be worth more if it is left untreated, whereas a mid-grade diamond with a few chemical inclusions won’t be worth much as a white diamond, but will be more valuable as a treated coloured diamond. So in both of the methods above, you need to start with a natural diamond that has a few chemical inclusions to get the best colour results.
These treated coloured diamonds are nowhere near as expensive as natural fancy coloured diamonds. However, they are stunningly beautiful and are used in jewellery regularly as you have the durability of diamonds in a range of joyful colours! It is important (and a legal requirement) that gem dealers divulge that these are treated diamonds.
Other methods for colouring diamonds include:
Chemical treatment: This method involves the use of chemicals to alter the diamond's surface colour temporarily.
Coating: This method involves applying a thin layer of material, such as a coating of resin or a metallic finish, to the diamond in order to alter or enhance its colour temporarily.
Another method for improving diamonds and other gemstones:
Heat treatment: Heating a naturally coloured diamond or gem causes any impurities or defects in the gemstone to either evaporate or migrate to the surface of the gemstone (where they can be polished away). This leaves the crystal structure of the gemstone more pure and uniform, resulting in an improved Clarity and a more homogenous colour. Again, any treatment or enhancement of a gem should be mentioned to the buyer.
What colour will a treated diamond go?
It’s the same as in natural coloured diamonds and coloured gemstones - it totally depends on which chemical is hiding in the host mineral, here are some examples:
Boron: Boron impurities can give gemstones and diamonds, a blue or purple colour.
Chromium: Chromium impurities can give rubies a red colour and sapphires a pink colour
Iron: Iron impurities can give gemstones, such as diamonds and sapphires, a yellow, brown, or green colour.
Nitrogen: Nitrogen impurities can give diamonds, a yellow or brown colour. In some cases, nitrogen can also give diamonds a pink or purple colour, depending on the concentration and distribution of the impurities.
Copper: Copper impurities gives turquoise its blue or green colour and sapphires a green colour.
Titanium: Titanium impurities can give sapphires, a yellow, orange, or pink colour.
Manganese: Manganese impurities can give gemstones, such as spinel and beryl, a pink or purple colour.
In the case of blue sapphires, the blue colour is caused by Iron and Titanium impurities in the crystal structure of the gemstone. These impurities absorb certain wavelengths of light, causing the gemstone to appear blue to the human eye.
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