Although colour Diamonds can be found naturally, they are incredibly rare. In fact natural Red Diamonds are said to be the most expensive item on the planet and the most luxurious item known to man.
Colour appears naturally in Diamonds when impurities become trapped in Diamonds as they crystallise in the Earth’s mantle (Diamonds and Peridots are the only two gemstones that can form in the intense heat of the molten lava in the mantle). In order for Diamonds to form (crystallise) successfully they actually need a combination of intense heat (approximately 2000 degrees Fahrenheit - 1093 degrees Celsius)and an incredible amount of pressure. The chances of impurities being naturally trapped in Diamonds in such an inhospitable environment is infinitely remote, hence the rarity of natural colour Diamonds.
In order to make colour Diamonds more accessible and more affordable, there are now three different treatment processes that can be applied by man to add permanent colour to a Diamond. It is important to note that any of these treatments may affect the value of the Diamond.
High Temperature (HPHT)
Effectively this treatment recreates the same environment in which the Diamond was formed 90 miles below the Earth’s surface several billions of years ago. This technique is sometimes used on some White Diamonds simply to improve their appearance and in others where there are impurities of nitrogen trapped within the gem, it turns them a wonderful yellow to yellowish green colour.
This is the most common form of treatment for coloured Diamonds and it is similar to the process that has been used to turn seemingly colourless Topaz into wonderful Swiss and London blues. A similar treatment was first discovered in 1904 when Sir William Crookes, who was a chemist by trade and gemstone collector by night, discovered that you could change the colour of a Diamond by using radiation.
How does it work? Well, whereas natural coloured Diamonds receive their colour from impurities, irradiation promotes changes in the gem’s atomic structure.
There are four slightly different processes currently used by the gemstone industry to irradiate Diamonds: all are safe and the majority of irradiated Diamonds on the market today have been treated in very expensive laboratories in New York. The colours from the irradiation process tend to be very dark and in fact nearly all Black Diamonds are treated by irradiation and heat. In1950, scientists realised that after the irradiation process had been completed, if you then heat treated (known as the ‘annealing’ process) the gemstone, beautiful, lighter shades could be formed. The overwhelming majority of Blue, Red, Green and Orange Diamonds on the market today have undergone this dual process.
One thing my good friend Rahul tells me (he owns Lotus Colors Inc; one of the largest coloured Diamond companies in the USA) is that when you put Diamonds through this process, as you are not introducing any other elements in the way you would with gemstone diffusion, you never know what colour the Diamonds will be at the end of the process!
One of the few colours that cannot be created by HPHT or Irradiation is pure pink. Therefore a few years ago there was a vast amount of development undertaken by a few USA Diamond suppliers to create a coating that turns Diamonds pink.
Once they mastered the technique, as it is impossible to predict what colours will be produced from the irradiation process, in order to fulfil customer orders for specific hues and tones, they also started to coat Diamonds in other popular colours.