Natural fancy coloured diamonds are very rare and expensive. Blue is one of the rarest and most desirable colours. The Hope diamond, which can be viewed in the Smithsonian Institution in Washington D.C. is the most famous blue diamond in the world and the largest at 45.52 carats.
The attempted Millennium Dome Diamond Robbery was an attempt to steal 12 large diamonds valued at a total of £200 million, an average of over £16 million each. Eleven out of the twelve diamonds were fancy coloured blue diamonds! The twelfth (non-blue) diamond weighed 203 carats.
Is It Natural?
Natural Blue diamonds are so rare that most jewellers have never seen one and will never own one. In recent years, methods of producing intensely coloured diamonds, including fancy blue, have been developed. The process probably recreates the conditions which existed millions of years ago to produce natural fancy coloured stones. The treatment can only work with a small minority of diamonds and involves irradiating them causing the colour change, usually followed by heat treatment to stabilise the colour.
Blue diamonds can be enhanced or treated. If this fact puts you off owning one, then please stop to consider that every diamond has been enhanced by facetting and most coloured gemstones are heat treated to enhance their colour.
Quality for quality, fancy blue diamonds are more expensive than ordinary near-colourless ones. The processing adds to the costs so it is generally only worth treating diamonds of high clarity. The diamonds selected for treatment usually start off a one of the less desirable colours such as brown or yellow. There is no certainty about the final colour that any particular stone will be after treatment.
What About Sapphires?
Why bother to get so excited about blue diamonds, when we could use sapphires instead? The very best sapphires are quite expensive and they still do not have the sparkle that blue diamonds possess. In addition even though sapphires are very hard and durable, diamonds are many times harder and even more durable.