T
ake a white diamond. The greater its transparency and sparkle, the higher its value. For coloured diamonds, the opposite is true: their value increases with intensity of colour, red and green being among the rarest hues.
A tripling of value in twenty years
The past two decades have seen a spectacular rise in fancy colour diamond prices. According to the Fancy Color Research Foundation (FCRF)*, since it began collecting data in 2005, the overall index has risen 202.1%. Pink diamonds have increased 389.8%, blue diamonds 239.5% and yellow diamonds 47%.
Even as the market has stabilised, auction results continue to show the extent to which exceptional gemstones can command astounding prices. In May this year, at Christie’s Geneva, the 5.5-carat Ocean Dream set a world record for the highest price paid at auction for a fancy vivid blue-green diamond, when it crossed the block at CHF 13.567 million.
This price surge comes down to the most basic equation: on the one hand, extremely limited supply and, on the other, exponential demand for the rarest stones. The Gemological Institute of America (GIA) estimates that only one in ten thousand diamonds displays sufficiently intense colour to qualify as fancy colour.
Different colours have different origins. This can be the presence of trace elements, for example yellow diamonds are coloured by nitrogen and blue diamonds by boron. Green diamonds, on the other hand, occur through exposure to natural radiation, while the majority of pink diamonds are the result of distortion within the crystal structure. However, nature does only part of the work. It takes a special pair of hands to reveal the beauty contained within a coloured diamond rough.
The fifth C
This is where Paul Chieveley-Williams, of Diamwill B.V., comes in. We met him at the GemGenève fair. This diamantaire, whose passion for gemstones began in childhood, is adamant that a diamond is more than the 4 Cs — colour, clarity, cut, carat — on a certificate. He firmly believes that there is a fifth C: charm.
Behind this subjective and somewhat romantic notion of “charm” lies a complex technical reality: a white diamond and a coloured diamond are cut and polished according to different optical principles.
Paul Chieveley-Williams describes this complex process with a simple analogy: “All the facets of a diamond work in one of two ways: they either serve as windows, letting light in, or as mirrors, reflecting light that has already entered the stone. Sometimes you want to take out colour and sometimes you want to put colour in, and you do this by altering the mirrors and the windows. Mirrors and windows. That’s diamonds. Every facet is one or the other.”
Whereas a cutter aims to maximise the light that leaves a white diamond to produce as much brilliance and scintillation as possible, a coloured diamond must reflect as much colour as possible when viewed from above. Or as Paul Chieveley-Williams explains: “The facet sizes, angles and orientation of a white diamond are designed to make the stone appear as white and brilliant as possible when viewed face up. For coloured diamonds, the opposite applies. Fancy colour diamonds are cut so that the angles and azimuths of the crown and pavilion facets direct the most intense areas of colour towards the culet. This allows the culet facets to act as mirrors, reflecting as much colour as possible when the stone is viewed from above. This is why coloured diamonds are graded face up.”
As Chieveley-Williams reminds us, there is no one set of rules when cutting a coloured diamond: “Every stone is different, every diamond is different, every material is slightly different.” Pink, green, yellow, blue… each colour is the consequence of specific factors and each stone is unique. A stone that’s too dark can need more mirrors that will allow more light and colour to escape. Conversely, a stone that’s too pale needs more internal reflection for more intense saturation.
