Grading diamonds

Colour The single most important factor in grading and valuing coloured diamonds is the colour of the stone. The colour saturation of the diamond is compared to the lightness or darkness of the colour to determine the grading, or quality of the stone (see table). The stones at the top end of the grading spectrum, such as the intense and vivid grades, are the rarest pieces in the marketplace with the strongest colour saturation and the highest values. Furthermore, the rarer colours that appear less frequently in nature will command a higher value than the more common colours.

GIA Colour Grading Scale

Cut- Cut has the strongest influence on the diamonds brilliance. In a well-cut stone, rays of light entering the diamond reflect back to the eye of the observer. In a coloured diamond, the unique mixture of colour that the viewer experiences is termed face up colour. The cutter of fancy coloured diamonds is an artist using the coloured diamond rough material to create individual masterpieces with perfectly faceted dimensions and a vibrant colour composition. Radiant and brilliant cuts in rectangle, asscher, oval, heart and pear shapes are often used to maximize the colour saturation and enhance the sparkle of the stone.

Carat Weight - The size of a diamond has an impact on its price and is a major factor of rarity. The metric carat, which equals 0.20 gram, is the standard unit of weight for diamonds and most other gems. Coloured diamonds tend to appear naturally in smaller sizes compared to other diamonds and gemstones. In fact, very few pink diamonds from the Argyle mine in Australia are over one carat in size. At last years Argyle tender, the largest pink diamond was 2.03 carats and most of the stones were between a half-carat and one carat in size. Because coloured diamonds have a higher price tag and are more readily available in smaller sizes, there is an active sub-carat collector market for these stones.

Clarity - Diamonds contain minute imperfections called inclusions. The majority of coloured diamonds contain inclusions because of the chemical structure and pressure required to create one. Coloured diamond connoisseurs will acquire a stone based on the colour saturation and consider clarity as a secondary issue. Instead of using a loop to examine the stone, they use different light sources as their guide. The question they ask is: How does the stone look in natural sunlight as opposed to artificial light? The third most expensive stone ever sold was a 0.95 carat red diamond for $926,000 per carat in 1987. This stone was heavily included but because of its rich strawberry colour, it sold for a world record price. A comparable D-flawless diamond would sell for $20,000 per carat.