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A diamond is like a prism that divides light into an array of colours. A colourless diamond allows more light to pass through it than a coloured one and it goes without saying that the less colour a diamond has, the better its diamond grade.
The ideal diamond is a colourless one and is the most rare and also the most expensive. “D” is the highest grade given to a colourless diamond.
Colour is the result of a diamond's composition and this stays constant over time. It can be said that a colourless diamond is like a clear window which permits greater light to pass through it than a diamond which has colour.
Also of interest is the fact that diamonds may be artificially modified. However, in such an event, this must be mentioned under the section: “Comments” on the diamond’s certificate. (Express Diamonds do not carry artificially enhanced diamonds).
The differences in colour of diamonds are subtle and over 90% of gem diamonds have a basically yellowish colour.
As mentioned diamonds graded “D” are of the highest value because of their lack of colour. “E” and “F” grades follow and once again these grades are noteworthy.
“G”, “H”, “I”, “J” colour grades are excellent grades in value too and have no noticeable colour to the untrained eye. “K”, “L”, “M” colour grades are faint yellow diamonds.
“N”, “O”, “P”, “Q”, “R” are very light yellow diamonds.
“S”, “T”, “U”, “V”, “W”, “X”, “Y”, “Z” are light yellow diamonds.
It can be said that, diamonds graded “D” through “F” are the most valuable because they are rarer. These diamonds are highly desirable, however, attractive diamonds can still be purchased at grades slightly less than colourless.
Again it should be noted that diamonds graded "G" through "I" demonstrate no colour to the untrained eye.
Coloured diamonds are rare to find. Coloured diamonds are formed when the chemical composition of molten mass is not the same everywhere. During the composition process, minor changes occur in the chemistry of the diamond, thus creating coloured diamonds.
Coloured diamonds include: black, pink, purple, red, yellow, green, blue, brown, champagne, orange and cognac.
Coloured diamonds are very attractive and because they are rare, they are highly desirable and in great demand.
In regard to price, this is determined by the concentration of colour in the diamond. For example, intense pink diamonds are very valuable gems. At the 1989 Christie's auction in New York, a 3.14 carat Argyle pink diamond sold for $1,510,000.
The Argyle Mine in Australia, is the world's biggest diamond mine and it produces rare pink diamonds as well as beautiful cognac and champagne coloured diamonds.
Blue is another rare and desirable colour. In recent years, methods have been developed to produce intensely coloured diamonds. Treatment involves irradiating the diamond to bring about colour change. This process is followed by a heat treatment to stabilize the colour. However, even enhanced (treated) diamonds are difficult to find.