Most diamonds are colourless or very light yellow, greenish-yellow, yellow, brown or grey. They are called Cape-series diamonds after the first source of diamonds in South-Africa. But it doesn’t mean diamonds cannot have different colours. They can be orange, red, violet, green, blue, purple or black. Intensely coloured diamonds, the so called ‘fancy colours’ – pink, blue, red or green are extremely rare to find in nature, therefore their prices are extremely high. To visualise the rarity of fancy colours imagine that the yearly production of all fancy intense and vivid blue, pink, green, red and purple easily fit in an espresso cup.
According their colour, diamonds fall into one of the two groups:
- White to Cape colours + equivalent colours
- ‘Fancy colours’
White to Cape-coloured diamonds
White to cape-coloured diamonds are most common. 90-95% of diamonds fall in this category. The colours vary from colourless to light yellow (from D colour to Z colour). They are normally graded in laboratories by comparison with reference stones, the so-called master stones.
Diamonds are graded for colour by placing them table down in a V shaped white paper card. This is being done to cancel out the reflection and brilliance of the diamond, this is the only way to make an honest comparison between different stones. Colour grading is done under very white fluorescent light bulbs, the so-called diamond light, this is necessary as the differences between different grades are minimal and a different light source can significantly alter the perception of colour.
I remember a story told to me by my grandfather where a friend of his, also a diamond dealer went to Africa in the 60s to purchase rough diamonds. As he came back, he was extremely satisfied with his purchases and predicted a large profit to be made by reselling the goods he had just bought. Once reached Antwerp he entered our office and proposed him the goods firsthand. Once the goods were on the table the diamond dealer could not believe his eyes. The diamonds were all of much lower colour than he initially remembered, this was because the light in Africa is much brighter and a lower coloured diamond can look whiter than it actually is.
Equivalent coloured diamonds
The equivalent colour diamonds are diamonds that instead of having a light tint of yellow usually have light shades of brown, grey or green, they are graded in the same way as cape-coloured diamonds.
Fancy coloured diamonds
Diamonds in different colours than colourless or lightly tinted ones are called Fancy colours. Once a diamond has a certain saturation of colour it is called a fancy colour diamond. These are beautiful and extraordinary rare stones. The source of colour in fancy colour diamonds has many origins depending on the colour, intensity of colour and their origin in the world. Their colour is assessed on three dimensions: hue (colour of the stone, e.g. blue, purplish-pink), saturation (intensity of the hue, e.g. faint, light, intense, dark) and brightness (the amount of light present).
Fancy colour grading
Fancy colours are differentiated in two different categories, straight and mixed colours. Straight colours are diamonds which after careful analysis contain only one single body colour, for example Fancy Intense Pink. Mixed colours usually contain one or more modifying colours, for example Fancy yellowish green.
The first part of colour analysis is to look for the dominant colour of the stone, once that has been determined the diamond grader will observe the diamond to search for modifying colours in the stone and if found determine the intensity of these colours. It can happen that the saturation of modifying colours are the same as the body colour or that each of the colours have a different saturation. The way coloured diamonds are named is by putting the least saturated colour first and dominant one as last.
- Fancy intense purplish pink and a fancy intense purple-pink.
In the first stone pink is the dominant colour and purple is a modifying colour, in the second stone both pink and purple have the same saturation in the diamond.
- Fancy brownish yellowish green and brownish yellow-green, in the first stone Green is the dominant colour, yellow is a slight modifier and brown is of even lower saturation, in the second stone you have an equal saturation of yellow and green and brown is the modifier.
Fancy colours can have different saturation of colours, they can vary from faint to deep. Not all colours can have all saturations .