There are two scales of grading for a diamond’s colour.
- The degree of ‘whiteness’
- The fancy colour scale
The ’Whiteness’ Scale
The ‘whiteness’ scale plots the relative position of a diamond’s dody colour on a ‘colourless’ to (normally) yellow scale. That is because the carbon atoms most readily react with nitrogen causing the yellowish (or brownish) tones. As we all see colour differently, diamonds are graded in a laboratory against at set of GIA (Gemmological Institute of America) master stones graded D-Z. This scale is believed to start at D as no diamond is truly ‘white’ and some also suggest its ‘D’ for diamond. Diamonds are placed table down and under northern daylight equivalent (no sunlight that is – south of the equator stones will be placed in southern daylight equivalent). The further down the alphabet the more saturation of ‘tone’ is seen. Between each letter slightly more colour is observed. D/E/F however, are still pure ‘white’ is it just the degree of transparency that differs. G/H/I are classed at slightly tinted white. G for example will face up white (due to the brilliance) and only face down as slightly tinted. Most human eyes can begin to detect the colour to the naked eye around ‘H/I.’
For fancy colours the grading is reversed, graded beyond Z at the end of the alphabet it is the hue, saturation and tone that is assessed. Usually in order of rarity yellow, brown, sometimes green, blue, orange and pink, rarely red and purple. Aapproximately only 1 crystal in 10,000 is a fancy colour, therefore they are incredibly rare. The value of fancy colours value determined by fashion too.
The causes of colour vary. As detailed the yellowish, brownish tones are caused by carbon’s reaction with nitrogen, blue is similarly caused by a reaction with boron, green is exposure to radiation (It should be noted this can be an entirely natural phenomenon from the earths’ crust when the diamond has grown near radioactive rocks). Pink is when there is a default or change in the crystal lattice system and lower selective absorption of light. Black is mainly from multiple inclusions.
Fancy Colour Grading
Fancy diamond colour is graded along three different axes. They are hue (the actual colour), tone (the relative lightness or darkness of the colour), and saturation (how strong or weak the colour is).
Hue is most often described as a combination of two or more colours, it can be up to three. When the first colour is listed in an adjective form and the second colour in a noun form (i.e., Orangy Yellow), the first colour is the modifying colour and the second colour is the primary. If they are evenly balanced it will be stated as ‘Orange Yellow’. Pure colour stones are very rare and therefore more valuable.
The saturation of these hues is then described with one of nine descriptors: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark, Fancy Intense, Fancy Deep, Fancy Vivid.
You may have heard of “Champagne”, “Cognac” and “Coffee” diamonds, these actually refer to different types of brown diamonds that have been positioned with more appealing or romantic labels. These terms are not technically used in diamond grading (due to the lack of definitive definition descriptions), I but I believe, has opened up the market to the beauty of all diamonds. To clarify ‘champagne’ diamonds are light brow, cognac is usually used to describe a diamond that is orangish-brown because cognac is a deep golden-orange colour and ‘coffee’ is usually used to describe a diamond that is a deep brown or vivid brown colour.