Grading of fancy colour diamonds is a complex and specialized process. To complete the grading accurately you will need highly trained graders from authorized laboratories such as the GIA (Gemological Institute of America).
In diamonds, colour rarity equals the value.
When talking about white diamonds, the value is based on the absence of colour, meaning colourless diamonds are the rarest.
When it comes to fancy colour diamonds, the most valuable colours are rich pinks, blues and greens. Diamonds with red, green and blue medium to dark tones are extremely rare. Even very slight colour differences can have a big impact on the price of fancy colour diamonds.
Diamonds with a noticeable hint of any other hue than yellow and brown are considerably rarer. Even in light tones, as long as they show colour, they are qualified as fancy colour diamonds. For example, GIA fancy colour diamond colour-grading system is designed to accommodate the fact that not all coloured diamonds have the same saturation.
Diamonds with red or reddish colours, also known as “rose-coloured” are extremely rare and very highly valued. In this range, pure pinks are more popular than diamonds that are orangy, purplish “mauve”, greyish or brownish.
It’s worth mentioning blue diamonds as well. They are extremely rare and generally have a slight hint of grey. Their colour is caused by the presence of boron impurities, meaning the more boron, the deeper the blue colour.
Green diamonds are typically light in tone. Their colour is often muted with a greyish and brownish cast. Green diamonds get their colour when radiation displaces carbon atoms from their normal position in the structure. This can happen naturally when diamonds deposit lies near radioactive rocks or artificially as a result of treatment.
Brown is the most common fancy diamond colour. Brown diamonds range in tone from very light to very dark. They were considered good only for industrial use until the 1980s when they began to appear in the Argyle mines, Australia. For marketing purposes, the Australians gave them names like “cognac” and “champagne”. Nowadays, brown diamonds are popular in many mid-level jewellery designs.
The second most common fancy colour of diamonds is yellow. In trade yellow diamonds are called “canary” for the same marketing purposes.
Fancy white and grey diamonds. Yes, they also exist. White ones have milky white colour and display beautiful flashes. Greys are getting popular for vintage style jewellery designs. The grey colour is probably caused by a high consistency of hydrogen as an impurity element.
Colour is the most dominant value factor when talking about fancy colour diamonds. Even diamonds with many inclusions that are of low clarity grade are highly prized if they are fancy colour. The only reason which can lower the diamond’s value is inclusions that threaten the gem’s durability.
Size and shape can influence a fancy diamond colour. The larger a diamond is, or the deeper is the pavilion, the richer and more intense the colour is.
In general, large fancy colour diamonds are rarer and more valuable than small ones, which is also true for all other diamonds.