Coloured Diamonds have never been more in demand, however less than two percent of the world’s Diamond production is considered fancy-coloured. While every colour is therefore rare, the most difficult hues to source are Red, Green and Blue. Finding stones with the ideal medium to medium-dark tone is even rarer, and it’s important to remember that even then, no Diamond’s colour will ever rival the intense saturation found in the world’s best Rubies, Emeralds or Sapphires.
Truly colourless Diamonds are made up of a hundred percent pure carbon. However, most Diamonds, regardless of whether you can see it with your eye not, contain some amount of Yellow, Brown, or Grey. Like coloured gems, the colours that can be found in Diamonds are often due to trace elements. For example, just as trace iron can turn a Sapphire Yellow, nitrogen will make a Diamond Yellow. A distortion in crystal structure, sometimes referred to as a “colour centre” can also create a new hue, or very commonly, be the result of a combination of both conditions.
While “colourless” Diamonds are graded on a D-Z scale, with D-graded Diamonds being extremely rare and completely colourless, coloured Diamonds graded as having more colour than a Z-grade are considered "fancy colours" and graded on their own scale.
What are Yellow Diamonds?
Yellow Diamonds get their sunny colour from the most prevalent trace element found in Diamonds: nitrogen. These are considered Type I Diamonds and make up over ninety-five percent of world’s Diamond supply. Most of the stones in this category contain a lot of nitrogen and yet are still near colourless. These are considered Type Ia. More rare are Type Ib gems, which are Yellow Diamonds with a more scattered nitrogen atom pattern, which tends to create a more saturated Yellow colour that is more likely to be on the “fancy” colour grade scale. When shopping for Yellow Diamonds, beware that many are cut with deeper proportions than is considered ideal in order to increase the saturation of their colour face-up. This means that their carat weight will often be heavier than their face-up size appears, which can sometimes offer less value for your money.
What are Red Diamonds?
Red Diamonds are by far one of the rarest gems on Earth. Often caused by a distortion in their crystal structure, or more commonly, internal “graining” which occurs while they grow. The latter is mostly responsible for Pink Diamonds. The more graining the Diamond incurs, the more Pink it will be. While Pink Diamonds were once very difficult to source, and remain so today, the Argyle Mine in Australia was once a very fruitful source that created a very strong market. However, it has since closed. While a true Pink gem is generally more sought-after than Purplish-Pink or Orangish-Pink, true Orange Diamonds are also considered one of the hardest hues to source, and while their colour is likely a combination of multiple factors, scientists are still not completely sure how they get their beautiful fiery shades.
What are Blue Diamonds?
Blue Diamonds are also one of the rarest colours, and are mostly a result of trace amounts of boron. Like the Hope Diamond, these Diamonds are considered Type IIb, and very interestingly can also conduct electricity! (Diamonds which are truly colourless and contain little to no nitrogen, like the Cullinan, are considered Type IIa.) The more boron a Diamond contains, the more Blue it will be, however many Blue Diamonds also contain a lot of Grey. Very rarely, Greyish-Blue stones can also be caused by trace amounts of hydrogen.
What are Green Diamonds?
Green Diamonds are so rare, that they are most often found in very light saturations only, and generally considered more Yellowish-Green. While many Green Diamonds on the market are the result of treatment, natural Green Diamonds can occur when Diamond deposits are formed near radioactive rocks, which causes atoms to be displaced from their crystal structure.
What are Brown Diamonds?
Brown Diamonds are the most common and were the first known Diamonds to be used in jewellery by the Romans as early as the 2nd Century BC. Depending on their saturation, they have the benefit of sometimes having a Pinkish tint, and get their colour from the same internal graining as Pink Diamonds.
What are Black Diamonds?
Once used mostly for industrial purposes, Black and Grey Diamonds have become more fashionable in recent decades. They often owe their colour to graphite inclusions or a high amount of hydrogen, and when not cut as completely black, can sometimes be marketed as “salt and pepper” or even "galaxy" Diamonds. When shopping for these stones, it’s important to ensure that they do have surface-reaching inclusions or other clarity characteristics that will affect their durability long-term.