Diamonds are available in wide variety of colors like yellow, red, blue,
pink, green etc. In general, when we talk about color of diamond, it means
presence or absence of color in White diamonds (graded between 'D' (colorless) to 'Z' (off-white or tinted light yellowish diamond) grade on the
GIA International Diamond Grading Scale.).
However, when tint of color is found to be very intense, then such a diamond is not graded on the scale of 'D' to 'Z'. It is rather placed in the category of Fancy Colored diamond. It is important to note that grading of fancy colored diamond is different from grading of white diamond.
Price of white diamonds decrease with increase in yellow tint, while in case of fancy-colored diamonds price is directly proportional to the intensity of color.
Grading of Fancy Colored Diamond
Fancy color diamonds are extremely rare diamonds and are thus very expensive. Factors like cut, carat and clarity influence little, while intensity and richness of body color plays important role in determining value of a fancy color diamond.
Grading of fancy diamonds involve following 2 steps:
Fancy diamonds are graded by GIA under nine categories:
Among all fancy-colored diamonds yellow diamond is most common while red, green, blue and pink are extremely rare.
Fancy yellow diamond color grading
You may also like to read about how diamond gets its color.
How is color of fancy-colored diamond described?
Fancy color diamonds are available in various colors. To describe the diamond’s color, it requires combination of basic or dominant hue (primary color) name and any modifier hue (secondary color) name that might be necessary. For e.g.:
Synthetic or Treated Fancy Colored Diamond
Natural fancy colored diamonds are rare and expensive. So, colored diamonds are also produced artificially just like Synthetic Diamonds. The artificial coloring of diamonds can range from permanent and stable to temporary that fade over the period of time.
Although at times temporary coatings are
also done to enhance the beauty of diamond. In this process very thin layer of chemicals and plastics is coated over diamond to mask undesirable body color of diamond.
Other techniques of color treatment - like HTHP (high temperature high pressure) and Irradiation - are also used to enhance the color of natural colored diamond so that diamond fetches higher price.
These techniques can lighten or darken or completely change the color of diamond. Through HTHP color enhancement process, diamond can be made colorless to pink, yellow, blue or green. HTHP-treated diamonds are very difficult to be detected without the aid of advance lab equipments.
Heat treatments can turn yellow and brown diamonds into fancy colored diamonds like intense yellow, red, blue, green.
Remember that, it’s the jeweler’s responsibility to inform the customer of any treatment done on the diamond and if the diamond requires special care for handling or cleaning.
Advanced gem grading labs - like GIA - don't issue grading reports to diamonds subjected to temporary color treatment (coating). For HTHP color treated diamonds, they issue report with clear mention of color enhancement, along with laser inscription on girdle of diamond to identify it as HTHP color treated.
Fluorescence in Colored Diamonds
When diamonds are exposed to ultraviolet (UV) light, it excites the electrons in diamond which in turn leads to absorption of energy. Now, in order to return back to their stable state, these electrons need to release the absorbed energy. The absorbed energy is released in the form of visible blue light (sometimes of other color), which is called Fluorescence.
Fluorescence comprises of different colors like blue, green and orange although blue is the most common color. Effect of fluorescence on colored diamond depends on the color of fluorescence and on the basic body color of diamond.
While, fluorescence has negative effect on the value of white diamond (Presence of fluorescence in white diamond), in case of fancy diamond, it has a positive effect as it enhances the diamond’s appearance. It adds extra glow to the diamond’s color.
Famous Fancy Colored Diamonds
It’s true that fancy color diamonds have gained popularity in recent years. But some large fancy colored diamonds have interesting history associated with them, making them famous like The Golden Jubilee or infamous like The Blue Hope.
Fancy colored diamonds - mainly yellow, blue and pink - are highly valued and rare assets. Found randomly across diamond mines around the world, these gems are adored equally by gem-collectors and high-end jewelry buyers.
According to Fancy Color Diamond Index, the price of fancies (especially yellow, blue and pink) has since 2005 shown drastic appreciation (167% as of 2014) in value, outperforming other assets in the same time period.
It was found that both blue and pink were apparently unaffected by global financial crisis, with blues keeping their value and price of pinks increasing in that period (2008 - 2010). You may read this article for more on Fancy Color Diamond Index.