If, like most people, you think that diamonds are colorless, you won't always be right. In fact you'll be right about only a very few, very expensive stones. Diamonds are the most highly prized gemstones in the world, but there's much more variation among them than meets the eye of the casual observer.
Ask an expert what color a diamond is and he'll answer you with a question: what diamond? That's because diamonds come in a whole range of colors. We're not talking here about fancy diamonds, the pink, blue, green or canary yellow gems which are highly prized among collectors. We're talking about one of the most important characteristics of a diamond when it comes to putting a value on it.
Diamond color is one of the four criteria for evaluating diamonds which are known as the four Cs. The other three are cut, carat and clarity. These are the properties which define a diamond and which determine the price at which it is sold.
So just how is diamond color evaluated? The most common way is by use of the color scale introduced by the Gemological Institute of America in the 1940s. This cut through a lot of confusion which had earlier existed when various producers and dealers used their own systems. The industry welcomed the GIA scale as a way of standardizing diamond color grading.
The GIA color scale ranks diamonds on a scale from D to Z. At the top end of the scale is the D grade which is the highly prized colorless diamond. Moving down the scale, man made diamonds the stones become progressively more tinged with yellow, until the bottom grades where the diamond are very clearly yellow, but not yellow enough to be sold as a fancy diamond.
When experts want to establish a grade of diamond color, they use a calibrated set of master stones for comparison. Each of these conforms exactly to a grade on the GIA diamond color scale. Diamond color grading is difficult because the light dispersion, the sparkle and brilliance, can confuse the eye and make it almost impossible to make this color comparison by looking through the upper facets of the diamond, which are designed to maximize brilliance. Thus the diamond is placed with the under side facing up on white paper and examined through the base in standardized lighting. This precision is important because the nuances in diamond color between the top grades of diamonds are very slight.
We think of diamonds as pure carbon crystal, but very few diamonds are really pure and it's the impurities that account for variations in diamond color. Almost all diamonds have nitrogen atoms dispersed throughout the stone and, because nitrogen absorbs blue light, this gives the diamond a yellow appearance. Only the top, D grade, diamonds are absolutely colorless, but E and F grades are also referred to as colorless and the difference will not be apparent to the untrained eye. Even stones as low as G or H grade on the diamond color scale will appear white unless directly compared with a higher grade.
