In most diamonds, this term actually refers to the absence of colour. The less colour in the stone, the more desirable and valuable it is. The GIA (Gemological Institute of America) D to Z colour-grading scale is the industry’s most widely accepted grading system. The scale begins with the letter D, representing colourless, and continues, with increasing presence of colour, to the letter Z. Many of these colour distinctions are so subtle that they are invisible to the untrained eye; however, these distinctions can make a very big difference in price.
Clarity refers to the absence of inclusions and blemishes. Natural diamonds are the result of carbon exposed to tremendous heat and pressure deep in the earth. This process can result in a variety of internal characteristics called inclusions and external characteristics called blemishes. Grades run from ‘Flawless,’ with virtually no imperfections, to ‘Included,’ which contain a significant number of imperfections. Evaluating diamond clarity involves determining the number, size, relief, nature, and position of these characteristics, as well as how these affect the overall appearance of the stone. While no diamond is perfectly pure, the closer it comes, the higher its value.
This is not a reference to a diamond’s shape, but to the proportion and arrangement of its facets and the quality of workmanship. Diamonds are renowned for their ability to refract light and sparkle so intensely. We often think of a diamond’s cut as shape (round, baguette or princess), but a diamond’s cut grade is really about how well a diamond’s facets interact with light. The amount of brilliance, sparkle and fire in a diamond is determined by cut. Precise artistry and workmanship are required to fashion a stone so its proportions, symmetry, and polish deliver the magnificent return of light only possible in a diamond. Its cut is crucial to the stone’s final beauty and value and of all the diamond 4Cs, it is the most complex and technically difficult to analyse. Grades range from ‘Excellent’ to ‘Poor.’
Not so much a measure of a diamond’s quality, carat is actually a measure of its weight. A metric “carat” is defined as 200 milligrams. Each carat (written 1.00ct) can be subdivided into 100 ‘points’. This allows very precise measurements to the hundredth decimal place. A jeweller may describe the weight of a diamond below one carat by its ‘points’ alone. For instance, the jeweller may refer to a diamond that weighs 0.25 carats as a ‘twenty-five pointer.’ Diamond weights greater than one carat are expressed in carats and decimals. A 1.08 carat stone would be described as ‘one point zero eight carats’. All things being equal, diamond price increases with carat weight, because larger diamonds are more rare and more desirable. However, two diamonds of equal carat weight can have very different quality and price when the other three Cs are considered, so it’s important to remember that a diamond’s value is determined using all of the 4Cs, not just carat weight.
Diamonds in the normal colour range are colourless through light yellow and are described using the industry’s D-to-Z colour-grading scale. Fancy colour diamonds, on the other hand, are yellow and brown diamonds that exhibit colour beyond the Z range, or diamonds that exhibit any other colour face-up. These rare specimens come in every colour of the spectrum, including, most importantly, blue, green, pink, and red.
Diamonds in the D-to-Z range usually decrease in value as the colour becomes more obvious, whereas the opposite happens with fancy colour diamonds: their value generally increases with the strength and purity of the colour. Large, vivid fancy colour diamonds are extremely rare and very valuable. However, many fancy diamond colours are muted rather than pure and strong.
Fancy colour diamonds come in almost any colour you can imagine. Red, green, purple, and orange are generally the most rare, followed by pink and blue. Yellows and browns are the most common fancy colours, but they’re generally less valuable than the rarer colours.