Diamond grading is to a customer what the state of Nirvana may have been to Buddha, and meant to bring peace of mind.
Laboratories grade polished diamonds for diamond dealers and retailers, who are its primary customers. The bad news is many independent labs internationally offer over-grading services for a fee and not many consumers learn this because diamonds are bought as jewellery or investment and rarely resold for liquid cash at market value. Unfortunately, many consumers, although familiar with the grading language, are not cued in on the nuances of diamond grading.
A diamond is graded on its 4Cs — Carat, Clarity, Colour and Cut with colour and clarity grading being a qualitative, or subjective assessment with most impact on price.
The Four Cs
Diamond carat weight is the most objective assessment as a one carat weight, equal to about 200 milligrams, is subdivided into 100 points, to provide precise stone weight. It is the only parameter which is expected to remain constant across laboratories. The diamond price generally increases with carat weight as larger diamonds are rarer. However, a stone with a clean weight, like one carat or half carat cost more. Thus other factors being equal, a clean one carat stone may cost more than a 1.10 carat diamond, even though you cannot perceive the difference.
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Diamond clarity is graded on the absence of inclusions or imperfections and flaws as seen under 10 x magnification and is a qualitative assessment. The GIA grades diamond clarity on a 11 point scale ranging from Flawless, the highest grade to Included, which has three levels, with I3 being the lowest grade and the most flawed. The grades, Flawless (FL) followed by Internally Flawless (IF), (rarely found), and VVS 1 and 2, upto VS2 are given to diamonds with highest clarity, in which inclusions or imperfections cannot be seen with the naked eye and hence experts call these categories ‘eye clean.’ Even a Slightly Included or SI1 clarity grade, as given by GIA, HRD or AGS labs, will be eye clean half the time and can offer good value.
The HRD lab, however, refers to all stones with imperfections invisible under 10x magnification or eye clean stones, as Loupe Clean plus (LC+). The HRD would thus grade a VVS1 diamond, as certified by GIA and others, as a LC-, thereby including an extra category of grading, which is followed by a VVS2 category.
Like clarity, a diamond is graded for the absence of colour, or colourlessness, which again is a qualitative assessment under controlled lighting and viewing conditions, against a set of master stones of established colour value. This grade ranges through the alphabets from D, the highest grade, to Z, being the lowest grade, as the colours go from colourless to yellow to brown. While D to F is the premium range, a stone graded by a strict laboratory as H, or I, may appear as near colourless to the naked eye, and offers good value for money. Do not go below J colour.
Colour grading by labs like GIA, AGS and HRD is strict, while labs like IGI and EGL are known to be more generous and grade a diamond higher on colour. Interestingly, many labs use machines that can automatically grade colour. Differences in colour grade may arise between laboratories due to variations in colour of the master stones, which need to be regularly boiled and cleaned.
This grade, the most complex to assess, reflects how well a diamond is cut, allowing it to transmit maximum light, which is crucial to its beauty and value. Most laboratories grade the cut for round diamonds, not fancy shaped ones, in which it is more difficult to assess the ideal proportions. The type of cut, like brilliant or step cut, is secondary. The cut scale ranges through five grades from Excellent to Poor. However, the AGS Lab introduced an ‘Ideal Cut’ grade which is one grade higher than the Excellent grade of other labs besides grading the cut on a number scale from 0-10 to allow for finer differentiation.
Based on these 4Cs, laboratories issue a diamond certificate, which includes additional information about a stone’s proportion, polish, symmetry and fluorescence besides a graphical depiction of the location of the inclusions or flaws found in the diamond. A lab also evaluates a stone for any treatment, including fracture filling, usually done to hide the flaws, resulting in a detailed diamond report.
The industry accepts that diamond grading is not an exact science and a difference between labs, one grade up or down in clarity and colour is accepted.