The Girlfriend's Guide to Jewellery

by Anne Wallner Rss
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20: The Language of Diamond Grading

Diamonds are described in terms of what we refer to as the 4 C’s: cut, colour, clarity and carats weight. These days, now that Canada is the world’ s third largest producer of diamonds, by weight, some us want to say we need ‘Five C’s’: cut, colour, clarity, carat weight and of course, Canadian! For now we’ll settle on those original four C’s as they are listed on grading charts. We will look at them in their order of impact on a diamond’s beauty and the language used to describe and quantify them.

There are two primary diamond-grading systems used and recognized around the world. One system has been developed by the American Gem Society (A.G.S.) and the other by the Gemmological Institute of America (G.I.A.). Each of these grading systems assigns a cut, colour and clarity grade to a diamond and verifies the weight of the loose stone. It should be noted that grading reports or ‘certs’ as they are known do not assign dollar values to stones; they are grading reports only. Grading reports or certificates from both the AGS and the GIA are very highly regarded and are recognized around the world.

The AGS system is used exclusively on loose diamonds. It is a three part numerical grade with ‘0’ being the highest grade and 10 the lowest in each of the three categories of cut, colour and clarity. The fourth C is carat weight, which is not subject to grading.

The GIA system may be used on both loose and set diamonds. It is noted on the appraisal if the stone was graded loose or set. Each category of cut, colour and clarity has its own grading scale. The scale for grading cut runs from Ideal as the highest grade through Excellent, Very Good, Good, Fair and Poor at the low end. The colour scale runs through the alphabet starting at D for a colourless grade through to Z, each subsequent letter grade indicating slightly more body colour that the one before it. The clarity grades start at Flawless at the high end and run through Internally Flawless, VVS 1 and 2, VS 1 and 2, SI 1 and 2 and I 1 and 2 at the low end.
We do see diamonds of lower quality than are described by these definitions but they are generally not considered to be of ‘gem quality’.

While a grading report includes a cut, colour and clarity grade as well as the weight of a loose diamond an appraisal does this and goes one step further to include a value. An appraisal will include the combined value of the stone and the setting. On a set stone an appraisal will include the value stone and of the setting. The GIA system may be used on both loose and set diamonds and as such is the grading system used on most finished jewellery appraisals. An appraisal describes the quality of gemstones, considers the value of the setting and assigns a combined value to them.

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