The Diamond Guide

A diamond embodies a moment, and the feeling it evokes for the wearer will forever be symbolic of that particular momentous occasion.

There are a host of factors to consider when buying a diamond, including the ‘four Cs’: carat, colour, clarity, and cut. Individually, they are all important, but when combined, they distinguish good diamonds from the very finest gems. Our diamond guide sheds light on the art of diamond grading.


The word ‘carat’ comes from the carob seeds that early diamond traders would use when weighing their diamonds. Today, carat refers to a diamond’s weight, with one carat equal to 0.2g. Carat weight isn’t directly related to size or price: a diamond can be cut deeper or shallower, meaning two one-carat stones can have very different proportions, while price is affected by a combination of cut, colour and clarity, along with the carat weight. Furthermore, certain carat weights – such as one or two carats – are in greater demand, so their price is disproportionately higher than slightly lighter or slightly heavier stones.


Every diamond is unique, and carries its own set of internal ‘birthmarks’ as a result of the chemical processes involved in its creation. These are known as inclusions. Imperfections on the outside of a diamond created during the cutting and polishing process are known as blemishes. The GIA grades a diamond’s clarity on a scale that ranges from Flawless (no internal inclusions or external blemishes) to Included (obvious inclusions, visible to the naked eye). Diamonds with fewer imperfections are rarer and therefore more valuable. Pragnell’s engagement rings only feature diamonds with a clarity rating of SI1 (slightly included) or higher, meaning their inclusions are visible under 10x magnification, but our gemstone buyers ensure they are not visible to the naked eye.


Often used to describe a diamond’s shape, the cut on a GIA certificate actually refers to how well the diamond has been cut and polished. A well-cut diamond reflects light internally and then returns it through the top of the stone, making it look livelier and more brilliant. Diamonds that are cut too deep or too shallow will lose light, making them appear less sparkly and decreasing their value. The GIA also assesses a diamond’s symmetry and balance, and how well it has been polished. The resulting cut grade ranges from ‘Excellent’ to ‘Poor’. Pragnell believe cut is the most important C, as it gives the diamond life; therefore we only use diamonds whose cut is graded ‘Very Good’ or above.


Only a tiny proportion of diamonds are composed of pure carbon – known as Type IIA. These stones are incredibly sought after and valuable. All other diamonds contain varying degrees of nitrogen, which introduces yellow or brown tones to the stone. The GIA grades a diamond’s colour on a scale from D to Z, with D representing pure white, colourless stones, and Z representing yellow-hued stones. Diamonds graded D, E and F are considered colourless and are rarer than diamonds with a lower colour grade. Pragnell’s engagement rings feature diamonds that are graded from D to H. While barely noticeable to an untrained eye, a change of two or three colour grades has a huge impact on a stone’s value: being flexible with colour often means customers can buy a bigger stone for their budget. Furthermore, well-cut stones often appear whiter than their certificate might suggest. That’s why it is important to discuss the various options with an expert.


Every certified diamond comes with a unique report which lists its carat weight and cut, colour and clarity grading, along with the precise measurements of that particular stone. The report includes a diagram of the diamond on which the size, shape and placement of any inclusions or blemishes are marked, along with information about the diamond’s polish, symmetry and fluorescence. This certificate is a guarantee that the stone is a natural diamond, and that it has been cut and polished in line with industry standards. At Pragnell, we look beyond the information on a certificate. Our gemmologists sift through thousands of diamonds to find those whose quality and beauty reflect above and beyond their GIA grading.

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