The Four C’s of Diamond Quality – How Jewellery Evaluation Companies Value Gems

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As any and all jewellery evaluation companies will tell you, all diamonds are most definitely not created equal. While every gem is a small miracle in itself, resulting from just the right combination of factors, temperature and a long, long time frame, the price a stone can command relies on many different factors, both natural and man-influenced.

As one of the best trusted and most popular diamond and jewellery evaluation companies in Johannesburg, we are often asked about the valuation process, and our answer is always “it’s all down to the four C’s”.

So what are the four C’s? All jewellers and diamond evaluation companies use this process to determine the worth of a diamond, so it’s worth familiarising yourself with the criteria:


While fancy coloured diamonds are quite popular at the moment and can be exorbitantly expensive, this only applies to extremely strong colours, such as deep blues and reds or very strong, vivid yellows. Perfectly colourless diamonds are still king of this game, with dazzling white being the most sought after. Stones with weak colours are regarded as inferior. The diamond colour scale used by diamond evaluation companies starts at D (perfectly colourless), and runs all the way to Z (light colour), before entering the scale of “fancy” coloured diamonds.


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The majority of mined diamonds are not perfect. Most contain what are known as “inclusions, or small flaws and variations in the stone. An inclusion is often made of specks of uncrystallised black carbon or other elements, and these can usually only be spotted with the use of a magnifying tool. Other flaws which can affect clarity are surface scratches, chips and tiny pits on the diamond’s facets.


carat weight


Carat Weight

Most people will view the size in carats as the ultimate indicator of a diamond’s value, but this is not necessarily the case. Most jewellery evaluation companies in Johannesburg and around the world will tell you that a small, perfectly colourless, flawless and well-cut diamond is far better than a large one that is riddled with impurities and a bad cut. One Carat is equal to 200mg.


Cut is perhaps the most important aspect of a diamond’s value. A good cut can increase the value of an inferior stone, just as a bad cut can ruin the value of a good quality gem. Because of how labour intensive the cutting and polishing process is, as well as the effects that a good or bad cut can have on the final product, this practice often accounts for a large percentage of the final sale value of a diamond.

If a diamond is cut incorrectly, it will fail to sparkle and will not sell. A cut that is too shallow is known as a “fish eye”, and can make the stone look glassy and cheap, with no sparkle and little variation in how the light catches the facets. A cut that is too deep will make the stone look dark and also diminish the sparkle that is so sought after by diamond fanatics.

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If you ask about the four C’s when you’re shopping for diamonds, it is likely that you will make a more informed and wise decision, rather than just focusing on getting the biggest stone you can afford. The creation of the four C’s means that diamond quality can be communicated in a universal language, and diamond customers can now know exactly what they are purchasing.

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