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Diamond Quality Guide

Dennis Smart FGA, DGA
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Owen Smart Jewellers - London Road Kettering

Your Guide To Diamond Quality

Don't be worried by all the jargon. We'll try to keep it simple:-

The value of a diamond is defined by 4 criteria. These are called the 4 C's:

Carat Weight

As with all precious stones, the weight of a diamond is expressed in carats. One carat (Crt.) equals 1/5 of a gram. A carat is divided in 100 points so that a diamond of 25 points equals 1/4 a carat. The larger diamonds are much rarer and their value increases exponentially with size. A diamond of 1/2 a carat has a approximate diameter of 5.2mm , one of 1 carat 6.5mm and one of 2 carats 8.2mm.

Although the weight of a 0.50 carat is half that of a carat diamond the size difference is only 25%. This is because most of the weight of a diamond is at the bottom part of the stone.


Although the majority of gem diamonds appear to be colourless, others can contain increasing tinges of yellow or brown, some of which are referred to as champagne diamonds.

Diamonds are graded using a colour scale that ranges from 'D' (completely colourless) to 'Z' (tinted yellow). The nearer to "D", the more valuable the diamond.


Almost all diamonds have imperfections - minute traces on non-crystalised carbon or small none diamond crystals, also called inclusions. The clarity grade is based on how many and how pronounced these inclusions are. The drawings below give you an illustration of the qualities.

Most are not discernible by the naked eye and require magnification to become apparent. Inclusions are nature's fingerprint and make every diamond unique. However the fewer there are, the rarer the diamond will be.

Put simply, the fewer blemishes the more expensive the diamond.

Clarity therefore is the term used to indicate the extent to which the diamond is free from these natural inclusions.


Of the 4 C's, cut is the one most influenced by Man. The other 3 are dictated by nature.

The cut or make of a diamond will influence its sparkle, for it is the polisher's skill that releases its beauty. It is the cut that enables a diamond to make best use of light. When a diamond is cut in good proportions, light is reflected from one facet to another and then dispersed through the crown or the top of the stone.

If the cut of the diamond is too deep, some light escapes through the opposite side of the pavilion or bottom.

If the cut is too shallow, light escapes through the pavilion or bottom before it can be reflected.

For further information or guidance please contact us on 01536 513612.