Essentially the qualities of a diamond are explained by four factors. These four characteristics determine the rarity, the value and of course its beauty and it is important that you understand the 4C's before buying that exquisite diamond.

Cut is the only diamond characteristic directly influenced by man - the other three are dictated by nature.

The cut indicates the physical shape of the diamond, and refers to the angles and proportions a skilled cutter forms in the diamond. It is the cut that causes the light to be dispersed and to reflect from each of the facets.

The beauty of the diamond depends on the way it reflects light, and the cutter must shape the facets in such a way as to admit and reflect the maximum amount of light, so that the diamond sparkles with fire, brilliance and scintillation.

Shape is a matter of personal taste, with the most popular being the round brilliant. Other shapes include the emerald, pear, marquise, princess, oval and heart.

While many people might say that diamonds appear colourless or clear, most contain subtle tones of yellow and brown. Therefore the degree of colourlessness has an influence on its beauty and thus price. For example the completely colourless, icy white diamonds are extremely rare and are priced accordingly.

Diamond colours are graded according to letters of the alphabet, starting at D the exceptionally white and exceptionally rare, right the way through to the letter Z, the tinted yellowy/brown colour.

A diamond's clarity is determined by the degree to which it is free from naturally occurring inclusions, often called 'nature's fingerprints' or the 'diamonds birthmarks'.

These inclusions were formed billions of years ago under the intense heat and pressure, from minerals or gasses, or other gemstones that may have been trapped inside the diamond as it cooled.

These inclusions are usually invisible to the naked eye, but their size, location and number can dramatically affect the stream of light through a diamond, causing the fire and sparkle to be lost.

These inclusions show as tiny specks or crystals that may look like feathers or clouds inside each diamond. However, many are invisible to the naked eye requiring magnification under a standard 10x magnification loupe before they become apparent. The fewer inclusions, the greater the clarity, the rarer the stone and the more valuable the diamond.

As with all precious stones, the weight of the diamond is expressed in carats (originating from a naturally occurring unit of weight: the seed of the carob tree). Diamonds were traditionally weighed against these seeds until the system was standardised. One carat is now fixed at a weight of 0.2 grams.

One carat is divided into 100 points. Therefore a diamond weighing 50 points is half a carat, 25 points a quarter of a carat and so on.

The larger diamonds are much rarer than their smaller counterparts. Indeed hundreds of tons of soil, rock and ore must be excavated in order to uncover a single one carat gem quality diamond, and less than 1% of all women will ever own a one carat or larger diamond.

Size is the most obvious factor in determining the value of a diamond. But remember two diamonds of the same carat weight can have very different values, depending on the cut, colour and clarity so it is important that all four characteristics are taken into account.