UK Jewellery Shops

The 4 Cs and how diamonds are graded in a nutshell.

The worldwide standard for certifying diamonds has been developed as the 4Cs method. This stands for the cut, clarity, colour and carat of a stone. By defining these characteristics, these four criteria can be assessed and scientifically validated by laboratories across the globe. The final result of the grading of a polished stone is a certificate or report issued by a gemological laboratory.

One of the main factors in determining the quality of a diamond is its colour. It is deemed acceptable to grade the colour of a diamond both by a trained eye, or a scientific instrument. The final colour can only be decided once it has been cut, as the colour of it as a rough stone may not be indicative of the final results. The optimum colour of a stone is gauged on a scale ranging from colourless (the rarest and most precious) to slightly coloured.

The clarity of a stone is determined by how flawed or flawless it may be. This is determined both on its internal and external characteristics. These characteristics can also help in sorting natural diamonds from synthetic or simulated stones, and identify individual stones, too. Trained gemologists use specific equipment to determine a diamond's clarity, based on the number and size of inclusions, whether it is discernible to the naked eye, and whether it has an influence on brilliance. An initial stone examination will be performed under 10x magnification. There are two key types of characteristic involved with determining the clarity of a diamond: inclusions, and blemishes. An inclusion will be found inside the diamond, whereas a blemish will be on the surface of the stone.

It is an extremely rare stone that is flawless or internally flawless. Common flaws within a diamond are inclusions, which are tiny crystals and minerals embedded in the stone; white grain lines, created by irregular crystallisation; feathering, which form small cracks within a stone; and cleavage, which is cracking without feathering. If hit at the right angle, a stone will split across the cleavage. Clarity can also be affected by enhancements. Although not illegal if declared to the buyer, enhancements to stones affect their clarity. Inclusions may be removed by laser drilling, which leaves a tiny white dot on the surface of a stone and laser trails visible via magnification. Fractures to stones can be disguised by applying filler, which is generally invisible to the naked eye, but can be detected under magnification.

Diamonds are special enough that they have their own unit of measurement - the carat. The weight of a carat has been established as being 200mg, or 1/5of a gram. It is then divided into 100 points per carat. The name is believed to have derived from the seed of the carob tree. Carob seeds of about 200mg were seen as a reliable measure for weighing diamonds before accurate scales for low weights was available. Carat weight is an important measure of the quality and value, and a one-carat stone is exponentially more valuable than a .99 point one. It's worth pointing out that carat weight is not related to the similar sounding karat, which refers to the purity of gold.

The cut refers to the quality of the cutting and shaping of the diamond, not the shape of the stone. The art and ultimate aim of polishing a diamond is to maximise its brilliance and luminosity. A diamond that is cut too shallow or too deep will be less brilliant, and therefore less valuable. The cut is the only factor of a polished diamond's value that is determined by human hands. Cutting diamonds is believed to have originated in the early 14th century, in either India or Europe - we can't be sure which.

Cut stones of 0.25 carats and above can be graded, and are decided by the polish and proportions or symmetry of the stone. Factors affecting a stone's symmetry are its depth, table size, crown angle and height, the angle and depth of the pavilion, the thickness of the girdle and the size of the culet. Trained graders will then evaluate the quality of the cut.

Fluorescence is the light that some diamonds emit when exposed to UV rays. Around a quarter of all diamonds shows some degree of fluorescence, but only a small percentage of these impact their appearance. In over 95% of fluorescent diamonds, the colour seen under UV light is blue. Very rarely, then can also be yellow or white.

The strength of fluorescence has no noticeable effect on the appearance of most diamonds. In plenty of cases, people have been seen to prefer the appearance of diamonds that have medium to strong fluorescence. In rare cases, some diamonds with very strong fluorescence can appear to look hazy or oily. However, overall, a diamond that is fluorescent has the same integrity as one with no reaction to UV.