Selecting a diamond

When selecting a diamond, the following 4C's criteria is used: Nature dictates the characteristics of colour, clarity and carat whilst cut is directly influenced by humans.

Carat

Carat is a standard unit of weight for diamonds. 1 carat = 0.2 grams and 100 points = 1 carat.

The price of diamonds does not increase linearly with weight. There are various weights above which there is a steep increase in value. The most notable transition is at 1 carat where the highest quality diamond will cost significantly more than an equivalent diamond quality weighing 0.95 carats.

Clarity

Clarity relates to a diamond's relative freedom from inclusions and blemishes. These inclusions can comprise cracks, carbon spots, minerals and bubbles and originate when the diamond is forming in the earth. When light enters a diamond it is reflected and refracted out. If there is anything disrupting the flow of light in the diamond, such as a crack, a proportion of the light reflected will be lost. The highest grading is FL (flawless), followed by IF (internally flawless), then VVS (very very slightly included), VS (very slightly included), SI (slightly included) and P (piqué, or included - often visible to the naked eye).

Colour

This refers to the intensity of colour or lack of colour in a diamond. Colourless diamonds are graded alphabetically from D while descending alphabetical letters to Z are assigned to increasing amounts of grey or brown colouration. D colour diamonds are the most valuable in the white range. Colours that fall beyond Z enter into the category of fancy colours. They are assigned descriptive names, such as ’fancy intense yellow’ or ’fancy vivid purplish pink’. With fancy coloured diamonds, the more intense the colour, the greater the value. An intense coloured stone is of much greater value than a D colourless diamond because of its relative scarcity.

Cut

The cut refers to the overall proportions and symmetry in transforming a rough diamond to a polished diamond. These factors affect the brilliance and scintillation (fire) of a diamond. A well cut diamond will reflect light internally from one mirror like facet to another, dispersing it through the top of the stone. Cuts that are too deep or too shallow lose or leak light through the side or bottom, affecting the diamond's brilliance. The most common cut for a diamond is round brilliant, for which specific proportions and facet arrangements have been accepted by the diamond industry.

There are various shapes of diamonds and jewellery designs, including: baguette, emerald, heart, marquise, oval, pear, princess, radiant, triangle, round single-cut and round brilliant.