The 4 C's of Diamonds
Diamonds are cut according to an exact mathematical formula. A finished diamond has 58 "facets," which are the small, flat polished planes cut into a diamond, so that the maximum amount of light is reflected back to the viewer's eye. This reflection is called "brilliance," and is extremely important in evaluating the quality of a diamond. Cut also deals with the shape of the diamond. Traditional shapes are round, emerald, marquise, pear, oval and heart.
Brilliant-cut diamonds have 33 facets above the girdle (the crown) and 25 below (the pavilion). They also have specific angles/proportions e.g. the pavilion facets are at a 40 degree angle to the girdle.
Although a diamond may be any colour of the spectrum, grading a cut stone for colour means deciding the amount by which it deviates from the whitest possible (truly colourless). Completely colourless diamonds are rare, and therefore, more valuable. The best way to see the true colour of a diamond is to look at it against a white surface.
Although most diamonds are a shade of white, they do come in all colours - pale yellow, canary, pink, red, green, blue and brown. These are called "Fancy Diamonds" and they are valued for their depth of colour, just as white diamonds are valued for their lack of colour. The famous Hope Diamond is blue, and the well-known Tiffany Diamond is canary.
"Irradiated diamonds" are artificially coloured by bombarding the stones with atomic particles or gamma rays.
A diamond's clarity is determined by taking into account the number, size, placement, colour and nature of any internal "inclusions" or external surface irregularities. Inclusions are nature's birthmarks - imperfections such as spots, bubbles or lines. They were formed in the diamond when it was crystallized from carbon millions of years ago. These marks make each stone unique, for no two diamonds have the same inclusions in the same places.
Whist the fewer the inclusions the more valuable the diamond, it is important to note that the inclusions themselves are the surest basis for distinction between natural minerals and synthetic stones.
Carat - Weight
Carat is the unit of weight used for diamonds, a word derived from the use of carob seeds to balance scales in ancient times. A carat is equal to 200 milligrams and there are 142 carats to an ounce. Carats are further subdivided into points. There are 100 points to a carat. For example, a 45-point diamond weighs a little less than half a carat. Because larger diamonds are quite rare, they have a greater value per carat.
To estimate the carat weight of a well-proportioned diamond, especially if it is mounted (in a ring, for example) jewellers may use a gauge with a series of holes to denote various weights. However, specialist equipment is needed to obtain a more accurate measurement of carat weight.