Diamonds - the 4 C's
The first of the 4C’s to define, the Carat Weight of the diamond. The carat weight measures the mass of a diamond. One carat is defined as 200 milligrams. The point unit—equal to one one-hundredth of a carat (0.01 carat, or 2 mg)—is commonly used for diamonds of less than one carat. All else being equal, the price per carat increases with carat weight, since larger diamonds are both rarer and more desirable for use as gemstones.
The price per carat does not increase smoothly as the size increases. Instead, there are sharp jumps around milestone carat weights, as demand is much higher for diamonds weighing just more than a milestone than for those weighing just less. As an example, a 0.95 carat diamond may have a significantly lower price per carat than a comparable 1.05 carat diamond, because of differences in demand and due to the rarity of finding gem quality diamonds in larger sizes.
Diamond clarity refers to the quality of diamonds relating to the existence and visual appearance of internal characteristics of a diamond called inclusions, and surface defects called blemishes. Inclusions may be crystals of a foreign material or another diamond crystal, or structural imperfections such as tiny cracks that can appear whitish or cloudy.
The number, size, colour, relative location, orientation, and visibility of inclusions can all affect the relative clarity of a diamond. A clarity grade is assigned based on the overall appearance of the stone under 10x magnification.
Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. However, large clouds can affect a diamond's ability to transmit and scatter light. Large cracks close to or breaking the surface may reduce a diamond's resistance to fracture.
Diamonds with a higher grade of clarity are more valuable, with the exceedingly rare "flawless" graded diamond fetching the highest price. Minor inclusions or blemishes are useful, as they can be used as unique identifying marks analogous to fingerprints. In addition, as synthetic diamond technology improves and distinguishing between natural and synthetic diamonds becomes more difficult, inclusions or blemishes can be used as proof of natural origin.
Diamond colour is graded by comparing a sample stone to a masterstone set of diamonds. Each masterstone is known to exhibit the very least amount of body colour that a diamond in that colour grade may exhibit. When sample stones are compared with the master stone, the grader assesses whether the sample has more, less or equal colour to the masterstones.
Grading laboratories will possess a complete set of masterstones representing every colour grade. However, an independent grader working in a retail shop will possess a range of masterstones that covers only the typical grade range of colour they expect to encounter while grading. A typical grading set of masterstones would consist of five diamonds in two grade increments, such as an E, G, I, K, and M. It is not common for a grader to possess a D masterstone, as the E masterstone is more useful in dividing the D and E colour grades. The intermediate grades are assessed by the graders judgement.
Diamonds in the normal colour range are graded loose, with the table facet facing downward and pavilion side upwards. When colour grading is done in the mounting, other techniques will apply and the grade will usually be expressed as a range (for example F-G)
"D" colour has a unique "icy" look to it. Diamonds that rate toward the colourless end of the range are sometimes known as "high-colour" diamonds, and those toward the other end, "low-colour" diamonds. These terms refer to the relative desirability (as demonstrated by market prices) of colour grades, not the intensity of the colour itself.
A diamond's cut has the greatest influence on its sparkle and brilliance. Cut not only refers to the shape of the diamond, but more importantly to its proportions. When assessing a raw diamond, an experienced diamond cutter will determine which shape best suits the stone. The shape chosen determines the number of facets a finished diamond will have. Light reflects through the facets producing its brilliance.