The Four C's
In the twentieth century, gemologists have developed methods of grading diamonds and other gemstones based on the characteristics most important to their value as a gem. Four characteristics known informally as The Four Cs are now commonly used as the basic descriptors of diamonds - Carat, Cut, Colour, and Clarity.
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 cut of a diamond describes the manner in which a diamond has been shaped and polished from its beginning form as a rough stone to its final gem proportions. The cut is graded from 0–10 on the basis of how well the diamond handles the light coming into it from above, with 0 being perfect and 10 giving off less sparkle.
Often diamond cut is confused with "shape". Here are some of the most common diamond shapes:
The finest quality as per colour grading is totally colourless, which is graded as a D colour diamond across the globe, meaning it is absolutely free from any colour. The next grades, E or F colour diamonds, have a very slight trace of colour, which can be observed by any expert diamond valuer/grading laboratory. However when studded in jewellery these very slight coloured diamonds do not show any colour.
Slightly coloured diamonds are graded as G, H, I or J colour diamonds. A diamond can be found in any colour in addition to colourless. Some of these coloured diamonds, such as pink, are very rare.
Clarity is a measure of internal defects of a diamond called inclusions. 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.
Diamonds are graded by the major societies on a scale ranging from flawless to imperfect.
- FL - Flawless
- IF - Internally Flawless
- VVS1, VVS2 - Very Very Slightly Included
- VS1, VS2 - Very Slightly Included
- SI1, SI2 - Slightly Included
- I1, I2, I3 - Included
Diamonds become increasingly rare when considering higher clarity gradings. Only about 20% of all diamonds mined have a clarity rating high enough for the diamond to be considered appropriate for use as a gemstone; the other 80% are relegated to industrial use.
Most inclusions present in gem-quality diamonds do not affect the diamonds' performance or structural integrity. When set in jewellery, it may also be possible to hide certain inclusions behind mounting hardware such as prongs in a way that renders the defect invisible. However, large clouds can affect a diamond's ability to transmit and scatter light. Large cracks close to or breaking the surface may increase the likelihood of a fracture.