The cut of a diamond pertains both to the shape (round, marquise, princess, etc.), and to the make (how well it is cut for proportion and finish). The cut gives each diamond it's unique sparkle and brilliance by allowing the maximum amount of light to enter and reflect back out of the diamond.
While nature determines a diamond's colour, clarity and carat weight, the cut and make are the only factors in diamond grading that are controlled by human hands.
The major diamond shapes are:
While many diamonds appear colourless, or white, they may actually have subtle yellow or brown tones that can be detected when comparing diamonds side by side. Diamonds were formed under intense heat and pressure, and traces of other elements may have been incorporated into their atomic structure accounting for the variances in colour.
The scale for grading ranges from D which is totally colourless, to Z which is a pale yellow or brown colour. Diamonds that are ‘colourless’ (graded D, E or F) are very rare and demand premium prices. The untrained eye will find it very difficult to distinguish between D, E or F grades.
G, H, I and J are ‘near colourless’ and represent excellent value for money. G and H are sometimes called ‘rare white’ and are the most sought after in the ‘near colourless’ group.
The diamond's clarity is a description of its internal purity. With fewer imperfections within the stone, the diamond is more rare and has a higher value. The clarity scale was developed by the Gemological Institute of America (GIA) to quantify these imperfections. The American Gem Society (AGS) uses the same standards as the GIA; however, the AGS uses a numerical system where "0" is the cleanest (GIA "IF") and "10" is the most imperfect (GIA "I3").
All diamonds are systematically graded and plotted under 10X magnification. If a trained grader cannot see a clarity characteristic at 10X, it does not affect the clarity grade.
Five Factors That Determine Clarity
All of the above factors are taken into consideration when a diamond is assigned a clarity grade.
Diamonds and other gemstones are weighed in metric carats: one carat is equal to 0.2 grams, about the same weight as a paperclip.
Just as a dollar is divided into 100 cents, a carat is divided into 100 points. For example, a 50-point diamond weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on the other members of the Four C’s: clarity, color and cut. The majority of diamonds used in fine jewelry weigh one carat or less.