Clarity refers to a stone’s relative position on a flawless-to-imperfect scale. Clarity characteristics are classified as inclusions (internal) or blemishes (external). The size, number, position, nature and color or relief of these characteristics determine the clarity grade. Very few diamonds are flawless, showing no inclusions or blemishes under 10x magnification. If other factors are equal, flawless stones are most valuable.
Grading color in the normal range involves deciding how closely a stone’s bodycolor approaches colorlessness. Most diamonds have at least a trace of yellow or brown in their body color. With the exception of some natural fancy colors, such as blue, pink, purple or red, the colorless grade is the most valuable. The GIA Diamond Grading System uses letters to represent colors, beginning with D (colorless) and ending at Z (light yellow or brown).
The proportions and finish of a polished diamond are its cutest. Cut can also mean shape, as in an emerald cut or marquise cut. The proportions are the size and angle relationships between the facets and different parts of the stone. Finish includes polish and details of facet shape and placement. Cut affects both the weight yield from rough and the optical efficiency of the polished stone; the more successful the cutter is in balancing these considerations, the more valuable the stone will be.
The metric carat, which equals 0.200 gram, is the standard unit of weight for diamonds and most other gems. A carat weighs about the same as a small paper clip. Just as a dollar is divided into 100 pennies, a carat is divided into 100 “points.” This means that a diamond of 50 points weighs 0.50 carats. But two diamonds of equal weight can have very different values depending on their clarity, color and cut.