The Four C's
Color
Most commercially available diamonds are classified by color, or more appropriately, the lack of color. The most valuable diamonds are those classified as colorless, yet there are stones that have rich colors inluding yellow, red, green and even black that are extremely rare and valuable. Color is graded on a letter scale from D to Z, with D representing a colorless diamond.
Carat Weight
In addition to color, clarity and cut, weight provides a further basis in the valuation of a diamond. The weight of diamonds, and all other gemstones, is measured in carats. Smaller diamonds are more readily available than larger ones, which results in higher values based on weight.
Cut
The beauty of a diamond resides not only in a favorable body color, but more importantly in its optical properties, in particular the high refractive index and color dispersion. Only when precisely calculated planes and angles are used in the cut of a diamond does the stone attain its greatest possible beauty.
Clarity
The clarity of a diamond is determined by the number, location and type of inclusions it contains. Inclusions can be microscopic cracks, mineral deposits or external markings. Clarity is rated using a scale which contains a combination of letters and numbers to signify the amount and type of inclusions. This scale ranges from FL to I3, FL being Flawless and the most valuable.