The four Cs are the four characteristics traditionally used to determine the quality and value of a diamond carat, cut, clarity, and color. The characteristics of a diamond are graded and categorized by the diamond industry to establish its retail value. Quality diamonds are often graded by a qualified expert and carry a certificate of authentication. This is typically through a third-party lab such as GIA, EGL or AGS.
A diamond's cut; it's shape and facets- is what makes it sparkle. The more faceted the cut, the grater the sparkle. The most famous shape and cut, according to the Cape Town Diamond Museum, is the round brilliant, with 57 facets.
Other popular shapes include the rectangular emerald (44 facets), the process cut (50or 58 facets), the oval (56 facets), the slender marquise (58 facets), and the pear (58 facets).
Clarity measures the purity of the diamond and the presence (or absence) of tiny flaws. The clearer or more flaw free the diamond, the more brilliant and valuable it becomes. Internal flaws are referred to as inclusions, while external ones are called blemishes. Jewelers and gemologists use a scale from FL (flawless) to VVS (very, very slightly included) to SI (slightly included) to I (included), with number gradations for each category, to rate clarity.
A diamond’s mass, or weight, is measured in carats. A metric carat is 200 milligrams, and each carat can be subdivided into 100 points. Diamonds that are more than one carat are expressed in decimals, as in a 1.25-carat diamond. The price per carat increases according to a diamond's size since large stones are rarer.
Diamonds come in many colors and are categorized as either white—essentially colorless—or fancy. Because distinctions of color among stones are subtle, experience and training are required to color-grade a diamond. These variations make a major difference in diamond quality and price. Depending on the hue and intensity, a stone’s color can either diminish or enhance its value.