In purchasing a diamond, you will hear of the four Cs – Cut, Color, Clarity, and Carat-Weight.
Cut determines how light is reflected. A well-cut diamond will reflect the light and refract it back out to your eye. Because cut determines the brilliance of the diamond, it should never be compromised. Cut also refers to the number of facets that a diamond has. For example, the most common cut, the round brilliant, has 58 flat, polished facets that reflect the maximum amount of light. This diagram shows the different aspects of a diamond that determine its cut.
Diamonds are cut using a mathematical formula to ensure that the top and bottom of the diamond are proportional. Poorly cut diamonds will be too shallow or too deep, affecting the way light travels through the diamond. An ideal cut diamond ensures that the light entering a diamond reflects precisely from facet to facet, and then bursts back through the top to your eye, creating the sparkling brilliance that you expect from a beautiful diamond.
The Color of a diamond actually refers to its lack of color. A colorless diamond is graded on a scale from D through Z, D being colorless and Z having a yellow or brown appearance. The less color a diamond has, the more rare and valuable it is. The diamonds below show the range of colors. The diamond on the left is considerably more valuable than the diamond on the right.
In addition, diamonds are available in a wide range of colors. These diamonds are called Fancy Color Diamonds and range from the faintest pastel pink or yellow to deep shades of green and or orange. The more vivid a colored diamond the more valuable it will be. Fancy color diamonds are graded on two factors, hue and intensity. When grading fancy diamonds, the Gemological Institute of America uses nine grade categories: Faint, Very Light, Light, Fancy Light, Fancy, Fancy Dark, Fancy Intense, Fancy Deep, and Fancy Vivid.
Internal and external flaws in a diamond affect its clarity by interfering with the passage of light throughout the stone. Imperfections such as spots, lines, or bubbles are referred to as inclusions. The fewer the inclusions, the more valuable the diamond. Clarity is graded on a scale ranging from flawless (FL or IF) to imperfect (I). A flawless diamond has no visible inclusions under 10x magnification.
Carat-Weight does not, as many people believe, refer refers to the size of a diamond. Instead, carat is the term used to measure a diamond's weight. Normally, a larger diamond will weigh more. However, if a diamond is cut poorly you will be paying for extra weight, not for a larger brighter diamond.