Of the 4 Cs, the cut has the greatest effect on a diamond's beauty. In grading, cut evaluates the cutter's skill in the fashioning of the diamond. A diamond has facets that allow light to enter it, become refracted, and exit in a rainbow of colors. A more well-cut diamond does a better job of showing off its dazzling beauty, because having the correct proportions will more effectively refract light out the top of the stone to the viewer's eye.
Diamonds have the unique ability to manipulate light very efficiently. This ability is maximized only by cutting and polishing the diamond to an extremely high level of precision. This also requires that the cutter is willing to put forth a great deal of time and effort, adhere to very strict geometric standards and, most importantly, be willing to sacrifice carat weight for superior craftsmanship. The American Gem Society Cut Grading System considers not only the proportions of a diamond, but also the craftsmanship of its overall symmetry and polish. It is unique in that it uses the latest in technology to analyze the cut’s impact based on the diamond’s light performance.
