The cut of a diamond affects how well a diamond returns light back to the viewer's eye, resulting in what we call fire, sparkle or brilliance.
A well cut diamond will appear brilliant and fiery, while a poorly cut diamond may appear dark or lifeless regardless of how good the color or clarity may be. Not only do well cut diamonds have the most sparkle they may also appear larger than a poorly cut diamond of the same carat weight.
The American Gem Society (AGS) has a scale to measure the quality of a diamond cut, ranging from 0 (ideal) to 10 (poor).
Use the scale tool below to see the affect the cut of a diamond has on the reflective capabilities of diamonds.
The pattern of surfaces (or facets) you see on a diamond represents the quality of the cut and has a direct effect on the overall sparkle of the stone. When a diamond is cut to good proportions, light reflects from one facet to another, then reflects back through the top of the diamond. If the cut of a diamond is too deep, some light escapes through the side of the stone. If the cut is too shallow, light escapes through the bottom of the stone before it can be reflected, thus reducing its brilliance.