Quality of a Diamond

The quality of a diamond's cut is widely considered the most important of the four Cs in determining the beauty of a diamond; indeed, it is commonly acknowledged that a well-cut diamond can appear to be of greater carat weight, and have clarity and colour appear to be of better grade than they actually are. The skill with which a diamond is cut determines its ability to reflect and refract light. In addition to carrying the most importance to a diamond's quality as a gemstone, the cut is also the most difficult to quantitatively judge. A number of factors, including proportion, symmetry, and the relative angles of various facets, are determined by the quality of the cut and can affect the performance of a diamond. A poorly cut diamond with facets cut only a few degrees out of alignment can result in a poorly performing stone. For a round brilliant cut, there is a balance between "brilliance" and "fire." When a diamond is cut for too much "fire," it looks like a cubic zirconia, which gives off much more "fire" than real diamond. A well-executed round brilliant cut should reflect light upwards and make the diamond appear white when viewed from the top. An inferior cut will produce a stone that appears dark at the center and in some extreme cases the ring settings may show through the top of the diamond as shadows. Several different theories on the "ideal" proportions of a diamond have been and continue to be advocated by professional gemologists. Recently, there has been a shift away from grading cut by the use of various angles and proportions toward measuring the performance of a cut stone. A number of specially modified viewers and machines have been developed toward this end. They included the FireScope, a.k.a. SymmetriScope or IdealScope (tests for light leakage, light return and proportions), Hearts and Arrows Viewer (test for "hearts and arrows" characteristic pattern observable on stones exhibiting high symmetry), GemEx BrillianceScope (tests for direct light performance results of a diamond), Isee2 Beauty Evaluator (tests for diffused light performance results for round or octagonal diamonds), and ASET (test for AGS cut grade). These viewers and machines often help consumers determine the light performance results of the diamond in addition to the traditional 4 C's. Along with this shift there are a few companies that provide results on these viewers and machines in addition to the original 4c's. The GIA has also developed criteria for grading the cut of round brilliant stones