The GIA is a scientific and educational institution for diamond resource information, and its grading system is recognized worldwide. The cut of the diamond is perhaps the most important of the C's because the quality of the cut is what gives the diamond its brilliance and beauty and strongly contributes to the diamond's value. The cut of the diamond is fashioned by human hands and is the only C that is not determined in nature. Diamond cutters cut and polish diamond rough by hand into objects of beauty. It requires a master stone cutter to fashion an ideally cut diamond.
Facets are the tiny planes on the diamond's surface, which give it sparkle and fire.
The manner in which the facets are angled to each other and the diamond's proportions determine the brilliance, dispersion and scintillation, or its light refraction, display of spectral colors and their movement, respectively. The ideal cut of the round brilliant diamond, as we know it today, is credited to Marcel Tolkowsky, who published his findings in 1919. His proportions for the ideal faceting of the diamond are mathematically driven. The proportions for fancy shape diamonds, such as oval, pear, and marquise, allow for a little more leeway. Therefore, the better cut diamonds will demand a higher value and price.