A diamond’s cut is not only about its shape, but how effectively the stone can return light back to the viewer’s eye. A well-cut diamond will appear very brilliant and fiery; while more poorly cut stones can appear dark and lifeless, regardless of color or clarity. Not only do well-cut diamonds appear more brilliant, they can also appear larger than other stones of the same carat weight. An ideal stone has both increased brilliance as well as increased diameter relative to more deeply cut diamonds. The cut-grading system developed and used by GIA applies to standard round brilliant diamonds in all clarities across the D-to-Z color range. It assigns one of five cut grades: Excellent(EX), Very good(VG), Good(G), Fair(F), and Poor(P).
Each and every diamond will have its own unique set of properties and proportions.
Understanding Brilliance, Dispersion ,Scintillation & Finish
Well-proportioned diamonds exhibit three different properties: brilliance, dispersion and scintillation.As light strikes a diamond’s surface, it will either reflect off the table of a polished stone or enter into the diamond. The light that reflects is considered a diamond’s brilliance. Brilliance is the flash of white light one will see when looking at a stone. As light travels into a stone, some of rays are divided into flashes of color, which is called dispersion. Fire is the result of dispersion, which is the separation of white light into its spectral colors. As an observer moves a diamond back and forth, the flashes of color are called scintillation. Grading the cut of a polished round brilliant diamond involves visually assessing these elements as well as measuring the stone’s proportions and considering their relationships to each other. A diamond’s final detailing-its finish-is made up of polish and symmetry. Polish is the overall condition of the diamond’s facet surfaces. Symmetry refers to the exactness of the shape and plcement of the facets. Polish and symmetry affects the diamond cut and can have an affect on its value and brilliance as well.
Putting it all Together
Use this interactive tool to see how depth and table percentages can affect the brilliance in a round diamond. These factors all work together to determine a diamond’s appearance.
Note: this example is for a round diamond only – fancy shapes have their own set of unique preferred proportions.
The most popular shape is the round brilliant diamond. Other shapes are usually referred to as “fancy shapes,” and include marquise, princess, emerald, asscher, oval, radiant, pear, heart, triangle and cushion. Each diamond shape has its own set of guidelines that determine the quality level of its cut.