How is The Cut of a Diamond Graded?

Determining a diamond's cut grade, however, goes beyond simple measurements of width and depth. Using an optical measuring device, a three-dimensional model is created to determine the diamond's proportions and angles.

The interrelations between these various dimensions will greatly affect how light reacts once it enters the diamond and how it behaves once it exits the diamond. By using sophisticated computer modeling, it is possible to trace light behavior and measure its levels of brightness, fire and scintillation - the face-up appearance of the diamond.

• Diameter: The width of the diamond as measured across the girdle.


• Table: The largest facet of a diamond - the top.


• Crown: The portion of a diamond extending from the girdle to the table.


• Girdle: The thin edge that runs around the diamond - where the crown and pavilion meet.


• Pavilion: The bottom portion of a diamond, extending from the girdle to the culet - which is the tip.


• Culet: The facet at the tip of a diamond. The preferred culet is not visible with the unaided eye (graded "none" or "small").


• Depth: The height of a diamond measured from the culet to the table.

Polish and Diamond Symmetry

Polish and symmetry are two important aspects of the diamond cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the diamond's facets. With poor polish, the surface of a facet can be dulled, and may create blurred or dulled sparkle. With poor symmetry, light can be misdirected as it enters and exits the diamond.

The polish and symmetry grades are clearly listed in each diamond detail page and within the GIA or AGSL diamond grading report. For the most beautiful diamond, look for a symmetry grade of excellent (EX), very good (VG), or good (G) for a GIA graded diamond, and ideal (ID), excellent (EX), very good (VG), or good (G) for an AGSL graded diamond.

Avoid diamonds with symmetry grades of fair (F) or poor (P), as the alignment of their facets may misdirect light so severely that it affects the brilliance of the diamond.

Acting as a prism, a diamond can divide light into a spectrum of colors and reflect this light as colorful flashes called fire. Just as when looking through colored glass, color in a diamond will act as a filter, and will diminish the spectrum of color emitted. The less color in a diamond, the more colorful the fire, and the better the color grade.

• D: Absolutely colorless. The highest color grade, which is extremely rare, without flaws.


• E: Colorless. Only minute traces of color can be detected by an expert gemologist. A rare diamond, without flaws.


• F: Colorless. Slight color detected by an expert gemologist, but still considered a "colorless" grade. A high-quality diamond.


• G-H: Near-colorless. Color noticeable when compared to diamonds of better grades, but these grades offer excellent value.


• I-J: Near-colorless. Color slightly detectable. An excellent value.

Diamonds graded better than H are colorless or near-colorless and their color is typically undetectable to the unaided eye. I and J colors usually have faint yellow color, especially if you place them into white gold or platinum.

These diamonds are graded on a different color scale than white diamonds. Since the scale above ranges from the best to the worst quality in a white diamond, the yellow color in fancy-yellow diamonds cannot be found on this scale.