The cut of a diamond determines its brilliance. There is no single measurement of a diamond that defines its cut, but rather a collection of measurements and observations that determine the relationship between a diamond's light performance, dimensions and finish. Most gemologists consider cut the most important diamond characteristic because even if a diamond has perfect color and clarity, a diamond with a poor cut will have dulled brilliance. Some of of the more popular "cuts" are the Princess cut (square), Emerald cut (rectangular), Marquise cut, Oval cut and Pear cut amongst others.

	Brilliant cut round - This is the most traditional and popular of all the diamond shapes. It has 58 facets and is cut to maximise the 'fire' and sparkle of the stone. This shape of diamond is most commonly found in solitaire diamond engagement rings.
	Princess cut - This shape has grown in popularity in recent years, providing an excellent alternative to the brilliant cut round diamond and, by having 76 facets, often displaying even more brilliance than its round counterpart. Most commonly found in solitaire diamond engagement rings.
	Emerald cut - The Emerald cut diamond is 'Step-cut' and has rows of facets, usually 48 to 50, that resemble a staircase. The look of an Emerald cut diamond is subtle and understated, with less ‘fire’ than a brilliant cut round diamond, but provides style and elegance. Most commonly found in diamond trilogy rings and more contemporary diamond rings.
	Marquise cut - This takes its name from a legend that the Sun King desired a stone to be polished into the shape of the mouth of the Marquise of Pompadour. It has a total of 56 facets. Ideal for solitaire diamond engagement rings and diamond pendants.
	Oval cut - The oval cut diamond provides an excellent alternative to the brilliant cut round diamond, whilst displaying the same amount of brilliance through its 56 facets. Ideal for solitaire diamond engagement rings and diamond pendants.
	Pear cut - Another alternative to the brilliant cut round diamond and contains a total of 58 facets. Ideal for solitaire diamond engagement rings and diamond pendants.
	Radiant cut - This is a straight-edged rectangular or square stone with cut corners. With a total of between 62-70 facets, the radiant cut can offer an excellent compromise between the rectangular shape of the Emerald cut and the square shape of a Princess cut, whilst having all the sparkle of a princess cut diamond. Most commonly found in diamond engagement rings, with shoulder diamonds.
	Heart cut - This ultimate symbol of romance is essentially a pear-shaped diamond with a cleft at the top. Ideal for diamond pendants.

The width and depth can have an effect on how light travels within the diamond, and how it exits in the form of brilliance
	Too Shallow: Light is lost out the bottom causing the diamond to lose brilliance. Too Deep: Light escapes out the sides causing the diamond to appear dark and dull.

Cut Determines Brilliance 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 and how it behaves once it exits; 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.

Diameter: The width of the diamond as measured through the girdle. Table: The largest facet of a gemstone. Crown: The top portion of a diamond extending from the girdle to the table. Girdle: The intersection of the crown and pavilion which defines the perimeter of the diamond. Pavilion: The bottom portion of a diamond, extending from the girdle to the culet. Culet: The facet at the tip of a gemstone. The preferred culet is not visible with the unaided eye (graded "none" or "small"). Depth: The height of a gemstone measured from the culet to the table.

Polish & Symmetry

Polish and symmetry are two important aspects of the cutting process. The polish grade describes the smoothness of the diamond's facets, and the symmetry grade refers to alignment of the 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 AGSL or GIA diamond grading report. For the most beautiful diamond, look for a symmetry grade of ideal (ID), excellent (EX), very good (VG), or good (G) for an AGSL graded diamond, and excellent (EX), very good (VG), or good (G) for a GIA 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.