Cut is often confused with the shape of the stone.  The shape refers to the outline of the diamond in a specific faceting style. Examples of this are the round brilliant, emerald cut, marquise, asscher and the princess cut.  Here are a few examples of the faceting styles of a few of the most popular diamond shapes.

Round Heart Cushion Asscher Trillion Princess Radiant Pear Oval Emerald Marquise

The cut of the stone refers to the angles and proportions of the diamond.  Based on scientific formulas, a well-cut diamond will internally reflect light from one mirror-like facet to another and disperse and reflect it through the top of the stone. The display of brilliance and fire in a well-cut diamond shows the care taken by the cutter and is reflected in the price of the stone. Diamonds that are cut too deep or too shallow lose or leak light through the side or bottom, resulting in less brilliance and ultimately, value.

The Gem Trade Lab (GTL), a division of the GIA, is currently conducting an extensive study on variations in cut and what effects those variations have on the fire and dispersion of light in the stone.  While only preliminary results have been published, those results confirm that many cutting configurations disperse light in high ranges.  The eye of the viewer will choose the stone with the best combination of fire (white light return or WLR) and dispersion (disperse color light return or DCLR).  When buying a diamond, have your jeweler show you various cuts, and make your decision based on which diamond is attracted to your eye.

Taking the time to study the following links may help you better understand the effects variations of cut have on the fire and dispersion in diamonds.

Click Here to Download Detailed Studies in PDF Format

1998 Study from the Gemological Institute of America

2001 Study from the Gemological Institute of America