Cut refers to the angles and proportions a skilled craftsman creates in transforming a rough diamond into a polished 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. This results in a display of brilliance and fire.

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.

 

Cut is the only one of the 4C's that is influenced by the human hand. the rest (color, clarity, carat) are created naturally as diamonds form in the earth.

Diamond cutting requires great skill and training. The cutter must polish tiny surfaces known as facets on the the rough diamond. This process is what creates the crown, culet, table, girdle and pavilion of the diamond.

The facets, when arranged in precise proportions, will maximize brilliance and sparkle. To cut a diamond perfectly, a craftsman will often need to cut away more than 50% of the rough diamond.

Cut also refers to the shape of a diamond;round, marquise, pear, or heart for example.

Since a round diamond is symmerical and capable of reflecting nearly all the light that enters, it is the most brilliant of all diamond shapes and follows the proportion guidelines above.

Shapes other than round do not follow the proportion guidelines shown. Non-round shapes, also known as "fancy shapes", will have their own guidelines to be considered well-cut.

Cut and cutting style work in harmony to create a diamond's brilliance. Cutting style is categorized into three basic types: step-cut, brilliant-cut and mixed-cut. The difference among these three types is the facetting arrangement of each style.