Many consider the cut of a diamond to be the most important of the 4Cs as it is the quality of cut which unlocks a diamond's fiery brilliance. It is the skill of the cutter in proportioning the size and angles of a diamond's facets that will determine the level of beautiful brilliance which meets the eye.
The image below demonstrates key aspects of a polished diamond's anatomy. The relative proportions of these features, and their related angles, determine the effectiveness and quality of the cut.
A cutter's aim is to maximise the amount of light, which a diamond reflects back to the eye. The proportions of the diamond are therefore measured precisely to encourage the light to reflect around the inside of the stone and back out to the viewer, thereby increasing its brilliance.
A stone that is cut too shallow looses light through the bottom; one that is cut too deep loses light from the sides and may appear darker. A stone cut to 'ideal' proportions allows the light in, and then reflects it back up through the crown of the stone to the viewer's eye, thereby creating the diamond's beautiful brilliance.
The Cut is therefore graded according to its geometric proportions, as these determine the behaviour of light within a stone.
The higher the cut grade the more expensive the stone will be. Cut gradings are listed in the table below.
Particular attention must be paid to the symmetry of the cut and its final polish, as both have a significant effect on the diamond's brightness and overall quality.
Poor symmetry can cause light to be misdirected as it enters and leaves the diamond, and can affect the diamond's brilliance.
Symmetry is rated as:
Polish grade describes the smoothness of the diamond's facets, and is important to determine sparkle. The symmetry grade refers to alignment of the facets, and with poor polish, the surface of a facet can be dulled or blurred. Polish gradings are as follows: