Cut, one of the 4Cs of diamond quality, refers to the relative quality of the proportions and finish of a polished diamond.

Cut has two meanings in the diamond and jewellery industry, the first of which relates to the shape and style of a polished diamond, such as Round brilliant or Emerald cut. See diamond shapes.

The second meaning of cut, which relates to the 4Cs and is discussed here, describes the relative quality of the proportions and finish of a polished diamond. In the diamond trade, this is commonly referred to as 'Make'. Finish refers to the quality of a diamond's polish, the condition of its girdle and the precision of the faceting.

The cut (or make) of a diamond is the most important of the 4Cs and is a complex area of study that is ongoing in the major diamond grading laboratories. Make is the only one of the 4Cs that man, the diamond cutter, can control. Polished diamonds should be considered optical instruments and, ideally, all light entering a diamond should be internally reflected back to the observer.

It is important to note that only round diamonds have a cut grade on diamond grading reports — diamonds of other shapes do not.

The diamond cutter analyses a rough diamond to determine how to extract the most beauty from it. In a commercial environment, they also cut a diamond to retain the most weight possible and, therefore, increase its perceived value, to the uninitiated. This retained weight can be detrimental to a diamond's face-up appearance and will be displayed as either being very lumpy (small diameter) or very spread (wide diameter). This ties in with the minimum diameters that are recommended when purchasing round brilliant diamonds. See carat weight.

pavilion depth excellent
excellent cut
excellent cut profile

Diamonds cut with Excellent to Good proportions allow a maximum amount of light to be returned to the observer and thus have more brilliance and fire.

pavilion depth nail
cut nail
cut nail profile

A diamond with a deep pavilion will appear dark in the centre due to the leakage of light from the pavilion.*

pavilion depth shallow
cut shallow
cut shallow profile

A spread "fisheye" diamond with a shallow pavilion creates a white circle at the edge of the table when looking down on the diamond, which is actually the reflection of the girdle at the edge of the table.*

* Diamonds with cut grades of "Fair" or "Poor" can have overly deep pavilions creating light leakage in the pavilion or overly shallow/spread pavilions creating the "fisheye" appearance. As a result, does not list diamonds with "Fair" or "Poor" make.