The cut is perhaps the most fundamental attribute to consider when it comes to judging a diamond. However, it is also often one of the most complex and confusing terms. We have used cut in its most common form, which describes how well a diamond has been made from its rough form, rather than what shape it has been fashioned into (see Diamond Shapes), or the type of cut process applied by the diamond polisher (i.e. brilliant cut versus step cut).
How a diamond is cut and polished from its rough form is what determines its brilliance, fire and scintillation, or overall sparkle. For this reason, cut also plays a large part in determining the price of a stone and it is therefore important to be acquainted with all the factors that affect the quality of a cut before purchasing.
In order to understand diamond cut, it is necessary to know the anatomy of a diamond as well as how different proportions and percentages affect the movement of light through a stone. Based on these considerations, diamond cut is graded by a certification body; the GIA employs a five-point scale ranging from excellent and very good to good, fair and poor, while other laboratories such as the AGS may use alternate scales and terminology replacing “excellent” for “ideal,” for example. Excellent or Ideal cut grades are awarded to diamonds with the highest level of sparkle intensity, while Fair and Poor grades imply poorer light reflection and therefore less sparkle. Most laboratories and certificating bodies only provide cut grade for round diamonds although a few have extended grading to other diamond shapes. For more information, see the Cut Grade section below. To read more about the differences between individual grading laboratories see the Diamond Certificates section.