All you need to know about diamonds: CUT

All you need to know about diamonds: CUT

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, 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.

The cut is mainly influenced by the harmony between the table and depth percentages and crown and pavilion angels, either causing the diamond to dissipate light (poor cut) or optimally refract and reflect light (excellent cut). The table and depth percentages are calculated as follows:

Depth Percentage

Depth Percentage: The higher the number, the deeper the stone. The lower the number the shallower the stone.

Table Percentage

Table Percentage: The higher the number, the bigger the table looks. The lower the number, the smaller the table looks.

Table and depth percentages affect how light travels within the diamond and impacts a stone’s brilliance. If a cut is too shallow, light escapes out from the sides and the diamond loses brilliance. If the cut is too deep, light is lost from the bottom and the diamond appears dull or dark.

Normal curve showing the relationship between depth and grading

GIA have developed a grading system, which take these and other important factors into account to provide a scientific assessment of a diamond’s sparkle. Seventy Seven Diamonds uses the GIA classification of Excellent, Very Good, Good, Fair and Poor (not displayed on the website) grades to help customers assess diamond quality. The table below displays the GIA grading classifications relating to cut.

Excellent (or Ideal) Very Good Good
Ideal CutDiamonds classified as Excellent or Ideal cut offer the most sparkle, dispersion and fire and are considered to be of the highest quality. Light moving through an ideal cut diamond bounces almost fully back out the top of the stone and brings its brilliance into view. Fine CutDiamonds classified as Very Good offer slightly less brilliance and scintillation than the excellent cut. However, as the difference between the two is almost indistinguishable to the unaided eye, very good cuts offer better value for money than excellent cut diamonds. Good CutDiamonds classified as “Good” usually allow some light to escape during the reflective process, although once again, the difference between this and the very good cut diamonds is small therefore good cuts offer great value for money and make for a more affordable option.
Shallow and Deep Cut

Light moving through a shallow cut diamond is lost out of the bottom of the stone and the lack of light play makes shallow cut diamonds appear lifeless. Light moving through a deep cut diamond escapes out from the sides, darkening all or most portions of the stone.The poor sparkle performance of Diamonds classified as Fair or Poor cut may be noticeable to the untrained eye, and are for this reason also less costly.

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 certifying bodies only provide cut grade for round diamonds although a few have extended grading to other diamond shapes.

For more information regarding diamond cut contact us at Seventy Seven Diamonds at


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