The Essential 4C's
Diamond Cut Grading
The cut is mainly influenced by the harmony between the table and depth percentages and crown and pavilion angles, 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:
Percent Depth: The higher the number, the deeper the stone. The lower the number, the smaller the stone.
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.
GIA has developed a grading system, which takes 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)
Diamonds 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.
Very Good
Diamonds 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 diamond
Good
Diamonds 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.
Fair/Poor
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.
OTHER FACTORS AFFECTING CUT
Symmetry
When the facets of a diamond are well balanced and aligned, the stone has symmetry, which is critical to creating optimal brilliance and scintillation. Errors in symmetry include facets that are not properly aligned, improperly shaped facets, or an off-centre table.
Polish
After a diamond is cut, each facet must be polished. The process can leave scratches or marks on the surface, which are like streaks left behind after cutting the diamond. If a diamond has no or very minor scratches, the polish is of a high grade. Scratches, lines, burn marks from excessive heat, or rough girdling could reduce a diamond’s polish and, if significant, affect the overall cut grade.
Symmetry
The relationship between the crown and the pavilion angles has an effect on the appearance of a diamond. The angle and depth of a diamond’s pavilion must be correct to capture and reflect light optimally. A slightly steeper wing angle can be complemented by a shallower crown angle and vice versa.
In diamonds with extremely deep pavilions, the entire surface of the table appears to be darker, creating what is known as a “nail head”. Stones with shallower pavilions often produce a “fish-eye” effect due to the reflection of the girdle in the mass of the diamond.