Diamond Cut Grading
The Essential 7C's
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
Depth Percentage: The higher the number, the deeper the stone. The lower the number the shallower the stone.
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.
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)
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.
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
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
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
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.
After a diamond is cut, each facet must be polished. The
process can leave surface scratches or marks, which are like streaks
left behind after a car is waxed. If a diamond has no scratches or very
minor ones, the polish is of a high degree. Scratches, lines, burn marks
created by excessive heat, or rough girdles could downgrade the polish
rating of a diamond and if significant, could affect the overall cut
The relationship between the crown and the pavilion angles has
an effect on the appearance of a diamond. A diamond's pavilion angle
and depth must be correct to capture and reflect light optimally. A
slightly steep pavilion angle can be complemented by a shallower crown
angle, and vice versa.
In diamonds with extremely deep pavilions, the whole surface
of the table appears to be darker creating what is known as a
"nailhead". Gems with more shallow pavilions often produce a “fisheye”
effect due to the girdle’s reflection in the diamond’s table.