Today’s diamond manufacturers follow proportions set by the Gemological Institute of America to cut and grade their diamonds. The GIA does not classify any diamond as ‘Ideal Cut’, rather, the highest cut grade is ‘Excellent’ as far as they are concerned.
Proportions in a diamond basically refer to the relationship between the measurements, percentage and angles of the facets. All of these different measurements contribute to a diamond’s display of brilliance and light dispersion and impact the final beauty and value of your diamond. Any deviation from these proportions will lead to light leakage from your diamond and affect the cut grade.
Proportions of a Diamond
The following gives an idea of the relative proportion that is recommended by GIA.
Table % – 52% to 62%
Crown Angle – 31.5° to 36.5°
Total Depth % – 57.5% to 63%
Crown Height % – 12.5% to 17%
Pavilion Angle – 40.4° to 41.8°
Pavilion Depth % – This (Pavilion Depth %) and pavilion angle are directly related to each other. If you increase the pavilion angle, the pavilion depth increases and if you decrease the pavilion angle, the pavilion depth decreases. This has a direct impact on the light return as it is responsible for total internal reflection.
Girdle Thickness% – Thin to slightly thick
Culet Size – None to small
What do these numbers tell me?
Because proportions impact the light return of your diamond, they will have a direct and noticeable impact on the overall beauty of your diamond. So, when choosing your diamond, go for the highest grade as far as proportion is concerned.
How do proportions affect price?
As with other parameters in your diamond, if your diamond has a proportion grade of ‘EX’ or ‘Excellent’, your diamond is more beautiful and consequently, more expensive. GIA does not give a proportion grade above ‘Excellent’.
