Some diamonds are much more beautiful, brilliant and fiery than others. Beautiful diamonds have proportions that minimize the amount of light that is lost through the bottom of the stone. Beautiful, well cut diamonds are more valuable and more desirable than darker, poorly cut stones.
Cut has the greatest influence on the beauty of a diamond. A beautiful diamond is one that ranks high on all of the following factors of "Cut".
1) Light Return/Light Loss: The proportions and angles of the diamond, whereby certain proportions and angles will return more of the light entering the diamond and return it to the eye of an observer. Other proportions/angles will allow light to leak out of the bottom or the sides of the diamond, and less light is returned to the ob- server.
2) Light Return Geometry: Certain proportions/angles will increase the amount of white light (brilliance) returned and will simultaneously decrease the amount of color flashes (fire). Other proportions will increase the amount of fire and simultaneously decrease the amount of brilliance. Fire and Brilliance have an inverse relationship.
Brilliance: The total amount of white light, both external and internal, returned from the diamond to the eye of the observer.
Dispersion or Fire: The flashes of color, resulting from the dispersion or separation of white light into its component spectral colors, that is returned from the diamond to the eye of the observer.
Scintillation: Sparkles, reflections and flashes of light from the diamond as the stone, observer or light source moves.
3) Perceived Symmetry: The overall symmetry of the shape of the diamond.
Light Return/Light Loss
The proportions and angles of the diamond, whereby certain proportions and angles will return more of the light entering the diamond and return it to the eye of an observer.
Other proportions/angles will allow light to leak out of the bottom or the sides of the diamond, and less light is returned to the observer.
A beautiful diamond will return practically all of the light that enters into the stone back to the observer's eye.
Light Return Geometry
Certain proportions/angles will increase the amount of white light (brilliance) returned and will simultaneously decrease the amount of color flashes (fire). Other proportions will increase the amount of fire and simultaneously decrease the amount of brilliance.
A beautiful diamond will return as much light as possible back to the eye in a nice balance of white light (brilliance) and spectral colors (fire). This balance results in a stone with high scintillation.
Brilliance: The total amount of white light, both external and internal, returned from the diamond to the eye of the observer.
Scintillation: Sparkles, reflections and flashes of light from the diamond as the stone, observer or light source moves.
Dispersion or Fire: The dispersion or separation of white light into its component spectral colors.
For round diamonds, the Ideal Cut Round Brilliant has the range of angles and proportions that returns the maximal amount of light with a pleasing balance of brilliance and fire
Diamond Cut and Its Effect on Value
A poorly cut diamond that leaks a lot of light will hold less value than a diamond of similar weight, color and clarity that is well cut. Just how much less is determined by two factors. First, the current market conditions, the supply and demand for poorly cut diamonds of that weight and quality is a major determining factor of value.
A secondary determining factor of the value of a poorly cut diamond is the hypothetical weight and hypothetical value of the stone if it were to be recut to better proportions. Take, for example, two 1.00 ct Round Brilliant Cut diamonds, both with GIA Gem Trade Laboratory grading reports stating G color and VS2 clarity.
Diamond "A":
1.00 ct. GIA Diamond Grading Report
G-color VS2-clarity
6.48-6.50x3.95mm
Ideal Cut (verified by Sarin Report)
Table% = 55
Depth% = 61
Wholesale value of Diamond "A": 1.00 x $7,200 = $7,200.00 per stone
There are several diamond price sheets that appraisers throughout the nation consult to estimate the wholesale value for diamonds. The Rapaport Diamond Report is likely the most widely used.
Diamond "B":
1.00 ct. GIA Diamond Grading Report
G-color VS2-clarity
6.08-6.14x4.02mm
Deep Cut
Table% = 58
Depth% = 65.8
Estimated yield if Diamond "B" were to be recut to Ideal Proportions = 0.82ct.
Wholesale value of Diamond "B": 0.82 x $4500 = $3690.00 per stone
Actual value would be determined by a willing buyer and seller in the diamond marketplace.
Evaluating Cut
The Diamond Specialists has two completely different ways to help evaluate the "Cut" of a diamond.
Method #1 - Comparison to Idealized Standards
With certain shapes there are certain parameters for specific angles and proportions that are known to produce a more beautiful diamond. With the proper equipment, it is easy to compare the parameters of a diamond to the known standards.
Method #2 - Assessment of Light Loss and Light Return
Our Diamond Photoscope assesses the light that is actually lost or returned by a particular stone.
Comparison to Idealized Standards
Standards for Round Brilliant Cut Diamonds
American Gem Society Cut Grading Scale.
The AGS Cut Grading is based on five parameters. These are the:
Table % (ratio of the table measurement to the diameter measurement) Crown Angle in degrees of angle Girdle Measurement % (ratio of the girdle measurement to the diameter measurement)
Pavillion Depth % (ratio of the pavillion depth measurement to the diameter measurement)
Culet % (ratio of the culet measurement to the diameter measurement)
AGS rates each of these parameters on a scale from 0 to10 with 0 being the best.
The AGS Cut Grade that is assigned to a particular diamond is the lowest grade given to any of the individual parameters. AGS also grades "Polish" and "(Facet) Symmetry" seperately using the same scale. The AGS Diamond Quality Report lists all of this information.
A diamond with a "0" in all the parameters would have a cut grade of "0" and would be an "Ideal Cut". Further, a diamond that has a "0" Cut Grade, a "0" Polish Grade and a "0" Symmetry Grade would be a "000 Cut" or a "Super Ideal Cut" diamond.
The GIA Gem Trade Laboratory Diamond Grading Report does not give as much information on Cut. If a diamond with a GIA report is found to meet the AGS "0" cut grade then it is considered an "Ideal Cut". If is a diamond with a GIA report has an AGS "0" cut grade and it has an "excellent" or "very good" Polish and "excellent" or "very good" Symmetry then it would be a "Super Ideal Cut stone".
