Why Do Two Diamonds of The Same Color, Clarity and Carat Weight Differ in Price by Thousands of Dollars?
Until recently diamonds were graded only for color and clarity. No lab actually gave an overall grade for the cut of the diamond, comparable to a color or clarity grade. That changed in 1996 when the American Gem Society Laboratories developed a Diamond Quality® Certificate (DQC) with one person in mind: you! This is the first and only diamond reporting certificate to guarantee authenticity and provide accountability for the jewel’s grade. The Certificate is for round brilliant cut diamonds, using a 0-10 grading scale (0 being the top grade).
The Performance-Based Cut Grading System
The American Gem Society Laboratories team began researching diamond cut in 2000, working closely with Dr. José Sasián at the University of Arizona in Tucson and other experts in diamonds, optics, and computer programming. The result is a new methodology that analyzes the light performance and proportions of a three-dimensional image of a faceted diamond.
The previous proportion-based grading system for the standard round brilliant cut only addressed averages for the table diameter percentage, the eight crown main facet angles, and the eight pavilion main facet angles. Therefore, it was two-dimensional in nature. With the new performance-based cut grading system, the optical effects of all the facets are evaluated. This is the most technologically advanced, yet easy-to-use, cut grading analysis available today.
There are three categories in the American Gem Society Cut Grading System — Light Performance, Proportions, and Finish. Within these categories are eleven factors:
Light Performance – Brightness, Dispersion, Leakage, Contrast
Proportions – Durability, Tilt, Weight Ratio, Girdle Thickness, Culet Size
Finish – Polish, Symmetry
The closer you cut a round diamond to “ideal” proportions the more weight is lost from the rough. Higher labor and less yield from the rough equate to higher price.
Further, different labs use somewhat different standards for their ideal or excellent classification than the AGS lab which maintains one of the highest standards of any lab for cut grading.
There will be vast differences in price and appearance for ideal diamonds from different labs. These differences make comparing diamonds, without actually seeing them side by side impossible.
The Internet has a huge variety of “bargain” ideal cut diamonds, but are they really a bargain?
| Definitions: | |
| Brightness: | The amount of white light returned to the observer. |
| Brilliance: | Brightness with positive contrast effects. |
| Contrast: | The light and dark patterns seen when observing a diamond. It can produce a positive or negative optical effect. This usually is caused by, but not limited to, the observer’s head. |
| Dispersion: | The separation of white light into spectral colors. |
| Durability: | The diamond’s resistance to chipping or breaking. |
| Leakage: | Areas that do not return light. |
| Scintillation: | The combination of white and colored sparkles seen as the diamond and/or the observer and/or the light source(s) move. |
| Tilt: | The point at which the girdle reflects under the table of the diamond and is defined by the minimum pavilion angle allowed for each table size. |
| Weight Ratio: | The millimeter footprint of a diamond versus its weight. |
