Gem Certification & Assurance Lab, Inc. introduced a new cut grading system for diamonds. The system factors in traditional gemological criteria of proportions and finish. However, GCAL says it is based primarily on direct assessment light performance.
“In the past decade, cut has become one of the most important of the famous 4 Cs for diamonds—so important it is now a recognized factor in diamond grading,” said Donald A. Palmieri, GCAL’s founder and president. “Until now, however, cut grades have been based on theoretical computation and computer simulation—not measurement of actual light performance.”
The GCAL cut grade uses a 100-point rating system that scores a diamond for proportions, finish, and light performance. It then integrates the three scores into a final tally and cut grade.
“Those superbly crafted diamonds which earn top point scores for proportions, finish and light performance are awarded the highest designations of ‘Ideal’ or ‘Excellent,’” Palmieri said.
The GCAL cut grade system relates three important elements of cut:
Proportions: A round diamond is measured for ten cutting factors. The first six—table percentage, depth percentage, crown angle, pavilion angle, girdle thickness and culet size—comprise the preliminary category in the GCAL cut grade associated with proportions. Based on a point system, the stone is given one of five quality grades: excellent, very good, good, fair, and poor. The maximum number of points for proportions is 30.
Finish: The same five quality grades are used to rate for polish and external symmetry. The maximum number of points for finish is 30; a maximum of 15 points each for polish and for external symmetry.
Light Performance: This consists of two readings using GCAL proprietary technology—the first for optical brilliance (a contrast measurement of the diamond’s light return versus its light loss); and the second for optical symmetry (the degree of perfection of its light reflection pattern). The maximum number of points for light performance is 40; a maximum of 20 points for each of the two elements of light assessment.
Following the assignment of points, the three factors are analyzed and a final score is given using GCAL’s five-grade quality ratings system from excellent to poor. If a diamond achieves scores of 30 points for proportions, 30 points for finish and 40 points for light performance, it earns a final grade of “Ideal.”
“If any one of the three scores is less than perfect, the diamond cannot achieve a grade of ‘Ideal,’” Palmieri said.