The light performance test was developed to grade the cut of a diamond. Learn more at
Light Performance of Diamonds
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After years of research by a team of AGS Laboratory experts and a renowned optical physicist, Dr. José Sasián from the University of Arizona, the all new performance based evaluation of diamonds was adopted as the AGS standard for grading the cut of a diamond. It is a patented process using ray tracing technology and the only scientifically vetted grading system in use today.

Previously, the evaluation of the proportions only addressed 17 (in blue) of the 58 facets on a round brilliant diamond – the table, the 8 crown facets, and the 8 pavilion main facets. The percentages and angles were measured and then the averages were used to determine the cut grade. Today, the AGS Performance-based cut grading system measures and evaluates all 58 facets in three dimensions!

The light performance of a diamond depends on the cutter’s decision on the angles and placement of the facets and the skill to place those facets at precise angles. It also takes time to polish the facet to a bright and smooth finish. Just as minute scratches can dull a glass surface, a poor polish on a diamond can reduce the brightness of its sparkle.

The quality of a diamond’s cut is determined by its light performance, proportions, and finish.  Overall, the cut grade can influence the value of that diamond by up to 50% or more! To learn more about the cut quality, ask your AGS jeweler to explain the importance of performance, proportions, and finish. Then ask to see a selection of diamonds in the ASET device. It’s simple and it’s fun to see the performance of a diamond in red, green, and blue!


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Mission Statement

The American Gem Society (AGS) is a nonprofit trade association of fine jewelry professionals dedicated to setting, maintaining and promoting the highest standards of ethical conduct and professional behavior through education, accreditation, recertification of its membership, gemological standards, and gemological research.

The Society is committed to providing educational products to inform and protect the consumer and to contributing to the betterment of the trade by creating industry standards to protect the jewelry-buying public and the fine jewelry industry as a whole.

AGS Laboratories, founded to support the AGS mission, is a nonprofit diamond grading laboratory with a mission of consumer protection. Adhering to the AGS Diamond Grading Standards, AGS Laboratories is dedicated to offering diamond grading reports that provide consistency and accuracy based on science.

American Gem Society

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