choosing the right cut - round brilliant sunstonechoosing the right cut - round brilliant sunstone

Choosing the Right Cut: A Faceter’s Guide

Choosing the right cut for a piece of gem rough is an art. Learn how to balance brilliance with color and other factors before cutting.

10 Minute Read

Maximum Potential Shape

First, determine the maximum potential shape of your rough. This will simplify the rest of your decisions and choosing the right cut. For help with preforming your gem, read my article on the minimum cutting technique.


Brilliance is the goal of every faceter. After all, no one wants to spend that much energy on a lackluster gem. However, brilliance is one of the least understood principles of gemology. The term refers to how much light is reflected from the inside of a gem, expressed as a percentage. For example, a measurement of 86% means that 86% of the light entering the stone is returned to the viewer.

Ray tracing software, such as GemRay, can measure brilliance. Since some of these programs were created for the optical industry, when you apply them to gemstones they’re somewhat less than perfect. Nevertheless, they yield better data than a collection of subjective observations.

Refractive Index and Brilliance

There’s a direct relationship between the refractive index (RI) of a gem and how much brilliance it’s capable of displaying. An experienced gemologist can take a good guess at the identity of a stone by its brilliance. For example, a veteran…

Donald Clark, CSM IMG

The late Donald Clark, CSM founded the International Gem Society in 1998. Donald started in the gem and jewelry industry in 1976. He received his formal gemology training from the Gemological Institute of America (GIA) and the American Society of Gemcutters (ASG). The letters “CSM” after his name stood for Certified Supreme Master Gemcutter, a designation of Wykoff’s ASG which has often been referred to as the doctorate of gem cutting. The American Society of Gemcutters only had 54 people reach this level. Along with dozens of articles for leading trade magazines, Donald authored the book “Modern Faceting, the Easy Way.”

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