Faceters must consider numerous factors before cutting a piece of gem rough. Although gemstone brilliance receives the lion’s share of attention, you’ll need to balance that with potential size, color management, and profitability, too. Choosing the right cut for your gemstone is an art.

Maximum Potential Shape

First, determine the maximum potential shape of your rough. This will simplify the rest of your decisions. For help with preforming your gem, see “The Minimum Cutting Technique for Gemstones.”


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…