Calibrated Gem Cutting Machines versus Jam Peg

Most custom cutters use calibrated machines. Every setting is precisely controlled. Factories, on the other hand, use simple “jam peg” machines for the majority of their cutting. Factory cutters attach a rough gem to a long peg, which is inserted, “jammed,” into a vertical plate with multiple holes. The holes give the cutter an approximate angle. Skill and experience determine the rotation.

Cutting with a jam peg machine requires great skill, but the work is never precise. Since the angle and location of a facet greatly affect the brilliance of the finished gem, this method usually produces less than ideal gems. Factories use it because of the minimal time required.

Calibrated machines take less skill to operate than a jam peg but give superior results. However, finishing a gem takes much longer. Nevertheless, the quality difference is so remarkable that new standards have been set for cutting colored stones. “Native cut” gems have almost disappeared from the market. Even some factories now offer gems cut with calibrated machines.

In this article, I’ll discuss faceting styles for use with calibrated machines. Jam peg cutting isn’t covered here.

Step and Brilliant Cuts

At the most…