Gem Cutting

By Teri Champigny

How it has changed over the years (50% of the original rough diamond is lost during the cutting of a round brilliant gem).

How does a lump of mineral or crystal become a dazzling diamond, ruby or sapphire? It's an amazing process called gem cutting or lapidary and makes all the difference in the final value of the stone. It was developed first in Venice in the early 1300's and was seen in Paris and Bruges in the mid-1400s. Good cutting is a precise art that catches the light just so, and captures the beauty of the gem. Poor cutting destroys it.

Most gems start out actually being sawed with a special lapidary saw into a rough shape, such as square, round, pear or marquise. It's then ground with a diamond-infused wheel to further refine the shape. The gem cutter uses a series of finer and finer abrasives to get closer to the clear heart of the gem. Cabochon gems are polished to a smooth overall surface, sometimes held by hand, but more often fixed or "dipped" with wax or adhesive to a dowel to hold it while the lapidary polishes the stone.

Transparent stones are most often faceted, a process where flat planes of the stone are cut and polished over the surface in a precise, symmetrical pattern. It's critical that the planes match up perfectly, or the beauty of how the light is captured by the facets will be lost.

If a stone is cut to flat or not polished, the brilliance of the gem will also be lost. When a stone is properly faceted, it captures the light so it bounces around inside the stone, giving it the sparkle we love and that helps determine the value of the gem. If the stone is cut too flat, or the facets don't meet precisely, the light doesn't bounce off the angles in the facets to maximum effect.