Gem Outline Shapes

12/23/2017

For this post we will take a look at faceted vs rounded girdles and their effect on the appearance of the gemstone. Most "western" cutters learn gemcutting by following diagrams produced with the gemstone design software called GemCad. It's a fantastic tool, but one of the limitations is that it produces cutting instructions with straight faceted girdles instead of a smoothly rounded girdle on such shapes as rounds, pears, ovals, etc. Most common gemstone shapes cut with a strict adherence to GemCad instructions result a total of 16 such girdle facets, producing a "16-gon" mathematical figure called a hexadecagon, rather than a true round, oval or pear shape.

There is always some artistic license when cutting stones and for some fancy cuts a faceted girdle may be required, as it is for squares, octagons, rectangles, hexagons or other shapes with straight sides. Many new cutters believe that faceted girdles are a sign of a "precision cut" gemstone, but a rounded girdle can also be cut and polished in a precision manner - it just takes a little more time and effort to produce what we think is a more refined look. You would never see a ideal-cut diamond or an high-value colored gemstone with faceted girdles; you shouldn't need to settle for these either.

In addition to the aesthetic aspect, there's also a functional reason to round the girdles. Many jewelers hate faceted girdles because it makes stone setting more difficult. A rounded girdle also facilitates the use of settings with any number of prongs, with no need for awkward fittings such as a 6 prong setting on a 16-sided stone. A rounded girdle also works better with a bezel setting, as the metal can then be pushed into place more smoothly around the girdle.

Here are a few examples of faceted and rounded girdle outlines, with the GemCad-type faceted girdles on the left and rounded girdles on the right.

Round brilliant