By Adam Kelliher
The short answer: a faceted stone is cut with many flat faces, angled to bounce light around inside and flash it back out. It suits transparent material. A cabochon has a smooth dome and no facets, and it suits opaque or translucent stones like agate, turquoise and moonstone, where you want to see the pattern and colour inside rather than sparkle.[1]
This is the question I get from people starting out: should this stone be faceted or cabbed? The answer starts with understanding how each cut handles light.
Anatomy of a faceted stone
- Table: the large flat facet on top.
- Crown: everything above the girdle, including the table and the angled facets around it. It guides light in and back out to your eye.[1]
- Girdle: the widest edge, where the crown meets the pavilion and where the setting usually grips the stone. Too thin and it chips. Too thick and it looks bulky.[1]
- Pavilion: the cone-shaped bottom half. Its angles bounce light back up through the crown.[1]
- Culet: the point at the bottom, sometimes polished into a tiny flat facet so it doesn't chip.[1]
Why pavilion angles matter
Each gem has a critical angle that depends on its refractive index. If the pavilion facets are cut steeper than that angle, light reflects inside the stone and comes back out the top. Cut too shallow and light leaks out the bottom, leaving a dull see-through patch in the middle called a fisheye. Cut too steep and the stone looks dark.[1] That's why faceting is about precision. The corners of each facet have to meet cleanly for the light to work.[1]
Anatomy of a cabochon
A cabochon has a smooth domed top and a flat or slightly curved back. It's cut for opaque and translucent material and is usually set in a bezel, where metal wraps around the edge.[1] Our step-by-step cabochon post shows how one is made.
Why the dome matters
This is the part people often get wrong. A faceted gem sparkles because its flat faces catch light and throw it back as a bright white flash. A cabochon is designed to do the opposite: cut down that glare so you can see into the stone.[1] If a cab is left with a flat top, light bounces off it the way it does off a wet road. The face washes out under bright light and you lose the banding and colour you cut it for.[1] A full dome keeps the light in a controlled range, so the detail shows. My advice in the book is blunt: dome your cabs completely.[1]
Which to choose
- Transparent and clean? Facet it. Faceting relies on light passing through the stone, and faceted stones are typically transparent or translucent.[1]
- Opaque, banded, patterned or included? Cab it. The dome shows off what's inside.[1]
- Starting out? Begin with cabochons. They're simpler to shape and to set than faceted stones, which is why I call them the training wheels of stone setting.[1]
- Want both? Cabochons can carry facets too. Rose cuts, checker cuts and freeform faceting add flat planes to a domed surface for extra sparkle.[1]
Setting follows the cut
Cabochons usually go into bezels. Faceted stones are usually held with claws or prongs so light can get in around them.[1] Browse cabochons and loose faceted gemstones, or read the full reasoning in Beyond Cabbing.
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Sources
- Adam Kelliher, Beyond Cabbing: Volume I (cabochon design, flat tops and blowout) and Volume II, A Lapidary Glossary (cabochon, critical angle, crown, culet, facet, faceted stone, girdle, pavilion).