Choosing Between a Cabochon and a Faceted Stone

A cabochon has a smooth domed top and no flat facets anywhere on it; a faceted stone has flat planes cut at calculated angles so that light entering the top leaves through the same face.

What faceting is for

Facets are mirrors. Each one is cut at angles chosen from the stone's refractive index, so that light passing through the crown is returned instead of leaking out the sides. A well-cut faceted stone stays bright as you tilt it. A badly cut one shows a washed-out window in the middle or goes dark around the edges.

That is why faceting works with transparent material and rarely works without it. If light cannot pass through the stone in the first place, there is nothing to reflect.

What cabochons are for

A dome is the right answer in four common situations.

• The material is translucent or opaque, and light return is not the point.
• The stone carries a pattern that needs a curved surface to appear: a star, a cat's-eye, play-of-color, or a sheen.
• The rough is too fractured or too included to hold a clean facet edge.
• The color is so strong that a thin faceted stone would go dark, and a deeper dome holds the color better.

Those optical effects depend on the shape of the top. Cutting a star sapphire into facets destroys the star, because the star is formed by light reflecting off fine parallel needles inside the stone and needs a dome above them to bring the reflections together.

What each cut fits in a setting

Cabochons have a flat base and no girdle, which makes them straightforward to set. Bezels, tube settings, and flush settings hold them securely and can cover the edge entirely. They sit low, which suits pendants, earrings, and rings that see hard wear, since a low dome catches on fewer things. A very tall dome in a ring will knock against doors and counters, so the height matters more than the outline.

Faceted stones are held by prongs or by a shaped bezel that seats the girdle, and they are more exposed. The girdle is the thinnest part of the stone and the most likely place to chip, so a setting's job is to keep it covered while the table stays visible. Faceted stones remain the standard choice for rings meant to look bright from across a room.

How to choose

Start with the setting and the job rather than the stone. A pendant or a pair of earrings can carry almost any cut. A ring worn daily should be built around a stone that can take knocks.

For a cabochon, look at the dome first. It should rise evenly, with no flat spot at the top and no dip where the dome meets the edge. A low, flat dome tends to sit there looking lifeless. Check that the pattern reads from the front and stays visible when the stone is tilted, because you will not always look at it straight on.

For a faceted stone, check the outline for symmetry, then look at the middle. A dark center, a blown-out bright center, or an obvious window all mean the cut spent light instead of returning it. Ask for a side or profile photograph, since proportions tell you more about a cut than a straight-on view.

Ask the seller for photographs taken dry in daylight and from the side, and choose the cut that suits the setting you already have rather than the one that looked largest in the picture.