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Cabochons

Posted by Andersons Bead Room on 8/14/2014

The term cabochon comes from the Middle French caboche (head), and is a gemstone which has been shaped and polished, as opposed to faceted. The resulting form is usually a convex top with a flat bottom.

Cutting And Faceting

Cutting en cabochon is usually reserved for being applied to opaque gems, while faceting is usually applied to transparent stones. Hardness is also taken into account as softer gemstones with a hardness lower than 7 on the Mohs hardness scale are easily scratched, mainly by silicon dioxide in dust and grit. This would quickly make translucent gems unattractive, so instead they are polished as cabochons, making any scratches less evident.

Stars Make Exceptions

In the case of asteriated stones such as star sapphires and chatoyant stones such as cat's eye chrysoberyl, a domed cabochon cut is used to show the star or eye, which would not be visible in a faceted cut.

The Traditional Ellipse

The usual shape for cutting cabochons is in an ellipse. This is because the eye is less sensitive to small asymmetries in an ellipse, as opposed to a uniformly round shape, such as a circle, and because the elliptical shape, when combined with the dome, is attractive. An exception is cabochons on some watches' crowns, which are going to be round.

The Cutting And Grinding Process

The procedure is to cut a slab of the rough rock with a slab saw, and then next, to stencil a shape from a template. The slab is then trimmed to the closest proximity near the marked line using a diamond blade saw, which is called a trim saw. Diamond impregnated wheels or silicon carbide wheels can be used to grind the rough rock down. Most lapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks.

Dopping

Once the piece is trimmed it can be "dopped" or completed by hand. "Dopping" is normally done by adhering the stone with hard wax onto a length of wooden dowel called a "dop stick". The piece is then ground to the template line at which point the back edges may be beveled, and finally the top is sanded and polished to a uniform dome shape.

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