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Acabochon (/ˈkæbuʃɒn/; from Middle French caboche 'head') is agemstone that has been shaped and polished, as opposed tofaceted. The resulting form is usually a convex (rounded)obverse with a flat reverse.[1] Cabochon was the default method of preparing gemstones before gemstone cutting developed.[2]
Cuttingen cabochon (French: "in the manner of a cabochon") is usually applied to opaque gems, while faceting is usually used for transparent stones. Hardness is also taken into account as softer gemstones with a hardness lower than 7 on theMohs hardness scale are easily scratched, mainly bysilicon dioxide in dust and grit. This would quickly make translucent gems unattractive—instead they are polished as cabochons, making the scratches less evident.
In asteriated stones such as starsapphires andchatoyant stones such as cat's eyechrysoberyl, a domed cabochon cut can show the star or eye, which would not be visible in a faceted cut.
The usual shape for cutting cabochons is anellipse, because the eye is less sensitive to smallasymmetries in an ellipse, as opposed to in a uniformly round shape, such as a circle, and because the elliptical shape, combined with the dome, is attractive. An exception is cabochons on somewatches' crowns, which are circular.
The procedure involves cutting a slab of the rough rock with a slab saw, and then stencilling a shape from a template. The slab is then trimmed near the marked line using adiamond blade saw—called a trim saw. Diamond-impregnated wheels orsilicon carbide wheels can be used to grind the rough rock down. Mostlapidary workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks.[citation needed]
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, the back edges may be bevelled, and finally the top is sanded and polished to a uniform dome.
The cutting and carving of gems were probably first done in ancient Babylon several thousand years before Christ.
