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A cabochon (; ) is a gemstone that has been shaped and polished, as opposed to
facet Facets () are flat faces on geometric shapes. The organization of naturally occurring facets was key to early developments in crystallography, since they reflect the underlying symmetry of the crystal structure. Gemstones commonly have facets cut ...
ed. The resulting form is usually a convex (rounded)
obverse Obverse and its opposite, reverse, refer to the two flat faces of coins and some other two-sided objects, including paper money, flags, seals, medals, drawings, old master prints and other works of art, and printed fabrics. In this usage, ...
with a flat reverse. Cabochon was the default method of preparing gemstones before gemstone cutting developed.


Application

Cutting ''en 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 the
Mohs hardness scale The Mohs scale of mineral hardness () is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of various minerals through the ability of harder material to scratch softer material. The scale was introduced in 1812 by th ...
are easily scratched, mainly by
silicon dioxide Silicon dioxide, also known as silica, is an oxide of silicon with the chemical formula , most commonly found in nature as quartz and in various living organisms. In many parts of the world, silica is the major constituent of sand. Silica is one ...
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 star
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sa ...
s and chatoyant stones such as cat's eye
chrysoberyl The mineral or gemstone chrysoberyl is an aluminate of beryllium with the formula Be Al2 O4. The name chrysoberyl is derived from the Greek words χρυσός ''chrysos'' and βήρυλλος ''beryllos'', meaning "a gold-white spar". Despite ...
, 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 an ellipse, because the eye is less sensitive to small
asymmetries Asymmetry is the absence of, or a violation of, symmetry (the property of an object being invariant to a transformation, such as reflection). Symmetry is an important property of both physical and abstract systems and it may be displayed in pre ...
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 some watches' 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 a
diamond blade A diamond blade is a saw blade which has diamonds fixed on its edge for cutting hard or abrasive materials. There are many types of diamond blade, and they have many uses, including cutting stone, concrete, asphalt, bricks, coal balls, glass, an ...
saw—called a trim saw. Diamond-impregnated wheels or
silicon carbide Silicon carbide (SiC), also known as carborundum (), is a hard chemical compound containing silicon and carbon. A semiconductor, it occurs in nature as the extremely rare mineral moissanite, but has been mass-produced as a powder and crystal s ...
wheels can be used to grind the rough rock down. Most
lapidary Lapidary (from the Latin ) is the practice of shaping stone, minerals, or gemstones into decorative items such as cabochons, engraved gems (including cameos), and faceted designs. A person who practices lapidary is known as a lapidarist. A lap ...
workshops and production facilities have moved away from silicon carbide to diamond grinding wheels or flat lap disks. 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.


Gallery

Image:moonstone.cabochons.arp.jpg, Moonstone cabochons in a jeweller's window Image:Cabochon on watch crown.jpg, A round
sapphire Sapphire is a precious gemstone, a variety of the mineral corundum, consisting of aluminium oxide () with trace amounts of elements such as iron, titanium, chromium, vanadium, or magnesium. The name sapphire is derived via the Latin "sa ...
cabochon on the crown of a men's dress
watch A watch is a portable timepiece intended to be carried or worn by a person. It is designed to keep a consistent movement despite the motions caused by the person's activities. A wristwatch is designed to be worn around the wrist, attached b ...
. Image:amber.pendants.800pix.050203.jpg,
Amber Amber is fossilized tree resin that has been appreciated for its color and natural beauty since Neolithic times. Much valued from antiquity to the present as a gemstone, amber is made into a variety of decorative objects."Amber" (2004). In ...
pendants. The oval cabochon
pendant A pendant is a loose-hanging piece of jewellery, generally attached by a small loop to a necklace, which may be known as a "pendant necklace". A pendant earring is an earring with a piece hanging down. Its name stems from the Latin word ' ...
is 52 × 32 mm (2 × 1.3 in).


References


External links

{{wiktionary, cabochon
Cabochon Making 101
Gemstone cutting