The world of gems
The term cabochon is derived from the ancient French word Caboche, a head and a relatively flat stone that is formed with a smooth, polished, dome-shaped front surface, unlike faceted (cut) stones that have several flat surfaces on the front surface. The shape of a polished cabochon, as a rule, is a dome in the front and a flat base. Source The cabochon shape is most often used in the manufacture of rings and other jewelery, such as earrings, bracelets, pendants and necklaces, usually embedded in a metal frame that connects them with other decoration items. Cabochon processing is usually used for grinding opaque and translucent stones. In addition, this type of treatment is usually used for relatively soft stones (Mohs hardness is below 7). The cabochon shape is necessarily used for stones with optical effects — for example, for star sapphire or cat’s eye (chrysoberyl), since these effects can only be seen on the convex surface of the cabochon, and they are invisible if the stone is cut into shapes with several flat surfaces. Cabochons are more often made in the form of an oval, since the human eye is more difficult to notice deviations from the ideal shape of the oval than of a circle. However, round cabochons are also very common. Cabochons can have other shapes: drop-shaped, pear-shaped, heart-shaped or even arbitrary. There is a special form of cabochons – the so-called “carbuncle”, in which the base of the cabochon is not flat, but concave, usually parallel to the front convex side (imagine two domes one above the other). It is used most often in dark transparent stones. The formation of a stone with a thin wall reveals a deep color, lost in the traditional cabochons of a slightly larger size, because of which the stone looks too dark: dark brown, dark blue and even black. Manual cabochon processing begins with cutting a flat blank of a certain thickness from a raw piece of rock or mineral. The second step is marking the desired form using a template. The formed rough plate is attached (usually with the help of wax) with one wide side to a wooden stick for easy processing. The stone is cut and polished to obtain the desired basic shape, and then the front side of the cabochon is shaped into a dome, which is finally polished with a fine abrasive. Cabochons can look like a high or low dome with a chamfer on the edge of the back wall or without it and have zones of polished surfaces. There is the possibility of processing, combining cabochon and faceted stone. In the obverse, the stone acquires a dome-shaped form, that is, it is a cabochon, and on the back side there are applied many faces intended to reflect back the rays of light that have penetrated through the obverse of the stone. It is difficult to work on cabochons made of soft minerals, such as chrysocolla, malachite, turquoise, etc., or with uneven minerals such as jasper, zoisite, jasperite, since different parts of the stone have different hardness. Therefore, if it is unskilful to grind such stones, their surface may become wavy. Often when developing large cabochons made of soft and / or thin material, for example, turquoise, the cabochon is strengthened with a base of durable material, synthetic or natural. This is typical of the United States. In addition, in the cabochon of opal is often resorted to processing in the form of a doublet or triplet. The doublet is a thin plate of opal, glued to a substrate of durable natural stone (usually from the parent rock). In the triplet, the upper side of the doublet is covered with another additional plate, usually made of transparent quartz, which practically forms the upper surface of a domed cabochon, aimed at protecting opal from mechanical damage and as a magnifying glass that enhances color effects. All this allows you to make cabochons from a material that otherwise would not be suitable for jewelry purposes due to its small thickness and / or insufficient strength.
