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Home > Gemstones > Shapes in Gemstones
Shapes in Gemstones

Here are the different shapes of Gemstones after cutting.

Using the Gemcutting and lapidary techniques, gemstones are generally shaped into forms like the following:

CabochonsCabochons
One of the simplest lapidary forms is the cabochon, a stone that is smoothly rounded and polished on top, relatively flattish, and either flat or slightly rounded on the bottom (which may be either polished or sanded). This form of cutting is often used for opaque or translucent stones, but is also frequently used for transparent materials that contain too many inclusions to yield a good faceted stone. Coloration and patterning provide the major interest in such stones. Merely holding the stone in the fingers often performs cabochon cutting, or cabbing, but it is more commonly done by dopping (attaching with adhesive wax or glue) the stone to a wooden or metal dopstick. This facilitates twirling the stone to form smooth curves and avoid flat areas during grinding, sanding, and polishing. A typical cabbing machine holds several wheels representing a progressive series of diamond or silicon carbide grit, turned by a common arbor and motor, and a water supply that provides a coolant/lubricant to wash away debris and keep the stone from overheating as it is ground and sanded on progressively finer wheels.

Faceted StonesFaceted Stones
Faceting is most often prepared on transparent stones. Flat facets are cut and polished over the entire surface of the stone, usually in a highly symmetrical pattern. The stone is dopped (usually with adhesive wax, epoxy, or cyanoacrylate glue) on a metal dopstick, which is then inserted in a handpiece that allows precise control of positioning. The cutting angle is adjusted vertically via a protractor and rotationally via an index gear. The facets are then ground, sanded, and polished on a rotating lap, while water or another liquid acts as a coolant and lubricant. When one side (top or bottom) of the stone is finished, a jig is used to transfer the stone to a dopstick on the opposing side.

A faceting machine usually utilizes a motor that turns a lap, a water supply, an adjustable handpiece with index gears and a protractor, and an adjustable mast or platform to hold the handpiece assembly. Most commercially available gemcutting machines employ a mast, but a few employ a platform.

There are two different approaches to faceting machine - mast-type and handpiece and platform.

In recent years, innovative faceters have employed techniques such as concave facets, grooves, and combinations of faceting and cabbing to produce new forms in faceted stones.

SpheresBeads and Spheres
Spheres are primarily sawed into cubes or dodecahedrons and then ground to shape between two pipes or rotating concave cutters, allowing the stone to rotate freely in any direction to form a perfect spherical shape. As with other lapidary processes, gradually finer grades of abrasive are used to grind, sand, and polish the stone. While beads may be faceted, they are more commonly cut and polished as small spheres and then drilled to allow stringing. Bead mills are used to grind and sand large quantities of beads simultaneously. They typically employ a grooved lap and a flat lap between which the beads are rolled and worn to shape. After shaping and sanding, tumbling usually polishes beads.

Inlays
In an inlay, a gemstone is cut to fit and glued into a hollow recess in another material (metal, wood, or other stones) and then the top ground and polished wash out with the surrounding material. Stones most commonly used for inlay are strongly colored opaque stones such as black onyx, lapis lazuli, turquoise, tiger-eye, etc.

Intarsias and Mosaics
In both intarsia and mosaic work, small bits of different colored stones are fit together and the top cut and polished to present a picture or other interesting pattern. Strictly speaking, a mosaic is constructed on top of a flat base of another material (usually stone), while an intarsia (also known as Florentine mosaic, or pietre dure) is set flush into the surface of the base material. The optimum intarsias and mosaics were traditionally of Italian origin, but intarsia has enjoyed something of a renaissance in recent years with the fine work of artists such as Jim Kaufmann and Nicolai Medvedev.

Cameos and Intaglios
Cameos and intaglios are alike in that both usually are carved portraits in stone or seashells. They differ in that cameos are raised portraits, while intaglios are carved down into the surface of the material. Both typically take advantage of different colored layers of material. The finest cameos and intaglios have traditionally come from Italy (usually shell) or Germany (usually agate).

Sculpture
Gemstones are capable of being carved, like other materials, into almost any form, limited only by the talents of the sculptor. Carving is accomplished with a variety of diamond-impregnated steel bits, saws, and grindstones.

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