Thursday, November 11, 2010

Gemstones - From Rough to Finished

Gemstones used in jewelry are stones that have been worked by a gem cutter, also known as a lapidarist. Most gemstones look markedly different in their naturally occurring rough state than when they are used in jewelry. The art, knowledge and skill of the gem cutter can turn a chunk of rock into a beautifully cut and formed gemstone.

The rough gemstone is assessed by the gem cutter to determine the best utilization of the individual stone's qualities. Some stones are skillfully broken apart along naturally occurring fracture lines. This is cleaving. Diamond and topaz are the two gems that are usually cleaved. This is done to not only create more rough stones from the main stone, but to strengthen the remaining stones. If they were not cleaved, the natural lines of cleavage could ruin the stone.

There are a variety of methods to work gemstones. Pieces of gemstones too small to be worked are sometimes tumbled. They are placed into a barrel with different grades of grinding mediums and slowly rotated. The grinding medium used is for rough polishing and shaping, with succeeding mediums of finer grit to produce more polish and luster. Stones from a matte finish to a high luster can be produced this way. After the stone has been tumbled, holes are drilled into it for stringing.
Stones may also be cut with saws impregnated with diamond, the hardest naturally occurring substance on earth. Stones can then be ground, sanded and polished into different shapes and finishes. Some of the more familiar shapes of finished gemstones:

Cabochon Stones - This shape is produced by grinding, sanding and polishing the stone so that it is rounded on top, and flat or slightly rounded on the bottom. The stone can be circular or oval in shape. Most often used for translucent or opaque stones. It is also used for transparent gems that have too many inclusions (internal cracks in the stone) to be faceted.

Faceted Stones - Most faceted stones are transparent stones. Flat faces (facets) are ground into the stone, usually in a consistent pattern. Most diamonds are faceted, but it is also done for other transparent gems like the ruby, sapphire, citrine, peridot, etc.

Beads - Stones are first cut into cubes or other symmetrical shapes and then ground between two concave rotary grinders. The stones are free to rotate during this procedure, and after successive grits a bead is formed. Beads can be faceted, but are most often drilled with a hole for stringing.

Inlays - A gem is cut to the same shape as a hollowed out place in another material such as wood, metal or other stones. Then the face of the piece is ground smooth thus making the gemstone flush with the surrounding material.

Mosaics - Different sizes of stones are used to create in random or in a pattern on a piece of metal, wood or stone, then ground smooth.

Intaglios and Cameos - These are carved portraits in seashell or stone. A cameo is a raised portrait. With an intaglio the portrait is carved down into the material.

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