RETURN TO INDEX OF ALL ARTICLES • RETURN TO LAPIDARY ARTS ARTICLES

LAPIDARY ARTS ARTICLE

Sawing gemstones
by MIKE BALDWIN

04.02.01--The process of cutting and polishing gems is called gemcutting or lapidary, while a person who cuts and polishes gems is called a gemcutter or a lapidary (sometimes lapidarist). Gemstone material that has not been extensively cut and polished is referred to generally as rough. Rough material that has been lightly hammered to knock off brittle, fractured material is said to have been cobbed. In most gem sawing, a thin circular blade usually composed of steel, copper, or a phosphor bronze alloy impregnated along the outer edge with diamond grit and rotating at several thousand surface feet per minute literally scratches its way through a gemstone. A liquid such as oil or water is used to wash away cutting debris and keep the stone and the saw blade from overheating, which could cause damage to both the stone and the sawblade.

Several sizes of circular rock saws are frequently used by most gemcutters: (1) A slab saw, typically 16 to 24 inches in diameter, is used to cut stones of several inches thickness into relatively thin slabs--often 1/8 to 3/8 inch thick; (2) A trim saw, typically 6 to 10 inches in diameter, is used to cut smaller stones into thin slabs or to cut small sections out of slabs; and (3) A faceter's trim saw, typically 4 inches in diameter, is used with a very thin blade, to saw small pieces of expensive rough.

There are also jigsaws that employ either a reciprocating wire or a continuous thin metal band. These are useful for cutting curved lines that are impossible with circular saws. They are also useful in minimizing waste on extremely valuable rough material. All gems are cut and polished by progressive abrasion using finer and finer grits of harder substances.

Diamond, the hardest naturally occurring substance, has a Mohs hardness of 10 and is used as an abrasive to cut and polish a wide variety of materials, including diamond itself. Silicon carbide, a manmade compound of silicon and carbon with a Mohs hardness of 9.5, is also widely used for cutting softer gemstones. Other compounds, such as cerium oxide, tin oxide, chromium oxide, and aluminum oxide, are frequently used in polishing gemstones.