Agate Cutting
Posted on June 17, 2008
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Now, cutting is carried out by steel laps, the edge of which is coated with silicon carbide, and although electricity has taken the place of water power, a few agate mills still remain. In these, the large grinding wheels revolve partially submerged in the running water, the rate of revolution being about three times per second. The cutter lies in a horizontal position and presses the stone against the surface of the revolving wheel. Some stones are finished on electrically driven laps, but the stone revolving wheels are considered to be more suitable for accurate work. Polishing is effected by hard, wooden laps, to which various materials have been applied.
Besides being extensively used in cheaper forms of diamond jewelry rings, agate bearings are used in delicate balances for supporting the steel knife edges and the pan holders. The cutting of such bearings in agate for various instruments is of some importance, and this branch of the lapidary industry was developed in England during the war.
Both onyx and sardonyx are carved into cameos, the contrasting layers lending themselves to particularly effective results. They are usually finer and certainly more durable than the shell cameos imported from Italy. Many fine old agate cameos exist, mounted as seals and brooches. The material was used for such purposes in very early days; a pre-dynastic tomb in Egypt discovered fairly recently at El Gerzeh revealed a necklace of agate and carnelian beads. Various material virtues were, of course, ascribed to agate; Pliny wrote that Sicilian agates were good for wounds inflicted by spiders and scorpions, and that the Indian stones “are possessed of similar properties and other great and marvelous properties as well.”
Mithridates is said to have possessed some 4,000 cubes of sardonyx, while it will be remembered that the precious ring which Polycrates threw into the sea to defy fortune was also of sardonyx.
Onyx cups and vases were made in considerable numbers over the past few centuries, and fragments of ornaments and vessels abound in ancient Roman ruins. Appian wrote that 2,000 vessels of onyx were captured at Talaura with the treasures of Mithridates. Epiphanius also wrote that oriental princesses took delight in drinking from onyx cups. Such workmanship must have called for much skill and care, for incipient flaws are easily developed into large cracks in polishing.
The most noted of the ancient onyx cameos is the Mantuan Vase at Brunswick. It was cut from a single stone in the form of a cream jug and is about seven inches in height. The raised figure on its outside represents Ceres and Triptolemus in search of Proserpine. The Museo Borbonico contains an onyx measuring eleven by nine inches, representing the apotheosis of Augustus, and this splendid specimen is supposed to be the largest in existence.
Theophrastus wrote that agates were first found in the river Achates in Sicily, from which the name of the stone is derived. “Onyx” comes from a Greek word meaning the human nail, while Mocha, near the Red Sea, was an ancient source of the stone of the same name.
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