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Ch. 5: Gem History Properties

Ch. 5: Gem History Properties Page of 515 Ch. 5: Gem History Properties Text size:minus plus Restore normal size   Mail page  Print this page
ON GRINDING.
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machine, consisting of a circular horizontal plate of cast-iron, fourteen or fifteen inches in diameter, called a skive, suspended on a spindle, and capable of being put into rapid motion by means of a larger wheel, five or six feet in diameter, and turned by an assistant.. From the centre to the circumference of the iron plate, are lines· or shallow grooves, formed by rubbing it in that direction with a fine grained gritstone : these grooves serve to retain the mix­ture of oil and diamond-powder with which the plate is charged. In order to keep the diamond perfectly steady while the polishing of each facet is going on, the following contrivance is had recourse to :—a copper cup, called a dopp, about three quarters of an inch in depth and in width, and furnished with a stem about four inches long of stout copper wire, is filled with plumbers' solder, which also pro­jects in a conical form beyond the rim of the cup : in the apex of this cone, tlie solder being softened by heat, the diamond is imbedded with one of the facets projecting. The stem of the cup is now put into very powerful pincers, Which screw up with a nut and a wrench or lever, and thus hold it perfectly tight. The handles of the pincers (made of wood, and called tongs) are broad, and terminate in two feet, about an inch high, so that when laid horizontally, they are supported exactly as a pair of candle snuifers are> the studs fixed to the handles of the snuifers representing ing the legs of the pincers, and the single stud near the point of the snuffers representing the inverted copper cup holding.the diamond is placed on the plate, the pincers rest­ing on their legs on the wooden bench or. table that sup­ports the plate, and pressing at the same time against an upright iron peg ; the broad part of the pincers between the legs and the. diamond, is then loaded with weights, both to steady the machine, and to increase the pressure of the diamond against the skive. Mattel's being thus ad
Ch. 5: Gem History Properties Page of 515 Ch. 5: Gem History Properties
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