OILSTONE. - The Turkey Oilstone can hardly be considered as a hone slate, having nothing of a lamellar or schistose appearance. As a whetstone, it surpasses every other known substance, and possesses, in an eminent degree, the property of abrading the hardest steel, and is at the same time of so compact and close a nature, as to resist the pressure necessary for sharpening a graver, or other small instrument of that description. Little more is known of its natural history than that it is found in the interior of Asia Minor, and brought down to Smyrna for sale. The white and black varieties of Turkey oilstone, differ but little in their general characters, the black is, however, somewhat harder, and is imported in larger pieces than the white.
2. - Oilstones Fitted in Cases. - The rough irregular pieces of oilstone scarcely ever exceed about 3 inches square and 10 inches long, and are generally about one third smaller; when cut into rectangular forms it is done with the lapidary's slitting mill and diamond powder, the blocks are then rubbed smooth with sand or emery on an iron plate. The piece of oilstone is generally inlaid in a block of wood, in which it is cemented with the putty used by glaziers, and to avoid the deposition of dust a wooden lid is usually added; the lid is sometimes covered with a thick piece of buff leather which serves to absorb the oil from the tool and is used in the manner of a razor strop. The oil employed on the oilstone should be indisposed to dry or thicken, in this respect sperm oil is the best, but neats-foot oil is nearly as good, and has no offensive smell.
The joiner often puts three or more small points in the stock or bed of the stone, that it may take a firm hold of the work bench when dabbed down thereupon; and the turner adds two fillets so that it may fit transversely on the bearers of the lathe.
3. - Oilstone Slips, are small pieces of this useful stone cut into different forms by the lapidary. Some oilstone slips are wide thin pieces, the edges of which are rounded to adapt them to the curvatures of gouges, and such slips are usually cut wedge form, that the semicircular edges on the one slip may be of two sizes and curvatures; these are used for gouges, for various figured tools used by turners, and also for plane irons for mouldings. Other Oilstone slips for polishing are cut into pieces from /4 to 3/4 inches square and 3 to 6 inches long, to be used after the manner of files, by mechanicians, watchmakers and other artizans.
4. - Oilstone Powder. - Fragments of oilstone when pulverised sifted and washed, are much in request by mechanicians. This abrasive is generally preferred for grinding together those fittings of mathematical instruments and machinery, which are made wholly or in part of brass or gun metal; for oilstone being softer and more pulverulent than emery, is less liable to become embedded in the metal than emery, which latter is then apt continually to grind, and ultimately damage the accuracy of the fittings of brass works. In modern practice it is usual, however, as far as possible to discard the grinding together of surfaces, with the view of producing accuracy of form or precision of contact.