Lapidary (Lat. lapidarius, a stone cutter, from lapis, a stone), a workman whose trade is the cutting and polishing of small ornamental stones. His apparatus consists almost exclusively of wheels or disks for grinding down, slitting, and polishing the faces of minerals. These are of a few inches diameter, made of lead, pewter, brass, or iron, and of various soft alloys, and some used for smoothing the softest minerals are of willow or mahogany. The metal wheels are called laps. The term mill is applied to them all, and some are distinguished as slitting mills, others as roughing, smoothing, or polishing mills, of all which there are varieties adapted to the different degrees of hardness of the minerals. The polishing mill for the softest stones is formed of a coil of list, wound with the edges outward; it is also sometimes made of bristles like a brush, or of wood covered with buff leather. For slitting purposes an iron disk is employed of 8 or 9 in. diameter and 1/200 of an inch in thickness. The various disks used by the lapidary are adjusted to a vertical spindle, and one of them is set in the table or lapidary's bench, so as to revolve horizontally just above the surface.
Its axis extends beneath the table, and is there connected by a belt with a driving wheel attached to another vertical axis, which also passes through the table and terminates above in a winch or crank. This is turned with the left hand while the stone is guided upon the mill with the right. The mills are fed with moistened diamond powder or emery and water; and as the hard powder imbeds itself in the soft metal, this becomes merely the medium for holding the abrading material, and the softer substance apparently grinds and cuts the harder objects that are applied to it. A raised edge around the table prevents the dispersion of the diamond powder or emery. Close to the mill is a round iron rest set in the table, which can be turned nearer to or further from the disk. This is for supporting the arm of the workman in holding the stone to the wheel; or, when its upright extremity is capped with a wooden socket, which is perforated with a number of holes, it serves to retain at any desired angle a stick upon the end of which is cemented the stone to be ground in facets. By this contrivance the exact inclination required is given to the faces of ornamental stones. Diamond powder for the mills is prepared by grinding the waste particles in steel mortars till they lose their sparkling appearance.
It is applied mixed with olive or sperm oil. The slitting mill is charged with it around the extreme edge, and it is carefully renewed as required. It is more economical for this use, and applied to the surfaces of other mills for grinding the facets of hard stones, than emery; but the latter powder with water is employed for the more common class of stones. It is used of various degrees of fineness, and in such quantity that there shall always he a loose portion of it between the stone and the metallic surface of the lap. Polishing is effected by successively using finer and finer powders. The hardest small stones are finished on laps of copper or of pewter, and others on lead, and the powder used is rotten stone, which is plentifully applied with water. To make it adhere, the face of the metal is hacked in lines with the edge of a knife. For very soft stones, as alabaster, after these are smoothed upon a lead or wood mill with flour emery, the list mill is employed with pumice stone and water, and after this the buff leather disk with fine putty powder and water. The last polish is sometimes given with the hand and putty powder. - In the East Indies, wheels and rubbers are made of corundum or emery imbedded in lac resin.
For the former about one third of the bulk is lac resin and two thirds is the powder. This is carefully stirred, a little at a time, into the melted resin; the mass is then kneaded and rolled upon a stone slab upon which fine corundum powder is sprinkled, and finally it is flattened into a disk with an iron rolling pin. The wheels are made of different degrees of fineness, and when used are set upon a horizontal axis, which the workman, sitting on the ground, causes to revolve with a spring bow, holding the stone in his left hand against the wheel, which is occasionally moistened and sprinkled with corundum powder. The rubbers contain a much smaller proportion of corundum; and the finest have intermixed the grindings of agates, carne-lians, etc. Grindstones are used for giving shape to gems only in the works at Oberstein on the Nahe in Germany, where agates are fashioned into the form of various articles, as buttons, clasps, stamps, paper weights, mortars for chemical purposes, etc. Stones of large size are run by water power, and the workmen lie down in front of them when at work, the body being supported by a sort of stool.
They acquire wonderful dexterity in giving the shape they desire to the hard stones, and produce with extraordinary rapidity playing marbles of perfectly globular form. - For full details of the processes of the lapidary, vol. iii. of Holtzapffel's "Mechanical Manipulations " may be consulted; also " A Popular Treatise on Gems" (New York, 1859-'67), by Dr. L. Feuchtwanger, and "Diamonds and Precious Stones" (New York, 1874), translated from the French of Louis Dieulafait by F. Sanford. (See also Diamond, and Gem.)