The following instructions on cutting and polishing carnelians, or cornelians, are equally applicable to other stones of a medium degree of hardness, such as agate, amethyst, aquamarine, beryl, bloodstone, Brazilian topaz, carbuncle, cat's-eye, chalcedony, chrysolite, chrysoprase, crystal, elvans, emerald, felspar, flint, fluorspar, garnet, heliotrope, jade, jaspar, lapis lazuli, mina nova, onyx, opal, paste gems, peridot, plasma, porphyry, quartz, sard, sardonyx, serpentine, and topaz. First, the rough carnelian is slit on the slitting mill, which is a thin iron plate revolving at a moderate speed round a vertical spindle, the edge of the slicer being charged with diamond dust and plenty of the lubricant - oil of brick. The carnelian is lightly pressed against the edge of the slicer. The second operation is rough-grinding on a lead mill which resembles the slitting mill, except that the revolving table is of lead. The carnelian is moved to and from the centre of the rapidly revolving lap, which is fed with coarse emery and water, until the marks made by the slitting mill are removed.

The coarse emery marks are removed on the lead mill with flour emery, and then, in the case of stones not smaller than 1/3 in. in diameter, the polishing is commenced on a hacked or jarred lead lap, the abrasive material being rottenstone moistened with water; rottenstone would not adhere sufficiently to a smooth polishing-lap. The lap is hacked or jarred by Holding an old table-knife blade near the middle between the thumb and finger, the knife-edgs resting on the lap at something less than a right angle, so that the knife meets the lap edge foremost when the lap is revolved. The knife is held very slenderly so that it is caused to jump and vibrate and thus make a series of slight grooves or furrows in which the finely powdered rottenstone can lodge. The wheel, afterwards, is revolved in the opposite direction and cross grooves are cut. If the stones have a diameter less than 1/3in., and if they are rather hard, pewter polishing-laps are used; copper laps are employed for the smallest and the hardest stones, but in all the cases the laps require to be hacked and fed with powdered rottenstone and water. Rounded or convex stones may be worked with emery on a wood mill, then with pumice powder on a list mill, and finally with putty powder on a leather lap.

These laps have greater elasticity than the metal ones, and are more suited to the globular forms of stones. To cut facets, a lead wheel with emery, and then a pewter wheel with rottenstone,are employed; for harder stones, a copper lap replaces the pewter one. Small stones, which cannot be held in the fingers, are cemented centrally in the end of a wooden stick. By holding the stick vertically over the lap, the "table" or central facet of the stone is cut; the stick is inclined to certain angles for the eight, twelve, or more facets contiguous to the table. Two, three, or four series of these facets generally are required at different inclinations. The horizontal position of the stick serves to cut the girdle or central band around the exterior edge of the stone. The correct inclinations of the stick are found by placing its upper end into one of several holes in a vertical post fixed alongside the lap.