Thin works of moderate size that are too yielding to be applied with the fingers, or those that would become too hot to be conveniently held, are temporarily fixed upon a thin piece of wood by driving two or three pins into the wood, around the edges of the work, and very small objects are sometimes cemented upon a small piece of wood. In these cases, however, the flat position of the work upon the lap cannot be so readily appreciated as when the work is held directly in the fingers. Large works may be correctly placed upon the lap without difficulty, as their size serves at once as a guide, and prevents the general accuracy given by the file being accidentally depreciated.
When the work is first commenced it may with advantage, if not very small, be slidden to different parts of the surface of the lap to equalize the wear, but towards the conclusion the work should be held in the one position, and the uniform wear of the lap may be ensured by applying the work to a different part of the lap every time that it is placed upon it.
When fresh emery is required on the lap it should be applied by preference at the commencement of lapping the article, in order that the emery may at first cut rapidly, and be gradually worn finer with the progress of the work, so as to leave a smooth surface at the conclusion.
Flat works in steel, are sometimes polished on iron laps supplied with crocus, but more generally, after being lapped with fine emery, they are smoothed with fine emery paper wrapped around a file and moistened with oil, and the works are lastly polished with small rubbers, as explained on page 1075. Flat works in brass are finished as described on page 1039.
Facets on steel jewellery, such as beads, studs, buttons, the ornaments on the hilts of dress swords, and similar objects, are ground to form on horizontal laps, such as fig. 1039, fed with fine emery, and are afterwards polished after the general method of cutlery.
The small solid beads employed in common articles are prepared from sheets of iron of suitable thickness; the plates are first punched in a fly press, with small holes of the proper size for the passage of the wire, by which the beads are strung, the pieces of metal to constitute the beads are then punched out with a circular punch a little larger than the intended diameter of the beads, and having a small central pin that fits into the hole previously punched, in order to ensure the latter being in the center of the bead. The pieces are next fixed on a pointed steel wire and rounded at each end with a file. They are then case-hardened in bone dust enclosed in sheet-iron boxes, a layer of bone dust and one of beads being placed alternately until the box is filled; the whole are then case-hardened, after the method explained, page 260, Vol. I. For cutting the facets the beads are fixed singly on pointed steel wires, and applied to the horizontal lap supplied with emery and water; no guide is employed for these common beads, but the wire is held at the proper inclination, and twisted in the fingers to cut the facets in succession at the one end, and the bead is then inverted on the steel point for its completion. The scratches left by the lap are removed either in the rumble, or by stringing them on wires, and applying them to revolving wheel brushes, fed with oil and emery of various degrees of fineness; rottenstone is next employed in a similar manner, and the beads are finally polished by rubbing them in the naked hand with putty powder or crocus.
Large hollow steel beads for the best works, are raised from either the best charcoal iron, or decarbonized cast-steel plates after the general method explained in Chap. XIX., Vol. I The metal is punched out in a fly press, first as a concave disk, and by alternate punching and annealing the sides are brought to the cylindrical form, the bottom is then removed, and the ends are gradually closed in with punches, leaving a small hole at each end of the hollow sphere; the beads are then roughly filed and case-hardened. The facets on the large beads of the best kind both hollow and solid, are sometimes more exactly cut by fixing them on pointed wires inserted in wooden handles, that, instead of being cylindrical, are made as polygonal prisms of various numbers of sides, according to the numbers of facets required in the work; a horizontal wooden bar is placed at a suitable height on one side of the lap, and the flat sides of the handle are rested in succession upon the horizontal bar; this gives the correct number of facets to every bead, and the angle at which they are laced is regulated by the height of the bar and the inclination of the handle. The beads are lastly strung on wires, smoothed on wheel brushes, and polished by hand in the same manner as the small beads, but more carefully.
Round and oval studs are in like manner punched as flat or concave disks out of decarbonized sheet steel, and rounded with the file; but before they are case-hardened the shanks are attached by soldering, and covered with small lumps of clay to prevent them from being affected by the hardening process. For cutting the facets, they are held in small hand vices or pin tongs, sometimes inserted in polygonal handles, and applied to the lap in the same manner as the best beads. For polishing the studs, they are closely arranged in a flat block covered with cement, that is softened by heat to allow the shanks of the studs to penetrate. The whole surface is then smoothed with emery and water, applied with hard flat brushes rubbed in all directions either by hand or machinery; after the emery, rottenstone is employed in the same manner, and the final lustre is given with putty powder or crocus on the hand. See Tech. Repos. 1830, p. 275. Facets on gold and silver, and the flat parts of jewellery generally, are cut and polished on revolving wheels after the same general method as that pursued by the lapidary for cutting facets on stones, but the gold cutters commonly use vertical laps mounted much after the fashion of fig. 1030, in order that they may use both the side and the edge of the lap for different parts of the work. The laps are made of pewter, or an alloy of tin and zinc of different degrees of hardness according to the size of the work. They are turned very true and flat on their surfaces with the sliding rest, and left quite smooth.