Stones that are rounded to a cylindrical or conical form, such as a drop for an earring, are cemented sideways upon a stick, and the one-half ground to the semi-circular section; they are then detached from the stick, and cemented with the other side outwards, and this is similarly wrought. Of course, some care is required to grind the two semi-circular sections exactly opposite to each other; and when this has been done as nearly as possible, the stone is successively cemented in two other positions at right angles to the first two, in order to expose the junctures of the two curved surfaces first produced, and which are then corrected.

Stones that are to be ground into spheres, for beads or the heads of pins, are, in like manner, required to be cemented in at least four positions before they can be brought sufficiently near to the required form. The method of grinding spheres perfectly true has been already explained in sect. iv. of the foregoing chapter; but, of course, this amount of accuracy is not required for lapidary purposes, as, generally, the form is only required to be sufficiently correct to satisfy the eye. With the view of expediting the process of grinding stones that are much rounded, and also to preserve the lap used for flat surfaces, one lap is generally set aside, to be used only for rounded works, and, from constant use, the side of this lap becomes worn into numerous hollows, of different sizes, some of which are generally found to nearly fit the curve of the stone being ground. This materially lessens the difficulty of producing spherical surfaces, and the edge of the same lap is, in general, rounded off, to serve for concave works.

In grinding a pebble to the shape of a heart with rounded sides, the pebble, if much thicker than the intended heart, is first cut to the suitable thickness with the slicer; it is then marked from a card pattern, and nipped nearly to the form and size. The edges are then squared, the square angle of the lap being employed for making the indentation at the top of the heart. So far, the stone is generally held in the fingers; and when the outline has been thus produced, the stone is cemented on a stick, the edges are chamfered all round, and the stone is rough-ground to the rounded form, smoothed, and polished; the second side is then treated in the same manner.

Small stones cut in the form of a shield, as for a signet ring, are, in the same manner, first wrought to the outline of the shield while held in the fingers, although these stones are often not more than one quarter of an inch in height. In holding such small stones, some care is, of course, required to avoid bringing the fingers in contact with the lap, which would be likely to grind through the skin even before the operator was fairly aware that they touched the lap, the grinding action being almost insensible until the outer coat of the skin is worn through.

Stones that are semi-transparent, such as garnets, are frequently left round on the face, or cut en cabochon; but such stones, if left of the full thickness, would be too opake to display much brilliancy; and, therefore, with the view of increasing the transparency, garnets cut en cabochon, and called carbuncles, are generally hollowed on the under side, to make them thinner. The hollow on the under side is ground upon small spherical grinders of lead, called balls, made of various thicknesses and diameters, but mostly about the size of bullets. The balls are mounted upon a small conical spindle, that is fitted to the ordinary lapidary's bench; the hole through the balls is also made slightly conical, so that they may be retained upon the spindle by the plain fitting, and allow of being readily detached for the substitution of other balls of different sizes. Similar balls, made of pewter, are employed for polishing; and it is, of course, necessary that the grinding and polishing balls should be, as nearly as possible, of the same size.

For cutting small mouldings, or hollows, in the edges or sides of stones, the lapidary employs little lead mills, not exceeding about three inches diameter; they are generally held by a plain fitting, upon the same spindle that carries the ordinary mills, and which is made somewhat conical for the purpose. The edges of these mills are principally used, and they are made of various shapes and thicknesses, but mostly with rounded or angular edges, in order to penetrate the cavities of hollow mouldings, and the rounded parts are chiefly produced by rolling the work over the edges. The small diameter of these mills allows of delicate works being better seen, and, from the velocity being less at the edge of the mill, the position and progress of the work is also more readily appreciated by the sense of feeling.

In cutting a seal-handle, with an octagonal section, and a rounded top, such as fig. 1146, the stone is first sliced into the pyramidal form indicated by the dotted lines; the sides are then flattened and the angles removed upon the ordinary roughing mill, to bring the stone to the octagonal section, and the top is rounded. The indentations at a a are then cut upon the angle of a mill having a square edge. The curved portion at b is cut upon a mill with a slightly rounded edge, which also serves for removing the principal portion of the material from the large hollows at c; and these are afterwards corrected either by applying the stone transversely upon a lap with a rounded edge, turned to the required curvature, or by applying the stone longitudinally upon a square-edged mill, of about two inches diameter, the curvature of which would correspond with the hollows in the figure. The small flutes in the rounded top are cut with a mill of small diameter, having a narrow rounded edge. In cutting the handle, figs. 1148 and 1149, the stone is roughed out to the general contour upon mills with rounded edges of appropriate thicknesses. The stone is first wrought of an elliptical section throughout, by continually twisting it round in the fingers. The two longest sides are then flattened by holding the stone firmly in the fingers, and traversing it backwards and forwards a small distance upon the edge of the mill; the four angles are removed in the same manner, and the two narrow ends of the irregular octagon are formed by portions of the original ellipsis, the curvature being scarcely perceptible in the lower part of the handle. The two large flutes, a, are cut by traversing the stone over a mill of about two inches diameter, with a rounded edge; and the four small flutes are cut upon a similar mill, of smaller diameter.

Figs. 1146.

Lapidary Work Slitting Cutting And Polishing Flat  30090


Lapidary Work Slitting Cutting And Polishing Flat  30091


Lapidary Work Slitting Cutting And Polishing Flat  30092


Lapidary Work Slitting Cutting And Polishing Flat  30093