CHALK when simply scraped, or else crushed under the hammer, is occasionally used in polishing bone, ivory, and some few soft substances, it cuts much the finely powdered rottenstone. It is however to be observed that the wheel should be made first to revolve in the one direction, and then in the opposite, that the marks of the hacking-knife may cross each other.

2. - Smaller and harder stones are more commonly polished on a pewter than a lead lap, and for the smallest and hardest stones a copper lap is preferred; but all the polishing tools, of what metal soever they may be made, are hacked as above described, and used with rottenstone and water.

3. - Rounded or Convex Stones, or those said to be cut en cabochon, whether of Carnelian or even several of the harder stones, are in many cases successively wrought by means of the wood mill with fine emery, the fist mill with pumice-stone, and leather lap with putty powder, precisely as described under the head Alabaster. This is done on account of the greater elasticity of these apparatus, which enables them to ply more conveniently to the globular forms of the works to be polished, and avoid wearing them in ridges or flat places.

4. - Facetted Works on all stones and hard substances, are for the most part cut by the Lapidary after one of three different modes. First, for pastes or artificial stones, and many soft stones, as amber, carnelian, jet, etc, the facets are usually cut on a lead wheel with emery, and polished on pewter with rottenstone. - Secondly, for some of a harder kind but inferior in hardness to sapphires, the succession of tools is a pewter lap and fine emery for the cutting, and a copper lap with rottenstone for the polishing. - Thirdly, for sapphires, the chrysoberyl, and rarely for some few others likewise, a copper lap with diamond powder is used for cutting the facets, and a copper lap with rottenstone for polishing them. - And fourthly, with the diamond, two stones are rubbed in a peculiar manner the one against the other to cut the facets, and they are polished by means of the dop, and an iron lap or skive fed with diamond powder; this process is more fully described in vol. 1, page 176.

5. - From the comparatively small size of the stones and gems that are cut into facets, they cannot generally be held unassistedly in the fingers, the stone is consequently cemented centrally upon the end of a round stick of wood, nearly like a drawing pencil. The stick when held vertically, gives the position for grinding the central facet or table of the stone, the stick is inclined to a certain angle for the eight, twelve, or more facets, contiguous to the table; of which facets, two, three, or four series are commonly required at different inclinations, and, lastly, the horizontal position of the stick serves in cutting the girdle or central band around the exterior edge of the stones.

The several inclinations of the stick on which the stone is cemented, are easily determined by placing the upper end of the stick into one of several holes in a vertical post, fixed alongside the lap, and this retains the inclination very accurately and simply, but all these matters will be further elucidated in the 34th chapter on Lapidary Work generally.

6. - The following substances are worked by the lapidary in nearly or exactly the same manner as carnelian, and descriptive articles are introduced in the catalogue upon each of these particular substances, pointing out their principal external features, and also any peculiarities of method, pursued either by the lapidary or other artizan, as the case may be, in working them.

(substances treated by the lapidary like carnelian.)

Agate

Amethyst

Aquamarine

Beryl

Bloodstone

Brazilian Topaz

Carbuncle

Cat's-eye

Chalcedony

Chrysolite

Chrysoprase

Crystal

Elvans

Emerald

Felspar

Flint

Fluor Spar

Garnet

Granite

Heliotrope

Jade

Jasper

Lapis Lazuli

Marble

Mina Nova

Onyx

Opal

Pastes

Peridot

Plasma

Porphyry

Quartz

Sard

Sardonyx

Serpentine

Topazes.