The lithographic stones of the best quality are still procured from the quarry of Solenhofen, a village at no great distance from Munich, where this mode of printing had its birth. They resemble in their aspect the yellowish white lias of Bath, but their geological place is much higher than the lias. Abundant quarries of these fine-grained limestones occur in the county of Pappenheim, along the banks of the Danube, presenting slabs of every required degree of thickness, parted by regular seams, and ready for removal with very little violence. The good quality of a lithographic stone is generally denoted by the following characters; its hue is of a yellowish gray, and uniform throughout; it is free from veins, fibres, and spots; a steel point makes an impression on it with difficulty; and the splinters broken off from it by the hammer, display a conchoidal fracture.
The Munich stones are retailed on the spot in slabs or layers of equal thickness; they are quarried with the aid of a saw, so as to sacrifice as little as possible of the irregular edges of the rectangular tables or plates. One of the broad faces is then dressed, and coarsely smoothed. The thickness of these stones is nearly proportional to their other dimensions; and varies from an inch and two-thirds to 3 inches.
In each lithographic establishment, the stones receive their finishing, dressing, and polishing; which are performed like the grinding and polishing of mirror plate. The work is done by hand, by rubbing circularly a movable slab over another cemented in a horizontal position, with fine sifted sand and water interposed between the two. The style of work that the stone is intended to produce, determines the kind of polish that it should get. For crayon drawing the stone should be merely grained more or less fine according to the fancy of the draughtsman. The higher the finish of the surface, the softer are the drawings; but the printing process becomes sooner pasty, and a smaller number of impressions can be taken. Works in ink require the stone to be more softened down, and finally polished with pumice and a little water. The stones thus prepared are packed for use with white paper interposed between their faces.
Lithographic crayons.—Fine lithographic prints cannot be obtained unless the crayons possess every requisite quality. The ingredients composing them ought to be of such a nature as to adhere strongly to the stone, both after the drawing has undergone the preparation of the acid, and during the press-work. They should be hard enough to admit of a fine point, and trace delicate lines without risk of breaking. The following composition has been successfully employed for crayons by MM. Bernard and Delarue, at Paris:—
| Pure wax, (first quality) | 4 |
| Dry white tallow soap | 2 |
| White tallow | 2 |
| Gum lac | 2 |
| Lamp black, enough to give a dark tint | 1 |
| Occasionally copal varnish | 1 |
The wax is to be melted over a gentle fire, and the lac broken to bits is then to be added by degrees, stirring all the while with a spatula; the soap is next introduced in fine shavings; and when the mixture of these substances is very intimately accomplished, the copal-varnish, incorporated with the lamp black, is poured in. The heat and agitation are continued till the paste has acquired a suitable consistence; which may be recognised by taking out a little of it, letting it cool on a plate, and trying its quality with a penknife. This composition, on being cut, should afford brittle slices. The boiling may be quickened by setting the rising vapours on fire, which increases the temperature, and renders the exhalations less offensive. When ready, it is to be poured into a brass mould, made of two semi-cylinders joined together by clasps or rings, forming between them a cylindric tube of the crayon size. The mould should be previously smeared with a greasy cloth.
M. Lasteyrie prescribes a more simple composition, said to be equally fit for the lithographer’s use:—
| Dried white tallow soap | 6 | parts. |
| White wax | 6 | — |
| Lamp black | 1 | — |
The soap and tallow are to be put into a small goblet and covered up. When the whole is thoroughly fused by heat, and no clots remain, the black is gradually sprinkled in with careful stirring.
Lithographic ink is prepared nearly on the same principles:—