The stone most used in England is found at Corstan, near Bath: it is one of the white lias beds, but not of so fine a grain, nor so close in texture as the German stone, and therefore inferior; but it is good for transfers, and does tolerably well for ink drawings or writings. All calcareous stones may be used in lithography, because they imbibe grease and moisture; but a stone entirely calcareous does not answer well; there should be a mixture of alumina and silex. One of the most certain indications of lithographic properties, is the conchoidal fracture: all stones of this kind will be found good, if they are also hard, have the fineness of grain, and the homogenousness of texture that are necessary. It is however said that none have yet been found equal to those obtained from the quarries of Solenhofen, near Pappenheim in Bavaria, and that the lithographers of eminence in Paris use no other. In order to sustain the pressure used in taking impressions, a stone, 12 inches square, ought not to be less than 1 1/4 inch thick, and this thickness should increase with the area of the stone.
The stones are first sawn to a proper size, and are then ground smooth and level by rubbing two of them face to face, with water and sand. They must be very carefully examined with a straight edge, to ascertain that they are perfectly level in every direction. This applies only to the side which is afterwards to receive the drawing, as the natural division of the stone is sufficiently true for the back. When the stones have thus been ground perfectly level, they are well washed, to free them from any of the coarser grains of sand which may have been used in smoothing them. They are then placed on a board over a trough, and they are again rubbed face to face with sand and water, but with a sand of much finer texture than that previously used. The greatest care must be taken to have the sand sufficiently fine; and for this purpose it must be sifted through a small close sieve, as a single grain of sand of a coarser texture than the rest will scratch the stone, and these scratches will afterwards appear in the impression taken from the stone. When the stones have been rendered sufficiently fine, and their grain sufficiently smooth, they must then be carefully washed and afterwards wiped dry with a clean soft cloth.
This is the plan adopted to prepare the stones for chalk drawings, but to prepare them for ink drawings or writings, the following method is the best: - After the process just described has been completed, the stones are well washed to get rid of the sand, and they are then rubbed to together, face to face, with powdered pumicestone and water. After they are made perfectly smooth, they are again washed and wiped dry, and are then separately polished with a large piece of pumicestone.
To clean the stones after they have been fully used, sand is strewed over the surface, which is sprinkled with water and rubbed with another stone, until the writing or drawing upon it has completely disappeared. It must then be washed in aquafortis, diluted with twenty times its bulk of water; and the stone is then prepared for a new drawing or writing, by being rubbed with fine sand or pumicestone as before. The longer drawings remain on stones the deeper the ink or the chalk penetrates into their substance, and consequently the more of the stone must be ground away to remove them; this is also more necessary with ink drawings or writings than with chalk, owing to the greater fluidity and consequent penetrability of the former.
The substances used by the artist upon the stone, are either lithographic ink. or lithographic chalk. The former has been described under the article Ink, (which see;) but -
The Ink for making transfers should be somewhat less burned, and therefore softer than that used for writing or drawing directly upon the stone.
Lithographic chalk should have all the qualities of a good drawing crayon. It should be even in texture, and carry a good point. The following proportions are recommended: 1 1/2 oz. of common soap, 2 oz. tallow, 2 1/2 oz. virgin wax, 1 oz. shell-lac. The rest of the process is the same as in making the ink. Less black should be mixed with the chalk than with the ink, its only use being to colour the drawing, that the artist may see the lines he traces. When the whole is well mixed, it should be poured into a mould and very strongly pressed, to expel any air that may collect in bubbles, which would render it spongy.