LITHOGRAPHIC STONES, are a fine oolite, a peculiar kind of fine granular limestone, principally obtained from the interior of Germany.
The surfaces of lithographic stones are required to possess different degrees of smoothness, according to the subject for which they are employed. When the drawing is to be made at once upon the stone, a certain amount of roughness or granulation is necessary, or it will not so well abrade the lithographic drawing chalk, and this granulation is required to be more or less fine according to the kind of drawing. But much smoother surfaces are required for those stones upon which the transfer process is to be employed, as for lithographic writing, which is first executed on paper, and then transferred to the stone, by passing them together through the press.
The stones are, 1st, rubbed smooth with another lump of lithographic stone, and silver sand applied With water, the sand is prepared of different degrees of fineness by sifting, as explained under the head Emery, the coarsest sieves employed have about 80 wires in the inch, the finest about 120. The stones for chalk drawing are left from the sand of appropriate fineness, but those required for the transfer process are, 2ndly, smoothed with a lump of pumice-stone and water, and 3rdly, polished with a piece of snake stone, also applied with water.