The Transfer.—Transfer-paper for lithographic purposes is made in the following way oz.
gum tragacanth is dissolved in water, strained, and added to 1 oz. glue and oz. gamboge; 4 oz. French chalk, oz. old plaster of Paris, and 1 oz. starch are powdered, sifted through a fine sieve, and ground up with the gum, glue, and gamboge; sufficient water is then added to give an oily consistence, and the compound is brushed on to thin sized paper. The drawing or writing, made on the prepared side of the transfer paper, is wetted on the back, and placed, face downwards, on the stone, which must previously be slightly warmed, say to about 52° (125° F.). The stone is passed through the press four or five times; the paper is then damped, and carefully removed.
Drawing on the Stone.—The subject is first traced on the stone in red, great care being taken not to touch the stone with the fingers. Or the drawing may be done by means of a black pencil ; bnt this is objectionable, as it is difficult to distinguish the line from that made by the chalk or ink. Then, having a rest to steady the hand, the drawing is gone over with the chalk, pressing it with sufficient firmness to make it adhere to the stone. For flat tints, considerable practice is necessary to secure an even appearance, which is only to be obtained by making a great many faint strokes over the required ground. Lights may either be left, or, if very fine, can be scraped through the chalk with a scraper. If any part is made too dark, the chalk must be picked off with a needle down to the required strength.
Preparing for Printing.—After the drawing on the stone has been executed, and is perfectly dry, a very weak solution of nitric acid (1 part in 100 of water) is poured upon the stone, which not only takes up the alkali from the chalk or ink, as the case may be, leaving an insoluble substance behind it, but lowers, to a small extent, that part of the surface of the stone not drawn upon, thus preparing it to absorb water with greater freedom. Place the stone in a sloping position, then pour the solution over it, letting it run to and fro until it produces a slight offer vescence. Then wash the stone with water, and afterwards pour weak gum-water over it. The acid, by destroying the alkali on the lithographic chalk, causes the stone to refuse the printing ink except vvhere touched by the chalk; the gum-water fills up the pores of the stone, and thus prevents the lines of the drawing from spreading. When the stone is drawn on with ink, there must be a little more acid used with the water than when the drawing is made with chalk. The
roller charged with printing-ink is then passed over the stone, which must not be too wet, and the impression is taken by passing through a press, in the usual manner, the processes of watering and inking being repeated for every impression. If the work is inclined to get smutty, a little vinegar or stale beer should be put into the water that is used to damp the stone.
Engraving on Stone.—The stone must he highly polished. Pour the solution of aquafortis and water over it, washing it off at once. When dry, cover with gum-water and lamp-black; let this dry, then etch with a needle, as on copper. It is necessary to cut the surface of the stone through the gum, the distinction of light and dark lines being obtained by the use of fine- and broad-pointed needles. Rub all over with linseed-oil, and wash the gum off with water. The lines on the stone will appear thicker than they will print.
To Imitate Woodcuts on Stone.—Cover with ink those parts meant to be black ; scratch out the lights with an etching-needle ; the lines which come against a white background are best laid on with a very fine brush and lithographic ink.
To remove a Transfer.—The existing transfer is ground away by rubbing it with another piece of stone, putting sand between, using finer sand as it gradually wears away ; then it is ground with rotten-stone, till of the requisite fineness for the next transfer.
Transferring from Copper to Stone.—In transferring from copper to stone, use is made of pre pared paper, that is, ordinary unsized paper, coated with a paste of starch, gum arabic, and alum. About 60 parts of starch are mixed with water to a thinnish consistency over a fire ; have 20 parts of gum ready dissolved, and also 10 parts of alum dissolved; when the starch is well mixed, put in the gum and alum. While still hot, coat the paper with it in very even layers ; dry, and smooth out. Take an impression from the copper with the transfer-ink ; lay the paper on the stone, damp the back thoroughly with a sponge and water, and pass through the lithographic press. If all is right, the impression will be found transferred to the stone, but it will, of course, require preparing in the usual manner. The great advantage gained is, that very many more impressions may be printed from stone than from a copper plate, and very much more quickly.