Page:Encyclopædia Britannica, Ninth Edition, v. 14.djvu/723

 LITHOGRAPHY 699 spots, and of a clear grey colour, is selected. It is first ground and pumiced to free it from scratches. A small quantity of the finest gravel sand, or &quot; graining-sand,&quot; is sprinkled over the surface, and a few drops of water added; a smaller stone of the same size and hardness is placed above, face downwards, and moved about with a circular motion ; water is added from time to time, and fresh sand when needed. Care must be taken that no scratches are caused by grains of coarser sand finding their way to the stone; the stone is afterwards washed in clean water and dried, and the grain tested with a crayon. If it prove too coarse or too fine, or if scratches are dis covered, the graining is done over again. The drawing is then traced upon the stone. As it has to be reversed, the tracing is fastened face downwards ; red tracing paper is introduced between, and the outline care fully gone over with a steel tracing point or a hard pencil. The tracing papers are then removed, and the surface of the stone protected with a sheet of plain paper. The hand-board is placed across to keep the warmth of the hand from causing the condensation of moisture resulting from its coming in contact with the paper covering the stone. The paper covering the part of the drawing to be first commenced is then removed. The crayons are pointed with the knife, cutting from the point upwards. Great care and cleanliness are necessary to prevent injury to the work. If the artist wishes to talk he ought first to cover up the surface of the stone, as a drop of saliva falling upon it prevents the penetration of the chemical chalk, and a white spot will be the result when the drawing is &quot; brought up &quot; by the printer. If the stone is touched by greasy hands, the form of the fingers and of the skin will appear in black. The drawing is commenced by outlining; For this pur pose the hardest chalk (copal) may be used, but No. 1, when it will answer the purpose, is better. The &quot; tinting&quot; or shading follows ; lights may be picked out with the scraper or penknife, and ink used when sharp, dark touches are desirable. It is difficult to rectify mistakes ; prevention is better than cure. In reversing the drawing a small hand looking-glass will be found useful. When completed the drawing is &quot;etched.&quot; There are two different ways of applying the acid one by flooding the stone with nitric acid diluted with water, the other with acid diluted with gum-water, applied with a flat, soft brush about 4 or 5 inches in width. Although this opera tion appears simple, it is not without risks ; much of the success of the impressions depends upon it. If the stone is too strongly etched, the delicate tints and lines dis appear ; if not etched strong enough, the drawing is apt to lose clearness, and run smutty in printing. When the etching is completed, the water is drained off and the stone gummed and allowed to dry. It may then be put into the hands of the printer for proving. Pen and Brush Method. -The surface of the stone is ground and afterwards polished with Water-of-Ayr stone or snake-stone. The drawing or writing is traced upon the surface in the manner already described. The principal drawback in this method is the necessity of reversing writ ing and lettering, which cannot be done without consider able practice. Its advantages over the transfer method scarcely compensate for the additional difficulties. The etone is etched as in chalk drawing before passing into the printer s hands. Engraving on stone is chiefly useful in the reproduction of drawings by architects, civil engineers, &amp;lt;fcc. Its advant ages are accuracy and sharpness in drawing and printing. A thin film of gum is spread on the surface of the stone, and when dry washed off; a dark ground is then laid on by rubbing in Paris black, lied grounds also are sometimes used. The tracing, if on a black ground, is made with paper prepared with chrome yellow, if on a red ground with Paris black. The method of engraving is simple. The tools are strong needles, firmly fixed in cane handles, and good spring dividers ; the incised lines show white upon the black or red ground. When the work is finished they are filled up with fatty ink, and the stone cleared with water and a piece of coarse flannel. In printing, the stone is damped in the usual way, but the ink is applied with a dabber instead of a roller. Lithography on Paper, or Transfer Lithography. By this method the work is done on paper, and afterwards transferred to the stone. The paper has been already described, as also the instruments used in writing and drawing. The ink is prepared by rubbing a small quantity into a saucer of white delft or china, the saucer being first heated to make the ink adhere ; water is then added, and the ink rubbed with the finger till it dissolves. Care has to be taken to make it of the proper consistency. If pale and thin, it will not transfer properly ; if too thick, it will not flow freely from the pen or brush, and will spread in transferring. The paper should not be handled or touched, except at the edges. Finger marks from a moist or greasy hand will roll-up black. A piece of clean white paper is kept under the hand when working. The same line must not be gone over twice while wet, as the composition on the surface of the paper is apt to get mixed with the ink and destroy its qualities. In drawing on chalk transfer paper the crayon is used instead of the brush or pen. Dark touches may be put in with ink, and the lights picked out with the knife. The stone for the reception of transfers is polished free from perceptible scratches, and is generally warmed to make it more susceptible of receiving the ink. The transfer is placed face downwards on the stone, pulled repeatedly through the press, and afterwards removed to the trough, where hot water is poured over it. It is then peeled off, leaving the ink and the composition on the stone ; the latter is washed off, and the stone gummed and allowed to dry. The work is afterwards &quot; proved&quot; by rolling-up, cleaning, etching, and taking the first impressions. The transfer method is also applied successfully to the reproduction by lithography of engraved plates, wood en gravings, and type. Photo-Lithography. By this method copies of prints or drawings executed in clear lines or dots can be produced. They may be either of the same or of altered dimensions. The copying is done by photography upon glass ; but, as it is necessary that the negatives should have straight marginal lines, ordinary photographic lenses are not adapted for the purpose &quot; rectilinear,&quot; &quot; aplanatic,&quot; &quot; symmetrical,&quot; and other varieties being used instead. The negative is put into a photographic printing frame, and a piece of sensitive transfer paper placed face downwards upon it, the glass side being exposed to the light. The time of exposure varies according to the intensity of the light and the quality of the negative. When sufficiently exposed it is carried into a dark room, the photographic print taken out of the frame, laid face downwards on a stone coated over with transfer ink, and pulled through the press. It is then soaked for a few minutes in water warmed to the temperature of 100, and the inked side of the paper carefully sponged with gum-water to remove the transfer ring ink from the parts upon which the light could not act. After being washed in warm water it is allowed to dry, and is then transferred to the stone and printed from in the usual manner. Zincography so nearly resembles lithography in its principles that a very few words of explanation will be sufficient. Zinc plates possess the advantage of costing less