LITHOGRAPHY. 



493 



press A A A A, consists of four stout legs, firmly 

 fixed to the floor, and spread out like the feet of a 

 desk stool, as is seen in the figure, in order to insure 

 stability. The upper ends of these feet are connected 

 by four strong bars forming the support of the press. 

 Two uprights rise from this frame, one on each side 

 of the press ; the one next the eye being shown at 

 13. Each of these uprights has a smooth cylindrical 

 rod, which serves as a guide to the platten or scraper 

 box C, so that it may move easily up or down in a 

 direction perpendicular to the table of the press, 

 which is shown at D. This table moves on rails, in 

 a manner similar to the table in the press of earl 

 Stanhope (See Printing Press in this work), and on 

 the table the stone is put from which the impression 

 is to be taken. The platten, or scraper box, is 

 pressed down by means of the lever E, which is 

 brought down in the direction of the table rail, and 

 its lower extremity being formed like a wiper, or 

 having a curved shape, drives down a spindle in the 

 centre of the platten, and presses it on to the table. 

 There is a spring fastened to the middle of the spin- 

 dle, and fixed to the side uprights, which causes the 

 scraper box to rise so soon as the lever E is allowed 

 to rise to the position represented in the engraving. 

 There is a roller crossing the press, and on a level 

 with the top of the frame, which is turned by the 

 handle G, and so situated that when turned, it causes 

 the table to move under the scraper box. F repre- 

 sents the tympan, a rectangular iron frame, moveable 

 on a joint at the bottom, which frame is covered with 

 parchment similar to the tympan in the press for type 

 printing. The scraper is a wedge-formed plate of 

 steel, fixed into the bottom of the platten with its 

 edge downmost, and nicely adjusted by screws so 

 that it may lie parallel with the face of the stone 

 lying on the table of the press. The operation of 

 the press is simply this : the stone being prepared 

 with the drawing in a manner that will afterwards be 

 ilcs cribed, is laid on the table, the paper is laid over 

 it, and the tympan brought down. The table is then 

 mo ved forward to the scraper, the long lever is 

 brought down, and the handle G is turned so as to 

 draw the stone under the scraper, which is kept 

 pressing upon the tympan ; the pressure is then taken 

 o fF, and the stone moved back to its former position 

 by turning the handle G. 



The manner of preparing the stone depends upon 

 the kind of work to be executed. To prepare them 

 for printing chalk drawings, two stones of the requi- 

 site dimensions are selected, one of which is placed 

 in the table formerly described, with a little finely 

 powdered quartz or hard sand (silver sand is the best 

 that can be procured in this country). A little 

 water is then put on the stone, and the other stone, 

 being placed upon it, they are ground by giving the 



up[>er stone small circular sweeps in various direc- 

 tions. Sand and water being constantly added, 

 the grinding is continued until the surfaces of the 

 stones are quite level. The sand must be passed 

 through a sieve, in order to obtain it of equal grain. 

 When ground, the stone should be carefully washed. 

 When dry, the stone ought to have a uniform colour, 

 and be perfectly free of scratches. M. Jobard, a 

 lithographer, in Paris, has lately discovered an 

 improved method of grinding, which consists in 

 using a spoonful of starch along with the sand. The 

 greatest care is necessary in cleaning the stone of 

 both starch and sand, by means of a brush and 

 water. 



When the stone is to be prepared for ink drawings 

 or writings, it must be polished. The grinding 

 process, already described, is first pursued, and the 

 polish is then given in the following manner. The 

 circular motion is continued, and water but no more 

 sand is added, until no grains appear, the polishing 

 being given by the sort of paste formed by the water 

 and the attenuated sand. The stone is now washed, 

 and the same process is continued with powdered 

 pumice stone. A fine polish is thus obtained ; but 

 the finishing is effected by polishing the stone with a 

 large piece of pumice stone until the polish is equal 

 to that commonly given to marble, i. e., until 

 objects are seen reflected from the surface when the 

 eye is placed near it. 



When a drawing or stone has been used, it must 

 be carefully taken out by rubbing two stones toge- 

 ther with water, and that immediately after coining 

 from the press. Ink drawings are much more diffi- 

 cult to efface than chalk ones. When all traces are 

 effaced, the stone must be washed with dilute nitric 

 acid, the acid being five per cent, the bulk of the 

 water. 



Ink for this kind of drawing should be insoluble in 

 water, flow easily from the pen, not liable to spread 

 on the paper or stone, to which last it should adhere 

 firmly, have great solidity on being treated with 

 the acid solution, and, lastly, a good body of colour. 

 An ink having these properties is formed by a compo- 

 sition, the parts being taken by weight : 



Dried tallow soap, . . 30 parts. 



Mastic in drops, . . .30 



Subcarbonate of potash, . . 30 



Chinese or table varnish, . . 150 



Lamp black, . . . . 12 * 



The tallow being well dried, the whole of the 

 materials are put into a clean copper vessel, which 

 "s placed on a brisk fire. Keep stirring until the 

 melting and mixing is completed, when they are to 

 je poured into a mould of metal that has been heated 

 to a considerable degree. The metal is heated so 

 as to prevent the composition from cooling too 

 rapidly, in order that it may the more easily be cut 

 nto regular strips. Such is the mode of preparing 

 ;he ink for the stone. When the drawing or writing 

 s to be done on paper, and from thence transferred 

 to the stone, ink of a tougher nature is required, which 

 may be composed as follows : 



Dry soap, . . . jOO parts. 



White wax, without tallow, . 100 



Sheep's fat, . . . .30 



Gum lac, . . . .50 



Mastic, .... 50 



Lamp black, . . .30 



Transfer or autograph paper is prepared thus : 

 take smooth common-sized paper and lay a coat of 



An inferior kind of ink isg>iven in some works, consist 

 of equal parts of candle tallow, virgin wax, shell lac, 



.oinmon soap, and one twentieth part of the whole weight 



if lamp hlack. 



