132 



LITHOGRAPHY 



Zinc plates are sometimes used in lieu of stones ; they are prepared by graining the 

 surface with fine sand, rubbed over by means of a small piece of the metal. Zinc 

 takes a finer surface than stone, and yields more delicate impressions ; but great care 

 is necessary in keeping it dry, so that it does not corrode ; this is almost the only 

 objection to its more general use, for it is fur more convenient to handle and move 

 about than heavy stones. 



Lithographic Crayons. Fine lithographic prints cannot be obtained unless the 

 crayons possess every requisite quality. The ingredients composing them ought to be 

 of such a nature as to adhere strongly to the stone, both after the drawing has under- 

 gone the preparation of the acid, and during the press-work. They should be hard 

 enough to admit of a fine point, and trace delicate lines without risk of breaking. 

 The following composition has been successfully employed for crayons by MM. Bernard 

 and Delarue, at Paris : 



Parts 

 Pure wax (first quality) ...... 4 



Dry white tallow soap ...... 2 



White tallow .2 



Gum lac ......... 2 



Lamp-black, enough to give a dark tint . . .1 

 Occasionally copal varish 1 



The wax should be melted over a gentle fire, and the lac, broken to bits, is then 

 added by degrees, stirring all the while with a spatula : the soap is next introduced 

 in fine shavings ; and when the mixture of these substances is very intimately accom- 

 plished, the copal varnish, incorporated with the lamp-black, is poured in. The heat 

 and agitation are continued until the paste has acquired a suitable consistence ; which 

 may be recognised by taking out a little of it, letting it cool on a plate, and trying its 

 quality with a penknife. This composition, on being cut, should afford brittle slices. 

 The boiling may be quickened by setting the rising vapours on fire, which increases 

 the temperature, and renders the exhalations less offensive. When ready it is to be 

 poured into a brass mould, made of two semi-cylinders joined together by clasps or 

 rings, forming between them a, cylindric tube of the crayon size. The monld should 

 be previously rubbed with a greasy cloth. 



The soap and tallow are to be put into a small goblet and covered up. When the 

 whole is thoroughly fused by heat, and no clots remain, the black is gradually 

 sprinkled in with careful stirring. 

 Lithographic ink is prepared nearly on the same principle : 



Parts 



16 



6 



6 



12 

 8 

 1 

 4 



The mastic and lac, previously ground together, are to be carefully heated in the 

 turpentine ; the wax and tallow must be added after they are taken off the fire, and 

 when their solution is effected, the soap-shavings are to be thrown in. Lastly, the 

 lamp-black is to be well intermixed. Whenever the union is accomplished by heat, 

 the operation is finished ; the liquor is left to cool a little, then poured out on tables, 

 and, when cold, cut into square rods. 



Lithographic ink of good quality ought to be susceptible of forming an emulsion so 

 attenuated that it may appear to be dissolved when rubbed upon a hard body in dis- 

 tilled or river water. It should flow in the pen, but not spread on the stone ; capable 

 of forming delicate traces, and very black, to show its delineations. The most essen- 

 tial quality of the ink is to sink well into the stone, so as to reproduce the most 

 delicate outlines of the drawing, and to afford numerous impressions. It must, 

 therefore, be able to resist the acid with which the stone is moistened in the pre- 

 paration, without letting any of its greasy matter escape. 



M. de Lasteyrio states that, after having tried a great many combinations, he gives 

 the preference to the following : 



Parts 



Tallow soap, dried 30 



Mastic in tears .30 



White soda of commerce 30 



Shell-lac 150 



Lamp-black 12 



