236 Lithographic Process, 



pitched chest before noticed, a composition of aquafortis, and 

 20, 30, or 40 parts of water is poured over it. Experience alone 

 can teach the exact strength of the acid, or the proper duration 

 of its action. The stone having been properly bitten in, should 

 be washed with water ; and, when dry, covered with a solution 

 of gum arabic in four or five parts of water. In two or three 

 minutes, a few drops of water and of oil of turpentine should be 

 spread over the surface of the stone ; and then, by means of a 

 woollen rag, the whole of the drawing may be wiped off. The 

 surface of the stone should then be well wiped with a damp rag, 

 so that it may be every where slightly wet, and immediately 

 charged with printing ink by passing a printing roller several 

 times over it. The stone may then be printed ; to simplify which 

 operation, M. Senefelder gives very copious instructions ; to 

 which we must refer our readers. 



The lithographic chalk is used on the stone in the same man- 

 ner as common black chalk is used to produce a drawing on pa- 

 per ; a coarser or smoother grain having first been communicated 

 to the stone by rubbing it with the finest gravel sand, and a lit- 

 tle soap water. The chalk will not however bear so much cor- 

 roding as the ink. In general therefore, for that purpose, to one 

 part of aquafortis, a hundred parts of water may be added ; and 

 the darker shades may be further bit in bv means of the flat var- 

 nishing brush and stronger acid. The printing of a chalk draw- 

 ing on stone is extremely difficult, and requires strict attention 

 to a variety of cautions recommended by M. Senefelder; who 

 likewise explains at considerable length the way in which defects 

 or accidents may be remedied ; and describes a mode of producing 

 a very agreeable effect by using two plates ; on the one of which, 

 a sort of middle tint is bitten in all over, with the exception of 

 the high lights of the subject, and in the other the shades are ex- 

 pressed. Several stones may thus be brought into play; and a 

 variety of colours thereby introduced. 



The transfer manner M. Senefelder considers as the most im- 

 portant part of his invention. The paper for this manner must 

 be previously prepared with a thin starcli, mixed up with French 

 chalk, plaster of Paris, and gamboge. The drawing or writing 

 is effected on it with a dilution of tlie chemical ink in soft water. 

 When dr\-, the back of the paper must be sponged with very 

 weak aquafortis until it is thoroughly soaked, when the super- 

 fluous moisture must be absorbed by blotting paper, and being 

 placed with its face on a clean stone, the whole must be passed 

 two or three times through a press. When taken out, it must be 

 put into the pitched chest, and a solution of aquafortis in water 

 (one part of aquafortis to a hundred parts of water) be poured 

 over it so as to wet the whole surface. Pure water must then be 



poured 



