GRAPHICS. 173 
The invention of lithography was not a result of scientific speculation, but 
was for the most part an accidental phenomenon, intelligently observed and 
turned to good account. The real essence of lithography lies in the so- 
called chemical printing; for in the preparation of the stone there is mueh 
that is identical with the process of etching. This chemical printing is 
based on the repulsion that exists between grease and moisture, and the 
attraction that grease has for grease. Thus, in order to get a design on the 
stone, and afterwards to prepare it for printing, the design is drawn with 
some fatty substance on the nicely ground and polished stone, which must 
then be submitted to a chemical preparation, and all the places which are 
not drawn upon must be rendered impervious to grease by saturating them 
with a solution of gum-arabic, which sinks into the pores of the stone, and 
by washing them over with water. Ifnowaroller charged with a fatty ink 
be passed over the dampened stone, all the strokes of the drawing, being 
greasy, will take ink from the roller; but the moistened parts of the stone, 
which are also made mucilaginous with the gum, will strongly repel the 
fatty ink, and thus remain perfectly clean. If, then, we lay upon the inked 
stone a sheet of damped paper, and pass the two under a press with a pretty 
sharp pressure, the paper will take the ink from the stone and exhibit an 
impression of the design. The wet sponge is passed over the stone again, 
again it is inked, and an impression taken ; and thus, by repeating the pro- 
cess, thousands of impressions may be taken from asingle drawing. 
The design is put on the stone in very different ways; all the modes of 
drawing which are applied to paper have been made applicable, by the use 
of more or less precaution, to stone also. We will consider the principal 
modes more particularly. 
1. Tae Pey-wanner. This manner was the first, that invented by 
Sennefelder. In order to draw in the pen-manner on stone, the artist makes 
use of extremely elastic and very finely pointed steel pens, by means of 
which, and with an ink composed of wax, tallow, soap, mastic, and shellac, 
and colored with some soot, he draws his design completely on the smoothly 
ground and polished stone in the same manneras on paper. In order to 
prevent the ink from spreading on the stone, the latter is covered with a 
very fine coating of spirits of turpentine or soap and water. When the 
drawing is completed, which must be done with the greatest neatness and 
circumspection, taking particular care not to touch the stone with the hands 
or with-anything else of a greasy nature excepting the ink, the next thing 
is to prepare it for printing. Over the stone is poured a very weak dilution 
of nitric acid (12°), which has the effect of converting those portions of the 
calcareous slate which have been impregnated with fat by means of the 
drawing, into oleo-margarate of lime, a fatty substance insoluble in water. 
When the stone has thus been etched in, it is rubbed over with a solution of 
gum-arabic in water of about the consistence of syrup. This gum-mucilage 
penetrates into the pores of the stone wherever there is no: ink, and fixes 
itself so fast that it cannot be washed out again. ‘The stone is now ready 
for printing. When this operation is to be performed, the stone is laid on 
the press. The press is a frame-work consisting of two stands, between 
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