THE GEAPHOTYPE. 
209 
brushed the surface with a dry tooth-brush. “The lines 
of the drawing/* says Mr. Fitzcook,* “ being literally com- 
posed of stone, withstood the assault of the tooth-brush; 
but the intervening particles of exposed chalk succumbed and 
vanished in a cloud of snowy dust, leaving the impregnable 
lines standing in relief, inviting a proof of their strength by 
printing on paper. This could not be done until the whole 
mass of chalk was changed into stone by saturating it with the 
liquid glass, but in half an hour the chalk block was inked and 
printed from in the ordinary way by burnishing.** 
A number of experiments led to the following general method 
as the most perfect. Instead of a simple slab of chalk, a 
chalk surface upon a metallic plate is adopted. French chalk 
is reduced to the finest possible powder by grinding, and then, 
in order to separate the coarser particles from the finer ones, it 
is thrown into water, and the sediment which first subsides is 
removed and again ground. These operations are repeated 
several times, until a high degree of pulverization has been 
attained. The- powder is next repeatedly sifted through a 
wire cloth, which contains 10,000 holes to the square inch, and 
is now ready to be laid upon the smooth metallic (zinc) plate. 
When this has been done, the layer is covered with a perfectly 
smooth steel plate, and is submitted to intense hydraulic 
pressure. The chalk surface has then only to be sized before 
being ready for the artist. In drawing upon the graphotype 
block, the outline is first traced with red chalk as in the 
ordinary way. The artist then employs sable-hair pencils and 
an ink which is composed of lamp-black and glue, which 
dries so rapidly that as soon as one set of lines are drawn they 
may be crossed by another series without any danger of blotting. 
As soon as the drawing has been completed, the surface is 
rubbed gently with brushes made of silk velvet or fitch-hair, 
till the portions of chalk intervening between the inked lines 
are disintegrated and removed to the depth of the eighth of an 
inch. The drawing is now in relief upon the prepared surface, 
and the next operation consists in hardening it. This is done 
by soaking the block in a solution of an alkaline silicate (water- 
glass) : the silica combines with the lime, and thus converts the 
surface into one which is virtually stone. 
At this point the purely graphotype operations are at an 
end ; but the reader must not suppose that the block which 
has thus been prepared and petrified is used to print with. It 
might be so employed, but since it would not stand the me- 
chanical “ wear and tear ** of the printing processes, it is not 
placed in the machine. A mould is taken of it, and from this 
* Journal of the Society of Arts , December. 
