446 LITHOGRAPHY. 



and even burning them in an iron vessel. When 

 cold, the mass is rubbed on a tile with water, like 

 Indian ink, and put into a pen or brush. 



The lithographic chalk is formed of 2 oz. of tal- 

 low, 2J oz. of bees-wax, 1 oz. of shell lac, and 

 If oz. of common soap. These are also united by 

 heating as before ; when cold it is cut into slips, 

 and used as a crayon. 



When the drawing is made on the stone with 

 the pen and ink, or with the chalk or crayon, some 

 water, having in it a little nitric acid, is poured 

 over the stone, which slightly corrodes the sur- 

 face ; gum-water is then laid on with a brush, and 

 the stone is left to dry ; it is now ready for print- 

 ing from. 



To print from the stone, the printer proceeds to 

 wet the surface of it with a sponge with water, 

 and then applies the printing ink, by a roller. 



The printing ink, made of equal parts of burnt 

 oil or varnish, and lamp-black, sometimes with the 

 addition of wax and tallow, adheres to the lines 

 which have been drawn with the lithographic ink 

 on the stone, while the water prevents it from 

 sticking to the rest of the surface. The lines alone 

 are thus charged with printing ink. Some damped 

 paper is now laid upon the stone, and passed 

 through a press, by which an impression is obtained. 

 The stone is again wetted, and the printing ink 

 applied for a second impression, and so on. 



The process is the same for printing chalk draw- 

 ings ; but they are more difficult to print, and give 

 fewer impressions. 



This art has made considerable progress on the 

 continent ; in this country it has advanced more 

 slowly, chiefly from the secresy employed in the 



