ENGRAVING IN AQUA TINTA. 433 



The principle of the process consists in corrod- 

 ing the copper with aqua fortis, in such a manner, 

 that an impression from it has the appearance of a 

 tint laid on the paper. This is effected by cover- 

 ing the copper with a powder, or some substance 

 which takes a granulated form, so as to prevent the 

 aqua fortis from acting where the particles adhere, 

 by this means causing it to corrode the copper 

 partially, and in the interstices only. When these 

 particles are extremely minute and near to each 

 other, the impression from the plate appears to the 

 naked eye exactly like a wash of Indian-ink ; but 

 "when they are larger, the granulation is more dis- 

 tinct ; and as this may be varied at pleasure, it is 

 capable of being adapted with great success, to a 

 variety of purposes and subjects. 



This powder, or granulation, is called the aqua* 

 tinta grainy and there are two general modes of 

 producing it. 



We shall first describe what is called the powder- 

 grain, because it was the first that was used* 



Having etched the outline on a copper-plate, 

 prepared in the usual way by the coppersmith (for 

 which see the article etching), some substance 

 must be finely powdered and sifted, which will melt 

 with heat, and when cold will adhere to the plate, 

 and resist the action of aqua fortis. The sub- 

 stances which have been used for this purpose, 

 either separately or mixed, are asphaltum, Bur- 

 gundy-pitch, rosin, gum-copal, gum-mastich ; and in 

 a greater or less degree, all the resins and gum- 

 resins will answer the purpose. Common rosin 

 has been most generally used, and answers toler- 

 ably well ; though gum-copal makes a grain that 

 resists the aqua fortis better, 



VOL. II. F F 



