ISO l.i:G.TUiB;E .XI. 



iiisli, is usually blackened with smoke, giitltlie drawing is placed on it, with the 

 interposition of a paper nibbed over with red chalk, which, when the drawing 

 is traced with a wooden point, adheres to the varnish, in the form of the out- 

 line: or if it is re(iuired that the ultimate impression be turned the same way 

 as the drawing, an intermediate outline must be procured in the same man- 

 ner on a separate paper, and then transferred to the plate. All the outlines 

 thus marked are traced with needles, which make as inany furrows in the 

 varnish, and leave the copper bare: tjie shades are inserted with the assist- 

 ance of the ruling machine, wherever parallel lines can be employed. The 

 plate tlms prepared, and furnished with an elevated border of a proper con- 

 sistence, is subjected to the action of the diluted nitric acid, until all the 

 parts arc sufficiently eorroded, care being taken in the mean time to sweep 

 off the air bubbles as they collect, and to stop out, oi; cover with a new ya,r- 

 nish, the lighter parts, which aje soonest completed. When the varnish is re- 

 moved, the finishing touches are added with the graver: and if the plate re- 

 quires further corrosion, the varnish jnay sometimes be replaced, without fill- 

 ing up the lines, by applying it on a ball or cushion, taking care to avoid 

 any oblique motion. It is said that the acid sometimes operates so as to un- 

 dermine the metal on each aide, adad to render the furrows wider as they be- 

 come deeper, and that for this reason in etchings, as well as in mezzotintos, 

 the later impressions are sometimes darker than the proofs; but this is by no 

 means universally true. It is well known to chemists, that glass may be cor- 

 roded in a similar rjaanner by means of the fluoric acid. 



An etching may also be expeditiously executed by using a varnish mixed 

 with mutton fat, and drawing upon a paper laid on the plate ; the varnish 

 then adheres to the back of the paper, under the lines which are drawn, and 

 is immediately removed when the paper is taken off, without the use of 

 needles. Sometimes the outlines only are etched, and the plate is finished in 

 mezzotinto. 



In the mode of engraving called aqua tinta, the outline having been first 

 etched, the shades are also produced by corrosion, the parts being prepared 

 by various methods, so as to be partially protected from the action of the 

 iicid. Sometimes a little resin, very finely powdered, is sifted on the plate, 

 •whioh is:then sufficiently warmed to make the particles adhere to it; some- 



