MODELLING, PERSPECTIVE, ENGRAVING, PRINTING. 93 



varnish then adheres to the hack 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 heen 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 

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

 which is then sufficiently warmed to make the particles adhere to it ; some- 

 times it is varnished with a spirituous solution of resin, which cracks 

 throughout in drying : and if a strong line be any where required, it may 

 be traced with a mixture of whiting with some adhesive substance, before 

 the varnish is laid on ; this will cause it to break up at that part ; or the 

 varnish may be partially removed, by rubbing it with spirits or with an 

 essential oil. The lighter parts may be covered, during the corrosion, with 

 a second varnish, which defends them from the acid. This mode of en- 

 graving succeeds very well in imitating the effect of drawings, but the 

 plates are soon worn out. In order to judge of the state of the work, an 

 impression of any part of the plate may be taken off, by pouring on it a 

 little plaster of Paris mixed with water. 



Musical characters are usually stamped with punches ; in this country, 

 on plates of pewter, but in France generally on copper. Mr. Rochon * 

 has invented a machine for stamping letters on copper, instead of printing, 

 but the method does not appear to have been practically employed. 



In whatever way the plate may have been engraved, when an impression 

 is to be taken from it, it is covered with printing ink of the finest kind, by 

 means of stuffed balls, and then wiped, chiefly with the hand, so that the 

 ink is wholly removed from the polished surface : it is then placed, with 

 the moistened paper, on a board, between flannels, and strongly pressed 

 in passing between two wooden rollers. By frequent use the plate loses its 

 sharpness, and sometimes requires to be retouched ; hence arises the 

 greater value of first impressions ; but by proper precautions in cleaning 

 the plate, its delicacy may be preserved for a long time. 



An impression, while it is moist, may be reversed, by passing it through 

 the press with another paper. And by writing with a peculiar ink, even 

 common letters may be thus copied on thin paper, and the impression will 

 be legible on the opposite side. Mr. Montbret proposes to put some sugar 

 candy into the ink, and to take a copy on unsized paper by means of a 

 hot iron.f 



A simple and elegant method of multiplying drawings has been lately 

 introduced by Mr, Andre. The drawings are made with an unctuous com- 

 position, in the form of a crayon or of an ink, on a soft stone of a calca- 

 rious nature, somewhat like a stone marie. When the drawing is finished, 

 the stone is moistened, and imbibes so much Svater that the [unctuous] 

 printing ink will not adhere to it, except at the parts where the crayon or 

 tne ink has been applied [for neither will water adhere to grease nor grease 

 to water] ; and in this manner an impression is procured, which has much 

 * Nich. Jour. 4to, Ui. 61. f Ibid. 8vo, i. 147. 



