ON MODELLING, PERSPECTIVE, ENGRAVING, AND PRINTING. 121 



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

 out in drying ; and if a strong hue be any where required, it may be traced 

 with a mixture of whiting with some adhesive substance, before the varnish 

 is laid on; this Avill 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 tliem from the acid. This mode of engraving 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 in- 

 vented 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 ffannels, and strongly pressed in pass- 

 ing between two wooden rollers. By frequent use the plate loses its sliarpness, 

 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, e\cn 

 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. 



A simple and elegant method of multiplying drawings has been lately in- 

 troduced by Mr. Andr^. The drawings are made with an unctuous compo- 

 sition, in the form of a crayon or of an ink, on a soft stone of 4 calcarious 



VOL. I. li 



