ON MODELLI^'G, PERSPECTIVE, ENGRAVING, AND PRINTING. IIQ 



the chawing, if it is not executed in black lead, is generally prepared by 

 passing a pencil over its principal features, and the outline is transferred to 

 the plate, which has a thin coat of white wax laid on it, by placing the draw- 

 ing on it, and rubbing it with a burnisher ; sometimes a drawing in Indian ink, 

 especially if freed from a part of its gum, may be transferred in this manner 

 without the application of a pencil. When written characters are to be en- 

 graved, the plate is laid on a cushion, so as to be readily turned under the 

 graver, which is a great convenience in forming curved lines. 



In laying on equable shades of considerable extent, much labour is saved 

 by the use of a ruling machine, which enables us to draw lines, at any re- 

 quired distance, very accurately parallel, and either straight, or following 

 each other's gentle undulations, in order to avoid the appearance of stiffness. 

 This machine, like the dividing engine, is sometimes adjusted by the revolu- 

 tions of a screw, and sometimes by the oblique motion of a triangular slider. 

 Besides the cutting graver, which is of a prismatic form, terminated by an 

 oblique surface, other instruments are occasionally employed; the dry needle 

 makes a very fine line, and leaves the metal that it has displaced, to be rub- 

 bed off by anothei- tool. Sometimes a number of detached excavations are 

 formed by a pointed instrument, and the projections are afterwards removed; 

 this is called stippling. A burnisher and some charcoal are required for 

 erasing the strokes of the graver, when it is necessary, and for polishing the 

 surface. It is seldom, however, that a plate is begun and completed by dry 

 engraving only. 



For engraving in mezzotinto, the plate is roughened, by scraping it in 

 every direction with a tool made for the purpose, so that an impression from 

 it, in this state, would be Avholly dark ; the lights are then inserted, by re- 

 moving the inequalities of the surface, in particular parts, by means of a 

 smooth scraper, and a burnisher. As the plate wears in printing, some of 

 these parts are liable to have the grain a little raised again, so that the lights 

 are less clear in the later impressions than in the proofs. It is well known, 

 that in common engravings the proofs are usually the darkest throughout. 



The most expeditious and most generally useful mode of working on cop- 

 per, is the process of etching. The plate, being covered with a proper var- 



