ELECTROPLATING AND ELECTROTYPING. 179 



wooden blocks. The edges are cut with a circular saw, and the 

 profiles of the metal are planed according to a determined 

 caliper. The borders are obliquely filed so as to disengage 

 the top part, and the plate is mounted on a piece of oak or 

 mahogany. 



Before effecting the mounting the electro must be carefully 

 examined, and should there be any depression found it should 

 be straightened by slightly tapping it at the back. 



The machine (Fig. 30), the working of which can be under- 

 stood by a mere reference to the illustration, is intended for 



FIG. 30. 



Machine for regulating the Thickness of Plates. 



reducing the plates to very regular thicknesses, and the 

 machine (Fig. 31) for shaping the wood backings on all their 

 faces. These two machines are indispensable for obtaining 

 good electros, which are easily brought up in the printing 

 machine or press. 



STEEL-COATED ELECTROTYPES. When an electro has to 

 be used a great number of times it is useful to cover it with an 

 iron pellicle. By this means the duration of the electro is pro- 

 longed, and a more artistic impression obtained than with the 

 copper only. The deposit must be exceedingly thin, otherwise 



N 2 



