60 ELECTROTYPE PROCESSES. 



letting the copper remain. Some operators, when it can be done, 

 remove the plaster, and wash over the inside with an alloy of tin and 

 lead melted. In this case the copper must previously be cleaned by 

 washing first in a solution of potash, and then with chloride of zinc : 

 the latter mode will cause the alloy to adhere to the copper, and give 

 it strength. In either of these cases the deposit must not be very 

 thick, or it will throw the figures out of proportion, such as the 

 features of a bust, &c. Any slight roughness of deposit may be 

 easily smoothed down by means of fine emery. 



The Preparation of Non-metallic Moulds to receive Deposit. 



Having detailed what we have found best for obtaining moulds of 

 objects for the purpose of electrotyping, we proceed to the manner 

 of obtaining a deposit upon these moulds. Were any of the plaster 

 or wax moulds attached to the zinc, and immersed in the copper 

 solution in the same manner as described with the penny- piece 

 (page 48), no deposit would be obtained, because neither the plaster 

 nor the wax is a conductor of electricity. Some substance must now 

 be applied to the surface, in order to give it conducting power: there 

 are several ways of communicating this property, but the best and 

 most simple, for the articles under consideration, is to apply common 

 black lead (already referred to) in the following manner : A copper 

 wire is put round the edge of the medal, or, if wax moulds are used, 

 a thin slip of copper may be inserted into the the edge of the mould, 

 or, being slightly heated and laid upon the back, the two will adhere. 

 A fine brush is now taken (we have found a small hat-brush very 

 suitable,) and dipped into fine black lead, and brushed over the sur- 

 face of the medal ; the brushing is to be continued until all the face 

 round to the wire upon the edge, or slip of copper forming connec- 

 tion, has a complete metallic lustre ; a bright polish is necessary to 

 the obtaining a quick and good deposit. 



In brushing on the black lead, care should be taken not to allow 

 any to go upon the back or beyond the copper connection, or the 

 deposit will follow it, and so cause a loss of copper, and make the 

 mould more difficult to separate from the deposit ; being, as it were, 

 incased. If the electrotypist take the labour himself of filing off all 

 the superfluous copper from the edge of his deposited medal, it will 

 do more than any written precautions to teach the necessity of prevent- 

 ing as much as possible the deposit going further than is necessary. 

 When the face of the mould is properly black-leaded, the copper 

 wire connected with it is attached to the zinc plate in the porous cell, 

 and the mould immersed in the copper solution : the deposit will 

 immediately begin upon the copper connection, and will soon spread 

 over every part, covering the black-lead polish with less or more 

 facility according to the state of the solutions and other circumstances 

 to be afterwards noticed. When the deposit is considered sufficiently 



