312 Mr. E. Solly, Jun., on the Precipitation of 



fouled with dust and impurities of various kinds which can 

 hardl}^ be kept out of the sulphate of copper, and which be- 

 coming gradually covered over by reduced copper, cause in 

 the face of the metal when finished, the appearance of black 

 specks; this is avoided in the form described. Another 

 convenience is that two, three, or even four moulds may 

 be operated upon at once, and any one may be removed at 

 pleasure without disturbing the others. I have been thus 

 minute in describing the apparatus requisite for the process, 

 because it is very commonly supposed, that as the process is 

 called " Voltaic precipitation," a powerful voltaic battery, 

 complicated and expensive apparatus, and a complete know- 

 ledge of electricity is requisite for its performance; whilst in 

 fact the great beauty of the process consists in its extreme 

 simplicity, requiring only a slight acquaintance with the most 

 elementary laws of that science. 



When the mould employed is pwfectly clean and sharp, 

 and the process has been properly conducted, the copy ob-. 

 tained is of pure and brightly metallic copper, usually of a pink 

 colour. If a copy of a medal thus taken, and after having 

 been removed from the mould have a small quantity of cop- 

 per precipitated upon its face, it assumes a most beautiful 

 dead silky lustre, which with very little if any injury to the 

 sharpness of the work gives it a very beautiful play of light 

 and shade. 



The colour of the precipitated copper appears to be very 

 much influenced by the nature and condition of the mould ; 

 and by paying attention to this circumstance, it may be ob- 

 tained of a great variety of shades of colour. I have sometimes 

 thought, that the colour of a voltaic cast of a medal is de- 

 pendent on the nature of the metal, of which the original 

 medal is composed ; because I frequently observed that cop- 

 per precipitated in a fusible metal mould made from a silver 

 medal, had a remarkable whiteness, whilst those similarly 

 made from copper medals were red, and from gold had a 

 yellow colour. On endeavouring to ascertain whether these 

 effects were really dependent on the nature of the original 

 medal, 1 found that so many little causes seemed to influence 

 the results, that it was almost impossible to draw any certain 

 conclusions with regard to these curious peculiarities of colour. 

 The surface of the deposited copper is exceedingly apt to 

 tarnish from exposure to air, frequently becoming partially 

 bright orange, and sometimes even of a brilliant red colour. 

 When heated up to nearly a red heat it acquires a uniform 

 iron grey colour which is perfectly permanent. The preci- 

 pitated metal is rather brittle, though very elastic ; 'but by 



