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 perfectly clean and sharp, 
and the process has been properly conducted, the copy ob- 
tained is ofpure 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 
