690 GALVANO-PLASTICS. 



mersed as cathode into a solution of a cyanide of gold 

 or silver, the conductor is covered with a film of gold 

 or silver respectively, which, with certain suitable pre- 

 cautions, may be made to adhere as firmly as the film of 

 gold or silver produced upon bodies by the older 

 methods of gilding or silvering. 



The layer of copper which has been precipitated 

 upon a cathode immersed in solution of cupric sulphate 

 may be removed after it has become sufficiently thick, 

 and forms then a more beautiful and faithful impres- 

 sion of the original than can be obtained by any other 

 means, Those portions of the surface of the cathode 

 which are raised of course appear hollow in the cast, 

 and vice versa; but if the first cast be used itself as 

 cathode a second cast is obtained, which is in every 

 respect a most faithful copy of the original. These 

 facts form the basis of the arts called electro-metallurgy 

 or galvano -plastics. It is thus that copper plates and 

 woodcuts are multiplied. An engraved copper plate 

 or block of wood can only be used for a certain number 

 of impressions, because the soft surface of the copper 

 or wood is soon worn away; but by employing the 

 galvanic current in the manner above indicated a great 

 number of casts may at once be obtained from the 

 original plate or block, and these may be used like the 

 original for producing good impressions on paper to 

 any extent. 



A galvano-plastic copy of a coin may be very easily produced. 

 It is, however, best to make first a hollow cast of the coin in 

 stearine, for the removal of the firmly adhering deposit from the 

 original is often very difficult and can scarcely be accomplished 

 without damaging it. The cast taken from the stearine is moreover 

 at once in relief like the original coin. 



