COPPERING. 159 



scouring it. (In general, a simple saturated solution of sulphate 

 of copper with 10 per cent, of free acid is used.) 



It is evident that a coating of copper so deposited can be 

 possessed of no other solidity than its own, and the latter is 

 entirely dependent on the thickness and the tenacity of the 

 deposit. M. Oudry was accordingly led to effect depositions 

 having one half millimetre on ordinary objects and one milli- 

 metre and more on the fine works. If to that thickness is added 

 those of a layer of plumbago and three layers of insulating coat- 

 ing material, it will be readily conceived that such a system of 

 coppering is only suitable in the case of very large objects. In 

 the case of small objects, such as a bust for example, the nicety 

 of the details would be irretrievably spoiled by these five layers, 

 and it would amount to sacrificing to too great an extent the 

 artistic worth of the object for the purpose of attaining its pre- 

 servation. It is nevertheless certain that this process has really 

 become a branch of industry, and that it is the first one which has 

 been applied on a large scale. All the lamp-posts of the city of 

 Paris, the beautiful fountains of the Place de la Concorde and 

 of the Place Louvois, and a considerable number of statues and 

 bas-reliefs have been coppered at Auteuil, in the inventor's 

 factory. 



M. Oudry's son, a few years ago, modified the original 

 process, replacing the insulating coatings of paint and the 

 plumbago coating by an immersion of the cast-iron objects in 

 a thick paint composed of hot oil and copper dust in suspension 

 in the liquid. The objects, when taken out of this bath, are 

 dried in the oven and then rubbed with a metallic brush and 

 some copper dust. They are finally taken to the ordinary 

 sulphate of copper bath. 



This process is rather more simple than the preceding one, 

 but the result is practically the same. The layer of boiled oil 

 separates the cast iron from the galvanic copper deposition; 

 the copper dust added to the oil is only intended for ren- 

 dering the surface of the pieces conductive of electricity, and 

 the metallic deposit must always be of a certain thickness 

 in order to be resisting. We should observe that M. Oudry 

 senior's process was unhealthy in this respect, that it entailed 



