The Art of Electro-plating and Gilding. 345 



of rendering the surfaces of Iris cast perfectly conductuous, and 

 establishing an uninterrupted connection between the guiding 

 wires and the surface to be deposited on. Spite of every pre- 

 caution, and the most careful observance of prescribed rules, he 

 is almost sure, in his early attempts, to have the mortification 

 of seeing the silver deposited in abundance and perfection upon 

 so much of the guidmg wire as may dip below the surface of 

 the plating solution, while his cast or model is as free from the 

 smallest particle of the precious metal as it was before immersion. 



Plaster of Paris (a material more commonly used, probably, 

 than any of the above-named) requires preliminary treatment 

 before applying the substance (blacklead) which is to make it 

 more conductuous ; for, if the blacklead be added to the bare 

 plaster, it separates and peels off in flakes almost immediately 

 after putting the cast into the solution. Various modes of 

 preparation have been devised, but there is one which I have 

 found very generally applicable, and which will most likely 

 serve in a great majority of instances that come under the 

 operator's observation. It consists in saturating the plaster- 

 cast with a mixture of oil and wax. Take equal weights of 

 beeswax and sweet oil, warm them sufficiently to reduce the 

 former to a liquid state, and then place the plaster-cast in the 

 mixture, moving it about so that every part of its surface may 

 absorb a considerable quantity ; when cold, the plaster will be 

 found to possess a firm, tenacious, and somewhat adhesive ex- 

 terior, admirably adapted for the reception of the substance 

 next to be applied. 



The cheapest and most easily accessible substance for ren- 

 dering surfaces conductuous is plumbago, or blacklead, names 

 which would suggest the idea that lead entered into its compo- 

 sition, whereas, when pure, they are quite free from that metal. 

 Its correct name is carbide of iron,* and consists of carbon and 

 iron. Neither the name or composition of the substance, how- 

 ever, is of any great consequence in so far as its present use is 

 concerned, for we have to do with its conducting power, and 

 not with its chemical properties. In applying it to plaster 

 casts, a soft brush is the best implement to use, and with this 

 it may generally be applied dry, especially if the cast be 

 slightly warmed, so as to render the wax with which it is 

 saturated a little adhesive ; in other cases, breathing upon the 

 object will do equally well : but a few hours' experience will 

 aid the operator much more than whole pages of written in- 

 struction. When sealing-wax models require coating, they 

 should be moistened with spirit of wine with the same view. 

 Gutta-percha moulds take the plumbago readily without any 



* According to some chemists ; but later researches go to prove that the 

 oxides of iron and manganese are in a state of mere mechanical admixture with 

 the carbon, and form no definite chemical compound with it. 



