HISTORY OF ELECTRO-METALLURGY. 13 



when in relief, would have been broad at the top and narrow at the 

 bottom. I took another plate, gave it a coating of the wax, and had 

 it written on with a mere point. I deposited copper on the lines, 

 and afterwards had it printed from. 1 



" I now considered part of the difficulties removed : the principal 

 one yet remaining was to find a cement or etching-ground, the tex- 

 ture of which should be capable of being cut to the required depth, 

 without raising what is technically termed a burr, and, at the same 

 time, of sufficient toughness to adhere to the plate, when reduced to 

 a small isolated point, which would necessarily occur in the operation 

 which wood-engravers term cross-hatching. 



" I have since learned, from practical engravers, that much less 

 relief is necessary to print from than I had deemed indispensable, 

 and that on becoming more familiar with the cutting of the wax- 

 cement, they would be enabled to engrave in it with great facility 

 and precision. 



" I tried a number of experiments with different combinations of 

 wax, resins, varnishes, earths, and metallic oxides, all with more or 

 less success. One combination that exceeded all others in its tex- 

 ture was principally composed of bees' wax, resin, and white lead. 

 This had nearly every requisite, so that I was enabled to polish the 

 surface of the plate with it until it was nearly as smooth as a plate 

 of glass. With this compound I had two plates, five inches by 

 seven, coated over, and portions of maps cut on the cement, which 

 I had intended should have been printed off. I applied the same 

 process to these as to the others, immersing them into dilute nitric 

 acid before putting them in action ; indeed, I suffered them to re- 

 main about ten minutes in the solution. I then put them into the 

 voltaic arrangement. The action proceeded slowly and perfectly 

 for a few days, when I removed them. I applied heat as usual, to 

 remove the cement, but all came away, as in a former instance the 

 voltaic copper peeling off the plate with the greatest facility. I 

 was much puzzled at this unexpected result ; but, on cleaning the 

 plate, I discovered a delicate trace of lead, exactly corresponding 

 to the lines drawn on the cement previous to the immersion in the 

 dilute acid. The cause of this failure was at once obvious : the 

 carbonate of lead I had used to compound the etching-ground had 

 been decomposed by the dilute nitric acid, and the metallic lead 

 thus reduced had deposited itself on the exposed portions of the 

 copper plates, preventing the voltaic copper from chemically com- 

 bining with the sheet copper. I was now with regret obliged to 

 give up this compound, and to adopt another, consisting of bees' 



1 This plate was shown to friends, and also specimens of printing from it, in 

 1838. 



