1874.] Correction of Engraved plates hy 'Electro-dejposition. 3 



it damages the engraving in the parts surrounding those erased, sonaetimes 

 to a wide extent, and thus necessitates considerable labour and loss of time 

 in retouching and restoring the damaged work. 



2nd. The hollows formed at the back of the plate by the hammering, 

 render the plate of an unequal thickness, causing difficulty in the re-engra- 

 ving, springiness in the printing, and greatly increasing the wear of the 

 plates in the vicinity of the corrected parts. 



In the English Ordnance Survey Office and other institutions where 

 special appliances exist for reproducing electrotype copies of the engraved 

 plates, this injurious method of ' knocking up' is in som.e cases superseded by 

 scraping off the faulty details from the intermediate relief copy of the 

 original plate and then obtaining from it a fresh electrotype plate on which 

 the parts that have been removed are represented by a smooth face of copper. 

 This system is entirely free from any injurious effect on the original plate 

 but is tedious and expensive. 



So long ago as July 1856 Marshal Vaillant brought to the notice of 

 the French Academy of Sciences an ingenious method invented by M. George, 

 an engraver in the Topographical Bureau of the Depot de la Gruerre, who 

 proposed to avoid the defects of both the above systems by the electro- 

 deposition of copper in the hollows formed by the erasure of the names, 

 lines or other detail to be corrected. Alterations can thus be effected 

 without the risk of damage to work already done on the plate ; the uniform 

 thickness of the plate is preserved ; the time required for carrying out the 

 corrections is little more, and in some cases less than would be occupied in 

 knocking up ; while this method is always quicker and more economical 

 than the plan of scraping details from the relief plate and then re-electro- 

 typing. 



This valuable process is largely used at the Depot de la Guerre, Paris 

 but so far as I could ascertain, it is but little known in England, and though 

 I have visited some of the principal geographical establishments in Europe, 

 the only, other institution in which I saw or heard of anything of the 

 kind was in the Military Geographical Institute at Vienna. 



As the method I have adopted is in a measure, a combination of the 

 Paris and Vienna systems, it will be advisable to give a brief description of 

 both.* 



In M. George's method the engraved plate is first of all covered with a 

 thin transparent bituminous varnish or etching ground. The parts to be cor- 

 rected having been carefully and cleanly cut out, the cuts are surrounded for 

 about half an inch, with a thick coating of Brunswick black, and the remain- 

 der of the plate all but one corner is thickly coated with wax. A trough 



* Fixll details will be found in my " Report on the " Cartographic Applications of 

 Photography" of which there is a copy in the Society's Library. 



