I 



1878.] to the Beprocluction of Maps and Plans. 103 



Owing to the imperfection of photographic appliances in those early 

 days of the art, the results obtained by Niepce could not have been very 

 satisfactory, but with better appliances the same process has yielded in the 

 hands of Niepce de St. Victor, the nephew of the inventor, Amand Durand 

 and others, results which prove its practicability, and its capabilities for 

 reproducing images direct from nature or for copying fine line engravings 

 and similar subjects, for which latter it is much better adapted.* 



A process on this principle has been very successfully used at the Im- 

 perial State-Printing Office, Berlin, for the engraving of plates for bank 

 notes and other purposes, and I have also tried it myself with fair success. 



The following outline will give an idea of the operations. f 



A perfectly smooth copper plate, having been thoroughly cleaned and 

 polished, is coated with a solution of asphaltum in turpentine, to which a 

 little oil of lemon is added. It is then carefully dried in the dark so as to 

 preserve an even coating, free from dust. 



The image may be impressed upon the sensitive surface by sun-printing 

 through an ordinary negative on glass, but as there is by this plan great 

 risk of losing perfect sharpness by want of close contact between the glass 

 and the copper plate, it is better to remove the collodion film from the 

 negative and transfer it on to the surface of the asphaltum, so that it may 

 be in absolute contact with it all over, and thus secure the utmost possible 

 sharpness of the image. The collodion film is loosened from the glass in an 

 acid bath, containing 1 part each of sulphuric and acetic acids in 320 parts 

 of water, and the transfer is then effected in a bath of 1 part glycerine and 

 4 parts of water. The transferred film being dry, the plate is ready to be 

 exposed to light, and as the asphaltum is not very sensitive, the exposure 

 is somewhat long — extending from 6 to 36 hours ; but it is better to over- 

 expose and to w^ork in diffused day-light rather than in the full sunshine. 



When the plate is judged to have been sufficiently exposed, the collo- 

 dion film is removed and the asphaltum surface is rubbed lightly with a tuft 

 of cotton dipped in olive oil, to which after a short time a little turpentine 

 is added. The image gradually begins to appear, and by degrees the 

 unaltered asphaltum is all removed, so that the design appears in clear brown 

 lUpon the polished copper. The plate is then washed with soap and water 

 md allowed to dry. 



The next operation is the etching or biting in of the image. The back 

 [of the plate having been well coated with a thick varnish of asphaltum, to 

 )rotect it from the action of the acid, the plate is plunged into a trough 



* See ^ Traite pratique de Gravure Reliographique sur Acicr et sur Verre\ par M. 

 [iepcc de St. Victor. 



t Full details will be fuund in my * Report on the Cartographic Applications of 

 ?hotography,'' p. 79. 



