TOG J. Waterhouse — The A2yplleation of Photography [No. 2, 



Daguerreotype Etching. — Many attempts have been made to engrave 

 the beautiful and delicate photographic image formed on the Daguerreotype 

 2)late. Thus, Donne simply etched the image with dilute nitric acid, which 

 attacked the silver forming the shadows, leaving the whites protected by 

 the mercury untouched. Grove etched the plates with the aid of the 

 galvanic battery. Fizeau first etched as deeply as possible with dilute 

 muriatic acid and then, having filled up the hollows with drying oil, 

 deposited gold upon the lights ; the oil having then been removed, the plate 

 was bitten with dilute nitric acid. In order to render the silver plate more 

 capable of standing the wear and tear of printing it was covered with a thin 

 film of copper, which could easily be removed and renewed when required. 



Other processes were also put forward, but they all failed, from the 

 difiiculty of biting the image to a sufficient depth and of obtaining the 

 requisite ' grain' to enable a large number of impressions to be pulled off. 

 None of them seem to have ever come into practical use and, like the 

 Daguerreotype, they have almost fallen into oblivion. 



If with the superior knowledge and appliances of the present day, any 

 such process could be successfully worked, it would probably offer many 

 advantages over any other etching process, especially for maps and other 

 works in line. 



Several ingenious processes of chemical engraving applicable to photo- 

 graphy have been ^poposed by Messrs. Garnier and Salmon, Yial, Dulos 

 and others ; but as they do not appear to have come into j^ractical use, it 

 will be unnecessary to enter into details regarding them. Descriptions of 

 them will be found in Eoret's ' Manuel du Graveur \ 



Though they have the advantage of rapidity, all these processes, in 

 which the image is obtained by etching or biting in with acids or other 

 etching fluids, are open to the objection that for all subjects containing 

 fine and delicate lines the etching and stopping out require almost the 

 same manipulative skill and care as in ordinary engraving, and the processes 

 consequently become expensive to work. There is also a tendency for the 

 lines to become coarse and heavy. In those gelatine processes in which 

 the etching fluid acts through the gelatine it gradually loosens the latter 

 from its support and attacks the parts which should not be bitten at all. 

 These defects are to a great extent obviated in the processes we are now 

 about to consider, in which the printing plates are produced by the electro- 

 deposition of copper on the photographic image. 



Electrotyping methods. — In nearly all the electro typing methods the 

 printing plate is obtained by depositing copper on a gelatine relief obtained 

 by the agency of light, or on a cast in plaster, gutta-percha, &c. taken from 

 such a gelatine relief. 



If a dry film of chromated gelatine on a suitable suj^port be exposed to 



