562 PHOTOGRAPHIC ENGRAVING 



PHOTOGRAPHIC EN-GRAVING. The first who appears to hare had any 

 idea of engraving by the influence of sunlight was Nicephore Niepce. According to 

 M. Aime" Girard, the first proof taken by him by means of this process bears date 

 1827. This process was very simple: it consisted in spreading a thin layer of bitu- 

 men of Judaea upon a copper- or pewter-plate, which was then placed in the camera 

 obscura, where it was allowed to remain some hours, until the bitumen had received 

 the impression of the external objects towards which the lens had been directed. On 

 withdrawing the plate, it was submitted to the action of the essential oil of lavender, 

 which dissolved those portions of the bitumen not acted upon by the light, leaving the 

 metal bare, while the remaining bitumen produced the design. Passing the plate 

 afterwards through an acid solution, the acid acted on the metallic plate, while the 

 other parts were preserved by the protecting varnish. 



Six years later, that is, in 1839, M. Daguerre made his discovery of the ' Daguerreo- 

 type ' public. In the meantime, he had considerably improved on Niepce's process ; 

 but although many, and some tolerably successful, attempts were made to engrave the 

 pictures produced by these processes, none were quite successful. 



The next process to which we shall refer is that of M. Fizeau. He took a 

 Daguerreotype plate, and submitted it to the action of a mixture of nitric, nitrous, 

 and hydrochloric acids, which did not affect the whites of the picture but attacked 

 the blacks with a resulting formation of adherent chloride of silver, which speedily 

 arrested the action of the acid. This he removed by a solution of ammonia, and the 

 action of the acid was continued. This process he continued until a finely-engraved 

 plate was the result ; but the lines of this plate were not deep enough to allow of 

 many prints being taken from it. To remedy this, he covered the plate with some 

 drying oil, and then, wiping it from the surface, left it to dry in the hollows. He 

 afterwards submitted the plate to an electro-chemical process which covered the raised 

 parts with gold, leaving the hollows, in which the varnish remained, untouched. On 

 the completion of the gilding, the varnish was removed by means of caustic potash, 

 and the surface of the plate, covered with grains de gravure, producing what is techni- 

 cally termed an aquatint ground, and the deepening of the lines -was proceeded with 

 by means of the acid. The Daguerreotype plate was by these means converted into an 

 engraved plate, but as it was silver it would have worn out very soon ; to obviate 

 which an impression was taken on copper by the electro-chemical process, which could 

 of course be renewed when it showed signs of wear. 



M. Claudet and Mr. Grove both produced some very good . engravings on the 

 Daguerreotype plate, but these processes have proved rather curious than useful. 



On October 29, 1852, Mr. Fox Talbot patented a process, which was similar to a 

 process previously used by MM. Pretsch and Poitevin, as regards the substance first 

 employed, viz. a mixture of bichromate of potash and gelatine - f but the remaining 

 portion of the process was conducted on the same principle, though in a different 

 manner, to that of M. Fizeau. 



Mr. Mungo Ponton discovered the use of the bichromate of potash as a photographic 

 agent ; and Mr. Robert Hunt subsequently published a process, called the ' Chromo- 

 type.' In both these processes the peculiar property of the chromic acid, liberated 

 under the action of sunshine, to combine with organic matter, was pointed out. MM. 

 Pretsch, Poitevin, and Talbot, only availed themselves of this pi'evious discovery, and 

 in each instance gelatine was rendered insoluble by the decomposition of the bichro- 

 mate of potash under the influence of actinic power. By dissolving off the still soluble 

 portions of the gelatine, either metal could be precipitated by the voltaic battery, or 

 an etching produced. 



In 1853 M. Nie.pce de St, Victor, the nephew of Nicephore Niepce, took up his 

 uncle's plan, and with the assistance of M. Lemaitrc, who had also assisted his uncle, 

 endeavoured to perfect it ; but, though he modified and improved it, his success was 

 not very great it was always found necessary to have the assistance of an engraver 

 to complete the plate. 



After this many others, among whom may be enumerated MM. Lerebours, Le- 

 mercier, Barreswil, Davanne, and, finally, Poitevin, endeavoured to obtain a design 

 by similar means on stone. The last appears to have succeeded. His method is 

 based on the chemical action of light on a mixture of gelatine and bichromate of 

 potash, as above. This mixture, which when made is perfectly soluble in water, 

 becomes insoluble after exposure to the light. His mode of proceeding is as follows : 



He spreads the mixture on the stone, and. after drying, lays the negative upon 

 it, and exposes it to the light. After a suitable exposure the negative is removed, 

 and the portions not acted upon by the light are washed away with water, and the 

 design remains with the property of taking the ink like an ordinary lithographic 

 crayon. The stone is then transferred to the press, and proofs taken in the usual 

 way. It is said that pictures have been obtained from the stone after 900 copies had 

 been pulled. 



