1857.] and Electricity to the production of Engravings. 347 



On now removing the ink, ordinary diluted nitric acid may be safely 

 applied to the plate, to deepen still more the shadows without any 

 danger of destroying the lights of the picture. This last step causes 

 M. Fizeau's etchings to possess greater vigour than those obtained 

 by Donne's or Grove's processes. The danger is, that under-biting 

 may remove the half tints. However, some beautiful results ob- 

 tained by the late Mr. Hurliman, a skilful engraver of Paris, attest 

 the worth of this method. M. Fizeau, foreseeing that the wear and 

 tear of tlie silver plates might be considerable, thought to use the 

 electrotype process to produce fac-similes of the engraved plates, 

 reserving the original plate unworn to supply any further demands, 

 thus allowing any number of impressions to be struck off. Plates 

 so electrotyped by the speaker twelve years ago, some of which were 

 afterwards worked upon by an engraver, were placed upon the 

 table. The patent right in this process will soon expire. 



The processes of the third and last division were, it must be 

 confessed, very desirable, notwithstanding the numerous satisfactory 

 specimens obtained, and still to be obtained, by the processes pre- 

 viously described. The truth seemed to be that none of the pro- 

 cesses gave uniformly satisfactory results : hence the necessity of 

 being acquainted with the capabilities of all the chief known 

 methods, and of impartially comparing them with a view to pro- 

 duce any special required result. 



Mr. Henry Fox Talbot opens the third division by his method, 

 known as the gelatine and bichromate of potash process, in which a 

 steel plate is covered with a liquified jelly, containing bichromate 

 of potash in solution. This jelly was allowed to dry upon the plate 

 after the manner of Niepce's varnish; and the gelatined plate 

 might be used in a similar way to reproduce engravings or the 

 images of the camera ; the light, as in Niepce's case, doing its 

 work by altering and hardening the gelatine whenever it fell with 

 sufficient intensity. On removing the plate from the light, and 

 immersing it in water, it was found that the gelatine had become 

 comparatively insoluble where the light had acted, but it retained 

 its usual solubility over those parts which were in shadow. Thus 

 the metal could be partially laid bare, as we have seen was the case 

 in the bitumen process ; the lights now would consist of the altered 

 gelatine, and the shades be represented by the bare metal ; it is 

 evident we have only to pour an acid upon the plate to obtain an 

 etching : but here some care and ingenuity will be required. Nitric 

 acid acts so energetically and so uncertainly on the steel plate, 

 that but little success would attend its employment. Accordingly, 

 Mr. Talbot was led to seek a better engraving liquid. This was 

 found in a solution of bichloride of platinum, which appeared to act 

 in the desired manner. The advantage of any process on steel 

 plates would be obvious, from the great number of impressions that 

 so hard a body would yield under the wearing action of the printing 

 press. It might here be observed that the bitumen process had 



Vol, TI. 2 jb 



