178 On a new Photo-Lithographic Process. 



3rd. The utter impossibility of timing the exposure, which, 

 if not done exactly, occasions the loss of a great deal of time 

 and chemicals, and obliges the operator to begin again. 



4th. The reverse nature of every impression produced, the 

 result of working from a common negative. 



M. Poitevin, in the year 1856, patented a process based 

 upon the alterative action of light on gelatine or gum when 

 associated with bi-chromate of potash. The stone, or other 

 material prepared to receive the design, has its surface 

 covered with a layer, produced by running over it a solution 

 of gelatine, or some such substance, in conjunction with 

 bi-chromate of potash, and is then exposed to the action of 

 light " in the camera, under a negative, or under a positive." 

 After exposure it is wetted with water, and the lithographic 

 ink rolled in, which attaches itself only to the parts acted 

 upon by light, inasmuch as they remain dry and unaffected 

 by the water ; it is from this inked surface that impressions 

 can be multiplied in the press. 



The description of this process as given in M. Poitevin' s 

 specification, is exceedingly vague, diffuse, and contradictory, 

 I believe designedly so — an opinion supported to some 

 extent by a statement made by Mr. Malone, at a meeting of 

 the Photographic Society, London, December 7, 1858, two 

 years and eight months after date of patent (see Photo- 

 graphic Journal, Dec. 11, 1858, page 93) ; after stating that 

 M. Poitevin was working on stone, and that he (Mr. 

 Malone) saw him expose a stone in his garden at Paris, he 

 says, " I observe that he keeps the secret to himself," but 

 taking M. Poitevin's process as it stands in his specification, 

 it is subject to the following critical remarks, viz. : — 



1st. If he exposes in the camera, or under a positive, as 

 he suggests, he will, as he himself tells us, produce a nega- 

 tive picture on the stone, the use of which it is impossible to 

 conceive. 



2nd. If he exposes under a negative in the way he de- 

 scribes, he will produce a " direct positive" on the stone, 

 and a reversed positive on the printed impressions, which are 

 useless, save in the case of portraits of an inferior description. 



3. In any case the delineation on the stone, or other 

 surface from which he prints, will wear out, and give only a 

 few impressions, owing to the film of altered gelatine which 

 exists between the stone and the ink, not resisting the com- 

 bined effects of water, and the pressure and friction of the 

 press, a fact strongly commented on by Mr. Pouncy, at the 



