CHAP. VIIL] HELIOGRAPHY PHOTOLITHOGRAPHY. 313 



CHAPTER VIIL 



HELIOGRAPHY PHOTOLITHOGRAPHY. 



I. DIFFERENT PERMANENT PROCESSES WITH CARBON AND 



PRINTING INK. 



WHATEVER process may be employed for fixing daguerreotype or 

 photographic proofs, it is certain that they do not possess the per- 

 manency given by the ordinary impression made with almost inde- 

 structible printing inks. Any photograph can be reproduced almost 

 indefinitely by printing, and thus increasing the chance of preserving 

 the image obtained ; but each positive proof may be deteriorated in 

 the long run, and its clearness impaired under the prolonged 

 influence of light ; and finally, supposing this problem of permanency 

 be solved, there would still be, in the printing of positives, vast differ- 

 ences between the typographic and lithographic printing of engravings, 

 both as regards cost and time. 



It is not to be wondered at then that, from the first, this difference 

 has been fought against, by endeavouring to transform the photographic 

 proof into a real engraving block in relief or copper plate, or litho- 

 graphy. This was the problem pursued by Niepce, from his earliest 

 labours, and which numbers of artists and men of science have since 

 tried to solve. We will glance at the principal methods adopted, 

 and the results at which they have arrived. 



About 1841, M. Fizeau tried to reproduce the images on Daguerre's 

 plates by electroplating : the copper deposited by the galvanic pile 

 moulded itself on the surface and represented the reliefs inversely, 

 that is to say all the points to which the mercury had spread formed 

 the lights. By using this mould to obtain an inverted proof, the 

 plate itself was reproduced, and it only remained to print it by the 



