74 PHOTOGRAPHIC PROCESSES. 



CHAPTER V. 



Photographic Processes. 



From among the many processes used in photogra- 

 phy we select the two best known, and most gener- 

 ally practised, referring the reader for further details 

 to works devoted to that subject. 



The wet collodion process will first claim our 

 attention, not only on account of the priority of 

 its invention, but because the gradations of the re- 

 sulting image and the fineness of the deposit give 

 a beauty to the results, hitherto unapproached by 

 any other method. Unfortunately on account of the 

 lengthened exposure required, its employment in 

 Micro-photography with high powers, is only possi- 

 ble when sunlight is the source of illumination ; but 

 with low powers, and when an exposure of not more 

 than ten minutes is necessary, it is generally ap- 

 plicable. 



The size of plate required for Micro-photography 

 is the carte- de-visite or quarter plate; the best ob- 

 tainable are made of imprimatur glass. 



If used before, for the production of a negative, 

 the old picture can be removed from the glass by 

 warm water and a soft rag, then washed in a strong 

 solution of caustic potash to remove grease ; dipped 

 in water again several times, next in nitric acid, and 



