CHAP, vii.] PHOTOGRAPHY ON PAPER AND ON GLASS. 301 



able under the action of light, it is washed in a solution of hyposulphite 

 of soda, or in a bath of bromide of potassium ; the iodide of silver 

 which has not been decomposed is thus carried off', and the image is 

 fixed. 



By help of the negative image thus obtained a positive proof can 

 now be produced, by a process analogous to that originally used by, 

 Niepce in copying engravings. The negative proof is soaked in wax, 

 so as to render the paper translucid, or even transparent. This proof 

 is then placed on a sheet of sensitized paper, and the two sheets, 

 between two glasses, are then exposed either to the direct rays of the 

 sun or to the diffused light of day. Under the influence of the light 

 the sheet of sensitized paper is impressed with a positive image, 

 invisible at first, but developable by gallic acid as before. 



II. PHOTOGRAPHY ON ALBUMINIZED GLASS. 



Photography on paper became rapidly popular, and if the proofs 

 lacked much of the delicacy of the daguerreotype plates, and if minute 

 detail was absent on account of the grain and of the fibrous texture 

 of paper, the new pictures were, on the other hand, more appreciated 

 by artists. Moreover, in this second phase of the art, improvements 

 cropped up with astonishing rapidity. 



Proofs were made on waxed or gummed paper with a surface so 

 highly polished that the most delicate details could be reproduced. 

 But soon a new discovery, made by a nephew of Niepce, M. Kiepce de 

 Saint- Victor, opened up a new path for photography, which is still 

 the one most generally followed. Instead of taking a metal plate, 

 like Daguerre, or a sheet of paper, like Talbot and Blancquard-Evrard, 

 for the deposit of the sensitized coating, M. Niepce de Saint-Victor 

 succeeded in depositing the sensitive compound on a highly polished 

 plate of glass, and producing on it a negative proof. The transparency 

 of the glass, its durability, the polish of its surface, its cheapness, all 

 these advantages have by degrees induced photographers to substitute 

 it for the metallic plates of Daguerre, and for the sensitized paper. 

 Before arriving at the process most generally adopted at the present 

 day, which is photography on collodion, we will describe the process 

 of M. Niepce de St.- Victor : The sensitized coating with which he 



