PHOTOGRAPHY, SCIENTIFIC ASPECTS 



TALBOT'S "CALOTYPE" PROCESS 



Meanwhile another European scientist was making 

 important discoveries in the same field that were to 

 prove quite as momentous a little later, as those of 

 Daguerre. Fox Talbot in England, about the time 

 that Daguerre announced his discovery, discovered a 

 process of photographing on paper, which he called 

 "calotype" or the "beautiful picture" process. This 

 did not differ very greatly in general principle from the 

 process of Daguerre, save in the fact that paper was 

 used in place of metal plates. But Talbot's ' ' calotypes ' ' 

 were the forerunners of modern paper photographs, 

 just as daguerreotypes are the direct ancestors of modern 

 negatives. 



In Talbot's process, the surface of the paper was pre- 

 pared by brushing it over with a solution of silver nitrate, 

 and allowing it to dry. It was then dipped in a solution 

 of potassium iodide for two or three minutes, until silver 

 iodide was formed, and was then treated with a solu- 

 tion of what is known as "gallo-nitrate of silver." If 

 the paper so treated were exposed to the camera image 

 for a few minutes, this image would be reproduced, as in 

 the case of the silver-surface plates of Daguerre, the 

 developing-process being hastened by soaking the paper 

 in more of the gallo-nitrate solution. The paper was 

 then washed thoroughly, dipped in a solution of potas- 

 sium bromide for a few minutes, and again washed and 

 dried, a permanent paper print, or photograph, being 

 the result. 



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