A Manual Of Photography

88 HISTORY OF PHOTOGRAPHY. I have purposely retained the words which I employed in 1841, being satisfied that we shall eventually witness their realization in the production of a most beautiful and sensitive process. Section VII.—Positive Photographs by One Process. About the same time, Mr. Talbot, Sir John Herschel, Dr. Fife, and myself, discovered the very remarkable property of the iodides in bleaching the darkened salts of silver. Many very beautiful results may be thus obtained. The manipulatory details published by Dr. Fife were simple in their character, but arrived at by a long series of inquiries. It is now quite easy to prepare photographic papers on which the hydriodic solutions shall act with perfect uniformity:— Soak the paper for a few minutes in phosphate or muriate of soda, removing with a soft brush any air-bubbles which may form on it. The superfluous moisture must be wiped off with very clean cotton cloths, and the papers dried at common temperatures. When dry, the paper must be pinned out on a board, and the silver solution spread over it, boldly but lightly, with a very soft sponge brush. It is to be instantly exposed to sunshine, and, if practicable, carried into the open air, as the more speedily evaporation proceeds the less does the silver penetrate the paper, and the more delicate it is. The first surface is very irregular, being as before described, and represented in fig. 2. As soon as the surface appears dry, the silver solution must be again applied as before, and the exposure repeated. It must now be exposed until a fine chocolate-brown colour is produced equally on all parts of the surface, and then, until required for use, be carefully preserved from the further influence of light. If the paper is to be kept long, the darkening must not be allowed to proceed so far as when it is to be speedily made use of. In darkening these papers, the greatest possible attention must be paid to the quantity of light to which they are sub- mitted, every thing depending on the rapidity of the blackening process. The morning sun should be chosen, for the reasons before stated. A perfectly cloudless sky is of great advantage. The injurious consequence of a cloud obscuring the sun during the last darkening process, is the formation of a surface which has the appearance of being washed with a dirty brush. This is with difficulty removed by the hydriodates, and the resulting pictures want that clearness which constitutes their beauty.