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24 THE ADVANCE OF PHOTOGRAPHY
of this, a solution of proto-sulphate of iron could be used if desired.
Very delicate, clear negatives were obtained by this process, which yielded much more beautiful paper prints than the original paper negatives of Talbot. A very essential improvement was subsequently made in the preparation of photographic paper by coating it with white of egg, according to the process of Niepce de St Victor. This gave the paper a brilliant surface, and a warmer and more beautiful tone to the prints upon it, thus giving the pictures a brighter appearance than those produced upon the ordinary paper.
Thus Talbot's process, which at first seemed hardly worth notice compared with that of Daguerre, was gradually so perfected by successive improvements that it ultimately took precedence of Daguerre 's. After 1853, paper pictures from collodion negatives came more and more into vogue, whilst the demand for daguerreotypes fell off, and the production of the latter soon ceased altogether, except in some few places in America.
Wet Plate Process. — As the wet plate process is now very little used except in the studios of process block manufacturers, it might be of interest to give at some length an account of the various operations to which the plate was subjected in preparing a negative by this old method. The preparation of the plate must take place in the dark room, a yellowish light being used.
The first operation required in preparing a sensitive plate — an operation which requires great care — is the cleaning of the glass. The plates, after being cut by the diamond, are placed for some hours in nitric acid, which destroys all impurities adhering to the surface. The acid is removed by washing, and the plate is then dried with a clean cloth. To the uninitiated it would then appear perfectly clean, but it must be subjected to further polishing, by rubbing with a few drops of spirits of wine ;