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Collodion                                               Collodion Processes
then add B very gradually with constant shaking, and finally 5 parts of pure glycerine. The emulsion should now be allowed to stand for six hours. Baryta or enamel paper is always used as the support, and the edges of a sheet are turned up, the paper laid on a sheet of plate glass, and coated with the collodion just the same as though it were the glass itself. It is then allowed to set and dry. It is printed in just the same way as any ordinary gelatino-chloride paper, and may be treated and toned in the same way; but it will be found that the paper is very apt to curl up in the solutions. This may be avoided by laying the print on the bottom of an empty dry dish, and pouring very hot water on to the collodion film, allowing it to soak for a minute and then washing thoroughly, either in plain water or salt water, as suggested for gelatino-chloride paper. The best results are obtained with the simple sulphocyanide bath. One important precaution to be observed in the use of this paper arises from the fact that, if bent sharply across, it will crack.
For a list of books on Collodio-Chloride see Aristotype ; and for particulars as to toning, fixing, and treating by short exposure with subsequent development, see Gelatino Chloride.
Collodion. The vehicle used in wet-plate processes for holding the haloid salts necessary for the formation of the sensitive film. It is prepared by dissolving Pyroxyline (q.v.) in a mixture of equal parts of alcohol and ether, and it is a transparent glutinous liquid, which, when poured upon any sur-face, leaves, by the evaporation of the solvents, an attenuated film of pyroxyline highly transparent and structureless, also well adapted for the purpose for which it is required. The usual strength is as follows : -
Pyroxyline ...
Alcohol, -820 sp. gr.
Ether, 725 sp. gr. ... Methylated alcohol and methylated ether may be, and are, largely used on account of their cheapness. A special kind of collodion, called enamel or leather collodion, is used for Enamelling Prints (q.v.). (See also following article, Collodion Processes.)
Collodion Processes. A short account of the Wet Collodion Process will be found under the heading Wet Collodion