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308 STOTT Voi 49, No. 4
In the entire process the only stage that need be dark is the blackand-white development and sufficient treatment in the hypo or stop bath to arrest development.
Numerous papers have been published and many patents granted which describe methods of converting a silver image on only one side of duplitized film to silver iodide. Various methods for applying a solution to only one side of the duplitized film have been described by Kelley,2 Brewster,3 Capstaff,4 Mason,5 Troland, Ball, and Andrews,6 and others. Miller7 and Cory8 have described methods of converting a silver image in a photographic film to silver iodide suitable for mordanting a basic dye.
These mechanical .methods of iodizing one side of duplitized film are effective when properly handled, but considerable care must be exercised to prevent print damage from accidental treatment of the opposite side of the film. In some cases these methods may require slow film movement throughout the process and thus seriously limit production capacity for a given plant area.
Therefore, at this stage of the process one side of the duplitized film has been suitably prepared such that by immersion in a basic dye solution the silver iodide will function as a mordant to cause deposition of the dye in proportion to the density of the original silver image. Before this treatment, however, it is necessary to remove the excess iodine left in the film as a result of the iodizing treatment. This has been described by Wall9 and involves treating the film in a dilute solution of sodium bisulfite.
After a wash to remove reaction products from the previous treatments, the film is immersed in a solution of basic dye. This dye will mordant only to the silver-iodide image without affecting the silver image on the opposite side of the film. Thus this operation may be done by total immersion of the film in the dye solution. Choice of various dye mixtures or single dyes as a satisfactory colorant for the print made from the bipack orthochromatic negative depends on many factors beyond the province of this paper.
The film is then washed thoroughly in water to remove the excess dye in the gelatine of the film. Miller7 and Cory8 have described methods of backwashing the film with solutions of weak acids to hasten the removal of excess dye and give stain-free high lights in the final print.
Crabtree and Matthews10 have published a toning formula which will convert a silver image to a Prussian-blue image. The film may