1930 Uvachrome British Patent - 333,392
There are various defects in coloured photographs made on this principle [dye-imbibition] which strongly affect the result and diminish the value of the process. They are in the main a loss of detail in pictures with heavy shadows and a limitation of the number of copies which can be produced. The poor quality of the shadows is a result of more or less over-exposure, and the limited number of copies is due to the fact that the relief gradually becomes saturated with dyestuff and retains this so strongly adsorbed that diffusion into it of further quantities of dyestuff becomes difficult and gradually impossible. By treating the strongly coloured reliefs with oxidising agents that destroy the dyestuff, the latter can be elimintated so that the relief becomes again effective in that it can be again coloured and used for the imbibition process, but the copies obtained in this manner differ in character and only a few imbibitions are possible at all.
The improvements introduced by the present invention lead not only to clear and detailed shadows free from objection, but also to the production of a large number of copies.
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