... to turn the blue color into a green was devised by Mr. Paul Roy. It is as follows: Dissolve 7 parts of borax in 100 parts of water, and acidify the solution with sulphuric acid added drop by drop until the litmus paper becomes red; then, in the same manner, neutralize with aqueous ammonia not in excess, but just enough to show an alkaline reaction; this done dissolve 1 part of powdered catechu and filter. In this the proof is immersed after development ... — Photographic Reproduction Processes • P.C. Duchochois
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