A simple and certain method of reducing over-printed proofs has been one of the wants long felt by all photographers. It is well known that in every photographic establishment even the most careful printers cannot always be sure of getting the exact depth of tone required, and proofs occasionally get overprinted. Of course prevention is better than cure; but, when a remedy is necessary, the method here described answers admirably. Potassium oyanide totally destroys the print, even when used moderately strong. By using a weaker solution, it is well under control, and the exact depth can be readily obtained; but during the washing to remove the cyanide, the action of the latter continues, and will spoil every proof. Several methods to arrest the action of the cyanide have been tried without success. It was then proposed to use the cyanide in such a weak state that but little should be held in the paper, only sufficient to reduce the print to the required depth; for this purpose, make a bath of only 4 drops saturated solution of cyanide to 1 pint water. The prints immersed at first show no signs of getting lighter, but after about an hour the most perfect results are obtained with prints considerably overprinted. With lighter pictures, a less time is required.
Proofs treated in this way lose nothing of their tone during the after-washing, which should be thoroughly done, and, when dry, retain all the brilliancy of an ordinary print.