Removing pyro stain from negative

Peter Schrager

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Made pyro negatives but doing cyanotype requires a much less dense negative..any suggestions regarding removing the stain??
Thanks Peter
 

Rick A

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Try soaking in stop bath for a few minutes, then wash.
 

Andrew O'Neill

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As Rick said, a soak in acid stop bath can reduce the stain. If you don't have acid stop bath, then trya solution of sodium sulfite. Years ago I tried to intensify a negative in KRST. Although it intensified the silver, it significantly reduced the stain.
 

Ian Grant

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The stain is very stable, well with Pyrocat anyway. I use an Ilford Olive-Brown Toner IT-8 which uses a simple Pyrocatechin re-developer after a Dichromate re-halogenating bath but often use Pyrocat HD as the re-developer, I've tried reducing the stain on scrap test prints and it's not easy, any thing that works is likely to destroy the image entirely

You can of course reduce the silver component. Better perhaps to accept longer expoure times.

Ian
 

koraks

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Just regular ferrous sulfate FeSO4. It was referred to as proto-sulfate of iron or vitriol back in the 1800s.
The only questionable ingredient in the formula is the alum, as it's not specified. I assume it would be regular potassium alum though, and not e.g. chrome alum.
 
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