Pyrocat-HD A:B Ratios

[thronobulax]

I normally seminstand develop film in 1.5:1:200 Pyrocat-HD for 60 min. For very high dynamic ranges, I will (rarely) increase the dilution to 1.5:1:250 or 300.

What I am trying to better understand is what changing the ratio of A:B does to developer action.

Can anyone suggest a resource that describes this or otherwise has an explanation?

Thanks

 

[~RJ]

Not sure. Off the top of my head, using it 2:1:200 and various permutations with 1:2:200 Pyrocatechol using Potassium Carbonate in Stock B as an activating (electron donor/radical) changes times for the toe-shoulder curve.

I'm not using it anything near semi-stand though - perhaps you have a copy of the Book of Pyro or Anchell's Darkroom cookbook.

I'm finding with the Pyro family developers, it's very much personal experimentation and workflow with little generalisability. There are many online formulae and substitutions and most have turned out to be lukewarm streak disasters when the activation time using the ratio of B too low for me. The Pyro group on Flickr are very active although lately have been marketing their own versions of Pyrocat: I've reverted back to using traditional Pyrogallol which is more straightforward and more established as a formula.

 

[thronobulax]

I like PMK negatives a lot but because of the high aerial oxidation rate (I open tank process) it's a nonstarter for semistand. I wrote a long and windy treatise on my travels to semistand last year (URL below) and I've found that - for me, for most situations - it produces the best negatives I've ever made. But I really miss those PMK cloud edge effects.

tundra/Stand-Development

gitbucket.tundraware.com