Potassium Ferricyanide and TF-4

Discussion in 'B&W: Film, Paper, Chemistry' started by cbphoto, Jan 4, 2014.

  1. cbphoto

    cbphoto Member

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    I haven't done any print bleaching in a few years, and back then I used Farmer's Reducer with its included hypo mix. I ordered some straight PF, and have TF-4 fixer on hand. Can someone give me a starting point for mixing the two together for combined "live view" bleaching, as opposed to sequential? Is TF-4 ok to use? Also, I've read numerous threads and articles on the topic that have recommended some very long fixing times for after the bleaching. I am wary of fixing fiber based paper for too long due to the difficulty of washing it out. Is there a special reason for these times, or am I ok to just do the usual 60 seconds in TF-4? I'm starting with prints that are already washed and dried, but I may in the future bleach before washing, so I guess those are two separate questions. Paper is MGIV and I do not intend to tone. Thanks in advance.
     
  2. Gerald C Koch

    Gerald C Koch Member

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    There are two ways to use Farmers reducer. If you are bleaching with the ferricyanide first and THEN use the hypo you can use a fixer as a one shot. However if you are using the method which combines the ferricyanide AND the hypo you need to use sodium thiosulfate alone and not some fixer formulation. Other chemicals in the fixer may interfere with the bleaching action.
     
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  3. cbphoto

    cbphoto Member

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    Got it. Thanks. I can pick up some plain hypo at B&H on Monday. Any tips on mixing, and what ratio would produce what kind of results?
     
  4. Gerald C Koch

    Gerald C Koch Member

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    The following link describes ho to mix the solutions and how to use them.

    http://www.ohio.edu/people/schneidw/vico222/222Handouts/farmers.pdf

    First practice on a few test films or prints. As stated in the article the directions produce a very rapid reduction. For slower action reduce the amount of solution B. Mix only what you can use as the mixed solution keeps for only a few minutes. When used as a combined solution Farmers is a subtractive reducer for over exposed films and prints.
     
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  5. erikg

    erikg Member

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    The link written by my old grad school class and house mate Bill Schneider. Cool! Bill always presents well researched and tested info.
     
  6. cbphoto

    cbphoto Member

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    Great explanation! Thanks.

    One more question: I've read that reducer can be made to affect highlights only(or just much more quickly) for a contrast boost or brightening of high values, or can be made to reduce overall density, like dodging. Is the difference in mixing the components together vs in sequence?
     
  7. erikg

    erikg Member

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    It's in how you use it, on a wet print the reduction is more over all, where as with a dry print the highlights reduce first. Some printers would deliberately print dark and then bring the whites back with this technique.
     
  8. Gerald C Koch

    Gerald C Koch Member

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    There are three kinds of reducers; sub proportional, proportional and super proportional. They effect the highlights and shadows differently. Farmers reducer used with solution A and B mixed together is a cutting (sub proportional) reducer. It reduces densities equally across high and low density areas. When Farmers is used as a two bath, ferricyanide solution followed by hypo solution, this gives you a proportional reducer that is the reduction is proportional to the density values High densities are reduced more than low densities and you get a lower contrast range. Alternatively, you can use a super proportional reducer which affects the highlight densities a lot more which means you will get an even lower contrast range.
     
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  9. cbphoto

    cbphoto Member

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    Thanks! So just to make sure I get it: if I want to lower density in highlights/midtones/shadows, say for a hard to dodge area like an over-burned building edge against a sky, stick with the mixed A+B approach. For a general contrast/highlight bump, go with sequential. How does one do the super-proportional method?
     
  10. Gerald C Koch

    Gerald C Koch Member

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    For a super proportional reducer you have to use different chemicals. Such a reducer is used for very contrasty negatives and is seldom needed.