Pyro Stain Mechanism

Discussion in 'B&W: Film, Paper, Chemistry' started by Annie, Jun 7, 2004.

  1. Annie

    Annie Member

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    Just wondering what is actually occurring during pyro development. Is it the gelatine between the grains that is being stained? Are the silver halides reacting with the pyro and exuding a type of chemical aura or cloud or are they somehow influencing their surrounding substrate so that it is more amenable to accepting the stain.

    Thanks!
     
  2. Aggie

    Aggie Member

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    it is like having two grains of sand. The pyro is more like water that surrounds each, and then attracts the other. They connect and become one instead of two. That is what pyro does when it stains. It sourrounds the grain and connects the dots.
     
  3. Annie

    Annie Member

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    Thanks Aggie!

    Actually there was one other thing I was wondering about........ Here in the Pacific Northwest there is a type of Arbutus tree that sheds it's bark instead of it's leaves and this bark is contains very high concentrations of phenolic tannins, up to 20% I believe, ( the indigenous people have used it in the tanning process for aeons). As the tannins of this particular species are of the pyrogallol class I was just wondering what strength of brew would be a good starting point for mixing up a developer concoction... (seems to me there was a brew using green tea, but I can't locate a formula) I like the idea of shooting some images of these trees (they are particularly poetic in their forms) and processing the negatives in a developer made from their own essence.

    Cheers & thanks again...... Annie
     
  4. Donald Miller

    Donald Miller Member

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    The basis for pyrogallol began with a nut that was refined to arrive at gallol. From this the gallol was refined still later through heating the gallol mixture...hence the pyrogallol name. Insofar as the staining mechanism...the pyrogallol stains and tans the gelatin carrier of the silver halide in the film emulsion. In an effective developer this staining action is proportional to silver density and acts as additional density to the transmission of certain light spectrum. An effective developer carries the further property of a low general stain which would act as additional film base fog.

    Insofar as your local trees...I have no idea as to the bark's effectiveness as the basis of a film developer since pyrogallol is a benzene as well. If bark or some other componant of your local trees is a benzene based compound, it may very well have an application as a developing agent. The only way that this could be determined, to my knowledge would be to distill the efluent from the bark. Then this could be used in a trial and error manner or subjected to chemical analysis. Insofar as the amount of chemical to incorporate in your proposed developer, I would begin by determining the percentage of pyrogallol incorporated in developers such as ABC Pyro. www. michaelandpaula.com or www. unblinkingeye.com have published formulas on their sites.

    The one cautionary note that I would mention is that benzenes are readily absorbed through the respiratory system and through the skin as well.
     
  5. Annie

    Annie Member

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    Thanks Don,

    Good info and good advice as always! Guess I can get some kind of cauldron going in the back field and see what I come up with.

    Cheers, Annie
     
  6. Ole

    Ole Moderator Staff Member Moderator

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    You could of course just boil up some bark, filter the liquid, domp in a few teaspoons of lye and try it... It's amazing what will actually develop film: Polluted river water, urine, bog water, coffe, you name it. All it takes is a weak reducing agent and (usually) an alkali.

    The reason pyro compounds give a proportional stain is that the reduction product between the pyro (the benzene ring actually) and the silver halide will tan the gelatine. So the more halide reacts to form silver, the more the pyro byproducts will tan and stain the gelatine. Simce this happens quickly there's only minimal diffusion taking place, so the staining occurs around the silver grain - but with a diffuse edge. Thus each silver grain has a slightly larger diffuse stained spot which very effectively masks the grain boundary.
     
  7. juan

    juan Subscriber

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    So, does this mean that when I'm photographing in the swamp, with it's tannin rich water, I can make my exposures, throw the film holders in the water and let them sit for 45-minutes or so (minimal agitation), pull them out, wash them in plain water, then throw them in a bucket of fixer in the back of my truck, drive up the road about 10-miles, take the negatives out of the film holders, clip them to a string stretched across the bed of the pickup, and they'll be dry and ready to print when I get home?
    juan
     
  8. Aggie

    Aggie Member

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    The Jeff Foxworthy method of film developing.
     
  9. Tom Hoskinson

    Tom Hoskinson Member

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    No wash?
     
  10. Ole

    Ole Moderator Staff Member Moderator

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    I think someone might object to the four buckets of lye you'll have to add to the swamp first... But as far as I know, properly peaty water and a little lye will give a recognizable image. I don't know about the quality, though.

    I've never tried this, but I seem to be making myself curious here :confused:
     
  11. Annie

    Annie Member

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    'I've never tried this, but I seem to be making myself curious here'

    I'm on it...... I lugged home a few gallons of brackish bog brew this morning!
     
  12. Donald Miller

    Donald Miller Member

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    I have given some thought to the earlier recommendation of lye (NaOH) added to your brew.

    I would not personally use that in a film developer unless it was very dilute. The ph would be excessive. The accelerator(s) that seems the most applicable to film developers would be sodium carbonate (NaCO3) or potassium carbonate (KCO3).
     
  13. Ole

    Ole Moderator Staff Member Moderator

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    Any alkali can be used, I used lye as an example. At least it was intended as such. But since the quality and type of developing agent in peaty water is utterly unknown, I would go for very high pH - dilute lye. This brown goop also tends to be slightly acidic.

    Besides, I don't think this kind of developer can be "optimised" in any way. It will remain a curiosity, and not a source of cheap high-quality developer. So the type of alkali is unimportant - but I know I'm going to use lye (sodium hydroxide).
     
  14. Annie

    Annie Member

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    Primitive chemistry is an amusing diversion and sometimes the results are surprising. I have made about a dozen images using various primordial soups and raw emulsions. Recently when I was using black iris pigment for a paper emulsion (this makes an image similar to cyanotype but a violet colour..... exposure is measured in days) I applied a mild solution of neutral pH fixer and the image 'disappeared' and the experiment ended up forgotten on a table near a window..... rediscovered it a few days later and it had revealed a watery version of its former self in an ochre colour... and it is getting darker every day it basks in the sun. For me standardizing and optimizing is not the objective.... it is rather like a type of folk art where you end up with a enchanting 'photographic whirligig'.