Oops... How'd I forget...?

Discussion in 'The Darkroom' started by JamesD, Apr 5, 2006.

  1. JamesD

    JamesD Between darkrooms

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    Okay, so about a week ago, I was doing some darkroom work, and when I finished up, I left the dev, stop, and fix out, intending to go back in the next morning.

    Well, it never happened. In fact, with "real life" getting in the way, I completely forgot I left it in there. Brown crud in the dev and stop trays... and a tray full of fixer crystals.

    Obviously, the dev and stop are done-fer, but what about the fixer? Can I redissolve those crystals and use them? It was fresh fixer, far from exhausted. Or, shoudl I just dispose of them and mix fresh?
     
  2. Torus34

    Torus34 No longer a newbie, moving up!

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  3. Alan Marcus

    Alan Marcus TPF Noob!

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    Alan Marcus 50 + years photo engineering

    The fixer is a solution that removes unexposed and undeveloped silver salts (halides) from the photographic emulsion. Two chemicals are widely used. Ammonium rhiosulfate and sodium thiosulfate (hypo). Both are excellent fixing agents, the latter is slower thus requires more time to work. A fixing solution mainly contains water which is the solvent for the fixing agent. Additionally, a fixing bath contains a pH adjuster which sets the pH to the aid side. Acetic acid is almost always chosen for this task. It is a weak aid and thus excellent for neutralizing the alkalinity of residual developer carried into the fixer ridding piggyback on film or paper. Since development can only take place in an alkali solution, once the film/print is bathed in acid fixer, the material is safe and white light can be turned on. Additionally the fixer contains sodium sulfite, a preservative. Developer carryover adulterates and dilutes the fixer. Developer carryover reacts with dissolved oxygen in the waters of fixing bath to produce a staining compound. The preservative neutralizes this staining tendency thus lengthens the life of the fixer. Both film and paper are based on a gelatin medium which is the glue that hold the silver salts to the film or paper base. Yes, the same gelatin used to make the deserts we love to eat. When wet, gelatin is soft, easily scratched and slightly soluble in water. The fixer also contains potassium alum, a hardener used to firms up the gelatin so we can handle the film or prints.

    The fixer, when dried reverts to power and crystals. All can be re-dissolved and the fixer will rework. However, acetic acid is a violable acid. When it dries it evaporates into the atmosphere leaving no residue. A dried up fixer thus has lost its acetic qualities. Why brother, fixer is one of the least expensive of the photo solutions. If it were an emergency, I would add hot water to a dried up fixer and attempt to you it without hesitation. You can easily test a fixer. Dunk a piece of undeveloped film into the fixer as if it were a tea bag. The film starts out opaque and turns clear as the fixer works its magic. If you use a watch and time this reaction (time to clear), twice this time is the safe fix time for paper and film. Film didn’t clear? Discard the spent fixer.

    Alan Marcus
    ammarcus@earthlink.net
     

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