a challenging question

Discussion in 'The Darkroom' started by panzershreck, Sep 15, 2005.

  1. panzershreck

    panzershreck TPF Noob!

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    using water as a substitute for a stop bath (and everything else not developer/fixer), anybody know how to measure the temperature without a thermometer of any kind?
     
  2. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Without using a thermometer of any kind you don't have anything to measure the temperature with. The best you can do is guess - which isn't a measurement. And isn't advisable where photochemistry is concerned.
     
  3. warped_baller

    warped_baller TPF Noob!

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    I have a feeling that water won't work as well as stop bath. I need proof.
     
  4. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Developer chemistry is a reduction process and needs an alkaline environment.
    Water merely dilutes the dev so that it continues to work with potential overdevelopment problems.
    The dev on the film/paper still being active, when it goes into the fix it can precipitate out dissolved silver present in the fix. This gets coated on to the film/paper as dichroic fog.
    Both of these things are undesirable so they are best avoided.
    Acidifying the stop bath neutralises the alkalinity in the developer, stopping it from working virtually instantaneously. This also means there is no carry over into the fix.
    Acid stop is normally Acetic acid with a pH indicator. Spirit vinegar (the clear stuff) is pretty much the same and will work fine. Just dilute it about 1:30 or 40.
     
  5. DocFrankenstein

    DocFrankenstein Clinically Insane?

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    That's how my mommy used to do that. You just have to wash it thoroughly.

    But what you'll notice is that the picture is still developing as you wash it. Obviously it's not what you want.

    Get some vinegar as hertz recommended
     
  6. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    There are darkroom products where the manufacturer recommends avoiding an acidic stop bath. I use Diafine film developer and TF-4 fixer; both of these products advise using water as the stop bath.
     
  7. Hertz van Rental

    Hertz van Rental TPF Noob!

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    Dichroic fog tends to be more of a problem with paper than with film, but this is because it is caused by a high concentration of silver in the fix. You only get this with re-use.
    With paper, you tend to put a lot of sheets through the same batch. Each time a sheet is processed then more silver goes into solution, increasing the risk.
    The same happens with film if you re-use the fix, but you rarely get to the same levels of concentration except in a lab (or if you are really frugal).
    Diafine - as are most other two bath developers - is an exception.
    The developer and the alkali are kept in seperate solutions. This limits the degree of processing which it can undergo. Development stops once the available reactants in the film are used up and so all the 'stop' is doing is washing off the worst of the residual chemicals.
    In actual fact if you didn't put the film in the wash, development would still have stopped. This is why only water is recommended - any acid stop in it is purely redundant. It has not part to play in the process.
    As for the fix. Most fixers are acidified with Acetic acid because of dichroic fog. The acid kills any developer carried over to stop it happening. Apart from stopping development at a precise point the stop will extend the life of the fixer.
    With Diafine you could safely use a non-acid fix as there will be no reactive developer left in or on the film anyway.
    To sum up:
    If using a 'traditional' single bath developer always use an acid stop bath to stop development precisely, extend fixer life and avoid dichroic fog.
    If using two bath developer (eg Diafine) then just use water as a stop bath.


    Apologies KSM - I have only used two bath a couple of times (long ago) so tend to forget about them entirely when discussing photochemistry and development.
    I will try to remember in future, seeing as how they are increasing in popularity.
     
  8. loopy

    loopy Brave little froggy...

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    I use water as a stop, never had any problems.

    Save yourself grief, buy a thermometer. I got a cheap one from a pet store... works great.
     
  9. ksmattfish

    ksmattfish Now 100% DC - not as cool as I once was, but still

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    I just like to point out that there are other methods and chems to try out, and they don't all work the same. :) Most folks are probably using single bath developers, and acid fixer.

    I think that Diafine particularly lends itself to the occasional film developer, as it appears to be almost idiot proof, so I'm sort of surprised it's not more popular. It controls the contrast, temp doesn't matter so much, time doesn't matter so much, tends to give a speed increase, it's fairly cheap, and it lasts a long time.

    I like TF-4 fixer (alkaline fixer) because it lasts longer, and washes faster.
     

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