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Stop Bath

Discussion in 'Everything Film' started by T_Sargeant, Nov 12, 2005.

  1. T_Sargeant

    T_Sargeant Well-Known Member

    I know this may seem like a silly question... but what does a stop bath do? Either for film dev, or print dev? I realise that it's designed to "stop the developer" but surely if you've got your exposure spot on when developing a print you don't really need it stopped as it won't develop any further, all you really need is a wash? In fact, if you're quick, surely a wash would work just as well for both? I only ask because my college don't actually have a stop bath (well, they do, but it's just water) so I was slightly worried whether there'll be any long term effects on my prints, especially as I'm now starting to sell some.
     
  2. pilliwinks

    pilliwinks Well-Known Member

    There are exceptions, but as a general rule developers only work in alkaline conditions, so pouring in an acidic stop bath halts the development almost at once. Using water, you slow down the reaction by dilution.

    [Details on the exceptions can be supplied if you really want to know]

    As far as developing times go, once you pass a certain minimum time, the shadows in a negative don't gain any extra density; it's the highlights and midtones that get darker. This translates to increased contrast. If you have access to an older edition of Michael Langford's "Advanced Photography" (I think it's that book) there is a very interesting set of negatives iluustrating this point. This was cut from the current edition...

    So, stopping the development stops excessive contrast building up. Neither films nor prints are normally developed to finality. It is possible to gain extra contrast in a print by prologing development (within reason; you will get fogging if you overcook).

    Like most brief explanations, there are exceptions to most of the above, but the general rule is as stated.

    As far as print life goes, the stop bath (or lack thereof) won't have any effect.
     
  3. pilliwinks

    pilliwinks Well-Known Member

    My error. The illustrations are found in "Basic Photography", 3rd edition, 8th impression, 1974, between pages 256 and 257.

    The two facing pages show the effect on the negative of increased and reduced development, and increased and reduced exposure. It is a great pity that this information didn't make it to the later edition(s).

    The actual value of a stop bath will depend of course on how long the development time is. Paterson System 4 tanks are said to be the fastest available tanks for filling and emptying (assuming that you are using a daylight developing tank). By contrast, my Combi-Plan tanks for 5x4 take 25secs to fill and/or empty. That is quite a percentage of a (say) five minute developing time. If your developing time was very short, you would of course make allowances for this in the time.

    My developing times are in the 15min region.

    On re-reading carefully my original post, I still stand by it as a general statement, but I can provide exceptions to everything I wrote...

    Also apologies for the typo in the post above, seen too late to correct.
     
  4. Benchista

    Benchista Which Tyler

    You simply allow for this by starting to empty the tank at t-e minutes, where t is the total development time and e is the time taken to empty the tank. I've been using this method for 25 years, and never used a stop bath in that time.

    MODERATOR'S NOTE: If you ever want to modify a post after the edit time has expired, drop a PM to a Moderator and we'll do it for you - not a lot of point this time, as the following posts would make no sense, but perhaps worth remembering.
     
  5. taxor

    taxor Well-Known Member

    Tom,
    On the face of it, there is some force in your argument re: the use of a stop bath. When printing, you could do with out a stop bath and some people do indeed make do without. Personally, I think it is a mistake and a false economy. There would be more developer 'carry-over' to the fixer and a concomitant reduction in its capacity. This is obviously not a good thing if one wants to make prints that last! ;)
     
  6. pilliwinks

    pilliwinks Well-Known Member

    Agreed, you allow for the draining/filling time. My point (so badly expressed as to be invisible!) was that as developing times become shorter, any inaccuracies in the time for pouring become proportionally greater. I always aim for developing times that have a built-in margin by being relatively long (15 mins and 18 mins for my commonly used films).

    The point about developer carry-over raises an interesting question in my mind though; since the original reason for this question was the use of facilities and chemicals not your own, I wonder about the freshness of the fixer. This could have a very real effect on print permanence.
     
  7. T_Sargeant

    T_Sargeant Well-Known Member

    Yeah, the fixer isn't always particularly fresh, this is one of the reasons I hope to set up my own darkroom, but I imagine that washing prints between dev and fix, would extend the life of the fix (as opposed to not washing them)?
     
  8. pilliwinks

    pilliwinks Well-Known Member

    The life of the fixer will be extended if it's less contaminated, but you still have a problem if you want archival prints.

    One of the by-products of fixing prints is insoluble and hard to remove by washing. As this builds up in the fixer, fixer may still fix, but be a lot harder to wash out.

    The normal solution, if you want archival prints, is to use two fixing baths (so that the "bad" stuff gets dumped first into the first bath) and then continue fixing in the second bath.

    Follow that with hypo eliminator and lots of washing (but not enough to detroy the paper).

    I am assuming fibre prints, not RC, by the way. The rules change for RC...
     
  9. T_Sargeant

    T_Sargeant Well-Known Member

    How? (do the rules change for RC)
     
  10. pilliwinks

    pilliwinks Well-Known Member

    Mostly it's the same, but the thing that makes RC paper RC is that the paper has a plastic coating. Fibre based papers need lengthy washing to get the chemicals out of both the emulsion and the underlying paper. The coating on RC papers means that the paper can't absorb the chemicals in the first place - except through the edges. That's the important point here, because it means that the longer the paper is exposed to the chemicals, the more will actually get in. Without the coating, conventional papers get wet; the paper under the plastic coating doesn't. So, RC papers should ideally not be in the chemicals longer than necessary. In addition, you don't want to wash them for as long a time to prevent the water getting into the paper.

    Ilford's recommendation is 2 minutes in running water for the wash, and 30 seconds fixing time (that's using their paper and fresh fixer).

    I should perhaps also add that if you read many books on printing, you will find that many people have nagging doubts about the permanence of RC prints. If you can (and are interested enough) take a look at "The Elements of Black and White Printing" by Carson Graves, and "Post Exposure" by Ctein.

    I use RC papers for proof prints only - it's much quicker making my contact sheets on RC. But, I'm a Luddite...
     

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