Citric acid as stop bath?

Discussion in 'B&W: Film, Paper, Chemistry' started by kram, Jul 14, 2007.

  1. kram

    kram Member

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    Has anyone use citric acid as a stop bath for film and paper? The only info I have says 20 grams per liter. Is this for film or paper? What concenration do people use (grams per liter) for film and paper? Do people prefer acetic acid instead (the smell gets to me, thats why I want to try citric).

    Regards

    Mark
     
  2. jeroldharter

    jeroldharter Member

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    Not sure. Many people say just use water if the acid bothers you. you could also use very dilute stop or buy some of the prepared odorless stop baths.
     
  3. Chris Breitenstein

    Chris Breitenstein Member

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    I use citric, and am afraid to use more then 10g per liter with paper and 5g for film. St. Ansel claims the emulsion will molt if you over stop, Im guessing the same would occur with to acidic of a bath.

    The paper stop will last for about 30 sheets.

    With film 5g is more then enough. After placing the film in the bath it only takes a few seconds for the film to stop, and I have heard that when the film becomes "sticky" (or at least less slippery) the film has been stooped.

    Yours;
     
  4. David A. Goldfarb

    David A. Goldfarb Moderator Staff Member Moderator

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    Acetic acid stop lasts longer in general. I use a water stop myself, but if you feel you need a stop (for instance, if you develop by inspection and want to be able to leave negs in the stop tray for a few minutes and then move the whole batch to the fix at once), and don't like the acetic acid stop, a citric acid stop isn't a bad alternative.
     
  5. Ole

    Ole Moderator Staff Member Moderator

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    I can't stand the smell of vinegar, so on the rare occasions I use a stop bath at all I use citric acid.

    Two heaped teaspoons per liter, or half a 50-gram packet in a trayful of water - about two liters, give or take a halff-liter or so.
     
  6. Alex Hawley

    Alex Hawley Member

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    I use citric acid for paper at 20 grams/liter. I used to use the Ilford indicator stop until I read its ingredients one day; citric acid. Hmmm. Finished the bottle and have mixing my own ever since.
     
  7. matt miller

    matt miller Subscriber

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    For film, I use a plain water stop. For paper, I use a citric acid stop. I don't really meaure it, I just use two heaping teaspoons per liter (like Ole says). I've never had any problems with it. Dirt cheap too.
     
  8. User Removed

    User Removed Guest

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    Funny you say that, because I remember Dennis at Yavapai telling that to me about 5 years ago also! I'm sure that is who you heard it from as well.
     
  9. Roger Hicks

    Roger Hicks Member

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    Works fine, but capacity is far smaller than acetic.
     
  10. kiku

    kiku Subscriber

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    Hi Mark: I use "Orbit Bath" for film and paper. It is odorless and is used as a stop bath and a hypo clearing agent. It is now marketed by Calumet. Sorry, but I have no experience using citric acid.
    Cordially, Howard Tanger

     
  11. Bob F.

    Bob F. Member

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    I generally use commercial citric acid stop with indicator (Fotospeed or Ilfostop). No idea what the concentration is in mg/l - diluted as per instructions - but have used 20mg/l of citric acid when I ran out unexpectedly. Used for both paper and film.

    Only down side I have noticed is that it supports life if left in my Nova vertical tank for too long. In fact, I think the last lot was in there so long, several small civilizations grew up, fought miniature wars and wiped each other out. That would explain the slime I found when starting to print one day...

    Cheers, Bob.
     
  12. kram

    kram Member

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    Alex, I am using the Ilford stop bath - it's fine, but I only have a small amount left and i have to make a long trip to my local photo store which carrys stop. However, with citric acid I can pop out at lunchtime to my Wilkinsons and get some citric acid from there - easy.

    So far 10-20g/l for paper and 5 g/l for film. Any other value which people use?
    I suppose the main area ith will be used is for paper (large surface area - more evaporation - more smell in dark room). Time of 30 or 60 seconds for 10g/l for paper, or no real preferrance.

    If the solution is made up does it go of (if kept in a half empty bottle)? life time of one month would be OK.
     
  13. Alex Hawley

    Alex Hawley Member

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    In my experience, the solution longevity depends on how many prints have been run through it. I haven't kept count, but its on the order of fifty 8x10s. Other than that, I've used mine for up to two months from mixing.
     
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  15. nworth

    nworth Subscriber

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    Citric acid produces a stop bath with a rather low pH. This can be a problem with both film and paper, although citric acid stop baths usually work well. Citric acid is required as the stop bath for amidol developers, since acetic acid is not acid enough to stop amidol's vigorous development. (It also helps control stains with amidol.) One problem with citric acid is that it is a bacterial growth medium, so you can't keep the solution very long. People who use pyro developers have complained that the low pH inhibits the stain. In any case, Kodak SB-8 was 15 grams of citric acid in one liter of water.
     
  16. dancqu

    dancqu Member

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    Processing film and paper one-shot including fixer,
    I've no reason to use a stop bath of any sort. Dan
     
  17. Dwane

    Dwane Member

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    I prepare a concentrated solution of SB-8 by dissolving 300 grams of citric acid in enough water to make one liter. I then take 50 mLs of this and dilute it to a liter for a working strength stop bath for printing. I dump the working stop bath at the end of the printing session. The liter of concentrate lasts about a year for me (20 printing sessions), and I've never had any problems with it.
     
  18. photographs42

    photographs42 Member

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    I started using Citric acid recently and it works very well. I dilute a rounded coffee scoop (I think it’s about two teaspoons) into a gallon of water. It usually lasts through a print session and I dump it, as I do all of the working strength chemicals, after each session. Even if you are a hobbyist, stop bath is too cheap to fool with saving it. As for determining when it is exhausted, if the print doesn’t go from slimy to non-slimy in 30 seconds or so, throw it out and make more.

    I got my citric acid from a store that sell brewing supplies and I think I paid about $5.00 for four pounds. That’s pretty cheap!

    FWIW I have never liked indicator stop bath because I found that the indicator tint doesn’t wash out rapidly and test patches gave me false information in delicate highlight areas because of the tint.

    Jerome
     
  19. psvensson

    psvensson Member

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    Boric acid, sold as cockroach powder, is another nice odorless stop bath. I think its pH is around 5, higher than that of citric acid, which means it buffers better, much like acetic acid.
     
  20. kram

    kram Member

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    Cheers all,

    I have used it twice - for papers since my last post. I normally use frsh at each session. Thanks for the info Dwane, useful to know. As it happens, it dissolves very easily so I might just make it up on the hoof. The citric acid I use give 55-60cm3 per 50g (depending on settling) so call it 1g/cm3. I have some baking (or should I say my wife) measuring spoons in 2.5, 5 and 10cm3 which are proving useful.


    PSVENSSON - Boric acid -good to know of another acid to use. What g/litre would you recommend?
     
  21. psvensson

    psvensson Member

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    I haven't really measured by weight - I just take two tablespoons or so to 1.5l water. From the silvergrain wiki:

     
  22. PeterB

    PeterB Subscriber

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    My Citric stop bath fails to indicate well

    The indicator in my Fotospeed (SB50) Citric Acid stop bath doesn't seem to be working. I poured heaps of bi-carb soda into a freshly made up batch and it barely turns blue. What is the indicator and where can I get some from ?
    The 1/2 full SB50 concentrate is probably about 3-4 years old.

    thanks
    Peter

     
  23. Bob F.

    Bob F. Member

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    The Darkroom Cookbook suggests 9.25g of bromcresol purple and 1g of sodium hydroxide with distilled water to make 250ml of indicator but where you would get bromcresol purple from, I have no idea...

    I suspect that it would take one of our resident chemists (of which I am definitely not one) to work out how much sodium bicarb it would take to neutralize the amount of citric acid in a batch of a particular stop bath given their respective pH (I suspect moles (or possibly some other small burrowing creatures) feature prominently in the equation, but that's as far as I dare venture)...

    My guess would be that if the stop is still yellow and does eventually turn blue/purple then it may be fine - some litmus paper which is cheap enough will confirm. Or not.

    Good luck, Bob.
     
  24. PeterB

    PeterB Subscriber

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    Calling any chemists out there !

    Thanks Bob. I'll see if any chemists can help me work out the amount of sodium bicarb to add per mL of working solution of SB50 ODOURLESS STOP BATH to turn it blue. The MSDS doesn't list the indicator but does list Citric acid at 20-50% in the concentrate, and it is diluted 1+19 with water.

    regards
    Peter
     
  25. Tom Hoskinson

    Tom Hoskinson Member

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    IMO that is Good advice from Bob F.

    Bromocresol Purple is a colorometric pH indicator. Visual transition from yellow to purple occurs between pH5.3 (acid) and pH 6.8 (weakly basic).

    A replacement colorometric pH indicator like Litmus Paper will work just fine to show if the stop bath solution is still acidic.
     
  26. alanrockwood

    alanrockwood Member

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    I'm not really sure what the purpose is of an acid stop bath. Of course, the acid does stop development, but it seems to me that a plain water stop bath will do the job (somewhat more gradually) by dilution of the developer, particularly if the water treatment is done with adequate reproducibility and agitation, and provided that the overall development process is calibrated to include the more gradual effect of a plain water stop bath, which could include extending the development by a few seconds.

    Please clue me in if there is something absolutely essential that the acid provides. I may be missing something.