[RA4] trying to understand the stop bath.

Discussion in 'Color: Film, Paper, and Chemistry' started by perkeleellinen, Mar 21, 2010.

  1. perkeleellinen

    perkeleellinen Member

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    I've given up using diluted white vinegar as a stop in RA4, mostly because I was getting blue streaks on my white borders from time to time.

    This is to ask why I might have been getting those streaks.

    I noticed our white vinegar at home is 6% acidity, I've been diluting it 1:4. Is this too strong? Might the stop be carried into the blix and interfering in its function? If so, is the role of stop not only to halt development but also to prepare the paper for blix?
     
  2. Photo Engineer

    Photo Engineer Subscriber

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    The stop is not strong enough! And, you may not have enough agitation in the stop.

    The blueish color is the symptom of developer interacting with blix at an alkaline pH without good agitation. So, the stop is too weak and you are probably not agitating enough.

    Under ideal conditions, you do not need the stop. But that is another story.

    PE
     
  3. perkeleellinen

    perkeleellinen Member

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    Too weak! And I thought too strong. I found agitating more worked better.

    So, the streaks are from developer and blix interacting in the tray / slot or are they interacting on the surface of the paper? In other words, does a blue streak mean ruined paper or ruined blix? If I get a streak do I replace my blix or replace my stop?
     
  4. hrst

    hrst Member

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    I think that you need to rehearse your practices of agitation and draining the paper. I've never had any slightest trace of streaks, and I've mostly used citric acid instead of acetic acid, which, according to PE, is not as good at all. And my dilutions are sometimes too weak. Still no problems. I think it's because I drain the paper for 15 seconds at a 45 degree angle so that most of the developer leaves the paper, shake gently to get rid of last drops, and then I put the paper quickly to stop bath and agitate it quickly. Then, maybe with a quick rinse in water and again, draining well, I go to blix and start by good agitation for first 30 seconds. Then I put the lights on and take it more easy. This way, I've recently had no problems, if we don't count iron stains and retained silver and halides caused by Tetenal's defective blixes :D.

    I have found RA-4 process to be quite forgiving.
     
  5. Photo Engineer

    Photo Engineer Subscriber

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    If you get streaks, you replace only the stop using one that is more concentrated. I use 2% Acetic Acid.

    PE
     
  6. perkeleellinen

    perkeleellinen Member

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    Thanks, glad that I don't have to chuck the blix when this happens. I'm going to give some thought to how I transfer the paper between the stages, certainly at the moment I go straight to stop from dev without letting the paper drain too much (probably a practice I got from film where the development stage needs stopping at a precise time). I think this may be causing the stop to exhaust or weaken.
     
  7. Photo Engineer

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    HRST;

    If you are getting iron stains on your prints, the blix is deficient in EDTA or has a pH that is too alkaline. I suggest adding about 2 g/l of Na2EDTA to your stop. Make sure that the pH does not rise.

    PE
     
  8. hrst

    hrst Member

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    Iron stains were completely a property of Tetenal blix which also had crud in it. Haven't run in these with Kodak chemistry. Tetenal goes bad as a 1-part concentrate when sitting in the factory's and retailer's shelf for a year.
     
  9. Photo Engineer

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    Yes, I know how fast a 1 part blix goes bad. I did the original R&D at EK on this in 1966. I found a way around it. :D

    PE
     
  10. ricksplace

    ricksplace Member

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    I am using one part Kodak LORR blix. Some of my concentrate is at least 5 years old. So long as the bottles are airtight, they seem to last well.
     
  11. pentaxuser

    pentaxuser Subscriber

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    Steve You might want to switch to Fotospeed stop. It is acetic acid and is diluted at 1+29 so a one litre container makes 30 litres which makes it very cheap - even cheaper than some lower priced stop such as Champion which needs a greater ratio of stop to water. Agphotographic sells it. I have used Fotospeed stop for several years in both colour RA4 and B&W printing without problems.

    Pure citric acid powder may be OK but I'd alway be dubious about what else goes into household vinegar. Great for chips but maybe not so good for RA4 paper


    pentaxuser