C41 dark spots

Discussion in 'Film and Processing' started by keithhayes, Apr 3, 2021.

  1. dark circles.jpg darkcircles2.jpg Recently, I switched from using Cinestill/Unicolor kits to Flexicolor chemicals. I never had this issue when using the kits. I haven't been able to find another photograph that replicated my issue on the web. My best guess would be air bubbles? If so, does this happen during developing, bleaching, fixing...? I couldn't be more gentle during agitation. Any guidance is greatly appreciated.
  2. They're almost certainly air bubbles stuck to the film during developing.
    A bleach-fix problem would result in lighter spots in the positive.
    Durr! Agitation should not be gentle. The whole idea is to mix fresh developer with the stale stuff stuck to the film surface.
    You need to jolt the tank down fairly hard to dislodge any air bubbles immediately after filling the tank.

    Those dopey Youtube videos showing a slow motion wrist-roll of the tank are a menace, and the people that put them out obviously haven't the first clue about film processing!

    Standard and time-honoured method of inversion agitation:
    1. Fill the tank as quickly as possible and fit the lid.
    2. Invert the tank swiftly and hold it upside-down for a couple of seconds.
    3. Right the tank and bang the bottom of it on a rolled up towel or cloth to dislodge any air bells (bubbles).

    Repeat steps 2 and 3 and then every 30 seconds during development.

    I've been using that agitation regimen for well over 40 years with both stainless and plastic tanks, and for B&W and colour development. Never had an air-bell problem in all that time.

    Youtube! (Spit!) Bunch of chimps with video cameras would be less dangerous and more informative.:rolleyes:

    Nice scans BTW. Home done or sent away?
    Last edited: Apr 4, 2021
  3. They may be bubbles but they could also be splashes of liquid after the film dried, or nearly dry.
  4. If you look at example #2, top right, you can see that one of the spots shows a slight 'comet tail'. That's typical of the trail left by an air bubble as it travels slowly up the film before detaching itself. Classic; as shown in every decent textbook's examples of developing faults.
  5. I am not sure I jolt the tank quite that much, but I do hit the tank after agitating,
    and have never had that problem.

    It might also depend on how you pour into that tank and, even more, that there
    are no bubbles in it before you pour.

    Mixing powdered developer takes a lot of stirring, and I now have a magnetic
    stirrer. If you stir too much, you can get air bubbles into the solution.
  6. Some developers contain sodium hexametaphosphate (Calgon) or other surficants that reduce the surface tension of the solution, and so reduce the tendency of air bubbles to stick to the film.

    I suspect that the difference between the Unicolor and Flexicolor kits might be in the type or amount of surficant included. Since the surficant plays no active part in development and is pretty much an optional ingredient.

    I used to add a tiny amount of wetting agent to my developer when I lived in an area with an extremely hard mains water supply. But too much wetting agent can cause foaming, and is just as bad as none at all.

    Banging the bottom of the tank after inversion is probably the best option. Film doesn't bruise easily!
    Last edited: Apr 5, 2021
  7. I usually hit the tank with my palm, while holding it with the other hand.
    I don't have anything good to bang it on, otherwise. I think that is what
    my grandfather told me, but I am not sure about how hard.

    As far as I know, the recommendation on Photo-flo is not to add it
    to developers, or other photographic baths. That might be for the reason
    you say, that it might cause more bubble instead of less.
  8. The MSDS datasheets for ID-11 and D-76 (supposedly the same formula) show that one of them contains a metaphosphate 'water softener' while the other doesn't. I can't remember which is which off hand.

    Anyhow. I went so far as to fit my SS tanks with adhesive foam pads, so that I could knock them on the worktop without damaging either the tank or the work-surface.
  9. I usually do mine in print trays to catch any spills. Not so good for banging against.

    Foam pads do look nice, though.
  10. And the short development time for C41 makes even a short time significant. Many developer data sheets warn about developing times less than 5:00, but then C-41 is 3:15.
  11. You can use the heel of your hand or your thigh to knock the tank, but that tends to hurt a bit with lengthy development times.:confused:
    Maybe having a padded baseball bat to hand?

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