Streaks on Negatives

Discussion in 'Film and Processing' started by stuart_pratt, Apr 22, 2019.

  1. This is a section, of a 6 x 6 FP4 neg (approximately 25% of the neg) exposed at box speed, and developed in Paranol S (Rodinal), 1+50 22mins at 20 degrees, 30 secs agitation then 1 inversion/ minute. I've not used this developer until recently, but all the last few rolls have been fine, but they were all 35mm. These are the first 120 negs I have processed in Paranol S. I have progressively cut the recommended time, as the first time, negs were fried and contrasty at 30mins. I have reduced agitation from the recommended 1 inversion per 30 secs to 1 /minute too. Might this reduced agitation cause these streaks which appear on most of the negatives, but are generally more subtle than this example which is the worst case.? Might there be another cause?

    Orrible neg.jpg
     
  2. You say that this is a portion of the negative - are those streaks across the short dimension of the film strip, or along its length? Also, was the developing tank full such that the film was fully immersed during development?
     
  3. Interesting point. I had assumed they were across the width of the film, but now that you have raised that, I've checked and they run along its length. Yes, film was fully immersed, tank requires 500ml for 120, I used 600ml.
     
  4. Those marks are narrow and might be drying marks. What's your wetting agent and drying procedure?
     
  5. I think these are drying marks. The top coat is clear gelatin, underneath is gelatin with the light sensitive goodies imbedded. Gelatin is chosen because it is transparent, flexible, has low solubility, plus it swells when wet. This swelling allows the fluids of the process to enter and exit with ease. When the film is hung out to dry, the gelatin shrinks back to almost original thickness.

    Without a proper wetting agent or squeegeeing, water droplets remain. When hung out to dry, these droplets run under the influence of gravity.

    The streaky water on the film causes uneven drying. The area under the streaks dries more slowly thus shrinkage under the streaks is retarded. The result is, the films surface will be uneven as to thickness. You can prove this by looking at the film by reflected light. While difficult to see at first glance, the image will show bas-relief (some parts stand out higher than others).

    No cure but you can try re-washing then treatment with a wetting agent and drying. Usually not reversible however printing the negatives wet by projection will likely mitigate.
     
    casey_c likes this.
  6. Inversion wash with tap water, final rinse in distilled, with a few drops of wetting agent. Hang film in shower cubicle, pour final rinse water over both si
     
    casey_c likes this.
  7. I think maybe I'll measure properly the wetting agent in future. I've always relied on 'a few drops' but maybe this might not be sufficient.
     
  8. Note that when under developed / under exposed, marks like these tend to show up more often. How did the negs look to your nakid eye?
     
    stuart_pratt likes this.
  9. Everybody seems dead set against them, but I always use a double sponge tool to remove excess water. Just keep it clean to avoid scratches. In many decades I never had a scratch. Also never had drying marks!
     
    akocurek likes this.
  10. Excellent!

    Seriously though the negs are fine.
     
  11. Too much wetting agent can be as bad as none. It can cause water rivulets to 'bead up' on the film surface, and that looks like what's happened here. Especially if the wetting agent also contains an alcohol to encourage rapid drying. (A formulation I don't recommend.)

    The detergent surfactant in the wetting agent can dry before it's drained off and leave a smudged trail just as visible as water hardness.

    The good news is that a re-wash - using just 2 drops/litre of wetting agent - should remove the rivulets.

    Distilled water should need very little wetting agent BTW, since there's no water hardness or other contaminant to overcome. The 2 drops/litre I mentioned above should be enough. Depends on how mean the manufacturer has been with the liquid soap or detergent!
     
    Last edited: Apr 22, 2019
    stuart_pratt likes this.
  12. Thanks for that. I’m now wondering whether I put wetting agent in twice, or something like that? Also, the volume of water used was lower than normal, as I was at the end of the bottle. This could be what’s happened then. I’ll re-wash and see if I can get rid of the marks.
     
  13. Conrad, is the sponge tool you mentioned the one we use in the kitchen?
     
  14. SCL

    SCL

    When I used to use the sponge technique, the two sponge pieces were mounted on plastic tongs and you merely lightly squeezed them as you moved the device down the length of the film.
     
    celasun likes this.
  15. Thank you for your description. It sounds safe enough.
     
  16. My tool is old. It's a strip of stainless steel bent into a U shape. The ends have a long toothed fork, with a "photo" sponge shoved onto each one. The sponge is generous to prevent the stainless from getting near the film, which would of course be a disaster. Other designs use plastic. IMO, the key is fine grain sponges and great care in keeping the thing clean. I soak it in the same wetting agent as I use for the film, squeeze it out, then make a gentle pass down the film. Drying time is very short this way too. I keep an open plastic bag on the darkroom shelf and, after rinsing the tool, just put it in the open bag to dry- keeps the dust off.

    Rubber blade designs have also been used. They can work OK too, but when they get old, the edges get hard and crack and you get horrible scratches. Never liked 'em much.
     
    celasun likes this.
  17. Thank you Conrad, I will try making something similar.
     

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