gas bubbles on negative mystery

I've read that gassing in stop bath shows up as black/dark bubbles, but these are light. 4x5 film, SP445 development tank, Rodinol 1:50 8 minutes, I fill the beaker with water then dribble a little 28% acetic acid into it (less than a teaspoon), the idea is that as it pours into the tank it mixes itself. I presoak in water with heavy agitation, agitate developer at start then exponential 1 min, 2 min, 4 min etc. I agitate the stop bath and use it for 30 sec or less, agitate fix at start then about every minute. I've never had this problem before. I know for certain the film was in the SP445 holder with emulsion-side out so it is not an issue with the film holder bars. Could it be from filling the SP445 tank since it takes a while to fill- maybe I need to tap it on the table as I fill it? but presoak should have eliminated any chance of air bubbles?

What film is it ? It might be a defect already present on the film, the circles are evenly spaced, and as you say: airbubbles would show up undevelopped and thus black.

Cor

Have you examined the film closely, shine a light on it to see if its a deposit on the film? A rewash and soak in distilled water before hanging to dry might get rid of it.

I'd refix, rinse, dry again just to rule out deposits.
If it's cheap film, sacrifice a sheet and see that it looks perfect out of the box.

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Originally Posted by ibabcock

I fill the beaker with water then dribble a little 28% acetic acid into it (less than a teaspoon), the idea is that as it pours into the tank it mixes itself.

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Why?? I think this practice has the potential for introducing undesirable effects. There's no reason not to prepare the stop bath in advance. Heck, just use water alone, for that matter.

I'm with Paul on this one. If someone has such sloppy working methods as to just dash a bit of acid in a beaker of water and call it stop bath, then what other sloppy habits could account for damage to film... Don't take this the wrong way; I'm encouraging you to develop better working habits. It's not hard to mix a ~1.5% stop bath from 28% acetic acid: Just mix 1+63 as per Kodak's instructions (2 oz per gallon or equivalent thereof; metric is ~15ml/liter). EZPZ

FWIW, despite your less-than-precise mixing, the defect does not look like emulsion damage due to too-strong stop, i.e., formation of gas bubbles in the emulsion from the reaction of acid with the alkaline developer and bursting of same, thereby damaging the emulsion. This would show up over the entire surface of the negative, not in a line only in the middle. The problem looks like an abrasion to me, i.e., a scratch. Examine the negative carefully with a good magnifier; both sides. I'll bet you'll be able to see the defect. If you think it is from the manufacturer, it's time to examine a fresh sheet. You might not even have to sacrifice one if it's something you can feel in the dark.

Best,

Doremus

It does look like a scratch. There used to be a product called Edwal No Scratch that was handy for printing negs with scratches. I suppose mineral oil might be worth a try. *Looks like Freestyle sells it.