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Air Bells on Medium Format Negatives


jim_norman2
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I've been using Paterson tanks for many years. Over the last few

months, I've had a number of occasions where I've gotten air bells

on the negatives. I don't pre-wet, but I'm careful about rapping

the tank on the sink surface after pouring in the developer. As

best I can tell, nothing about my film choices (Tri-X and Plus-X) or

developer (D-76 1:1) has changed. I'm stumped. Any suggestions as

to cause or ways to eliminate the problem? Most puzzling is that it

happens or not in both small and large tanks.

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I have seen many Paterson tanks damaged by getting banged onto tables. Paterson tanks will last a long time if they are treated properly. You may tap the side of the tank tank with your palm. When I use a Paterson tank I invert and right the tank five times after pouring in the developer. That usually solves the airbell problem.

 

When you develop 120 or 220 film in a Paterson tank the film is wound with the same spacing it has for 35mm film. I think that the standard spacing for a 16 oz. stainless steel reel/tank combination is better. The wider spacing doesn't allow air bubbles to get trapped as easily. When I develop 220 film I prefer to use an old Nikor tank with a very wide spaced reel. I have to use more chemistry but I find the loading easier.

 

Stainless steel reels and tanks go for very little on eBay and the 120 reels are seldom dameged like some 35mm reels are because they are nade of thicker and stronger wire. If you try it you may prefer the sdtainless steel equipment for 120 film.

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If you use Photo-Flo or any similar product in the tank for the final rinse step (as some of us who follow the Ilford archival sequence do), be sure to rinse the tank and reels thoroughly after each session. Any residual surfactant when rewetted, especially in combination with certain developers, can produce foaming and bubbles.

 

This appears to be a greater risk with plastic tank/reel systems because of the square-section shape of the spirals and closer spacing. Stainless reels use rounded wire and have more spacing - they're less likely to trap foam or bubbles.

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A number of years ago, make that decades, I read an article that said rapping the tanks does not always completely dislodge air bubbles. Their technique for tank development was to shake the tank very quickly where the top of the tank moved between 10:00 O'clock and 2:00 O'clock. The subject of the article was on development problems and main thrust was on proper agitation. After the discussion on how to agitate a tank the article was very resolute that rapping was not completely effective, there were photos of 120 film with small air bubbles trapped in the film. After reading the article and incorporating the developing techniques, I never had developing problems with tank development. Before reading the article my 120 negatives suffered from lack of uniform development and air bells.

 

Paul

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