PaulW
Allowing Ads
Many thanks for your suggestions everyone. A technical person I contacted suggested that:
Hi, yes, its a common problem I see a lot. It is due to: excessive agitation, only just enough dev, and using wetting agent in the tanks! What happens is, is that when you wash the film, it never really gets rid of all the wetting agent from inside the tank and on the spirals. When you next develop, and shake the tank, the dev foams, and because a) the foam floats, and b) the top of the dev is only just at, or above the top edge of the film, the foam bubbles stick to the top edge of the film and causes under-development in those areas.
The “only just enough dev” can’t be the main issue as this also happens in the middle & bottom reels in a multi reel tank (so well under the surface), but the bubbles theory makes sense. I think this is happening at the top edge of the film (I’ll check next time). His suggestions were to thoroughly clean the spirals, don’t use wetting agent & gentle agitation by gentle inversion with a swirl at the end. Interestingly I’ve never seen this with the few 35mm films I process: perhaps the sprocket holes affect bubble formation?!
I’ll do some experimenting (including identical films with different processing, one by me, one commercial) & report back if I find a solution. However I have never seen this on the occasional colour film I expose, which are always sent for commercial processing, so this MUST be happening in my darkroom, not in the camera!
Paul
Hi, yes, its a common problem I see a lot. It is due to: excessive agitation, only just enough dev, and using wetting agent in the tanks! What happens is, is that when you wash the film, it never really gets rid of all the wetting agent from inside the tank and on the spirals. When you next develop, and shake the tank, the dev foams, and because a) the foam floats, and b) the top of the dev is only just at, or above the top edge of the film, the foam bubbles stick to the top edge of the film and causes under-development in those areas.
The “only just enough dev” can’t be the main issue as this also happens in the middle & bottom reels in a multi reel tank (so well under the surface), but the bubbles theory makes sense. I think this is happening at the top edge of the film (I’ll check next time). His suggestions were to thoroughly clean the spirals, don’t use wetting agent & gentle agitation by gentle inversion with a swirl at the end. Interestingly I’ve never seen this with the few 35mm films I process: perhaps the sprocket holes affect bubble formation?!
I’ll do some experimenting (including identical films with different processing, one by me, one commercial) & report back if I find a solution. However I have never seen this on the occasional colour film I expose, which are always sent for commercial processing, so this MUST be happening in my darkroom, not in the camera!
Paul
