Do longer stopping and fixation times have any influence on the quality of the film?

Question

I recently picked up wet photography again. I kitchen-sink developed some B/W Ilford FP-4 films with

• Ilfosol 3 at 1+17 for 7 minutes
• Amaloco S-10 stop-bath ( I dont know the english term for that) at 1 minute
• Amaloco X-55 - ProfFix. fixing at 5 minutes.

All at 20 degrees Celcius

But I was wondering if longer (not shorter, I understand that) processing of stopping and fixation as described on the bottle has any influence on the quality/behaviour of the film.

EG: If I did 7 minutes of fixation instead of 5 minutes.

Answer

Wow, I haven't thought about that stuff in years. Keep in mind what the stopbath and fixer are for.

The stop bath has two purposes, to immeditely cease the developing process, and to protect the fixer. The developer is alkaline and the fixer acid. Even just a few drops of developer in the fixer will degrade it much more rapidly than it would get depleted just by use. In that sense, the stopbath is a sacrificial bath that is cheaply replaced. Basic stopbath is just dilute acetic acid. Indicator stopbaths include a die similar to litmus paper that changes color when the acidity goes down due to having absorbed too much developer. A longer stopbath doesn't do much useful. The development process is stopped pretty much immediately as the pH is changed due to the acid. The remaining bits of developer are also neutralized quickly. The main issue is for partially porous substrates where the stopbath needs a little time to diffuse thru and neutralize the developer. A good example of this is old fashioned paper prints. It would take maybe 10 seconds or so for little bubbles to stop coming off the edges as the stopbath diffused into the paper and reacted with the developer. In fact this was a good way to know when the stopbath had completed and when to replace the batch. If it took more than maybe 30 seconds, then the stopbath was worn out.

The job of fixer is to remove the unexposed silver halide. The developer has already reduced the exposed silver halide. However, over time even without developer the remaining unexposed silver halide will become exposed and change color. The fixer removes this unexposed silver halide from the emulsion. This process runs to completion. Once gone it's gone. There is considerably leeway in the length of the fixer bath because not much happens once the unexposed silver has been removed. However, eventually other things happen like the emulsion or backing starts getting dissolved or excessively water-logged, which can soften it and make it more susceptible to scratching until finally dried again. I've also heard (not totally sure this is true) that more of the salts in the fixer slowly diffuse into the substrate, which makes properly rinsing the film or paper more difficult and longer. This would imply that excessively long fixing times can be offset be longer washing times, but again, I'm not sure about this.

Of course the chemists that designed the paper and chemicals thought about all this and distilled it down to a set of easy to follow instructions. The best thing for you to do is to simply follow them. Unless you're a chemist specializing in this area, I wouldn't try to get creative. There may be unintended side effects, some possibly long term.

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