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.

  • 1
    \$\begingroup\$ The English term is "stop bath". :) \$\endgroup\$
    – mattdm
    Dec 18, 2011 at 15:58

4 Answers 4


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.

  • 2
    \$\begingroup\$ Just one little addition -- the fixer (for film) usually incorporates a hardener as well. Extreme over-fixing can make the emulsion brittle, reducing the lifetime of the negatives if reprints are important (they'll craze and chip with use). You usually have to go well beyond double time to get to that point, though. \$\endgroup\$
    – user2719
    Dec 19, 2011 at 14:16
  • \$\begingroup\$ Excelent explanation. Just an anecdote. I once leaved a film too much time on the fixer (Lets say a cuple of hours) then the emulsion just peel of by touching it. I think it was ok when it dry. I supose I did not touched again. \$\endgroup\$
    – Rafael
    Jun 9, 2016 at 13:13

The stop bath (usually dilute acetic acid or even water) neutralizes the developer and stops the development process almost as soon as the film becomes in contact with the stop bath. There is no point to continuing the stop bath any longer than this, but it will do little harm when development occurs in perfect darkness. When developing with a safelight, you want to minimize the amount of exposure to the safelight until the fixing has started, so you want to make the stop bath time as short as possible and get the film or print into the fixer right away. (The same neutralizing effect also happens without a stop bath, if you were to go straight to the fixer, but then a great amount of the fixer would become "exhausted" and requires you to use fresh fixer much more often.) Therefore use only as much time in the stop bath as is needed to be sure the film has come in contact with it, usually 15 - 30 seconds. (Often that's the time it takes just to pour the stop bath in and then out of a developing tank.)

If you leave a film or print in the fixer too long, I recall reading that it can oxidize: it will turn brown and lose contrast. (It might be interesting to run a few experiments with blank film strips or bits of photographic paper. :-) It is important not to under-fix, because that can leave the film slightly sensitive to light, causing it to darken and lose contrast over time. There is a lot of latitude, though; my experience is that most fixing occurs within the first few minutes (or even seconds, with fresh fixer at a high temperature) and you can keep film or prints in the fixer for ten times as long without harm. The difference between 5 and 7 minutes is of no consequence. (I haven't observed any problems in my negatives even after 40 years and I recall not being too fussy about fixing times.)

A good technique to get the most out of your fixer, and to be surest of the results, is to maintain two bottles of fixer: one old and one new. Use the old fixer first, right after the stop bath, then after a minute or two, switch the film over to the new one. Eventually (after many uses) after the old fixer starts looking cloudy or brownish, discard it, cycle the "new" into the role of the old, and make a new batch of fixer. This is easiest to carry out for fixing prints, because you simply add one more tray to the pipeline (developer--stop bath--old fixer--new fixer--wash).

In short, you need to pay close attention to procedure (timing, temperature, and technique) during development, get into the fixing stage as soon as possible, and then you can relax. Just remember that you have a film or print sitting in the fixer: take it out before your next break and don't forget about it altogether!

  • \$\begingroup\$ I think if you leave it in fixer for a long time you can develop crystals on the film/paper as it evaporates (memory is a bit fuzzy, has been awhile) \$\endgroup\$
    – MikeW
    Dec 18, 2011 at 17:49
  • \$\begingroup\$ That outcome is conceivable, @MikeW, if fixing is not followed by sufficient washing. \$\endgroup\$
    – whuber
    Dec 18, 2011 at 19:58

I have left film and paper in fixer for long periods of time (an hour or two) with no discernable effects. You can safely fix for 10-15 minutes if you want. It won't degrade the film, but it shouldn't improve the quality/durability either if you've fixed the recommended time.

  • \$\begingroup\$ I believe the concern primarily lies with longevity of the film (or paper). Typically it will come out fine, but (as I recall) might deteriorate more rapidly over time if grossly over-fixed. \$\endgroup\$
    – whuber
    Dec 18, 2011 at 19:59

I have left paper in fixer for nearly 24 hrs and it does craze (look like fine hairlines running though parts of the image) and some parts, in streaks, did turn a rusty colour.


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