No, YOU DO NOT NEED A STOP BATH for film -- not even for alkaline fix.
PLEASE, could you please stop spreading misinformation.
You can use it, you might even want to use it (I don't see a reason, but this is a matter of taste) but you don't need to. Using the recommended procedure of washing with three water changes dilutes the alkalinity so low that any buffer in fixer will take care of it.
Acid stop is not magic. It just maintains pH. It DOES NOT stop the development instantly, it still takes time for acid to diffuse in emulsion (correct words would be: it's somewhat faster than water.) It DOES NOT magically kill contamination, all it does it maintains pH by neutralizing alkalinity of developer. Of course, by doing this, it guarantees that even when there is developer contamination in fixer, it won't work at pH that low. But, by a decent 4-step water stop, you can eliminate most of the developing agent in fixer in the first place.
E6 uses no stop bath even when it's a color process where the stopping speed is very important for color balance and crossover. Usage of water has been designed in process times. Water works! It stops the development in a consistent enough time even for a color process, let alone BW work. And consistency is what counts.
And how do you define "contamination of fixer"? If you are talking about rising pH, you are right, using acid stop bath will actually lower the pH, but if you are talking about "contamination from developer", the game is clear: using water bath with three water changes as suggested will LOWER the fixer contamination from developer compared to a stop bath! Especially, if you compare to reusing the stop bath. This is not probably so important, fixer withstands contamination from used stop bath (and thus, developer) quite well, but you are talking about contamination as your argument against water bath, and you are wrong. Using water baths as suggested leads to less contaminated fixer.
And I'm sure if we go deeper into chemistry, we find many small facts to favor acid stop or water stop. Both have their supporters, both have their arguments. And both work.
Both work, use what suits your personal needs and taste! This is not very important matter so let's not make it religious and let's keep doors open.
Last edited by hrst; 10-10-2010 at 08:07 PM. Click to view previous post history.