Quote Originally Posted by Diapositivo View Post
In theory some residue of developer will benefit the bleach bath as it creates the right pH. In practice if you want to reuse bleach without polluting it the better solution is an "acid stop" bath which serves both purposes, make an acid environment and avoid polluting bleach with developer. That's what I read here on APUG. Your mileage may vary.

"Acid stop" can either mean acetic acid or citric acid.

From my notes:
Acetic acid: economical, effective, not risky for the film, dangerous for persons, polluting, stinking, reusable, well preserved; can be used more times when diluted at 2%. For one-shot better using 1% or 1.5% dilution.

Citric acid: more expensive, not dangerous, odourless, must be used on the same day of dilution, and some people report the possibility of problems (my notes not very specific).

I chose acetic acid. I still have to perform my first C-41 bath, my "chemistry" is still sealed. Hope I'll do it in the next few weeks.
There are a couple if things that are not quite right in the above.

1) Developer is a base, or alkali, this means that a developer will increase the PH, until it's either neutral (7) or higher. An acid stop will keep an acid bleach an acid.
2) Acetic acid is what gives vinegar it's kick. The dilutions used in photography, typically 1% to 2%, is actually lower then that used for cooking use, typically 5% to 8%. This means if you run out of stop bath, go to the kitchen, grab the white vinegar from the cupboard and cut it 1+4 with water and you have a stop bath. If you have higher concentrations then for household use, it could be dangerous. Most acetic acid for stop bath is produced chemically these days, it's not the acid that could be dangerous, it's the impurities that could be in it, from the chemical process. Not much you can do about the smell. Another option would be to pick up a bottle of Ilford odourless stop bath, which is citric acid, mix according to the instructions and you should be pretty close. Mix according to need, in other words if you need 250ml of solution, mix that amount.