When it comes to film developing, it seems like everyone has their own way of doing it. Especially when it comes to some very specific techniques. Almost nothing is more controversial than the debate of stop bath vs water. Once, on a forum, I asked people how they used photo flo, and I must have got 23 different answers. The honest-to-Betsy truth though, is that there are many ways to get a developed negative or print, and photographers, as well as chemists have been experimenting for decades on what is optimal.

Optimizing Development

That’s what we’re diving into today: optimizing your development and specifically, how to properly use stop bath. There is an argument out there that seems to perpetuate, that using water is just as good as stop bath. If you’ve said this, you’d be right. But you’d also be very wrong. As it turns out, even I had used stop bath incorrectly for almost a decade, and I’m willing to bet many of you have as well.

First off, we can all agree that the main function of a stop bath is to halt the development of the film as quickly, and completely as possible. Using water does not stop a development, but dilutes the remaining developer, and this becomes more crucial when developing times are under ten minutes.

There is a secondary use for stop baths that is not as commonly known, and that is to prepare and condition film for a hardening fixer. Hardening fixers are not as commonly used these days but if you are, a stop bath is highly recommended.

You’re Doing It Wrong

The truth of the matter is that even if you’re using a stop bath, you’re probably using it wrong.

In terms of a conventional indicator stop bath, the first lesson is do not rely on the indicator. Why is the indicator useless? I’ll explain. Kodak did their own research on stop baths, and except with an absolutely fresh mix, conventional baths stop development so slowly, that you may as well use water. That is why so many of us saw little to no difference in results when comparing the two, not because water is just as good, but because an exhausted stop bath is just as bad.

The ideal pH for a stop bath is four to five, with the safest maximum being five. The dye that is used to let you know it’s no good anymore is called Bromocresol purple. It is yellow at pH 5.2 or lower, and purple at 6.8 or higher. In other words, the stop bath will have been inactive long before you see a colour change.

Also, it is recommended that you dispose of fixer when it becomes yellowish or cloudy, because it is a sign of sulfur precipitation. Conventional stop baths may carry over dye, disguising this effect.

If you are going to continue with an indicator stop bath, the best practice is to use it as a one-shot. Mix a fresh batch with each development and dispose of afterwards. However, a conventional stop bath, one that contains 1-2% acetic acid, doesn’t stop rapidly. To instantly stop film development, a buffered stop bath is required.

Buffered Stop Bath VS Water: A Clear Winner

During my research I came across a listing for a buffered stop bath called Sprint Block Stop Bath and their description gives a pretty good explanation as to why you should use it.

“In conventional stop baths, the acid ingredient which stops development is hazardous, unpleasant to use and can damage prints. Acid can break down print sizing which normally protects fibers from fixer thiosulfate contamination, a major cause of deterioration. Plain water stop baths eliminate the side-effects of acid, but do not stop development as effectively, and
can cause stains, emulsion swelling and reticulation.

Block is an acid solution, but the acids are buffered to minimize the side-effects. Buffering protects print fibers for greater permanence, reduces emulsion swelling, staining, reticulation and eliminates odors. Block will also prevent carbonate gas ruptures of films (pinholes) when used as directed.”

Conclusion on Stop Bath vs Water

There you have it, stop bath vs water, they both kind of lose. We’ve all been doing it wrong on some level. Personally, I used stop bath as a one shot before I discovered this, because I had much of it from thrift hauls. Once my film journey resumes I’ll definitely be using this as my stop bath.