Do I need to use a stop bath when developing or printing film?

It’s fairly obvious why you need developer and fixer when working with film. But if you’ve ever done some research on the intermediary stop bath step, the answers aren’t always as clear.

On one side, there are many people who will never stop using stop baths, and others who claim they get excellent results without bothering. I’ve even spoken to a couple of lab technicians who have foregone the step altogether to save time developing rolls for customers. So do you really need to use a stop bath? 

You don’t need to use a stop bath when developing film. But using a stop bath is recommended because it immediately arrests development and protects the integrity of your fixer, which requires an acidic solution to function. However, there are fixers that don’t need a stop bath.

For the most part, a stop bath is a necessary tool to have on your shelf. But there are some situations where you don’t need to use it. And in my personal opinion, I enjoy being able to skip this step, because it takes time and requires you to use more water. And any way to reduce water usage is a big win in my books. 

What does stop bath do?

Before we get into the intricacies of using stop bath, we need to know how it works and why it’s important. 

The developer solution is most often basic, while the fixer is acidic. That means that if there’s any developer left over on the film, it will neutralize some of the acidic fixer, which can reduce its useful life.

The stop bath is also the only way to immediately stop the developing process. When you’re working with T-Grain films, small changes in the development time (as little as 10%) can make a big difference in the contrast of the negatives. Using a stop bath will ensure that the developing time is standardized, and reduces the possibility of developer acting longer on the film than you want it to.

So using a stop bath is one step towards creating repeatable results with film photography.

What happens if I don’t use a stop bath?

Not using a stop bath can prematurely reduce the effectiveness of your rapid fixer solution. Fixer solutions do contain buffer solutions to ensure it works at least a couple of times, but if the rapid fixer is exposed to too much developer, it will lose its ability to completely fix film.

If that happens, the film will come out looking milky and cloudy, which can be solved by simply dunking it into a fresh batch of fixer. In the worst case scenario, the film may be only partially fixed. It’ll look normal after developing, but over the years the film will slowly and permanently turn black. 

If you’d like to avoid using a stop bath, the best way to ensure your fixer lasts a long time is to wash the film multiple times after the development cycle. Otherwise, you can use a fixer solution that doesn’t require fixing. 

Do I need to use a stop bath for prints?

When printing film, a stop bath is integral to making sure the print lasts as long as possible, especially when using fiber-based papers. This is because it takes a lot longer to properly wash a print than it does to wash film.

Paper is more likely to hold the developer in the fiber mesh, which means more developer will transfer into the fixer solution. If you have a stop bath between the developer and the fixer, then that developer will be neutralized, and won’t harm the fixer solution. But if you skip the stop bath solution, the fixer solution will exhaust prematurely, and can cause the prints to turn black over the next days, weeks, or months.

Making prints requires a lot of care and attention to detail. In this case, skipping the stop bath solution isn’t recommended. As well, the stop bath also completely stops the developer from acting on the paper. So to get consistent results, it’s important to use the stop bath step in your printing workflow.

The one time when it’s okay to skip the stop bath is if you’re using a type of fixer that doesn’t require an acid environment, like the ones mentioned in the next section.

Are there any fixers that don’t require a stop bath? 

There are some fixers available that provide the same functionality as rapid fixer without needing a stop bath. These are typically labelled as neutral fixer solutions, and they contain a large amount of buffer that keeps them working at neutral pHs. 

The most common neutral fixers are made by Sprint and Eco-Pro, and they provide the same archival benefit as rapid fixers from Kodak and Ilford. 

Neutral fixers still require the same storage conditions as regular fixers, meaning the solutions will break down over time if they’re not stored in well-sealed bottles free from oxygen and other contaminants. Check out this article to learn more about the best methods for storing film develop and fixers to extend their useful life, among other methods to reduce the environmental impacts of film. 

How long does a stop bath last for, and how do I know it’s working? 

Stop bath is one of the only film developing solutions that doesn’t have a shelf life. Like Rodinal, stop bath will last almost indefinitely, even if it’s not stored perfectly. In fact, I’ve used the same mixed litre of acid stop bath for more than a year, developing 50+ rolls of black and white film without running into issues with my fixer solution. 

If you buy a commercial stop bath from manufacturers like Sprint, Kodak, and Ilford, they will most often come with a solution indicator that changes color when the acid is depleted. 

For Kodak and Ilford, that stop bath will change from yellowish to a blue/purple color that’s strongly visible, even under a safelight. Even if these solutions cost a couple dollars more than just buying strong vinegar at the supermarket, that indicator alone makes it more than worthwhile. 

The problem with citric acid stop baths

However, there is one other case where you shouldn’t use a stop bath even if the solution hasn’t changed color. There are stop bath solutions made from citric acid, which doesn’t have the same pungent smell as the typical acetic acid solutions. But, because citric acid is found in lemons, limes, orange, tomatoes, and other acidic fruits, there are bacterias that have adapted to those conditions. 

That means that bacteria can get into a bottle of citric acid solution, and actually thrive in those conditions. And if there’s bacteria inside your stop bath, it will find its way into the emulsion and break it down over time. 

The way to know if bacteria is getting into your solution is to look and see if there are any clumps that form in the bottle. Pour the stop solution into a clear beaker before introducing it to the development tank if you don’t have a clear bottle to store it in. And if you see these clumps, just pour the solution down the drain. Then, clean the bottle thoroughly with soap and water, mix up a new batch of stop bath, and continue with developing your film. 

If you only noticed this issue while there’s developer in your tank, wash the film thoroughly, and keep the tank full of water, agitating it once per minute to make sure there are no patches of uneven development while you wash and mix up the stop.