There are always debates on whether stop bath is critical in black and white processing. Let me share my personal comment below.
The function of stop bath is:
- stop the developer action immediately so there will be a very accurate development time for the film.
- it prevents the carryover of developer to the next processing step – usually fixer for B&W negative processing, to preserve the life span of fixer.
In order to achieve these functions, stop bath uses either method below to stop the developer action:
- chemically stop the action of the developer.
- Or most commonly, provides an acidic environment to the film so the action of developer, which usually only works in alkaline environment, will be halted.
Therefore, most common stop bath are acidic solution such as acetic acid or citrus acid, and sometimes we can use diluted vinegar as stop bath as well. Some commercially available stop bath have indicator in it so you can keep using it until it changes color when it expires.
One Drawback of using Stop Bath
As far as I know, there is one drawback of using stop bath. Some developers contain sodium carbonate or sodium hydrogen carbonate as pH buffer and therefore, carbonate will be soaked in the film emulsion after the developer has been drained out from the processing tank. When the acidic stop bath pours in, the carbonate will react with acid to form carbon dioxide gas which will expand in the film emulsion and damage it. This may cause tiny “pin hole” visible on the emulsion. If you have experienced such problem before, you better not to use stop bath then.
Below are 2 images from 2 film strips, one has undergone stop bath and the other has just plain water wash instead of stop bath.
- Nikon F6 + AIS35/1.4
- Sekonic L858D spot mode metering, shot at 1/500, f/11-16
- Ilford HP5 Plus processed in TMax Developer at 24C for 6 min (continuous agitation for the first 30 sec, agitation 5 times every 30 sec)
- Then stop bath or water wash, then fixer for 6 minutes for both.
- Nikon LS9000ED + Vuescan scanning to DNG format
- ACDSee Photo Studio 2020 to adjust the exposure only with reference to the white wall at the lower middle, to about 195-210 code value, for both images
The left image used stop bath and the right one used tap water wash, both continuously agitated for 1 minute before fixing. There is no significant difference in the tone of these two images.
The above images are the magnified lower right corner of the original images. Again, there is no significant difference on the image tone.
You may need to use a stop bath if:
- You want repeatable and accurate results for every film processing.
- You want to preserve and maximise the life span of fixer to lower your cost.
If you are just like me, processing a few rolls of film per year and in fact, all processing solutions are only used one time, then stop bath may not be necessary for you.
Please note that I did the test using TMax developer but the result may be different if other developers, or other processing technique were used. Other developers may behave differently when diluted in the water bath which may cause some further development of your film.