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At what pH is a stop bath considered exhausted?

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Water does not "stop" development, but it does seriously retard (slow) it. There is still some developer carry over when you use water between developing and fixing. This will shorten the life span of whatever fixer you use. If you use fixer as a single shot and dump, this is not a problem. If you reuse fixer, as many do, you will need to change fixer more often, using a two bath method is highly recommended.
 
I think an indicator stop bath is a good idea. If you are a visual person, as most photographers are, the change from yellow to purple means you need to replace it.
 
Using an indicator is an excellent way to determine if it's getting ready to toss. I don't have the reference at hand, but years ago I read that stop bath should be under pH 5.2 (which, I'm sure is not coincidentally the point where bromcresol purple starts turning from yellow).

I stopped using stop bath after getting some pinholes when developing film. Ruined a few nice shots. I found water worked fine, as many others have here. I eventually stopped for paper too when I started using a neutral fixer. I've never had a stained print, or other issue attributable to not using a stop bath.
 
Tom1956 said:
Because it halts development dead, hardens the gelatin, and protects the longevity of the fixer. Just makes best sense.
Click to expand...

As Tom points out, a stop bath makes sense.
 
cliveh said:
I think an indicator stop bath is a good idea. If you are a visual person, as most photographers are, the change from yellow to purple means you need to replace it.
Click to expand...

pH paper works for me. I have an infinite supply.
 
markbarendt said:
You do realize that plain old water will work as a stop bath, right?

The difference is mostly in how fast it stops development, water just takes a few seconds longer than fresh stop.
Click to expand...

In addition to the above comments, using stop bath helps the hypo last longer.
 
RattyMouse said:
I'm not over thinking this. You guys are! :laugh:

I'm looking for a number. At what pH is stop bath considered exhausted? Give me a number. That's all I want.
Click to expand...

I do not have a pH meter, however since you want a number how about 5? Why? Because is you are doing a Suduko puzzle and you are not sure what number to put in a square, inserting 5 will on the average and the mean square error will provide the smallest probability of error. :crazy:
 
You will not get reticulation from a stop bath using today's films.

And, your question applies to both color and B&W.

And, that "squeak" test is quite applicable as you know being a chemist Ratty. Acids make gelatin less squeaky! :smile:

PE
 
Photo Engineer said:
You will not get reticulation from a stop bath using today's films.

And, your question applies to both color and B&W.

And, that "squeak" test is quite applicable as you know being a chemist Ratty. Acids make gelatin less squeaky! :smile:

PE
Click to expand...


:laugh:
 
Photo Engineer said:
You will not get reticulation from a stop bath using today's films.

And, your question applies to both color and B&W.

And, that "squeak" test is quite applicable as you know being a chemist Ratty. Acids make gelatin less squeaky! :smile:

PE
Click to expand...

PE, I work in such a specialized field that most of my general chemistry skills have long since evaporated away. Sadly, I would fail many basic level college chemistry tests if given with no prep! :cry::errm:
 
Well, there is a typo there. Acids make gelatin MORE squeaky!!!!!

Sorry about that.

Bases make gelatin MORE squeaky.

And dear Rat, I raised the issue of you being a chemist because you did it earlier in a post about the safety of D76 vs Xtol. So, I figured...... Well....... Anyhow, sorry. This is how I made my living for about 50 years. Squeaking emulsion with my fingers! :D

PE
 
Photo Engineer said:
Well, there is a typo there. Acids make gelatin MORE squeaky!!!!!

Sorry about that.

Bases make gelatin MORE squeaky.

And dear Rat, I raised the issue of you being a chemist because you did it earlier in a post about the safety of D76 vs Xtol. So, I figured...... Well....... Anyhow, sorry. This is how I made my living for about 50 years. Squeaking emulsion with my fingers! :D

PE
Click to expand...

Oh I'm a chemist alright PE, no doubt about that. It's just that my experience in the last 20 years has been in a very specialized field and as a result, a lot of my basic chem knowledge has drifted away. Especially inorganic chemistry! :sad: No one should assume that I know everything. Or even anything.
 
Geez, what a night. Bases make gelatin LESS squeaky. I have no excuse for my errors. I've got too much on my mind tonight including the heavy snow and cold weather. I guess I have brain freeze. With wind chill it was -25F here today.

Sorry guys.

PE
 
I know how you feel. It's 42°F out there right now and I've got 5 logs in the Ashley going on. Cold.:D

I'm glad to know I unwittingly glommed on to such a scientific term as squeaky. But I felt like fellows would know what that meant. Your thumb squeaks on it. Antonym of slimy.
 
I have always tested my stop by dipping my fingers in the developer to make them slimy, then into the stop to see how fast it makes them squeak.
 
Since RattyMouse asked for hard numbers, here are hard numbers:
  • All common development agents (except Amidol) need pH > 6.0 to become active ---> any bath at or below pH 6.0 will act as a stop bath.
  • Another factor to consider is buffering. Acetic Acid and Citric Acid, the two most commonly used acids in stop bathes, are decent buffers up to around pH 6.0, so the pH 6.0 threshold holds.
 
However, the higher the pH, the longer a stop takes to stop development. Just as the less buffer capacity decreases overall capacity.

PE
 
A film you have to be super careful about stop bath with is Efke 25. Just recently discontinued, so there still some around. An odd duck with
respect to the gelatin, but lots of people, including myself, found uses for it. I'd use indicator stop bath with just a tiny hint of yellow, nothing
more. Probably amounted to around 1/4% acetic acid at that point. But did the job.
 
Rick A said:
Water does not "stop" development, but it does seriously retard (slow) it. There is still some developer carry over when you use water between developing and fixing. This will shorten the life span of whatever fixer you use. If you use fixer as a single shot and dump, this is not a problem. If you reuse fixer, as many do, you will need to change fixer more often, using a two bath method is highly recommended.
Click to expand...

Depends on your fixer. I'm about to order some TF 5 to use with prints. It's alkaline so water stop is recommended.


Sent from my iPhone using Tapatalk
 
Last edited by a moderator:
I use water for my amidol print developers, for which I use a citric acid preservative, and otherwise, for TF4, simply use an intermediate water
rinse between acid stop bath and the fixer itself. I mix stop bath weak, regardless, and always dump it at the end of the day, just like everything else. Don't take chances.
 
Michael is correct. TF-5 is just a tad acid so that there are no fumes,, but TF-4 is alkaline and has a slight bit of ammonia odor. I use a stop with both for safety sake and to preclude any chance of overpowering odor.

A water stop should never be used with prints or LF negatives as you can get severe non-uniformity problems.

Pinholes are not an issue with most all modern films.

PE
 
Humm ok then. I've used both water and acid with prints and never had problems. I was planning to go to water for Foma even in 4x5 though I've not had problems before with (citric) acid. Maybe 1/2 strength?


Sent from my iPhone using Tapatalk
 
Roger, try making an 11x14 print with a water stop! :sad:

You will be lucky to get a good print if there are uniform gray areas in it such as a portrait.

PE
 
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