At what pH is a stop bath considered exhausted?

Roger Cole · Mar 1, 2014

I've done it and not had a problem. Not larger than 11x14 though and it doesn't mean I wouldn't the next time of course.

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Sirius Glass · Mar 1, 2014

PE please remember that Roger knows more about film and chemistry than you will ever know. ROTFLMAOABMHATW

cowanw · Mar 1, 2014

No matter how rigorous the source of the information, it still has to be applied to the individual circumstances.
I use a Jobo Expert drums for 8x10 on a Simma roller base (like a Beseler). It is filled standing up on a bit of an angle to prevent an air bubble blockage and the volume of solution fills up one or two of the chambers first will the other chambers remain empty until the drum is placed horizontally and started rolling.
I worried that the bottom of he film would be stopped before the top or the film in the two or three unfilled chambers would be stopped much later.
My decision was to empty the developer, consistently timed, and fill the drum on the rotating base with tap water using a hose to direct the water into the drum. This distributes the water quickly. Water is 1000 fold more acidic than my developer and the volumes of residual developer and wash water provide another 100 fold difference in hydrogen ion availability.
There is of course no doubt that stop bath is much faster. But in the case of a Expert drum on a rotating base (which I suspect is a common usage) that speed may be a problem.
On the other hand developer activity drops off dramatically as pH drops. At ph 7, many developers (not all) may take 45 minutes or more to develop film
Truth be told though, ten seconds one way or another may be less important than being able to flood the film in my workflow.

Photo Engineer · Mar 1, 2014

Guys, I am not worried about the rate at which pH drops, I am worried about the uniformity of the pH change. As film and paper become larger in size, that non-uniformity can show up. Now, with a film having a 10 min development time vs a paper with a 2 min development time, the rate of change is considerably more important with the paper than with the film due to the rate of development.

I use Jobo tanks as well for prints up to 16x20 and film up to 4x5. I use a stop - always! With 35mm and 120, not so much.

PE

Roger Cole · Mar 1, 2014

Sirius Glass said:
PE please remember that Roger knows more about film and chemistry than you will ever know. ROTFLMAOABMHATW

WHATTT????

Something must be coming across very much not as intended.

I just said I had made 11x14 prints with water stop without noticeable problems, and I have. That's all. It could certainly be possible and maybe I just didn't look close enough.

If PE says it's ok and even preferable to use acid stop with TF-5, I will.

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Photo Engineer · Mar 1, 2014

Roger, you said nothing wrong. Sirius was not Serious!

PE

Roger Cole · Mar 1, 2014

Thanks PE. I used to print on RC which changes little once it hits a couple minutes development and then when I went to FB I found I liked the look better with very full development, 3-5 minutes. That may be why I didn't see a problem with 11x14 prints. Now that I am printing a lot on Ilford MGWT FB I use 2 minutes but I haven't used water with it either. I probably won't now, unless just to experiment to see if I can see this. Thanks for the tip!

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L Gebhardt · Mar 1, 2014

PE, like I said I've been using a water stop for the last few years. I've never had uneven development that I've attributed to the water stop, but I have had some uneven development with 4x5 film in Pyrocat in a hand tank. I eventually went back to XTOL in the jobo and the issues went away. Do you think Pyrocat would be more prone to this than XTOL? I assume the combi plan would be. Maybe I should try the combo again with stop bath. I did like the sharpness of the negs, just not the uneven skies.

I've never noticed an issue with water stop for paper, but it's certainly possible. I'll keep an eye out for it and go back to stop bath if I see any issues. Thanks for raising the issue.

Photo Engineer · Mar 2, 2014

Larry, anything is possible here. I don't use Pyro, but I do know that Sulfite levels and the pH at which Sulfite is present are factors in producing uneven stains. That is only from written knowledge, and not personal experience.

My work is best done without Pyro and other such developers due to the nature of my work.

So, sorry that is the best I can do.

PE

Jaf-Photo · Mar 3, 2014

Sometimes habits move in circles.

I ditched acid stops for water after reading about it in forums. I thought it worked fine, until I compared water stopped negatives with acid stopped negatives, and found the latter more consistent in development.

So I started using acetic acid again.

Now, I don't understand why I gave up the acid, as it provides more control, and convenience at that.

jp498 · Mar 3, 2014

One of my reasons for experimenting with water stop bath was either the efke50pl or foma100 film, I don't remember which, it was very soft and I got pinholes and one of the suggestions was a water stop bath, and the chemical reaction of basic film hitting acid stop bath might produce bubbles damaging the film. Then I got into pyro developers which specify a water stop bath. works for me and my combinations of kodak and ilford film.

Photo Engineer · Mar 3, 2014

Those bubbles only take place if you use a carbonate based developer, and many film developers use Borax instead. However, most pinholes are due to having not used a prewet and these "bubbles" are really air bubbles trapped on the film during early development.

A true pinhole from a stop leaves an actual depression in the emulsion by blowing off the emulsion due to gas pressure. It is very very rare to see this. You might see it if you use Dektol and an unhardened or very soft film.

PE

Ian Grant · Mar 3, 2014

jp498 said:
One of my reasons for experimenting with water stop bath was either the efke50pl or foma100 film, I don't remember which, it was very soft and I got pinholes and one of the suggestions was a water stop bath, and the chemical reaction of basic film hitting acid stop bath might produce bubbles damaging the film. Then I got into pyro developers which specify a water stop bath. works for me and my combinations of kodak and ilford film.

I use Pyrocat HD without a stop bath in all formats 35mm to 10x8 with no issue in around 8 years, it's better not to use a pre-wash unless you're using a rotary processor, it's not recommended by the film manufacturers and may in fact case issues with some films.

A stop bath is OK with Pyro developers it has no effect on the staining but half normal strength is preferable, just as there's no problems with fixers like Hypam or Ilford & Kodak Rapid fixer and the staining.

Ian

Photo Engineer · Mar 3, 2014

The original Kodak B&W instruction manual recommends a prewet for B&W films. I have posted the original photos from the manual showing the old tray processing method for roll film, but they applied it to all films in an effort to prevent air bubbles from forming on film and thus forming "pinholes". Air trapped on the surface of film forms something that looks similar but is called airbells or air bubbles.

You can distinguish pinholes from airbells because airbells are not associated with small crater like defects in the emulsion caused by escaping gas which causes pinholes. True pinholes are very very rare. They are generally only found when a Carbonate developer such as Dektol is used for soft film, or when you have a very deep tank photofinishing process in which the hydrostatic pressure in the tank becomes high enough to trap gas and then release it during a paper process using something like Dektol. See Eaton's book on photographic processing for details, or my log ago post with the quote from Eaton and also Haist.

PE

tnabbott · Mar 6, 2014

Tom1956 said:
I'll never agree with the "plain water stopbath" people. I always liked Kodak's way.

I agree. I used water as a stop bath initially and the negative would have streaks and other indicators of uneven stop. I started using stop bath and that went away. I think it may have been the tap water in my area at the time, but that is part of the reason for stop bath-it removes some of the uncertainty that comes with the local water supply.

Gerald C Koch · Mar 8, 2014

L Gebhardt said:
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).

Bromcresol purple was chosen because the bath will appear colorless under an amber safe light and black when the bath is no longer useable. However it is not the best choice of indicators because of its wide range from 5.2 to 6.8 pH units. The bath has become unusable long before there is any noticeable color change. An indicator with a narrower and lower pH range would have been a better choice.

Roger Cole · Mar 8, 2014

Unusable before color change? Really? I don't wait for a deep purple but I generally do wait for the amber look to become clear. I've never seen evidence of uneven stop.

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Tom1956 · Mar 8, 2014

69 posts on a subject as easy as pie. When the print still feels slimy in the stop is the sign to look for. As long as the print feels tacky or squeaky when you plop in in and give the tray a rock or 2, is the assurance all is well. I fail to see all the discussion. The purple is just there to tell you to pour it out before you even bother to pour it in the tray. I've seen stopbath be yellow in the bottle one day, and purple a few days later, just sitting in the bottle. The cheapest chemical in the darkroom.

Gerald C Koch · Mar 8, 2014

Roger Cole said:
Unusable before color change? Really? I don't wait for a deep purple but I generally do wait for the amber look to become clear. I've never seen evidence of uneven stop.

At a pH of 5.5 bromcresol purple still appears to be yellow. It is only at a pH of 6.0 that it will appear to be starting to change. With an amber safelight the change may not be apparent.

Roger Cole · Mar 8, 2014

Interesting. I can, of course, just mix up fresh but an indicator is handy. It is cheap but the citric acid based stop I use isn't quite AS cheap as acetic - still, it isn't fixer by any means.

Photo Engineer · Mar 8, 2014

When you insert a print into nearly exhausted indicator stop, and it is still amber, you will see a flush of black around the print as the pH suddenly rises, and then with agitation it will become amber again. This is the sure sign that you are nearing the end point of the stop.

That is how I do it anyhow, and it works. You can actually see the trail of black from the print and then watch it vanish.

Also, you notice the drop in the vinegar smell.

However, if you use tongs or gloves, you cannot use the squeak test!

PE

Roger Cole · Mar 8, 2014

I use tongs and citric acid so no squeak or smell test but I can use the trailing indicator, thanks!

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Gerald C Koch · Mar 8, 2014

Photo Engineer said:
Also, you notice the drop in the vinegar smell.

This is what I do. As an aside there is a group of chemicals which are used as indicators for color blind chemists. They emit a characteristic odor when the end point of a titration is reached.

Photo Engineer · Mar 8, 2014

Interesting about color blind chemists! At EK, we underwent a rigid color sensitivity test when hired and every few years after that, to insure "perfect" color vision. Those who fail could not work in any color sensitive areas, especially the Color Photography Division.

So, this may have been unknown in KRL.

PE

MattKing · Mar 8, 2014

I was going to say something about other film manufacturers seeming to favour colour blind chemists, but I decided against it.

At what pH is a stop bath considered exhausted?

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