At what pH is a stop bath considered exhausted?

RattyMouse · Feb 26, 2014

I am making my own stop bath and am wondering at what point should I toss it. Is it OK to use as long as it is measurably acidic? (pH <6.0). Or, should it be something stronger, like 5.0 or 4.0?

Thanks!

RattyMouse · Feb 26, 2014

Ack!!! I meant for this to be in the b & w forum!!

fretlessdavis · Feb 26, 2014

My understanding was that it needs to be lower than 5.5, but the lower it gets, the higher chance for reticulation/damage.

Sirius Glass · Feb 26, 2014

When it gets blue.

fretlessdavis · Feb 26, 2014

You can always buy a bulk indicator-- IIRC it's mixed 1:1000, so one bottle will last forever. Pair that with bulk citric acid from a brewer's supply, and you'll have a massive stockpile of Ilfostop for the price of a single bottle of Ilfostop.

Athiril · Feb 26, 2014

Bromocresol Purple would be my indicator of choice.

Tom1956 · Feb 26, 2014

You can feel it on the print when the stop bath starts getting old. Fresh stop bath make the print feel tacky when you first put it in.After a while the slimy feeling from the developer takes longer to turn "tacky" or "squeaky" feeling, till a point where it stays slimy feeling.. Or the yellow goes brownish on its way to purple. This is not rocket science--you'll know when it's no good any more.

markbarendt · Feb 26, 2014

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.

jp498 · Feb 26, 2014

Use a non-acidic fixer like tf5 and water is the recommended stop bath. This combination removes most of the odor we associate with darkroom work.

Tom1956 · Feb 26, 2014

What good is photography without the smells in the darkroom?:crazy:

RattyMouse · Feb 26, 2014

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.

If the difference is only 1 or 2 seconds, why does ANYONE use stop bath?

Tom1956 · Feb 26, 2014

Because it halts development dead, hardens the gelatin, and protects the longevity of the fixer. Just makes best sense.

BTW--you could conceivably slice up a cool cucumber from your garden into a bowl, pour in a little stop bath, and sprinkle on a little salt and pepper for some mighty fine eatin'.

markbarendt · Feb 26, 2014

It may take 20-30 seconds instead of 10, so you may pour off your developer 10-15 seconds early say at 9min 50sec, instead of 10min. Sometimes no development adjustment is even needed.

markbarendt · Feb 26, 2014

Tom1956 said:
Because it halts development dead, hardens the gelatin, and protects the longevity of the fixer. Just makes best sense.

BTW--you could conceivably slice up a cool cucumber from your garden into a bowl, pour in a little stop bath, and sprinkle on a little salt and pepper for some mighty fine eatin'.

Hardens the gelatin, sure about that?

As to protecting the fix water does the same thing, just takes a hair longer (and smells better).

Tom1956 · Feb 26, 2014

markbarendt said:
Hardens the gelatin, sure about that?

As to protecting the fix water does the same thing, just takes a hair longer (and smells better).

Hardens it more than it was while it was in the developer. Though I wouldn't go so far as to call it "a hardener".

Xmas · Feb 26, 2014

Tom1956 said:
Hardens it more than it was while it was in the developer. Though I wouldn't go so far as to call it "a hardener".

the imperative reason for an acidic stop bath is to reduce the probability of stains with some developers... Real horrible with a print. It does reduce alkaline carry over into fixer as well.

with non prehardened film or plates you might have used a hardened bath.

with non prehardened film you run more risks of reticulation with an acid stop manufactures would caveat this...

Ansell A and Barry Thorton used a borax post bath with film cause an 'instant' stop was not what they wanted

web gossip is wonderful stuff

flash26c · Feb 27, 2014

Besides the fact that it is so cheap, why chance anything, dump it after you're finished.

BradS · Feb 27, 2014

Ratty, you're really over thinking this. Plain tap water works just fine....Kodak indicator stop bath is exhausted when it turns blue (instead of dark yellow) but, I never keep it that long.

Tom1956 · Feb 27, 2014

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

RattyMouse · Feb 27, 2014

BradS said:
Ratty, you're really over thinking this. Plain tap water works just fine....Kodak indicator stop bath is exhausted when it turns blue (instead of dark yellow) but, I never keep it that long.

I'm not over thinking this. You guys are!

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

markbarendt · Feb 27, 2014

RattyMouse said:
I'm not over thinking this. You guys are!

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

Okay, we might be overthinking, but if that's true then you are under thinking it.

There isn't an exact answer.

The stop doesn't just quit working at a given PH. The first film or paper that is run through the stop is going to stop really fast, next one a bit slower, slower again for the next:it's a progressive change. If you are using indicator stop it is my understanding that when it turns color it has essentially reached a point where "it is as effective as water" and some of us think water is effective.

So you need to define what "exhausted" means.

MartinP · Feb 27, 2014

As the function is to lower the alkaline pH of the developer and stop it's actions, then one also needs to consider the developer and the size of the print and trays, as well as the pH of the second-bath (with water being more-or-less neutral, pH7).

With a small print it is relatively easy to give evenly fast submersion and vigorous agitation to the whole print surface, while with a larger print this becomes much harder to to achieve perfectly -- in water, working by massive dilution of the carried-over developer, that could mean a visible difference from one area to another. An acidic stop-bath does it's job chemically and hence much more quickly than the dilution action of water.

Whether this is significant depends on the print, the developer, the critical standards of the printer and the use to which a particular print will be put. So, as usual, the correct answer to the question is "it depends".

Jaf-Photo · Feb 27, 2014

The classic stop bath is acetic acid diluted in water to 0.7 percent. This is a very cheap liquid that you could reuse a few times and then toss and replace.

The benefit over water is that you stop the dvelopment instantly and uniformly across the negative, which provides greater control and consistency.

RattyMouse · Feb 27, 2014

markbarendt said:
Okay, we might be overthinking, but if that's true then you are under thinking it.

There isn't an exact answer.

The stop doesn't just quit working at a given PH. The first film or paper that is run through the stop is going to stop really fast, next one a bit slower, slower again for the next:it's a progressive change. If you are using indicator stop it is my understanding that when it turns color it has essentially reached a point where "it is as effective as water" and some of us think water is effective.

So you need to define what "exhausted" means.

Does the indicator flip at 7 or is it higher?

Anon Ymous · Feb 27, 2014

RattyMouse said:
Does the indicator flip at 7 or is it higher?

The indicator is bromocresol purple and it doesn't "flip", it's a gradual transition. Have a look here. I toss it when it has that dirty colour, about pH 6. It's still acidic.

At what pH is a stop bath considered exhausted?

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