Citric acid as stop bath?

alanrockwood said:

I'm not really sure what the purpose is of an acid stop bath. Of course, the acid does stop development, but it seems to me that a plain water stop bath will do the job (somewhat more gradually) by dilution of the developer, particularly if the water treatment is done with adequate reproducibility and agitation, and provided that the overall development process is calibrated to include the more gradual effect of a plain water stop bath, which could include extending the development by a few seconds.

Please clue me in if there is something absolutely essential that the acid provides. I may be missing something.

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Alan:

This is subject to correction by the chemists here, but I believe that the two basic advantages of acid stop bath are:

1) dependable, quick and consistent cessation of development; and
2) protection for acidic fixers.

Clearly, point 2 does not apply for alkaline or neutral fixes. Point 1 is much more meaningful for production printing than more deliberate, 1 at a time printing workflows. It can also be useful in group darkrooms, because it can serve as a reminder to check whether fixer capacity has been exhausted. Finally, it is useful if water is at a premium, and a running water stop bath is impractical.

In my case, the last time I used acid stop was when I printed my postcards for the postcard exchange. The time before that was when I was working with a group in a school darkroom. Other than that, I use a water rinse.

Matt

Way back in the dawn of photography, one of the "benefits" of acid stop was that it removed the "unsightly stain" formed by some developers...

Ole said:

...it removed the "unsightly stain" formed by some developers...

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Barry

alanrockwood said:

I'm not really sure what the purpose is of an acid stop bath.
Of course, the acid does stop development, but it seems to
me that a plain water stop bath will do the job (somewhat
more gradually) by dilution of the developer, ...

Click to expand...

I side with those who maintain that it's purpose is to assure
the acidity of an acid fix. The as little as 10 seconds in acid
stop recommended by one supplier will give the film or paper
a superficial acidic character; good for an acid fix.

So why be concerned. Every one knows an alkaline fix will
work. Why not just go directly from developer to fixer; at
least for those not worried by the few additional seconds
of lingering development. Besides, working with one-shot
chemistry one may toss the fix in with the developer.
I don't do that myself but Mr. Gainer has and may
do; others as well. Dan