Once the desired degree of development has been
reached, the process must be stopped quickly to avoid
overdevelopment. This can be achieved through a
simple water rinse, but an acid stop bath is more
effective in neutralizing the alkaline activators and
stopping development almost instantaneously.
A dilute solution of acetic or citric acid makes
for a powerful stop bath. However, with developers
containing sodium carbonate, the acid concentration
must be kept sufficiently low to avoid the formation of
carbon-dioxide gas bubbles in the emulsion, because
this may lead to ‘pinholes’ in the emulsion.
in short, after conducting a proper film test, an acid stop bath is an efective way of using the test data and stopping development when we need to. thi avoids after developmentand confusing resultswith overdeveloped highlightsand unrealistic speed points. the question is not why/ it is why not?pinholes and air bubbles as a reaction with sodiun carbonate can also be avoided by using a half-strength stop bath for films.
as in the malboro commercial
Originally Posted by Ian Grant
Re: Stop Bath.. How important?
OMG.!! I did not know that. I wonder what citric acid could save....
Originally Posted by zsas
With nothing between developer and fixer, it means that you are carrying a lot of crap into that fixer. It means that the fixer exhausts faster, and the chance of retained chemistry goes up!
As format size goes up, then a stop becomes more critical for uniformity. You must stop development quickly or you will get some sort of blemish on the final image. This is particularly important with LF and ULF films and very big enlargements.
PE - also true with Alkaline fixers, such as TF-4 and TF-5?
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George, TF-5 is mildly acidic.
That said, YES I use a stop bath. After all, with TF4 there is no stopping action to speak of.
However, a rinse after the stop is useful with TF4 or TF5 to extend the life of the fix.
If you use only a water rinse, with no stop, you should use running water and not just a still water rinse. And, a rinse still can allow defects due to continued development.
Yay mods merged thread...
Originally Posted by Bill Burk
and save them from suffering a cold too
Originally Posted by tim k
The Haist book says that acid stop bath is important to condition the film gelatin for acceptance of fixer..
Grant does not say that a stop conditions the gelatin. What he does say is that a stop is important for uniformity and for maintenance of fixer activity and he does say that it is better than nothing at all and better than just a rinse.
He has nearly a chapter on this and it is permanently marked in one of my copies of Haist. Now, taken out of context and paraphrased, one might write that the gelatin is conditioned, but this word covers such broad territory, it could lead to another "myth" about analog photography!