Stop Bath.. How important?

If acetic acid is not diluted enough (wrong proportions) it can result in pinholes in the negatives. I found this out the hard way 40+ years ago. Since then I have used water only for film which has worked well. Recently, though, I have been using a citric acid stop bath for prints which smells much nicer than acetic acid. I may try it on film as well.

wiltw said:

And your point is...? The fact that the Zone System was written around contrast enhancement or reduction during film processing does not get rendered as totally immaterial with modern films, even if Ansel quit doing his own processing.

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He was using older thick emulsions, modern thin film emulsions don't really respond to water bath development. To control highlights with water bath development the negative is placed in water before the high lights have fully developed to hold them back. But we are talking about giving full development.

But after a rinse modern thin emulsion negatives have little developer left in them anyway.

Ian

While Adams did later withdraw conventional water bath technique (used in a famous photo in 1936) as no longer applicable to modern emulsions, due to streaking, there is a modified procedure which advocates (The film developing cookbook By Stephen G. Anchell, Bill Troop) the water bath to affect contrast of the negative without the streaking issues.

wiltw said:

While Adams did later withdraw conventional water bath technique (used in a famous photo in 1936) as no longer applicable to modern emulsions, due to streaking, there is a modified procedure which advocates (The film developing cookbook By Stephen G. Anchell, Bill Troop) the water bath to affect contrast of the negative without the streaking issues.

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Using an alkali bath (Sodium Sulphite) instead of water will have other effects, despite the pH the sulphite will slow the rate of diffusion initially.

But as you yourself said you've used water as instead of stop abath for nearly 50 years so you know it works

Ian

Well, here are some additional comments on these recent posts.

1. You don't have to diffuse the acid through the emulsion, only the proton, which is the smallest of all ions. I have seen the rate of pH drop when using acid on alkaline films. It is virtually instantaneous on a wet film. Today's thinner films make acidification very rapid. How was this tested? Among other things we coated /gel/dummy emulsion/indicator dye/support and then looked at the spectrum of the indicator dye vs time. We also used a surface pH meter but that was too slow!

2. Pinholes would only be possible with Carbonate developers, poorly hardened film or thick film. This effect has not been demonstrated since the 50s and even then an acid stop was still recommended. It was also only seen in deep tank processing, not tray or tank developing.

3. If you use a rinse after development, it must be done with running water not with standing water. If you can, check the rinse water pH sometime if you are using a standing rinse. You will see that it is quite alkaline and it will vary depending on what you put into it in terms of film, paper and developer that is carried over. For example, D8, D11 or D19 will generally give you more adverse effects than D76 or Dektol. Films with development times less than about 5 minutes will show more effect than those with 7 minutes or greater. There is a hazy area in between.

4. A true stop also contains Sulfite, although plain acid will do. This Sulfite helps prevent stain formation and form a more soluble version of HQ if it should be oxidized to the Quinone form.

PE

with a running water stop bath for at least one minute i never saw problems, even with alkaline stop bath, although is a bit on the strech line to use just a change of water... but if you use an acidic fixer maybe you won´t have problems, i have saw people not using stop bath and having no problems, but...

So far this thread is over run with testimonials.
Kind of reminds me of the miracle vitamins mail filling my mailbox.
Very little factual data.

Sort of like the smoke screen surrounding junk science...
http://www.webexhibits.org/bogus/4.html

PE informs us as to what is actually happening in the emulsion.
From his information, I can make an informed decision.

Reinhold

www.classicBWphoto.com

Amen

Reinhold said:

So far this thread is over run with testimonials.
Kind of reminds me of the miracle vitamins mail filling my mailbox.
Very little factual data.

Sort of like the smoke screen surrounding junk science...
http://www.webexhibits.org/bogus/4.html

PE informs us as to what is actually happening in the emulsion.
From his information, I can make an informed decision.

Reinhold

www.classicBWphoto.com

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You pour the water in, you shake it al about, but then the dance steps stop you pour it all out and do the same with the fixer, start dancing again, then pour back do the same for longer with a few changes of water

Then you get great negs, after finishing fixing & washing.

Ian

Well, that is quite good Ian, but the thing is that problems with the tail end of any process, B&W or color, may not show up for 5 - 20 years!

So, you may see a perfect print or negative when initially dry but depending on the tail end (stop, fix, wash) or (stop, blix, wash) etc. errors will not show problems for years.

PE

Photo Engineer said:

Well, that is quite good Ian, but the thing is that problems with the tail end of any process, B&W or color, may not show up for 5 - 20 years!

So, you may see a perfect print or negative when initially dry but depending on the tail end (stop, fix, wash) or (stop, blix, wash) etc. errors will not show problems for years.

PE

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Are you suggesting that somehow an insufficient stop bath will cause the negatives to be unstable years after they have been fixed, washed, and dried?

If so, is there any evidence that this happens and/or a mechanistic explanation of why it happens?

Alan;

Yes, of course. You may have missed my post earlier about HQ and Metol.

Metol is very soluble in acid (as compared to base), and HQ is more soluble in base than in acid. Interesting opposites these two guys! An Acetic Acid - Sulfite Stop followed by any pH fix is able to remove both products more easily by making the soluble acid salt of Metol and extracting it, and by Sulfonating the HQ and Quinone. This renders them all more soluble in any subsequent fix of any pH if they are not extracted outright by the stop bath.

Retained HQ will oxidize to Qunone (yellow) and if stored in damp conditions it will form Quinhydrone (green) which was once used in Quink, a green ink sold years ago. Retained Metol browns.

So, one objective of a process train is to remove the developing agents, a fact overlooked by many. And, there is no good test for retained developing agents.

To continue, with color materials, the stop bath is intended to removed color developer (PPDs) from the color coating and as you season in the Acetic Acid stop, it turns pink. Add a dash of Sulfite and it becomes clear as it reacts with the pink oxidized PPD. If these prints are kept, they first turn pink, then brown and being fading.

If you wish more information, I can go on with this for another page or so as I lost a Christmas vacation due to this type of problem. I was called in to troubleshoot exactly the problem related to the lack of a stop bath. So, I am not giving a fictional account, I guarantee you!

PE

Photo Engineer said:

Alan;

Yes, of course. You may have missed my post earlier about HQ and Metol.

Metol is very soluble in acid (as compared to base), and HQ is more soluble in base than in acid. Interesting opposites these two guys! An Acetic Acid - Sulfite Stop followed by any pH fix is able to remove both products more easily by making the soluble acid salt of Metol and extracting it, and by Sulfonating the HQ and Quinone. This renders them all more soluble in any subsequent fix of any pH if they are not extracted outright by the stop bath.

Retained HQ will oxidize to Qunone (yellow) and if stored in damp conditions it will form Quinhydrone (green) which was once used in Quink, a green ink sold years ago. Retained Metol browns.

So, one objective of a process train is to remove the developing agents, a fact overlooked by many. And, there is no good test for retained developing agents.

To continue, with color materials, the stop bath is intended to removed color developer (PPDs) from the color coating and as you season in the Acetic Acid stop, it turns pink. Add a dash of Sulfite and it becomes clear as it reacts with the pink oxidized PPD. If these prints are kept, they first turn pink, then brown and being fading.

If you wish more information, I can go on with this for another page or so as I lost a Christmas vacation due to this type of problem. I was called in to troubleshoot exactly the problem related to the lack of a stop bath. So, I am not giving a fictional account, I guarantee you!

PE

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Something to think about and discuss further. Thanks.

Ian Grant said:

A great many people who use Adox/EFKE films never see a problem.

Ian

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I'm one of them. Efke is the only source I can find for 2x3 sheet film, and works fine for me.

ron

what if you use developers that do not contain HQ or Elon ?

jnanian said:

ron

what if you use developers that do not contain HQ or Elon ?

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Depends.

Phenidones are hydrazine derivatives but AA is the only freebie here. Unfortunately, AA has a bad rep. IDK if it is deserved or not, but it is not the best developing agent IMHO or it would be all over the place in developers. It is tricky and messy.

So, go formulate a good developer. I know of a few.

PE

PE, you are diplomatic, knowledgeable, intelligent, generous and experienced. Thank you for the effort you devote to this website.

Photo Engineer said:

To continue, with color materials, the stop bath is intended to removed color developer (PPDs) from the color coating and as you season in the Acetic Acid stop, it turns pink. Add a dash of Sulfite and it becomes clear as it reacts with the pink oxidized PPD. If these prints are kept, they first turn pink, then brown and being fading.

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Does this apply to color film, too? The Kodak publications I've seen don't mention a stop bath per se. For instance, my Kodak Color Darkroom Dataguide (1996) specifies C-41 steps of developer, bleach, wash, fixer, wash, and stabilizer (p. 22). The description of RA-4 (p. 48; also p. 49) does mention stop bath, but says it's "optional." If a stop bath is likely to increase the longevity of my C-41 negatives, I'll certainly add that to my procedure.

Photo Engineer said:

...
1. You don't have to diffuse the acid through the emulsion, only the proton, which is the smallest of all ions. I have seen the rate of pH drop when using acid on alkaline films. It is virtually instantaneous on a wet film. Today's thinner films make acidification very rapid. How was this tested? Among other things we coated /gel/dummy emulsion/indicator dye/support and then looked at the spectrum of the indicator dye vs time. We also used a surface pH meter but that was too slow!
...
PE

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Except under very special conditions you cannot have protons diffusing alone without also having diffusion of a counter ion (an ion of negative charge) in the same direction or diffusion of an ion of the same charge in the opposite direction.

The reason is because you must maintain electrical neutrality, or at least a very close approximation to electrical neutrality. For example, if diffusion of the proton gets too far ahead of diffusion of the counter ion what happens is the build up of an electrical field with opposes the concentration gradient and cuts off further diffusion. (To put it in terms the electrical engineers use when discussing transport of charge carriers in a semiconductor, the drift current opposes the diffusion current.)

One can estimate how much unipolar diffusion is allowed. Suppose that an emulsion were 10 microns thick. Further suppose that the relative dielectric constant of the wet emulsion approximates that of water (i.e. ~80). Further suppose that the pH of the emulsion drops from about 9 to about 7. I think these are all conservative assumptions as emulsions are, I think, usually a little thicker than this, the dielectric constant of the emulsion will be somewhat less than the dielectric constant of water, and the drop in pH for an acid wash will be greater than indicated above.

Next, suppose for sake of discussion that the diffusion is nearly unipolar, i.e. dominated by proton transport. under the assumptions discussed above one can calculate the charge imbalance built up in the emulsion and estimate the voltage induced by this charge imbalance. It works out to about 10 volts.

It is impossible for such a large voltage to be built up by diffusion. The most you can get is something of the order of thermal energy (about 0.025 electron, or about 40 times lower than the 10 volts implied by the calculation above). Therefore, unipolar diffusion of hydrogen ions cannot be a dominant process in a stop bath process. Therefore, diffusion must be ambipolar and therefore determined in large part by the diffusion coefficient of the counter ion. This diffusion coefficient will not be vastly different from the diffusion coefficients of developer molecules. Therefore although diffusion of the acid into the emulsion may be faster than diffusion of developer from the emulsion, it is not likely to be even an order of magnitude faster than diffusion of the developer, or in other words it will be on the same general time scale as diffusion of the acid.

I am not contradicting your claim that diffusion of acid into the emulsion will be fast. What I am saying is that diffusion of developer out of the emulsion will also be fast. However, there is also a possible curve ball mother nature may throw at us. If the developer becomes adsorbed or bound to the gelatin molecules or other emulsion components this could slow the transport of developer from the emulsion.

Assuming fixer is going to be used just once then discarded or it is going to be the last time this particular fixer is being used, are there any scare stories or even actual facts suggesting that it's not a good idea to pour out the developer then pour in the fixer without a stop bath or water bath? I'm assuming acid fixer and film, not paper.


Steve.

You run a much higher risk of dichroic fog staining the emulsion Steve. If the fixers being used one-shot it's also likely to be made up at a lower concentration raising the risk further.

Photo Engineer said:

So, one objective of a process train is to remove the developing agents, a fact overlooked by many. And, there is no good test for retained developing agents.

PE

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So assuming the same diffusion takes place with a water rinse compared to a stop bath then all's equal. In practice the lower pH of an acid stop bath should reduce the rate of diffusion as it reduces the swelling of the emulsion.

If an emulsion is placed in stop bath then we assume development stops, but if it's then placed back in an alkali solution some further development takes place dependant on the residual retained developing agents.

It's good agitation whether a water rinse or stop-bath that's most important.

Ian

Forgive me, but all this reminds me of the old story of the group of philosophers aguing about how many teeth a horse has. Finally, one of the philosophers suggests that they find a horse and actually count the number of teeth. The others turn on him and beat him severely.

Nowhere in all these comments is there any citation of an actual independent scientific study. I'm sure there must be a least one.

Ian Grant said:

You run a much higher risk of dichroic fog staining the emulsion Steve. If the fixers being used one-shot it's also likely to be made up at a lower concentration raising the risk further.

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The reason I asked is because I have done this a couple of times although I always mix the fixer up to normal strength.

I have not seen a problem and was not expecting there to be one but thought it was worth asking the question.

I suppose my assumption was that as the fix is acidic then it should stop development just like a stop bath only more so. Another assumption here is that the fixer is more acidic than stop. I have never tested either and don't intend to.

I think there is a good mix of trying out different things and listening to the wise advice of others in this thread. I think the trying of different methods is important even if it goes against the wise advice because if we never tried anything out we would never learn anything new.


Steve.

alanrockwood said:

Except under very special conditions you cannot have protons diffusing alone without also having diffusion of a counter ion (an ion of negative charge) in the same direction or diffusion of an ion of the same charge in the opposite direction.

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Alan;

I suggest no such thing as a unipolar diffusion. I am suggesting neutralization!

The coating is alkaline with enough hydroxide ions present to achieve the desired pH of the developer. The protons move in to meet the hydroxide ions and they reach the bottom of the coating in a rush so fast that it is difficult to measure.

Meanwhile the Acetate ion and the Sodium ion lazily diffuse towards each other. So, neutralization is virtually instantaneous, but equillibration is much slower.

That is what I am describing. The rapid movement of Hydrogen ion to neutralize the hydroxide ions present in the coating. At the same time, excess Hydrogen ion is protonating the Metol.

PE

srs5694 said:

Does this apply to color film, too? The Kodak publications I've seen don't mention a stop bath per se. For instance, my Kodak Color Darkroom Dataguide (1996) specifies C-41 steps of developer, bleach, wash, fixer, wash, and stabilizer (p. 22). The description of RA-4 (p. 48; also p. 49) does mention stop bath, but says it's "optional." If a stop bath is likely to increase the longevity of my C-41 negatives, I'll certainly add that to my procedure.

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I use a stop bath for color paper to promote uniformity and remove the developing agent. The developing agent (CD3) is not very soluble. The CD4 used in C41 is much more soluble and can be removed by the bleach which is more acidic than the RA blix. The same is true of E6 which uses a more acidic bleach and a slightly acidic reversal bath.

PE