Stop Bath.. How important?

[Photo Engineer]

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

Gerald;

There are none published AFAIK. I have published on this several times in internal EK reports. The color problem was so severe that Ektacolor 30 was almost taken off the market for a short period in 1970, but we just added the stop.

You see, the original EP3 process was Develop, Blix, Wash, Stab. Kodak wanted a 2 step EP2 process so they got rid of the Stab at the last minute which was a pH 4.5 Citric Acid bath. The image stability tests showed no problem, but in real life the prints were turning pink after about 6 months. The bulk of our tests had been done with the Stabilzer, and we saw no problem removing it.

In our tests we ran a 2 week wet and dry oven test and saw no problem, but then over that Christmas when the problem was first seen in the trade we tested the prints daily and after about 2 -3 days we saw a pink stain and then the stain vanished. Prints affected this way then browned in a few years and began turning red.

Adding the stop bath fixed 2 problems. It extracted the CD3 from the coating thus eliminating the dye stability problem and it gave better uniformity in the Jobo processors which were just becoming popular at that time.

Why get rid of the stabilizer at the last minute? Well, it was an extra solution and all of the stabilizing agents were in the coating for the first time. The effect of the final stabilzer was minimal (or so we thought). So, it was deemed that EP2 was the thing to go with. Moral of the story - test many ways and don't make last minute changes!

This was my first introduction into the definite merits of the Stop bath. And, just to be clear, I was only one worker on the project and only one of the workers on the solution. Others made as much or more contribution to fixing this than I did.

PE

 

[Ian Grant]

Mason indicates that a water wash is sufficient (p201) - Ron you have the same edition I think, there's not a single reference cited.

He goes on to say that a stop bath or wash is superfluous with a well buffered acid fixer, he usually references the Hypam formula ph 5.2-5.4, in other parts of the book as it was Ilford's main fixer from the 50's to today.

He's saying that a wash or stop bath cuts developer carry over, and that a stop bath does arrest development faster and helps prolong the life of the fixer. That must have been Kodak's view at that time (mid 70's) as well.

Ian

 

[Photo Engineer]

Yes, Ian, he does, but he also goes on to say that if you use an alum hardener in your fix (as in KRLF), then you can get a precipitate of Aluminum Hydroxide due to the alkalinity carried over. He also restricts this to acidic fixes. There is no mention of neutral or alkaline fixes which are quite popular today. So, his statement is, on the face of it, very very narrowly confined to acidic, non hardening fixers.

PE

 

[alanrockwood]

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

But PE, if the hydrogen ions diffuse very fast, with the other ions diffusing very slowly, it is the very definition of unipolar diffusion.

You simply cannot have ions of a certain charge (such as hydrogen ions) being transported without having a very nearly equal amount of a combination of 1) charge of opposite polarity transported in the same direction (the counter ion, such as acetate ion) or 2) charge of the same polarity transported in the opposite direction (such as sodium ions). This is well known physical chemistry.

Therefore, you simply cannot have a nearly instantaneous inrush of hydrogen ions unless it is balanced by either a virtually equal inrush of counter ions or an outrush of ions of the same charge or some combination of the two processes.

As for hydroxide ions, if they are diffusing in the opposite direction of the hydrogen ions then it simply compounds the problem of maintaining local charge balance.

As an interesting aside, a lot of people don't realize the enormous power of electrical repulsion when a charge imbalance is very large. Just for the heck of it try calculating the electrostatic energy of a mole of charge evenly distributed in a sphere of one liter volume. Believe me, you wouldn't want to be standing even a few miles from it as the whole thing explodes from the pent up energy.

 

[Steve Smith]

So, his statement is, on the face of it, very very narrowly confined to acidic, non hardening fixers.

Which leads neatly into my next question:

For the last couple of years I have been using Peter Hogan's Prescysol developer and his alakaline fix. The data sheet states ' Four or five, 10 second rinses in fresh water is ok, or you can use our Alkali-STOP™'

Any thoughts on the relative merits or otherwise of water or stop in an all alkaline environment?


Steve.

 

[Mainecoonmaniac]

I use water as a stop bath

I've experienced pinholes on my negs some times using stop bath so I just use water. You might want to stop development a smidge to compensate.

 

[Photo Engineer]

But PE, if the hydrogen ions diffuse very fast, with the other ions diffusing very slowly, it is the very definition of unipolar diffusion.

Alan;

Again, you misunderstand. In the diffusion of ions through gelatin, Hydrogen is the fastest and Hydroxide is second in rate, therefore you have an inrush of Hydrogen meeting Hydroxide and a wavefront of neutral water forming as the Hydrogen diffuses downward and Hydroxide moves upwards. When the wavefront reaches the bottom of the coating (or in our tests the undercoat with indicator dye), you stop the reaction. This is virtually instantaneous.

There is a tiny gradient in charge which appears to be taken up by a shift in the equilibrium of the overall medium. Diffusion of Sodium and Acetate for example take place at only a slightly lower rate due to size and this is partly overcome by both shifts in equlibria and in the slight charge imbalance (if any) which takes place. Overall, in the average coating, all diffusion is done in about 15" or less, but the neutralization appears to take place in less than 5".

The two major researchers at Kodak on this were Liang and Tong. They developed a diffusion model for water, hydroxide, acid, dyes and other chemicals through emulsions.

One experiment had the acid anion and proton anchored in place through polymerization of the anionic portion of the acid molecule. They then showed the rapid diffusion of hydroxide into the acid layer to neutralize the alkali. Or, conversely, the proton (hydrogen ion) diffused upwards into the alkaline medium. This led to the development of proper barrier layers in instant products BTW and showed how diffusion and neutralization took place in coatings when acid and base were both present. This "timing layer" was crucial due to the rapid diffusion of either Hydrogen ion or Hydroxide ion. They had to be held back from each other while the development took place and the dyes diffused.

PE

 

[Photo Engineer]

Which leads neatly into my next question:

For the last couple of years I have been using Peter Hogan's Prescysol developer and his alakaline fix. The data sheet states ' Four or five, 10 second rinses in fresh water is ok, or you can use our Alkali-STOP™'

Any thoughts on the relative merits or otherwise of water or stop in an all alkaline environment?


Steve.

I have no idea, but it seems that they do suggest a stop, albeit an alkaline stop.

PE

 

[Steve Smith]

I have no idea, but it seems that they do suggest a stop, albeit an alkaline stop.

I think I will send Peter Hogan an e-mail and ask the question. My thought is that as the whole system is alkaline, the major contribution the stop gives is to arrest the development quickly.

However, Prescysol is usually used in semi-stand mode and has the same time (10.5 minutes) for all films. Extending the time, even doubling it, doesn't change anything much so I'm not sure a stop bath is of much use if all it does is quickly stop the development.


Steve.

 

[Photo Engineer]

Steve;

In an earlier post, I said that a stop is more important in situations where development is rapid. So, this is true with papers and with films that are developed less than about 5 minutes. In fact, consider E6 which has a first development of 6 mins at 100 F. This is a weak developer and the water rinse is perfectly acceptable, considering that it is followed by an acidic reversal bath. So, I think that there are very visible exceptions to the "rule" that a stop bath is essential. In fact, that is what makes things so confusing or at least indefinite to many people.

PE

 

[Thomas Bertilsson]

Can I draw the conclusion that a stop bath is recommendable with black and white films?

I have not always used one, but decided a while back to use it, just because it's how I was taught once by a photographer that used black and white film for many decades, showing old negs that looked as fresh as new ones, and it made sense to not try to save pennies on something I wasn't sure was going to work.

For a while I disregarded what I had learned, and used water as stop with alkaline fixer and Pyrocat developer. It was in a switch from that pyro developer and alkaline fixer to a more standard developer (replenished Xtol) and Hypam that I switched to using stop bath again.
I know that if I mix the stop bath properly, it will have no adverse effect on the film (no problems so far), but I thought that perhaps using water only would affect the film adversely in the long run.

It's very hard for me to filter out the practical details from all the science, which I admittedly don't understand.

I am helping a few people to get started in film photography (very excited about that), and they ask questions that are sometimes hard to answer. The reason to use a stop bath, for me, has been to neutralize the remaining developer as well as insuring that there is no developer remains in the emulsion, potentially causing problems down the road.

What conclusion can we draw from all of this discussion, focusing on black & white film?

Thanks,

- Thomas

 

[Photo Engineer]

Thomas;

Let me summarize a few things.

If you use a wash after the developer, you use running municipal water, not a still bath because that is not very good. It builds up contaminants. Therefore, if you use running local water, you are dependent on the quality of the local water and the rate at which you feel comfortable running the wash. Using distilled water would be better, but expensive to keep running.

If you use short development times, you run the risk of higher non-uniformity if you use a wash after development.

If you don't rinse well, you may affect the fix and may affect the removal of developing agents from the coating.

Using a good water rinse with running water, really a mini wash, after development can work. It can also have an impact on your final films or prints. OTOH, a stop bath is designed to eliminate the variability of the process and to work with all types of water. It more or less guarantees a uniform process and lower contamination.

So, a wash can be used with good quality running water, but a stop is preferred. The worst condition is trying to wash with hard water both after development and after fixing or using a still water rinse.

And, we must remember that alkaline and neutral fixes are becoming the norm today whereas just 10 - 20 years ago, acid hardening fixers were the norm. Even so, a stop can be used with these newer fixers.

PE

 

[Q.G.]

The interesting thing, i think, would be if using a water rinse instead of a stop bath would lead to long term problems.
That it works goes without saying. Many people (me included) have skipped the stop (with film) and rinsed with water instead, and got the negatives the way they should be.

But what about that residual developing agents thing?
I have some rather old 'unstopped' film that is as good as the day it came out of the tank. So the effect or lack of it may depend on some unknows (to me). Perhaps i haven't waited long enough (i doubt that it would matter to me how it turns out to be when i have to wait as long again ). And perhaps another film, processed in another developer would not keep that well 'unstopped'?

 

[Ian Grant]

Conclusions on Stop bath use

With fixers like Hypam, Ilford & Kodak Rapid Fixer etc (unhardened) a stop bath is not needed. A water wash will help, and suffice.

A stop bath is beneficial in prolonging the life of a fixer -Acid or Alkali

A stop bath is very important where the carry over is greates, Fibre based papers, and advised with RC papers


As films rinsed in water will have very little carry over it's up to you if you use one, but more important when dev times are very short, or you want maximum capacity from a fixer


Ian

 

[Thomas Bertilsson]

I take that as a recommendation to use a stop bath. Since it does no harm, I have nothing to lose, and it adds a degree of protection against possible future ill effects of developer contaminants in the emulsion. Better safe than sorry.

Thank you for taking time to explain it in terms I can understand!

- Thomas

Thomas;

Let me summarize a few things. <snip>

Using a good water rinse with running water, really a mini wash, after development can work. It can also have an impact on your final films or prints. OTOH, a stop bath is designed to eliminate the variability of the process and to work with all types of water. It more or less guarantees a uniform process and lower contamination.

So, a wash can be used with good quality running water, but a stop is preferred. <end snip>

PE

 

[Photo Engineer]

Yes, the possibility of unwanted effects is all I am trying to bring to everyone's attention here.

There are basically 3:

1. Nonuniformity based on operator technique in rinsing (or overall work flow) and water supply.
2. Retained developing agents may cause staining after a number of years.
3. Problems with short development times due to rapid development rate.

All 3 are interrelated.

PE

 

[Thomas Bertilsson]

And, since my negatives will be incredibly important to those finding them a hundred years from now, I had best take that precaution...

 

[Q.G.]

Yes, the possibility of unwanted effects is all I am trying to bring to everyone's attention here.

There are basically 3:

1. Nonuniformity based on operator technique in rinsing (or overall work flow) and water supply.
2. Retained developing agents may cause staining after a number of years.
3. Problems with short development times due to rapid development rate.

All 3 are interrelated.

PE

You mentioned before, PE, that there is no reliable test for residual developing agents.
But is there no way even to get an approximate idea about the presence (or absence) of such things?

Not that it would make much sense to test while processing. You might as well just use a stop bath if you worry about the effects not using one might have.
But anyhow, it's nice to just know.

 

[Steve Smith]

I take that as a recommendation to use a stop bath. Since it does no harm, I have nothing to lose.

That would be my interpretation too. However, I like to question everything. If someone tells me I have to do something, I want to know why and what will happen if I don't do it.

I suppose when seen as just words on the internet it can appear argumentative but it's not!


Steve.

 

[Thomas Bertilsson]

I like precautions, Steve, but I respect your hunger for knowledge.

I just want something that works, so I can move on, stop thinking about it, and make more photographs.

Takes all kinds, doesn't it?

 

[fotch]

While I have occasionally used water rather than a Stop Bath, it was because either I ran out of stop bath or got a streak of lazy/cheapskate and did without. However, I make enough mistakes without trying, I prefer to try to do the best I can and accept the recommendations of the major manufacturers and use a stop bath. This thread has been very interesting with both points of view and for me, points to the need for stop bath.

Its kind of reminds me of discussions with people who will argue to their death that it has not any effect on them, such as smoking, eating fat foods, excess salt in food, no seat belts, and hundreds of others.

JMHO

 

[Photo Engineer]

If your method works, then use it! I don't wish to force anyone into a workflow that does not fit them.

There is no test for retained B&W developers AFAIK, but there is a weak and unreliable test for color developers that is difficult to carry out. I have forgotten the details, but it involves the ability of a color developer to form a dye.

Of course, there are analytical methods to test for the presence of retained developing agents.

If you see an old print, say 50+ years old on FB paper, and it is brownish with mottling, this is probably due to retained developer as much as it is to deterioration of the paper. It looks different than retained silver or hypo and the retention of silver or hypo would show up more rapidly I think.

Most good workers have no problem with modern materials, but my opinion is "why take a chance". I use a water rinse with film sometimes myself, but I have had years of experience, know my equipment, know my process and know my water quality!

PE

 

[Ian Grant]

YOU CAN USE WATER - KODAK THEMSELVES SAY SO !!!!!

2. Retained developing agents may cause staining after a number of years.

PE

The only flaw here is that stop bath doesn't remove all the residual developer, it doesn't have time to.

Usually the recommend stop bath times are short 10 seconds is one manufacturers suggestion.

So a 1 or 2 minute rinse might actually have a greater effect on removing developer from the emulsion.

In nearly 140 years of Gelatin film emulsions there's never been a theory or evidence that residual developer has lead to any deterioration of a negative, despite the fact that Ilford, Agfa, Kodak and others didn't recommend a stop bath with many films & plates.

In addition they were suggesting a rinse in water after development in highly active developers, with dev times of 2-4 minutes which rather seems to indicate that statements 1 & 3 are rather unlikely scenarios given that most of us develop now in far more dilute modern developers.

1. Nonuniformity based on operator technique in rinsing (or overall work flow) and water supply.
3. Problems with short development times due to rapid development rate.



Ron's comment about a problem with a 1970 colour paper clearly indicates that carry over with FB papers is a far greater problem due to the dev that's soaked into the paper itself. RC Colour papers came in slightly later.

________________________________________________________________________________________

Food for thought this is what KODAK currently say with film developing:

We can assume Kodak know best, which is what Mason (Ilford) & by default Levenson (Kodak) said as well mid 70's

FINAL STEPS
Rinse at 65 to 75°F (18 to 24°C) with agitation in KODAK
Indicator Stop Bath or running water for 30 seconds.

That's up to date Kodak information so lets cut the Bull-shit, that's in the current Tmax data sheet, and in other film data sheets as well.

Ian

 

[Steve Smith]

And this is Ilford's recommendation from their FP4+ data sheet:

After development the film can be rinsed in water but we recommend that an acid stop bath is used

The Delta films' data sheets say the same thing.


Steve.

 

[Thomas Bertilsson]

Fuji Acros spec sheet:

"For the stop bath a 1.5 % acetic acid solution is recommended. Immerse the film in the bath at 15 to 25°C (59 to 77°F) for 20 to 30 seconds while agitating."