Stop Bath.. How important?

[Xylo]

Just continue to use the fixer until your hypo check drops indicate it is exhausted

I've been doing something similar for a number of years, except I use bits of film leader to time how long it takes to clear the film, then I double that.

 

[alanrockwood]

It's funny because I have the feeling that the stop bath has very deep roots. Lets not forget that back in the old days, the gelatin emulsion wasn't as well hardened as it is today. We all know that an alkaline PH will help soften the emulsion. So if you have an already soft emulsion, (even though it isn't hardening) using an acidic stop bath would have benefits.... I must admit that with the advancements in chemistry, the use of the stop bath is not as important as it once was...

That reminds me there was once a young homemaker named Alice whose procedure for making roast beef included cutting a small piece from each end of the roast. When Alice's very young and curious daughter asked why remove the ends of the roast Alice replied that she learned the procedure from her mother, and that she would ask her mother at the next opportunity. Alice's mother had a similar answer, "I learned it from my mother." Alice then decided to ask her grandmother the same question the next time she would visit her at the rest home. The mystery was finally solved! Alice's grandmother, who was by then quite old but still had a good memory, replied "My Dear Alice, when I was a young bride my roasting pan was too short to fit the whole roast, so I had to cut the ends off the roast to make it fit the pan."

 

[faberryman]

That reminds me there was once a young homemaker named Alice whose procedure for making roast beef included cutting a small piece from each end of the roast. When Alice's very young and curious daughter asked why remove the ends of the roast Alice replied that she learned the procedure from her mother, and that she would ask her mother at the next opportunity. Alice's mother had a similar answer, "I learned it from my mother." Alice then decided to ask her grandmother the same question the next time she would visit her at the rest home. The mystery was finally solved! Alice's grandmother, who was by then quite old but still had a good memory, replied "My Dear Alice, when I was a young bride my roasting pan was too short to fit the whole roast, so I had to cut the ends off the roast to make it fit the pan."

I take it that you think Kodak scientists asked their mothers whether they should recommend using stop bath, and that using stop bath is just an old wives tale.

 

[alanrockwood]

I re-read your example. Why are you bothering to use carry over developer molecules? Why not just say, as in your example, out of 500ml of developer, you will have 5ml of carry over developer, or 1%. 1% ain't much, so nothing to worry about. That seems to be the essence of your argument. All that carryover developer molecules stuff is just unnecessary window dressing.

Query: what are your scientific credentials, particularly in the field of chemistry?

My PhD was in chemistry, with physical chemistry emphasis. I spent my career working in the fields of physical chemistry, instrumentation development, and clinical chemistry.

I framed my example in terms of developer molecules because much of the previous discussion about developer carryover seemed to be framed in terms of carryover of developer, meaning the developer compound itself. However, it could be that carryover of alkaline buffer is what is detrimental to the fixer, not the developer molecules themselves. In any case, the same discussion pretty much applies to buffer molecules as well because by the time the carried-over buffer molecules reach the fixer they will be diluted by a huge factor and will probably be too few to matter because the acid in the fixer will overwhelm the week effect of the hyper-diluted buffer.

If the alkalinity of the carried-over buffer is indeed the potential problem then the carryover could produce a slow degradation of the fixer over a period of time, though I doubt degradation from that cause would be very noticeable. compared to fixer exhaustion by reaction of the fixer's thiosulfate with silver halide in the film.

 

[alanrockwood]

I take it that you think Kodak scientists asked their mothers whether they should recommend using stop bath, and that using stop bath is just an old wives tale.

Whos knows? Just speculating on a possible reason here, but more likely they just continued to use acid fixer when processing film because that's the way they always did it (and acid fixer may have once served a necessary purpose), but decades later they never got around to testing whether it was really necessary. They probably had more pressing projects to attend to, and if they would have found that water was good enough then it would have decreased the sale of one of their products.

In any case, if Kodak did investigate the issue then why didn't they ever publish the results? I assume that the results of such a study have never been published because no one posted here on the results of the investigation?

 

[faberryman]

My PhD was in chemistry, with physical chemistry emphasis. I spent my career working in the fields of physical chemistry, instrumentation development, and clinical chemistry.

I framed my example in terms of developer molecules because much of the previous discussion about developer carryover seemed to be framed in terms of carryover of developer, meaning the developer compound itself. However, it could be that carryover of alkaline buffer is what is detrimental to the fixer, not the developer molecules themselves. In any case, the same discussion pretty much applies to buffer molecules as well because by the time the carried-over buffer molecules reach the fixer they will be diluted by a huge factor and will probably be too few to matter because the acid in the fixer will overwhelm the week effect of the hyper-diluted buffer.

If the alkalinity of the carried-over buffer is indeed the potential problem then the carryover could produce a slow degradation of the fixer over a period of time, though I doubt degradation from that cause would be very noticeable. compared to fixer exhaustion by reaction of the fixer's thiosulfate with silver halide in the film.

With respect to the first sentence of your response, I do not recall anyone referring to the "developer compound itself". The entirety of your response beyond the first sentence is a red herring.

 

[faberryman]

Whos knows? Just speculating on a possible reason here, but more likely they just continued to use acid fixer when processing film because that's the way they always did it (and acid fixer may have once served a necessary purpose), but decades later they never got around to testing whether it was really necessary. They probably had more pressing projects to attend to, and if they would have found that water was good enough then it would have decreased the sale of one of their products.

In any case, if Kodak did investigate the issue then why didn't they ever publish the results? I assume that the results of such a study have never been published because no one posted here on the results of the investigation?

So you think that PE just made up the tests he described back in 2017 in a discussion in which you were a participant?

 

[alanrockwood]

With respect to the first sentence of your response, I do not recall anyone referring to the "developer compound itself". The entirety of your response beyond the first sentence is a red herring.

I dunno, how about post number 1164 by faberryman which seems to be framed in terms of developers? Though I admit that the post doesn't include the word "molecules"?

Additional note added: It is of course possible that I am mistaken about much of the previous discussion being framed in terms of developer carryover.

 

[alanrockwood]

So you think that PE just made up the tests he described back in 2017 in a discussion in which you were a participant?

Can you cite the post number for us so we can go back and read it? Also, where are the results of the study published so we can read and evaluate the actual results?

Additional note added: It is of course possible that I am mistaken about much of the previous discussion being framed in terms of developer carryover.

 

[faberryman]

Can you cite the post number for us so we can go back and read it? Also, where are the results of the study published so we can read and evaluate the actual results?

It was actually 2019. Here is the link:

Stop Bath.. How important?

RA4 colour negative print chemistry, is 45 seconds in the developer bath, then 45 seconds in the bleach/fix bath. Or 45 seconds in the developer bath, 15 seconds in a stop bath 15 seconds in a wash bath, 75 seconds in a bleach bath, 45 seconds in a wash bath, 45 seconds in a fixer bath, 90...

www.photrio.com

Your post was #623 and his post was #624. There are more of your and his posts before and after posts #623 and #624.

I do not know if the Kodak studies were published. Many manufacturers' internal studies are not published. But as long as you are asking for Kodak's published studies so you can read and evaluate the actual results, perhaps you could provide links to your published studies so we can read and evaluate your actual results supporting your argument that stop bath is unnecessary.

 

[JerseyDoug]

To add another variable to the discussion, in their Technical Data Sheet for Fomapan 100 Classic Foma says, "When the development time has elapsed, the film is recommended to be shortly rinsed in distilled water or dipped in a 2 % acetid [sic] acid solution for 10 seconds." It's the first recommendation I've seen for distilled water, which incidentally is what I use.

 

[alanrockwood]

It was actually 2019. Here is the link:

Stop Bath.. How important?

RA4 colour negative print chemistry, is 45 seconds in the developer bath, then 45 seconds in the bleach/fix bath. Or 45 seconds in the developer bath, 15 seconds in a stop bath 15 seconds in a wash bath, 75 seconds in a bleach bath, 45 seconds in a wash bath, 45 seconds in a fixer bath, 90...

www.photrio.com

Your post was #623 and his post was #624.

I do not know if the Kodak studies were published. Many manufacturers' internal studies are not published.

Thanks for that reference to PhotoEngineer's post. Please note that PE simply said that the change of pH in the emulsion was nearly instantaneous, which by implication would probably result in a nearly instantaneous arrest of developing action. However, in that post PE makes no claim that a water-based stop bath produces results that are inferior.

There is no fundamental reason why an instantaneous termination of developing action is in any way superior to a slightly more gradual termination of development, nor are there any publicly available results that show this to be the case, at least not to my knowledge.

 

[alanrockwood]

To add another variable to the discussion, in their Technical Data Sheet for Fomapan 100 Classic Foma says, "When the development time has elapsed, the film is recommended to be shortly rinsed in distilled water or dipped in a 2 % acetid [sic] acid solution for 10 seconds." It's the first recommendation I've seen for distilled water, which incidentally is what I use.

Here's another reference to using water as a stop bath: Phototherm used to make film processors. Their standard process used water as a stop bath. This can be found in the following link. https://www.phototherm.com/ssk4i.PDF. Here's the relevant line from that file:

WATER wash 2:00 23.9 5 also acts as stop.

 

[faberryman]

I dunno, how about post number 1164 by faberryman which seems to be framed in terms of developers? Though I admit that the post doesn't include the word "molecules"?

Additional note added: It is of course possible that I am mistaken about much of the previous discussion being framed in terms of developer carryover.

No, I was quite straight forward, as was everyone else in the discussion. I was talking about developer, not developer compound.

 

[faberryman]

Here's another reference to using water as a stop bath: Phototherm used to make film processors. Their standard process used water as a stop bath. This can be found in the following link. https://www.phototherm.com/ssk4i.PDF. Here's the relevant line from that file:

WATER wash 2:00 23.9 5 also acts as stop.

Why would you rely on marketing material and instructions from a manufacturer of film processing machines over that of manufacturer of photographic film and processing chemicals. What about published studies from Phototherm?

Moreover, water does not act as a stop except to the extent that it rinses (most of) the developer away. That which remains continues the development action. Thus, "carryover film developer molecules". When you use a water rise, the stopping action occurs at the fixer stage. Phototherm doesn't know what is talking about.

You certainly seem to be grasping for straws.

 

[alanrockwood]

No, I was quite straight forward, as was everyone else in the discussion. I was talking about developer, not developer compound.

Which component of the "developer" are you referring to? There are two components, developer compound and buffer. Which is it?

It doesn't actually matter, because, as I already discussed, for all practical purposes dilution affects both components the same way.

 

[alanrockwood]

Why would you rely on marketing material and instructions from a manufacturer of film processing machines over that of manufacturer of photographic film and processing chemicals. What about published studies from Phototherm?

You certainly seem to be grasping for straws.

Not grasping at straws, just showing a second example where an established entity used water as a stop bath.

 

[MattKing]

If everyone employed a flowing water stop bath as completely and effectively as a Phototherm Sidekick processor does, there would be little advantage to using an acid stop bath.

 

[alanrockwood]

Here is (or was) a third example of a manufacturer recommending water as a stop bath and against using acidic stop bath. It comes from a post at Photo.net. I am going to quote the whole post and then give a link to the post. Please note who posted it, someone from Ilford Imaging USA, so I assume he is giving authentic information about Ilford's former recommendation.

Please note one subtlety in the post below, which is that it's not clear whether the author is referring to film processing or print processing, though it seems he is more referring to print processing since he mentions "Dektol". However, the original post in the thread was in the context of negatives, i.e. film processing.

Also note that the author of the quote below does not say that there is anything wrong with using water these days, only that a mild acid stop bath is OK to use.

"Water or stop bath can be used after development. As others have pointed out, stop bath will be quicker, but in practice, a water bath will also stop the development rather quickly, especially since by the end of the development time, it is going rather slow anyway.



In the past, ILFORD recommended using only water. The reason was that if the development is halted to quickly, you can get acid-shock reticulation, which is the result of the rather violent chemical reaction taking place on the surface of the film. With today's films, and less aggressive stop baths (such as the ILFORD ILFOSTOP, which is citric acid based rather than acetic), the danger is eliminated. However, if you are using Dektol, you may run a risk with using a stop bath, as the developer is much more active than those usually used for film.



I would not recommend skipping this step altogether. While that may work okay with some developers, in many cases it can lead to dichroic fog on the film, especially if the fixer is not totally fresh. This fog will show up as a slightly silvery sheen on the film, or can sometimes have a color to it, resulting in an apparent stain. The use of a stop bath or at least a good water rinse will eliminate this possibility.



David Carper

ILFORD Imaging, USA"

Here's the link: https://www.photo.net/forums/topic/34634-stop-bath-vs-tap-water/

 

[alanrockwood]

If everyone employed a flowing water stop bath as completely and effectively as a Phototherm Sidekick processor does, there would be little advantage to using an acid stop bath.

Actually, just to be clear, if by "flowing water" you mean water that is continually added and removed from the bath, phototherm does not do that. Instead it drains developer, then adds a fixed amount of water, the same as the amount of liquid as the other solutions used, and then does continual agitation of that fixed amount of water for a fixed amount of time before emptying it and adding fixer.

 

[faberryman]

Which component of the "developer" are you referring to? There are two components, developer compound and buffer. Which is it?

It doesn't actually matter, because, as I already discussed, for all practical purposes dilution affects both components the same way.

I am not referring to the separate components of the developer. I am referring to developer as a whole. The stuff you pour in the developing tank. You don't pour in or pour out the components separately. Nor do you carryover one without the other.

I know where you are trying to go with this. Let's cut to the chase, can the developer and buffer components, independently or together, be inside and outside the developing tank at the same time?

 

[alanrockwood]

One of the objections to using water as a stop bath is the hypothetical problem that it could lead to uneven development. I have done a simple simulation to see if this seems likely. I will post the results below.

I did four simulated runs. Two of which had an instantaneous stop to simulate an acid stop bath, and two of which had a gradual stop to simulate a water stop bath.

Here were the conditions in a little more detail:

Simulation 1: Constant rate of development for 1000 seconds, followed by an instantaneous stop that lasted another 1000 seconds, for a total of 2000 seconds.

Simulation 2: Constant Constant rate of development for 1100 seconds, followed by an instantaneous stop that lasted another 900 seconds, for a total of 2000 seconds. The idea here is to simulate the possibility that exposure of the film to the stop bath may be uneven across the film.

Simulation 3: Constant rate of development for 800 seconds, followed by a gradual (exponentially decaying) rate of development with a time constant of 200 seconds for a total of 2000 seconds. This simulate a development time of 800 seconds and a stop bath exposure of 1200 seconds during which development continues at a decreasing rate. These times were adjusted to give the same overall development as simulation 1. This is to simulate that a person would choose conditions that would mimic the acid stop bath as closely as possible.

Simulation 4: Constant rate of development for 1100 seconds followed by an exponentially decaying rate of development to simulate a water stop bath. Total time – 2000 seconds.

Added note: I can post figures (plots) showing the results of the simulation if anyone is interested in seeing them.

The rates of all four simulations were integrated to give total development. Here are the results.

Simulation 1, development=999.5 arbitrary units.

Simulation 2, development=1100.5 arbitrary units

Difference between simulations 1 and 2 (to simulate uneven development)= 101 arbitrary units

Simulation 3, development=999.5 arbitrary units

Simulation 4, development=1099.2 arbitrary units

Difference between simulations 1 and 2 (to simulate uneven development)=99.7 arbitrary units

Note that the rate at which development decayed was chosen in this simulation to be unrealistically gradual. This extreme choice was intentional to see if I could produce an observable effect. However, for all practical purposes the degree of uneven development is the same in either case, but if there is a difference it ever so slightly favors water stop to give more even development.

However, although this simulation showed no advantage for instantaneous termination of development, it is a simplified simulation that does not include all possible effects, and also please note that the ultimate test is experiment, not theory. Nevertheless, I find it impossible to think of a good physical reason why an instantaneous termination of development should produce more even development than a gradual termination of development.

Also, I do understand that there are anecdotal reports that for print development water stop can produce less even development, but I have found no reports that this applies to film development. As far as print development is concerned, could it be due to the fact that the solutions might be changed less often, leading to much higher carryover than in film development?

 

[alanrockwood]

I am not referring to the separate components of the developer. I am referring to developer as a whole. The stuff you pour in the developing tank. You don't pour in or pour out the components separately. Nor do you carryover one without the other.

I know where you are trying to go with this. Let's cut to the chase, can the developer and buffer components, independently or together, be inside and outside the developing tank at the same time?

In the hypothetical dilution calculation I posted the dilution factor was 10,000 fold by the time the carried-over developer mixes with the fixer . Do you really think that a bit of developer solution at a 10,000 fold dilution will have any significant effect on the process?

Also, the same amount of developer compound is carried over in either case (water stop or acid). The only difference is that the tiny amount of buffer in the carried-over solution has been neutralized by the acid in an stop bath but not in a water stop bath. Plus there is a small amount of un-neutralized acid from the stop bath that is carried over in the case of an acid stop bath. However, on a practical level, none of this can matter because by the time the buffer is diluted by that amount it is completely swamped by the acid in the fixer and will have no noticeable effect on the process. The same goes for the excess acid carried over from the acid stop bath.

 

[faberryman]

I don't think any further discussion will be productive, so I cede the floor to you.

 

[Tim Stapp]

Given the short developing times of the film that I use (6 minutes, rotary in JOBO), I prefer to use an acidic stop bath. As Sirius Glass has often said, "It's just so expensive."

It's an expense that I'm willing to spend. It stops development immediately. It's in every film maker's process. Who am I, someone with only a high school chemistry background to argue with the film maker's R&D process.

My water is hard enough that it will leave deposits in a glass/jar left sitting overnight. EVERYTHING photo chemical wise is mixed with distilled water.