Stop Bath.. How important?

alanrockwood · Feb 6, 2019

Photo Engineer said:
I am aware of Jay's work. I also posted above about stopping rate and diffusion. I'll extend that here.

We at EK coated a layer of indicator dye, then coated a thick pad of gelatin above that. We used that as a dye source in a cuvette in a spectrometer. Dumping in acid stop vs water showed that the neutralization of the indicator was instantaneous vs water. This was a pH 7 indicator. More sophisticated tests showed that that tiny hydrogen atom diffused almost infinitely fast vs all of the other ions present. In fact, IIRC, we never were able to get a figure on the actual rate of the H+ ion but could measure OH- which is not big at all. The HQ and other organics were lumbering beasts by comparison though.

The dye changed color quickly and uniformly over the sheets tested with acid, but changed in areas with the plain water.

BTW, this was done with and without agitation, but for the sake of the experiment, I don't believe that the agitation was very good - IMHO, at least as far as my memory serves.

In any event, this is one reason why Kodak recommended using a stop as per my earlier post.

PE

Thanks for explaining your test results. I can identify one weakness in the study for plain water. I don't think the pH change is the main effect that slows and eventually stops development when using pure water, but rather from diffusion of developer out of the emulsion. As described the tests did would not probe the rate of diffusion of developer out of the gelatin.

Did you do densitometry testing to compare film processed using an acid stop bath vs. with water? There are at least three parts of such a test: 1) comparing the densities for the two cases using equal time in the developer. If they are different then 2) testing whether adjusting the development time of the water branch of the test could result in equivalent density/contrast, and 3) comparing evenness of development in the two cases.

By the way, I was trained as a physical chemist, so I am aware that the diffusion rate of hydrogen ion is very fast. Mechanistically, the usual reason put forward for the rapid diffusion of hydrogen ion is through a shuttle effect (the Grotthuss mechanism). This could be called an "effective diffusion rate" though I haven't seen that term used. Basically, if we could follow an individual hydrogen ion we would see that it does not actually have an extremely high diffusion rate. What happens instead is that a hydronium ion transfers a proton to a neighboring water molecule, leaving behind a water molecule in the location of a original hydronium ion and creating a new hydronium ion at a neighboring location. That hydronium ion can then transfer a proton (not necessarily the same proton) to one of its neighbors. Consequently, the proton that arrives at some destination is generally not the same proton that started the process.

Photo Engineer · Feb 6, 2019

I did not do the tests. They were done by Tong and Liang of KRL and may be in the literature. I read internal documents and talked to both of them personally but do not have more detail except for some comments.

HQ, Metol, Phenidone and other reducing agents that develop are usually Anionic or non-Ionic and organic. They are large molecules compared to OH- and H+ ions as well as Borate, Sulfite and Carbonate to name a few. The developing agents are known to stay in film and paper into the fix unless removed somehow. Haist shows a plot of Metol removal and describes a lack of HQ test methods for retention. There is also a test for PPDs based on color.

With this in mind, a pH cycle has been determined to be the best method for removal of developing agents and this is best done by using an acid stop and an alkaline or neutral fix. This is exactly what is suggested by some for RA4 and C41 elsewhere, but has not been followed up on for B&W.

As for the shuffle, it could be measured using Deuterium, except that Deuterium is bigger than H+ and thus has different mass and diffusion rate.

I wonder how fast a Planck Star would diffuse?

All kidding aside, lots of these studies were undertaken for instant products and the development of stopping layers and timing layers. You will find that the pH drop is the most significant factor in cessation of development. That has been studied.

PE

falotico · Feb 6, 2019

Photo Engineer said:
I wonder how fast a Planck Star would diffuse?

PE

I have been using a Planck Star in my stop bath for both negatives and prints but I can't compare diffusion rates because the relativity of time is all messed up. I get good highlights, though.

alanrockwood · Feb 6, 2019

falotico said:
I have been using a Planck Star in my stop bath for both negatives and prints but I can't compare diffusion rates because the relativity of time is all messed up. I get good highlights, though.

"Good highlights" I love it.

Deleted member 88956 · Feb 7, 2019

SchwinnParamount said:
Water Vs. stop bath and film development

In the last couple of months, I've seen odd density variations in my Plus-X and FP4+. On the long edges of each frame is a subtle area of increased density which runs the lenght of the frame.

I develop in a steel tank with steel reels of course. For the last couple of years I've been using water as a stop bath as I was told I risk pinholes in the film when using stop bath of too strong a concentration. Rather than determining the correct concentration, I switched to water as it is 'supposedly' as effective as stop bath.

I switched back to stop bath for my most recent roll of film and the density problem also disappeared. There were no other process changes. Is it possible that a water stop bath is less effective in stopping development at the edges of the film where it is in contact with the reels?

Stop bath is certainly better at halting development than water, but I have never used it nor have I ever seen any side effects. As someone had already stated, it would be beneficial in very short developing times, hence stronger developer used, hence need to shut it down on time as best possible. Having said that, I can't see a situation when such a development would be warranted except some very odd time and place.

alanrockwood · Feb 7, 2019

Photo Engineer said:
As for the shuffle, it could be measured using Deuterium, except that Deuterium is bigger than H+ and thus has different mass and diffusion rate.

Warning: chemistry potholes ahead! Please skip of you are not a molecule-head like some of us.

I agree that Deuterium could be used to test the shuttle. I also agree that it would have a different (lower) diffusion rate. One could use a mass spectrometer to perform the experiments. (I say "always use a mass spectrometer" if you can. I spent most of my career in mass spectrometry labs.) However, there is an interesting subtlety, which is that the apparent diffusion rate will be the same, regardless of whether you insert protons or deuterons at the source, if the experiment is performed in natural water. The reason is that after the first exchange or two the deuteron stays behind, and the shuttle is carried forward by protons supplied by the natural water. One would need to do the experiment in heavy water to avoid this "switcheroo" effect. All else being equal, diffusion rates are proportional to the square root of mass, so protons should diffuse 1.4 times faster than deuterons. Another thing is that there are some smaller effects besides just the mass effect. They arise from the fact that deuterium is not chemically identical to hydrogen. There are a number of reasons for this, but many of them go back to concepts like "zero point energy" and related effects in quantum mechanics. In my lab we often observed that deuterated compounds could be chromatographically separated from non-deuterated compounds, to some extent at least. This turns out to cause problems if one is using deuterated "internal standards" as part of a quantitative analysis scheme using chromatography combined with mass spectrometry.

PE

Photo Engineer · Feb 7, 2019

ZPG? Now lets move on to the Casimir Effect.

Lets not lose the fact that a Stop helps for reasons related to pH drop and the presence of the developing agents and other things.

PE

alanrockwood · Feb 7, 2019

Photo Engineer said:
...HQ, Metol, Phenidone and other reducing agents that develop are usually Anionic or non-Ionic and organic. They are large molecules compared to OH- and H+ ions as well as Borate, Sulfite and Carbonate to name a few. The developing agents are known to stay in film and paper into the fix unless removed somehow. Haist shows a plot of Metol removal and describes a lack of HQ test methods for retention. There is also a test for PPDs based on color.

With this in mind, a pH cycle has been determined to be the best method for removal of developing agents and this is best done by using an acid stop and an alkaline or neutral fix. This is exactly what is suggested by some for RA4 and C41 elsewhere, but has not been followed up on for B&W...

All kidding aside, lots of these studies were undertaken for instant products and the development of stopping layers and timing layers. You will find that the pH drop is the most significant factor in cessation of development. That has been studied.

PE

Let's explore the issue further from a scientific perspective, but first let me be sure I understand the point(s) you are making.

Are you suggesting that a change of pH facilitates the removal of developer from the emulsion, or just that the change of pH simply deactivates the developer, presumably by changing it from an anion form to a neutral form, while leaving the developer in the emulsion? It is important to get this straight first because I am hearing more than one rationale in this thread for the purpose of stop bath, one being to stop further development, and another to prevent carryover of developer into the fixer.

Getting this straight is important because simply changing the developer from an anionic to a neutral form within the emulsion via a reversible acid/base reaction is not enough to prevent carryover of residual developer left in the emulsion unless the developer is actually removed from the emulsion prior to transferring the film to the fixer. This is particularly relevant if an alkaline fixer is used because if the pH of the fixer is very high the alkalinity of the fixer will simply convert the residual developer left in the film back to an active (anionic) form.

Also, are you suggesting that changing the developer from an anionic form to a neutral form will facilitate its diffusion out of the emulsion? Related to that question, are you suggesting that the anionic form will not diffuse out of the emulsion?

From a scientific perspective these concepts are important to clarify first. Then we can discuss the relative roles of pH (i.e. acid/base chemistry) vs. diffusion in the function(s) of an acid stop bath and a water stop bath.

tezzasmall · Feb 7, 2019

Sorry, but I can't read any more posts about stop bath!!!!!....

I've glanced over the last dozen or so and that's it, so carry on if any of you want to but I'm going to ignore this thread from now on.

So now I've said that, do you all put milk in first or tea / coffee first? Answers on a postcard, but I can't guarantee I'll read any of them, although the used stamps will go to charity.

Terry S

alanrockwood · Feb 7, 2019

I think it is useful to look at the from the point of view of an analogy. Suppose one is taking a 5 km trip by automobile. Consider two cases. A) The driver drives at 70 km/hr and then slam on the brakes just barely before getting to the destination. B) The driver decides to start the deceleration a little earlier, takes her foot of the gas and applies very light pressure to the brakes, i.e. decelerates in a more gentle manner. The driver in scenario B might even decide to coast to a stop.

Is scenario B more "effective" than scenario A? No. They arrive at the same end point, albeit in a slightly different manner. Is Scenario A more effective than scenario B? No. They arrive at the same end point, albeit in a slightly different manner. Are the two scenarios identical in every respect? No. One takes more time than the other, but if time is not of the essence then it doesn't matter which scenario to use. There are also other minor difference, e.g. in the amount of resources used.

Photo Engineer · Feb 7, 2019

Alan, here is an example suggested by Haist. A Metol and HQ developer is run directly through a good wash and then a neutral or alkaline fix. This leaves behind a substantial amount of HQ and Metol. The wash should remove it. However, due to solubility (remember how hard it is to dissolve Metol, even if it is the Sulfate salt??), Metol and HQ can be left behind. What is found in testing, is that Metol can be removed in a Stop, and HQ can be removed in a neutral or alkaline fix! This is barely the tip of the iceberg so to speak.

Anchell and Troop quote Ansel Adams on stops and then stated the pros and cons based on Adams positive position. Haist gives details of tests by Henn and Crabtree related to uniformity and devotes about 20 pages to stops.

PE

Sirius Glass · Feb 7, 2019

alanrockwood said:
I think it is useful to look at the from the point of view of an analogy. Suppose one is taking a 5 km trip by automobile. Consider two cases. A) The driver drives at 70 km/hr and then slam on the brakes just barely before getting to the destination. B) The driver decides to start the deceleration a little earlier, takes her foot of the gas and applies very light pressure to the brakes, i.e. decelerates in a more gentle manner. The driver in scenario B might even decide to coast to a stop.

Is scenario B more "effective" than scenario A? No. They arrive at the same end point, albeit in a slightly different manner. Is Scenario A more effective than scenario B? No. They arrive at the same end point, albeit in a slightly different manner. Are the two scenarios identical in every respect? No. One takes more time than the other, but if time is not of the essence then it doesn't matter which scenario to use. There are also other minor difference, e.g. in the amount of resources used.

Case A in Control Theory is called Bang Bang Control and is more energy efficient than Plan B.

alanrockwood · Feb 7, 2019

Sirius Glass said:
Case A in Control Theory is called Bang Bang Control and is more energy efficient than Plan B.

What is meant by the term "efficient"?

faberryman · Feb 7, 2019

So I wonder if, after 14 years and 641 posts, anyone using stop bath has shifted to water, and if anyone using water has shifted to stop bath? I have only been following the thread for about three years. but I have been using stop bath for forty five years, and continue to use stop bath, without any ill effects. If ever I find myself without stop bath, I'll use water until I have stop bath available again, all without losing any sleep.

alanrockwood · Feb 7, 2019

Photo Engineer said:
Alan, here is an example suggested by Haist. A Metol and HQ developer is run directly through a good wash and then a neutral or alkaline fix. This leaves behind a substantial amount of HQ and Metol. The wash should remove it. However, due to solubility (remember how hard it is to dissolve Metol, even if it is the Sulfate salt??), Metol and HQ can be left behind. What is found in testing, is that Metol can be removed in a Stop, and HQ can be removed in a neutral or alkaline fix! This is barely the tip of the iceberg so to speak.

Anchell and Troop quote Ansel Adams on stops and then stated the pros and cons based on Adams positive position. Haist gives details of tests by Henn and Crabtree related to uniformity and devotes about 20 pages to stops.

PE

Solubility issues throw an interesting twist into the analysis.

Photo Engineer · Feb 7, 2019

There are many little known or hidden aspects of many analog photo materials which were investigated thoroughly at EK but are not widely known (if at all) outside of the company.

Among other things, the Henn and Crabtree work involved sheets of film imbibed with indicator dyes and then being studied for uniformity as a function of stop or wash with varying types of stop and also variations in agitation to look at uniformity.

Mason writes at length about his work in calculus describing the effect of wash, and I suspect that it also has great impact on a wash after development. I have posted quite a bit on this work in threads on washing.

PE

SchwinnParamount · Feb 7, 2019

GLS said:
Why use acetic acid when you can use citric acid? Cheap as dirt, less need be used and it has no smell.

I kind of like the smell. It certainly wakes me up when I accidentally sniff concentrated acetic acid fumes wafting out of a newly opened bottle. Especially if I've been enjoying a decent scotch in the darkroom before developing my film.

SchwinnParamount · Feb 7, 2019

David Lyga said:
Well, I experimented heavily with both film and prints and this was the highest dilution that I could be comfortable with. At my dilution, there is NO QUESTION about an immediate, complete stop to all development. When I used the same solution for a second print it also stopped development immediately (was not slippery on the immersed hand). But by the third try, it was 'so so'. Thus, conservatively, I adopted these dilutions as perfect for the one-shot situation. Maybe you don't wish to change solutions after each print or so, but with film, it is the perfect 'solution' to adopt.

By the way, (and I have said this before) I have adopted a 'one tray' schedule for all my printing needs. I use small quantities of solution and empty the tray after each chemical time is up. This is best to do with only small prints (up to 5 x 7 or maybe up to 80 x 10). I have a 'dump' bucket ready and easy to reach in the dark (I never have used a safelight in over 50 years in the darkroom). I have measured quantities (according to tray size) of stop and fix ready to pour in the dark. I know that all of this sounds strange, but I would not go back to the three tray system for anything. This is actually easier and I have the decided advantage that each and every print attempt uses completely fresh solutions. My small quantities of solution are adequate, as I rock the tray for the duration of development and keep the print face down. I waste nothing and use no more chemicals than others do. After fix, I pour two changes of water: this prepares the tray to start with the next development and partially removes the hypo from the paper. The prints are washed, together, when I have finished.

I do a lot of things that are truly strange. For example, if I had all of Trump's money, I still would not use a washing machine, ever. I have not used one for at least three decades. Each night I wash clothes (or sheets or jackets) in a bucket filled with warm water, Dawn dish liquid, and a little bleach. This way, in 15 minutes I have washed, thoroughly rinsed, and wrung out to hang up to dry. I have NO accumulated dirty clothes and the cleanliness is, I feel, even better than with a washing machine. Better system for me, but, it sounds terrible to those who think they know better.

I have never tried citric acid for a stop bath. Honestly, why should I? Acetic acid is great, easily attainable, and one can even use household vinegar. I try not to look for trouble in life, but if someone utterly convinced me that citric acid had more advantages, I might try it. But, I am happy the way acetic acid works is and there is virtually no smell at my dilution. What most of you fail to understand about photo chemistry is that it is formulated to make up for the sloppiness that so many have. My developers, stop baths, and fixers are ALL highly diluted. For example, my fixer is used at one half paper strength for paper and at paper strength for films. My normal temp is 80F (my ambient) and I have NO problems with diluting in this way. Why work according to the 'sloppiness' that is factored into these formulas? I work intelligently, and I work without trying to get more out of my formulas. They work beautifully. For most film development I use the cheapest formula that can be considered, and it works beautifully: DEKTOL 1 + 24. That works well for Pan F+. For something like TMY 400 try 1 + 14. Times are within a good range: about 5 minutes for the Pan F and about 8 minutes for the TMY (at that 1 + 14 dilution). Sometimes the standardized literature does not remove the sloppiness factor (like ASA took forever to recognize that films are faster than the old speeds used to state). Remove the 'sloppiness' factor from your work. - David Lyga

David, are you a Luddite? Well, blessings to you, my friend.

SchwinnParamount · Feb 7, 2019

blockend said:
I haven't used a stop bath for film for 20 years, with no perceivable degradation of the negative. However I wash thoroughly between development and fix, about 2 minutes with multiple changes of water and constant agitation. The fixative shows no sign of contamination. I have an unopened bottle of ten year old Ilford Stop in the chemical cupboard, I'll use it when I next print for old time sake.

Would you (the global you, not the Blockend you) rather spend 30 seconds stopping development with cheap diluted (Thanks David Lyga) stop bath or 2 minutes fussing with multiple water changes? Let's assume you live in Arizona where water will soon become precious.

SchwinnParamount · Feb 7, 2019

pentaxuser said:
Stop Bath - How Important? I'd say very important to the contributors since the thread has now run for nearly 14 years
It may be less important to the OP or we have covered all the bases and he knows all there is to know since he was last seen about 2 years ago

pentaxuser

I'm baaack! (formerly schwinnparamount)

SchwinnParamount · Feb 7, 2019

alanrockwood said:
I think it is useful to look at the from the point of view of an analogy. Suppose one is taking a 5 km trip by automobile. Consider two cases. A) The driver drives at 70 km/hr and then slam on the brakes just barely before getting to the destination. B) The driver decides to start the deceleration a little earlier, takes her foot of the gas and applies very light pressure to the brakes, i.e. decelerates in a more gentle manner. The driver in scenario B might even decide to coast to a stop.

Is scenario B more "effective" than scenario A? No. They arrive at the same end point, albeit in a slightly different manner. Is Scenario A more effective than scenario B? No. They arrive at the same end point, albeit in a slightly different manner. Are the two scenarios identical in every respect? No. One takes more time than the other, but if time is not of the essence then it doesn't matter which scenario to use. There are also other minor difference, e.g. in the amount of resources used.

Why can't the driver in scenario A be the woman? My mother would certainly have fit the profile of the scenario A driver while my father and come to think of it - my middle son - fit the B scenario to a tee.

SchwinnParamount · Feb 7, 2019

faberryman said:
So I wonder if, after 14 years and 641 posts, anyone using stop bath has shifted to water, and if anyone using water has shifted to stop bath? I have only been following the thread for about three years. but I have been using stop bath for forty five years, and continue to use stop bath, without any ill effects. If ever I find myself without stop bath, I'll use water until I have stop bath available again, all without losing any sleep.

I'm actually going back and forth on the issue. I'll wait until Ron and Alan have come to agreement on the chemistry end of it. Although, I must say.. Ron played his ace card with the solubility argument. I am genuinely impressed with the dye tests that he describes. I may just stick with my acetic stop bath - although at a lower concentration.

blockend · Feb 8, 2019

John M Austin said:
Would you (the global you, not the Blockend you) rather spend 30 seconds stopping development with cheap diluted (Thanks David Lyga) stop bath or 2 minutes fussing with multiple water changes? Let's assume you live in Arizona where water will soon become precious.

Film photography is all about fussing with liquids. Unless you can afford to send everything to a lab and professional printer, of course. People who consider the process convoluted, migrated to digital imaging years ago. Only the fussers are left, and we revel in it.

Deleted member 88956 · Feb 8, 2019

blockend said:
Film photography is all about fussing with liquids. Unless you can afford to send everything to a lab and professional printer, of course. People who consider the process convoluted, migrated to digital imaging years ago. Only the fussers are left, and we revel in it.

Exactly, not that digital isn't convoluted, and certainly is capable of making one convulse.

blockend · Feb 8, 2019

Witold said:
Exactly, not that digital isn't convoluted, and certainly is capable of making one convulse.

Digital tools lead people to believe that inside every bad photograph is a good one waiting to get out, if only you spend enough time tweaking. The general output suggests there's no photograph so bad that Lightroom and Photoshop can't make even worse.

Stop Bath.. How important?

Deleted member 88956

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