FB paper and cold water

F4U said:

Isn't HCA just mostly re-named sodium sulfite? Seems like I saw that said somewhere

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Yes, but the word "mostly" is important here.
The other main agreement is sodium metabisulfite, which makes up about 20% of the mixture by weight.
IIRC, the main role of the latter component is that it helps ensure that the ph of the chemical is appropriate for doing its job - if it is off, the sodium sulfite is much less efficient in doing what it is supposed to.

Sodium sulfite is the main magic ingredient of black and white photography.

john_s said:

I have read from reliable sources that a wash aid (sodium sulphite mostly) enables much more effective washing in cold water*. Maybe you could carry a couple of 5L bottles of warm water to the darkroom and let the print go through such a bath for a while before taking it upstairs.

I use a Nova vertical slot print processor and I acquired a spare additional slot and I do just that: quick rinse after fix, then in the wash aid for a few minutes, then into the cold water washer.

I can find a source for that statement if you like.

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the point is that heat energy speeds up chemical processes, but print washing is not exclusively a chemical process. Therefore, fb-washing will work at slightly lower temperatures, even not as well and not as fast. Wash a little longer or more often after HCA and you should be OK!

RalphLambrecht said:

the point is that heat energy speeds up chemical processes, but print washing is not exclusively a chemical process.

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Can you please explain to all of us where the actual difference between 'chemical processes' and a "non-chemical wash process" is in terms of temperature dependency? I'd expect this to relate to mobility of ions and such aspects of, well, physics essentially, and as such trace back to the same set of root causes. But apparently this is not the case, given your statement. I'd like to understand this better, so please explain.

Don_ih said:

Note that the water can be as low as 35 degrees F.

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There is no reason to doubt Kodak. Thanks for sharing this bit.

Don_ih said:

There was likely still fixer in your paper after the first wash, since you used no clearing agent. A very long wash is required at a cold temperature in that instance - something in the order of 2 hours, maybe? There was very little ammonium thiosulphate in your tray of very very diluted Kodak Selenium Toner. Hardly any would have gone into the paper - more thiosulphate may have been coming out of the paper into that tray. Then the final 1 hour wash got rid of the rest of it. Probably. Maybe.

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You are probably right, although the 45 minute wash prior to toning was at least effective enough to avoid staining in the toner.

I rinse prints and then put in toner. It doesn't stain. But I use neutral rapid fix. (Acid stop bath, then into water, then into tray 1, then tray 2 of fix.) Acid makes washing more difficult.

koraks said:

Can you please explain to all of us where the actual difference between 'chemical processes' and a "non-chemical wash process" is in terms of temperature dependency? I'd expect this to relate to mobility of ions and such aspects of, well, physics essentially, and as such trace back to the same set of root causes. But apparently this is not the case, given your statement. I'd like to understand this better, so please explain.

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I can't speak for what Ralph meant, but processes relevant here include both chemical reactions of ions in solution, and things like adsorption of fixer onto paper. Whether one wants to describe the latter as a physical or chemical process or both is not transparent. Anyway, I suspect that some of these processes have different dependences on temperature. For example, and this is merely intuition part-informed by experience: I think that if one tries to develop and fix film or paper in solution at 5-10 deg C (40-50 F), it will work very poorly if at all, and development is unlikely to go to completion. (Years ago, I tried printing in an unheated basement darkroom without warming the developer, and it was pretty terrible.) On the other hand, I think if you try to wash film or paper in equivalently cold water, you'll get at least some wash effect, and you might be able to wash out most or nearly all of the fixer, it will just take longer.

reddesert said:

if one tries to develop and fix film or paper in solution at 5-10 deg C (40-50 F), it will work very poorly if at all

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This is because the activity of developing agents drops of non-linearly (or put better, beyond-exponentially) as temperature drops. This is well-understood, but does it bear relevance to the remark that washing is not strictly a chemical process? I appreciate your response, but it doesn't answer the question. And while I'll be the first to admit that the question I asked bordered on pedantry, the reason I asked it is because I feel the 'explanation' offered in the first place by Ralph was deeply tautological. It just doesn't help understand what's really going on.

Maybe we should divide things into chemical reactions and other processes. In reactions, there is an transformation of one set of substances to another; i.e., a process that involves rearrangement of the molecular or ionic structure of a substance, as opposed to a change in physical form.

Other processes, like diffusion, adsorption, absorption, diffusion, ion exchange, etc. do not involve the above transformation; we might well call these "non-reactive."

Washing prints involves, for the most part, these latter, non-chemical processes. While the speed of chemical reactions has a known proportional relationship to temperature changes, other non-reactive processes may not be (are probably not) as definitely linked to temperature change.

Nuclear reactions and decay are not chemical reactions either.

Best,

Doremus

Doremus Scudder said:

While the speed of chemical reactions has a known proportional relationship to temperature changes, other non-reactive processes may not be (are probably not) as definitely linked to temperature change.

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Why not?

I feel we're still knee-deep in tautology land.

Well, I wouldn't say that expressing something more precisely is tautology...

In any case, after a bit of, admittedly, superficial researching, it seems that most of the non-reactive processes that I mentioned are also influenced by temperature change, speeding up as the temperature increases. I don't know if there are coefficients or other factors that govern rates of things like diffusion, absorption, osmosis, etc., or if their respective rates increase proportionally to temperature change. Nevertheless, they all seem to happen at faster rates with increasing temperature.

This, of course, means that print-washing is going to be more efficient at higher temperatures. We just don't know exactly how much without testing the washing efficiency in relation to temperature.

Koraks, if you've got some better information or knowledge about this, I'd love to hear it.

Back to the OP: If you must use cold water, then your wash will take longer than the times given for 20°C. How much longer is the unknown, which you need to test for using the HT-2 test.

Best,

Doremus

Doremus Scudder said:

Koraks, if you've got some better information or knowledge about this, I'd love to hear it.

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No, in fact I don't; my question is an honest one, and given that I have good reasons to suspect that the effects are quite complex as your research has probably also suggested, I was surprised at the apparently definitive answer @RalphLambrecht provided. This suggested a deeper understanding of the physics and/or chemistry involved, and I would have loved to hear a little about it.

My reasoning on the subject would be that for chemical reactions, bonds need to be broken and re-made I assume are significantly stronger than the bonds you'd encounter in a physical wash process. After all, in the former case, molecules break apart, in the latter, they very crudely put only rub and stick together. I'm not a chemist, and while I'm vaguely aware of different types of intramolecular bonds and the notion that the energy required or released in breaking and/or re-making such bonds depend greatly on the substances involved, I couldn't begin to understand on that shallow basis how temperature would affect all chemical reactions as such, as opposed to all physical processes. Yes, in general, it can be expected that both will proceed at a higher pace. But can it be so easily/readily stated that the temperature dependency would be any more or less for either of these groups of processes? And/or are the differences between specific processes (chemical or physical in nature) larger than the on-average differences between the chemical vs. physical process groups? I really wouldn't know, and given the complexity involved, I'm again surprised at how definitively some appear to be able to state the relative magnitude of such temperature dependencies, and the notion that such a dependency would be much less relevant for a wash process.

I would think it likely that diffusion is at least partially a thermodynamic process.
And a lot of thermodynamic processes are affected by temperature.

Not having conducted any experiments on these matters (and I fully expect the entire lot of people in this thread have also conducted no experiments), I'm going to stick by what Kodak has recommended for the past eternity. I'm pretty sure they did the proper experimentation and research.

Use Hypo Clearing Agent. Then you can use cold water.

Doremus Scudder said:

This, of course, means that print-washing is going to be more efficient at higher temperatures. We just don't know exactly how much without testing the washing efficiency in relation to temperature.


Back to the OP: If you must use cold water, then your wash will take longer than the times given for 20°C. How much longer is the unknown, which you need to test for using the HT-2 test.

Best,

Doremus

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What you said above made me check with the Ilford instructions for MG developer and what I found there was that in term of water temperature it only uses the phrase above 5 degrees C and then gives set times for both RC and FB paper

There is of course a difference in the times but no table of times and temps, nor any mention that even at a much higher temp of 20C a difference in washing efficiency arises

That is not to say that there is no difference but it does seem to suggest that Ilford considers temp above 5C doesn't make enough difference to warrant a mention

Just a thought on my part prompted by what Ilford says and what it doesn't say

There may be studies that have been done on this but if there are then you'd have thought that if the differences in washing temps/time are significant, more would have been heard on the subject

pentaxuser

pentaxuser said:

What you said above made me check with the Ilford instructions for MG developer and what I found there was that in term of water temperature it only uses the phrase above 5 degrees C and then gives set times for both RC and FB paper

There is of course a difference in the times but no table of times and temps, nor any mention that even at a much higher temp of 20C a difference in washing efficiency arises

That is not to say that there is no difference but it does seem to suggest that Ilford considers temp above 5C doesn't make enough difference to warrant a mention

Just a thought on my part prompted by what Ilford says and what it doesn't say

There may be studies that have been done on this but if there are then you'd have thought that if the differences in washing temps/time are significant, more would have been heard on the subject

pentaxuser

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Under the the processing heading in the technical sheet for FB paper it states 'wash in fresh running water at 5c or more'.
However, under the optimum permanence heading, it states a water temperature of between 18-24c

koraks said:

No, in fact I don't; my question is an honest one, and given that I have good reasons to suspect that the effects are quite complex as your research has probably also suggested, I was surprised at the apparently definitive answer @RalphLambrecht provided. This suggested a deeper understanding of the physics and/or chemistry involved, and I would have loved to hear a little about it.

My reasoning on the subject would be that for chemical reactions, bonds need to be broken and re-made I assume are significantly stronger than the bonds you'd encounter in a physical wash process. After all, in the former case, molecules break apart, in the latter, they very crudely put only rub and stick together. I'm not a chemist, and while I'm vaguely aware of different types of intramolecular bonds and the notion that the energy required or released in breaking and/or re-making such bonds depend greatly on the substances involved, I couldn't begin to understand on that shallow basis how temperature would affect all chemical reactions as such, as opposed to all physical processes. Yes, in general, it can be expected that both will proceed at a higher pace. But can it be so easily/readily stated that the temperature dependency would be any more or less for either of these groups of processes? And/or are the differences between specific processes (chemical or physical in nature) larger than the on-average differences between the chemical vs. physical process groups? I really wouldn't know, and given the complexity involved, I'm again surprised at how definitively some appear to be able to state the relative magnitude of such temperature dependencies, and the notion that such a dependency would be much less relevant for a wash process.

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I can, sort of, address this, but it will be long. Please keep in mind: (1) this is empirically-based theory; the only way one gets the rate coefficients discussed below is by measuring them, so one can't tell the OP that it's safe or unsafe to wash in cold water from first principles. You still have to do the residual hypo test to be sure. The reason I felt OK previously claiming that the temp dependence of development is stronger than that of washing is empirical: I know developing in even ~55F cool tap water is a lost cause, but that washing in water around that temp seems to be doable if you wash long enough, and Kodak makes a much bigger deal about development temperature than wash temp. (2) I'm a physicist, not a physical chemist.

Now, what is the temperature dependence of a chemical reaction? These are usually described by the Arrhenius equation, https://en.wikipedia.org/wiki/Arrhenius_equation

k = A * exp (- E_a / RT), or: ln k = -E_a / RT + ln A

k is the reaction rate constant, A is a prefactor specific to this given reaction, E_a is the "activation energy" also specific to a given reaction: https://en.wikipedia.org/wiki/Activation_energy , R is the gas constant 8.3 J/K/mole, and T is the absolute temp, degrees Kelvin. (You could use the Boltzmann constant k_B instead of R if you like its units better). RT has units of energy (per mole).

This is where the common saying that chemical reaction rates go exponentially with (absolute) temperature comes from. A physical interpretation is that the activation energy E_a is a potential barrier that the reactants have to overcome to complete the reaction, and at high temps, the increased energy of the reactants lets them overcome it more easily. (This is an oversimplification, but it explains a lot.) That's why even an exothermic reaction that releases energy doesn't happen instantly.

It is sometimes said, like on the Wiki page for the Arrhenius equation, that for typical reactions at room temp, an increase of about 10 deg C will speed the rate up by 2-3 times. (If you look at a developing time-temp chart, this is about right for the development reaction, +10 deg C may halve the developing time.) Let's differentiate the equation for ln k:

d ln k / dT = E_a / R * T^-2
d ln k = (dT / T) * E_a / RT

This shows that the ratio E_a/RT governs how fast the reaction rate increases with temperature, separate from the prefactor A. If I raise the temp by 10 C, from about room temp 293 K to 303 K, dT/T = 10/293, or one part in 30. If my reaction rate k increases by 2-3x, ln k increases by 1. That says that E_a / RT ~= 30. So the activation energy Ea is around 30x larger than the energy RT at ambient temp. The reaction is suppressed by a factor of exp(-30), which is a tiny number. That's why it takes several minutes to develop silver, even though we are talking about molecular processes and molecules are really small and do things in microseconds. AFAIK, the reason useful reactions happen at all is that there are a lot of molecules, so many encounters every microsecond, of which a few get over the activation energy barrier; and that the prefactor A is numerically large. (This is where a real physical chemist would explain it better.)

It wasn't actually that easy to find activation energies for ordinary chemical reactions in solution, but for example I googled this paper by N. Shinozuka and S.Kikuchi: https://www.jstage.jst.go.jp/article/photogrst1951/1964/14/1964_14_13/_pdf/-char/ja
where they measured the activation energy of the D-76 film development reaction at E_a ~ 16 Kcal/mole. Converting the units, for 20 C (293 K) that gives E_a / RT ~ 27. So a quite typical reaction, where it has this huge activation energy E_a and thus a steep rate/temperature dependence. Generally, developers are all trying to do the same thing, reduce silver halides to metallic silver, which is why you can use the same time-temp dependence for different developers. However, some other chemical reaction could have a somewhat different E_a and different rate/temp dependence.

Okay, so that describes chemical reactions, what about physical processes like the diffusion of molecules into liquid or the adsorption of fixer molecules attaching onto paper fiber surfaces? A physicist finds the formula exp (-E/ (k_B*T)) very familiar, as most processes near a thermodynamic equilbrium have states described by something like a Boltzmann distribution with this exponential tail to high energy, and the molecules in the higher energy states are more likely to do something (like overcome the potential barrier to stick themselves to a fiber). So something like the Arrhenius equation also describes many other physical processes; the wikipedia article mentions its use for diffusion, for example.

But there's nothing that says that the activation energy for a diffusion process has to be similar to that of an ionic chemical reaction; that ratio E_a / RT is critical because it tells how steeply the rate depends on temperature. I don't know the activation energy for diffusion and certainly not for adsorption onto a fiber or film substrate; I'm sure there are several different values, because for example we all know that fixer doesn't stick to film or RC paper the way it does to fiber. I agree with what koraks said above, that it seems like intermolecular attraction (such as fixer sticking to things) would require less energy than ionic reaction, which would make E_a/RT smaller and the reaction less dependent on temperature. But that's just handwaving by me. What is important is that there is a solid physical basis for the different processes having different temperature dependencies. To say more, one would have to find more measurements of activation energies.

Thanks @reddesert; that's a good argumentation/exploration that I can get behind. What I still find difficult to ascertain is whether (or, more specifically: on what basis) we can assume that a wash rate will be less temperature-dependent than the rate of a chemical process - and, practically speaking, how effective a wash at 5-10C will be. In particular, my concern includes the fact that at such low temperatures, the gelatin will contract and become less permeable to water, which limits the rate of flow of water through the paper base at least in one dimension. This is in addition to other effects that can play a role.

reddesert said:

What is important is that there is a solid physical basis for the different processes having different temperature dependencies.

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Different, yes - although we can safely assume that there are also differences within the clusters of chemical vs. mechanical/physical processes. Just look at the difference in temperature vs. activity for a group of developing agent. It's far from a homogeneous picture and relationships like the Arrhenius equation turn out to be only very, very coarse estimates. So there will be differences - sure. What I can't tell is what the practical implication of those differences are, and whether it's possible to state on the basis of the axiom that a wash process is a physical as opposed to a chemical process, it won't be very temperature-dependent.

Elmarc said:

Under the the processing heading in the technical sheet for FB paper it states 'wash in fresh running water at 5c or more'.
However, under the optimum permanence heading, it states a water temperature of between 18-24c

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Thanks Do we know that this "optimum permanence" is definitely connected to maintaining this temp range above and that as low as 5C makes this impossible? If might be that at 5C the time needed is very long and not a length of time that Ilford felt that most users would want to use either from a time or water consumption aspect so using the 18-24C range is more convenient and within what most users of darkrooms might achieve

I would not want to use water at 5C if I could help it but I might be able to achieve say 10C or slightly above but if I were stuck with 5C then I'd want it to be made clear that I had to recognise that it was below what was the minimum temp required for archival permanence and be referred to some scientific study that demonstrated this

pentaxuser

It would seem to me from the above, that the dynamics involved in washing fiber-base paper as functions of temperature are chaotic enough that empirical testing is the easiest and most-practical way to determine how much wash time is needed at a given temperature.

So, back to the recommendation to the OP to do the both a residual silver and residual hypo test if they are using chemistry and wash water below the range of temperatures that the manufacturers have tested and have data and recommendations for.

Best,

Doremus

Yes, agree @Doremus Scudder - I think it's a clear-cut case of "YMMV"!