Guidance on managing basic pH in homebrew chemistry

GBS · Jul 10, 2020

Hi!

I'm struggling to recall much of what I learned in college chemistry. Please go easy, I don't want to say how long ago that was.

Will you kindly offer your methods for controlling pH in development? I'll be working with ECN-2 and C-41, and expecting to start with distilled water, but that could vary someday.

1) what pH meter do you use?
2) which of the following developing chemicals require fine adjustments after the recipe is mixed, and what do you use to adjust up and down?

ECN-2 developer - Kodak's formula minus anti calcium and anti foggant
C-41 developer - haven't dialed it in, but assuming I'll try @stefan4u's C-27 or the formula @RPC posted here, both excellent resources--THANK YOU!

ECN-2 stop - Kodak's sulfuric acid formula
C-41 stop - 3% acetic acid (will b&w indicator stop work? vinegar?)

ECN-2 & C-41 - Ferricyanide bleach

ECN-2 & C-41 - Illford rapid fix

ECN-2 & C-41 - Kodak final rinse

3) Tangential question: do you have a recommendation for a clearing wash other than water, and if so, does it have critical pH to adjust?

Thanks so much! Really excited to get started!

AgX · Jul 10, 2020

The Kodak industrial processing guides for instance have a section "Specifications" where they state the pH for most baths, and the respective tolerances.
But to make use of that you will have to understand (electronic) ph-metering. Which means more than just unpacking a new device.

Concerning homebrew baths the above figures though hardly will be applicable and one may wonder whether a ph-meter is of use at all, as likely one only will have a ballpark of ph-values.
And then maybe a ph indicator paper (best resolutioin available is 0.2ph) is sufficient.

GBS · Jul 10, 2020

Thanks for the input! I'm familiar with indicator paper.

I'm a touch confused, please forgive me. Are you saying I don't bother with adjusting the pH? Is the paper resolution too low? The developing formulas all have target values. I know what developers should be, but I don't know how to test and adjust.

Thank you

AgX · Jul 10, 2020

What I meant was, that metering a pH for mixing or process control only makes sense, if one got the respective aim-pH.

Such aim-ph at a commercial bath unlikely is the same as for a bath made from scrap without knowing the precise formula of the commercial bath.

So you need aim-pH values for the homebrew formulas. Have you got these? And the respective tolerances?

GBS · Jul 10, 2020

Thanks for your time.

Yes, I have values and tolerances.

For example, one developer is 10.00 +/- 0.03, another is 10.25 +/- 0.05. Bleach is 6.5 +/- 0.5. I'm testing a few mixes, so I won't list all the values, but save for 1 or 2, I have them all.

I will be starting with distilled water (checking for 7.0 pH however possible), but cannot fully rely on distilled water for every instance in the future.

I'm asking

1) how to adjust: developer pH up or down
2) How crucial is the stop bath pH and how to adjust?
ECN stop - sulfuric acid based
C41 stop - acetic based (can I use vinegar or Kodak indicator? I don't have a "value" for this, only the recipe)
3) How crucial is the bleach pH and how to adjust:
Potassium Ferricyanide + Sodium Bromide
4) how crucial is the fix pH and how to adjust?

5) Tangential question: do you have a recommendation for a clearing wash other than water, and if so, does it have critical pH to adjust?

Thanks again

Mr Bill · Jul 10, 2020

Hi, I haven't taken pH readings in probably 30 years (?), but back in the day did probably several tens of thousands of them in a large photofinishing operation. I'll just say that it is not as simple as meets the eye, at least in the cases of the high pH developers. The meters we used were research grade units made by Corning and Orion Research (Orion later became, I think, Thermo, and maybe Fischer Thermo today). They had a 3-decimal readout, not that you would use the third decimal, but that you could see how fast the reading was changing, and thus judge when it became stable. I think that the more modern meters figure this automatically. We always used separate pH and reference electrodes because it is much easier to troubleshoot. Plus you had most selection.

As a general rule I would suggest, for a low cost system, don't read "seasoned" samples, and don't count on having accurate readings for the (high pH) color developers. I think a low cost meter is likely fine for the lower pH things like bleaches and fixers, and even b&w developers. But if you plan to use such a meter to make fine pH adjustments on a color developer... I think you would be well served to buy a packaged mix first, use this to see what your meter/electrode "expects," then use that as your aim value for your own custom developer.

There have been a couple threads on here that get into a little more detail, and may be worth reading. I put in some links to Kodak data on pH readings, from the H-24 motion picture manual. These will give you much more detail on the subject. In one of these links I see that member Serge Lavrenchuk has recently updated his experiences, and is probably worth reading.

Here's the links:
https://www.photrio.com/forum/threads/ph-meter-help-for-developer-measurements.167613/#post-2180462
https://www.photrio.com/forum/threads/recommendations-of-books-on-how-to-make-c-41-chemistry.61242/

Mr Bill · Jul 10, 2020

Regarding some of your other questions, in general: only the developer is fairly critical with regard to pH. The guide as to whether a pH of something is critical is in the tolerances given, which you seem to have. So there are pretty loose tolerances for bleach and fixer.

I can't say much about the stop baths as I've never used them in a color process; my experience is in commercial processing where there is no such need. But I would say that the more important thing is how strongly the thing is "buffered" rather than a precise pH value. This is gonna be a result of the formula used, not of the pH value. Personally I wouldn't even bother reading a stop bath pH unless you're just wondering if it still has an acidic value.

With respect to what to use for pH adjustments, I'd say that whoever supplied the formulas ought to have recommendations. If they don't you could use the Kodak H-24 manual, found online. I believe that in the formula sections they will have recommendations for pH adjusters. Failing that you could look at the formulas and try to use something similar. For example, if a fixer uses ammonium thiosulfate, you can see that there will be some ammonium ion in the mix, and so you can conclude that ammonium hydroxide would be compatible for raising the pH. Make sure that you take the appropriate precautions with everything, etc., and all other disclaimers.

AgX · Jul 10, 2020

Mr Bill said:
I think you would be well served to buy a packaged mix first, use this to see what your meter/electrode "expects," then use that as your aim value for your own custom developer.

Bu this still means that the selfmade bath should have the same true pH as the commercial bath.
I do not get this. Already different versions of same type of bath from same manufacturer got different pH values.

Mr Bill · Jul 10, 2020

AgX said:
Bu this still means that the selfmade bath should have the same true pH as the commercial bath.
I do not get this. Already different versions of same type of bath from same manufacturer got different pH values.

I actually meant this to only mean for the color developers. If these have different pH values it would probably only be for some special idiosyncrasies of a replenisher. But once it gets into a processor tank (ready to develop film/paper) there should, as far as I know, be only one specific aim value for each of C-41 and RA-4 developers. Do you know of any cases where this is different?

In the case of the "secondaries," bleach and fix, there could be different values for the different types. But I think that a cheaper pH meter will be fine in these pH ranges. It's only in the high pH color developers where the meter problems show upn

GBS · Jul 10, 2020

Mr Bill said:
There have been a couple threads on here that get into a little more detail, and may be worth reading. I put in some links to Kodak data on pH readings, from the H-24 motion picture manual. These will give you much more detail on the subject. In one of these links I see that member Serge Lavrenchuk has recently updated his experiences, and is probably worth reading.

Thank you for the links--and your thorough and thoughtful reply. I figured everything after the developer was likely close enough as long as it was mixed to instructions. I'll have a look at the links--I already read through the second one before posting. I appreciate the effort; there's so much info here, sometimes it's hard to find.

The developer mixes are different ones I've mostly come across here. I'll link to one, for example:
https://www.photrio.com/forum/threads/color-negative-developer-near-to-c41.42731/#post-612215

Each one I am looking at is slightly different, and some have different chemicals, but all are in the same ballpark (forgive my unscientific phrasing). I plan to follow the recipe with distilled water, but am unclear how to test/adjust. Or do I just assume all is well if I follow the mix? 0.03 tolerance seems low, but again, I'm relearning a lot of this.

AgX said:
So you need aim-pH values for the homebrew formulas. Have you got these? And the respective tolerances?

Yes, I have values and tolerances. For the example in the link above: pH is 10.16 at 25°C +/- 0.05

Thanks again for your time.

RPC · Jul 11, 2020

If you use a ferricyanide bleach, a stop/clearing bath is required after the developer. I use a 2-minute, 2% acetic acid stop bath with 10 grams/liter of sodium sulfite added, followed by a 2-minute running-water wash. This provides good protection of the ferricyanide bleach from oxidation from the developer, which would result in a bad brown stain on your negatives.

The ferricyanide bleach I use has 80 grams/liter of potassium ferricyanide and 20 grams/liter of potassium bromide. Use for 3 minutes at 100F, followed by a long running-water wash, about 5 minutes, before the fixer.

The C-41 developer formula I posted in your link is the one I would use. It is very close to the actual Kodak C-41 developer formula. I have tried it without even checking or adjusting the pH and gotten excellent results, but when I do adjust developers, I aim for about 10.1-10.2.

GBS · Jul 11, 2020

RPC said:
If you use a ferricyanide bleach, a stop/clearing bath is required after the developer. I use a 2-minute, 2% acetic acid stop bath with 10 grams/liter of sodium sulfite added, followed by a 2-minute running-water wash. This provides good protection of the ferricyanide bleach from oxidation from the developer, which would result in a bad brown stain on your negatives.

The ferricyanide bleach I use has 80 grams/liter of potassium ferricyanide and 20 grams/liter of potassium bromide. Use for 3 minutes at 100F, followed by a long running-water wash, about 5 minutes, before the fixer.

The C-41 developer formula I posted in your link is the one I would use. It is very close to the actual Kodak C-41 developer formula. I have tried it without even checking or adjusting the pH and gotten excellent results, but when I do adjust developers, I aim for about 10.1-10.2.

This is hugely helpful and concise, thank you @RPC!!! Your formula was one I keep coming back to, so it's great to hear your feedback.

A few questions, if I may:

1 - HOW do you adjust the developer pH (if necessary)?
2 - whats the exhaustion rate of the bleach (# or approx # of 35mm x36 rolls per L)?
3 - can the bleach be revived, or is it best (easiest) to start over?

Oh, one more: how many rolls can 1L of the developer you like handle? Can that be extended by increasing dev time slightly?

Thanks so much. I've been reading and bookmarking and making spreadsheets, but it's down to a few things I can't quite figure out on my own.

koraks · Jul 11, 2020

GBS said:
1) how to adjust: developer pH up or down

Up: sodium or potassium hydroxide, drops of a 10% solution work OK.
Down: I use acetic acid, but sulfuric acid will likely also work.

2) How crucial is the stop bath pH and how to adjust?

It's not critical.

C41 stop - acetic based (can I use vinegar or Kodak indicator? I don't have a "value" for this, only the recipe)

Vinegar works OK. I use cleaning vinegar which is around 7% as far as I can tell. Concentration isn't critical.

3) How crucial is the bleach pH and how to adjust:
Potassium Ferricyanide + Sodium Bromide

Not too critical, but you want to prevent the pH of this one from dropping too far in order to prevent Prussian blue from forming. Use a wash step after the stop bath and before bleach.

4) how crucial is the fix pH and how to adjust?

Again, not very crucial. Any neutral fixer is fine. Optimal fixer pH for color is somewhere around 6.5 or so. You don't want to get it too acidic as it may mess with the cyan dye in particular.

5) Tangential question: do you have a recommendation for a clearing wash other than water, and if so, does it have critical pH to adjust?

What do you mean by a 'clearing wash'?
Anyway, wash steps work fine with water. Tap water works perfectly fine if you have a somewhat decent water quality; if you distrust it, use one of the various ways to get purer water. I don't see how pH control would be necessary for plain water.

RPC · Jul 11, 2020

GBS said:
This is hugely helpful and concise, thank you @RPC!!! Your formula was one I keep coming back to, so it's great to hear your feedback.

A few questions, if I may:

1 - HOW do you adjust the developer pH (if necessary)?
2 - whats the exhaustion rate of the bleach (# or approx # of 35mm x36 rolls per L)?
3 - can the bleach be revived, or is it best (easiest) to start over?

Oh, one more: how many rolls can 1L of the developer you like handle? Can that be extended by increasing dev time slightly?

Thanks so much. I've been reading and bookmarking and making spreadsheets, but it's down to a few things I can't quite figure out on my own.

I have never tested the exhaustion rate of the ferricyanide bleach, and I know of no way to regenerate it. I just use it twice and throw it out with good results.

I use the developer once and throw it out as I like it to be fresh. It can be reused with increased development time, and I would increase it as you would the Kodak developer. There is a chart out there somewhere that shows time increase per re-use, I think it might be in this forum somewhere but I have no link.

Koraks has explained how to adjust the pH.

GBS · Jul 11, 2020

koraks said:
Up: sodium or potassium hydroxide, drops of a 10% solution work OK.
Down: I use acetic acid, but sulfuric acid will likely also work.

It's not critical.

Vinegar works OK. I use cleaning vinegar which is around 7% as far as I can tell. Concentration isn't critical.

Not too critical, but you want to prevent the pH of this one from dropping too far in order to prevent Prussian blue from forming. Use a wash step after the stop bath and before bleach.

Again, not very crucial. Any neutral fixer is fine. Optimal fixer pH for color is somewhere around 6.5 or so. You don't want to get it too acidic as it may mess with the cyan dye in particular.

What do you mean by a 'clearing wash'?
Anyway, wash steps work fine with water. Tap water works perfectly fine if you have a somewhat decent water quality; if you distrust it, use one of the various ways to get purer water. I don't see how pH control would be necessary for plain water.

@koraks Thank you! This is hugely helpful. I really appreciate your time and effort. I've dug and dug, but some of the final nuances have evaded me. As far as clearing wash: I've come across a thread here with a mix, not just plain water. I know it's not that common, so I was curious if anyone had additional input.

RPC said:
I have never tested the exhaustion rate of the ferricyanide bleach, and I know of no way to regenerate it. I just use it twice and throw it out with good results.

Thanks! I have another thread about the exhaustion rate going here. I'm trying to learn if regeneration is something I can manage. The bleach formula is for ECN-2, which is different than C41, so I'm not sure if that's helpful. I'll look for the development time chart--that's something I'd love to see. If you remember where it is, please let me know!

Anon Ymous · Jul 11, 2020

@Mr Bill Instead of buying commercial chemical and see what the pH meter reads, it would be better to use the buffer solutions that you need anyway with a pH meter. Usual buffer solutions are at pH 4, 7 and 10, the last one being very close to C41 developer pH. Using a pH meter without calibration with a buffer solution isn't very wise anyway.

@GBS IMHO, pH paper strips aren't very accurate, you'd be better served by a pH meter. There are very cheap, sub $10 ones, which you'd better avoid. Buy one with two calibration points, but make sure you also buy buffer solutions. You can find some "pen type" meters at about $20 or thereabouts, which is probably the cheapest ones you should invest in.

koraks · Jul 11, 2020

GBS said:
@koraks Thank you! This is hugely helpful. I really appreciate your time and effort. I've dug and dug, but some of the final nuances have evaded me. As far as clearing wash: I've come across a thread here with a mix, not just plain water. I know it's not that common, so I was curious if anyone had additional input.

The link doesn't work, so I'm not sure which wash step you are referring to. If this is about the final wash (also referred to as stabilizer or conditioner), you'll find good info here: https://www.photrio.com/forum/threads/the-definitive-word-i-hope-on-color-stabilzers.89149/
Long story short:
* Modern C41 films don't require an actual stabilizer (like formalin or one of its precursors), but antifungal chemistry along with a wetting agent are still used in final wash/conditioner baths.
* For ECN-2 films, it's unclear what their requirements are in terms of a conditioner. Some argue it doesn't need any, some argue it does. I don't know.
* If you want to DIY something for C41 film, I'd propose to just use a final rinse of demineralized water with a wetting agent (e.g. Photoflo). If you want to use it for ECN-2 films as well and want to err on the safe side for long-term permanence of the dyes, you could add a little formalin to it.

GBS · Jul 11, 2020

Anon Ymous said:
IMHO, pH paper strips aren't very accurate, you'd be better served by a pH meter. There are very cheap, sub $10 ones, which you'd better avoid. Buy one with two calibration points, but make sure you also buy buffer solutions. You can find some "pen type" meters at about $20 or thereabouts, which is probably the cheapest ones you should invest in.

@Anon Ymous Thanks! I appreciate the input. I'm in the US and see pen types on Amazon, for example. Not sure where to get them locally. For example only, would this work? There doesn't seem to be a calibration method, and it says for "water." I'm unclear on how developer could damage/interfere with the electrodes.

koraks said:
The link doesn't work, so I'm not sure which wash step you are referring to. If this is about the final wash (also referred to as stabilizer or conditioner), you'll find good info here: https://www.photrio.com/forum/threads/the-definitive-word-i-hope-on-color-stabilzers.89149/
Long story short:
* Modern C41 films don't require an actual stabilizer (like formalin or one of its precursors), but antifungal chemistry along with a wetting agent are still used in final wash/conditioner baths.
* For ECN-2 films, it's unclear what their requirements are in terms of a conditioner. Some argue it doesn't need any, some argue it does. I don't know.
* If you want to DIY something for C41 film, I'd propose to just use a final rinse of demineralized water with a wetting agent (e.g. Photoflo). If you want to use it for ECN-2 films as well and want to err on the safe side for long-term permanence of the dyes, you could add a little formalin to it.

@koraks sorry about the bad link. the question is about clearing "bath" in addition to water wash between development steps.
https://www.photrio.com/forum/threads/diluted-c41-tested.175919/
I'm fairly up to speed on modern final rinse techniques. But--coincidentally--I actually just asked you about old vs. new stabilizer in a different thread.

Anon Ymous · Jul 11, 2020

@GBS The one you linked to is probably of the sub $10 category and better be avoided. In order to see what kind of calibration method and number of points it uses, you need to see the instructions, or contact the seller. I suspect this particular meter has a single calibration point. This means that it is fairly accurate at this point, but the farther away you go from it, the less accurate it becomes. Don't know where you could buy one, there's no reason not to buy one on-line.

RPC · Jul 11, 2020

@GBS The stop (acetic acid) and clear (sodium sulfite) steps can be combined as I indicated above, and a clear step is not really needed after the bleach if you replace it as I do with a long 5 minute wash.

GBS · Jul 11, 2020

Anon Ymous said:
The one you linked to is probably of the sub $10 category and better be avoided. In order to see what kind of calibration method and number of points it uses, you need to see the instructions, or contact the seller. I suspect this particular meter has a single calibration point. This means that it is fairly accurate at this point, but the farther away you go from it, the less accurate it becomes. Don't know where you could buy one, there's no reason not to buy one on-line.

@Anon Ymous Thank you. I found one for $40 and a pack of calibration mixes for $10.
Is there a concern that the electrodes will be damaged from development chemicals? (I won't use the meter for stop, bleach, or fix).
Also--when working with ECN-2, should I be concerned about adding sulfuric acid to adjust developer pH, considering the stop bath is made from sulfuric acid? Or are we talking drops to adjust--which won't damage the developer?

RPC said:
The stop (acetic acid) and clear (sodium sulfite) steps can be combined as I indicated above, and a clear step is not really needed after the bleach if you replace it as I do with a long 5 minute wash.

Thank you for being patient with me. I assume the 5 minute wash is under running water? If so, will a clearing bath help reduce wash time? I'm fine skipping the clearing bath mixture and washing only, but also happy to save water where I can. Thanks a ton!

Mr Bill · Jul 11, 2020

Anon Ymous said:
@Mr Bill Instead of buying commercial chemical and see what the pH meter reads, it would be better to use the buffer solutions that you need anyway with a pH meter. Usual buffer solutions are at pH 4, 7 and 10, the last one being very close to C41 developer pH. Using a pH meter without calibration with a buffer solution isn't very wise anyway.

Hi, you may have missed the part, post #6, that I have read pH values on tens of thousands of photo chemical samples using research grade pH meters. Or if you did, perhaps you are just making the (erroneous) assumption that they were not properly calibrated.

My point is that color developers can be very difficult to get correct readings on. Somewhere in one of my links I had put a link to Kodak method ULM-191-2, Measurement of Photographic Processing Solutions in the Kodak H-24 processing manual. Here is an excerpt from the section on electrodes:

"Because of the effect of the complex matrices of photoprocessing solutions on the glass membranes of pH electrodes, a significant difference has been observed between different mabufacturer's pH sensing glasses. CORNING Rugged Bulb pH Electrode 476024 serves as the Kodak standard for Processing solutions. ...
...
Thus, if one chooses to use electrodes other than those recommended in this method, one MUST verify that no bias exists between measurements made with the recommended CORNING pair of electrodes and the electrodes under investigation."

Now, in my personal experience reading probably thousands of color developer samples even the "correct" electrodes can have problems. I've only seen a couple of cheaper meter/electrode combinations compared, and they read so differently from our standard gear that the lab equipment rep who brought them in was extremely embarrassed, saying that he "had no idea" how bad they would be. Now, this was circa 1990, so perhaps the situation is much improved since then. However, I remain skeptical, thus my recommendation to not trust such a meter explicitly for a color developer sample (these remain the most difficult photographic samples to get good readings, especially if they are seasoned).

Thus my recommendation to actually mix a known-good commercial developer to establish a baseline pH aim for the "unknown" pH electrode. Fwiw, as I recall, the Kodak-recommended pH electrodes were selling for roughly $200 US back in the day. So it seems unlikely that a home developer will be using one of these. As a note, we also found the Ross electrodes to give good results, but at even higher cost.

Anon Ymous · Jul 11, 2020

@GBS Don't worry about ruining the electrode of the meter with photochemicals, be it developers, bleaches, fixers, whatever. Eventually, all electrodes are worn by use, but they're not that sensitive. Also keep in mind that you have to rinse the electrode well after every use. I rinse mine in running water, followed by a rinse in deionised water. Do not wipe the electrode, do not scratch, rub, touch it. If it is stored in a potassium chloride solution, keep it there after use.

PH adjustment is always performed dropwise. You typically use fairly dilute solutions, like 10% sodium hydroxide, or sulfuric acid and add slowly, with some agitation.

Anon Ymous · Jul 11, 2020

@Mr Bill I don't doubt that you have a lot of experience in this area, but IMHO today's pH meters aren't that bad. Perhaps they wouldn't last very long in an industrial scale environment, but they're good enough for amateurs. I have mixed several formulae and didn't see great deviations when using reasonably pure chemicals and this includes C41 developers.

GBS · Jul 11, 2020

Anon Ymous said:
Don't worry about ruining the electrode of the meter with photochemicals, be it developers, bleaches, fixers, whatever. Eventually, all electrodes are worn by use, but they're not that sensitive. Also keep in mind that you have to rinse the electrode well after every use. I rinse mine in running water, followed by a rinse in deionised water. Do not wipe the electrode, do not scratch, rub, touch it. If it is stored in a potassium chloride solution, keep it there after use.

PH adjustment is always performed dropwise. You typically use fairly dilute solutions, like 10% sodium hydroxide, or sulfuric acid and add slowly, with some agitation.

@Anon Ymous Thank you. This seems reasonable for home use, where the alternative would be to do zero checking/adjusting.

@Mr Bill Thank you. I did not miss your thorough and helpful posts. I'm sorry if it seems like I was ignoring the proper method and tools you shared. Where I continued to seek advice is as follows: Professional-grade and Kodak-recommended pH testing devices are somewhat unrealistic for my home use. That leaves me to: A) ignore the pH altogether, or B) do my best with what's available.

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