ECN-2/C41 Stop bath via Glacial Acetic Acid

[RoboRepublic]

I'm considering switching over to using glacial acetic acid, and was curious to the hive mind what sort of dilution ratio I would need to use for a stop bath for ECN2/C41 process? I want to keep things consistent, hence the usage of the glacial variety (instead of say, generic store bought vinegar)
Thanks!

 

[Quiver2]

Distilled white vinegar from the store is consistent at 5% dilution, and of a high purity considering that it is food grade. The only thing that glacial strength will gain you is time between having to get more. Also, as the growing season is about to start you might want to take a look in the pesticide and herbicide section of the garden centers. Last year at my local Walmart they had gallon jugs of 30% acetic acid (marketed as 30% "vinegar") as an environmentally friendly herbicide and insecticide. Quality on the label doesn't indicate any impurities, and I haven't seen any detrimental effects on my negatives.

 

[lamerko]

I'm considering switching over to using glacial acetic acid, and was curious to the hive mind what sort of dilution ratio I would need to use for a stop bath for ECN2/C41 process? I want to keep things consistent, hence the usage of the glacial variety (instead of say, generic store bought vinegar)
Thanks!

About 1% glacial acetic acid should be fine, it can be combined with 20 grams of sodium sulfite. The addition of sulphite can have a dual role - apart from helping to neutralize the developer, it also blocks the formation of dyes.

 

[lamerko]

Distilled white vinegar from the store is consistent at 5% dilution, and of a high purity considering that it is food grade. The only thing that glacial strength will gain you is time between having to get more. Also, as the growing season is about to start you might want to take a look in the pesticide and herbicide section of the garden centers. Last year at my local Walmart they had gallon jugs of 30% acetic acid (marketed as 30% "vinegar") as an environmentally friendly herbicide and insecticide. Quality on the label doesn't indicate any impurities, and I haven't seen any detrimental effects on my negatives.

I don't know how it is in the US, but in Europe they banned the sale of diluted acetic acid as a condiment. Vinegar must be naturally obtained by fermentation - this implies a lot of organic impurities and stabilizers (if there is no stabilizer, it starts to settle).

 

[cliveh]

Indicator stop bath, yellow when ok, purple, then throw away.

 

[koraks]

The only thing that glacial strength will gain you is time between having to get more.

Indeed. In exchange for that minor benefit, you get a serious health hazard.

About 1% glacial acetic acid should be fine

Yes. The concentration is non-critical. Anything from 0.25% up to the limit of sanity (let's say 5-10%) will work. I generally aim for 0.5-1%, but keep it at "a dash". Works fine.

Ron Mowrey told me that there was a reason for sulfuric acid being prescribed as the ECN2 stop bath, but he couldn't muster a clear reason why. Supposedly, it was to get rid of the developer quickly, but I never observed a problem in this regard with acetic acid - neither with ECN2 or C41 film.

I want to keep things consistent

Don't worry. The concentration is entirely non-critical.

 

[Samu]

I always use acetic acid stop for C-41, because it is easier for me to control the developing time this way. I normally use a 3% concentration. Something like 1% would suffice, but I am too lazy to mix it all the time. I change it when it gets too dark red. I have a big container of 60% acid, and 3% us easy to measure - 50 ml for a liter of stop bath. A bit stronger solution does no harm.

I don´t recommend using white vinegar bought from a grocery store, because it often contains some sugar.

 

[halfaman]

C-41 bleach is acidic (pH around 4.5) and works as a stop bath too.

 

[RoboRepublic]

Thanks everyone, looks like going the store bought route (in the US) seems to be a good option. If the acetic concentration is at 5% then it seems I need to use a 1:4 dilution ratioo, yielding 120ml acid + 480ml water to achieve my 600ml final volume. Is my math correct?
Would I be able to use this ratio for 10 rolls? As thats the yield I seem to get with some consistency from the developer (with modified times).

How does use of the acetic acid as a stop bath affect its disposal? Vinegar I suppose can down the drain, but once its used as a stop bath its not clear to me.
Thanks again for all the information!

 

[koraks]

If the acetic concentration is at 5% then it seems I need to use a 1:4 dilution ratioo, yielding 120ml acid + 480ml water to achieve my 600ml final volume. Is my math correct?

Yeah. But the dilution is non-critical, so it doesn't really matter.

Would I be able to use this ratio for 10 rolls?

Depends on the volume. I mix it fresh for each development run because it's cheap as chips and quick to mix. Why bother making things unnecessarily complicated? If you absolutely must (for reasons I can't fathom!) reuse an acetic acid stop bath, I'd mix it a little stronger; at e.g. 2% or so. How long it'll last depends on how much developer carryover there will be, which depends on the reels used, the kind of film processed, what kind of tank you use, if you use a Jobo with a lift etc. etc. etc. etc. In short - don't bother and just mix fresh.

Vinegar I suppose can down the drain, but once its used as a stop bath its not clear to me.

It's still vinegar, a little acetate (which is harmless) and a tiny bit of developer, which for all intents and purposes is also harmless. So yes, down the drain would be the sensible option.

 

[psfred]

ECN-2 using CD-3 requires strong sulfuric acid with sodium sulfite as the stop bath, acetic acid is not strong enough. Acetic is fine for C41, but it needs to be at least 2%, so maybe 1:1 grocery store white vinegar (which is now 4% and not 5% acetic acid!). If you are not using the usual C41 bleach (I use ferricyanide bleach for everything) you must include 10 grams per liter of sodium sulfite to inactivate any residual color developer.

 

[koraks]

acetic acid is not strong enough

What goes wrong if you use acetic? I've not noticed any ill effects so far.

PS: I use a PDTA bleach, not ferricyanide, with ECN2 films, if that matters.

 

[psfred]

I suspect that acetic acid doesn't stop the developer activity completely quickly enough for machine processing. There is a risk of continued base fog development as the remaining steps in machine processing are not light tight. Any remaining CD-3 needs to be completely inactivated as well and rendered easily removable in the wash step -- if using ferricyanide bleach, which many did, any carryover into the bleach turns into magenta blotches.

Photo Engineer (who passed away a few years ago) worked at Kodak for many years, and he stated that Kodak never found a better stop for ECN-2, else they would not have used sulfuric acid.

 

[RoboRepublic]

What goes wrong if you use acetic? I've not noticed any ill effects so far.

PS: I use a PDTA bleach, not ferricyanide, with ECN2 films, if that matters.

Would you have a formula for PDTA bleach? would be great to be rid of ferricyanide in the house

Ps. I switched to acetic acid 1:4 and it works for me as well. Maybe not scientifically the best, but looks good to my eye

 

[foc]

In commercial c41 processing, ferricyanide Bleach isn't used. So there is no stop Bath between dev and Bleach.

I remember , many years ago, mixing regenerated Bleach by adding glacial acetic acid to collected Bleach overflow.

Glacial acetic acid was always handled with extreme care.

 

[koraks]

Would you have a formula for PDTA bleach

There are formulas on Photrio, but I simply use Fuji bleach.

 

[RoboRepublic]

There are formulas on Photrio, but I simply use Fuji bleach.

Very difficult to find fuji bleach replenishment here in the US- you can barely find the 5L dev/bleach kits!

 

[Tumbles]

I remember Photo Engineer said that a sulfuric acid stop bath is a requirement for ECN-2, because it's necessary to form the correct dyes. Without it, the dyes may not be stable and archival.

 

[koraks]

I remember Photo Engineer said that a sulfuric acid stop bath is a requirement for ECN-2, because it's necessary to form the correct dyes. Without it, the dyes may not be stable and archival.

Sort of.

Sulfuric acid is stronger than Acetic. If it were Acetic, I really think Kodak would let us know. And the reason is to extract all of the CD from the film with a strong acid bath which thus gives better dye stability.

This is what he said to me when I inquired after it. The argument boils down to (1) getting rid of the developer, and (2) "my colleagues knew what they were doing so let's assume there is a reason". The extraction argument I believe should be seen in the context of high-volume machine processing, where the dwell time of the film in the stop bath is brief. In a home setup, you can easily extend the stop bath time and follow it with one or two rinses if so desired. I suspect that this ultimately achieves the same stability.

Btw, I also suspect that his wording was somewhat informal and not entirely accurate. CD remaining in the emulsion would oxidize at a later stage and thus pose a threat primarily to the unreacted dye couplers, not so much the already formed image-wise dyes.

Also, please don't take this the wrong way, but as in many, many cases, we end up in a situation where someone offers that "Photo Engineer said X or Y". This always ends up in a bout of "hermeneutics of the gospel of Mowrey" (which I'm certainly co-responsible for) and it only gets us so far. We should be cautious to not read more into his words than their literal meaning. And we should also keep in mind that his knowledge was sometimes (dare I say it...) limited - and he never argued otherwise! For instance, also on the topic of stop bath, I asked about citric acid for color processes and this is what he said:

I was taught to never use a citric acid bath as a stop for some reason. I knew it at the time, but over the years it has never come up until recently.

Sometimes, Ron was just like the rest of us. He passed on what he remembered, informally so, and while is knowledge was encyclopedic, it was not absolute, infinite or infallible.