Stop bath: citric acid or "regular"?

Odot · Feb 4, 2018

Is there such thing as a difference in quality? I wanted to try out the citric acid based and wondered how good it actually works. Thanks.

Huub · Feb 4, 2018

Quality wise there is no difference in results. Just follow the manual when dilluting and discard when the indicator makes it change colour.

Doremus Scudder · Feb 4, 2018

Working dilution citric-acid stop baths don't have a long storage life. Citric acid is organic and bacterial slime grows pretty quickly at room temperature in a citric acid stop, i.e., in a few days or a week. Acetic-acid stops can be stored till the capacity is reached. I use both kinds of stop, but mix the citric-acid ones "one session" only. I'll often save an acetic-acid stop for weeks in a bottle and reuse it; just depends on what I have around.

As far as quality and effectiveness, both types work just fine.

Best,

Doremus

RattyMouse · Feb 4, 2018

Doremus Scudder said:
Working dilution citric-acid stop baths don't have a long storage life. Citric acid is organic and bacterial slime grows pretty quickly at room temperature in a citric acid stop, i.e., in a few days or a week. Acetic-acid stops can be stored till the capacity is reached. I use both kinds of stop, but mix the citric-acid ones "one session" only. I'll often save an acetic-acid stop for weeks in a bottle and reuse it; just depends on what I have around.

As far as quality and effectiveness, both types work just fine.

Best,

Doremus

Acetic acid is an organic acid as well. Both citric and acetic are hydrocarbons.

Doremus Scudder · Feb 4, 2018

Ratty,

Of course, you're right. It's just that citric-acid stops will grow slime and acetic-acid ones don't. I'm not really sure why.

RattyMouse · Feb 4, 2018

Doremus Scudder said:
Ratty,

Of course, you're right. It's just that citric-acid stops will grow slime and acetic-acid ones don't. I'm not really sure why.

Citric acid has a much higher molecular weight than acetic acid (192.1 g/mol vs 60 g/mol), so my guess is that it is depleting far quicker than acetic acid stop baths. With the lower acidity, pH values rise quicker and bacteria grows.

I would use 3 times as much citric acid when making up a stop bath with this acid. Then you'd be at a like for like comparison.

Wayne · Feb 4, 2018

It must be something unique to your situation, because I've never noticed any slime or growth or cloudiness of any kind in my citric acid stop baths and I've been using them over periods of many weeks for many years. I have a partial bottle I havent used in months and its slime free. It will get dumped before I do any more B&W developing though, just because its been sitting and so cheap and easy to mix another batch.

Gerald C Koch · Feb 4, 2018

Working strength citric acid stop baths do grow slime if you try to store the used baths.

When used as directed both stop baths work equally well in stopping development as does water. The slight difference in speed between water and an acid solution is negligible.

spijker · Feb 4, 2018

I have the same experience as Wayne. I use Ilford Ilfostop which is citric acid based. I mix it in the recommended dilution with plain city tap water. I use it until the indicator tells me to change it, which can take months. No slime, no growth. Not in my Nova slot processor, nor in the PET bottle for film stop.

RattyMouse · Feb 4, 2018

spijker said:
I have the same experience as Wayne. I use Ilford Ilfostop which is citric acid based. I mix it in the recommended dilution with plain city tap water. I use it until the indicator tells me to change it, which can take months. No slime, no growth. Not in my Nova slot processor, nor in the PET bottle for film stop.

A commercially made citric acid stop bath will certainly be formulated with a biocide.

Try *just* citric acid and see if you get the same results.

MattKing · Feb 4, 2018

The Citric Acid based stop baths smell better/are almost odourless. Acetic acid based stop baths tend to have a stronger odour.
Citric acid based stop baths do provide a much better environment for bacterial growth than the acetic acid based ones - slime is much more likely.
In my market, if you compare the cost per litre of working strength solution, Ilfostop stop bath (1+19) is more expensive than the more concentrated Kodak Indicator stop bath (1+63).
Due to the odour and relative cost, I use Kodak Indicator stop bath for film, and Ilfostop for printing. If they were the same cost, I would just use Ilfostop.
I make up and store long term an intermediate stock solution (1 + 7) of Kodak Indicator stop bath, which is further diluted (11 + 7) for use when needed. The stock solution is easier to work with and doesn't smell nearly as bad as the full concentrate. I mix up working solutions of Ilfostop directly from the concentrate. I rarely keep either working strength solution more than overnight.

pentaxuser · Feb 4, 2018

There is really little more to be said. Matt has summed it up very well. All I would add is that Kodak concentrated acetic acid is a lot cheaper here in the U.K. and I'd be surprised if this wasn't the case elsewhere compared to Ilford citric acid. While I would not recommend placing your nose over the Kodak bottle or any other bottle of concentrated acetic acid when opening it, as the smell is strong, all you have to do is to keep you nose the normal distance away while you dilute and the smell diminishes to a barely noticeable level. I use a Nova Slot Processor and certainly I have never really been aware of any smell.

If you are very sensitive to acetic acid then there might be a case for citric acid but if not, then on cost grounds alone concentrated acetic wins hands-down as they say

pentaxuser

MattKing · Feb 4, 2018

Like most, I develop prints in trays. If I'm standing over the developer tray for a couple of minutes, I'm also standing over the stop bath tray. If I use the Kodak stop bath, I definitely notice the odour. With Ilfostop, not at all.
My bathroom/darkroom has a ceiling ventilation fan which I use. The ventilation is good, but it draws fumes past me, rather than away from me.

RattyMouse · Feb 4, 2018

I dont know why anyone would buy a stop bath. Grocery store vinegar is $1/gallon. Hard to beat that price.

MattKing · Feb 4, 2018

RattyMouse said:
I dont know why anyone would buy a stop batch. Grocery store vinegar is $1/gallon. Hard to beat that price.

Twice the price here (lowest Walmart price for 4 litres). And of course it takes way more space, which in my circumstances is important.

Sirius Glass · Feb 4, 2018

Citric acid based can grow slime while stop bath with indicator does not. Also as the name states stop bath with indicator has indicator which is great to have. And since any stop bath is so damned expensive, I get the best stop bath with indicator. Now I know that my spending the extra money on stop bath with indicator will strongly impact my finances that choice will force be to buy less film. Woe is me! Woe is me!

RattyMouse · Feb 4, 2018

MattKing said:
Twice the price here (lowest Walmart price for 4 litres). And of course it takes way more space, which in my circumstances is important.

I have a 980 sq foot house so I know what it's like to have space constraints!

Wayne · Feb 4, 2018

RattyMouse said:
A commercially made citric acid stop bath will certainly be formulated with a biocide.

Try *just* citric acid and see if you get the same results.

I use "just" citric acid that I mix myself from scratch.

RattyMouse · Feb 4, 2018

Wayne said:
I use "just" citric acid that I mix myself from scratch.

Well there you go. Commercially available stop baths almost certainly contain biocides. Home brewed ones won't.

Smudger · Feb 4, 2018

Two drops of bleach per litre keep my citric acid stop from growing stuff.

adelorenzo · Feb 4, 2018

I always discard the stop bath after a printing session or developing film.

I buy citric acid powder for like $6/kg. Using the recommended 15g per L that means I get about 65 L of stop bath per kilo. I have a scoop that holds about 15g so it takes seconds to mix up. No point in reusing it IMHO.

Wayne · Feb 4, 2018

RattyMouse said:
Well there you go. Commercially available stop baths almost certainly contain biocides. Home brewed ones won't.

There I go where? I don't get slime or growth of any kind.

williaty · Feb 4, 2018

The idea of storing used stop bath just boggles my mind! I'd never heard of such a thing before today.

I switched from acetic to citric acid stops for all my work because I HATE the smell of acetic acid. They work just fine and the powder is so cheap there's no hardship throwing it out at the end of a printing session or once a tank of film has been processed.

AgX · Feb 4, 2018

pentaxuser said:
All I would add is that Kodak concentrated acetic acid is a lot cheaper here in the U.K. ...

One does not need to buy Kodak acetic acid. At least here every grocery store has 400g 25% acetic acid for less than 1.50€.

Sirius Glass · Feb 4, 2018

williaty said:
The idea of storing used stop bath just boggles my mind! I'd never heard of such a thing before today.

I switched from acetic to citric acid stops for all my work because I HATE the smell of acetic acid. They work just fine and the powder is so cheap there's no hardship throwing it out at the end of a printing session or once a tank of film has been processed.

Stop bath is reusable, I store and use stop bath until the indicator starts to turn purple, like the instruction manual explains. Just RTFM and you will find that you can indeed reuse and store stop bath. If you screw the top on the bottle you will not smell the stop bath. Just keep one batch for film and another for prints.

Stop bath: citric acid or "regular"?

Odot

Huub

Doremus Scudder

RattyMouse

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RattyMouse

Wayne

Gerald C Koch

spijker

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MattKing

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Sirius Glass

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Wayne

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Smudger

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AgX

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Stop bath: citric acid or "regular"?

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