Film Stop Bath

[lensmagic]

How much glacial acetic per liter??

 

[Photo Engineer]

1 ml / 100 is 1%, and 2 ml / 100 is 2% (approximately).

This should do for starters. stops range from 1 - 2%.

PE

 

[lensmagic]

1 ml / 100 is 1%, and 2 ml / 100 is 2% (approximately).

This should do for starters. stops range from 1 - 2%.

PE

Thank you, PE. What dilution would you recommend for one shot use?

 

[kb3lms]

Lensmagic,
That's already a working solution that he gave you. No need to dilute further.

 

[msa]

That dilute, it's actually weaker than the vinegar in your kitchen. I'm not sure there's a benefit to further diluting it, you could use it one shot as is. If you're buying glacial, you'll certainly have plenty.

Honestly, though, I'm not sure I'd bother --get some pH test strips, or indicator, and test it periodically if you're worried. It works by neutralizing the developer, so as it's expended, the pH will approach neutral. (pH of 7) At 2%, I'd expect it to start around a pH of 3...and I'd probably neutralize it with a little baking soda and toss it by the time it got to 5 or so.

If you really wanted to conserve, you could replenish it periodically as it got close to neutral, but water is cheap....

 

[RalphLambrecht]

Film stop bath is a fairly non-critical processing step. In addition to simply washing the no-longer-needed developer away, its function is to neutralize the alkaline developer quickly and brings development to a complete stop. As msa said, the latter is achieved as long as the pH is below '7'. The former can be accomplished with a alternative water bath.

Some practitioners are concerned about the formation of unwanted gas bubbles in the emulsion, which possible with film developers containing sodium carbonate. This is less likely with a weaker stop bath (1%) and can be prevented with a preceding water rinse (in addition to or as a replacement for the stop bath).

Using stop bath one-shot, monitoring its pH or using a water stop bath instead are all possible scenarios, and you'll find supporters for all of them, but process consistency is more important than the difference between these options.

 

[cmo]

There are still some things I don't know exactly, maybe some of you can clarify these issues:

In rare cases film manufacturers recommend a very weak stop bath or to use water instead. I can recall such a recommendation for Efke films, but that might be outdated.

I remember that for some types of fixing bath an acetic stop bath is mandatory, for the "odorless" alkaline fixers I don't know what is the best solution.

I use citric acid to avoid the penetrating odor of vinegar in my tiny darkroom. How much would you use per liter, and how long would you use it, e.g. for how many films or how much paper?

In some cases the stop bath developed a lot of foam, and when opening a film developing tank there was a smell like acid. It happened a few times, I used XTol and citric acid, probably too much acid. There are some commercial stop baths that contain extra ingredients to stop this kind of smell, what could that be?

 

[RalphLambrecht]

Nothing is easy.

... In rare cases film manufacturers recommend a very weak stop bath or to use water instead. I can recall such a recommendation for Efke films, but that might be outdated. ...

As far as I know, it's more a recommendation for developers that contain significant amounts of sodium carbonate, because in combination with an acid stop bath, this can create air bubbles and 'pinholes' in the emulsion.

... I remember that for some types of fixing bath an acetic stop bath is mandatory, for the "odorless" alkaline fixers I don't know what is the best solution. ...

It's not mandatory for acid fixers. It's sometimes recommended with alkaline fixers. The concern there is that a plain water bath will not stop development quickly enough. Again, consistency is the key.

... I use citric acid to avoid the penetrating odor of vinegar in my tiny darkroom. How much would you use per liter, and how long would you use it, e.g. for how many films or how much paper? ...

No matter which of theses acids you use, you need a 2% solution. Feel free to reduce it to 1% if you experience pinholes in your film emulsion.

 

[Gerald C Koch]

Citric acid contains three carboxylic groups while acetic acid has one. Citric acid has a greater molecular weight than acetic acid. When all this is considered you would need a 1.5% solution of citric acid as a stop bath for films and papers. Dissolve 300 g of citric acid in enough water to make 1 liter of solution. Dilute 1+19 for use.

It's best not to try to reuse citric acid stop baths because they tend to grow mold very quickly on storage. The concentrate given above will keep since its high osmotic pressure kills many micro-organisms,.

 

[Photo Engineer]

The larger the format, the more critical is the use of a stop bath or very strong agitation in a running water rinse bath after development. This is to avoid any chance of nonuniformity.

The pinhole problem due to carbonate developers and soft films has been a non-issue with most films on the market since the 50s. In fact, George Eaton's book of that era is the last mention of pinholes, and even that was restricted to deep tank processing in which hydrostatic pressure prevented the release of CO2 as it formed. It formed at one time, as the film came up out of the deep tank. So, this is not likely with products from Kodak, Ilford and Fuji. It may be an issue with other products.

PE

 

[cmo]

Thanks, Gerald, that is good advice.

Can you imagine what kind of substance could reduce the amount of sulfur dioxide that is outgassed when the stop bath meets the remainings of the developer? That would be a nice addon to avoid the smell.

 

[Gerald C Koch]

Can you imagine what kind of substance could reduce the amount of sulfur dioxide that is outgassed when the stop bath meets the remainings of the developer? That would be a nice addon to avoid the smell.

Most chemicals that would absorb sulfur dioxide are basic and could not be added to the stop bath. I assume you are talking about making prints with fibre papers. When making prints try to avoid carryover by allowing the print to drain for a few seconds before placing it in the stop. You could also use a brief dip in plain water before the stop to remove any surface developer. Some photographers have an exhaust fan over the stop and fixer trays. Using fresh stop during long print sessions will also help.

 

[Gerald C Koch]

A 3% solution of boric acid can also be used as an odoerless stop bath. This solution will not grow mold and can be reused. Boric acid can be obtained from most drugtores. Buy crystalline boric acid and not the powdered form which is hard to dissolve.

 

[RalphLambrecht]

Gerald

Interesting suggestion. However, a 3% boric acid solution has a pH value of roughly 5, which compares to a pH of 2-2.5 for a more commonly used 2% citric or acetic acid solution.

How does this affect its use as an alternative stop bath?

 

[Photo Engineer]

A 1% to 2% acetic acid stop should be a little less acid than pH 2.5 I believe. Any acid solution should not be lower than about 3.0 nor about about 5.0 for a good stop.

A 1 molar solution or about a 6% solution (vinegar) would be more in the range of about 2.5.

PE

 

[ic-racer]

Since the Glacial acetic acid is pretty strong, and therefore can be diluted to a 28% stock solution. That is then diluted to get the working solution.

 

[msa]

Since the Glacial acetic acid is pretty strong, and therefore can be diluted to a 28% stock solution. That is then diluted to get the working solution.

Acid retards microorganism growth, which is an argument for keeping it stored in it's water-free form. That, and you're just using another storage container, and having to store it...

I'm not sure there's any benefit to making, and storing, stock solutions of acetic acid. You might as well dilute it directly into 1L or 1 gal. working solution bottles. It's not as if you're trying to age it, the way one might with some developers.

 

[MattKing]

I dilute the concentrated Kodak indicator stop 1 + 7 into a 16 ounce container. I then dilute the resulting intermediate stock solution a further 1 + 7 immediately before use.

I do this because the concentrate is so strong - if you spill even a drop it can stain, and it smells awful. As I am working in a temporary darkroom, I prefer to limit how much I handle the concentrate. I'm also limited in space when it comes to storing stock or working solutions.

 

[RalphLambrecht]

A 1% to 2% acetic acid stop should be a little less acid than pH 2.5 I believe. Any acid solution should not be lower than about 3.0 nor about about 5.0 for a good stop.

A 1 molar solution or about a 6% solution (vinegar) would be more in the range of about 2.5.

PE

PE

That's my point, but the suggested 3% boric acid solution calculates to pH 4.75, unless I made a mistake. Hence my question how this effects its usefulness as a stop bath.

 

[Photo Engineer]

Boric acid at that pH is well within the acceptable range for a stop. I have never tried it, nor do I have any formulas using it. So, other than being in the right pH range, it is all I can say.

PE

 

[Gerald C Koch]

It's not the pH that is important as long as it is below 7 and not acid enough to chew up the emulsion or paper. A single drop of concentrated sulfuric acid to a liter of water would produce a low pH but would be worthless as a stop bath because the solution would have little capacity to neutralize alkalis. This is why we use a moderate amount of a weak acid instead of a small amount of a strong acid for stop baths. Buffer capacity is the single most misunderstood point in photographic chemistry.

 

[Photo Engineer]

Gerald, it would work one time!

But in any event, Grant Haist devotes quite a bit of space to stop baths, pH and buffer capacity. I use 1% - 2% Acetic Acid quite successfully and do it one shot as Acetic Acid is so inexpensive.

PE

 

[cmo]

Boric acid at that pH is well within the acceptable range for a stop. I have never tried it, nor do I have any formulas using it. So, other than being in the right pH range, it is all I can say.

PE

One thing that speak against boric acid: it's reprotoxic.

 

[RalphLambrecht]

Boric acid at that pH is well within the acceptable range for a stop. I have never tried it, nor do I have any formulas using it. So, other than being in the right pH range, it is all I can say.

PE

I guess, I don't understand this part of your post:

Any acid solution should not be lower than about 3.0 nor about about 5.0 for a good stop.

 

[Photo Engineer]

If the pH is > 5.0 then it does not stop well. If it is below abaout 3.0 it will swell gelatin too much or destroy the hardness.

PE