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  #1  
Old 3rd April 2021, 07:50 PM
John King John King is offline
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Default Two Questions

The first is about the exhaustion of fixer baths for B&W prints and negatives. The old way for prints was an estimation of the area that could be treated before the fixer became exhausted, and for film, twice the clearing time.
I wonder if anyone has tried a replenishment method similar to that used for RA4 prints. This for Kodak is 10cc of new blix per 80 sq ins of paper. This is more precise and there is no need for unceremonious emptying the processor/storage bottle every so often. It should work so has anyone any idea of the replenishment rate I could use for paper fixer?

The second is about stop bath. I will only use the acetic acid version because the citric acid based stop bath will allow a fungus to grow on the surface if not regularly used.
Tonight when clearing out my storage cupboard I found a full sealed 1ltr bottle of citric acid based stop bath. It has been there for a good while.
Has anyone ever tried mixing citric acid stop bath with the acetic acid version? The acetic acid will certainly stop any fungal growth on the top of the working solution of the stop bath and as they both perform the same function it should work. Any thoughts? The smell does not worry me.
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I hate to throw anything out if it is possible to use it
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Old 3rd April 2021, 09:02 PM
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Rob Archer Rob Archer is offline
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I use Tetenal fixer test strips to check for fixer exhaustion but only use them if I've lost count of how many prints I've put through it. Personally, I err on the side of caution with fixer as I've had insufficiently-fixed prints from my early days of photography deteriorate. I think the build-up of silver in fixer as it approaches exhaustion would make replenishment tricky.

I've only had problems with mould on citric acid stop bath when I've left open trays of it for a week or more in a warm darkroom. Citric acid is cheap and environmentally pretty benign so it's not worth cutting costs with. I find a tablespoon of citric acid granules in a litre of water enough to do at least 20 10x8 prints.
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Old 3rd April 2021, 09:11 PM
Stocky Stocky is offline
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Mixing the two acids for a stop bath likely to be ok. (I'm not a chemist)

The limit to fixer function for FB paper is silver content, not fixing activity. This may be different for film (not absorbent base) and RC paper.

It seems that you are frugal in your use of chemicals which is laudable, but IMHO for fixing FB paper which is so expensive, extravagance in fresh fixer is the only way to go. I use two-bath fixing. There might be some saving by using a simple home made fixer for the second bath (sodium thiosulphate and sodium sulphite).
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Old 4th April 2021, 07:26 AM
Lostlabours Lostlabours is online now
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For B&W fibre based prints 2 bath fixing is the most efficient and economic way.

RC B&W papers and films tolerate a much higher Silver level in the fixers, the issues with FB papers is the semi-soluable Silver-Thiosulphate intermediary complexes form weak bonds with the cellulose in the paper base. These are equilibrium reactions and as the Silver level rises they become less soluable in water.

Replenishement is used in machine processors for B&W films and RC papers but with very precise control, it's not worth it for home use.

Don't use fixer already used for B&W films because of the higher Iodide content of modern film emulsions, this causes issues with FB papers.

Ian
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Old 4th April 2021, 08:38 AM
John King John King is offline
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Rob:- I don't use an open tray for fixing I have a 2 bath Nova for that although I develop in an open tray. The last time I used the citric acid stop bath I could have skimmed off the 'wool' and and made my partner an angora sweater!!!

Stocky:-I had not considered the build up of silver (Call it advancing years) so that idea will be consigned to the bin marked 'good idea rubbish in practice'). I think I will try a small mix when I renew my paper stop bath and see how it goes.

Lostlabours:- I don't use fibre based paper any more, come on, it is too expensive and I am on a water meter. (and a pension) The quality of MG5 has dramatically closed the gap between fibre and resin coated paper so the difference in quality is not worth the 33% extra in price.

Nor do I mix film fixer with paper fixer and never have done. My set up would make it very difficult to manage that. Films are processed in the utility room printing is done in my darkroom upstairs.

Thanks for you input anyway
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Old 4th April 2021, 12:14 PM
Terry S Terry S is offline
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I have read a lot recently about accidents caused by random mixtures of two or more acids in the darkroom, so it's always worth checking.

A quick search on DuckDuckGo came up with some good answers though, and it seems you need not worry about the mixing of these two acids.

Answers found include:

Eric Griffin, former Avionics Technician at United States Navy (1985-1988)
Answered 2 years ago·

I have actually done this experiment as part of my commercial research. Acetic acid being the weaker acid will tend to revert to the acid form and the concentration of acetate ions decreases at the citric acid dumps hydrogen ions into the solution. coincidentally this increases the vinegar like odor of the solution because it increases the concentration of the acid form of the acetic acid.


Ray Menon, studied at Rutgers University
Updated January 29, 2021·

If you mix citric acid with acetic acid, you will have a mixture of two acids. Essentially you will have lemon-flavored vinegar.

Acetic acid is monobasic, meaning it has only one carboxylic acid group that can give up a proton. Citric acid is tribasic, meaning it has three carboxylic acid groups that can give up protons. This means that it has three pKa values, for successive loss of each of the three protons that are lost from the neutral citric acid molecule. The two acids will essentially act independently.


Terry S
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Old 4th April 2021, 05:42 PM
John King John King is offline
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Quote:
Originally Posted by Terry S View Post

If you mix citric acid with acetic acid, you will have a mixture of two acids. Essentially you will have lemon-flavored vinegar.

Terry S
No good with Fish and chips then? Unless you have a Lemon Sole!

It is not worth the hassle, I will just dump the citric acid version. Acetic acid has to be one of our cheapest chemicals in the darkroom.
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Old 5th April 2021, 11:35 AM
tillari tillari is offline
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I used to test the paper fixer measuring the silver that contains. But it can turn inactive anyways. Nowadays I test my fixers (both film and paper) in similar ways. I cut a piece of film, put it in the fixer and look at the time it takes to get transparent. When that time is 2x the time it took when the fixer was fresh, it's time to change it.
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Old 7th April 2021, 03:38 PM
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I mix up a litre of fix for film use after 12 mixed formats it is disposed of it. I have pushed it to fourteen but the fix time gets to long. As for prints when the slot go's black or starts to look black I change it. I have been caught out.
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