heinrich
Hello,
Does anyone have any experience using citric acid as a stop bath? My wife can’t stand the smell of vinegar, and as the darkroom is an integral part of the flat, I’ll probably have to switch to citric acid in the long run.
So, I have the following questions:
How many grams per litre do I need for an effective stop bath?
How long does citric acid remain effective in solution before fungi and bacteria start to grow?
And can I use the cheap stuff from the washing powder aisle, or do I have to buy the expensive stuff from a chemist’s?
Thanks in advance for the information
Heinrich
Gast
Hello,
With pure citric acid, such as Heitmann citric acid from the chemist’s, you need 20g per litre to make a 2% stop bath, as is standard practice in a photo lab.
However, I would prepare a fresh batch for every darkroom session, as there is no indicator in it and you cannot tell when it has gone off. The stuff is so cheap that this luxury is really affordable, and it keeps you on the safe side.
Good luck and best regards,
Taher
Gast
It's me again,
I forgot to mention that the simplest solution is a citric acid stop bath with an indicator, e.g. this one from our host, just for the sake of completeness...
Best regards,
Taher
cfb_de
Hi Heinrich,
1 litre of tap water, add one or two generous tablespoons of citric acid (so about 20g – I used to weigh it out, but I don’t anymore) and that’s it.
This is one bath where, as a chemist, I won’t get too fussy if the measurements aren’t exact. A slightly acidic solution is enough here.
After use, pour it down the toilet/sink/washbasin. Rinse after thirty minutes. Your wife will also be pleased with the reduced limescale build-up in the basins.
For films, use half the strength (0.5–1 tbsp) and that’ll do the job too. At a decent agricultural supplier, citric acid costs about twenty-five cents a kilo; at DM it’s a bit more expensive, but still cheaper than, say, some ready-made stop bath.
Best regards,
Franz
Gast
Hello everyone,
Thanks for the info – so 2% is enough. Good to know; I should have realised that myself, as I also use a 2% acetic acid solution.
Best regards,
Heinrich
