Citric Acid - tell me the difference

[Larry]

I thinking about buying some Citric Acid bulk powder as a replacement stop bath and would like to know what is the difference between pharmaceutical & food quality grades.

My understanding from various google searches is that I need to mix 10g (1 desert spoon) of citric acid per litre instead of the usual acetric acid liquids @ 1+19. Therefore, is this tea/desert spoon size an optimum amount to mix? and can it also be used for RC paper as well as films.

Does citric acid come in different powdered strengths or is it a universal standard compound? Sorry chemistry is not my theme!

I've read about possible baterial growth forming in Nova tanks with citric acid but I alway use 1-shot and discard after use? so hopefully this shouldn't occur.

As I can't stand the smell of regular acetic acid (affects my asthma), I'm looking for less odour in my darkroom even with extractor fans and AC. In the past I used Fotospeed odourless stop bath chemistry which was very good but it's now very expensive for 5 litres of liquid.

Any advice would be most welcomed - many thanks.

[Mike O'Pray]

Larry I am no chemist either so there's the warning now:D. However I cannot think of anything that might be in food grade citric acid powder that is likely to affect it's use for photography and even if there was something that shortened the time before the "bugs" appear then a use and dump policy takes care of that.

I am still using what remains of my Ilford citric acid liquid and if the food grade powder is the same once mixed into a liquid then my experience is that bugs do eventually grow but it takes a week or two at least.

If you were to print several times a week I'd be tempted to leave it in the Nova slot and check how long it took before there was any sign of bugs.

No point in dumping it every night if it lasts say even a few days

Mike

[photomi7ch]

Thanks Larry for raising some good points. I have some citric acid waiting for when the bottled stop runs out. I had thought of using it as an emergence back up.

[peterlg]

I am using citric acid powder bought at the pharmacy, 18.5€/kg.
I mix it 20g/liter, have found that 20g equals four tea spoons with top.
It keeps at least one month in my NOVA slot processor without bugs or other creep appearing.
Peter

PS I don't use stop bath for film, only for paper

[Martin Aislabie]

The Citric Acid Stop Bath we buy from Ilford is :-

1) Much purer than the food grade stuff

2) Incorporates a pH dye to tell you when it is becoming exhausted.

3) Is buffered to retain its acidity over its working life.

However, if you want to try making your own, I would suggest you buy some indicator papers to sow the pH levels of your solution.

Stop Bath only wants to be slightly acidic - too strong and you might cause the emulsion to part company with the film base.

Don't try and store your own made up solution - chuck it away and start from fresh each day - the solution it will attract all sorts of undesirables.

Martin

[B&W Neil]

I use food grade citric acid in a lot of the alt processess I play with (it is often reccomended) and it is not kept when used as a bath. However, in a more concentrated form if keeps well and I use it at a few drops at a time to adjust the PH of various solutions. Buying / using food grade citric acid is the most cost effective way - especially in the large sized packs.

Neil.

[Leo Stehlik]

Same as Neil, I use mostly food grade citric acid - it does the job and costs very little ...

[NJHrs]

On the life of diluted Ilfostop question I had to dump my last pre-mixed 1 litre as it had little filaments growing in it. It was about 6 weeks old, my current bottle is now about 9 days old, stopped a really clean looking roll of Acros tonight done in Rodinal and still looks perfectly clear of filaments or bits floating in it. I have another 4 rolls of 120 to go so will just keep an eye on it. I am using brown 1 litre glass bottles by the way for my pre-mixed stop and fixer, I am also filtering both ways with paper coffee filters i.e. once out of bottle into jug and once again from jug back into bottle.

[NJHrs]

One other quick point, be careful with stale water used for mixing this stuff up. I also had to dump both a freshly mixed batch of stop and fixer recently that had bits in them as I spotted my big bag of filtered water had little bits floating in it. Now I am making sure I am never using water more than a handful of days old after its come out of the tap.

[Larry]

I did go ahead and ordered a tub from Amazon (very inexpensive) which arrived today and is labeled as suitable for pharm' and food grades usage.

It worked very well for my printing session this afternoon (Kentmere & Silverprint RC) in my Nova processor "1-min processing time". I mixed 10g (desert spoon) or 2x5g tea spoon size per litre. The compound desolves very quickly at 20C/68F - actually, it looks more like caster sugar it's so fine.

I will certainly be using this from now on instead of acetic acid as it makes the darkroom much fresher and pleasant. Did't realise how stinky regular stop bath was until you take it out of the equation.

Just wanted to share my thoughts having now tried it. Just wish I did this ages ago and realise I was probably paying over the odd's for branded liquids which probably contain more water than anything else.

Cheers

[B&W Neil]

Larry, good to hear that it has worked out well for you.

Don't worry about it going off in long storage; if it stored in an air tight tub / bag it keeps for a very long time. I usually buy it by the Kilo (food grade). Any form of citic acid disolves easily in room temp water.

Neil.

[Mike O'Pray]

I have just remembered,Larry, an occasional spoonful prevents scurvy or is that ascorbic acid? :D

Mike

[John King]

It is also used as a 'cutting' agent with certain Class A illegal substances!:wag:

[B&W Neil]

I have just remembered,Larry, an occasional spoonful prevents scurvy or is that ascorbic acid? :D

Mike

You could also eat a lorry load of oranges / lemons but your guts would complain :rolleyes:

Neil.