Plain Sodium Sulphite as a paper printing stop bath?

koraks said:

They're not circumventing regulations. There's no regulation in effect that prohibits sale of citric acid to individuals in Belgium. You were either misinformed by the shops you contacted, or there was some kind of misunderstanding in the communication between you and the stores you contacted. Hence my question which specific legislation they referred to - a question which remained unanswered, and probably will, because there is none.

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After a some searching, I finally found the Royal Decree of June 11th 2004 regulating the use of Citric Acid in food and the sale as a food supplement, and I can understand the misinterpretation of certain vendors (and myself) now...

koraks said:

Either way, nice that you've found some. There are of course many more options. For instance, di.be (I understand Di is a big drugstore chain in BE) has this: https://www.di.be/nl/the-fabulous-citroenzuur-2191053
Or via Bilsen: https://www.dbilsen.be/nl/citroenzuur-1kg.html
The stuff is literally everywhere, which is sensible since it's such a common and relatively benign/harmless material, not subject to any legislation (apart from proper labeling)...

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Philippe-Georges said:

........

And I have a pod of Sodium Metabisulfite I use for mixing Pyrocat-HD, next session I will mix 2,5% for a stop bath.
I now have to find out how long that one will last, perhaps by checking the pH but my (old-) pH meter isn't working anymore. But I read somewhere that there is an easy to find product used for swimming pools: something with '******red' in the name but can't recall exactly...
I will have a look at a DIY shop.

Anyway, thank you all for your answers and concern!

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Solution of metabisulphite will smell of SO2 which is not good for your nose. I use around 5% solution of it with pH adjusted up to around 5.5 to 6 with sodium hydroxide. I use a Nova slot processor so the surface area is small leading to minimal odour. At this pH it smells less. The pH stays reasonably constant in a printing session. Ryuji Suzuki wrote that very acidic stop bath is not optimal for FB paper. I think that this stop bath is compatible with my almost neutral fixer.

Philippe-Georges said:

the Royal Decree of June 11th 2004 regulating the use of Citric Acid in food and the sale as a food supplement, and I can understand the misinterpretation of certain vendors (and myself) now...

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I found that, too, but I could not imagine that anyone would manage to interpret that as a ban on the sale of citric acid. That decree is specifically about sherbet and the only mention of citric acid is in the context of "citric acid-equivalent" acids that can be present in a certain amount in fruit-based sherbet products especially if the fruit content is below a certain percentage. It doesn't deal with citric acid as such, or the sale of citric acid as an ingredient in products, let alone as a standalone product.

I'm sure the misunderstanding must stem from something else; this really can't be it. Even a very casual and uninformed reader cannot possibly mistake this directive as a ban on citric acid sales. It's just too far-fetched.

I suspect that the retailers you contacted may have told you something along the lines of "we cannot ship this product to your address" due to logistical constraints; e.g. they might not have been willing to ship a small quantity abroad, maybe you were inquiring into a product bundle that included citric acid but also other, controlled, substances, or perhaps they mistook your inquiry for something else than the simple purchase of something from their shop, e.g. as a request for the suitability of their products for photographic purposes.

Either way, rest assured that you can buy as much citric acid as you want.

john_s said:

Ryuji Suzuki wrote that very acidic stop bath is not optimal for FB paper. I think that this stop bath is compatible with my almost neutral fixer.

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FB paper tends to wash out better at a higher pH because it softens the sizing and gelatin layer, making the entire paper fabric more easily permeable by water. If you use a wash aid like sodium sulfite or even sodium carbonate after fixing, it doesn't really matter if preceding baths (fixer and/or stop bath) were very acidic. There's really no need to be overly cautious in terms of stop bath pH when handling FB papers. The main reason to prevent very low pH is as said to limit SO2 formation, which can be irritating to some users. That's all.

Your rather high pH can be problematic in terms of fogging if you use metol-based developers (e.g. D72 and many others), especially if you turn on the white lights until the print is entirely fixed. It won't matter much if you work under safelight conditions throughout fixing and preliminary washing.

The main thing is to think through your process and pay attention to the interaction of different variables. All too often I read/hear about crass generalizations about relatively minor details that in isolation of other process parameters aren't really reliable.

Anyway it is of lesser importance, I have found what I need and all that (mis-) interpretation is a after all a waste of time, i am preparing a nice printing session now!

That's right, good that you've apparently solved the issue - that's what really matters! I hope the problem stays away now!

And it is also good that people who visit our site from Belgium have some clarity about the status of citric acid there.

koraks said:

FB paper tends to wash out better at a higher pH because it softens the sizing and gelatin layer, making the entire paper fabric more easily permeable by water. If you use a wash aid like sodium sulfite or even sodium carbonate after fixing, it doesn't really matter if preceding baths (fixer and/or stop bath) were very acidic. There's really no need to be overly cautious in terms of stop bath pH when handling FB papers. The main reason to prevent very low pH is as said to limit SO2 formation, which can be irritating to some users. That's all.
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One function is to stop development and the acid does that. Another function of stop bath is to rinse out of the FB paper some developer as early as possible. It might not always be very important, but I use a fairly concentrated developer (normal strength ID-78) and I like the idea of having some of it at least washing out as soon as possible after the development. Maybe it's more important if one's fixer is not very acid, my choice for efficient washing. I do use a sulphite wash aid. We have tons of water here at the moment but it's not always the way it is.