How Do Baking Soda or Ammonium Hydroxide Help maintain a Silver Bath?

I'm maintaining my silver nitrate bath for wet plate collodion and have read that some practitioners, like Quinn Jacobson, use baking soda (sodium bicarbonate) or ammonium hydroxide during cleaning. I understand that the standard method involves UV sunning and filtering, but I'm curious about the specific role these chemicals play in maintenance:

1. What exactly does baking soda do in the silver bath? Does it help precipitate iodides or bromides by changing the pH?
2. How does ammonium hydroxide compare? What role does it play in maintaining the bath?
3. What are the advantages of using these chemicals over just sunning and filtering?
4. In my experience, I have used both baking soda and ammonium hydroxide for heavy maintenance. However, baking soda creates many precipitates, while ammonium hydroxide seems easier and results in less silver wastage. What’s your opinion on this?

For context, my bath turned cloudy after I added distilled water, and I suspect that iodides or bromides may have precipitated out. I used the same distilled water for a new silver bath, and there was no cloudiness, so I don't think the water is the issue.

I’m hoping to deepen my understanding before experimenting with these methods, so any insights or references would be greatly appreciated!


I really appreciate any help you can provide.

Both baking soda and ammonia will increase pH. I think the idea behind this, apart from 'recovering' the bath from too low a pH, is that the halide salts (iodide & bromide salts) dissolve easier at a low pH and this, in order to get rid of them, you'd have to raise the pH so they can precipitate out. Sunning helps the volatile compounds (alcohol and ether) to evaporate. In terms of pH, there's not a whole lot of difference between using bicarbonate or ammonia since both will raise pH. However, silver ions end to want to form salts and not all of those are soluble, which can result in loss of silver through precipitation. To an extent, this can often be countered by adding an acid (esp. nitric acid), but it becomes kind of a tricky balancing act of maintaining the right pH.

D_Quinn said:

before experimenting with these methods

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My suggestion would be: don't. Most practitioners will tell you that there's no need to muck about with your silver bath too much, and as far as I can tell, they're right. Periodically sun the bath. Filter it if there's stuff floating around in it. Maybe check pH and adjust it slightly if you want to keep it in a specific bandwidth, although plenty of wet plate photographers don't even do this. I would not recommend boiling the bath, adding carbonates, hydroxides etc. in attempts to 'clean' the silver bath unless it's absolutely necessary (i.e. the silver bath has gone hopelessly ineffective and is basically beyond recovery to begin with).

It's very easy to destroy a silver bath this way, which is an expensive exercise. Been there, done that.

D_Quinn said:

my bath turned cloudy after I added distilled water, and I suspect that iodides or bromides may have precipitated out. I used the same distilled water for a new silver bath, and there was no cloudiness, so I don't think the water is the issue.

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Distilled or demineralized water? There's a big difference, especially in this context. Demineralized water (which is what's usually sold in supermarkets etc. for household purposes) can be loaded with chloride ions as a result of ion exchange processes used in demineralization. It's actually quite common to see demineralized water being sold under the name 'distilled', even if it's not actually distilled water. Note that the formation of silver chloride depends on pH to an extent; at neutral pH, this will readily form, but in a solution acidified with e.g. nitric acid, this cloudiness may not form. So the fact that you saw cloudiness in one instance and not another in itself doesn't say much about where it came from.
Also keep in mind that adding water to an already watery solution that contains some halides, will not cause halides to precipitate out. So the most likely cause of the cloudiness you saw really was the formation of silver chloride due to the presence of chloride ions in the water. Apparently the bath you added the water to was not very acidic at that point; is this correct?

If it ain't broken, don't fix it!

@koraks
Thanks!!
That makes a lot of sense.

You're right — the bath wasn't very acidic at the time; I measured the pH to be around 5.

However, I don’t think the cloudiness was caused by chloride ions in the water. The purified water I used had the following specifications:

• Produced using an ultrapure water system
• Treated with reverse osmosis (RO), ion exchange, and ultrafiltration membranes to remove ionic substances, organic matter, particles, and microorganisms as much as possible
• Also sterilized with UV light

Given that level of purification, I believe the chloride content should be negligible, and likely not the cause of the precipitation.

Yes, that should be very pure water. Assuming it has not been contaminated since you obtained it, e.g. by pouring it over into another bottle/vessel that wasn't entirely clean.

From the chemical standpoint....be very careful when you use ammonia-solution with silver nitrate solution.
You can in the worst case get silver nitride https://en.wikipedia.org/wiki/Silver_nitride#Hazards which is very sensitive.

bj68

BJ68 said:

You can in the worst case get silver nitride https://en.wikipedia.org/wiki/Silver_nitride#Hazards which is very sensitive.

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In a watery solution this is not a problem. It can become a problem if the solution is boiled down into a sludge or even a dry cake. One more reason to not boil silver baths.

Thanks for your comments! I don’t plan to boil my silver bath. I’m aware that some sources recommend boiling it, but I’d rather be safe than sorry.

koraks said:

In a watery solution this is not a problem. It can become a problem if the solution is boiled down into a sludge or even a dry cake. One more reason to not boil silver baths.

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Yes and no....No, because normally you do not get the necessary concentrations in your silver nitrate bath with ammonia, but definitely yes, because even evaporation is enough for this problem e.g. if the waste evaporates.
In analytical chemistry, it´s used as Tollens' reagent and there are some reports of explosions see https://pubsapp.acs.org/cen/safety/19960108.html or https://eric.ed.gov/?id=EJ278495

Half OT: Silver nitrate and ethanol is a bad idea, too see Reference 3 in https://pubs.acs.org/doi/epdf/10.1021/ed047p741?ref=article_openPDF


bj68

BJ68 said:

even evaporation is enough for this problem

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But you never in practice get a silver bath to evaporate down to that level. There's a difference between a few ml of Tollens reagent being left in a test tube on a desk for a couple of days vs. a 500-2000ml silver bath that's generally kept under a lid when it's not being used, and that's generally in a (very) acidic condition if it's in active use to begin with.
Sure, if you were to leave a silver bath that's heavily loaded with ammonia (for whatever reason) to sit out there, open to the air, for days or weeks...but I don't see any realistic scenario in which this would happen.

BJ68 said:

Half OT: Silver nitrate and ethanol is a bad idea, too see Reference 3 in https://pubs.acs.org/doi/epdf/10.1021/ed047p741?ref=article_openPDF

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Not sure what this is about and the article isn't open access, apparently. I've never heard of anyone dumping large amounts of ethanol into a silver bath.

Look, at a theoretical level, there are all manner of hazards that in practice, fortunately just don't manifest. It's evidently a good idea to be careful with a silver bath; the main risks involved are nasty stains and damage to e.g. eye due to inadvertent splashing.

Okay....had my own experience with silver nitride...was set up under water as loud noise...luckily only a small amount without big disaster. So I am a little bit (to = zu in German) sensitive to that topic.....

For the second link see https://sci-hub.se/https://pubs.acs.org/doi/epdf/10.1021/ed047p741?ref=article_openPDF which should now work...

Made some silver nitrate 2018 see (in German): https://illumina-chemie.org/viewtopic.php?p=71147#p71147
and one cleaning method is recrystallization from hot water.
According to the above paper, to get the rest of water out you should use isopropanol, because washing with ethanol, can form silver fulminate, which is very shock sensitive.

bj68

BJ68 said:

Made some silver nitrate

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In general, I wouldn't recommend on a photography forum that people manufacture their own silver nitrate, and indeed, whenever the question comes up, people post cautionary comments along these lines. I understand you're well-versed in chemistry and amply aware of the risks involved, but the average darkroom worker isn't. So I understand that you're trying to caution against certain practices, but I feel that in a thread that's primarily about relatively simple 'maintenance' of a wet plate silver bath, it stretches a little far to start discussing risks in specific routes of silver nitrate synthesis. Btw, nice job on the synthesis and its documentation! Have you used this silver nitrate for photographic purposes as well? It looks pretty clean alright.

You are right...sorry for the off topic...

I haven´t it used for photography....and in the last picture, you see a little bit metallic silver, which was deposited in the process of melting, perhaps I got some dust in in it....

Reason for this trial was, that 2018 the "REGULATION (EU) 2019/1148" was in prearrangement in Germany and there was the possibility that "nitric acid" would be restricted to 10% for private use, so that could be a way to circumvent this restrictions (The tests with hydrogen peroxide where omitted). They restricted it (nitric acid) now to 3%, so you can forget it completely see https://de.wikipedia.org/wiki/Ausgangsstoffgesetz

Merde.....


bj68