Silver Nitrate Turning Milky

UKJohn

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Hi,

This is a continuation of my on-going problems with the salt printing process, when I did this at uni I had very few problems but now at home I am coming across several, although my working methods and cleanliness have much improved. Anyway the problem is this:

On mixing the citric acid solution (6g per 50ml) with the silver nitrate solution (12g per 50ml), both using distilled/de-ionised water, the silver nitrate turns milky within a few minutes, when this is brushed on to the paper it leaves what appears to be chalky patches. When printed the paper has gaps/blank areas which look like the sensitiser is not reacting with the salt - i.e. it looks like silver nitrate reacting to light rather than silver chloride.

As I am pretty confident that the salting process is fine (done using distilled/de-ionised water) I tried using straight silver nitrate (no citric acid) and had a significant improvement, but did experience fogging in the unmasked border.

I have used citric acid in my recipe prior to this problem and have never noticed the silver nitrate turning milky. Thus I'm thinking can the citric acid go off whilst in its raw/granular state? Has anyone else experienced a similar problem?

Any comments, info or solutions would be appreciated.

Cheers

John
 

Photo Engineer

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Usually, when silver nitrate solution turns milky, the water can be found to contain a halide or something that interacts with silver to form a precipitate.

PE
 

smieglitz

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I'll echo PE's observation. Try a different water.

For our community darkroom, I routinely obtain water deionized through a reverse osmosis still in the Chemistry department at the college where I am employed. We had a weird episode trying to do some zone system calibration once and after pounding heads against the wall for a week or so I happened to have a conversation with one of the chemistry profs on a totally unrelated topic, how the week was going or something like that. She mentioned in passing that the deionizer was producing acidic water for some reason. We apparently got the water on one of the days the still was malfunctioning before anyone realized it was happening. I bought a gallon of steam-distilled water at a local grocery and voila, film development problem solved.

Similar to buying new dead batteries...

Joe
 
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UKJohn

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Guys,

Interesting comments, especially since the silver nitrate solution has been made up from the same distilled water that the citirc acid was made with hasn't turned milky. It's still ok and clear in its brown bottle, it only turns milky once the citric acid is added. Could the citric acid in its granular state be contaminated do you think? I have ordered a fresh batch and will also source some new distilled water.

Thanks for your comments

John
 

Loris Medici

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Totally silly question:
Will mixing Silver Nitrate with Citric Acid cause formation of Silver Citrate?

If yes, this is a highly insoluble (in water) compound (according the web search I did, maximum concentration is around 280ppm or in other words, 1 part per 3500 parts water) therefore it's normal to have precipitation.

If solution doesn't get cloudy when only Silver Nitrate was added + the same water was used for both Silver Nitrate and Citric Acid solutions, then this indicates:

a) Silver Citrate is forming
b) Citric Acid is contaminated

????
 

Loris Medici

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I found this in a web seach:

2AgNO3 +C6H8O7 ( citric acid) = 2Ag +C5H6O5 (32ketoglutaric acid) + 2HNO3 + CO2

It seems that citric acid causes formation of colloidal silver. This isn't something that you'd want to happen -> colloidal silver should be formed by the action of light, not in-vitro...

I'm not a chemist -> I may be quite off the mark...


 

JG Motamedi

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I believe that Loris is correct. In time (usually a day or two) silver nitrate solutions preserved with citric acid will drop a white precipitate--this is normal. I had always assumed this was simply the citric acid coming out of solution, but I think it probably more likly that silver citrate is somehow being formed.

I can't surmise why the mouse was assassinated, but can tell you that I found a household of cockroaches living in my 5 gallon still.
 
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UKJohn

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JG i have in the past when storing combined silver nitrate and citric acid solutions had a white precipitate on the bottom of the bottle, no matter how much I shuck the bottle I couldn't get it to go back into solution.

However, in this instance the silver nitrate turns milky within a few minutes, not days, so has the citric acid been contaminated do you think?
 

JG Motamedi

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I can't say for sure, but certainly is worth a try. Buy a bottle of distilled water and try that. If it doesn't work buy some new citric acid. If that doesn't work buy some new silver...

Your bottles, mixing sticks, graduated cylinders, et cetera are all spotless, right?
 
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UKJohn

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JG,

I certainly think so. Mixing sticks are all glass, brushes hake and dedicated to the process, mixing cylinders/jugs are glass all of which are wahed in distilled water, I even have trays dedicated to each stage of the process to eliminate cross contamination. At the moment everything seems to point to the citric acid so I have just ordered a new batch and some new brushes as well. Other than that I'm becoming very frustrated lol but I'm sure it will come good in the end.

John
 
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