# Got brownish precipitate from palladium nitrate



## photographer (Oct 12, 2019)

I'm doing photo printing with palladium. The idea is to print an image in the paper with silver, and then treat it with a palladium salt solution, so the palladium oxidizes the silver and replaces it, "toning" the image. I tried doing this with a .1% w/v palladium nitrate solution, but it seems to precipitate all over the paper before getting to the silver: 

This happens whether or not there's silver on the paper. This is the paper I'm using: https://www.hahnemuehle.com/fileadm.../datenblaetter_dfa/Data-sheet-PlatinumRag.pdf

Does anyone have an idea of what it's reacting with or what the precipitate is?


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## Lino1406 (Oct 12, 2019)

Please state what kind of paper, how "printing with silver" is performed


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## photographer (Oct 13, 2019)

This is the paper: https://www.hahnemuehle.com/fileadm.../datenblaetter_dfa/Data-sheet-PlatinumRag.pdf

The printing works by coating the paper with silver sulfamate, ammonium iron (III) citrate, and a little bit of surfactant. The paper is then dried, and exposed to UV through the negative. The UV causes the iron to be reduced to 2+ by the citrate, which reduces the silver to metal.
The paper is rinsed in deionized water to remove the excess silver salt, then in disodium EDTA which removes some of the iron, then in sodium sulfite and sodium metabisulfite which reduces the remaining iron to dissolve it, then 20 minutes in tap water. After that I put the palladium nitrate on it.


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## Lino1406 (Oct 14, 2019)

My immediate suspect is Fe2O3 from Fe ions and NO3- ions. But all other components can participate, including the cotton paper. To know exactly I'd suggest to do a series of elimination tests, meaning doing the whole procedure without one of the components


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## photographer (Oct 14, 2019)

*EDIT: This seems to be wrong; see below.*

Well, I feel a bit silly now. It's not any of the other ingredients causing the palladium to precipitate, it's actually my tap water. I tried adding tap water dropwise to 50 drops of the 0.1% (4.34mM) Pd(NO3)2 and after about 60-70 drops it all precipitated out (although the pH stayed around 2). I'll try the process again with only deionized water and see what happens.


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## photographer (Oct 18, 2019)

It wasn't the tap water. I stored it in a glass bottle at 5% w/v in deionized water for a few weeks, and when I looked yesterday it had all precipitated out, leaving brown powder in a clear solution. At this point I'm at a loss as to the cause.


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