[alt-photo] Re: dilution of pt/pd - weak black from B&S

[Marek Matusz]

I wonder in general addition of nitric acid or even ferric nitrate would help with stability and life of ferric oxalate. The reason is that my ferric oxalate made from ferric nitrate and definitely containing residual nitric acid seems to be keeping for a very long time. Even in solution seems to be stable for months. Nitric acid would definitely bring the pH down and it is also an oxidizer and might prevent spontaneous reduction of iron (III) to iron (II) keeping iron in the proper oxidation state.

 

Marek
 
> From: ejnphoto at sbcglobal.net
> To: alt-photo-process-list at lists.altphotolist.org
> Date: Sat, 24 Jul 2010 09:41:07 -0500
> Subject: [alt-photo] Re: dilution of pt/pd - weak black from B&S
> 
> It may very well be that not enough time was given to the FO solution to get
> completely dissolved, it may be that the addition of the acid, allowed for
> it to complete the process. How soon after mixing did you try and use the
> solution of FO? 
> 
> Eric Neilsen
> Eric Neilsen Photography
> 4101 Commerce Street, Suite 9
> Dallas, TX 75226
> 
> www.ericneilsenphotography.com
> skype me with ejprinter
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> Let's Talk Photography
> 
> 
> 
> 
> > I had one student who bought some pure ferric oxalate from B & S, good
> stuff, nothing wrong with it, but it did not produce good platinum prints in
> the same way as the ferric oxalate as we had made in class without using
> molar solutions. The problem was solved by adding oxalic acid to the B & S
> solutions. unsurprisingly,we deduced that the ph of the dilution had to be
> more acid. From other experience we also deduced that he it needed to be an
> organic acid. Why should that be ? 
> 
> 
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