Galvanic Palladium Chloride Solution

Francesco Curcio (msepa.fcurcio@ntt.it)
Sat, 28 Mar 1998 10:05:15 -0800

Some time ago I decided to try Palladium printing with Dick Sullivan's
recipe for Ziatype.
Looking for Palladium chloride (PdCl2) in Italy, I found it in two different
forms: as a 10% solution made for galvanic use by goldsmiths, reasonably priced (!)
at about $500 for 1 liter (=100g of PdCl2), or as an analitical grade
chemical (solid salt) at almost ten times that cost.
I bought the galvanic solution and asked the guy how he manufactured it.
He said the pure metal was dissolved in Aqua Regia (the mix of
Hydrochloric and Nitric acid that attacks noble metals),
then the acids were extracted (?) for the most part from the solution.

I use 23 ml of it to mix 25 ml of my "B" Ziatype solution (palladium
chloride+lithium chloride) and it seems to work, but with some trouble.
I get deep cold blacks on most papers I use, but never a really smooth
pale gray, my skies are often uneven and grainy. I also have a long
(an hour at least) clearing process to carry on, alternating citric acid
and sodium sulfite baths, to get rid of a stubborn yellow stain.

Yesterday I checked the pH of the Palladium chloride solution I bought,
and I was astonished when I read 0.3-0.4. I know that a Palladium
chloride salt can only be dissolved in a slightly acid solution,
but this looks like pure nitric or hydrochloric acid!

Now the questions, if the chemically knowledgeable members of this list
can help:
1) What should be the normal pH of a 10% Palladium chloride solution
intended for palladium printing?

2) Could such a low pH have caused the grain and clearing problems I am
experiencing and be dangerous for the print longevity?

3) Would it be possible to raise the pH adding, say, Calcium carbonate or
Sodium hydroxide and still use the solution?

Thanks for any advise you may give

Francesco Curcio
Milano Italy