One could probably get nickel to precipitate from a salt and perhaps
keyed to a light sensitive material such as ferric oxalate. However, I
believe the reason that the technology emerged around platinum and
palladium is that these are Nobel metals. They have a
characteristically stable nature; that is they have a tendency to
resist corrosion. Remember that William Willis was designing an
archival image process. Metals such as silver, nickel, copper,
chromium, and others are not noble metals. Metals such as gold and
iridium are. Isn't it interesting that the more costly metals are Nobel
metals. Anyway, out of all, platinum is the most Nobel (if it can be so
coined). Another way to look at this may be that you get what you pay
for.
Another interesting question for the chemists out there is if any other
salts would work. When I mix the palladium solution, I use KCl instead
of NaCl because the Na in combination with heat causes the K2PtCl4 to
convert into K2PtCl6 resulting in black specks in the print. (I use
both platinum and palladium together.) If you would like formulas
E-mail me direct at jeffrey.d.mathias@worldnet.att.net. A word of
caution is that some other salts may be hazardous to work with. An
interesting ion used with the platinum process, that I've read about in
old literature on the subject, is ammonia, although I have never worked
with this nor seen any results.
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