My understand and experience is that the double metal salt Na2PdCl4 is
very hydroscopic, in fact so much that weighing it will show an increase
in weight due to absorbed moisture until it becomes mud. Unless this
material can be stored and handled without exposure to moisture, it is
too difficult to use consistently. PdCl2, even if it might be slightly
hydroscopic, has never presented any problem. I have some old crystal
which is still dry and seems to work the same, no noted differences in
prints and no noted precipitate (metal?). But it would be informative
to hear what a chemist at Engelhard might say.
As to the quality of the salt used, although table salt can be use for
NaCl2, keep in mind the price of PdCl2. It might be well worth the
small additional cost and will provide certain consistency to buy
reagent grade salts. And do keep in mind the color issue Eric mentions.
I prefer the potassium and litium salts and rarely use the sodium
because of color preferences.
When using a palladium solution, it is critical to check if the material
is completely dissolved under the conditions it is being used at the
time of mixing the coating solution. If not dissolved, warm the
solution by placing the solution bottle in a hot water bath until it is
warm enough that all is dissolved. Once mixed with the sensitizer, the
palladium solution should be dilute enough that all will stay in
solution. It is NOT recommended to warm sensitizer solutions beyond
that of a typical working area. However if warming is needed warm only
the amount to be used and no higher than 140F (even this may cause
harm.) When making the sensitizer solution, it is typical to take 24 to
48 hours for all to go into solution, do not heat.
—
Jeffrey D. Mathias