That is correct, ours it tetra sodium.
As a note, let me say that clearing seems to be a very individual problem.
Clearing ability can vary according to local variables, paper and local
washing water are the two major ones. I once had a customer who did a long
and involved study of platinum printing, very scientific and I believe,
still unpacked since our move to Santa Fe. His study showed that EDTA was
one of the more effective clearing agents, but we've had many cases where
it was not. HCl is one of the most effective, but it has its downside in
that it appears to degrade the subtle highlights of pure pd prints, that
is, if you have any subtle highlights.
It is my guess that in some cases there are secondary compounds that are
formed during coating and development that are insoluble in one or more of
the clearing agents. Ferric acetate appears to be one of these, and it is
generated by the use of acetate developers that have small quantities of
free acetic acid. Normal darkroom fix or hypo will stain prints yellow,
probably due to the sulfur (sulphur to you Terry).
At the risk of bringing the whole List down upon my head, I will mention
that the very very best clearing agents are, postassium cyanide, very weak
hydrofluoric acid and sodium fluoride. Obviously not in combination as
deadly gas will be formed. I have had prints sent to me variously stained
and uncleared that I was able to salvage and clear up beautifully in one or
more of these compounds There is a material sold in auto parts stores
called Eagle (brand) Mag Wheel Cleaner that is very dilute hydrofuoric
acid, I have not tried it yet, but it should make a dandy clearing agent
for those ring-around-the-collar stains that are impossible to remove. (I'm
not sure if will cure yellow waxy build up, though.)
Ok, the enxt question is, "How can they sell hydrofuoric acid in auto parts
stores?"
As I understand it, you can sell anything in the U.S. that is less than 1
part in 1000. Any mavens on the List knwo the details of this?
Dick