Hello Deserdog> Welcome
As for the question about used spark plugs> I have some knowledge from both sides on this subject>
It's my understanding the PT is a coating on the electrode of the plug
Now asuming your around auto's you know the little piece that I'm refering to.
1) processing them would take some time, as one would need to break away the tips and disgard the rest.
2) one would need LOTS!!!!! to even make the effort of time and processing worth while
3) Most of the time the plugs are run so long in an engine theres nothing left of the coating
So basically unless one could collect fairly Newer plugs and tons of electrodes they may find more to recover in other places.
ie, some potentiometers, reostats etc also have PM's.
Just my Two cents
JIM