Ralph,
Some have suggested adding a splash of polysulfide toner to selenium toner in order to replace that undocumented absence of the sulfide ion that was supposed to give the original selenium toner it's exceptional archival properties. (Ref: an Image Permanence Institute, Rochester paper which I don't have in front of me at the moment)
Your statement: a mix of selenium/sulfide toner is not very stable and does not last very long raises a question...
Is the instability due to the sulfide itself, or due to non-sulfide components found in typical sulfide toners?
I've experimented a bit with adding 10 or 20 ml per liter of plain polysulfide toner to a 1+20 selenium toner.
The selenium toned color is slightly warmer (rather nice), but I have not noticed a reduction in toner activity.
Your thoughts?...
Reinhold
www.classicBWphoto.com