A Hydrogen Peroxide Experiment And A Comment About PSE Certs

This is very educational -- thank you! On another forum, someone suggested a way that might remove the sulfur. Maybe you have some insight on this:

"Although sulfur is non volatile and non water soluble, it is soluble in toluene. Is there any chance that the note/stamp could withstand a toluene bath?"

The problem with toluene is that you might not be able to withstand it.
It is toxic, highly inflammable etc, etc. Its sale is prohibited in Europe (in concentrations higher than 0.1%), probably also in the States. Definitely not something I'd play with. I do not know what a solution would do to paper (it does heavily attack gum, though). It does smell rather pleasant which doesn't help either.

It's available in the US and only moderately challenging for the average consumer to find. Formerly it was a key ingredient in plastic model cement, and those products would dissolve and make many printed inks run. For model builders that would be experienced if they accidentally got cement on a printed sign for a model building. So my concern is less with toxicity and more with the likelihood of ruining a printed stamp design by dissolving the ink. You'd need to test toluene on a cheap sulfurized stamp that's OK to destroy … while wearing a respirator and working outdoors.

I think, from these last posts, toluene is something to be avoided with extreme prejudice.