I'm quite amazed by the experience indicated by most replies in this thread. I don't know what I am doing that's different, but my selenium toner diluted 1+9 lasts only 2 or 3 printing sessions (in total about 16 prints size 20x16) even though stored in abottle between sessions. On starting the second session, I find it has a heavy black precipitate and is often a murky grey colour with suspended sediment. If I filter it out of the bottle the suspended sediment clogs up even a Paterson filter.

Any thoughts?