How would one make a non-toxic pen out of osmium?
Osmium alloys with many metals, so it could be covered by an alloy. Osmiridium, an alloy with iridium, is even harder than pure osmium.

It would seem possible to dip the osmium pen blank in an iridium or osmiridium bath (at rather high temperature) to produce a long-lasting casing, rather like dipped chocolate cordials.

If you accept this answer, I'd be glad to receive an award of one of these pens. ;-)