For the Ring of Spell Knowledge, it says that you must encounter a written, active, or cast version of a spell.
So how does one determine if an active spell can be added to a ring of spell knowledge.
Take for example the spell barkskin. It exists both on the summoner spell list, and on the druids.
If you encounter a person who chugged a potion of barkskin and now has the spell active on themselves can you add it to your ring of spell knowledge?
Is barkskin arcane?
If so then I would say with the proper spellcraft check this should work.
There is an arcane version and a divine version, but as far as I know there is no way to tell the difference between the two once the spell is cast.
Detect Magic does not tell you if a spell is arcane or divine, not is there a difference in spell level between the two.
Well... hmm... I dunno. I guess I'd probably, as the GM, make some percentile ruling on how likely the potion was created by a divine vs arcane spellcaster and if it was created by an arcane spellcaster, then you could learn it, but not if it was divine.
Or I dunno, I'd probably just say "heck, if that's the single spell you want in your ring, make your spellcraft check and you got it."
The ring seems to indicate that it needs to store an arcane spell, but doesn't say that the spell needs to be arcane when you encounter it. Of course the arcane only is only strongly implied.
Could a wizard learn continual flame from a scroll that was made by a cleric?
If so couldn't a the ring be taught continual flame from a scroll made from a cleric, or a potion made by a druid?