Oddly, one time I was playing BD, equipped a 'Bone Spear' ring sometime in act 1, and later on in act 2 I found the character I equipped it on (who also had a nice sword equipped) was not doing Slashing damage, but was instead doing Bone damage!
No idea how you change from doing the Slashing of the sword (or any other weapon) to the Bone damage of that ring intentionally, though, as that character of mine definitely was NOT doing Bone damage for many fights right after equipping that ring. (and unfortunately, by the time he started using Bone rather than Slashing, he had a sword so much better that he'd be better off using Slashing. I promptly unequipped the Bone Spear ringy and he started Slashing instead of using Bone again)