Bone in vinegar

This is aquired by using certain one-time drop bones with a pot of vinegar during and after the Rag and Bone Man quest. Whichever kind of bone it is, it'll still look the same, but the examine will be different, for example:
 * There is a cave goblin skull in here.
 * There is a seagull wing in here.
 * There is a ghoul bone in here.