There are plenty of superstitions associated with them (it's bad luck to break them, they are portals to other worlds, and so on), but to say that they are "evil" I would personally say is incorrect. The item might have negative energy attached to it from a previous owner, but that can easily be taken care of.
Try cleansing it. Pass it through some incense smoke and visualize the smoke removing any energies or negativity attached to it. Say a chant, associated with your intent, as you pass it through the smoke if you think it'll help.