Lye won't do anything to enamel but etch it. Electrolysis, at the level used by hobbyists, doesn't seem to put much of a dent in it, either. Sandblasting could remove it, but at the expense of changing the patina of the metal underneath. In other words, it can't selectively remove enamel without altering the metal surface in the process. There are reports of using hand tools to meticulously work the compromised enamel off, but that sounds rather tedious.