This is a strange non-glass piece I got from an eBay seller in the Ukraine. It is not porcelain, not Bakelite or any other composition I have ever seen. I will rub off black on your fingers when handling the insulator. Any ideas what it might be made of? See the next pic for a view of the base. I also noticed recently that it is THREADLESS as well! Consensus seems to be that it is made of some kind of clay material.