Its porcelain or in the hobby we call it mud. Porcelain is one of the materials they used to phase out glass. They were used on everything from telephone lines to high voltage applications. Alot of the shapes and sizes mirror the shapes and sizes of the glass they were replacing
Thank you so much for the info. I had no idea it was that old. I was thinking like maybe 1960s.Ah, thanks for the new photos - that's a big help! From the look of it, I believe it's a pretty old unmarked piece from about 1905-19010, maybe Victor or Lima but I'd want to see it in person before hazarding a guess. It's quite a bit older than most porcelain insulators you'll run across. This style would have been used for low voltage domestic power distribution. If you're interested in value, the lack of a marking and the inner skirt chip makes it less desirable to collectors, perhaps 5.00 or so.