Hi all, I found this today while detecting. It’s a porcelain disk with a copper insert that is slightly concave. The insert has a design of a crescent moon on it. Thanks josh
On first glance and before I read your description of a copper insert I also thought part of a canning jar lid. Now that I seen it with that knob on the center I'll go with cold cream jar lid.
Lmaoooo I had to google 'is porcelain a metal' to figure out why a detector would hit on this. I guess some contain traces of aluminum and whatnot. Neat!