Found this broken piece in the creek bank. Southwest Pennsylvania. Farmhouse was built in 1922. Coalmining country.

Would have been about 18" in diameter. There is a rough coating in the glaze on the inside and outside of the bowl section. Abrasive enough that I figure it served a mechanical purpose. There are three grooves on the rim that aren't symmetrical to each other.

There might be a makers mark in the center of the glaze inside but I can't make it out. There is also a light blue/green stain on the bottom that might be a mark.

Any ideas?