Thanks Rock
I like that theory. I have pottery from Ohio that sinks straight to the bottom and is grit tempered. Some thin pottery is a bit more buoyant. This one sinks as well. On this piece, a fingernail test proves that some of the surface grit can be removed and will scratch the surface of the piece. After soaking it, the red color starts to remove, leaving a black color underneath. In my area, we have Langford, oneota and woodland traditions. the woodland pieces found here contain small lines that imply fingernail impressed-similar to this one.
An eye loop shows a lot more detail than pictures but will go w/pottery but the world may never know