It's gotta be a sunburst flask, you might just be having trouble with the perspective, Bass! Here I outlined one bottom edge. Of course the number/thickness of sun rays and the bands on the edge differs depending on which variant it is, but the way they are oriented is some pretty good evidence. There are probably a lot more variants than the ones that we've included as examples, but yeah, with the bands and rays, and the other kinds of finds he was getting, it's just gotta be. Which one exactly, who knows...
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