Need Unusual Tool & Silver Test

I guess it is my turn to pose 2 questions: Does anyone know of a
source for a “disc” cutter that cuts triangles, squares, ovals, etc?
Certainly others have wanted this before, but I cannot find one.

Secondly, how do you test an item to determine if it is sterling
silver or silver plate? I found an unusual handmade-looking bowl in
a thrift shop that cleaned up beautifully like silver. I’d like to
add a half-round edge to it, but fear I’ll ruin it, if it is plated.
I look forward to any and all replies. Many thanks.

Sherry Terao, Silversmith in Silver Spring, MD/USA
Member of Art Peace