Yes, it is a broken piece. I live in an old 19th century stone schoolhouse and found the old "dump" way in the back and have been digging up old china and glass. I've found some with identifying marks and much is from late 1800's to early 1900's.
I don't know much about blue willow and most of the blue willow I am finding is in tiny pieces so I was thrilled to find this cup bottom.
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