I was pleased to pick this up. There are only a handful of examples (low single digits) reported. It's the 20-cent 1st Issue Foreign Exchange, Scott # R41c, with a major double transfer down the left side and across the bottom, with some of the doubling extending into left side of the portrait.
The cancel date is late enough and the paper color and consistency is such that it could be silk paper, but unfortunately there are no blue silk threads, so it cannot be considered silk paper. There's a bunch of debris on the face of the stamp; it could use a bath.
The image below is a 1600dpi image if you want to open it in a new window to see the details more clearly.
