Bought it with a mirror in it, looks like a picture frame to me though. Any idea how old this might be, and what metal made of? A magnet sticks to it, but there are some spots turning green. There is a very faint stamping on the back that I have trouble seeing with a magnifying glass but it looks like N S B & something. Perhaps N S D & .... the s and the and symbol are very faint and I could be way off on those. Thanks for your input guys and gals!