Mold.
To answer your question, Nathan, this mold is for a sculpture piece I’m working on. SU’s sculpture department just put on their annual iron pour, and I jumped at the chance to get in on it.
Here’s someone’s flickr photo set from last year to give you an idea of the process. I left my iPhone in the car during the pour to avoid melting issues.
Anyway, it’s a pretty amazing experience. More photos to come of the piece.