Custom-molded and stenciled holiday trivet

This was my first time working with molding medium - I know I could have made a mold with lots more detail, but I decided to keep it simple. To make this trivet, I filled the mold with PermaStone plaster - it comes out really nice and smooth like stone. Can you guess what I used to mold this perfectly round shape? My full tutorial is over on the Activa blog, check it out!