HH has made a very good point. Whatever metal you use, ie: pewter, high speed babbit, or tin, do not overheat the metal. If you do, the wood will char excessively, give off gases as it does, and cause bubbles in your pour. I think tin stays clean and shiny the longest. Babbit and pewter darken and go dull and grey much more quickly. But that's not a bad thing.