What commercially available material can withstand 4500�F?

My friend has started his own forge (with wood, no less...) and he needs something to keep the heat from setting the wood on fire. I don't question his process because I know nothing about forges and I'm sure he's at least looked into them a little. He asked me recently if I knew of a place to get a crucible that could withstand 4500�F. Crucibles are mainly used for chemistry, and his forge is about 1.5ft x 1.5ft, so I doubt there are any crucibles that large. Are there any suggestions for my friend?