A foam pumpkin is hollowed out, carved into a jack-o'-lantern, then cast with molten bronze. The foam pumpkin is encased in casting plaster (investment). Once hardened, the plaster is placed in a kiln to burn out the foam, creating a void for the bronze to flow into. I don't have much experience doing this type of casting so it came out a little rough. Turned out pretty cool though, despite the imperfections.
鈻讹笍 3Speak