Lost foam casting in a process in which a foam model is made then buried in sand. As molten metal is poured it burns off the foam and fills that void with metal. It’s a fairly simple take on sand casting but like anything, the nicer your foam models looks the nicer your cast piece will come out.
And here’s a plaque being cast in bronze using the same process. This gentleman touches on some other points in the process like sand preparation, etc. His finished product comes out really good and it seems like the care taken in the preparation of his mold makes a big difference.