Melting Pewter on the Bunsen Burner phase change.

We melted pewter in a crucible over a bunsen burner in the classroom.
Notice how the outside of the lump seemed to be a skin filled with liquid metal that emptied out of the skin. this skin is oxidised pewter (tin oxide and antimony oxide)
Notice how when the pewter sets solid it looks like it goes frosty as the crystals form.