How can I clean up dross from my casting metal?

Ammonium chloride helps precipitate out the dross and clean up the metal for casting. Dross consists of impurities in the metal such as the oxide film that develops on the surface of molten pewter where it contacts the air. The impurities will float to the top of the metal where they can be skimmed off with a strainer.

This can be purchased at most chemical supply stores.