I was happily casting some 30 cal, 185gr boolits this weekend, and I was interrupted by the arrival of the wife with a car full of groceries. No problem. Wash hands, hump bags from car to house, put groceries where they belong, back to casting. Total time away from casting - about 15 minutes.
When I get back to the pot, there is an interesting mix of junk floating on the surface. Part of it is a greenish/yellowish colored substance that looks like dirt. There is also some dark red looking substance that has formed a crust on the top of the pot.
I skimmed this off and continued to cast.
What is this stuff? Is it impurities that finally had enough undisturbed time to float to the top, or is it an oxidized metal that is no longer in my alloy?