It just sits there and burns. Even worse are zinc and lead. Another thing to watch for is the fact that liquid aluminum is very reactive. If you drop a wrench in the pot, when you fish it out, it looks as if it's been dipped in acid. Literally eaten away.
Cleanliness is essential in working with aluminum.
Aluminum oxide is what some grinding wheels are made of. So a film of lapping compound settles on all the moving parts of the machine itself to say nothing of the operator. The dross formed on the crucible is nasty stuff too. You need to develop a technique of getting a ladle of liquid aluminum without getting any dross. I don't know exactly what your process is but if you have any specific questions, please feel free to ask.