Regarding: using a lid
I've come across some guys that say they've put a lid on to speed up the melt. I've done quite a few melts. This past summer an unexpected storm kicked up so I wanted to rush things along. I added the remaining ww's to an already molten one third potful and put the lid on. This is the first time I've done that (put a lid on). I'm guessing some zinc was at the bottom right on top of the already molted batch and trapping the heat with the lid was just too much. Well I've got eight 5 pounders stamped "Z". I won't use a lid again.
Just my .02 worth.
Good luck with your casting. It's not as hard as it sounds. It's not as easy as it sounds.