Hi Guys,
Thanks for your comments,
Mike I do use die castings in my melt together with 50% drawn aluminium, and have found that gives me a good casting that machines well, but your theory could be an explanation.
VT, I use table salt as a flux, and sodium carbonate to de gas the melt. There was a heavy crust of around
25mm on the melt, which would account for the powder coating.
I am now wondering if any aluminium look alike small bits of scrap with a much lower melting point may have entered the melt, for example pewter.
The mystery continues.
Cheers David