What ever it is it seems to be doing a pretty slick job. Looked like a nice surface finish. If it was cast iron, I would imagine the molds needing to be preheated.
It's a beauty. And it seals really well too. No flash at the seam between the two dies. I have piles and piles of aluminum chips and would love to try my hand at aluminum casting. And this guy seems to be doing it right.
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