Thread: Bullet casting- something strange to me is happening

Borrowed this explanation from the Cast Boolit Website
That blue is lead oxide ,normally happens to pure lead but can happen if you've got lead too hot and your tin and antimony has been skimmed off as dross . When lead is heated far past it's melting point, it begins to oxidize. The thickness of the oxide layer determines the color. It is exactly the same as the yellow/orange/blue/purple oil or gasoline sheen on water-- the thickness of the oil layer determines the color reflected back at the viewer. If you watch the overheated lead, the color of the dross will slowly change and ultimately become purplish and then black. The chemical composition hasn't changed, but the thickness of the layer is increasing, and thus the gradual color change.