I want to learn about casting

[fredj338]

Agree, surface sludge is likely just dros that needs skimming. If shiny alloy below, you are probably fine. As noted, when melting scrap anything, keep it below 730deg so zinc floats out.

[kevin c]

Be careful with the muriatic acid. I'm not just talking about PPE and holes eaten into your jeans, but also problems where you test and where you store the acid afterwards. Even tightly capped in the original container, once opened with the seal broken enough fumes can escape to corrode nearby metal, and with acid in a open container the same will happen much faster and worse to, say, tools on a pegboard above your work bench. A month plus later after acid testing alloys for zinc, I'm still finding badly rusted equipment.

ETA: Harbor Freight sells letter punches that can be used to mark lead ingots. You can do words and multi digit numbers by duct taping stamps together, though I find that getting an even impression of all the stamps is a bit tricky. Worthwhile for me; I have enough lead of different types that explicit markings back up the unsure memory of the content of ingots put up years back.