If zinc was in the lead.

[cs86]

I've read that even a little zinc in your lead will cause problems, and that a good indication that you have some zinc in your lead is that it curdles on top. I'm wondering if you do have a bit of zinc in your lead, what problems occur when casting?

The reason I ask is because I thought the other day that I had a little curdling at the top but wasn't sure if it was still melting down from the half pot I left in there or if I did have some zinc in that batch. Everything seemed to cast fine though. The molds filled out and boolits looked fine.

[H.Callahan]

If I recall correctly, one can have a little zinc in the mix without issue. Talking about somewhere in the .5-1% range. If your boolits looked fine, I suspect that you don't have a problem, either a miniscule amount of zinc or your "still melting down" scenario.

[fredj338]

If it flows & casts then you are fine. if not, then you may be able to flux it out. I had some zinc mixed into 15# blocks a friend gave me. Turned to mush as soon as I added it to my 40# Magma. What a mess. It wouldn't flow, even @ 850deg. So I fluxed several times w/ sawdust & then ladled half out & added more range scrap to get things going again.

[I'll Make Mine]

As long as the zinc is dissolved in the alloy, and the melt temperature is high enough to keep it that way, there's no real problem with zinc; it'll just make the alloy a little harder and very slightly less dense (i.e boolits will come out barely lighter). The problem is that only about 2% of zinc by weight will dissolve in pure lead (and it might be less in an alloy that also contains tin, antimony, arsenic, and so forth). When you have zinc that isn't fully dissolved, it'll start to solidify before the lead alloy does (this is what creates the "oatmeal" effect), and even if you pour hot enough to keep the zinc molten, it'll separate like oil coming out of water -- you'll either get a separated melt with lighter zinc on top of the lead alloy, or if you stir immediately before you pour, you may get either a stratified bullet or one with hard spots (and possibly out of balance) where zinc grains formed but couldn't float to the top before the lead froze around them.

The simplest way out if you don't have too much zinc is dilution; keep adding known good alloy until the zinc dissolves and stays dissolved (this may require a largish pot if you have a badly contaminated melt). The next simplest is to cool the melt as far as possible and skim out the zinc "oatmeal" -- this will inevitably take some good alloy, too, but you can worry about recovering the lead from the zinc later (pretty easy: melt the lot, hot enough for the zinc to flow, and pour it into a tall narrow mold -- piece of iron pipe with a cap on the end, for instance, well supported please so you don't pour molten metal all over the floor -- and by the time a large ingot like that solidifies, it'll be stratified; you can just break it at the line where the zinc meets the lead, and the lead part will be usable alloy).