How much Zinc in an alloy does it take to create a problem?

[Dthunter]

The Title says it all guys.

Is it 1%, 5%,10%?

[fredj338]

I am not sure but not much. I think that was the culprit w/ my Magma pot recently. I think I got a bit of zinc in it when I added a 15# block a friend sent me. I added it to about 20# of good alloy, got about ahlf way thru & it quit flowing. So I haev since dumped tha last bits, pretty funky looking, like clots of lead. So lesson learned the hard way.