Yep as mentioned you will skim off impurities. The secret to making lead stuff is the temperature.If the lead is at the right temp it flows and fills the mold correctly. Too cold..no good...too hot no good. I use to pour sinkers for fishing in the major river systems.I would lose a lot fishing and snagging in the riprap and structure. Poured thousands...never wore gloves when handling them while breaking off the sprues and stuff,probably hung my head over the pot too much....probably shouldn't do that.