Crusty, Yellow Impurities in my lead?

your lead is fine,just take paraffin wax,yes the same as candle and canning wax that you buy at the store. cut off a small chunk and carefully drop it into the hot lead it will smoke a lot and probably catch fire but that is alright, when it goes out you can sc all of the impurities right off the top,they call that fluxing the lead the wax will cause everything to separate from the lead and float to the top,old wheel weights will harden the lead for sturdier sinkers. I use them as 25% of the lead I mold bullets for my muzzle loader. it works great.