I was making my own slipsinkers for the first time. And while i was melting my old 8 oz. sinkers to make 2-3-4oz. sinkers, they seem to be leaving a lot of junk ( slag ) in the pot. Question is, Is this just impurities in the led ? Or maybe im melting them too fast and its burning, I dont know. Is it best to melt them as slow as possible ?