You can only get 2% of zinc into lead. What most people think is zinc contamination is actually calcium. That oatmeal looking lead is not zinc. Zinc will just float on top of the lead if you get too much of it in the lead. Just like water and oil. But the water sinks. And copper sulfate will remove some of the zinc. But all you will have to do to make the lead manageable as in easy to cast with is add the zinc lead to good lead in a 3 good to 1 bad lead mix. Or just turn the temp way up.
Zinc is not the problem child like some make it to be. Heck I know a few guys that actually put it into the lead on purpose to harden the lead. Yes it works very well for this. In about no more than .75%.
