Thank you for this report, which is the first to come to me about zinc contamination from modern wheel weights. First, understand that I've never had the problem, so my input will come from what customers tell me thay are doing and from a very knowledgable lead metalurgist named Dennis Marshal, who used to do quite a bit of writing for the Fouling Shot paper put out by The Cast Bullet Association.
What customers are doing with success, when using modern wheel weights is watching the melt closely and skimming when most of the wheel weights have melted but a few remain with no melt starting. These will be either steel or Zinc. Zinc melts at a lot higher temperature than lead, so this method seems to work just fine.
Her's my personal solution, which I haven't had to use because I have enough WW from before the zinc thing started, to last the rest of my life. -- I would peck each wheel weight with a welders slag hammer, keeping it good and sharp if it got dulled at all. I would lay the WW on a heavy steel or cast iron block to back it up solidly, then give it a peck with the hammer. Anyone will learn in a few minutes how hard a peck it takes to mark a lead WW quite deeply. And what the same force does to both zinc and steel. Take the steel and zinc ones to a scrap metal dealer and they will give you a decent price for them.
The tape on weights are pure lead. They can be saved out if you have a use for pure or very soft lead, or, if you don't have a preponderance of them, just thrown in with the WW. The small dilution they give will hardly change the castibility of your cleaned WW metal. If you have a large quantity of tape on weights, enough that your WW is softened, you can sweeten the mix with a small about of Linotype, or bullet casting metal., wich is available from several smelters.
I don't know of any solution which will save your contaminated metal, and according to Dennis, who's wisdom I trust fully, there is no solution for cleaning up the contamination available to bullet casters. He recommended that one scrap the bad metal and scrape the pot clean as possible, preverably sand blasting it to clean metal, as he said that a very small amount of Zinc would cause bullets to fall apart if dropped or even if a loaded cartridge were picked up by the bullet. Like out of a loading block. This after some aging time.
