I recently obtained a 5 gal. freebie bucket of wheel weights from a foreign car dealership. I noticed a quantity, perhaps 10%, "looked like they might be zinc". I kept my smelting temp on the low side, and sure enuf, a large portion of the flat stick-on types kept floating on top of the melt. (after the adhesive had burned off and fouled my airspace! ) I wish I could report on the actual smelting temp, but my thermometer does not have a fixture that would allow me to clamp it to the pot, etc. I also found several clip-on weights that would not melt, and a few were even stamped "zn" in a corner. The lesson I learned was that keeping the melt temp "low", allowed the zinc weights to be skimmed off with the clips. Maybe, I'll build a fixture that will allow me to use my normal casting thermometer so I can see how "low"is! Hope this helps those who try and cull out the suspect weights visually, cause you won't see them all!