Voltmeter? That's a new one to me. If you get a bottle of muriatic acid from the hardware store(unless it too, is banned now!!) it will fizz like the bajasus on zinc but just bubble slightly on lead. Steel reaction will be somewhere in the middle, tending more like lead. Zinc in acid will make you sit up and take notice. I don't worry about steel, it floats on the melt, just skim it off, done. There's another posting running around about using sulfur to clean up a molten mess of zinc contaminated lead, sounds like it should work............Lee