Kevin McElhone was asking how to clean zinc discs. Easy, dip them in a
warm solution of Harpic Lavatory Cleaner. That's the old powdered
crystal type and not the modern liquid. It is good for cleaning brass
as well. I have used it to clean zinc parts of organ pipes, and they
came out like new.
I suspect that one of the chemical components contained in the powder
likes to eat the surface off brass and zinc. Be careful not to leave
items in the solution too long, as they would eventually dissolve. Give
me a ring, Kevin, and I will explain in more detail.