As most of us know neither zinc (cast) nor aluminum are magnetic. They both also show a shiny silver color if you use a file on them, and neither spark if you use a wheel on them. So how can a person definitively tell the difference between the two? Most of the time I can tell generally by the weight in relation to the size, but sometimes the weight is just so that I cannot for sure say one way or another. Anyone have a tried and true method to tell these two from each other?