I am going through some things that came down to me thru the passing of family. I have found my grandfather's WW II dog tag. He was in the Persian Gulf command, a quartermaster. I would like to do a framed display of his war portrait and include the dog tag. The problem is that the tag is pretty dirty and discolored. It does not seem to be made of aluminum, It appears to be a bronze maybe. Does anyone know what these tags were made of and have a safe suggestion for cleaning it. Of course I want to be very careful.