I have several Les Paul style guitars, and have changed around hardware on a few of them, so I know what those parts are. I've acquired a few used instruments that may not be stock. I'm considering changing a few parts to tune them up a bit, but not sure what I'm starting from. Any tips for telling about metals in parts - for instance if you are handed an unknown tailpiece, how do you know if its zinc vs. aluminum? I'm aware of the use of a magnet to check for steel, and looking for a casting seam, but beyond that I'm not sure.