Aluminum will react with a strong base, ferrous metals won't. Probably the easiest to obtain is a drain cleaner; the kind you want will contain either sodium or potassium hydroxide. You'll probably need to scratch the surface (to break the oxide layer) under a pool of liquid. Magnesium is much less common due to cost & manufacturing difficulties.
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Tempered glass MUST be annealed before attempting to cut it, otherwise the whole piece shatters into little cubes as soon as any part of the surface is breached. An easy way to identify it is with 2 polarizing filters - put the glass between the 2 of them & rotate one of them; tempered glass will show a, "Maltese" cross pattern, plain glass won't.
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Roy
