no aluminum is bad, period. soft metals are generally very toxic, that includes (but not limited to) copper, lead and aluminum (not sure about 'tin' but i'd just generally stay away from it, look for nickel, or steel).

aluminum has been studied (effects of smoking it) and has shown to increase chances of getting alzheimers disease... which you definately don't want.... i realize some people cannot buy bongs, but don't just settle for something that's unsafe because you can't.

go to your local hardware store, there is EVERYTHING you could possibly need to build a bong in there, and a damn good one, for cheap as hell... just use your imagination, start with finding the 'body' of the bong, then go looking for a stem/bowl slide combination, or just a bowl (that can atleast be unscrewed) and put a carb on it... don't risk your health just to smoke...

remember steel or nickel (i know there are other metals but i can't think of any right now) hope this helps :thumbsup:

edit, use no cans, they are generally made of aluminum...