DentonDoc wrote on Apr 18^th, 2011 at 3:34pm:

wrote on Apr 18th, 2011 at 3:19pm: DD, Might be a heat transfer thing too. I assume the seamed box was empty when you heated it and you said the Altoid one had water in it. I've heard of boiling water in a birch bark bowl too. Yes.  That is quite possibly true. I've also seen film of people boiling water in a plastic bottle and one of the "drills" I did as a Boy Scout (many moons ago) was to boil water in a paper bag. So, it is pretty obvious that in those situations, much of the heat is being absorbed by the liquid rather than exclusively by the container. dd

If that's true, it would never get hot enough to take the solder if you had it full of water though. So how to seal it up to use for boiling water remains the question.

Line it with a plastic bag?  ;D