Regarding old epoxy, I've been told that the epoxy/hardener doesn't like to be stored below freezing (32F) because crystalization can occur and thus effect curing. However, if you're epoxy does end up crystalizing, all you need to do is put it in hot water for a while (can't remember if it had to be boiling).
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Yes, you are correct. If it crystallizes (you should be able to see the particulate), you can put the container in some hot water and stir to re-homogenize it.
