For what it is worth, I once asked a chemical engineer at G2 epoxies how to tell if epoxy was good (assuming for the moment that the issue if resin crystallization has been dealt with by heating, as described here by others). I was using the epoxy for guitar construction, and needed to be certain that the glue I was using was good in the long term. He advised me to mix a small sample up according to the standard ratio, let it set completely on some sort of plastic surface from which it can easily be removed. Once it is set, peel it off the surface to check it. If the set epoxy is hard and clear, you are good to go. The key is the clarity of the set epoxy. As I understood him, if polymerization is failing significantly, the epoxy will set up somewhat cloudy. By clear, I am not talking about color, just clarity. For example, good red wine, even the dark red stuff, is still clear.

: Hey Patsy, good to see you back!!

: I recently tested a some ancient old MAS epoxy, guessing the build
: happened in the 80's (it was given to me), and it seemed to
: perform flawlessly. It's so old the color makes honey look
: clear, a deep, dark red. Pretty cool looking, actually! Like
: you, I figured to use it on miscellaneous non-critical items....