Attack (that is the brand name) is very good at removing epoxy, but
also will take care of anything plastic as well! It shouldn't hurt a
glass test tube, but may damage anything inside of it, depending on
what you've got in there. We use attack in combination with an
ultrasonic. Simply fill a glass, or stainless steel cup with enough
Attack to cover the piece and set it on top of your ultrasonic rack,
the vibration will help loosen the epoxy.
As far as types of epoxy to use for clarity, 330 epoxy dries very
clear, but I find it brittle. An interesting solution could be an
epoxy-like substance call Envirotex. It states that it is not an
epoxy on the side of the box, but for jewelry purposes it is more
than suitable. Envirotex is actually used as a very thick clear coat
on surfaces such as tables and bar tops, the kind that have various
memorabilia submerged within. It's great stuff, and very clear, just
follow the instructions to the letter.
Hope that helps