> LEDs would be very neat as if you used clear ones the shell would
> vanish, making it look like they are little spots of light eminating from
> metal cups

The closer the refractive indices the more the two materials will
appear to be one. I used to be a resin chemist and we did a lot
(A LOT !!) of lunchtime experiments with clear polyester. I've
got a bag of PVA chunks that one day I want to make into giant
bubbles. For no particualr reason or for a reason I can no longer
remember

> One of my friends embedded a vacume tube in acrylic using that
> process. He said it worked fine, and you couldn't see the glass
> envelope at all. Make a nice nightlight for his dad

I've potted the innards of valves in polyester and they make good
ornaments. So do bugs, chips and all kinds of things. If I had the
time I'd like to get back into coasters. Particularly as nW PICs
now make it feasible to include displays. Heat is a problem as it
causes the plastic (polyester anyway) to expand away from the
object, which causes "silvering", which doesn't look professional.
The same also happens if the object has any liquid (eg moisture) in
it, as the exothermy of the curing causes a vapour layer if you don't
pre-coat

OTOH, using heat, including a sensor could make the coaster light
up and even change colour (RGB LEDs) as the temperature changes.
Might be too rough on small cells

Good hobby, bit smelly and messy though

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