On Wed, Mar 22, 2006 at 10:15:49PM +1200, Jinx wrote:
> > 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

Didn't think of that one... Now I am correct in saying that refractive
indices don't apply for solid objects right? Where the light hits the
object and heads directly back the way it came?

> > 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

Ahh thanks, I'll keep that in mind then. I recently embedded a watch
along with 6 batteries in parallel in polyester resin, I didn't have any
problems with silvering, but the plastics studio at school tends to be
really hot and dry.

A minute or two with a heat gun set on low should be enough to prevent
that right? At least for the surface moisture?

> 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

Do you mean that the cells, as in batteries, would be permenently
installed?

I've got a project on the backburner that would involve a flat disk with
embedded murcury tilt-sensors and solar-cells to run everything. I'd
throw in a bunch of super-capacitors for night operation. Just gotta
find a way to get sufficient power, it'd need a radio link to
communicate with a similar module inside, and super-capacitors just
don't store much energy.

> Good hobby, bit smelly and messy though

Not to mention the wonders of what methel-ethel ketone does in your
body...

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pete@petertodd.ca http://www.petertodd.ca
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