Edward,

Thanks for the details.

I haven't used much casting resin.
Way back in once-upon-a-time time when I was putting ships in bottles...

There are other fillers as well - talc for instance, wood flour, colloidal
silica (cabosil), cotton flox, etc.

I've had some "interesting" results using glass in epoxy.
They seem to help contain the exothermic heat in the cup and cause a run away
situation. It rises like bread and overflows the mixing cup!

But back to your issue...

I'd almost suggest that microbaloons are the wrong material for what your
work entails.

Perhaps a quick experiment with other stuff might be useful as I've not
had much problem with it developing bubbles in the mix.

West 406 (blended? colloidal silica) is good stuff, but it's available form
other sources cheaper.

Aircraft Spruce or Wicks Aircraft both carry it.

For my serious work I often mix silica and cotton.
Silica to thicken the resin and cotton to make it hard as a rock.
Balancing those two can produce a wide range of physical properties.

For what it's worth, cotton can be "dyed" before mixing.
It has possibilities...

The other question with composites is always - "how big"?
Smaller batches may show more variation in properties, but are more
controllable.

If you don't really need the transparency's of casting resin, perhaps
an epoxy? When fresh most epoxies are pretty much clear (well, not ALL).
West, for instance, is really clear when fresh, nut turns dark as the
catalyst ages.

Wish I could see what you are up to.
It sounds interesting.

Richard


http://www.maddyhome.com/canardpages...20%20micro.pdf

http://www.fiberglasssupply.com/Prod...s/fillers.html

http://www.favonius.com/soaring/additives/additive.htm

http://www.aircraftspruce.com/catalo...es/bubbles.php

http://www.wicksaircraft.com/catalog...423/index.html