> What material should the mold be made of?

Definitely not polystyrene because there's a lot of free styrene
monomer, which is quite an aggressive solvent that will attack
polystyrene and other plastics before it polymerises

Laminating film is good, just about nothing sticks to it. Glass is
OK too but you have to watch the catalyst level. More catalyst,
say over 1%, causes the resin to heat up noticeably as it cures.
When it cools and contracts it naturally pulls away from the glass

Which should be well-polished with wax or mold release BTW

If you use a lower catalyst level, for example with big pourings
with a low surface to volume area ratio you don't want to overheat
(they'll crack. In the lab we'd even have them catch fire if too much
promoter was in the resin), the downside is that the surface doesn't
move so much. What can happen then is that a part of the surface
may be left stuck to the glass, whilst the rest has shrunk away from
it, and leave a proud section like a thin scab

For my coasters I use spun stainless steel molds. All metals are OK
but the gloss you see on it is what you get, eg aluminium is easy to
work with but will always produce a dull finish

Most woods work but some have oils in that really interfere with the
cure. I can't use some NZ native woods without precoating them with
nitrocellulose laquer

> What is the silicone mold rubber used for and how does one use it?

Silicone mold rubber can be used to take castings of eg odd shapes.
Once cured it's very unreactive (it won't even stick to itself so you
can't modify a mold by adding bits). It's tough too and won't tear
on undercuts etc. For example you can turn the mold inside out to
remove the casting. Silicone rubber also lasts a long time and many
many castings can be made with one mold

On occassion I've used plasticine/plaster with a smear of vaseline
for a quick casting

Air (oxygen) is a ploymerisation inhibitor. So if you were casting in
an open box, a piece of laminating film or metal to cover the exposed
surface will ensure it cures hard. If you don't, the exposed surface will
stay tacky for quite some time after the body has cured
=20
> Also, do you know what resin he is using? Or something similar
> available in Canada?

Any company which sells fibreglassing resin will sell water-clear as
gel coat for example, or specifically for casting

eg http://www.fiberlay.ca/Fiberlay_Casting_MoldMaking.pdf

Fun for all the family. If they don't mind the smell that is. You would
not be poular doing this in the kitchen. I have my own shed/workshop
to do things like this in. And make sure you buy some acetone and rags
too. It's the best and cheapest way to clean up

There are a lot of fillers and glycol-based pigments too. I collect and
use the very fine MDF dust from my belt sander for instance. The cast
can be painted and shaped quite easily but overall is very much harder
than MDF
--=20
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