How to cast with alginate?

I'm having trouble casting reduced-size objects using alginate.

The object is to make a pair of earrings about 2/3 the size of a
pendant that I made a rubber mold from.
I have made alginate miniatures by troweling
wet alginate in the mold, removing it once it gels, and letting it dry
to shrink. So, I end up with a nice-quality reduced-size alginate
positive model. I'm using Rite-Dent Type "J" dustless Alginate.

What's the next step? The alginate doesn't burn, even burn under an
oxy-propane torch, It seems too fragile to make a vulcanized mold.
Am I using the wrong alginate? Is there another material that shrinks
and burns out cleanly? Do I need to make another mold from the
alginate?

Regards,

On Mon, 22 Dec 2003 08:01:09 -0800, in rec.crafts.jewelry "\"Alex Bobotek
wrote:


I have made alginate miniatures by troweling
wet alginate in the mold, removing it once it gels, and letting it dry
to shrink. So, I end up with a nice-quality reduced-size alginate
positive model.

You could use RTV silicones, or similar cold, non "press" type mold materials
(Castaldo's liquicast, for example) to make a mold of your alginate model, then
inject with wax.

I think the poper approach would have been to use the alginate to make a new
mold from an injection wax taken from your rubber mold. Then, once the alginate
had shrunk, you'd just need to make a new wax model from it. This can be a
little tricky with complex models, since the dried/shrunk alginate isn't exactly
flexible for a mold. But for open faced things like flat pendants, that's one
step less than making an alginate model, when then needs to be molded again, as
you've done.

But you might as well just make an RTV mold of what you've got now, since at
this point, that's the least additional work. You'll need the mold anyway if
you're to make a pair of the earrings... The trick is to do it with one of the
pourable mold compounds, not vulcanizing rubber that needs a press. Heck, you
might be able to do it with leftover alginate. It's not a great mold compound,
and certainly not a permanent one, but it does work, and it's fast. I don't
think it will stick to your dried piece, so that isn't likely to be a problem.
But if you're worried, mix a teaspoon of alginate first, and dab a tiny bit onto
the model somewhere where it's easily trimmed if it did stick.

Peter