How to Make a Mold for Silicone Casting

 So, many of you remember from last week that I did a pretty cool tongue sculpture out of oil clay.  Since it's a simple form and I am going to be casting it out of silicone,  I have elected to make a plaster mold.  Silicone doesn't really like to stick to much of anything but itself, so plaster is a good cheap molding option.  you can see here I started with a detail coat.

I quickly build a cardboard wall and seal the bottom and side with hot glue.  (Plaster sticks to lots of things, but it doesn't seem to like cardboard)

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I fill it up the rest of the way with plaster.  You don't want to have too much time between layers because plaster expands and contracts at different rates.  If you wait too long you will get strata in your mold and the different layers won't chemically bond.  It would make the mold more delicate and prone to cracking.  If you have more than a few minutes between layers of plaster be sure to wet the mold with water before applying the next layer.

Now that it set up I flip the mold over

Because of the shape, the foam core of the sculpture pops out so easily.

::pop::

The mold was still warm from curing, so the clay cam out without a hitch.

And here's the mold!

Next week: how to cast in silicone