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I have been looking for a way to reproduce a statue I have been working on. This statue is too large to mold using RTV Silicon because it would cost me a fortune.

To this effect I decided to do a test piece using plaster as the mold material. I only need one reproduction so I gave it a shot. That brings me to the BFG. I designed this badass gun to test plaster molds on clay original.
My original plans.
Plasticine is used to make a seem around the original. This will be where the mold splits.
Build up an edge to hold in the plaster when it is pored.
I used cornice cement instead of plaster because it is stronger.
The wet plaster can be brushed on to the original to capture all the details and remove any air bubbles. There is a limit to how much detail plaster can get though.
Poor in the rest of the plaster to make a thick mold half.
The finished product is OK considering what it is made of. Next I move to a new project that is a lot more complex.
Once the plaster has set the plasticine can be removed from the surrounding wall and from the base the original had been embedded in.
Build up a new wall to hold in the plaster for the second half of the mold. Paint on Vaseline so the new plaster will not stick to the old.
Poor the second half
Once the two halves are clean tie them together securely with tape and wire.
Split the mold in half and clean out the clay left from the original. This is scary because then the original is gone.
Put the mold into a bucket to catch any leakage. Plaster does not form a very goo seal to hold in the resin.
I used a cheap polyester resin to make this. I hope to use this on a much bigger piece so the price of polyester is about half that of urethane.
Finally smash off the mold to reveal the casting. Fill in any cracks and paint.