One of the first hurdles to overcome is how best to make the mold.
Most of the time the masters I make are glued onto a sheet of styrene, and, crucially, they have at least one flat surface and very little undercut.
Neither is true of the pieces of rock we are making copies of, and I'm not especially keen on using acres of fresh styrene sheet either. (Have you seen the price of it recently?)
So what I've hit on is to borrow a technique from two-part molding and place the piece of rock on bed of modelling clay which is stuck onto a reusable wooden board, and then has a styrene box built around it.
This then has the RTV poured into the box in the usual way and once that's set I can begin casting copies.
One of the things which I have noticed already in casting the first few pieces is how fast the resin sets.
Compared to the carriage and wagon sides I usually cast, which are comparatively thin, these rocks are quite thick in places and it's noticeable how much more heat is generated as the two parts of the resin cure and harden in front of your eyes.
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