How to make a two part silicone rubber mold or polyurethane rubber mold.
How to make an RTV rubber mold.


original model

1) The first photo shows the original model for which we want to make a mold. What makes this model complicated is:

• The holes under the neck and tail.
• The holes between the three feet on the ground.
• The leg lifted up and not touching the ground.
• The head and neck turned to one side and not exactly in line with the body.
• The relatively thin legs.

model without base

2) The first step is to un-complicate the model as much as possible before making the mold. We can make this model much less complicated simply by removing the horse from the base. The base by itself is a very simple mold - just put the base in a container, seal the bottom edge of the base with clay so the liquid rubber does not seep under it, and pour liquid rubber over it. After the horse and the base are cast separately, they can be put back together. This also allows for the flexibility of putting the horse on a different base, or not using a base at all.

If you are the creator of original sculptures that you will eventually want to make molds from, always sculpt the main figure separate from the base. And make other parts as separate objects also. For instance, if this horse had a rider, you would want to sculpt the rider as a separate object. If the horse was tied to a hitching post, you would want to sculpt the hitching post separately, and so on.

To make a two part mold of this horse, we will first bury the horse in clay, so that one half of the horse is in clay, and one half of the horse is exposed. This means one half of the body, one half of each leg, one half of the head and neck, and so on. The clay will form what is called the “parting line”. There is no requirement that the parting line be straight. It can undulate however necessary to follow the curves of the model.

3) Use a pallet board. A good pallet board is a large plastic board such as those sold as kitchen cutting boards. Roll out a slab of clay about inch thick on the pallet board, and lay the horse on it.

model on layer of clay

Take small balls of clay, and push them into place around the horse so they come to the approximate parting line.

clay to make rough parting lineclay to make rough parting line

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