The model for "ON A Roll" was fabricated from 15 pound sign foam. The sign foam was turned on a lathe, sanded and sealed with shalack. The first mold was a plaster, silica mix. This presented a problem, the rigid sign foam material was difficult to remove from the finished mold. After about 30 minutes of pulling, tugging and wiggling, I succeded in releasing the model from the mold without damaging either.
However, it was obvious I needed to re-think the model material. Something flexible was needed. So, I put a 1/4" clay blanket over the original model and built a plaster case over that, this left me with a 1/4" space to pour rubber over the original model. When the plaster case was dry, I removed the clay and set the plaster case over the original model. Through a hole I created in the plaster case, I poured the silicone rubber. This gave me a thin rubber mold in which I would pour a liquid rubber. The end result was a strong, yet flexible model.
Below is the finished rubber model and a mold made from R&R Glass Cast 910.