Jim and I were finally able to cast the Breastplate in Plaster tonight. Here is a documentation of our process. First I painted the model with Amaco plaster release.
Then I built up some wall of clay to hold in the plaster in places where it might run.
Jim helped me mix the Hydrocal plaster (purchased from Armadillo Clay in Austin). It’s a much harder version than the normal plaster you can get at a drug store, which is good for mold making. For a long working time we mix 1lb 2oz of water to 2lb 8oz of water. This starts out as a fairly liquid mixture and then is workable for about 15-20 minutes in summer temperatures. We always wear masks when using plaster because it is dangerous, and always mix the pater into the water.
The first layer of plater we paint on with disposable brushes. As it begins to thicken you can pour it on and then use the brush to spread it. By the end when it gets really thick you can work it with your hands like clay.
In between the layers of plaster we put layers of plaster bandages for extra support. You can also use burlap for this. We just happened to have the bandages handy.
For the final layer, you can dampen your hands slightly and smooth it to a nice finish which will be more pleasant as you work with the finished mold.
We will let it dry overnight, and unmold it tomorrow morning. Hopefully everything will work out beautifully. This is the largest cast we have done so far, so it is definitely a challenge.