Saturday, July 01, 2006
Making a two piece mold part 5
The next step is to determine the amount of plaster required for the mold and to apply the release agent.
In the top two photos you can see the measuring of the mold. You must measure the length, width, and depth of your mold. The depth should allow 1/2 inch of plaster above the top of the item you are making a mold of. Multiply the length times the width times the depth. Then multiply this number by 2 divide by 3 then divide by 15. This gives you the amount of plaster you need in cups of water required.
In the third photo you see the release agent being applied to all surfaces of the mold and the surrounding boards with a brush. I use a mixture of 1/2 murphy's oil soap and water. This is a cheap and very effective release agent. You can purchase special soap for mold making at ceramic stores but it is more expensive and doesn't work any better.
After the release agent has been applied you should take a damp sponge and sponge it off gently. Sponge off all of the surfaces that the release was applied to. Excess soap left on the surface of the clay or next to the model will cause the plaster to not set properly and will ruin the mold.