Plaster and Molds Part 2
This is the second in a series of 3 tips on Plaster and Molds. The last tip was on mixing and pouring plaster.
Tip #45 Ways to Use Plaster Molds
First it is useful to understand mold release. The purpose of mold release is to form a barrier between objects so you can separate them later. There are commercial mold release agents available, but people often use Vaseline, liquid hand soap, Pam Cooking Spray, Crisco, Vegetable Oil, liquid soap, or Murphy’s Oil Soap. Vaseline is thick and stiff, and thus tends to leave brush marks behind.
Plaster to Plaster
You can pour plaster into another plaster mold to make the reverse of it. You need mold release in this case, or the plaster will stick.
When using Murphy’s Oil Soap, sponge on the soap with a sponge full of hot water, rinse the sponge in hot water, and rub again. Repeat this process at least 5 times. You will see the water start to bead up on the plaster surface. Once this happens, repeat twice more for insurance.
Some more unusual methods of mold release are using shaving cream which is said to leave a lovely waxy film when dry. Or using a thin clay slip; the plaster absorbs the water and leaves a film of clay as a barrier.
Plaster Over Wet Clay
It can also be useful to use mold release on leather hard clay, prior to pouring the plaster. This is often not necessary.
One problem with various methods of mold release is they can clog the surface of the plaster, making it less porous, so clay sticks to it more. So mold release should be cleaned off as much as possible.