Sunday, July 02, 2006
Making a two piece mold part 7
The next step is to carefully remove the clay from the plaster, clean up the mold, create the keys, and seal it. Carefully peal the clay off of the plaster. If you are molding several items that are virtually the same be sure that you keep track of which one goes in which hole, because although they look the same they may not be identical. This is especially true of hand made beads. Also pay attention to which side of the bead is in the plaster and which is out. Sometimes the pieces will come out in the clay as you remove it and you will have to clean them and replace them into the mold. If you don't get them back in the right direction you can introduce gaps which will allow the second pour of plaster to seep into the cavity of the first half of the mold ruining it. Carefully clean off all of the clay from both the plaster and the pieces. It is ok to wash the mold under running water at this point to remove the clay and dry it off with a towel. Don't soak it in water for any long period of time, however, just a quick rinse off.
In the first photo you can see me using an x-acto wood carving tool with a round end to cut the keys into the mold. You can also use the end of a spoon or the handle or a mellon baller to do this. What you want is a smooth rounded hole that has no undercuts.
In the second photo you can see me using a shaper to cut of the square corner on the edge of the mold. This eliminates the sharp edge and also makes it easier to seal the mold to the boards for the second half.
In the third photo you can see me brushing the mold release agent (murphy's oil soap) onto the plaster. At least two or three coats will be required. Let each soak in and dry before applying the next. Be careful not to let it run down into the mold cavity. Although this will not ruin the mold it will cause the first few castings to absorb unevenly and stick to the mold. The soap will come out after a few pours, however, so it is not a total disaster. Even if you are careful you will usually end up with a tiny bit right next to the seam line and the first few castings in a new mold are likely to stick in the first half of the mold.