Mold making opens endless potential for creative expression. For thousands of years, potters have used molds both for forming and decorating and often both have been accomplished at the same time. Whether you choose to try press molds with slabs of clay or slip-casting molds for slip-cast pieces, you’ll discover that making ceramic molds provide a way to create uniform pieces that can save you time and provide you with the means to concentrate on surface decorations.
Plaster press molds are very useful when you are planning to make multiples of a form or an embellishment to a form. The prototypes can be made from clay.
Tips to keep in mind when making molds:
Prepare for your mold. Make sure your clay object is in place and that the image will be molded on the correct side. A common mistake potters make is to mix plaster only to realize everything’s not set up for pouring.
Before casting, make sure your model is set, the mold boards or cottles are secure, and all the surfaces you’re pouring onto are coated with a parting agent such as mold soap.
Prepare your work area. You will need a clean mixing container for the plaster, a scale for weighing the plaster, a measuring cup for the water and a rinse bucket.
Note: Plaster cannot be permitted to go down the drain, because it will form a rocklike mass. Even small amounts will accumulate over time.
To make a Basic Mold Start by making a good set of adjustable mold boards. Remember to always use a release agent, such as oil soap, on a porous surface before pouring plaster on it.
Make the walls for the mold around a board that measures 1 1/2 inches larger than your piece on all four sides (use laminated wood as this eliminates the need for a mold release).
Fasten the boards together with four spring clamps or C-clamps. If the boards are all cut accurately at right angles, the assembled form will keep plaster from leaking without the need to seal the joints with clay. Put a wad of clay on the outside of the base of each wall to keep the form secure.
Pour the plaster at least 1 1/2 inches over the top. Make sure the plaster is fresh (stored for no more than 6 months) and completely free of moisture. Once all the plaster is in, allow it to soak (slake) for one minute without any agitation.
Mix the plaster with a clean stick until it becomes a heavy cream consistency. When the plaster has reached a proper consistency, pour it into the form in a slow steady stream.
Shake the table (but not too much) to bring any air bubbles to the surface, and to settle the plaster out, making the top completely flat. To use the mold press the clay into the mold and be careful to not leave any air inside.
The best part is, once you’ve made the mold, you can use it over and over again. Also when you are done with the mold you can use it to dry your reclaimed clay.