How to Do a Slip Cast Ceramic Mold for Slumping Glass
A ceramic mold provides a convenient way to slump glass, and slip casting is used to make such molds. The mold you make must withstand prolonged heat, because it will be fired several times. It also must accommodate the weight of the glass, since some types of glass weigh more than the ceramic molds used. A mold designed for glass slumping should be made of strong clay and resist thermal shock. Plaster is used to make slip casting molds, and you can create a master mold to help you design other ones.
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Things You'll Need
- Plaster mold
- Slip -- a liquid form of clay
- Plastic fettle knife
- Mold strap
- Sponge
- Water
- Dusting brush
- Rubber scraper
- Small brush
- Trim knife
Instructions
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1
Clean the plaster mold, using the dusting brush. Remove any debris from inside the mold, so it doesn't become embedded in the casting. Use the rubber scrapper to remove stubborn debris.
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2
Join the mold pieces, using the mold strap. This will prevent splitting during the slip casting process. Use enough straps to secure all sides of the mold.
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3
Place the mold on your working surface. The mold’s pouring hole should be at the top.
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4
Mix the slip with some water, until it has a gravy-like consistency. Remove all lumps from the mixture, and make sure there's enough to fill your mold. Let it set for a few minutes, to allow the bubbles in the mixture to rise to the surface.
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5
Pour the mixture into a pitcher.
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6
Pour the slip into your mold cavity, in a steady stream. If you pour in the mixture too fast, air bubbles will become trapped inside the mold. Fill the mold to the brim. Some molds must be refilled as the level of the slip reduces, when the water is absorbed by the plaster.
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Allow the mold to set. The amount of time needed varies from a few minutes to several hours -- depending on the size of the mold and the type of clay used to make the slip. Stoneware takes longer to set than earthenware or porcelain.
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Open the mold once it has cast. Do not force open the mold, if it has not set completely.
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