How to Use a Slump Mold
Forming glass successfully with heat requires equal parts scientific precision and artistic vision, as well as a great deal of persistence. The process entails heating glass in a kiln over molds made of various heat-resistant substances. As the glass becomes soft, it either slumps into or drapes over the mold, thus assuming the shape of the mold as it cools. To use a slump mold, it must first be prepared properly so the molten glass will not adhere permanently to the mold surface.
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Things You'll Need
- Powdered kiln wash or shelf primer
- Glass container with a tight-fitting lid
- Clean water
- Hake brush or similar soft, wide brush
- Kiln
Instructions
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Measure one part dry kiln wash and five parts clean water into a glass container with a tight-fitting lid. Shake the container well to thoroughly mix the ingredients.
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2
Apply kiln wash to the slump mold with a hake brush or other wide, fine-bristled brush. Employ a fully saturated brush and use gentle strokes in one direction rather than a normal back-and-forth painting motion. Stir or shake the container of kiln wash occasionally to keep the contents well mixed. Spread a thin, even coat on the mold surface, working from the top to the bottom, and then spread another coat from left to right. Apply two more coats, one on each diagonal, from corner to corner.
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3
Allow the mold to air dry completely, up to 24 hours. Speed up the drying process by placing the mold in the kiln and bringing it slowly up to 500 degrees and then letting it cool. Examine the dry mold to see if the kiln wash has plugged any of the air release holes. Clean out the holes with a small nail if necessary.
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Place the mold in the kiln. Elevate the mold using kiln posts if possible. Position the glass carefully on the mold. Fire the glass according to the glass or mold manufacturer's recommendations or your own test schedule.
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Tips & Warnings
Using a sprayer to apply the kiln wash results in a smoother mold surface.
You can make your own kiln wash powder by mixing equal parts kaolin and hydrated alumina. The ingredients are available from pottery supply companies.
A stainless steel mold must first be cleaned thoroughly, heated to 1,200 degrees and allowed to cool, and then reheated to just under 500 degrees before applying kiln wash in order for the wash to adhere.
Although most molds require treatment with kiln wash, there are some that don't. When in doubt, check with the manufacturer for specific instructions on using a particular glass slumping mold.
Wear a filter mask when working with dry kiln wash powder or dust from the kiln or molds. The components of the powder can be harmful to your lungs.
References
Resources
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