How to Do Glass Slumping

The ability to shape glass has had a profound effect on the way we live.

Glass slumping is an intense process that involves shaping glass using heat. Staying safe during the heating process requires some important know-how. The glass doesn't get to a molten state but heats up enough to bend as gravity pulls it down. Slumping can be achieved in several ways such as slumping glass into a mold or draping it over one. Glass slumping requires close attention to the temperature in the kiln and frequent visual checks.

Things You'll Need

• Kiln
• Kiln wash
• Stainless steel bowl
• Piece of glass
• Pyrometer

Instructions

1. Prepare the kiln by vacuuming the kiln floor and applying kiln wash to the shelf. Follow the manufacturer's instructions to determine the correct amount of water to add to the kiln wash powder. Mix thoroughly and apply with a brush. The wash prevents glass drips from sticking.

2. Find a suitable stainless-steel bowl to use for slumping the glass. Sand the smooth outer surface with 100-grit sandpaper. Create crossed lines by sanding in two directions to rough up the surface. Heat the bowl in a 400-degree oven for 5 to 10 minutes. Use gloves to remove the bowl and apply at least five coats of kiln wash on the outside of the bowl. Heating the bowl makes it much easier to apply the kiln wash.

3. Place the bowl upside down on a kiln shelf. Center a piece of glass on top of the bowl. Measure the length from the center of the bowl to the rim. Compare that to the measurement from the center of the glass to the corner. The glass should not exceed the size of the bowl.

4. Place the glass in a way that you can see the glass when looking through the peephole. If the glass it too large, it will slump over the edge and onto the shelf. Use one sheet of glass for this firing to establish the right bowl shape. You can later slump the glass into a mold and fuse it with colored glass strips at a higher temperature.

5. Increase the heat gradually, raising the kiln setting every half hour. Keep an eye on the pyrometer. Perform frequent visual checks to see how the glass is behaving. Watch for the glass to begin slumping at around 1200 degrees Fahrenheit. Hold the temperature for 1 hour once it has reached 1300 degrees. Visual checks should confirm that the glass has slumped into the shape of a bowl around the mold.

6. Cool down the kiln slowly over 24 hours before opening the kiln. The steel will cool and shrink faster than the glass, so the glass should easily detach from the mold.

7. Soak the glass in water and scrub off any residue with a scouring pad or steel brush. Sand off any rough spots going from rough- to fine-grit sandpaper. The custom-made glass bowl is now ready for use. Re-fire to add colored glass or alter its shape if desired.

References

• Warm Glass: Molds for Slumping