wikiHow to Slump Glass

Glass slumping, sometimes called warm glass or glass art, is a form of artistic expression that uses the heat of a gas or electric kiln to melt 2 or more different pieces of glass together and fuse them into 1 piece. This newly formed glass is then placed over a ceramic mold. Both are placed inside the kiln, and the kiln is fired up. As the glass turns molten, it expands and slumps into the mold. It then goes through several processes before the finished piece is released from the mold and receives its final polishing. This method is often used to form exotic pieces of jewelry and beautiful dinnerware. Some glass pieces are created by allowing the newly formed glass pieces to flow over a mold, also called bending. This process is used to create items such as bowls and vases. Slumping glass should only be attempted under the direct supervision of a qualified expert as you will potentially be working with kiln temperatures as high as 1700°F (926.7°C).


  1. 1
    Place fused glass on top of a mold that has received a coat of kiln-wash, and place it in the kiln.
    • Make sure the glass piece you choose is not so big that it will flow out of the mold and pour over the sides, making it almost impossible to remove the glass from the mold.
  2. 2
    Fire the kiln to a temperature between 1200 to 1300°F (648.9 to 704.4°C), keeping an eye on the glass through the peephole. The glass will begin softening and turn glossy when the temperature nears 1000°F (537.7°C) and start slumping as it nears 1200°F (648.9°C).
  3. 3
    Make notes of temperature and slumping time.
  4. 4
    Allow the glass to soak, which means rest, until it begins to flatten and shape itself to the mold.
  5. 5
    Cool down the kiln to 1100°F (593.3°C) by either opening the lid or turning it off. Opening the lid allows faster cooling as the heat can escape from the kiln.
  6. 6
    Cool down the kiln to 1000°F (537.8°C) and maintain that temperature for 20 minutes. After 20 minutes, continue lowering the temperature to 600°F (315.6°C.) This will anneal the glass which helps relieve any built-up stress.
  7. Image titled Tempered glass tree
    Turn the kiln off completely, and allow the piece to cool naturally. This can take 24 hours or more, but it is important that the glass be cooled to room temperature before you begin the final polishing to obtain your finished piece.


  • Keep detailed records of your work, recording information such as temperature, time and procedures used. They will be invaluable if you need or want to recreate a piece.


  • If your kiln does not have a peephole, you will have to lift the lid to check progress. Wear eye protection if you must lift the lid.

Things You'll Need

  • Kiln
  • Eye protection
  • Ceramic mold
  • Glass pieces of your choice
  • Heat proof gloves

Article Info

Categories: Glass and Stained Glass Projects