Kilnformed Glass

Ingrid Layman

Kilnformed glass, also known as warm glass or fused glass, is the product of a 5-stage process of heating and cooling glass in a kiln to fuse two or more pieces of glass into one object.

The 5 Stages:
1. Glass is slowly heated to about 1500°F where the separate pieces of glass begin to fuse together.
2. Following the heating stage, the glass is held at the high temperature for a shorter or longer period of time depending on the depth of fusing desired.
3. Next, the glass is cooled as quickly as possible to the point just above where annealing begins. This quick descent is to stop the fusing process.
4. The glass then goes though another hold just below 1000°F for a period of time to relieve the stress in the glass and prevent it from cracking as it cools further. The kiln then is cooled very slowly though the stage known as the annealing stage.
5. Once the glass has stabilized, the final stage is to cool the piece the remaining of the way to room temperature.

Thanks to computerized kiln controllers, we are able to program our kilns to precisely control this 5-stage process and create a wide range of artistic effects.

Pot Melts: In this technique, glass pieces are placed in a clay pot and the glass is heated to approximately 1700°F. At this temperature the glass becomes the consistency of honey and begins to flow. This molten glass will drip through the aperture and collect onto a kiln shelf below. The choice of glass quantity and color and the way the colors are loaded into the pots produce a unique product with every melt.

Slumping or Draping: Once we are satisfied with the final design of our piece, we can add a three dimensional aspect by once again heating the glass to approximately 1200°F allowing it to slump into a mold or drape over a mold and assume its final shape.

The number of times a piece is in the kiln varies piece by piece. Some of our pieces are fused in one firing and slumped in the next. Most often though, our pieces must go through multiple firings to get the various affects and finishes that we want. With each firing, the risk of failure increases. We think the risk is worth the reward, when a piece comes out nice!

© Barbara Ridgley, www.twofriendsstudio.com

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