How to Fuse Glass in a Ceramic Kiln

Fusing glass in a kiln requires knowledge of glass working and familiarity with kiln functions. Glass expands during the fusing process and can crack when heated too quickly or too long inside the kiln. Determining the coefficient of expansion decreases the likelihood of cracking glass while fusing inside a kiln. The coefficient of expansion, commonly referred to as the "C.O.E.," measures the rate of glass expansion for each type of thickness of glass prior to fusing. Kilns must be set to the corresponding C.O.E. guide temperatures to have successful results when fusing glass. Do not mix glass that has differing levels of C.O.E., or cracking will result. Glass and kiln instructions guide artisans in determining the C.O.E. and should be followed to the letter when fusing glass.

Things You'll Need

• C.O.E. guide
• Protective eyewear and gloves
• Haik brush
• Kiln wash
• Windex glass cleaner
• Honey

Instructions

How to Fuse Glass in a Kiln

1. Apply kiln wash to the interior of the kiln with a glass haik brush. Brush the kiln wash in an upward direction only. Add a second layer of kiln wash, brushing at a 90-degree angle inside the kiln. Repeat step, brushing five more layers of kiln wash inside the kiln at a 90-degree angle. Heat the kiln for 15 minutes. Let cool naturally at room temperature before proceeding. Close the kiln vent.

2. Turn on the kiln and fire at 500 degrees F with the kiln lid vented halfway open. Firing the kiln causes excess liquid to evaporate.

3. Place a drop of honey onto the kiln shelf to hold each piece of glass in place during fusing.

4. Put cut glass objects onto the kiln shelf. Do not overlap or stack glass pieces.

5. Heat the kiln to 1,450 degrees F. Heat the kiln slowly, at a rate of 900 degrees per hour, until reaching a temperature of 1,000 degrees. Set the heat to the final 450 degrees half an hour after achieving a temperature of 1,000 degrees.

6. Fuse glass inside the kiln for 20 minutes.

7. Unplug the kiln viewing hole, and open the kiln lid completely to vent the glass quickly. Let glass stand at 1,000 degrees F for 5 minutes. Close the kiln lid, and plug the viewing hole. The kiln temperature will jump to approximately 1,200 degrees F.

8. Let the kiln cool to a temperature of 950 degrees F. Anneal the glass at this temperature for 30 minutes.

9. Remove the glass from the kiln after cooling to room temperature. Do not remove glass until it is cool to the touch, or it will crack.

Tips & Warnings

• The kiln viewing hole can be opened to check glass after fusing for at least 10 minutes in the kiln. Allow at least 6 hours for the cooldown process on thick or long pieces of glass. If the glass in nearly 10 inches long or two layers thick, the extra cooldown time is necessary to prevent the glass from cracking.

• Follow all kiln use and safety instructions thoroughly to prevent glass from cracking or injury to the operator.

Resources

• Warm Glass Website fusing information page
• Big Ceramic Store fusing glass help page