Firing glass in a kiln is not much different from firing pottery in a kiln. It must be completed very carefully with many safety precautions. A ceramic kiln is very common for firing glass. Just like with pottery, the most crucial part of this part for is the kiln process is to get the kiln to slowly reach temperatures up to 1,400-2,500 degrees. It is also crucial to keep an eye on the glass to make sure it does not crack, since glass is so fragile.
Put on gloves. Prepare the kiln for the slow heating process by rinsing the bottom with kiln wash. Using a cloth, reach down into the kiln and apply the wash onto the entire bottom of the kiln. Brush the wash in one direction across the bottom, creating a sort of mini wave that starts at one side. Repeat the process four times all the way across.
Leave the wash on the bottom of the ceramic kiln and fire it up to 500 degrees Fahrenheit. Once it hits 500 degrees Fahrenheit, let it cool naturally and slowly with the lid on. Next, use a separate soft cloth to distribute the glass wash along the bottom of the kiln, since you are going to fire glass. Repeat the same process as with the kiln wash, sweeping it from one side of the ceramic kiln's bottom to the other.
Leave the glass wash in the kiln and fire it up to 400 degrees Fahrenheit. Let it cool completely with the lid secured on.
Place your glass onto a kiln tray if desired, but make sure none of the pieces are touching. Start to fill it up at the very bottom. It is best to fire full ceramic kilns instead of just one or two pieces. Stemware should be turned upside down. Try not to place glass pieces toward the top of the kiln as this is where the most heat collects and it will cook these pieces faster than the others.
Close the lid to the kiln and make sure it is securely shut. Set the temperature for the firing process. The usual temperature for glass to be fired is around 1,000 to 1,300 degrees Fahrenheit.
Keep an eye on the glass pieces from the kiln peep hole to ensure it does not become cracked or blackened. These are signs of "overbaking." Typical time for the glass pieces to fire in a ceramic kiln is usually between 10 and 14 hours. This could vary depending upon certain circumstances.
Always be cautious when working with machinery such as a kiln that reaches excessive temperatures.