Firing ArtGlass clay
Remember you are firing powders bound together. It would be impossible to thermal shock this material by going up too fast. I choose 600 degrees per hour so that the binding agents have time to completely burn out. I use a kiln made by Jen Ken which is constructed of all fiber. Fiber kilns don’t take as much heat or time as brick kilns.
Brick absorbs more heat and the cool down time is also longer. Most people have kilns made from fire brick so we will start there.
First of all make sure the clay is completely dried before firing. Use a hot plate, oven, hot kiln top…check by putting the clay on a cool piece of metal. If steam shows up on the metal, it isn’t dry.
In a kiln constructed of mostly brick, fire at 600 degrees F per hour to 1325 degrees F. Check your glass by opening the kiln. Is it shiny enough for you? Is there the amount of texture you want? If it is not shiny enough, hold up to 20-25 minutes and look again. You don’t want to lose your texture and detail by getting it too hot or holding too long. Every kiln is different so watch it carefully the first couple times and take notes! Shut off the kiln and vent down to 1100 degree F to prevent further melting of the glass. Keep the kiln closed until about 150. Crack the lid until you can touch the piece without burning yourself!
If you want your glass clay piece to be flat and very shiny, you can take it up to 1450 degrees F and probably won’t need a hold time. I would not go hotter. If it isn’t flat enough, just hold it there until it is. Vent, anneal if the piece which is now solid glass and not powders according to standard glass annealing procedures for the size of piece you are making. I didn’t mention annealing above but if your textured pieces are larger than 4×4, anneal on the way down. Hold at 950 for 30 minutes and then just turn off the kiln. The heat of the brick will be enough to get it through the cool down. Again, if you are working really big, just follow all the rules of any glass fusing with the exception of the ramp up. You can take it up as fast as 600 degrees per hour due to the fact that it is loose unconsolidated powdered glass and not solid glass.
If you use an all fiber kiln, like the Bonnie Glo from Jen Ken, the only real difference is you may want to stop at 1320 degrees F and hold 15-20 mins. The fiber isn’t absorbing as much heat as brick and more is absorbed into the glass. You also don’t have to vent the kiln at the top end of the schedule so you can set it and forget it. The fiber kiln releases heat at the perfect rate. I never anneal if my piece is under 4×4 inches and thinner than 1/2 inch after firing. The glass will shrink 20 to 25 percent.
You will soon discover how your kiln works with this material and get consistent results.