The adventure of fire continues tonight while during the 23rd firing of my gas kiln a mug fell from the fire wall into the fire box right in front of the burner. I apologize for the pottery jargon. Let me briefly explain. The fire wall, aka, “bag wall” is a short wall of bricks that separate the stacks of pots from the “fire box”. The firebox is an area where the fuel is combusting, whether it be wood, or gas.
OK, so I decided to try to extract the pot by the handle and had to reheat the mug so it would release from it’s newly bonded surface of the kiln floor. You see, the kiln and the pots at 2400°F are sticky because of the soda glaze that coats everything in its path. I wasn’t able to move the mug because the firing was over and the molten union of mug and firebox floor had already solidified. So I reignited that burner and slowly, carefully reheated the mug. After about 10 minutes, the pot was glowing red (again) and I was able to pry it off the floor. Wow, I was super excited that it seemed to be in one piece despite its fall to the floor from about 15”. When ceramics is fired and at a temp of 2300-2400 degrees, its in a state known as pyroplasticity. I suppose the mug was more like a rubber ball than the dense ceramic object we all know after a pot has cooled. I can’t think of a better way to describe my theory.
After using a steel rod that I use to pull draw rings out of the kiln during the firing, I moved the burner aside and lifted the mug out of the kiln and laid it in a nest of leaves that were nearby, just like you would do if you were doing a rake firing, right? 😁
I covered the hot mug with more leaves and a clay sagger. It smoked quite a bit and then I heard a loud crack and thought to myself that the mug must’ve just popped, being in a thermal “shock”.