Thursday, November 20, 2008
Firing and Pyrometric cones
Just finished 11 hours firing. There were not much wind today.
When firing the kiln, we use the pyrometric cones as one of the guide. Cones measure the maturity of the glaze by time and temperature. If you fire quickly and reach the target temperature, the glaze sometime is not matured as desired. It is like the cooking turkey, you can cook outside of the bird golden brown quickly at higher oven temperature, but inside is not cooked well. Quick fired piece sometime does not have the depth in the glaze. Good firing requires the time and the temperature to develop interaction between glazes and the clay body,
I use cone 9, 10 and 11, 2332, 2377 and 2394F respectively. I set these cones on the clay and place inside the kiln where you can see through the spy hole.
As the firing getting close to the end, the cone starts to bend. Pictures above shows cone 9 down, cone 10 60-70%, and about 20 minutes of soaking to go.