Sunday, December 7, 2014

Raku Firing & Kiln Trouble

This was a busy firing week at school. We fired two and a half cone ten glaze firings in the gas kiln during the week and spent Saturday raku firing outside. We also fired several bisque and low temperature glaze firings in the electric kilns. Monday is the final critique for my beginning classes, so we are obviously getting as much work finished as possible.

Our school raku kiln shortly after we started firing on Saturday.

Now normally we don't fire half a glaze firing, but this was my first experience with a thermocouple that failed during the firing and caused the kiln to automatically shut off. The kiln went from 1949 degrees Fahrenheit at 4:20pm to 2400 degrees at 4:40 and the kiln shut itself off. I wasn't worried that it had actually gone up 450 degrees in twenty minutes, since the kiln has fired in a predictable way for dozens of firings and the pyrometric cones in the kiln weren't even soft. However, when I tried to restart it, the kiln kept automatically shutting off and I eventually gave up and let the kiln cool down.

Loading the barrel smoke firing.

Later I learned that the thermocouple is designed to read the highest possible temperature when it breaks, thus triggering the automatic shutoff. I also learned how to bypass the broken thermocouple for future firings. That night, however, I didn't feel comfortable taking the wiring apart during the firing. We let the kiln cool, added a few more cone packs to help us gauge temperature and refired on Saturday.

An independent student instructing a beginning student on how to load the barrel.

The raku firing this weekend went fairly well as far as weather and the pieces were concerned. We finished a bit early with all the pieces fired and my students helped clean up the leaves and paper in the kiln yard. The day was sunny and relatively warm by the early afternoon.

Adding shredded paper to the barrel before lighting it.

Our first propane tank froze up after the third firing.

Red/orange heat in the raku kiln top during firing.

After the firing I encouraged the students to move some of the detritus of the studio, including extra shelves, bricks and kiln posts to a different part of the kiln yard.

Pulling work from the reduction bucket after raku firing.

I think the students who fired were generally pleased with their work. The day included more students studying than most raku firings. We had intended to fire in November, but the weather prevented the firing. This firing was about as last-minute as it could have been as classes ended Friday and finals begin Monday.

A raku glazed piece cooling after post-firing reduction.

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