I fired the kiln on Friday. It was very claim warm day (80°F outside) until toward the end of the firing (about 2000°F), then the rainstorm came with gusts from the south. The winds started sucking air out from the kiln, and the oxyprobe reading hit zero. I needed to lowered the gas pressure while closing the damper, and close the windows at the studio. It heated up the studio very quickly, close to 100°F. It lasted about 30 minutes, and became less windy so I could open the windows. I opened the kiln today, and it was another good firing. I guess the oxidation at the later stage of the firing did not affect the result.
Here is before and after pictures. Glazes do not have the same color before and after firing. Glaze is a glass structure over the clay, and its color is refection of the metal particle inside the glass, and varies by the thickness of the glaze application. The thickness is hard to measure and observe. Redish color is from the red iron oxide.
These are new saggars with fireclay. It shows different colors on outside, tan and white, that reflect reduction and oxidation. However, I got good reduction inside the saggar as well as the bowls stored inside.
[Saggar firing is a technique for the firing of pottery. Saggars are ceramic, boxlike containers which can be used to enclose or protect ware in kilns. Traditionally saggars were made primarily from fireclay. Saggars have been used to protect, or safeguard, ware from open flame, smoke, gases and kiln debris: the name is a contraction of "safeguard". From Wikipedia, the free encyclopedia]
I have four to five firing done with the saggar placed at the oxidation spot, and got the good reduction constantly. The best result was achieved when the sagger was flipped over. I tried to placing the plate as a cover, with different gaps, that was not satisfactory.
I used the white stoneware body for the sagger, and it started to show a sign of the bloating. This clay is not meant to be the saggar and repeated firing. I made new saggars, with mixture of roughly 50% fireclay and 50% white stoneware. I hope this will last longer.
With the saggar, I was able to fire a relatively small piece related to the shelf space. I still like getting two small pieces rather than getting two seconds. Now I am getting close to 90-95% of good pottery out of the kiln. I am almost done throwing for now, and am ready to fire the kiln 2-3 times in next two weeks. Then I am ready for the first three shows.
Fired the kiln over the weekend. I placed a sagger with a small gap this time. It almost reduced. I think a gap was a bit too big, but this is the solution for the oxidation problem I was working on last couple years. I did not loose any pots in this firing, made me a BIG smile. The first four festivals for this summer are set. I updated the schedule.
Custom order planter under way.
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