Thursday, February 9, 2012

Going for more Ash Buildup

What a great firing we had yesterday. I started feeding the kiln small sticks of wood at 5 a.m. We finished up at around 7:30 p.m. That's a 14 1/2-hour firing. We employed a technique we read about in Japenese Wood-Fired Ceramics. Utilizing the pyrometer (high-fire thermometer), we brought the kiln from 2,300 degrees F. down to 2,100 and back up to 2,300 repeatedly for a couple of hours or more. This is supposed to create more buildup of ash on the pots. We also threw in a few handfuls of sawdust mixed with some ash collected in the bottom of the kiln's chimney.

We reached a temperature of around 2,500 degrees in the very front of the kiln. The picture at right shows the last pyrometric cone (cone 14) bent at the end of the firing. Cones are made to bend at specific temperatures and are the most accurate way of measuring the effect of time and temperature in a kiln.

The bowl on the right is glazed in a shino glaze, which received a lot of ash. You can see the ash as texture on the pot. The other pot is a tea bowl by fellow potter Phillip Pollet.

Cone 14 is quite hot. I'm not sure how accurate a reading you get when reading cones in the front of a wood kiln. They are blasted with ash and other volatilized compounds, which might affect their performance. Same goes for the pyrometer at this degree of heat. The digital display of temperature begins to fluctuate more than usual. If I can remember to do it, I'm going to set some cones in the front of the kiln next time behind a shelf post to protect it from the ash and see if it makes a difference.

We're pretty sure we reached cone 10 (2,340) toward the back of the kiln, and we're hoping for cone 8 or 9 in the very back (we neglected to place a set of cones in the very back where we could see them).

Here's a few more pictures:

 Pots on the floor of the kiln next to firebox

 A glazed bottle at the back of the kiln 

 Posing potters Levi and Michael...
Firebox door was left ajar, and a 
brick was pulled out.

Toward the end of the firing

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