Monday, 10 December 2012

Mini wood-fire kiln a sucess..maybe

I just finished a ten-hour firing of version two of my mini wood-fire kiln. Amazingly, I managed to get it to 1300 degrees C according to the pyrometer, but unfortunately the cones (7, 9 and 10) placed on the kiln shelf didn't go down. So, either I have a very inaccurate thermocouple, or some extreme hot and cold spots, which I think is more likely. I'm hoping that at least some of the pots on the ground level, next to the firebox, will have fully matured glazes. We shall see... it was an enjoyable experience anyway, and I was fully expecting to have to modify the design based on the results.


It seems my pyrometer was telling me porky pies, and nowhere in the kiln was the real temperature much above earthenware. :(  I suspect the pyro. may have been directly in the path of the hottest flames from the firebox and this gave a completely false reading.

The glaze had begun to melt on a few pots containing soda ash, hence a lower melting point, but on the whole, very disappointing results. The kiln was certainly burning wood efficiently and drawing plenty of flame through the ware chamber..problem seems to be that most of the heat went straight up and out of the chimney! While I was firing I had alot of problems getting the temperature to rise above 1050 degrees C so I thought the exit flue from the firebox might be too small, getting choked with embers. I'm now wondering if it was actually too large for the size of kiln..and that the chimney may have been too wide, pulling too much cold air through the kiln. The outside temperature was about minus 1 centigrade which probably didn't help!

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