Wood Firing

Wood Firing, August 28th 2008

This was the third firing I had seen so far since I joined the Department of Ceramics. In this firing, I got to know a lot of new things which I did not in the last two firings. Starting from the initial step i.e. the kiln loading, I saw the whole procedure that how to manage the inside space in a proper manner. I got to know some good tips, like Raania’s idea of adding fine wood shavings in the Wadding and that really worked as it came off easily from the test rings which we took out after different time periods to check if the glaze had melted properly. To initialize the firing, two gas burners were installed in firebox of the kiln for two- three hours in order to heat up the kiln. This was also essential so that anything even slightly wet, especially the wadding should dry up before starting the main firing.

After we started stoking the wood, we had to maintain the temperature so that it did not drop. For the first 1100 degrees, the pyrometer worked perfectly, but after that we had to rely completely on the cones. Keekar wood was stoked more than the thin wood because it burnt gradually as it was necessary to maintain a gradual rise in temperature. The thin wood pieces were also used in order to bring a rise in the temperature when there was a need. The whole day was a fun filled experience in which we listened to music, had lots of food and got to know something new at different parts of the firing. Our concepts about reduction and oxidation were cleared to a great extent. When the fire came out of the fire box in a manner that it seemed as if it is hungry for air, that was reduction. Similarly there was a time when a lot of fire was coming out from the back of the kiln which showed that at that particular period, reduction was taking place at the back of the kiln. On the other hand, if the fire was within the fire boxes, it meant that there was sufficient oxygen for combustion, thus meaning that oxidation was taking place. So basically, a cycle of Oxidation and reduction was being maintained by the adjustments of the dampers and the air ports.

In the second half of the firing, where the temperature was towards the higher side, flame started coming out from the chimney. The type of flame gave an idea of the fire inside the kiln. A short white flame (which is not very frequent) was a good sign that the heat is even and steady throughout the kiln. It is also known as a hungry flame which means that there is requirement for quick stoking. On the other hand, is a big flame which indicates that there has been a sudden rise in temperature. When it starts going down, it means that the temperature is dropping, therefore it’s essential to start stoking before the flame dies out completely.

Towards the end of the firing, quick stoking is required to see the short white flame therefore one must be quite alert.
In this firing, I got to know about a new term i.e. reduction cooling. To end the firing, the fire box is stuffed with wood so that it burns in the presence of little air present within the kiln. For this, all air ports are closed and after stuffing, the firebox is covered with slabs so that the fire dies out gradually and the wood burns in little oxygen.