The purpose of this firing was to fire the inner wall of the furnace to 1150°C, so the furnace would shrink and the walls would move inwards along the top of the firepit. The inner wall shrank downwards and inwards, but did not move at the base, leading to several cracks in that area. The outer wall also shrank, but not as much as the inner wall, and also not moving at its base. This lack of movement was disappointing as we had tried to build in the possibility of movement using plastic sheeting. The weight of the furnace (about 540kg) was just too much.

For this firing, we removed the shelf supports so that the furnace could be fired unhindered by anything inside it.

One graphic result of the shrinkage is seen in the photographs of the thermocouple. It was originally horizontal, but started to move as the temperature rose above 1050°C, ending up about 2" above the bricks it was originally resting on. At this height, the inner wall had shrunk downwards about 1" more than the outer wall, and the thermocouple had pivoted on the hole in the outer wall, causing it to move upwards.

At the end of the firing, we blocked up all of the entrance and exit holes and allowed the furnace to slowly cool overnight.

The graph of the planned firing schedule also shows our attempt to keep to it - not so easy when firing with wood! On the graph, each vertical line represents an addition of 10kg of wood.