All is Revealed! Opening the Wood fired kiln.

A wood fired kiln is like a living thing when it is full of heat and there is a muffled roar of flame from somewhere deep in its belly. After the firing, when the firebox is sealed, and the kiln is left to cool, the living thing slips into a deepening sleep. This kiln is well insulated, and it takes many hours for the heat from the chamber to seep through to the outer wall of the kiln, and the following day it is pleasant to run a hand over the outside, and to feel that warmth, it is like brushing the flank of a huge cow or horse!

Two days after the firing it is safe to slide open the chimney dampers and carefully pull a brick or two from the bricked up fire mouth, and maybe a spyhole brick from the chamber, to help air circulate. After a few hours of this, the door of the chamber can be unbricked, a few at a time, and as the gap in the chamber door widens, the potter gets a glimpse of the fired pots inside.

I am sure that levels of anxiety go up measurably in any potter at this moment, as it is when the work is seen, and better still when it is plucked still warm from the kiln and held in the hand, it is then that the potter knows if the firing has been a success and if there are any "treasures" to be found. This firing, being a first test firing after major changes to the kiln, was always going to be full of surprises and things to learn. The terracotta pots that filled the kiln's belly ranged from a rich brown to an orange-red and were able to tell me a great deal about how the heat in the kiln had been distributed.

In this case, rather hot low down in the chamber and cooler towards the arch of the roof. The variation had been expected, but it was helpful to see the evidence of it, and the range of heat from front to back of the kiln too, more subtle than that from bottom to top, but it was there never the less.

Unloading a wood fired kiln, even a comparatively small one, can take longer than you would think for it is not just a case of reaching into the kiln and pulling out pots, but nearly every pot in this firing had been fired on little pads of clay and sand called wadding and this had to be removed. Wadding lifts the pot a little way so it doesn't stick to the kiln shelves and also allows some circulation of heat under its base.

The wadding could sometimes be broken free from the pots just with gentle finger pressure, but most of it had to be smartly tapped with a little rubber mallet. This was always the case where the pot had got slightly overfired, as wadding and the pot had started to form a bond. As this was an earthenware firing that did not need to reach the heady highs of stoneware temperatures, I made the wadding from a mixture of builder's sand and earthenware clay, roughly equal parts of each. This worked quite well, and there were few real scars, and rarely damage done to the pot. The beauty of using earthenware clay and sand was that it would leave a mark the same colour as the pot*.

I was very thankful that most pots have fired well and there was no bloating or slumping of the clay in spite of some pots being fired to a very high temperature, and we will have some nice pots to put up for sale in our gallery.

Whilst most pots were a success, some small garden pots were a little damaged around their rims where I had fired them rim to rim and had separated the rims with wadding. In retrospect the wadding was probably not necessary, and it did chip a few of the small pots when the wadding was removed. I am sure we will have no problem finding a use for them in our garden!

One rather heavy bowl that got too hot did have some damage to its foot.... so I will probably use it as a bowl for bread making! After the wadding is removed, I usually take a few minutes cleaning the pot of any wood ash or debris (wood fired kilns can be rather messy), and I also make sure that the foot of the pot has no sharp edges or projections. Imperfections are sorted out with a diamond sharpening stone, such as is used for sharpening chisels or plane blades. I put together a video of unloading the kiln, and I hope this gives a bit more of an idea of the process.

*When I make wadding for a stoneware firing it has to be very refractory, and capable of crumbling away from the pot easily after the firing. For stoneware wadding I use a more complicated "brew" of alumina hydrate, china clay, a dash of ball clay and some stoneware grog, but some potters use a half and half mix of alumina and china clay. Other potters fill sea shells with clay and sit pots on those, like many things in life there are often multiple solutions to a problem!