Wood firing at Wytham Woods

It’s hard for many potters today to imagine a time before electric kilns. From research I discovered that Frances Richards would have fired her work in a kiln in her garden (possibly a number of different kilns built at different addresses or the same kiln deconstructed and rebuilt again) and coal or wood would have been used as fuel. I feel I’ve barely scratched the surface of the logistics of this process though. Did she build her own kiln? If so, whose designs was it based on? Where did she get the fuel for burning? I’ve read that pyrometric cones were used as early as 1886 but would she have had some available to her in the early 1900s?

While my choice to focus on responding physically to her pots and making a new body of work has meant having to leave many of these questions unanswered, one thing is for sure. The firings would have been hard work. In order to find out for myself just what was involved, I found an opportunity at the beginning of this month to get involved with the Oxford Anagama project, an initiative set up by anthropologist Robin Wilson of Oxford University in collaboration with Japanese potters from Bizen and potters from Whichford Pottery in the UK. An anagama (meaning cave) is a wood fired kiln with a firebox at one end and flue at the other, usually with a long chamber and traditionally built into sloping hillsides. Three of varying sizes have been constructed at the Oxford site in a field adjacent to the ancient woodland and environmental research site of Wytham Woods. Under the leadership of potter Tim Thornton a group of around 18 or so of us got together to fire the smallest kiln.

I arrived on the Wednesday at the end of October and got to work straight away splitting logs down to a suitable size. Geoff Jones showed us how to use froes and mallets to split the wood into thin sticks for side stoking (useful when the kiln is much hotter at the front than the back). We packed the kiln using six different recipes of wadding as an experiment to discover which recipes worked the best. Wadding is a kind of putty which is used to separate the pots from the kiln shelves and the kiln shelves from the kiln props as the fly ash in the atmosphere has a tendency to coat everything and glue the contents of the kiln together. Recipes vary and in past firings I have used a mixture of 7 parts alumina to 3 parts kaolin (china clay) with water and perhaps rye or sawdust added to increase bulk.

The firing schedule split us into groups of three of four, firing for four hours at a time. My shifts were at 8am to 12pm then again in the evening at 8pm-12am. We lit the kiln the morning of the Saturday after spending the previous two days packing the chamber. By the evening we were hitting 700C on the pyrometer and once we hit 1000C on Sunday afternoon we began taking the kiln into cycles of reduction and oxidation. We slowly climbed the kiln up from here in a zig zag pattern, up a few degrees then down again, up a bit higher then down not quite so low. By very early on Monday morning all the pyrometric cones in the front of the chamber were down (the highest measuring 1300C) and by lunch time so were all the ones at the back. It is interesting to note that is in fact ‘heat-work’ not simply temperature that these cones measure, they give an idication of when the clay has matured. Although we expected to need to keep firing into Tuesday night, the sight of the kiln shelves warping under the intese heat meant the decision was made to finish at 2.30 on the Tuesday afternoon.

We experimented with many variables, opening and closing the active dampers, opening holes at the top and base of the kiln, side-stoking and adjusting the size of the logs we fed in and where at the front we fed the logs in to adjust the flow of air. Everyone seemed to have different opinions on how the kiln should be fired and which adjustments should be made for optimum reduction of the glazes and speed of firing. The air flow needs to be great enough that the wood can have oxygen and the temperature can rise but too much air flow causes the temperature to drop instead. It’s a fine balance and Tim made an effort to train us to become accustomed to listening to when more fuel was required, when the louder whooshing sounds died down. It was not an easy task! Wood firing expert Sebastian Blackie dipped in and out to offer us advice and guidance, I would certainly suggest that if you decide to fire on the site to organise to have someone with this in depth knowledge to check in once in a while.

In order to put the kiln into cycles of reduction, we would firstly stoke hard to hit a high temperature goal on the pyrometer, then block off all the entrances and keep stoking while starving the kiln of oxygen. When we stoked like this we would get great billows of black smoke snaking out from the cracks in the kiln walls and out of the tall chimney. This is the point where carbon monoxide can build up a layer underneath the kiln’s protective roof where we sheltered so it’s important to keep stepping back to get fresh air and take notice if you start to feel dizzy or light-headed. These cycles of reduction though are important in order to bring out the colourants of the glazes, for example the iron to create green celadons and copper for reds. A clean burn (in oxidation) is often done for a period of time at the end of a firing to brighten up these colours once the oxides have been pulled to the surface.

Brushing over many of the technical details (wood-firing is a whole art in itself) I was fairly happy with the results. With very little time between signing up to take part and glazing work to take along, I managed to throw a handful of small pots in a Potclays White st Thomas body (taking inspiration from the vase forms of Frances Richards) and glazing with a pre-existing white reduction glaze I had made up a few months ago. As a result of the ash flying around in the kiln there is lots of surface variation, flecks of impurities and the colouring itself is an off-white, much closer to the colour of the Majolicas Frances Richards used than anything I could have achieved in an electric kiln.

*Update: These pots (sold) were exhibited between January and March 2020 at the Ceramics Gallery, Aberystwyth Arts Centre as part of the group exhibtion Tanio/Ignite: The Incubator Project