30 July 2010

Higham Hall in Cumbria ran a 7 day course ‘Japanese ceramics and kiln firing’ tutored by Shozo Michikawa. The course was offering an opportunity for potters with experience in studio practice to develop skills focusing on Japanese techniques and design. A full firing of the wood burning anagama kiln took place over 3 days and 2 nights and the week included individual instruction and demonstrations on hand building and throwing.

I have wanted to do this kind of firing for years to discover the reality of this rather fundamentalist branch of ceramics.

The kiln was built in 2003 and has only been fired 3 times. It has about one cubic metre of space for pots at the back of the chamber , the front being the fire box with no partition between the pots and the fire.

(This allows for a build up of ash which fuses with the clay to form a natural glaze -

that’s the idea anyway. Packing the kiln and the placing of work is a skill in itself as

different areas of the chamber receive different quantities of ash, heat, oxygen, flame, which all have an effect on the results.).

There were 10 of us split into two crews to cover the night shifts. During the days we took it in turns depending on stamina. (Gavin had to be frog marched to bed or he would have been there for the entire firing)

The firing plan was simply to fire the kiln very slowly to 200℃ then at 100℃ per hour until 900℃, then start and keep a reducing atmosphere for the rest of the firing until the wood ran out. Estimated to be 48 hours continuous firing. ( Not the famous 5 or 6 day

marathons but quite enough for beginners). We used 60% well seasoned pine sawmill

off cuts and We started the firing with a ceremonial offering of salt, fruit, seaweed

and salutations to Akiba San, the fire god of Seto region in Japan, to ask for a good and harmonious firing.

A small fire was lit in the ash pit mouth which went out, was lit again and with a bit of cosseting and a wax candle finally took hold. The pyrometer read 100℃ steadily for about 3 hours when it suddenly jumped to 450℃ at midday, so much for the slowly-to-200 plan.40% mixed hardwood.

Stoking the fire with equal amount of pine and hardwood gave a steady and regular rise in temperature until about 900℃ was reached after 10 hours. At this stage a reducing atmosphere was encouraged by heavy stoking and closing the fire door after each stoke to starve the fire of oxygen. Thick smoke emerged from the chimney and spy holes above the ware chamber.

A change of firing crew at 8pm took the temperature up to 1020℃ by 1am and the overnight crew achieved a steady rise to 1100℃ by 8am. The morning was quite hard going with the prospect of another 24 hours ahead but the weather brightened up. It’s a tiring process which doesn’t allow for distraction, one has to remain focused on the fire or the temperature fluctuates too wildly, but having to concentrate on only one thing is very peaceful in a multi tasking world.

The evening stokers took the temperature up to 1140℃ and then remained to help when the night crew arrived. By this stage we were stoking one or two small pieces of pine every 3-4 minutes. Trying to gain a few degrees of temperature with each stoke we eventually reached 1160℃ and managed to hold it there for about 5 hours.

about 3.30am on Wednesday the rain returned and Shozo decided there wasn’t enough wood left

for much longer. He got us stoking continuously, flames billowing from the fire mouth, the inter

ior of the kiln white hot, thick smoke and a red cone of flame rising from the chimney. Then after putting one last piece of wood each into the fire he smashed his piece on the ground, flung it into the kiln and closed the door. The firing finished at 4.30 and tired, grubby, satisfied potters wandered off to bed as daylight broke.

By thursday morning the pyrometer was reading 150℃ and the kiln deemed cool enough to unbrick the door. There was a good layer of ash covering the pots at the front of the chamber. Because of the pyrometer readings there was some doubt about how good the firing would be. We hadn’t been able to get the reading higher than 1160℃ and the chimney flame only appeared strongly around midnight Wednesday. The results coming out showed the pyrometer unreliable.

A cone 10 glaze (ave. 1250℃ ) placed towards the rear of the chamber was beautifully matured. There was some good fused natural ash glaze from the top left (stoking favoured that area) and a more matt, general deposit of melted ash on exposed surfaces.

Highlights of the week

  • Confidence gained from experience - loading ware, stoking during the different stages of firing, observation of the entire process
  • Knowledge gained from firing the kiln with a master potter (pretty good at sushi too)
  • Time to reflect and consider how this approach to firing could be used in my own work.
  • Homemade pizza at midnight cooked on the chimney flue!

It was a fabulous week which exceeded my expectations of the kiln and the firing process.

1 comment:

  1. The reason this is all out of line and the images in the wrong order is because my life is too short to battle with this ruddy site!!