Anagama Kiln
The Lost Anagama
This kiln was buit by Mike Oosterbaan
Loading – 11th May to 14th May 2009
I started the process of loading the kiln by building a wall. After checking how much work the contributing potters had brought along and the numbers of shelves, I realised that I had room at the back of the kiln that needed walling off. So I built a wall with holes at the bottom to allow the flames out to the chimney, then I set up the back two bungs and started the jigsaw puzzle that is kiln loading.
Luckily many of the potters had risen to the challenge of making big pieces and there was a good range of shapes and sizes to choose from. The loading actually took less time that I anticipated, with most bungs only having 2 shelves to break up the flame and allow for the varieties of shapes. Tumble stacking was experimented with where possible, but because of the raw nature of the pots and their construction, caution was the name of the game.
We had finished loading by Wednesday night, giving me all Thursday to built a wicket and do all the odd last minute jobs, like rigging lights for the night.
Firing – 14th May to 18th May
I lit the kiln at 6pm on Thursday night and the first stoking crew settled in for their first shift of 4 hours. Given the numbers of potters taking part (19 in all) it meant that each crew had up to 5 people and shifts rotated around 4 hours on, 12 hours off. The first stage of candling was to dry out the ware and warm the kiln up, also to start drying out the firebox. So a fire was built up outside the kiln with only the tips of the logs poking into the entrance of the lower stoking port. Slowly the ember bed grew and cascaded into the kiln.
At 10am on Friday the fire was slowly eased further into the kiln, as the embers were staying live much longer on the firebox floor. By midday the fire was now inside the firebox with only the ends of the logs sitting in the stoking port.
These early sessions are very peaceful, the only error you can make is haste, the fire burns quietly and the cavernous kiln sucks up the heat like a sponge. A leisurely firing process that leaves plenty of time for reading or chatting by the fireside.
4pm and we can see soot burning off the pots in the firebox, so we can confidently start stoking more wood, filling up the bottom stoking port. This raises the temperature fairly quickly so that some dull glow is seen in the first spy holes a couple of hours later.
Then by 9pm we have attained quite a bright orange at the first spy and good red colour in the first side stoke port. This slowly advancing colour change progresses through the kiln so that by 2am on Saturday the front of the kiln is over 1000 degrees and the ember bed is advancing towards the pots. This is the cue to change from stoking the bottom to stoking through the main stoking port, using the metal door to control the air and bricking up the lower stoking port to just act as a source of air for the embers.
The kiln is also now warm enough on the outside to start drying off some of the sopping wet wood we have, curtesy of the end of the golden weather and the sudden onset of a wet autumn. We also start experimenting with the blowholes to see if they help with the stoking rhythm – which they do, for a while.
This new stoking rhythm also really gets the kiln moving along, with flame flowing almost to the back of the kiln and heating it up to 800 degrees by 6am. New crews bring fresh arms and the kiln is insatiable for wood – wet or dry, so we quickly see the kiln change; by midday on Saturday the first cone 6 at the front is down.
This momentum is maintained and cone 8 at the front follows by 1.45pm. Flame now pushes all along the kiln and at 2.45pm the first hints of flame out the chimney on good stokes cheers everyone up. By 3pm I decide to slow the kiln down a bit and try to level out the temperature gradient from front to back. I pull out a passive damper brick and restrict further the air at the front. The stoking rhythm changes to cope with the reduced air flow and the emphasis is on keeping a hot ember bed glowing, being careful of wood selection for stoking and not over stoking. The cones at the front keep moving, but at a reduced rate and the cone 6 half way back in the kiln goes down by 6pm.
In an attempt to even out the kiln, side stoking is started about 9pm on Saturday, lightly at first, but soon a more vigorous rhythm is established that burns off embers at the front but builds them up over the pots at the side stoke ports. Playing with the active damper also creates more backpressure and flame. This helps bend over the cone 8 half way down the kiln and keep the night shift busy.
Sunday morning brings a more controlled approach, but the feeling is that the kiln is still drying out at the bottom and so a steady stoking rhythm is maintained that keeps shrinking the wood pile at a good rate. But that means that on Sunday we’re off to gather more wood – this time some fairly rotten poplar, more like sponges full of water than wood, it nevertheless burns well after a bit of drying.
The rest of Sunday is devoted to burning the last of the side stoke wood, with a particularly busy session in the middle of the night that got rid of a pile of bamboo and other tree clippings.
4am on Monday and with everything else burnt we now move onto the dry pine stacks we’ve been reserving for the final temperature push. The passive dampers are put back, and a bit more ember air is opened, allowing the kiln its maximum draw and a hot burn at the front. A very steady stoke, dictated by careful flame watching soon brings the whole kiln up to temperature, by 6am the back cone 8 is down, the cone 10 half way back is flat and the cone 12 at the front is molten. By 8am the back cone 10 is down, the cone 12 half way back is down and we still have a lot of pine to go. So I slow the kiln down a bit for about 3 hours, and at 11am we again give the kiln a final push and the last cone 12 at the back is bent half over.
Given how wet the Waikato is at this time of the year, and how much of our wood was wet when stoking we decide not to water cool the kiln, but simply clam it up, tidy up the mess and head home to sleep.
Unloading – Sunday 31st May
Unloading day dawns surprisingly warm and sunny, so unlike the rest of the weather we’ve faced during the firing. The wicket is taken down and the kiln is unloaded by a chain gang of willing and expectant hands, unluckily Charade’s hand was a casualty of a sharp shard. A swath of brown pots lying on the grass, guestimates at about 350 pieces in total, confronted everyone at the end of the unloading. Anthony and Lesley, guardians of the kiln, generously shouted us lunch and drinks to celebrate a successful firing. Everyone went home with treasurers and some disappointments – but that’s anagama firing.
