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Kiln plans

Firing log

February 2006 firing

Reflection on firing
Technical
February 2007 firing
March 2008 firing
Wysing anagama re-build 2006.
May 2007 firing

September 2008 firing

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The anagama kiln at Wysing Arts Centre in Cambridgeshire UK, was built by Izumihara Masanobu and other volunteers including Paul McAllister and Stephen Parry over the summer of 1997. Paul, Steve and myself have been firing the kiln since 1998. This kiln is much more challenging to fire than the Loughborough kiln due to the smaller firebox ( very small relative to the chamber size), and the lack of a grate (the fuel being dropped directly onto the kiln floor). The kiln was originally built to fire to around 1250C. The work that was fired in it was cyclical, in that, Masanobu only anticipated getting the front stack of pots out as finished. He packed the back of the kiln with pots to be bisc fired. These pots would then be at the front of the stack in the next firing. We have always attempted to fire to 1300C plus in this kiln, which we have achieved each time with around cone 10 (1280C) at the back.


In 2000 a salt chamber which was built by Paul and myself between the back of the anagama and the chimney, was knocked down and the chimney rebuilt to the correct dimensions for the anagama chamber and firebox size. This improved the firings considerably, the draw from the chimney now not being compromised by the volume of the salt chamber. It still took immaculately timed and delivered side stoking with split pine to coax the temperature to where we wanted it to be. The results produced from this kiln vary from the Loughborough kiln due to the variation in kiln design. The shape of this kiln is a more exaggerated upside down boat shape which creates its own unique micro climates and flame channels through the work within the packing space. Also, because we tend to fire this kiln for longer (four to five days), the accumulation of ash and the volume of flame borne alkalis in contact with clay surfaces are increased, drawing dramatic colouration from the clay bodies used. The increased duration is needed in part to achieve an even temperature throughout the kiln. The early part of the firings predominantly dry the kiln, which gets damp from being quite exposed. One of the most valuable assets of this kiln is that the wood is stoked onto a flat floor which also becomes the front packing space, this allows work to be stacked where it can be engulfed by the coals, producing wonderful charred and fire marked surfaces.


In February of 2006, Steve, Matthew Blakely and myself fired the kiln for the last time in this incarnation. For years we had often discussed the possibility of extending the front of the kiln to allow both for a grate to be fitted and also to create more packing space. The grate issue was a big drive for us. The air that could be let into the firebox was so limited and made it very hard to achieve the sorts of temperatures that we wanted. Air could only enter the firebox through the lower stoke hole, which meant that the coals burnt down either very quickly in the middle or, if the stoke hole was closed, the coals would stay too high to stoke enough fuel to gain temperature. After the February firing we decided that we would take the plunge and finally rebuild the kiln.


We began work on dismantling the front of the kiln in July 2006. As stated earlier the major asset that we wanted to build upon was the flat stacking space/firebox floor, increasing the space available for this zone. Also creating space for a large grate that would allow us to control the air being drawn into the kiln beneath the coals and being drawn up and pre-heated by them. The first job however was to knock down the existing front of the kiln. As the original front curved in from the sides towards the front we had to take the kiln back to just before this curvature started. This done, we marked out where we wanted the new firebox to be, working on the dimensions relative to what would finally be the overall packing space, the exit flue space and the chimney dimensions. (When the chimney was rebuilt the dimensions were kept generous to allow for alterations). The foundations were placed and a brick floor for the bottom of the grate was laid. Once this was done, a dry run was laid out to visualise where the sidewalls, and the door would sit. Our plan was to have the height of the grate the same as the old kiln floor. Once the outline had been agreed the bricks were motored in place using a fireclay/sand mortar. Also the front hot wall of the under grate area was built, in the process cleaning up the front of the old firebox area.


One of the problems which we anticipated was our ability to tie in the new structure to the old, due to the old kiln front being constructed using many small cut bricks (Please click here to view images from the original kiln building). The line to which we took the front back to, did not provide us with clear regular keying in points. We had to create some of these by knocking out half bricks in several places up the vertical wall and remaining arch, creating points which could be built out from.


When the vertical walls were nearing completion, we began work on the former for the arch. We wanted to stay as true as possible to the original sweep of this arch from front to back. Two cross section formers were built initially, the first to support the existing arch and the second to indicate the door height. (The height of the door had to allow for the grate and provide us with enough drop to allow us to stoke plenty of fuel into the firebox). Using flexible lathes we constructed the front to back curve of the arch and then cut two more cross section formers to provide some added strength. More lathes were laid from the back section of the kiln to the new front wall. Once the former was complete we could continue with the brickwork, building in two side stoke holes on either side. The first enabling us to side stoke into the firebox and the second to allow us to side stoke into the new flat packing space. At the point where the arch springs from the vertical wall a layer of inwardly tapering bricks were laid to change the direction of the hot face bricks, then subsequent layers of brick were laid along the line of the former with the first few courses being corbelled in to cover the left and right corners of the new firebox. The same method of tying in was used as in the vertical walls trying our best to interlock as many of the new courses with the old. Towards the top of the first brick arch, a row of bricks was laid on end down either side to act as a lock for the second layer of bricks. The key to this first arch was then formed using brick and rammed high temperature castable. A small blowhole was placed just above the new front packing space, a place to heat the kettle as much as a future guide to back pressure within the kiln. Any gaps between the back edges of the bricks were then rammed with dry fireclay creating a very strong primary arch.


The second layer of arch bricks were then laid over the top of the first ensuring that no brick meeting points duplicated the interior arch. These were locked into the up ended bricks in the primary arch and again the key brick was cast with high temperature castable and brick. Finally this secondary arch was rammed with fireclay to create a solid arch. Any holes that were unavoidably left where the new structure keyed into the old were also rammed with castable on both the primary and secondary arches. The internal kiln structure was complete.


The next job was to provide substantial buttressing for the new kiln. Due to restricted space around the kiln we decided on concrete to reinforce the structure. Roughly one ton of concrete was mixed for each side of the kiln and shuttered up the front and sides to just above where the arch sprang off the vertical walls The front corners of the kiln were identified as key points which needed strong reinforcement so plenty of concrete was cast at these points. It was also cast back and bonded to the existing concrete on the back half of the structure. New concrete was also added to the old, to raise the height, again to above the arch springing point and capped with heavy stones. Separate sections around the four side stoke holes were cast and bridged by stone. Finally the flue which extends for about a metre from the back of the chamber to the base of the chimney was re coated with a sand, fireclay, pearlite and cement mix to fill any cracks which had appeared over the years and once again make a good seal between the two structures.


With the eight hundred heavy bricks which we had to re-build the kiln we also acquired over a thousand secondary insulation bricks. It was decided that we would use these to provide the new kiln with good insulation. The previous incarnation of the kiln did not have any insulation to speak of, simply a skim of cement with a little straw mixed in. The capping stones for the concrete buttressing were then used as a bed to start laying these insulation bricks. Laid broad face on to the heavy brick structure and bedded in place with a fireclay and sand mortar. Being easy to cut with a saw made the job of keying this final arch at the top easier and again any gaps between the outside edges of these bricks were rammed with dry fireclay so that this final arch was also tensioned. Finally two large concrete slabs were laid at the front of the kiln, to provide a good stable working space when packing and stoking. In mid November 2006 the new incarnation of the Wysing anagama was complete. It had taken roughly six days work to get the kiln to this stage.


The kiln is now being left alone until January with the former still in place to allow the concrete to cure slowly and the whole structure to settle down. We aim to resume the work in the new year. This will consist of removing the former and cleaning up the brickwork from the inside and ramming any gaps which exist between the new and old structures internally. We are also going to extend the kiln shed to accommodate the longer kiln. We are aiming to fire the kiln for the first time in February 2007. This firing and the results will be posted on the site. Please click here to view packing, firing and unpacking images from this firing.

Ben Brierley 2007

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