Performance Kilns

These kilns illustrated below are a part of an ongoing series of ‘what if’ experiments. None of them would have been possible a century ago as it is the easy access to quality burners and fuel that allows us to consider making a block of ice into a kiln. This technology also allows us to explore ideas about fire, and its’ containment. Being potters we are all intrigued by fire, the transformation it brings to clay is well understood, but the nature of its work inside the kiln is less well so. For example, where exactly does the flame go in a kiln, if you open a door to peer in you affect the dynamics, so build the kiln out of ice, allowing you to see inside without altering the flame’s path.
But to be honest, a lot of this also boils down to sheer fun and a healthy suck it and see attitude.

Filing Cabinet Kiln
Potato Kiln
Wood Kiln
Ice Kiln
Phone Book Kiln
Sand Castle Kiln

Filing Cabinet Kiln

It was the result of a spoonerism, the result of looking at an old surplus filing cabinet and talking about different kilns or you could put it down to a fit of office vandalism, whichever explanation you prefer is fine by me. It seemed an interesting idea, and as we had our annual Guy Fawkes event to plan for, particularly pertinent.
I cut out the floors of all the top three shelves and inserted a mesh floor in the top draw. I then cut a small hole in the back at the bottom for a gas burner. The kiln was then filled with wood and fireworks and other useless combustibles, like office files. I found a sacrificial pot that cried out for a very special raku experience and popped in the top draw (nothing but the best for this pot) and kept it company with a pile of sparklers.
Once the crowd of eager ASP members gathered I lit the burner. Slowly the smoke oozed from the filing cabinet; after a while it seemed choked up, so I opened the bottom draw, for a bit more draw and away she went. Thinking it might be interesting to check on the top pot I went to peek in the draw, only to be given a hell of a fright as the fireworks started to go off and one shot the top draw out like a till draw. The kiln certainly got warm enough, the effects on the pot were interesting if not exciting, but to see such an icon of the office engulfed in flame was reward enough.

Potato Kiln

I was invited by the organisers of the Uku North conference to create a performance kiln, something to entertain people on the Saturday evening. I decided to try another incarnation of a kiln that Peter Lange and I built in Wales, 2013 as part of the International Ceramics Festival. Using the unlikely material of potatoes as a kiln building material was a hit at the ICF so I figured it was time a NZ audience got to see this marvel.
For Uku North I re-designed the kiln as an updraft beehive shaped kiln with two burner ports. Again I used #8 wire as structural support and bamboo skewers as a way to tie the potatoes together. I requested 5 bags of potatoes and turned up on Friday morning with templates, knives and burners.
The kiln quickly took shape and in no time curious bystanders were enticed into helping cut the 50kg of potatoes into potato wedge bricks. On the Saturday the kiln attracted lots of attention, with various predictions about the temperature it would likely get to. I had to load the kiln as I went, 2 shelves full of pots destined for a history making firing. Running short of spuds, I sent out a request for two more sacks and a pumpkin. These additions saw us get home with hardly a potato left over, the pumpkin formed an ideal chimney.
At 10pm on Saturday night, with the moon heading for an eclipse, I lit the burners on the worlds 2nd potato kiln. I started gently to warm up the pots inside the kiln. After half an hour the burners were cranked open and the spectacle of a pile of potatoes, held together with skewers, oozing flame everywhere pleased the crowd. It smelled delicious, it looked spectacular, the pumpkin was being flame roasted inside and out, I threw the salt in, the walls started to collapse and after 1 hour 10mins it was all over.
The pots got to about 800 degrees with some odd effects from the salt mainly. Some brave people tried the spuds, peeling off the charred outer layer to nibble the delicious part roasted, part steamed cooked potato. The pumpkin tasted best in my opinion.

The First Wood Kiln

The plot behind this kiln rests with Peter Lange, the other ASP Centre Director. He took it literally when a wood kiln was proposed to be built. After buying a couple of rail-way sleepers Peter, Mike and I set about constructing a very simply, if somewhat rustic, kiln. The walls and roof were all about 20cm thick pine, with the walls having the end grain pointing in. The floor was insulating firebrick and common brick.
A teapot of mine and a vase of Peter’s were to be fired, even salt fired if we could get it hot enough. Cones 6 (1220 degrees) and 10 (1300 degrees) were also placed inside. The kiln was lit with a big gas burner and caution was thrown to the wind as a race between the kiln reaching temperature or burning down began. We hoped that the embers would help insulate the kiln and slow down the rate the wood would burn. Cone 6 went down in a remarkably hasty half hour.
During this time we were also experimenting with chemical to change the colour of the flame; things like strontium chloride and various copper salts provided an interesting range of colours, all somewhat overwhelmed by the yellow of the burning kiln.
Once the cone 6 went down we started salting, We also had to start replacing the door, a weak point of our design, we ended up burning through three before the firing ended. Once cone 10 had fallen and enough salt thrown in we pulled out the pots as they were in danger of the imminent collapse of the kiln roof. We also needed to hose off the embers as we realised the wooden table this whole shebang was on would also soon start to burn.
One of the more remarkable artefacts to emerge from this kiln was not the pots (average), but the amazing burnt and charred wood itself.

Ice kilns

Where do these ideas come from? In this case it is a result of sitting around the large kitchen table at the ASP drinking large amounts of tea. Influences arrive from far and wide, like when we heard about the residency of potter Raewyn Atkinson in Antarctica and thinking how she could fire her pots. Throw in a bit of technical troubleshooting advice on how fast we think a block of ice can melt and bingo, the Ice Kiln is born.
Months later we achieve moderate success with our first attempt, 3 slabs of ice frozen in the kitchen freezer are assembled on a fibre base and a pre-heated bisqued pot is placed inside before we let loose with a large gas burner. This spectacle was photographed and it is those images that persuaded us to try and refine the idea and have another go. This time we had a deadline; Guy Fawkes night, our traditional time of mayhem. We acquired a large chest freezer and invested in a $100 block of ice. The block was 1000mm long by 400mm wide and 300mm high. I cut two slices off each end, then cut a block out of the centre. Then the two slices were placed on top, making a simple box kiln with no floor. A hole for the burner was cut in one end and then the whole kiln was put inside the freezer to re-freeze for a couple of days.
On the night I cut a hole for the chimney. A pre-heated sacrificial bisque pot was placed inside and the burner was lit. Once the outside of the kiln was cleared with water it revealed a beautiful clear box of flame, seconds later the ice developed large cracks, like crazing on pottery. But as it didn’t fall apart we let rip with the burner. We also experimented with letting off various types of fireworks inside the kiln, some of which shot out balls of fire, others changed the colour of the fire to pink or green. The finest were the small bright white strobe lights that lit up the whole kiln. It was great to see children putting their hands on the cold ice, whilst only 10cm away was a roaring hot flame, seen as clear as through glass. In the end the firing lasted about 45 minutes, after that the chimney hole was about half the kiln size.

Phone Book Kiln

When it comes to material selection for your next kiln and you want to try something a little experimental then Chris Southern is your man. After the ‘wood kiln’ experiment a new idea was needed and fuelled by the ever present cup of tea his genius came up with phone books. Although the idea was born it took until November 2005 before we sourced a sufficiently large pile (200 odd books), courtesy of AUT. The timing of the firing also tied in well with the Auckland Studio Potters usual Guy Fawkes extravaganza.
The design was simple, a tunnel leading to a hole in the roof as a chimney. The roof was patterned after the Minnesota Flat Top kiln, the walls a traditional stretcher course. We built it on an insulation brick base, a layer of fibre, then a wooden table top. We loaded it with an assortment of pots, mostly stolen from students as none of us wanted to sacrifice our pots in such an uncertain beast. Luckily our big gas burners had just returned from an overhaul and could provide the required BTU.
We lit up at 8pm and after an initial gentle start to try and save the cones we soon cranked it up – blowing up the cone pat and depriving us of any chance of figuring out the temperature. The fire soon took hold everywhere and filled the chamber with flame. We hoped that the tension on the roof would prevent it burning too quickly, however the force of the paper charring and expanding slightly slowly dragged the roof down into the chamber. The walls and chimney stayed in remarkable good shape throughout the firing and even after it was all over had only charred about 1/3 of the way in. The problem area was around the burner as so much air and heat around that area meant that it collapsed first. It was difficult to reach any high temperature as the kiln choked with so much fuel. In the end the highest we got was about cone 05 (1050 degrees C). We gave up with the burner when we realised that just pumping air into the kiln produced a better spectacle. Slowly the kiln disintegrated and fell apart, the pots inside remained unharmed and Peter Lange reached in with a pitch fork to retrieve them. Why he bothered I don’t know as a more disgusting bunch of blister glazed work you would be hard pressed to find. So all in all I great success as a spectacle, a dismal failure as a kiln.


Sand Castle Kiln

This kiln grew out of an experiment I played around with years ago with casting lead into a rigidised sand mould. I remembered that the sand went pretty hard and that it took the heat of molten lead. So this year (2009), to coincide with another ASP Guy Fawkes event I decided to have a go and build a sand castle kiln. My choice of materials was silica sand and bentonite. I did a few experiments first to figure out roughly how much bentonite I should be adding and came to a 15% ballpark.
On the day this meant mixing 50 kg of sand with about 6 handfuls of bentonite – a very precise and calibrated handful measure. The fabrication started with borrowing a few left over scoria rocks from Peter Lange’s kiln and using them as a foundation. Next a cardboard tube was used as a flame tunnel for the gas burner, covered with a layer of compacted sand and a foundation for the walls was bedded into the rocks.
The rest of the construction was made using sand pressed into a small, wooden brick shaped mould and each brick mortared with a sloppy sand mixture. This building method offered huge flexibility and the bricks were surprisingly rigid. My most useful tool was a sharp fish slice I used to cut the bricks into the various shapes I needed. At the top I decided to use some beer bottle in the hope of creating flame cannons latter.
I finished the kiln just as the first guests were arriving for the evening’s entertainment. The gas burner was installed and off the kiln went. There was a pot inside the kiln – a hapless victim that I pilfered from the abandoned pot table and so I did start the flame off a bit gently. Peter couldn’t resist adding a few chemicals to the flame and the most spectacular was again the copper compounds. Then, getting bored and curious to see if the kiln would crack and fall over I let rip with the burner. Nothing. The kiln belched flame as expected, but no disintegration – although a few, initially alarming, cracks appeared nothing moved. I tried blocking the flame from coming out the top to see if the flames would come out the bottles (after I had popped their bottoms out) but no luck. I think the kiln was too wet at the top and not hot enough. Still, the possibilities with this type of kiln, it’s ease of making and different methods that would be possible and the fact that after it is all over the whole thing will just disintegrate in the next shower of rain makes it an interesting idea to experiment further with.