The firing crew were Artemis, Brigitte and Svend. It was started slowly on Thursday morning and was slowly heated up with gas; at 4pm, the temperature was 200C so gas and hardwood were used. It was switched to just hardwood at 6pm. At 8pm, the temperature was 495C.
Brigitte worked the 10pm to 2am shift on Thursday evening then Svend took over until 6am Friday morning. Reduction started during Svend’s shift. Both Svend and Brigitte worked a 6 hour shift (6am to 12am and 12am to 6pm) during the day on Friday; Artemis joined the crew at 6pm and from then on, it was 4 hour shifts until Sunday evening at 6pm when Artemis had to leave. Svend and Brigitte carried on with the last part of the firing until 22:30 on Sunday evening.
During her shift on Friday, Brigitte switched from the main chimney damper to the passives because thick black smoke was coming out of the chimney and she was worried that it might disturb the neighbours who were working their horses in the field nearby. The smoke changed from sooty black to grey and became thinner.
Svend had ideas about shifting wood and restacking somewhere else as one of the stacks was bowed. This was going to be Svend’s and Brigitte’s job on Monday after the firing but it never happened as they were both knackered.
The heatwork itself was easy. Svend had some hardwood that had started to rot so he decided to use it to build a big ember bed to cover some jars that were placed in the firebox. This made the end of the firing very difficult as the ember bed was huge and it was depriving the back of the kiln of oxygen which was preventing the temperature to rise at the back. Svend and Brigitte had to riddle the embers a few time to help the wood burn down.
The end of the firing was extremely hard. Temperature would not climb in the middle nor at the back; it seemed that the team had lost the momentum. They had to restart at the front and wait to reach 1300C before attacking the sidestokes. In the end, they had to fire the back of the kiln first, sidestoking with softwood and continuing towards the front until the cones were down. Temperature was uneven, one side being hotter than the other; in the end Svend decided to stop when cones 11 were flat at the back and cone 12 was bending on one side.
The firing graph
Wood firing keeps me on my toes. This firing was no exception. It went exactly according to plan until the last day when we started the final stokes and the kiln began to choke on the ember bed. In retrospect, the problem was two fold. I deliberately did not put a grate in and I used mainly hardwood in the firebox. I wanted embers falling back over the pots in the front. That worked beautifully, except that because of the hardwood, the ember bed grew out of control and made it difficult to reach a high enough temperature at the front and deprived the kiln of oxygen for side stoking.
At one point, we left the kiln for an hour to allow the embers to burn down and took the front back up to temperature, but again, the ember bed grew out of control again and we lost the impetus for the side stoking. We then switched to very light side stoking and after many hours, the kiln suddenly took off and we were able to finish the firing.
Much of the front of the setting had been buried in embers and was underfired but very close by were some of the best pots I have ever had. All those embers meant copious amounts of ash on the pots and heavy reduction. What would I do differently ? Introduce a system of mouseholes and not use so much hardwood. But the truth of the matter is that good pots cost.
More photos in the next post
Leading up to the firing
Winter is Svend’s least favourite season: the shorter days combined with the gloomy weather put him in a sombre mood and he finds it hard to start making again after his winter firing. Once the sun starts shining though, and once his favourite flowers, e.g. primroses and blue-bells, start dotting the Devon hedges, he finds his rhythm again and set to work.
The year began with a delivery of wood, followed by the back-breaking work of wood splitting and stacking, and moving the wood that needs to dry off to a sheltered place. This usually means rearranging the wood stacks around the kilns. There is indeed more to wood-firing than sitting by the kiln and chucking a few logs in from time to time. Without the hard work of wood preparation, there can be no firing even if there are enough pots ready for the kiln.
It is also getting more difficult to source good suppliers who will deliver at a reasonable price. Svend used to get off-cuts from his local sawmills but both have closed. It has taken many years to persuade the local forester to take him seriously enough to sell him wood in the round in large quantities. He probably thought that Svend was some dreamy hippy and best avoided from a business point of view.
Svend made the usual tableware pots: various sizes jugs, different types of bowls. storage jars etc… He also put in lots of bowls thrown off the hump and some biggish jars. The big pots that are standing on the bench by the pottery window will be fired in the big kiln later this year. As well as unglazed pots, there is a number a celadon and kaki glazed ware, with two celadon large jars placed in the fire-box for ashing.
Making began slowly and took about two months, glazing a week and packing about three days.
The general course of the firing
Svend started with gas until 300C then both gas and wood were used until the alpha beta conversion. Wood only was used until the end of the firing. During the day on Friday, the crew consisted of Svend and Brigitte ; they were doing six hour-shifts each. On Friday night, Maddie Carracher of Kigbeare Studios and Darren Ellis of Maze Hill Pottery worked together on the 10pm to 2am shift, after which Brigitte took over again for four hours. On Saturday, Svend and Brigitte worked six hour-shifts again until 6pm when Deborah Mitchell of Zanzig in Cornwall arrived for the week end. From then on, the team, (Svend, Deborah and Brigitte) worked four hour-shifts each until Sunday evening.
Svend had intended the firing to last 48 hours, but it ended up lasting 60 due to problems at the end of the firing.
The bulk of the firing went without problems, except for an unexplained sudden drop in temperature at 5am on Sunday morning on Brigitte’s shift. The only noticeable difference was in the weather: the temperature seemed to have dropped just when there was a sudden gust of wind that lasted well past her shift. From 1180C, it dropped to 1120C and it was impossible to bring it back up despite using the usual tricks of playing with the passive dampers and trying different amounts of wood.
Deborah took over from Brigitte at 6am, followed by Svend at 10am. Brigitte then got up at 11am to join them for the finishing stage but Svend wanted to get more heat to the front of the kiln before the finish started properly so he sent the ” ladies” (he calls us his Svenettes) back to the house for a rest until 2pm.
Svend gives his own account of what happened on Sunday from 2pm onwards.
This has been one of the strangest and worst firings I have ever had. I have fallen off this bike so many times, but this time I really have scraped my elbows and knees. However, I am still intrigued enough to want to get back on. One way or another, I will learn how to ride this damned contraption.They say that you never learn by getting things right. I am wondering just how many more big basic mistakes I have to make before I begin to reap the rewards of all this experience?I have, afterall, been at it for 45 years.
This was the third firing of my small kiln.In it I was venturing out into the world of simple celadons. I am not methodical and that is one of the main reasons for getting things wrong in a big way.However, this time a good friend let me test fire all my new glazes in her gas fired kiln. They all worked and so I chose the four that I liked best and together with my three regular glazes, glazed all my pots and spread the different glazes equally through out the kiln. Unusually for me, everything was biscuit fired.
The kiln packing was my standard pack and went well. Because the kiln was damp I pre-heated with gas for 24 hours until there had been no steam at the chimney for several hours.The temperature was 300. Thereafter the firing followed a slightly faster firing curve than I normally do ( after all, everything was biscuited ). At a fairly early stage I decided to make it a 48 hour firing ( as if I have the power to decide these things ! ).
24 hours took the kiln to cone 9 beginning.The next 26 hours of deliberate flat lining took the kiln slowly to cone 10 and 11 over in the middle of the front. 3 hours later 12 was over and 11 over at the sides of the front and 9 and 10 over at the 2nd side stoke with 11 beginning. Everything was going according to plan apart from a few unexplained dips in the curve a little earlier on. Now it was come-uppance time and the kiln just lost momentum.Several hours later the kiln was still stalled and so I decided to go back to the front and start all over again.
The temperature climbed quickly on the pyro and when I could see that cone 12 was totally flat all over the front , side stoked for about half an hour and then stopped. At this point I took out some rings and could see that all the celadons looked fine. One was even exciting. Now I made my big mistake. Instead of cooling in oxidation down to 1000 , I clammed the kiln up with a big ember bed still burning. A small blue triangular flame at the blow hole showed that it was reducing. Usually this works well, but not this time.
On opening the kiln I found , as I had half expected, that the front, having been at high temperature for far too long, was very over fired. The next thing that I discovered was that all my new celadons had gone matt and crystalline and were a yellowish opaque off white. Basically I had destroyed the firing by cooling in reduction. My usual celadon does not seem to mind. All my new ones hated it. Oh well, shit happens.
This gallery contains 23 photos.
Below are a few pictures of some of the pots from the November 2013 firing. Svend fired his small kiln this past week end and a description of the course of action and problems encountered will follow soon. Thank you everyone … Continue reading
Svend fired the smaller kiln a couple of weeks ago. The crew were Svend, Harriet and Brigitte.
Svend had finished packing on Friday at midday and the gas on very low when Brigitte arrived at 1.15pm. The firing would last until Monday around 3:30pm.
A rough walk through the firing stages.
Svend was on the 6 to 10 shift, Harriet would do the 10 to 2 and Brigitte the 2 to 6. Brigitte and Svend had a bit of banter over which shift they would do as they both prefer the graveyard shift. Brigitte got to do the graveyard shift and Svend got to go for his swim everyday so everybody was happy. Team work !
An hour after the firing had started, Brigitte therefore came on shift; the gas worked by itself so her job was to move wood from the outside of the kiln-shed to the inside as it was raining badly, and also to get some hard wood ready for when Svend came on to change from gas to wood. Below are Brigitte’s two neat woodpiles in front of Svend perfect ones !
When Svend came on at 6pm, he continued firing with both gas and hard wood, and he changed over to just wood at 7pm. From then on, all members of the team worked solo. The task was to get a slow climb to reduction and then heat work with constant reduction until midday the following Monday. On Monday, all members of the team worked together to get all cone 12 down all over the kiln.
During the main part of the firing, we were stoking from the front and from the stoke holes at the fire mouth; there were two biggish pots in the firing chamber against the kiln walls that required a lot of ash, hence the side stoking. Svend was also side stoking the middle and the back of the kiln during his shift in order to even out the temperature and to get ash towards the back of the kiln. At the end of his stokes, Svend was throwing water through the front. See the videos below to see what I mean.
There are three theoretical reasons for throwing water in the kiln during reduction: firstly, when cold water comes into contact with the heat, it creates steam and a sort of explosion that lifts the ash and throws it everywhere in the kiln. Secondly, it supposedly intensifies the reduction. And thirdly, it clears out the smoke in the kiln. However, this is very dangerous, people could get scolded by heat and steam, therefore only Svend is allowed to do it.
At 4am Sunday morning, Brigitte reported that cone 9 was starting at the front and when she came back at 2pm the same day, it was completely down; cone 10 was pointing an hour later. By the end of her shift at 6pm, cone 9 was down on the right hand side, beginning on the left hand side and cones 10 and 11 were starting at the front. Throughout the main part of the firing, the right hand side of the kiln was hotter, but strangely, at the end of the firing, when the team was working together, the left hand side got hotter.
Below is a photo of the chart for more detail.
At midday on Monday, the team worked at getting cone 12 down at the front. By 2.30pm, the front was done, so they proceeded to the sides, throwing 3 sticks in each side and checking the chimney for smoke. When the cones were stubborn in one stoke hole, they worked on the next one to get a good advance there, then they would come back to the stubborn stoke hole until cone 12 was down. All cones were finally down by 3.30pm which meant the end of the firing so it was time to clam up the door at the front and to put the pyrometer away. Svend worked out that we used 3 cords of wood.
A few notes on some of the kiln’s features.
On Svend’s kilns, the side stoke holes are positioned half-way between the floor and the top of the kiln. This means that the stoke holes act like a passive damper and suck air through the kiln and prevent flames from lashing out of the kiln. If the stoke holes were positioned higher, they would act as a chimney and this would result in big flames and danger for the stokers.
Svend has built some passive dampers at the back of the kiln; they are used to minimise black smoke and to avoid upsetting the neighbours. When we use the passive dampers, the main damper at the chimney stays open. Below are pictures of the main chimney damper and of the passive dampers. In the picture of the passive damper, you can see a dark patch surrounded by orange flames: it is the cold air that gets in and that gets surrounded by the heat. The mixture of hot and cold air creates vortexes or turbulences that fight each other.
The flames escape through the chimney via a small arch (pictured below with the plywood still in place). When he packs for the next firing, Svend is thinking of building a wall of pots in front of the first arch in the picture, which separates the main kiln chamber from the tube that leads to the chimney so that the heat does not escape to fast. The tube gets really hot and pots that got fired in this tube in the last firing were badly dunted.
Svend fired the new kiln last week end (29th August to 1st September 2013). The kiln was very damp so 24 hours at 100C were needed to get rid of the moisture before the firing even started. Svend then started with gas overnight to slowly heat up and draw the moisture out of the glazes; the next day, the actual firing started very slowly with gas and hard wood, mainly beech, until the alpha-beta conversion was reached (roughly 573C). The reason for using hard wood is that hard wood is better for keeping a constant temperature than soft wood and the alpha-beta conversion stage being critical, it is important not to let the temperature fluctuate too dramatically. The actual firing lasted 72 hours.
After the alpha-beta conversion, soft wood ( birch and Douglas fir) was used and what is called “heat work” started and lasted until the end of the firing. The crew was stoking three sticks at a time and for three days and nights worked four hour shifts each. The aim during all firings is to get the temperature to rise slowly with constant reduction and to get ash deposits on the surface of the pots. During heat-work, Svend also does some side stoking to encourage fly-ash and embers to deposit on the pots placed nearer the sides, and also to level out the temperature throughout the kiln.
At the beginning of the firing, Svend draws a firing chart that each crew member will follow on their own shift. They record the temperature throughout the firing, the time when reduction was reached and any unusual event that may occur for future reference.
On the last day of the firing, the three members of the crew work together to reach cone 12. One is stoking the front of the kiln and the other two fire the first stoke holes until cone 12 is flat. They then go on to the next stoke hole until cone 12 is reached there and carry on so until the last stoke hole has been fired. During side stoking, two people have the job of stoking whilst the third person checks the chimney for smoke; when all the smoke has disappeared off the chimney, it is time to stoke again. When all cones are down, the firing is finished and the kiln is clammed up with a mixture of one part clay and two part sand.
Svend explains in his own words and in more details what happened in this firing in the section below.
Over to Svend…
THE NEW KILN.
Some years ago David Frith asked me to build a kiln at one of his events. The kiln I built was a small, simplified version of a Sawankhalok kiln I had built several times before. The kiln fired very easily and the three day firing produced some beautiful, heavily ashed pots. When I returned home I pulled down my existing kiln and built a slightly larger version of the kiln I had built for David. The kiln worked well for many five day firings until suddenly it began to oxidise. It took five more firings before I discovered the cause. The soft bricks had cracked around the door, leaving a half inch gap all around it, which translated into the equivalent of pulling two bricks out. Once repaired, the kiln worked well again but the soft bricks began to deteriorate and crumble and so I decided to rebuild it with some minor alterations, using hard bricks. This was the first firing of that kiln.
I started this firing on Thursday 29th of August at midday. I began with small household beech logs and a gas burner to dry the kiln out. At 10 pm I stopped the wood and left the gas burner in until I got up at 6 am. I turned the gas up and went for my swim. At 8 am I switched over to wood only, using birch logs.The temperature rose steadily throughout Friday and passed 900C in the early hours of Saturday. At that point the kiln was already reducing naturally as the ember bed was higher than the stoke holes in the fire box and so I switched to side stoking and for the next four hours, simply riddling the fire box embers and side stoking the kiln for embers and temperature. By Sunday morning the temperature had crept up to 1200C and by late afternoon it was 1280C on the pyrometer but cone 12 was flat all over the front of the kiln and so I began side stoking to finish. We got cone 11 over at the first two spy holes and then noticed that cone 12 was falling at the very back of the kiln. In order to avoid overfiring the back, I stopped the firing. The firing, with the help of Bee and Charlie, doing 4 hours on and 8 hours off , was very easy and the kiln very responsive. It did everything I asked it to do and in spite of being built of dense bricks, used no more wood than the previous kiln.
On Friday 6th September I unpacked the kiln with Brigitte and Bjorn. Although there were some very good pots at the front it very quickly became apparent that I had made some basic mistakes.
The biggest mistake was starting the finishing side stoking too soon. If I had side stoked into the firebox for longer I could have got cones 11 and 12 down at the sides before the back got too hot. The result was that the middle of the kiln was under fired and the back too hot . The clue was in the fact that the pyrometer was only reading 1280C. Had I gone on at the front until 1300C+, things might have been different. The next big mistake was using a celadon at the front which is good at cone 10 but watery and dripping at cone 12. The shame of it is that I have a perfectly good celadon for the front which is both stable and reacts beautifully to heavy ashing. But it was by no means all bad. Some of the pots are beautiful. Time to pick myself up, dust myself down and get right back in there again.