28 November 2010

Pots from the Martin Hadrava/Masakazu Kusakabe kiln in Klikov

Klikov clay after firing

Kiln floor looking towards firebox

Apologies for not being able to attribute the work to the makers. I arrived at the unpacking too late to see the first pots coming out but there were still a few on the kiln floor to give an idea of the ash deposits there. 

Chamber below chimney full of traditional  Klikov ware 

18 November 2010

Wood firing in Bohemia

chimney end of kiln
tall chimney
I haven’t fired my kiln for a while because I spent 2 months of the summer in the lovely Czech Republic, southern Bohemia to be more precise. However it wasn’t an entirely wood fire free time. Just as we were leaving home the postie delivered the latest issue of the Log Book (www.thelogbook.net) with an article about wood fire kilns in the Czech Republic. Talk about good timing. 
Side view of chimney showing damper and 2nd ware chamber
With a little research I learned that one of the potters mentioned, Martin Hadrava, was only an hours’ drive away from where we were staying in ČR.  So with some help from a Czech friend I got in contact with him and he was very welcoming and invited me to visit the next kiln firing. This was to be the inaugural firing of a new ‘smokeless’ kiln designed by Masakazu Kusakabe (see the book Japanese Wood Fired Ceramics by Masakazu Kusakabe and Marc Lancet) who would be there to oversee the firing. All very exciting as I saw him demonstrating a small version of this kiln at Aberystwyth in 2009. This is the largest version of the kiln which Kusakabe has designed. I don’t have the dimensions but you’ll see the scale of it from the photos.
Door to ware chamber, side stoke hole and fire box
Martin is based in a village called Klikov, near Suchdol nad Lužnici in the east of Southern Bohemia. The village is a traditional pottery village and I saw at least 5 kiln chimneys as we drove around looking for the new kiln. (Martin still uses one of the old wood fired ‘Kessel’ kilns, after a German design from about 1850, which he renovated, see more at www.klikov.net and www.hadrava.net ). We followed smart new signs across fields to a pottery which turned out to be closed, but we got directions and eventually found some open ground just outside the village with a couple of sheds and a big chimney. No point looking for smoke, all that indicated the presence of a kiln firing in process was a heat haze at the chimney top. Amazing considering that when we arrived the kiln was already at 1260℃. 
fire box mouth
There was quite a crowd, some directly involved in the firing process, some like me just wanting to observe. My two non potting friends who came with me were quickly drawn into the underlying excitement and anticipation of the process. I don’t think they had understood before how elemental it can be, a glimpse into the fire box was enough! I was there to see the draw rings pulled but didn’t get close enough to hear the discussions . The decision was made to continue firing. And at this point I had to leave, reluctantly, but decided to return for the unpacking a few days later.

30 July 2010

For anyone interested here's the firing log for the anagama firing last week

Anagama Firing with Shozo Michikawa at Higham Hall

19th - 22nd July 2010

9.30am Monday. Light fire in ash pit, smokey,

1 10.30am flames being drawn up into kiln, place some wood into

fire box but continue stoking in ash pit.

2 11.30 some smoke from chimney, strong flames in fire mouth, cease

stoking in ash pit. Mix of pine and hardwood

3 12.30pm 490°C Pyrometer now working! Rake out ashes, reduce mouth

of ash pit to increase draft.

4 13.30pm 600℃ Raining

8 17.30 880℃ Still raining

9 18.30 970℃ Breeze blowing directly into the fire box

10 19.3 960°C Everyone present for the first reduction - lots of wood into the

kiln and then close the door over the fire mouth to decrease

oxygen in the kiln. Lots of smoke and dark red horns of flame

from the spy holes over the ware chamber.

11 20.30 990℃ Bit of a party going

13 22.30 1000°C Darkness falls, stoking mostly pine, some hardwood

23.55 1020℃

15 00.30 1005℃ Drop in temp after big stoke

16 1.30am 1040℃ Tuesday, first chimney flame visible.

17 2.30am 1050℃ Much quieter now

18 3.30 1065℃

19 4.30 1080℃

20 5.30 1090℃

22 7.30 1100℃

24 9.30 1120℃

30 15.30 1130℃

33 18.30 1120℃ Sushi interlude

34 19.30 1140℃

38 23.30 1140℃ Pizza. Stoking little and often

39 00.30 1160℃ Wednesday

41 02.30 1160℃ Deep roaring in body of kiln, good chimney flame

42 03.30 1160℃ Running low on wood, heavy stoking to maximize reduction

04.00 Last massive stoke

04.15 Final stoke, one piece of wood each, close dampers fully, clam

up ash pit.

43 04.30 End of firing, daylight.

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.

19 May 2010

Pots from firing 10

Detail of standing stone

small pebbles and standing stone, dia 10cm

cutlery drainer and dish, ht 11cm

textured dish, dia 31cm

selection of mugs, ht 10cm

17 May 2010

Firing 10

3 May 2010

Up at 5 am to put the gas on. I chose the right day to fire today. It's already daylight and the birds are just beginning to sing. No clouds on the horizon. Back to bed for a couple more hours.

2 7am 97°C Turn gas up. Still sunny but gusting from the north

7.30 157°C Large log in with the gas on it

3 8am 185°C Wood slow to catch fire

8.30 212°C Removed a half course of chimney bricks to allow wind to increase draft. Gas off

4 9am 440°C Oops! now romping away. Removed damper brick

9.30 532°C Slowing down, damper closed

5 10am 540°C

6 11am 690°C

7 12 noon 818°C First heavy smoke

8 1pm 1024°C First sign of reduction flame in chimney

9 2pm 1115°C

2.30 1150°C First soda into firebox

10 3pm 1169°C Second soda in

3.30 1190°C Third soda in. Cone 5 down

11 4pm 1208°C Cone 8 bending

4.30 1190°C Lots of fluctuation, 1224°C tops

12 5pm 1213°C Cone 8 down

5.30 1221°C Maggie arrives to view firing

13 6pm 1199°C Firing down whilst beginning to clam up the kiln.

6.15 1175°C Beer at 5°C

this firing included a cone 9 test glaze on the top shelf from Elizabeth Westman so I was trying to soak the kiln at top temperature to see if I could get the test to melt well. All cone 8’s throughout the kiln went down and there was a good melt of soda with some carbon trapping.

Image shows chimney brick beginning to sag out of line. Probably due to the bed of sand we used to even out the bumpy concrete. Rebuild will be required soon I think. You can just glimpse the test glaze at the back - black shiny, green where thin, good melt. Will get cone 9s for next firing.

Can't wait.

19 April 2010

As I haven’t got a firing planned for the near future I wanted to write a brief description of the first wood firing. Not just the first in this kiln but my first ever. I hadn’t even helped or watched someone else’s firing. My college experience all took place on the third floor of a central London art school building, no wonder they didn’t encourage woodfiring. The closest I have been to a full firing was Joe Finch demonstrating a gas/wood firing for the Scottish Potters in 2007.
After building this small kiln and reading various books and articles I still wasn’t confident but there came a point in late spring when I was on my own at home and I thought ‘I’ve just got to do it and to heck with the results’.
I packed the kiln with oddments and experiments and shoved my raku gas burner into the fire mouth to dry the kiln out slowly for 2 or 3 hours (the west coast of Scotland has high humidity). I planned to fire to cone 6 to start with, not knowing how long it would take, but I put cones 7 & 8 in too, to be safe. And I thought I would bung in some soda too for effect.

5am the next day with the sun already rising behind the mountains across the Sound, I stumbled out of bed to relight the gas on low. Having no idea how long it would all take and because I was firing solo I had decided to go up to 250°C with gas (which meant another hour back in bed).
7am I was back at the kiln with cup of tea, turning up the gas.
8am I started feeding in small pieces of wood along with the burner.
8.30 larger pieces started going in
9.00 gas was turned off and silence descended apart for the birds singing and the crackle of wood burning. I fed another piece of wood into the fire and the peace felt as wide as the view. Now I know why I do this, I have a sense of completing the cycle which I don’t get from electric firing and almost get from raku firing but not quite.

The firing continued as with the subsequent ones. I put in soda soaked wood into the fire at about 1150 (about 500g soda) It was remarkably easy to get the kiln to cone 6 down so I continued until the pyrometer read 1250°C and cone 8 was bending at the tip on the top shelf. I allowed the fire to burn down a bit then bricked up the fire mouth and the chimney and retired.
The next day the temperature was at 250°C and by the evening cool enough to unpack. (After 10 firings I am trying to slow down the cooling by firing down to 1100°C and with extra panels of insulation). The results were pretty unremarkable but so exciting to feel the weight and density of the stoneware and follow the path of the flames in the markings across the pots

This was the perfect day. The sun shone warmly in a cloudless blue sky (no midgies (wee biting monsters)yet). A gentle breeze wafted away the smoke and nothing to distract from the feeding the fire and enjoying being alive.

14 March 2010

I found an article about a similar kiln in back issue no. 18 of The Log Book (The International Woodfired Ceramics Publication) www.thelogbook.net built by Petr Novak in the Czech Republic. He refers to it a fast firing kiln with ‘circulating flame’, possibly of German design from 1970s. When I bought my kiln Mr. Krajek implied that it was a well know design in Central Europe. I’m surprised not to have come across it before in UK but perhaps there are fewer opportunities to wood fire here. There is a seemingly endless supply of wood in CR which has huge areas of managed forest and woodland and wood is a common fuel for heating homes. In fact I know of at least 4 ceramists specialising in building ceramic stoves in the small area of Česky Krumlov (south Bohemia) but that is a whole other subject. And talking of Česky Krumlov (a wonderful UNESCO world heritage site with CR’s 2nd largest castle) in the museum there is a beautiful scale model of the town made in ceramic by Jana & Petr Pešek.

6 February 2010

Pots from firing no.9

Interior of the kiln from the side

You can see the build up of glaze from the soda on the bricks. The first firing gave them the most beautiful orange blush. I realised that I should protect them with a wash of alumina. I've no idea how long they will last or how viable it is to do this kind of firing in a kiln which has to be unbuilt to unpack.

I used about 500g of soda for this firing which went into the kiln at about 1170 C over half an hour giving the work a light soda glazing on their exterior surfaces.

These are the best pieces from this firing. Each of the pots has a transparent liner glaze on the interior.

Lidded terrine
ht 13cm
width 21cm

Casserole, makes a good coq au vin.
Slightly ovoid,
ht 10cm
width 23cm

Deep oval vessel
soda glazed
ht 15cm
width 20cm

Deep oval vessel
ht 15cm
width 17cm

Jug with no handle
ht 13cm
width 18cm

31 January 2010

Firing number 9 20 January 2010

I know it isn’t in chronological order but this is the most recent firing and the first of 2010.

Got up in the dark just before 6am and pulled several layers on top of my pyjamas. Cold and windy, gusting from the south east on the most exposed side of the kiln. But dry. I warmed the kiln through for 4 hours yesterday evening to dry everything out.

6am lit the gas burner, less than 0.1 psi, once the flame had stabilised back to bed.
7.30 Up again; dress properly and down to the kiln with cup of tea.
8.0 75°C 2hrs Gas up
8.30 140°C Small pieces of wood in.
9.00 180°C 3hrs larger pieces of wood catching, breakfast arrives, very good porridge.

10.00 398°C 4hrs Dry, S.E. 5to 6
11.00 597°C 5hrs
12.00 805°C 6hrs Coffee arrives
12.30 first heavy smoke from chimney at 860°C
First flames from chimney at 975°C
1.00 1000°C 7hrs
2.00 1100°C 8hrs Rain for next hour or so
3.00 1160°C 9hrs Heavy smoke
3.20 1170°C First soda in
3.30 1175°C Temperature fluctuating
3.35 1170°C Second soda in. Cone 5 mid kiln down, cone 5 at side spy hole bending
3.55 1200°C Last soda in.
4.00 1215°C 10hrs
4.20 1213°C Cone 7 mid kiln down, cone 8 beginning to bend
4.30 1220°C End of firing, start to fire down for hour or two
5.00 1100°C 11hrs brick up fire box, leave mouse hole open
6.00 905°C 12hrs reduce chimney hole to one brick, seal mouse hole.

I feed wood into the fire box and then reduce the draft by putting a brick in the fire mouth.
The kiln seems to stall somewhat at about 1080°C at which point I stop using the brick in the fire mouth.
After this I have to rake the embers to keep them down to get sufficient draft through the mouse hole.
I used about 500g bicarbonate of soda, mixed to a thick past with water. I put this onto thin pieces of wood, dry them out on top of the kiln and introduce them into the fire box one at a time. When the bright orange sodium flame diminishes I add the next one.
It wasn’t the most peaceful of firings (that was the very first) as Bertie the dog went to visit his girlfriend and R had to search for him (therefore the tea wasn’t supplied so regularly), then was some chain sawing and car hovering, but at least I could shut the radio up.