THE CONSTRUCTION OF AN ANAGAMA KILN

By Shiho Kanzaki

Reprinted with permission from Issue 6 of The Log Book - The International
Newsletter for Woodfirers and those interested in Woodfired Ceramics.
Designed and published by Coll Minogue & Robert Sanderson.
The Log Book, P.O. Box 612, Scariff, Co.Clare, Republic of Ireland.




In this article, I would like to describe the way I work with my anagama. Because there is a mutual relationship between the way an anagama is constructed and the way it is fired, I will explain my approach to firing and also give some details about the construction of the kiln.

My anagama kilns have a grate in the firebox area and also an interior chequered back wall. Traditional Japanese anagama had neither of these features. I was born and bred in Shigaraki. There were many noborigama in existence there when I was young. Especially in Shigaraki, noborigama were very large, having 11 chambers. The first ten chambers were for production wares, and the 11th or last chamber was for bisque wares. I took notice of the 11th chamber and considered its function before I built my anagama. I designed a ground plan for my kiln incorporating a back wall. Building this wall created a second chamber which is always fired empty. At that time, I did not consider including a grate in the firebox area. Then I visited many pottery centres in Japan - Bizen, Tokoname, Mashiko, Seto, Mino etc., to learn about anagama. I met Mr. Suketoshi Matsuyama in Mino, and I was surprised and interested to see his work with natural ash deposits, as the effects were similar to those which I had been striving to achieve for many years. I was also surprised to see his anagama, as it had a both a grate and a back wall. The height of the grate was about 1m from the ground, and the back wall had about seven holes in it, all of the same size.

When I asked Mr. Matsuyama why the kiln had a grate and a back wall, he replied "About the grate - it's too high. Because all of the cinder in a fire box drops down through the grate. So it's very easy to get high temperature. About the back wall - there is an empty space behind it. This room works for keeping the temperature well during a firing." I became Mr. Matsuyama's apprentice for two years from that date. I then returned to my studio, and changed the ground plan of my anagama, to include a grate, but having only a 50cm space between it and the ground. I build my anagama with a grate and interior back wall with seven holes, the same as my teacher's kiln. So although the grate and the back wall were not my own ideas, I developed them to resolve difficulties which I had experienced in firing. Since then, I have built 13 anagama kilns.

I always load only greenware into my anagama. Consequently I have to be careful, of course, that I do not cause the temperature to rise too quickly, during the early stages of firing. As you know, at about 230C, the moisture in clay turns to steam and 'gushes out'. It is at this stage that many pieces tend to break.

One of the reasons for my anagama having a grate in the firebox is so that I can easily control and adjust the temperature between the start of the firing and when 230C is reached. Because the firebox has a grate there is a large area under it. I call the opening to this 'under grate area' the lower fire-mouth. (See photograph 1). My kiln tends to be very damp, as half of it is built below ground level. Therefore I begin the firing with a little 'camp fire' outside of the lower fire-mouth, by placing firewood on the ground about 10cm from the opening (see photograph 2). This helps the kiln to dry out, and the temperature inside the kiln to slowly increase. I continue to stoke this small fire until the temperature inside the kiln reaches 100C., then I gradually move the fire into the lower fire-mouth. I stoke the wood into the area under the grate until the temperature reaches about 300C. I check the temperature at a spy hole which is situated about 40cm from the back wall, and 70cm up from the floor of the kiln. By starting the fire outside the kiln, I can control a gradual temperature rise, and with this careful planning I can successfully fire pots which are quite thick.

When the temperature reaches around 300C, I stop stoking the lower fire-mouth and begin stoking through the upper fire- mouth. At that time, I transform the lower fire-mouth into an air vent, as follows: I prepare two kiln shelves which together, are about 1.5 cm narrower than the width of the lower fire-mouth. These two shelves close off the left and right-hand sides of the fire- mouth, leaving an air vent in the centre, which measures about 3 or 4 cm in width. Next I place some bricks in front of the shelves. The bottom three are placed 2 or 3 cm out from the shelves (see photograph 3), while the remainder of the bricks on top, are placed directly against them. Air is drawn into the kiln through the space which is left between the bottom 3 bricks and the shelves. I will explain later why the position of the fourth brick is adjusted after seven days of firing.

All my firings last at least 10 days. After moving the stoking to the upper fire-mouth I continue firing for another 9 days or more. Once the temperature reaches about 850C, I create a reduction atmosphere. As I stoke firewood into the firebox, smoke and flames come out of the chimney and spy hole. As soon as the smoke and flames disappear, I stoke the firebox again.

During the firing, the flames generally tend to flow along the sides, by the walls and along the top of the kiln. It is very difficult to make the flow of flames go through the centre and bottom portion of the kiln, which is of course where all my pieces are stacked. So it was in an effort to remedy this situation, that I built the back wall (inside the kiln - near the back), with 9 to 14 holes in it (as required). The centre hole in the bottom of this wall is the largest, with smaller holes on the left and right-hand sides, and also at the top. (See photograph 4) Both the location and size of these holes may be easily altered before each firing. These adjustments, along with my decision to locate the main primary air vent in the centre of the lower fire-mouth opening, make it easier to concentrate the flame patterns into the centre of the kiln.

Each firing brings its own problems - and it is necessary to find a way through them. Usually the greatest difficulties arise after the seventh day of firing. Sometimes the problem is falling temperatures. When this happens, I have to check the volume of coals that have accumulated in the fire box - I have an idea as to what is the 'right amount'. When the coal bed seems right but the temperature is falling, I have to check both the primary air into the upper fire-mouth, and the secondary air coming into the lower fire-mouth. Sometimes I have to increase the amount of air flowing into both the upper and the lower fire-mouths. Also, I may have to open the damper in the chimney to increase the air flow.

The decision whether to increase the air flow in the fire- mouths or the chimney, is based on my experience. It would be difficult to tell in advance which adjustment to make: it is always different, and the decision is made according to the time of the firing, and the circumstances of the firing. I do know that too much air does not produce good results, so I make cautious changes - opening the fire-mouth or chimney only 5mm at a time.

If the coal bed is increasing and the temperature is dropping, I have to decrease the size of the coal bed. I usually begin by reducing the amount of wood in each stoke. Depending on the firing conditions, measures such as this may prove effective in lowering the coal bed and stopping the loss of temperature. However, if the size of the coal bed does not decrease by this method, another way should be tried. Normally my stoking cycle resumes as soon as the flames which come out of the chimney and spy hole have disappeared. But if I am trying to reduce the size of the coal bed, I wait an additional 30 seconds. I often look into the spy hole to make sure that the flames inside the kiln have faded, before stoking again. This approach may correct the size of the coal bed, and return me to a normal firing cycle.

Sometimes after following all these measures, I discover that the coal bed is still too large and that the temperature will not rise. At such times, one should suspect that the coal bed in the lower fire-mouth has become clogged up. If this is the case the coal mass can be broken up using an iron rod. This will often improve the situation. However, if after breaking up the coal mass the temperature is still stalled, it may be necessary to open the fourth brick in the lower fire mouth, thus allowing more air into the kiln. This usually corrects the situation and causes the temperature to rise again. Another point to remember is that if you require the flow of fire in the kiln to be faster, you can alter the volume of air into the kiln, by adjusting the size of the air vent in the centre of the front of the kiln. (see photograph 5)

I never use a pyrometer or pyrometric cones, so it is necessary for me to give my full attention to the colour of the flames in the kiln and to the colour and pattern of smoke and flames coming out of the chimney and the spy hole. From these observations I make judgments about the atmosphere and the flow of flames in the kiln. I fire according to my past experiences and as I perceive the natural variation of the firing atmosphere, from firing to firing.

Shiho Kanzaki was born and lives in Shigaraki, Japan. He has exhibited widely in Japan with many exhibitions (one man shows) at major department stores, including Mitsukoshi, Isetan and Matsuya. He has build some 13 different anagama kilns since 1972, and continues to fire four of them; three in Japan and the other known as the 'Kanzaki-Beamer dream kiln', built with Professor Karl Beamer, in Bloomsburg, PA, USA. Shiho Kanzaki is also the author of Honoo no En; Hito no En (Karma [Destiny] of Fire and Karma [Opportunity] of Humankind), first published in 1989. Shiho Kanzaki's web site is: http://www.the-anagama.com

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