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Stacking Woodfired Kilns                                                          by Owen Rye

First published in The Studio Potter, Vol. 28 No.2 June 2000 pages 24 to 26.

Woodfirers by either the nature of their work or by their nature as people develop many friendships. Those friendships either strengthen or strain when jointly firing an anagama kiln. Compatibility is in many aspects a factor in sharing these firings. Stacking the kiln is the first test of compatibility. From a technical viewpoint the pattern and style of stacking will determine how the kiln fires, whether tending towards oxidation or reduction, whether maintaining low or achieving very high temperatures, and whether depositing much ash or little on any individual piece of work. So if one partner wants high temperature oxidation with much ash and the other wants low temperatures, heavy reduction and little ash, they are faced with an impossible situation in pleasing both. There is usually no compromise except to say this firing is yours and the next mine. Aesthetic incompatibility calls on the diplomacy of good friendships in joint firings.

Chester Nealie and I have fired together many times and share aesthetic attitudes to the extent that there are no conflicts in stacking. Despite clear differences in the details and subtleties of our work, we have an understanding where it is possible for one to set the other’s work in the kiln and achieve the results the other would have wanted. Attending Different Stokes (the Iowa Woodfire Conference held in 1999) revealed other compatible woodfirers who could with ease join us and achieve a result to make them happy. Temporarily of course, for prolonged happiness is not a desirable state for artists; dissatisfaction is the pilot for flight further into the unknown where all artists should undertake their journeys. Contentment is the province of the dead.

So for example Jeff Shapiro could fire with us (or we with him). It may be unwise to single out someone who could not because they might feel rejected; but it would not be an act of rejection, more a statement of differing aims. Going on to ignore wisdom, our very good friend Tony Nankervis is an example of incompatibility in firing; he wants more heat, less ash and a different firing cycle. Not at all saying we should not fire together, because that is highly enjoyable, but saying that first we must decide whose firing it will be. Neither would I say that I would ever consider firing with some whose work is compatible; because personalities would clash.

We all know the importance of a good firing team for good results. A good stacking team is also very important. My regular firing partner Graham King is indispensable. We have been working together for many years and he knows now what I will need next, usually before I do. He also knows when I’m about to sit there in the kiln for 20 minutes thinking about what to do next, and goes off to do something else. Or when I will be working quickly and he is there to pass in whatever is needed. Sometimes I think he knows what I am doing better than I do. As a big bonus he also makes some fine work. Our arrangement is that he can put whatever he likes in the kiln, wherever he wants it, and it seems to work well for both of us.

Many potters focus all their energies on making and firing, but to me placing pots and other work in the kiln seems the most important part of the whole process. It is the art part of woodfiring and is aimed to take maximum advantage of the woodfire environment inside the kiln. As making relates to form, stacking relates to surface. The best forms are lost when stacking is wrong and transcendent when stacking is right

Pots stacked standing upright on their base will have only one surface dimension, which is the variation front to back. Pots stacked on their side along the direction of flame travel will have (when later displayed upright) a variation top to bottom with more ash on the end which faced the flame. They will have a variation front to back because one of these sides was uppermost and getting more flame and ash, and the other was protected underneath. Depending on how the wads were placed these pots will also have wad markings, with luck showing flashing colours and flame markings around the wads. This means at least three dimensions of variation.

So the difference between stacking upright and on their sides is a much greater richness and variation in the latter. Now – what if I place them at an angle to the flame flow; and at the same time at an angle to the horizontal? This changes the aesthetic from qualities of up and down and front and back, to diagonal movements around the form. More richness. And more again from the shape of the wads used. Pretty little round wads (the kind rolled into little balls by an assistant and passed into the kiln in a little bucket) leave monotonously polite little round wad markings, all the same. Ho hum. Now what I like is a form with a little eccentricity and bentness, placed at a weird angle in the kiln and wadded with a half handful of wad mixture slapped on the sides to give the same feeling of weird and bent in the wadmarkings. The use of shells in place of fireclay wads for stacking is another variation and carries the advantage that it provides a perfect excuse for a trip to the beach. The general principle here is that all parts of the process blend into a compatible whole – if the work is neat and tidy the stacking should be neat and tidy. If the form is bent so should be the stacking process. All together now, just like a choir or an orchestra.

Stacking also has a functional element in relation to the firing. Flame moves through the setting. A very tight setting will slow the flame, restrict its movement, and cause more reduction. A very loose open setting will see the flame whipping through with a tendency to draw much more air into the kiln and so move to oxidising. If there is such a thing as a ‘standard’ setting for a woodfired kiln I guess it would be loose in the front, tight in the back. Unless you use one of those abominations, a bagwall. Which ends up with all the beautiful ash which the pots should have had. Even pots that should not get ash should be hidden behind pots that should. I might sell a brick sized pot for $500, but I doubt I will ever meet the collector who will pay that for an ash-glazed brick.

A long chambered kiln like an anagama requires development of this idea of varying the setting from loose to tight. I tend to set the top front tight and the bottom loose so the flame will travel along the floor of the kiln, otherwise all the flame will go over the top of the setting. I then vary from loose to tight back through the setting so the flame does a kind of wave movement up and down through the kiln. The same goes for the horizontal – setting tight to the sides and then tight to the middle back through the setting so the flame does horizontal waves as well as vertical ones, and has to move the maximum distance through the setting. The turbulence this causes and the flame-slowing effect are as much part of my aesthetic as any aspect of form resulting from making techniques and clay manipulation.

For some years now I have left the ash and rubbish in the kiln after unloading. The first stage of stacking is to pass a hose into the flue through a passive damper slot in the chimney, and then sit at the back of the kiln washing out all the ash and wads. This gives a nice clean kiln with no dust, but more importantly if I leave the hose running for two days it saturates the kiln with water. This water contributes significantly to reduction in the kiln during firing, improving colors on the work. The extra reduction has implications for stacking. A wet kiln needs a more open stack in order to fire effectively. (Author’s note – read that last sentence again. It’s important).

My anagama works best when I stack a pile of upside down bowls up across the flue at the back. They act as a kind of permanent damper that does not need adjustment because I have enough experience with the kiln to know just how much flue opening gives best results. I also pack a very large pot, slender at the base and opening wider at the top, right in the middle front of the kiln. This acts as a flame divider, much like the pillar in early tunnel kilns that stopped the top of the kilns falling in but also increased the potential for reduction. Knowing that different zones in the kiln create specific kinds of surfaces on work means that I make different work for different parts of the kiln. This makes stacking easier because the work can be laid out in the studio in the order it will be needed for placement in the kiln. To keep everything alive I try to have some work in each firing that I am not sure about; life would be very dull if everything was known in advance.

I have come to the realisation that there is no such thing as a ‘technical’ consideration in woodfiring. Every decision is an aesthetic decision contributing to the sensory qualities of the work. As an example: most woodfirers by now have realised that plates and platters receive their richest flame makings on the underside, and consequently set them upside down to take advantage of this. Flame speed is a factor in the quality of markings produced – a fast flame speed will produce extended, comet like wadmarkings, and a slow flame speed will produce a series of haloes around the wadmarks. The type of fireclay used for wads will influence the colour of the wadmarks. To me all of these considerations are aesthetic rather than technical in nature.

The kiln design will be a major influence on the work fired in it. The Bizen-style anagama, with a very high front in the first chamber, will give a very slow-moving flame. A very steep tunnel-like kiln will give a very fast moving flame. Any design where the flame has to lift ash onto the work will produce very little ash, whereas a
Design that forces flame down to the work will deposit much more ash. A small chamber opening into a large one will see the flame slow dramatically, and a large chamber leading to a small one will speed up the flame. The potential for oxidation and reduction is influenced greatly by kiln shape. The relationship of the size of firebox and the size of chamber must also be considered. Stacking for fast flame is different to stacking for slow flame, and stacking for little ash deposit is different to stacking for heavy ash. Discovering what all these differences are, and how your personality and preferred style of work fir into this complex puzzle is the essence of woodfiring. Overall, we have only just begun to see some of the possibilities; for me it is a lifetime commitment.

It is easy to pick up some of the generalisations about woodfiring and produce some clichéd work. We see this in very large group exhibitions. The real difference between the best work and the rest is in the subtleties. Subtle color combinations, subtle shading of ash from fine to coarse, subtle combinations of clay qualities (coarse, fine, vitrified or porous) with these other considerations all contribute to quality. In stacking this subtlety is in part reflected in carefully considering the mix of work large and small, the spaces allowed between the pieces, and the myriad other questions which must be answered. Little wonder that as the years go by it takes me longer and longer to set an anagama for firing; currently it takes about five days to stack a relatively small kiln only about six metres long. It might take even longer when my new kiln is finished and everything has to be worked through again.