Euan Craig

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Responsible Wood

Euan Craig

“If you are concerned about the environment, you should give up pottery.” Somebody once said this to me and the comment has troubled me ever since. When I became a potter it was not because I wanted to save the world, but surely it must be possible to make pots, even wood fired pots, in an environmentally responsible way. As a father, I am concerned about the environment, not only for myself and my children, but for their children and generations to come. Our generation has inherited a world with serious environmental problems on a global scale, from ozone depletion to the green house effect, salination caused by deforestation and over irrigation, environmental hormones and pollution. The list goes on, and the common factor is that these problems have been caused by the irresponsible use of our resources for short term benefits and profits. The time has come to rethink our attitude to nature and to find a way of firing our pots which is a more efficient use of our resources without sacrificing quality or artistic expression.

Most certainly traditional wood firing techniques have provided us with a variety of beautiful works of art, irreplaceable treasures that nourish the human soul. The wood firing process enables a potter to achieve effects that other fuels cannot. The glaze making minerals that enter a kiln with the wood flame in the form of ash and gasses can turn the simplest of pots into expressions of natural beauty by simple virtue of the process itself. The fly ash will cause a coating of glass where it settles on the pots, and the gaseous salts etc will cause the silica in the surface of the clay to vitrify causing orange and red flashing. It must not be forgotten, however, that those techniques were developed in order to achieve the best quality pottery in the most efficient and economically viable way that the available technology could provide. The “noborigama” climbing kiln was developed to utilize exhaust heat to preheat successive chambers and therefore use less wood to fire more pots than could have been fired in a single chamber “anagama” kiln. In its day, it was the leading edge of ceramic technology. We are now faced with a different challenge if we wish to continue to use wood fired kilns: to make wood firing both economically viable and environmentally responsible.

Here in Mashiko, there used to be about thirty potteries, most of which had a number of staff and “deshi” apprentices and which used wood fired climbing kilns. There are now four hundred potteries, most of which are individual artist potters. This trend towards individual studios rather than larger production potteries is no different here than in the west. It is driven by the changing role of pottery in modern society, from a necessary domestic functional item (the production of which has greatly been taken over by cheaper, mass produced products) to a nonessential lifestyle choice. Potters are artists now, and they are marketing their work on aesthetic merit rather than price or even quality. Aesthetically many potters would like to fire with wood, but find it economically prohibitive to do so. The first problem is space, as the cost of renting or purchasing land, or even finding an appropriate site is difficult at best. Mashiko has a population density of 286.9 people per square kilometer, and land is at a premium. Add to that the cost of building the kiln and the kiln shed. The space required is not limited to the size of the kiln and the safe zone around it either, but also storage space for the wood, which tradition says must be dried for two years. Even the most efficient of climbing kilns will use 1,000 bundles of wood per firing. Each bundle weighs about eight kilograms and costs about 300Yen. If you are firing twice a year that’s thirty two tons of wood you need to stockpile.

A standard three chamber noborigama will hold two or three thousand pieces. It will take three to five days, and normally needs two shifts of three people to fire. An anagama will take five to seven days.  It is best to bisque in your kiln to dry it out and pre heat it, which can be done with cheap wood as you will brush and sponge off all of the ash that lands on the pots anyway, and that only needs one or two people to fire.

To cut a long story short, if you work out the logistics of set up cost, firing cost and labour, not to mention the fact that six months income depends on the success of one firing, it is virtually impossible for an individual potter to fire in the traditional way. There are ways around it of course. To have a separate income, for example, or have a smaller gas, oil or electric kiln for your bread and butter ware. The romance of wood firing is also a very effective marketing tool, man’s battle with the elements of nature, the struggle with the fiery beast, the sheer scale of the enterprise. If fired well the results from an “anagama” can be quite dramatic. If sold as Art objects rather than functional pottery they can demand prices which justify the high cost of producing them. The fact remains that eighty to ninety percent of potters opt not to bother with wood at all, as oil, gas or electric kilns are easier and cheaper to fire. Which brings us back to the environmental issue; the main culprit in global warming is not the burning of wood, but the burning of fossil fuels.

Wood burns because it consists mainly of carbon. Plants use photosynthesis to take carbon dioxide out of the atmosphere and separate the carbon from the oxygen, using the carbon as building blocks and giving off free oxygen into the atmosphere. When we burn this wood, we are reversing the process, recombining carbon and oxygen to produce heat. As a byproduct this creates carbon dioxide, returning it to the atmosphere. Fossil fuels, (that is coal, oil and natural gas) have been formed by trees and plants which removed carbon from the atmosphere aeons before humans evolved. In the primordial forests of prehistoric earth, when the earth was a carbon dioxide rich green house, plants and trees drew carbon from the air and gave off oxygen just as they do today. They then died and were buried under leaf mulch in swamps and rain forests, taking the carbon with them to the grave. Thus, with each passing generation of vegetation the carbon dioxide in the atmosphere decreased and the oxygen increased. Over the ages dinosaurs came and went, continents moved, and vast quantities of carbon were buried in the earth. Soluble minerals were washed away and pressure applied, compressing it into coal, oil and natural gas.

Human beings came on the scene in an oxygen rich atmosphere. We then started cutting down the trees and burning them to make pots, returning carbon dioxide to the atmosphere. As long as we didn’t burn more trees than we could grow the balance was under control. The carbon in those trees was taken out of the atmosphere in our era, so no significant alteration was being made to our environment. It was carbon in cycle. Then we discovered coal, and since Marco Polo brought the secret of its use back to Europe from China eight hundred years ago, we have gone out of our way to burn as much of it as we can. The use of oil over the last century or so has exacerbated the problem, as do electric power plants driven by fossil fuels. We are pumping carbon dioxide back into the atmosphere that has never been there in the history of human evolution. We are doing it at a rate that the forests of the world cannot cope with, and we continue to cut down those forests to fuel our kilns.

I find myself painting a very bleak picture. Gas and oil kilns are bad for the environment because they burn fossil fuels, and unless power is being generated by hydro, wind or solar sources, electric kilns indirectly contribute to the rise in CO2 levels. Firing with wood would be better, but traditional wood firing contributes to deforestation, as potters tend to burn more trees than they grow.

Artistically and environmentally, firing with wood is the best option. What we need is a kiln that will achieve the same effects as traditional wood kilns, but in a more efficient way: cheaper, easier and faster. When I was setting up my studio in Mashiko in 1994, these were the criteria I set for my kiln. I wanted a wood kiln that could be fired by one person. That meant that it needed to be able to be fired in one day. I wanted to fire once a month instead of twice a year, so that I had a more stable cash flow and a faster firing cycle to develop glazes and designs, so I decided that about 27 cubic foot or 0.8 cubic metres stacking space was ideal. I wanted to be able to fire with scrap wood, the offcuts from saw mills and the building industry, as that meant that not only was firing cheap, but trees were not being cut down for my firing. That wood is normally burnt to dispose of it in any case, so it is far better for it to be put to use in my kiln. It had to fire efficiently, getting the most fly ash and flashing possible from the least amount of wood. It needed to be easy and cheap to build, and not to take up too much space. It also had to be flexible and easy to control.

Having fired a wide variety of wood kilns; Anagama, Noborigama, Tunnel kilns, Beehive kilns, Phoenix and Olsen fast fire kilns among others, I designed and built a fast fire kiln that totally failed to achieve anything that I wanted. I knocked it down and started from scratch, failing a second time, but getting closer. I discussed the problem with David Stuchbery at Latrobe University in Bendigo, Australia, and he showed me a prototype fast fire kiln that he and Peter Reid had designed and built there. Based on that design, I developed the kiln which I have now been firing successfully for eight years.

The kiln can be built in a shed 3.6 metres square with ample room to spare. I was using wood offcuts from a house construction company to fire the kiln, which cost 16,000Yen (US$150) freight per 4 ton truckload. One truckload would do ten to twelve firings, so my fuel costs were about 1,600Yen (US$15) per firing. I am now using wood from a company which recycles industrial refuse. It is precut to a size which is easy to use immediately and bundled for easier handling. This saves me considerable wood preparation time, though it now costs 6,000yen per firing. This is still cheaper than firing with gas, oil or electrucity. It is possible to get scrap wood for free, but as I am firing monthly I have opted for a reliable but inexpensive source.

The work is once fired, eliminating the need for bisquing, which reduces labour, time, fuel costs and exhaust fumes. I stack about 400 pieces in each firing. There is no bag wall as such, the pots are stacked up to the fire face so as to maximize ash deposits. There are two parallel fireboxes opening at the front of the kiln, with fire grates just above half way up. The flame ports are at the back of the kiln, and the flame rises up the back wall to strike a sprung arch which is parallel to the fire flow. Most kilns will have the arch perpendicular to the fire flow, but a parallel arch will cause turbulence which reduces heat variation and cold spots in the kiln and will disperse ash further into the kiln. The flame then flows around and through the pots and down through an exit channel underneath the stack, between the fireboxes at the bottom of the kiln and out the back to the chimney. The damper is situated in the chimney at the back, but there are two sliding bricks at the front of the exit channel which can slide in to restrict exit space, forcing the flame to travel through the work and dropping the heat centre of the kiln. The door is the full width of the chamber, which makes stacking very easy, particularly large work, and pieces up to 80cm in diameter and 120cm in height could be fired in this kiln.

I preheat the kiln by firing both fire boxes from the front underneath the grates until the kiln reaches 600c, or after the alpha/beta quartz conversion at 573c, when the silica in the clay body expands by 2%. Firing too quickly at this temperature is the main cause of heat cracking. Usually I take seven hours to reach 600c, as all the pots are raw. Pre bisqued pots could be fired faster, but care must still be taken around 573c. I then start stoking the kiln on the top of the fire grates, throwing the wood to the back. The fire mouths are open throughout the firing, allowing the maximum possible amount of air to be drawn into the kiln by natural draft, preheating it as it flows over the embers under the grate. When it hits the wood at the back on top of the grate, it reacts instantly with the carbon in the wood, bursting into flame. I alternate stokes, so that one firebox is beginning to oxidize, therefore burning efficiently, as I stoke the other, which creates a reducing atmosphere.

It is important not to over stoke, as this will choke up the kiln, reducing airflow and stopping heat rise. More wood does not mean more heat. Heat is caused by the reaction of carbon and oxygen. Too much carbon and not enough oxygen mean incomplete combustion and poor heat production.

More wood does not mean more fly ash. Clogging up the kiln with too much wood means restricting air flow, so there is less wind to carry the ash into the kiln. Think of it in terms of a dust storm; the more wind, the more the dust gets blown around. If you put up a barrier it creates a lee of calm air where the dust does not carry. If you create a barrier in your fire box by putting in too much wood the ash will not be carried into the kiln to settle on the pots.

I half close the damper at 700c to give a neutral atmosphere, and by 900c the kiln is reducing naturally. I start with about 2kg of wood per stoke and lessen it to about 1.5kg by the end of the firing. Particularly around the 1100c mark you need to lessen the amount of fuel going into the kiln to maintain the same reduction and heat rise. There is a small flame port at the top of the door to show the reduction level. When I stoke, flame will spurt out of this hole, the free carbon searching for oxygen to combust. When this flame sucks back in, the kiln is in neutral and ready to be stoked again.

If you watch your pyrometer, you will see that there is a drop in temperature every time you stoke. This is because the wood is absorbing heat from the kiln before it reaches a temperature where the carbon is ready to react with the oxygen to create more heat. Your pyrometer will then rise again, usually to just above the temperature it was before the last stoke. If you are firing with a single fire box kiln, or stoking both fireboxes simultaneously, then this drop and rise will be quite significant. By stoking alternately one fire box is dropping while the other climbs, so there are not such violent changes in temperature. Just by changing the timing of each stoke you can keep the kiln in reduction virtually constantly, alternate between reduction and neutral, or between reduction, neutral and oxidation.

I reduce the kiln up to 1300c or seger cone 10 and soak for 1 hour. If you want more ash then it is best to reduce the temperature to about 1230-1250 and soak for a longer period. At this temperature range the ash is no longer fluid but remains sticky and new ash will adhere easily to the toffee like surface. Sandwiching handfuls of sawdust between two pieces of wood as you stoke can give heavier ash deposits in less time also. After the soak it is important to bring the kiln back up to 1300 to flux the ash deposits. I then allow the kiln to crash cool down to 1100c naturally. This takes an extra half an hour or so and prevents the formation of crystobalite, thus eliminating shivering. As I am firing with high silica porcelaineous clay, slow cooling at high temperature can cause the vitreous silica to form crystobalite, a form of silica which does not undergo the alpha/beta 2% shrinkage at 573c. As the pot cools, the free silica surrounding the crystobalite will try to shrink, and the pot will shatter, to all appearances dunted. This was a problem that I sometimes had until I visited David Eeles in England a few years ago. I later found a reference to it in Michael Cardews book, Pioneer Pottery.

From lighting the fire to closing the kiln up takes me fourteen and a half hours. Thirteen hours to 1300c, one hour soak, half an hour cooling. I then cover the fire mouths with spare kiln shelves, fire clay the cracks, close the damper and leave it to cool for 48 hours. Four hundred pots which were unglazed and raw before firing are now translucent porcelain, with fly ash and flashing throughout the kiln. The porcelain tends to become white if it gets too much ash, and I am particularly fond of the warm orange and red flashing that porcelain can achieve in a wood kiln, so I stack and fire to achieve more flashing than ash. It has taken 300-400kg of scrap wood and has cost me less to fire than a gas kiln. I could fire faster if I wanted, but the results from a six hour firing are no different from the results from a gas firing, which defeats the purpose of firing with wood. The fire box being open through out the firing means that the kiln is never starved for oxygen. Most of the heat is sucked into the kiln, and I usually fire in T-shirt and jeans. In a traditional kiln there is usually a back flash when the cover is off the fire mouth for stoking, making stoking quite dangerous at times. It is always wise to take safety precautions of course, using fire proof gloves and eye protection etc. but the protective clothing necessary for most noborigama and anagama can be extremely restrictive. There are no marathon firing shifts, no Spartan all nighters, no battle with nature. It is a gentle and efficient process. A cooperation with nature, depending on natural phenomena to do the work.

Nature is beautiful as a matter of course. It is efficient and simple. Even the most complex of Natural processes are performed without waste or struggle. It has long been my belief that if an artist wishes to create beauty then it cannot be done in imitation of or in conflict with nature, but rather by an understanding of and cooperation with natural phenomena. The better we understand those phenomena and the less we try to force our materials to our will, the more efficient and beautiful our process becomes. As a result the work we produce becomes more beautiful and expressive. Economically, the efficiency of the process can be an effective marketing tool, as it can lead to pots being more vital and beautiful, and many people will select pots based on those criteria.

Since I first built this kiln, many other potters here in Mashiko and other parts of Japan have built similar kilns, as well as potters in California and other US states, Australia, the Czech republic and elsewhere around the world. Each potter makes a different style of work, uses different clay, fires a different way, but it has succeeded in making wood firing economically and logistically practical for many individual potters. Most potters would like to be environmentally responsible, but not at the expense of aesthetics and quality, and not if it is going to cripple them financially. This kiln is not the only solution, but I would venture that it is a step in the right direction.


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