The Evolution of the Mule
Patrick Sargent [ b.1956 – d.1998 ]
This could be another tale of pottery on a shoe-string. Even in Switzerland, the fabled land of milk and money. There’s plenty of both seemingly, it’s just that the latter is harder to come by. You either have it or you don’t. If you don’t then the prospect of constructing a large kiln in a foreign country could possibly be a daunting if not impossible exercise. However, two and a half years of travelling and working in Europe, being totally unconcerned about clay and pots and kilns and firings, it came to a point where naturally I had to pick up the potting reins again. Pick them up certainly, but only on an all or nothing basis. The all being the kind of working and living situation with the kiln I’d always dreamed about since discovering clay for the first time. The nothing being a permanent change of direction – away from pots. From the heart, the second option could never have happened – out of circumstances it could well have come to pass. When making criteria eventually dictate only one direction, in this case some to anything more than minimal financial resources.
A big wood kiln requires a permanent space, it is not something you can easily take on holiday. It also needs enough room for at least a year’s wood supply, with planning permission usually a burdensome necessity. The man is therefore limited to owning his own property, with land, somewhere well out of town. This either calls rich relatives or several Hans Copers to sell. The only alternative is walking a tightrope by relying on the unceasing good will of a landowner, and finding someone suitable to put up with such a ridiculous escapade is not an easy task. To get all these prerequisites on one plate is an almost impossible occurrence. Even if it does become reality, there is then the problem of obtaining firebricks, and that is invariably a very expensive commodity.
Fortunately, my affair with making pots has always been concerned with the roots. Those simple beginnings and fundamentals of the pot making process that have seemingly and virtually disappeared as a direct result of modern trend. Roots speak of simplicity. Simplicity rarely costs a lot, especially when mother luck trots merrily alongside. There are a few potters interested in real fire, even fewer who really understand it, the majority preferring the lure and folly of techno innovation and contemporary modality. Thus objects are constantly produced from clay that may well be technically and intellectually brilliant but sadly lack little heartfelt aesthetic or loyalty to the origins of the craft.
As a result, my pot making development has been inextricably bound up with kiln development. Not in a technological manner, but in a way that I can only describe as something that results from a primaeval instinct and well considered perception. I envy that caveman for his feelings when he first discovered that fire bakes clay. Imagine the elation. I think I touch on it when I am firing. I certainly feel like jumping around and making unintelligible grunts. It’s born out of a feeling of understanding yet at the same time not understanding – of being in awe. The more I strive to capture the process of nature in the way I make and fire, the closer I get to the roots.
The kiln that now stands on a previously usable patch of Emmental dairy farming land, realises the dream of a decade. Its conception and construction born out of a mixture of pure good fortune and plain hard graft. The beginnings of it all originate with a much used and abused hole in the ground at Farnham ten years ago, a period still close to my heart and already written about at length in Pottery Quarterly Vol. 14 No. 54. It was at a time when I had a pottery heroes. Their early influences gradually mellowed over the years to a point where I can say my only influence now comes from my materials, my kiln, pots from previous firing, and sometimes, though goodness knows why, the perpetual and melancholic clonk of Swiss cow bells. I still have the heroes, though most of them passed on. The legacy of Hamada, Leach and Cardew, and treasured memories of those I knew such as Paul Barron and Henry Hammond – these alone are enough encouragement for to retain a dogged allegiance to traditional methods.
So it was in autumn 1988 that I happened to be present in the middle of a field with a Swiss farmer who I’d never met before, confronted with the possibility of achieving the almost impossible. He waved one hand haphazardly at the rising slope before us, said I could build here somewhere, and went back to milking his cows. There I stood, surrounded by rolling hills, pine forests and laidback Swiss farmsteads with my knees quaking in utter disbelief, as though I’d suddenly got the whole world in my hands. The ten year dream was about to become reality, I’d experienced the elation of that caveman, and I was searching for a shovel.
The Mule is a blend of well proven principles. The donkey and the horse both have their attributes but the mule, a beast of draught and burden has all of them put together. It is of course undeservedly noted for being stubborn, but probably only as a result of being mistreated by its owner. Thus like all my previous kilns, this one was also given a name, and as a conglomeration of ideas I’d been working on since Farnham, the Mule fitted well. Its predecessor, Bacchus, was a prototype – a pseudo Anagama (if there exists such a thing) from which I learnt even more about firing technique and kiln behaviour.
My previous workshop, a disused farm on the outskirts of Northampton, was a bleak place at the best of times, but as a pottery and a place for firing it served its purpose well. I lived and worked next to Bacchus in disused pig sheds for eighteen months and became labelled eccentric by the press because of it. However, since that first hole in the ground of Farnham, I’ve only ever been interested in wood fired single chamber cross draught kilns. A case of choosing the ride and sticking with it. If you die by the side of the road in the process so be it, but the choice is one of a devotee and an inbuilt mania to see it through. The cross-draught wood-kiln boasts two main characteristics not so inherent in other kilns. Firstly, dependent on the length, there is a decreasing temperature gradient from firebox to flue, and secondly, like it or not virtually all the pots end up with a front and back irrespective of how they were made. The latter is unavoidable, as a direct result of flame and ash on one side and flue on the other. I still don’t like to see my pots the wrong way round however subtle or beautiful their backs are. I periodically go through the house turning them round after unknowing visitors look at them and put them down back to front.
The former characteristic of decreasing temperature gradient I gave a lot of consideration. Up to a point you can go with the flow and place lower firing glazes at the back. An admirable solution and to work with rather than against that flow is very true to the natural processes on tap. However, I found myself relying more and more on the same vitreous slip and high firing Shino, and less on lower firing ash-glazes. A side-stoke half way up would be the obvious answer, or several, dependent on the length of the chamber. Principles used by our ancestors for centuries, of course. Nevertheless the inherent problem with the climbing cross-draught kiln is that the chimney naturally tends to suck the heat out of the back part of the kiln faster than its being fed at the front. Close the damper to counteract that and the kiln reduces and fails to gain any further temperature rise. Evidently necessary was some sort of back pressure.
In designing Bacchus the rest was relatively easy. A Bourry firebox was a foregone conclusion as I know it well. If it is built sufficiently large it will fire anything to whatever temperature you want with no fuss, providing of course the hole the other end of the kiln is big enough too. I wanted the floor of the chamber higher than the top of the firebox to induce positive pressure and I wanted the floor of the chamber to rise towards the flue. So I really needed a hillside but I had none. Just an empty pig shed. Not to be outdone, I built the equivalent of a hillside out of concrete blocks and rubble and perched the chamber on top of that instead. This would have left the base of the chimney three feet above ground level with only five before it exited the pig shed. Flames out of the stack can be great fun especially at night with a camera, but also have a habit of creating an unnecessary and disturbing commotion that any potter in his right mind would do well to avoid. How to get the back pressure I required with a long enough chimney in so little space? The answer was, as usual, a logical one. I built a double skinned chimney that incorporated a ‘flue’ from kiln floor to ground level and then back upwards again as a chimney. This configuration gave an extra eight feet of flame flow and wonderful back pressure, decreasing the temperature gradient within the chamber by about fifty degrees. Thus side stoking to raise the rear part of the kiln to the required temperature became a relatively short and trouble free exercise. In building the stepped floor, I hit upon the idea of stepping the arch too, so the height of the chamber at the back was the same as at the front. Being free standing with sprung arches, the whole structure required a fair amount of ironwork, something well within the capabilities of a hacksaw and home welder. Ironwork to my mind however, does not look right. It’s just not sympathetic.
Bacchus, at about eighty cubic feet, was simply not big enough. The most important thing was, that as a major experiment it worked, and worked well it did. It was capable of reaching 1300c° in fifteen hours, but I always used to fire for about thirty-six, and twelve of those at top temperature. I also required precious little wood. I built it, fired several times for nothing using demolition timber and then pulled it down. Burning my bridges I left dear old England with a dream of transposing Bacchus into a real Anagama sunk into the ground. At least twice as big, with a chamber like half an egg, completely self-supporting, and fire for much, much longer. Where, when and more importantly with what means gave me moderate cause of concern.
South in the Valais, nudging the Alps is a giant aluminium smelting works. Twice a year they have to reline the furnaces, and the resultant rubble is deposited in the forest. The biggest firebrick tip you ever did see. It took six days of digging them out sorting and then stacking on pallets before I had enough. Fifteen tons of grubby, well blasted, but high quality bricks, and I was black from head to toe covered in a not too healthy mixture of sweat and aluminium dust. While sitting in the sun on a campsite, a rather drunk but accommodating Italian driver was bribed into delivering them for me. The bricks worked out at £5 a ton, the lorry four times as much – but, I was well pleased.
Planning permission for the Mule took three and a half months. It went to five different Swiss offices. Some Cantons do not even allow wood kilns – a strange conception since most country dwellings are heated with wood stoves all the year round. I managed to get the shed up before the first snowfall. The farmer donated three trunks for the main supports and the rest was built from machinery packing cases. I paid only for the roofing sheets, and reluctantly at that. The first snow as good as buried the whole lot, but inside I was happily digging the hole.
The transition from inches to centimetres posed head problems at the outset, but I was in mainland Europe and metric is more logical. Thus the Mule was designed and constructed using metric rule. I do not build using any fixed parameters from other sources. I use a little experience (this is the eighth I’ve built) mingled with some common sense and instinct. I certainly fire by instinct. Not many people have it, maybe I’m lucky. There is such an unaccountable myth associated with wood-firing and a most absurd ineptitude to go with it. Lack of instinct answers a lot, and so does lack of gumption. Instinct is about feeling, conscious or unconscious, and gumption is plain initiative. Can you remember the last time you actually felt a gentle breeze on your face? Feeling the state of a wood kiln during firing is not that different. It is just a case of being aware. Designing and building a wood kiln that functions well is simply a logical understanding of the principles of combustion. Critical areas such as throat arch, bag wall space, flue exit and chimney section should not be built too tight. It’s much better to be over generous in these parts than to have a major problem later. For instance an over large chimney section can be controlled with dampers, if it is too small it has to be rebuilt. The firebox volume in relation to chamber volume is also important. It must be big enough. The firebox of Mule was designed specifically for easy firing, high temperature and a good ash deposit. The ashpit floor is half the length of the chamber. The chamber floor rises in six steps with a duct half way up to provide air for side-stoking. This air-duct reaches the outside world through clay drainage pipes on both sides of the kiln and is an absolute must for efficient combustion in the part of the chamber.
I found myself digging into a seam of gravel a metre down, which with a finishing bed of sand, provided a solid enough base for the floor and foundations, and good drainage as well no doubt. Digging the deep hole for the chimney was therefore a trifle tiresome, but the advantage of having most of it underground is that only a metre and a half from a total of six protrudes above ground level. This is of course environmentally friendly in terms of landscape and possibly impressive in the planning office, though which one I couldn’t say.
The Mule was built in order of firebox, kiln floor, chimney and flue together and finally the chamber. Finding scrap in Switzerland is not easy. I might just as well have been looking for a needle in a haystack. Nevertheless, I eventually secured all those little extras I needed. The firebox was braced with an iron frame to support the arches, and an old but elegant cast-iron bread oven door (with a primary air slot no less) was given a new lease of life as a Bourry firebox door. I had always wanted an ashpit with a door on a chain and pulley balanced by a counterweight but previously I had never got around to it – this time I did. It works magnificently. Gary Wood, an ex-student of Mike Dodd remarked that it was the only kiln he had come across with a self-flushing firebox. In fact the whole firebox works so well he could be right.
Note should be made here regarding throat arch, bag wall and bag wall space. I have come across many kilns that have been built with the bag wall space far too tight and almost without exception their owners complain of the age old problem – getting to temperature. Whatever the cause this can always be answered without having to look far. There is no myth. The throat arch is subject to the highest temperatures in the kiln, and if the bag wall space is too tight this leads to a wonderfully hot firebox but a miserably cold chamber. Flame has a volume and requires a certain amount of space to move, if restricted in the bag wall area it will not heat the chamber. Bacchus may look a little tight in this point, but for the chamber size the bag wall was just sufficient. For the Mule with a 2.25 increase in volume I enlarged the bag wall space comparatively. The bag wall equivalent is not only concave but is inclined away from the firebox, i.e. the bagwall space increases as it becomes chamber space. This is both constructional and theoretical. Such a wall, if built vertically and straight, will after several firings bow towards the firebox simply because it gets so hot. This naturally results in reduced bagwall space and irksome repair work. Flame volume increases up to a point the further away from the firebox it gets and then proportionately decreases towards the chimney exit. The increasing bag wall space permits easier combustion and the inclining ’bagwall’ is sympathetic to the flame-path which by its nature dislikes corners.
Relative Proportions (in cm.) : Bacchus : The Mule
Packing space : [2.2 cu. m.] : [5 cu. m.]
Ashpit length : 148 : 215
Chamber length : 283 : 400
Maximum width of chamber : 110 : 200
Maximum height of chamber : 90 : 140
Firebox to top of chimney : 290 : 440
Bourry firebox length : 110 : 140
Bagwall height : 75 : 104
I think the most enjoyable part of the whole exercise was building the chamber. Everything else was finished, firebox, chimney, floor, flues – all it needed was ‘top’. With one long baton sprung from end to end in a shallow arch I could visualize height to width proportions and the height of the arch at any given point from front to back. I then calculated, drew out and built seven U section formers from scrap timber (fridge packing cases to be precise).
With two of these positioned at either end and the remaining five, one on the front of each step, I could then form the main shape by pinning roofing batons over the whole lot. (figs. 1,2 and 3). It looked beautiful, just like an upturned boat in its early stages of construction. It seemed a shame really to cover it first in plastic, and then bit by bit with a single skin of well laid firebrick. Half way up, on both sides, I set in two spy hole ports and a side-stoke port. These were made as conical cylinders, thrown out of firebrick clay and fired in a test kiln that I had also built from scrap. Building the chamber took only two days, but after laying bricks for weeks in sub-zero temperatures knocking in the final one was a relief. I can clearly remember impatiently burying the entire construction under a great mound of earth and diving into the chamber with a hammer to knock out the former. (being buried the arch becomes self-supporting). After all the timber and rubble was thrown out of the entrance. I sat up the far end looking down and out of this great oval dome, with its six round skylights, shaking with some kind of primitive bewilderment, almost disbelief, at the beauty of it all. To think that all this would soon be white hot hardly bore thinking about. It was a long time before I came out again.
The finished arch was covered in a thick layer of high temperature clay mixed with sand and sawdust. At a later date, the very obliging farmer rebuilt his cowshed, and presented me with a trailer-load of old and very smelly red bricks. A layer of these was finished off with another clay layer of clay dug from the nearby forest, again mixed with sand and sawdust by foot. The chamber was now nearly half a metre thick at its thinnest point and well insulated. I threw side-stoke and spy-hole bungs from firebrick clay, and made a pair of quick action iron doors rigged up on pulley wheels for easy stoking. A little bit of luxury. The kiln floor and bagwall were finished off with a mixture of90% grog and10% clay. A bit more landscaping and it was finished.
The Mule took four months to build and was constructed entirely from scrap and recycled or found for nothing materials. It cost the equivalent of £1000 including all transport and all kiln furniture. I collected 150 large silicon carbide kiln shelves and 220 solid silicon carbide props from the back door of the local porcelain factory. Second-hand of course and destined for the scrap heap, but it’s amazing what you can still get for a crate of beer. Conversely I might mention that I heard of a 12 cu.ft. gas kiln that cost the equivalent of £5000. Later I came across a computerised electric kiln without a spy-hole of any sort. Ye Gods, what is happening, I thought to myself! How can anyone consider firing any kiln without being able to look inside it? It was then that I realised how long the arm of decay has become. Real Pottery could be called Real Kilns, Real Farming or Real Anything Else come to that.
Most Swiss country houses are made of wood and the ones that get pulled down to make way for more concrete provide a rich source of well seasoned pine for firing. The Swiss have little interest in demolition timber, it’s full of nails and difficult to stack neatly. For me it’s ideal and usually free. Wood from the gradually dying forests is not really suitable, it costs money and I have to keep it for at least a year before it’s dry enough to use. I am now firing for two to two and a half days. It gets longer every time. The lengthening of the firing cycle happening because I rely more and more on the fire to decorate. The longer the better. My making and decorating techniques have become very simple. I use only one or two Shino glazes, but mostly just a vitreous slip, nepheline syenite based. Sometimes nothing at all. Just clay. Just like that caveman. The critical factor with such a long firing is of course physical limitation. To fire for three days for instance requires a certain amount of conditioning which can only happen over a long period of time. I can never leave a firing even for a few hours in the hands of someone else. On the few occasions I ever have done they’ve always proved to be disasters, one way or another.
For firing and packing techniques refer to Pottery Quarterly Vol. 14 No. 54. An approximate outline of my current firing cycle is as follows:-
The first twelve hours – gradually to 400c°
The Twelfth to the thirty sixth hour – 400c° to 1300c° pausing for an hour’s clean burning at 850c°, followed by deliberate heavy reduction for the body from 920c° to 1000c° over two hours.
Thirty sixth to the forty eighth hour or more – natural cycle of oxidation and reduction brought about by stoking, the same as for 1000c° to 1300c°. During this time temperature rises to between 1300c° and 1350c°. Final two hours clean burning followed by fast cool over one hour to 1000c°.
One may be tempted to ask why? To fill it takes about two and a half months work, which means I only fire about three or four times a year. The learning is inevitably slow with such a long period between one firing and the next. Economically, both in terms of time and fuel it works. It is clearly a long term project. With each firing comes a little more understanding. The marriage of materials and flame together with draught being a constant source of investigation. I don’t think I could work anything less now – a big kiln, holy fire and buzzards circling overhead. Oh yes, that is the romantic side of it all – the reality is a kamikaze style existence, certainly with all the eggs in one basket and a fine line separating success or failure. The pursuit of that rarely attained harmony between clay, surface quality and fire is possibly my major motivation. The end result to most is an intangible abstraction. In a society hellbent on automation, it carries little validity or relevance, except maybe to a handful of personalities who somehow, in the midst of it all, retain some element of vision. Compromise has both a negative and a positive terminal. To take the negative terminal and consciously nurture it into the positive terminal of blend is one aspect of this vision immediately applicable to the definition of Quality, if Quality is ever definable. If a blend is designed to bring together the best of the two, then surely this is a move towards that Quality. In a sense I am looking to justify it all in one way or another, and Quality is the only justification as all the others are seemingly created to satisfy the ego. After all, it is a purely self-indulgent passion. On the horizon however rapidly approaches subtlety wearing the clothes of warmth, colour and touch. The pot still has its place.
If that pot is a direct product of the personality, and the personality directly influenced by its environment, then logically the pot becomes a straightforward breathing expression of the surroundings in which it was created. To a greater part the constitution of these surroundings consists of the purely sensual and physical, but not only. One cannot disassociate state of mind and mood. Many a strange looking pot has disgraced the exhibition rostrum when really it should long have been condemned to a life of shards. To have been born out of tune is not the fault of the pot. Its life, or death, is simply the responsibility of the maker.
John Maltby once said to me he couldn’t understand how a potter could be so deeply committed to such a mode of travel as a motorcycle. Boats were much more in keeping. I didn’t disagree, and I daresay if I made in the manner of John Maltby I would disappear in a boat for the odd afternoon as well. However, after three years longer in the saddle than thirteen at the wheel, the two go hand in hand to such an extent that one without the other would be inconceivable. If I owned a boat it would represent romanticism, the motorcycle represents the reality. Switzerland to England is a good day’s ride. It’s much faster and less troublesome in an aeroplane. Just like an electric kiln. To be in Zurich and then in London a little over an hour later with not so much as a ruffled hair is positively unreal – relatively speaking. Nevertheless, teetotal experience and the end result is hollow. In actual fact devoid of any intrinsic aestheticism or quality. The motorcycle is ridden out of pure necessity and an inbuilt genetic disorder that states I must have wind in my face while on the road. In any case Bernard Leach rode a motorbike….with Hamada in the sidecar.
I remember after I had finished all the heavy work going to the forest early every morning and bringing back a small sapling, or some moss, or a beautiful stone and setting it in its rightful place on and around the kiln. It all somehow fitted together. A kind of pot pourri of values which I am forever reconciling and kneading together into a harmonious whole. The long fire encompasses an element as potentially creative as the initial lump of clay and that by itself presents me with sufficient horizons for a lifetimes’ work.
Westerwald ball clay 65
English china clay 15
Nepheline syenite 8
Swiss quartz sand 12
For dark body add 1% iron.
Addition of grog and feldspar sand to taste,
and a higher proportion of china clay for the front part of the kiln.
Mixed by foot.
Nepheline syenite 50
Ball clay 30
China clay 20
Apply thickly by brush.
White shino glaze
Nepheline syenite 75
China clay 15
Ball clay 10
Orange shino glaze
Nepheline syenite 60
Ball clay 40
Here’s some of early work (made in the U.K.) by Patrick.