Mike's Pots

The International Conference of Craftsmen in Pottery and Textiles
Dartington Hall 1952

Dartington Conference 1952


By Michael Cardew

I think the proved title ought to be "The Usefulness of Science to a Craftsman Potter, How it can Help Him to Survive and to Succeed". Anybody who knows anything about science, and anybody who knows anything about me, can't help knowing that it is absolutely absurd that I should be talking to you at this moment. And I suggest that the second title should be "What not to do by one who has done it". The points at which the potter's craft comes into contact with science, i.e. sciences sciences is not just a terrible, frightful governess but it's the sciences there are so many points that it intimidates me even to begin to think about them all, and that's why I would rather prefer to begin with saying that I'm not a scientist, but I would say a person of average intelligence who, owing to an unfortunate streak of obstinacy and pigheadedness, has had a more than average share of technical troubles and technical disasters. So I think it will be best to begin with a series of personal avowals and to go right to the beginning and start with the question which always used to trouble me and puzzle me. People used to ask me "What made you want to become a potter?" I never knew what the answer to that was. But the other day I was reading a book by Laurens van der Post called "Venture into the Interior" quite a recent book. He's a South African author, and the book seems to be chiefly a sort of exploration and trying to find an answer to himself as to why it was that he kept on being drawn back to Africa. But that's not the point. The point is that in it I found a very, very useful phrase. This is not word for word, I'm afraid, because of course I left the book behind. But this is as I remember what he said. "Every day", he says, "we keep on announcing ideals which are oddly at variance with the things we do. It has become my constant practice to look for a man's deepest motive - his over-ruling passion in the results that he produces rather than in the eloquent avowals that he makes to himself and to others. All of us have motives and springs of which we are deeply unaware. This other side of life so brutally locked out of our consciousness that it can only call attent on to itself dumbly and obscurely in the joylessness of the results around us". And thinking back I thought it was chiefly a sort of dumb rebellion an inarticulate rebellion against this joylessness of the results around us - which made me first want to be a potter. Of course that was a longish time ago. Apd in those days and in that mood and when one was very young it seemed to me that the joylessness of the results could be summed up and described in one word "industrialism". And my revolt and revulsion from all the products of industrialism, direct and indirect, were vivid and quite uncompromising. I chiefly remember hating things. I hated the sort of common, mass-produced teapot. I hated it for its gratuitous dullness and unredeemed drabness. And then one was supposed to admire the products of really high-class firms - you know, the luxury goods; and I hated those even more. There was a third class of things which I specially hated, and that was, I'm sorry to say, the earliest products of the first - I suppose they were - art potters. Estimable people who devoted years and years to the discovery or the rediscovery of some obscure technical process or technical effect. But at the same time they seem to have been quite content to accept the standard body and the standard firing process. And so these products seemed to be merely my old enemies in fancy dress.

Well, that was how I felt. And since the only lovable, and therefore the only acceptable, pots were those that had been made by the pre-industrial or the primitive potters, it seemed, of course, as if the only way to produce something having the same qualities was to do it in the pre-industrial or the primitive way. Of course quite illogical, post hoc is not necessarily propter hoc, but when you're mortally engaged in a rebellion and a crusade consideration of such a thing as logic is brushed aside - quite logically, of course (LAUGHTER) as impertinent and quite irrelevant. Well, I was driven by this spirit of implacable and uncompromising rebellion. I began to take the first steps towards becoming a potter. Of course, if there had been any primitive potters or any pre-industrial potters in the neighbourhood, which there weren't, I should have tried to join with them. But what would have happened would have been that sooner or later I should have found that unfortunately the pre-industrial or the primitive potter has actually in modern life a receding place, a receding usefulness, and that they're every- where losing ground and getting engulfed by this enemy. Then, not being able to find any primitive or any pre-industrial potters, you try to start up independently or you try to join in a like-minded group. And as soon as you start to get down to work you find you're grappling with a highly technical oraft, and the scientific side of it is continually confronting you with problems. Well, according to your temperament, you either begin to grapple with the science of it or you refuse. Unfortunately, I was one of the 'refusers'.

I well remember at the Leach Pottery - where I was lucky enough to go for three years I think it must have been 1924, after Mr. Hamada had returned to Japan, we had the extraordinarily valuable experience of having Mr. Matsubayashi there for a whole year (APPLAUSE) and he used to give us evening classes in Pottery Science. And I think we should all have a good laugh if we could go back and see it. There were four or five of us sitting at the long table in the Pottery, and Mr. Matsubayashi gave us these very valuable lessons. I think most of the pupils were fairly good pupils. I remember particularly that Miss Bouverie was a very good pupil and she used to take copious conscientious notes. I remember also that Mr. Leach was perpetually interrupting the lecturer. (LAUGHTER). He was always asking the lecturer to turn physics into metaphysics, you know, and technology into ontology. But the worst of all was Mr. Cardew. Mr. Cardew simply sat there doodling. Doodling suns and moons on doodled little imaginary beer jugs and things. His notebook was full of that sort of rubbish. Hopeless. I remember about 20 years later I had a terrible thought about this ungrateful idleness on my part and I went straight off to visit Miss Bouverie and spent several chastened hours copying out her notes. (LAUGHTER AND APPLAUSE).

Well then, you go on penetrating further into the mazes of this craft, and then of course, again according to your temperament, you do one of two things. You either can continue doggedly in this line of trying to begin at the beginning, or you persuade yourself that perhaps after all it is all a bit difficult, and the end really justifies the means. The end being to make pots quickly and make a living and all that. And you start making compromises with this industrialism; because such compromises really amounted in my view to surrender. I'm thinking of the people who are numerous today, and they were numerous then, and I'm not so intolerant about it as I used to be, the people who buy their clay already mixed from somebody in Stoke-on-Trent, lovely plastic clay all done up in a parcel. Then you get your glazes all ready-made, ready-mixed if possible, and your pigments -everything ready-made and you buy a ready-made kiln and you fire it with some thing which is quick and comfortable, such as electricity or gas or something like that. And then of course you don't know anything about these things but if anything goes wrong you write a letter quickly to the Potters' Merchant and his technical service is at your disposal, and your glaze crazes all right - send down that crazeless glaze - it's quite quick and comfortable you see. That's one way out. And the idea of it, of course, is that in theory you'll be liberated to concentrate on Eric Gill's old friend 'Higher Things'. (LAUGHTER). I'm afraid 'Higher Things' isn't quite dead yet, you know. I've met the spectre of 'Higher Things' even at Dartington this past week. (LAUGHTER). Of course it's a perfectly reasonable idea. Free yourself from technical obstacles and your personality will be free to flow freely and without obstacle into the channel of expression that you have chosen for yourself, namely pottery. Well, it's very difficult to express the fallacy in that. There are, of course objections to that view. The most important one is (nothing to do with science) that human nature just doesn't work that way. A personality that dodges difficulties isn't going to be a particularly edifying personality even if it does flow freely into the chosen medium. The exp ession is not going to be awfully interesting. And there's an even more difficult point to make, which I always find difficult to express, that the expression you make with the materials is inseparable from the materials, in some very indescribable way. That there isn't one thing - the expressing artist and another - the expressed material. The material really takes charge, I think. And you've got to study the nature of the material as profoundly as you're capable of and with all your five wits not necessarily only with your analytical or your mathematical faculties - but all your five wits. In other words, scientific knowledge about your technical materials isn't really different in kind from your artistic knowledge. And then, of course, there's the third thing on a very much lower plane that if you're aiming at technical and commercial success it won't work either, because the day of reckoning will almost certainly come when you suddenly find your self thrown on your own resources, and you haven't got Wenger or you haven't got Harrison or you haven't got the various other firms or you're out in the wilds somewhere, and then you can't get it at second-hand any longer, and you wish you had it at firsthand. I still rather tend to think of that as a short-cut way of getting into pottery.

The other road is equally troublesome, equally objectionable. The second road of doggedly continuing your efforts to begin at the beginning. Without science it lands you in a position. you may be able to sustain it honestly for quite a long time but you can't sustain it in the long run. It's a road that takes you a terrible long way round. I remember getting into a state of mind at Winchcombe. Unconsciously, I suppose, I applied a criterion towards this technique. Could it have been used by a pre- industrial or by a primitive potter? You see, if the answer was 'Yes', it was all right to use it. If it was 'No', then you don't use it, it must be bad. And finally, you're driven into the position of a German philosopher - I don't know which philosopher it was - who wrote a whole book on the philosophy of "As If", and you have to live in a world of "as if". You create a pot "as if" you were a traditional potter, and you take refuge, of course, in saying what used to be a favourite saying of mine, "Well, traditional potters didn't know anything about science, but look at the lovely things they made." Well, of course, I see now that ignores three very important points.

Point 1. We see the surviving work of traditional potters, but we don't see their failures. Sometimes, if you go exploring a heap of wastes from an old kiln, you do get a glimpse of it. Probably we have no conception of how many failures they had. Point 2, a similar one, is that the evolution of their technique took hundreds and hundreds of years. And Point 3 is that they were traditional potters. They stayed in one place. They worked in a traditional way with a traditional clay and traditional materials of all sorts, and probably in a more stable society. And certainly today we can't always do that, and technical traditions have been very largely either lost or upset. For instance, using lead glazes has been upset by the Factory Act - to take a very simple example.

Well I suddenly realised, and I've been saying almost nothing else for the last two years at least, in technique there's only one substitute for tradition. Not that I'm under-estimating it, I mean tradition is the most important thing, but if we haven't got it there's only one substitute and that's science or the scientific approach. And you find it out if you attempt to introduce, for instance as a lot of my work has been in the last years trying to introduce, what is a new technique in a country where this technique hasn't got a tradition. And there is only one substitute, scientific method and scientific approach. So however intimidating it is to me, we have to come back to the point where the sciences touch the potter's craft.

That raises a rather interesting point because, of course, the main thing of the potter's craft is clay. And potters, as a matter of fact not only craftsman potters but industrial potters, up to the other day, they've been able to dodge this scientific issue because they've had to very largely whether they've liked it or not. They had to get along without science anyway because science had very little to tell them. Until very recently the sciences were not able to give a full and confident account of the potter's chief raw material. And I got that from Sir William Bragg - he wrote a book about 1920, a sort of popular science book about industries, and he said that whereas in other major industries like Metals and Fibres you know pretty well just what you're doing, in Clay they still didn't in 1920. And the result was the pottery industry, a large important industry, was muddling along in a purely empirical way. If anything went wrong they more or less asked the oldest man on the works what was wrong (LAUGHTER) and then they got it right, and nobody knew why it had come right. The whole industry remained extremely conservative and nobody really knew, except empirically, why the things that potters did to their materials worked or didn't work. Well, as I said at the beginning, I'm not a scientist and I am not the proper person to explain just how it is that the scientists have now found out, not all but a great deal more about our main raw material. I hope Mr. Burke is going to tell us. But the fact is that owing to recent advances in crystal-chemistry, electro-chemistry, and new techniques X-ray analysis, differential thermal analysis, electron microscopy the scientist's ideas on the nature and structure of the clay minerals and consequently on their behaviour are now beginning to take a clear and properly scientific shape. And consequently this is what interests me it is now possible for potters to supplement their intuitive knowledge of their materials with some scientific knowledge of them. And I would go further than that and say, not only possible but necessary. I find that very difficult to express. I try to say it by saying a good potter loves clay disinterestedly for its own character. Not merely because it's an obedient mirror for his own personal ideas. If he's going to be a good potter he must know his job, in the ordinary sense of the word, and be able to make pots. I used to think that was quite enough really, but it isn't. He must support this by a continual effort to understand scientifically the processes he is using. So I think I am trying to tabulate a whole series of new commandments for potters under the general heading of 'Know What You're Doing'. (APPLAUSE). I think there are four commandments.

Commandment No. 1 is 'Know your raw materials'. That's a very long one and involves a terrible lot of knowing, which I don't profess to have achieved. Start with clay, much the most important and much the most difficult. I should have mentioned just now that we were puzzled by clay. Everybody knew all along that every hole in the ground produces a different clay or a slightly different material, but there was an element of puzzle. The old books say Kaolin is Clay, but it's a funny thing that it is entirely lacking in the quality that is most characteristic of clay. (LAUGHTER). They have discovered now that there are between ten and twenty Mr. Burke will correct me if I'm wrong between ten and twenty varieties, and possibly even distinct mineral species of the clay mineral family which is a most intimidating branch of science which I don't pretend to be able to understand. You join the Mineralogical Society and then you join the Clay Minerals Group of the Mineralogical Society, and every month I think it is you get a typescript periodical that comes out. I was very excited when I heard about this and I got some of them but I didn't get very far. Not for want of the will but simply for want of the power. Well that, of course, obviously complicates things a good deal. All the time we had this other more familiar fact which makes clay such a difficult thing to standardise - the great bugbear of the mass-production potter, the fact that any hole in the ground can be a claypit. It may have several different clay minerals present in the clay fraction of the stuff that comes out of it. But it also has, with this mixture of clay minerals or possible mixture of clay minerals variable mixture of at least three or four clay minerals. It will also have a variable mixture of all the other minerals which are commonly found in company with clay and intimately mixed up with it, such as felspars and the forms of silica, the iron minerals of which there are about half a dozen, possibly the alumina minerals, not so much in England but in other countries you get them in Scotland I believe - calcite and limestone, ground calcite and dolomite, micas (very important ones), all very valuable, several different micas. So clay is obviously a very big subject, and all these variations can be due to a lot of things. It means you've got to go right back, and unless you're doing it seriously you obviously can't, but your interest in the thing drives you back to look into it. The variations may be due to the origin of the clay, which makes you study petrology, and in the original character of the parent rocks which produced the clay, and the history of that particular deposit how it came to be there - you'll have to read geology and sedimentary petrography - and then a chemical action takes place a study of the climate - and how much leeching went on, how much washing out of solubles and how soluble they were, and things like other troubles we get in the tropics like lateritisation, which has a very important effect on clays. Well perhaps logicially the clay mineral question ought to come first. That's the clay as a rock. You see there's clay as a rock and clay as a mineral. Clay as a rock is what you dig out of a hole in the ground, but clay as a mineral is what the scientist is dealing with really in his research laboratory. And they're recognised in three main groups the Kaolinite group, the Illite group and the Morillonite group. Forgive me if I pronounce the words wrong, but I'm a poor self-taught man and I very often make mistakes. (LAUGHTER).

Well, the Kaolinite group is, of course, kaolin - this type of material is just there around the corner in Devon and Cornwall. But it contains several others, notably Halloysite, which you get more on the continent than here, and a Halloysitic clay mineral which they're pleased to call the Fireclay Mineral - they haven't got a better name for it yet, but it is the mineral chiefly found in typical fireclays. When one's dealing with a fire- clay, one's dealing really with a different clay mineral. And of course ball- clays belong to the Kaolinite group predominantly, but the molecular lattice of a ball-clay is, I believe, slightly knocked sideways by its past history. That may help to account for its physical differences. Then the other extreme - the Morillonite group. The Kaolinite group is not so plastic as real plastic clay. It tends to be slightly lacking in plasticity and tends to be refractory, tends to fire white. The other end of the scale is the Morillonite group, which includes Bentonite, which however white it looks tends to fire not so white. It tends to be not so refractory and it tends to be extremely plastic with an extremely high shrinkage, and so on, and is a most dangerous material to get into your clay in a large quantity. In between is the intermediate group which I rather gather is the Illite group. I don't know why it's called "Illite". They're also sometimes called the Hydro-Micas, which is always a bit puzzling because all Micas are Hydro. But they do seem to be a kind of degraded Mica. ('Degraded' is a technical term - sorry!) (LAUGHTER). An extremely altered Mica. And it's very often found in brick clays. There's recently been some research done on Sussex clays and they seem to think that it's largely Illites. So if you've started using local clays, look out for Illite - I don't know what it does. (LAUGHTER). Even if I was competent we shouldn't have time to go into it in detail, but I'm rather raising all these bogeys in the hope that perhaps Mr. Burke may be able to help us.

After the clay minerals, which is the most mysterious and difficult to us non-scientific people it's the most difficult aspect of it there are all sorts of other things about clays that we've got to try and get to the bottom of. Grain size to start with. And the grain size distribution of any given clay rock has a tremendous effect on the working properties of it. I mean the clay rock comes out of the ground, and it contains a good deal of rock flower and a good deal of pre-quartz or other form of silica, perhaps a certain amount of calcite or powdered dolomite and a lot of micas. And what is the gradation, how is the grain size distributed? This you could do in a purely amateur way, a semi-scientific way, of separating in sieves. To do that scientifically is quite a long thing, but whenever I see a publication of a mechanical analysis of any clay rock, I leap upon it as food and try to get something out of it. What proportion of the total is above such a mesh-size, what proportion is below two hundred mesh or three hundred mesh, and in the sub-screen fraction, as they call it, what proportion is ultra-microscopic and what proportion lies close within the cerebrane? I think it's fifty or fifty-four microns, or something like that. A micron is a thousandth of a millimetre. And from there down to one micron is more or less imaginable sizes. And when you get below one micron it's awfully difficult, I think, to imagine what the stuff is really like, but ball-clays are very largely below one micron I believe. And its got a good deal to do with another thing plasticity which really is the essential thing, speaking personally. Of course, behaviour in the kiln is rather important. Plasticity is a very mysterious subject. I don't think that science has got to the bottom of that just yet, because it so subjective, and they're still trying to make an objective, quantitative - because science is always trying to be quantitative, and that's its value or one of its values a quantitative measure of plasticity. I notice our friends the clay miners over at Newton Abbot they've got a plasticity number or something now. I don't know how it is arrived at but I'm sure it is not really scientifically valid. Probably based on something either highly subjective or else nothing to do with plasticity. But it is a very mysterious subject plasticity and I know we're going to hear some- thing about it from Mr. Burke who really is a scientist and really is a practising potter.

Then there are other things, of course, like the behaviour of the clay in drying. What I think is important there is that we used to look upon drying in a sort of ananistic way like a struggle with something unseen - something that was going to dodge you or hit you behind the back or some thing. The thing is, of course, to be systematic and look at what is really happening and to look at it quite irrespective of whether you like it or don't like it. I mean it is the behaviour of matter, and I think a technical account of what happens in drying is an awfully interesting thing, and one can know it for years but if you haven't directed your conscious mind to it you don't get such value from it. I've known for years and years and years that most of the shrinkage happens soon after it is made, when it gets down from really sloppy plastic down to leather-hard and down to cheese-hard - the sort of state when it doesn't lose shape easily. Most of the shrinkage takes place then, but a good deal of the water hasn't yet left the clay. That is the sort of thing I mean. There's a beautiful picture in Mr. Bourry's textbook of what happens when you dry clay.

Speaking for myself, I could have gone on potting for ears and years and years, and I'm sure traditional potters did, knowing that sort of thing instinctively but never having thought about it systematically. And I think it is a very, very important thing to a modern potter to think about it systematically and to get what he can out of the technical literature on the subject. Shrinking and warping and how they happen. Behaviour in firing. We're still on clay- Commandment No. 1 - (I don't know how the time's going. Not much longer). Well, this thing of firing. Clay is a hydrous mineral and its got mechanically combined water. That's got to be got rid of. The clay's got to be really dry before it goes into the kiln. Many, many potters get licle failures due to that. They put a thing in that looks dry but it isn't. Then there's hydroscopic water that's why you have to start the fire slow. And when that's off, theoretically you can go ahead, but theoretically doesn't always work, of course, because different parts of the kiln have slightly different temperatures. The important thing in the firing is the water combination which breaks down at roughly 550 centigrade, and certainly from then on you have to be awfully careful. And then the hardening behaviour of clay on firing this amazing thing that Mr. Matsubayashi used to tell us about called 'sintering', which is a most remarkable conception, and I've never been able to find a scientific definition of sintering, but clay is the thing that does it that affects us. On firing it gets hard and rigid and emits a ring without the presence of any glass bond. I mean, you've got a thing that's stuck together without glue. I believe it is thought to be a kind of glue. The particles of the clay are supposed to be cemented together but there is no glass phase in the body, and in the case of absolutely pure kaolin I believe it is a fact that that continues to be so up to very high temperatures, and it's a very wonderful thing about kaolin. It only came over me recently it sounds pretty obvious but what a wonderful thing for potters kaolin is. Because it is one of the very few materials you fire it and from having been very soft it becomes this extraordinary hard thing with a ring, but still at high temperatures remains porous and rigid. I don't know any other material (maybe Mr. Burke can tell us) that hardens so much on firing and remains so porous. It is an extraordinary thing. Then the thermal history of kaolin when you fire it what changes it undergoes. 'Science for beginners' in pottery used to say, "Oh well, you see Kaolin is AL203.2Si02,2H20, and you get rid of the 2H2O and then you've got a bit of alumina and two bits of silica". Well, it isn't so. It's about 5500. They recognise it is a thing called Metakaolin now, and then at about 9500 you get another change coming over. I don't know how long it lasts. I've read that it does change again there, which has a practical importance for potters, because the change that happens there is a crystallisation, a separation of Metakaolin into a thing they call gamma alumina and something else (I don't quite know what), and it has an exothermic effect, that is to say, it generates its own heat. And that's a thing we've noticed for years and years and years and thought it was very odd, but we didn't know why. At certain stages in the firing it suddenly begins to go quickly and the temperature dashes up and you think "Oh, hat's lovely. We shall be finished about 4 o'clock in time for tea". And then about o'clock you stick again. Well, as time is very short I shall have to leave this extremely complicated and much-beyond-my-head question of clay and go into the other raw materials. You see, we're still at the stage of knowing your raw materials.

After clay you've got silica to tackle, which is an appalling raw material. Its commonest form is quartz, but there's calcydonic silica and there's opal. Calcydonic is crypto-crystalline or ultra microscopically crystalline, and opal is not crystalline at all I believe. And then quartz itself is a terrible material. It has two forms - a low temperature form and a high temperature form, and at 5750 centigrade it turns into beta-quartz, with disastrous results if you've got too much of it in your body and if you're sending up the temperature too far: Then there are three forms of crystalline silica stable at different temperatures. You've got quartz, a low temperature quartz and a high temperature quartz. But that's only quartz. If you keep on heating quartz long enough, if quartz was logical it would turn into tridymite first and then into crystobalite, but it doesn't it does the other thing. It turns into crystobalite first, which also has an alpha and a beta form and is unstable at low temperatures. And then if you keep on trying for weeks it arrives at its stable medium temperature form of tridymite. Crystobalite is the form stable above a very high temperature I've forgotten what. Tridymite is the form stable in the medium temperature. I mean in the sort of temperatures that we use. We never get tridymite in pots, but it's the form of quartz that's stable. Then, of course, there's another form of silica very important practically to potters diatomite. hat's another whole subject which I should like to know more about than I do. I feel that diatomite is a very important material for us. Well, finish with silica at present.

The felspars. There's a whole family of minerals called the felspar family, and a more closely related family chemically than the mica family also a large family. And consideration of felspars takes you right into the world of petrology and the whole question of magmas and how the world was made and the origin of igneous rocks and what happened when they began to cool and which are the most usual ones. Terribly important to know all that. (LAUGHTER). And a very interesting collateral family called the fels pathoids of which the best-known member, of course, is our old friend nephaline. We shall have to leave them and come back to them in discussion.

And then there's Class D - Others. "Others" is very large and sub- divides into three sub-classes. "Others" sub-divides into refractories, things that tend to act as refractories, things that tend to act as fluxes and things that are used for fluxes. The refractories are the alumina minerals certainly two, possibly three. They're hydrated aluminas - gibbsite, which you get in some clays some leeched and weathered, or hatever it is, clays. Clays that have had a certain kind of history become gibbsitic, or what used to be called bauxitic. Well, they may become bauxitic. Bauxite, if it is a mineral and not a rock. It is a rock, but it may be a mineral. Isn't that so, Mr. Burke? And diaspor, which I've never met. A very important American clay mineral found in association with American clays. All those are very useful as refractories. Then there's the alumina-silicate group which are related to china-clay there's sillimanite and two other forms, kyanite and andalusite, and of course mullite which is so rare in nature that it's of no practical importance. And odd ones in the refractory field like zircon they're all there got to be learnt about if you're in countries where you're liable to come across them. I don't think we do come across zircon much in England, but we do use sillimanite - got to know about that. Then the fluxes. This is mineralogy mostly, you see. All this raw material data is very largely a study of the minerals from which you get these things. Calcite, all forms of limestone which are innumerable (not quite innumerable but they're very numerous). I've neglected one which is very important to us here in England, though some of us don't know it, calcium fluorite, which is quite a big ingredient in our Cornwall stone which is what we commonly use here instead of felspar in bodies and in glazes. It has a very great effect on the Cornwall stone. It accounts for the fact that used to puzzle one that Corn- wall stone, if you leave out the fluorite in your technical consideration of it, it seems that Cornwall stone is really an inferior kind of felspar. And yet as a flux it's equal to felspar very often, due largely, I suppose, to the presence of the fluorite. If you get a bit of hard purple Cornwall stone its got these little dashes of purple all over it which are fluor-spar. Dolomite, which we get in England too and enormous quantities of it on the continent - it's much more used on the continent than it's used here. The magnesium minerals which are very popular in some quarters talc and so on. The boron minerals which we all have to import from our friends on the other side of the Atlantic. No other place we can get it from except Tibet, I think, and small quantities from Italy. The boron minerals, which are fairly numerous and very interesting. Very useful, we can't get on without them. Many of us can't. And an awfully interesting group we've been getting interested in lately the lithium minerals which you get in America, and the best place seems to be South-West Africa, which is very far away and a verv difficult country I'm told. The only member of the Conference who knew anything about South-West Africa has gone back, I'm sorry to say. He was a South African who was over here for a time. But lithium minerals are awfully useful. You know elements go in groups. Lithium is one of the group of alkali metals, and it's the lightest in atomic weight, I thin, of all the alkali metals and apparently as far as one can see - the most active. It goes with sodium and potassium. There's no lithium felspar, for a reason which I am sure Mr. Burke would be able to explain to us if we had time. The lithium mica is an extraordinarily useful flux but awfully difficult to grind; it's more useful to the brick-maker than to the glaze-maker. There's a lithium silicate called petalite, a high silica one, which we do get in Devonshire in Meldon stone, and which is one of the reasons why Meldon is a very useful rock - Meldon Stone, just North of Dartmoor here. And spodumene, which is nothing but a name to me and is evidently the best of the lot. They use it a lot in America. It's the one that comes nearest to the felspar composition and has four of silica instead of six, and they do use it a lot, I believe. A very useful flux. And there's another one - amblygonite, which is a phosphate, and I should think amblygonite/ would be an awfully useful thing an awfully useful mineral to experiment with for glazes especially anybody who is interested in a sort of parchment matt surface. Pure amblygonite at about 1300 makes a beautiful parchment matt. It's the phosphates, I daresay, that accounts for it.

Oh yes, one more thing with raw materials. How to use and interpret analyses. That's a thing a potter's got to be able to do, it seems to me. Because it's standard practice now for the firms you buy the clay from to give you an analysis. And I must say, speaking for myself, I used to say "It's all very wonderful, isn't it - 65 per cent silica S102, that's jolly interesting", and all that sort of thing, you see. And I feel there's a terrible lot one has to learn there. I mean the science of what's gone to the making of that analysis, for one thing, and what use that analysis is to you when made. The se are things that are well understood, of course, in the industry now, but we craftsmen-potters, some of us do and some of us don't, but I think we should.

Now then, 'Know your prepared materials'. That's Number 2. Know your prepared materials covers an enormous field. It starts with how to grind. What is the grinding process and what are the limitations of the grinding process? Can you grind as finely as ball-clay, or as finely as china clay, or not? How finely should you grind? The dangers and pitfalls of under- grinding. And the dangers and pitfalls of over-grinding. That's important practically to stoneware potters. It used to be alleged that some of the beauty of the old Chinese glazes was due to extremely fine hand-grinding. It always seemed to me that it might almost be equally due to extremely coarse hand-grinding. (LAUGHTER). But it may be true. I do know this - that when I was grinding for myself on a small scale in the Gold Coast, where you have to do your own grinding, you see, owing to inexperience and lack of technical and scientific knowledge we over-ground, and the glazes were awfully troublesome, but they were very, very lovely. And I think there may be something in the theory that the Chinese glazes were very finely ground. But there are awful dangers in over-grinding, as every industrial potter knows. The most familiar one being the 'creeping' of the glaze on the body. It's not the only cause of creeping, as one knows. There are many causes, but that is one. And Number 2 in Prepared Materials. Know how to make up your bodies or to modify your bodies, and what you want in a body, and how to control if you get too much of what you don't want. For instance, in fitting a glaze the thermal expansion of the body. How to cure crazing. How to cure the opposite which is far worse. How to mix the body. What's the real nature of the suspension, and how to control suspensions, and what the chemistry of controlling suspensions is. Not that we'd all necessarily want to do slip-casting. Personally, I don't want to do it at all. I'm sure it's a very important industrial process, and if I had to do anything or one had to collaborate with a big industry you'd have to know about this slip- casting, and how Monsieur Bourry arrived at his famous formula which is a very wonderful thing, I think, that formula. It always strikes me as being a very surprising fact that if you've got a pint of slip that weighs 24 ounces and you've been told, or taken it on trust, that a pint of water weighs 20 ounces - pure distilled water I always would have thought that it proved that there were four ounces of clay in the pint. But it doesn't prove anything of the sort. It has to be done by Mr. Bourry. There are much more than four ounces in that pint. Most odd! You see, that's where we artist-potters. or whatever we are, that's where we're up against an awfully difficult thing because we haven't got a mathematical head, (LAUGHTER) I mean I haven't. And then the chemistry of the bodies. How is it going to behave in the fire? And what are the physics and chemistry of the sintering of your body in the fire and the vitrification of it, and at what stages and in what way is the liquid and the solid phase developed when you're firing the vitrified body? What are the causes of bloating? And another awfully important thing thermal shock resistance. How to get it. How to control it. What methods to take. A very useful thing in pottery. If we could get a really thermal shock-resisting body and glaze it success- fully what a tremendous technical advance that would be. Really thermal shock-resisting bodies tend to be very expensive and difficult.

Lastly, of course, making refractory bodies for saggers. A tremendous amount of technical, scientific knowledge can be drawn on for that. I'm not saying one should acquire all these sciences. One should know where to go for it and try to use it.

Then, Number 3. 'Know your glazes'. It's a personal matter, but it fairly fascinates me, the whole fundamental theory of glass and what it is is, I think, a fascinating subject. And I feel that as a potter I can't be told too much about it. I do wish I understood the fundamental nature of glass, and the fact that there are only about three glass-making elements in the universe - silica, boron, phosphorus and germanium, which doesn't matter to me. (LAUGHTER). Then the classification of glazes and to know just what the glazes have got in them. If you buy frits, what are the frits made of and why are they made? What's the point of having frits at all? We must know bout them and the general chemistry of glazes. The Seger formula and just what it was that Herman Seger did the really (for pottery technology) epoch-making innovation of arranging the potter's glasses in that form, which the glass-makers, you see, don't use - only potters use it. Having the flux group on one side - RO as he calls it - and the alumina and other neutral oxides in the middle, and the silica on the right-hand side of the formula. This useful instrument which saves weeks of time and thousands of disappointments to every kind of potter - craftsman potter and industrial potter - was stretched afterwards to include the Boron glazes and to include the lead glazes and the fritted glazes. And it's still useful. It's rather distorted the original Seger formula - but it still is an awfully useful instrument.

Then, of course, (I've nearly got to the end) the physics of glazes. Thermal expansion, surface tension, causes of glaze troubles, causes of bubbles, causes of opacity, causes of crystallisation of glazes and mattness; measuring of hardness of glaze is very important; measuring of durability and solubility. The glaze body interface a fundamentally important subject - only the scientist can tell us about it. The glaze body interface is absolutely fundamental to pottery technique, and they do know something about it now. It's like a saw, apparently. It isn't what used to be called a "buffer layer". It isn't a sort of intermediate composition in between the two. Very important to the pure aesthetics of glazes. Changes of composition due to under-firing, over-firing, high fire, low fire, volatilisation of some ingredients all that. Science can help us.

And, of course, I've not said anything about the hardest of all. Commandment Number 4. 'Know combustion'. Because I don't know combustion. I can't control it and I don't know anything about it, and the more I learn about it the more convinced I am that I know nothing. The science of fire is really beyond me. But I'd be very grateful if somebody could tell me something about it. I've written some things down which may help to produce some questions. The design of the kiln. The use of excess air, which you've got to have, of course. The use of secondary pre-heated air. I do see something about that. Exothermic effects. Well, we know that's more the raw materials. Oxidation and reduction - familiar concepts which want a lot of careful scientific thinking about, I feel. And a systematic attitude towards firing, d' you agree? Degrees of Centigrade per hour. Speaking for myself, I went on for years without taking much trouble about that. I didn't take enough trouble. And then, of course, things like gas analysis too difficult! (LAUGHTER). Thermal insulation - theory of pyrology. Yes. Any questions? I can't answer them. (LAUGHTER).

Reproduced from the conference report with the permission of the Dartington Hall Trust Archive.

Dartington Conference 1952