ENAMEL OR MUFFLE KILN.Fig. 68
Enamel kilns are used for the final processes where the glazed pot is painted with over-glaze or enamel colours. They are of no great size and are made of fire-clay slabs or even iron plates when the enamel is soft. The flames play all round the muffle or fire-clay box during the firing, but no flame or fume is allowed access to the inside. (Fig. 68.)
In packing a kiln with biscuit or glaze much care, thought, and expedition have to be exercised. An experienced setter is essential in a factory if the pots are to have every chance in the fire, for all kilns vary and have their hot andcoolcorners. First, the floor is well bedded with quartz sand or flint that will not vitrify but will provide a good setting for the bottom saggars. These saggars are fire-clayboxes, round or oval, rarely square, and without lids, in which the pots are placed. Piled one above another they form thebungs, the bottom of one supplying the top of that beneath. These bungs are built at intervals that permit the flames to penetrate between them and give a good even fire all over the chamber.
In actual practice some parts of a kiln are hotter than others, and it is here that a good setter shows his capabilities, setting the thin wares in the softest places and putting the heavier biscuit or hard glaze in the hottest corners. With biscuit the setting is not difficult except where delicate or friable ware may need very careful bedding and propping. With clean saggars the biscuit may touch the sides, and a competent man will pile an enormous amount of biscuit into a kiln without risk. In the glost kiln the ware requires gentle handling and must touch nothing but the spur or support. The saggars are usually given a saggar wash of lead and stone to prevent them absorbing glaze from the wares, fora glazed pot placed too near a raw saggar is very likely to come out with a thin or dry patch.
When the pot is firmly placed on its stilt, a roll ofpuggingis placed round the rim of the saggar; this provides a firm bed for the next above it and also stops the entry of dust and flame. This pugging is made from clay or marl mixed with ground sherds, sieved gravel, or some non-vitreous dust to prevent it sticking to the saggars. The plugging is made malleable with a little water and rolled out by hand or pressed through a die. It will readily be seen that a carelessly built bung of any height may slip in the stress of firing, and its fall would most likely involve others, whilst any slight movement may be sufficient to cause a vase to topple off its stilt. In a down-draught kiln the bungs over any vent must be raised on fire tiles to permit the escape of the flames. When all the bungs are filled up and piled in position, the trials and cones placed, the hatch is bricked up. Spy holes are left where necessary, and the whole well clammed to prevent the loss of heat during firing. When fired, the hatch may be very gradually loosened to accelerate the cooling.
DOWN-DRAUGHT KILN.Fig. 69
The fireman’s job is one of the most arduous and important of all the prolonged processes of potting. Coming as it does at the end, it may make or mar kilns of great value, and it requires more than ordinary judgement and nerve. The chief troubles arisefrom bad or irregular draught or impure fuel. They express themselves in the form of clinkered holes, excessive smoke, and irregularly fired or sulphured ware. The termsulphuredis applied to pots that come out gloomy or dulled and is said to be equally due to a reducing fire or an oxidizing one. In the former an insufficiency of air causes excess of carbon in the kiln and the absorption of oxygen from the glaze. In the latter an excess of air (oxygen) allows sulphur vapour, if present, to attach itself to the glaze.
The fire bars, fire holes, and flues must be kept clear and the fuel carefully selected if these things are to be avoided. The aim, as previously stated, is a gradually increasing fire, sharper towards the finish. For this purpose some potters finish off with wood which gives a long flame free from sulphur and clears the glaze. Even when sulphured, a clear flame at the finish will remove many ill effects. The baiting should be fairly heavy at the start, lighter and more frequent towards the finish, when smoke in any quantity should be avoided.
For temperature gauges, the cones previously described are used and should be placed in an average place, screened as much as possible from draught or flame. Small sight pots and glaze rings placed near the spies can be hooked out and examined and are valuable aids, but their exposed position and the corrosive action of the flames must be taken intoaccount. Pyrometers are also used, but with all these aids the experienced fireman pays due regard to sight and colour.
For a craftsman, the kilns that have been described are unsuitable on account of their size, if they are not altogether beyond his means. But a kiln of some sort is indispensable to a potter. The craftsman is nothing if not inventive. Small trials can be fired in crucibles in an open fire or on a gas ring. I have heard of some preliminary success with a gas cooker, discounted later by a frontal attack from the cook. Considerable knowledge can be gained from small, easily constructed, experimental kilns.
The small trial kiln shown (Fig. 70) was constructed with a stout oldcrock, over which was built a core of bricks plastered with marl. The fire was started at each corner at the bottom, and when well alight, fed from the top with coke. A small spy at one corner closed with a piece of biscuit gave some idea of the progress of the firing. This, of course, had to be practically rebuilt at each firing, but as a makeshift was quite satisfactory.
CROCK WITH IMPROVISED SPY HOLE. CONE INSIDE.Fig. 70
CROCK BRICKED OVER & PLASTERED WITH MARL.Fig. 70a
The gas and oil kilns described in Chapter IX are excellent as far as they go, and indeed the only practicable kind for indoor schools. But their restricted size soon becomes irksome to a craftsman, whilst the expense of firing makes only the finest work remunerative. For over-glaze work they are excellent, but for some reason glazes fired in them seem to lack some of the richness and maturity the same glazes exhibit when fired in the slower and more soaking fire of a brick kiln. The dug-out kiln here depicted (Fig. 71) would be quite suitable for summer schools or for a craftsman making soft peasant pottery. The section and sketch will indicate its construction. The materials are hard bricks and stout old boiler plates, or sheet iron. To pack or unpack, the middle section of the roof would have to be removed each time, and all glazed pots would need protection from scalings and gravel from above. The roof will sag at any big heat, and if of thin iron, will need propping. The firing would be done with soft coal or wood; a very slow start, with a brisk draught and a long flame at the finish.
“DUG-OUT” KILN OF COMMON RED BRICK.Fig. 71
Of course the front will be hotter than the back, but if saggars can be obtained, the glaze may be placed in them to the front with the biscuit protected behind. Clay shapes fired up at the front may bend towards the fire, and any broken crocks should be used to screen them.
The making of rough saggars is not difficult if a supply of fire clay is to hand, or clay and grog will serve at a pinch. The clay is rolled out and the saggar stuck up, much as described on page32.Every joint must be carefully welded and the whole thoroughly dried. Then they are fired up in the kiln,verygently at first, and carried up to a temperature considerably above that which they will be subjected to when in use.
For small trial crucibles ordinary clay mixed with pitchers and powdered coke proves satisfactory; the coke when fired out renders the body porous and the heat penetrates more swiftly.
SECTION OF DUGOUT KILN.Fig. 71a
To construct the muffle kiln shown at Fig. 72 the aid of a competent bricklayer would probably be required. In this kiln glaze and biscuit would fire up without saggars, but will take rather longer. The plan and elevation of this particular kiln are given with all reserve. The design would probablyrequire considerable adjustment and modification before complete satisfaction was obtained.
SECTIONS OF MUFFLE KILN TO SHEW SUPPORTS. FLUES. ETC.Fig. 72
A down-draught kiln, although more difficult to construct than an up-draught, is more economical in the end and does its work more evenly. For the benefit of those that may like to build a small and moderately cheap kiln drawings are here given. This kiln was built by me when I had very little practical experience of kilns other than gas, but it served its purpose well. It was not banded, but this is essential if the kiln is to stand hard and frequent fire. Firebricks were used for the fireholes, flues, floor, core, and dome; strong stock bricks for the rest. The glazed ware, which was fired harder than the biscuit, was saggared in bungs as usual up to about five feet; the biscuit piled on top and protected by old saggars and cracked pots from the roughestfire. There were no bags in this kiln, but the saggars used were very strong and had stood a much greater heat than that to which they were subjected in this kiln, so that they showed very little wear or tear after twenty firings. The stack of sixteen feet gave a good sharp draught, increased if necessary by the addition of an iron chimney and regulated by an iron damper. A wind screen orhovelis advisable for rough nights, and some sort of roof is necessary to protect the crown from the weather. It is important to have the arch of the hatch very strongly built, as it has to stand a lot of strain, and an iron supporttoo near the fire soon corrodes and needs replacing. Another essential is that the site be as dry as possible and the foundation made solid with concrete; otherwise even a small kiln is liable to settle and crack. With a little extra expense a kiln of this kind could be banded round the impost and fireholes, thus considerably prolonging its life.
PLAN SHEWING ARRANGEMENT OF FIRE TILES FORMING MUFFLE.Fig. 72a
MUFFLE KILN BUILT OF FIRE TILES, FIRE BRICKS, AND COMMON REDS.Fig. 72b
POKER. SLICE. TONGS.Fig. 73
In firing this kiln about half a ton of coke and three quarters of a ton of good hard coal, giving a long flame, was used. Coke for the slow fire was first started on the bottom and maintained for sixteen or eighteen hours, lifted up on to the bars for another six or eight hours, when the saggars would begin to show signs of colour. The coal fire was then started about the 24th or 25th hour and continued another 18 hours, more or less, according to the varying conditions, making in all some 40 or 45 hours. This gave a very evenly graduated heat from cone 1 at the base to cone .03 at the top. Bags were tried experimentally, but whilst giving a more uniform heat, took much longer to fire up. At the finish of the firing the fireholes were bricked up, the damper closed when the fires died down. In about 24 hours the vent and the hatch were eased a little atthe top, and in 48 hours it was pulled down and the drawing commenced. Packed with the hard glazes at the bottom and the soft at the top this kiln answered excellently for the purposes for which it was required.
SAGGAR WITH A POT INSIDE.Fig. 74
The Educational Value of Pottery
“The principal point in Education is that one’s knowledge of the World begins at the right End.”—Schopenhauer.
—Schopenhauer.
The study of the fictile art of the potter, even from the theoretical side alone, cannot fail to quicken and broaden education. The antiquity of the craft, stimulating research amongst the records of ancient civilizations, brings to light customs and habits bearing very closely upon the earliest struggles of man to emancipate himself from mere brute surroundings. The primitive decorations rudely scratched on clay vessels antedate and forecast the hieroglyphic and sign languages of all nations.
It would be but hyperbole to claim that without clay the Mosaic tablets would have remained unwritten, but indubitably the clay cylinders of Assyria gave a strong impulse to the development of ciphering and writing and the spread of learning,—an impetus not to be derived from the obstinate granite medium so generally employed by the Egyptians.
It is this amenable ductile quality, so easilyreceptive of the most emotional touch, that has made and still makes clay such an admirable medium of expression for the young,—whether young in the history of the world or young in actual years. And this malleability is accompanied by a tenacity that permits slow building up, remodelling, and high finish, suitable to work of the most painstaking character. To this is added the fixed, unalterable quality imparted by fire, so that pottery more than any other craft preserves an imperishable record of the ages.
This positive chronicle is valuable alike to the savant or the student. Indeed the most trivial child’s toys of the Hellenes, the quaint water pots of the Peruvian peasant, or the unassuming tea bowl of the esoteric followers of Riku may chance to convey to the sincere student a clearer idea of the habits and thoughts of their producers than many a pedantic treatise or translation.
So lively shinesIn them Divine resemblance and such graceThe hand that made them on their shape hath poured.
So lively shinesIn them Divine resemblance and such graceThe hand that made them on their shape hath poured.
—Milton.
Coming down to points in close contact with the curricula of schools, we all subscribe to the dictum of Ruskin that “Everyone, from the King’s son downwards, should learn to do something finely and thoroughly with his hands.” What then moresuitable than sympathetic clay wherein to fashion the first fancies of the child mind. It is a medium at once attractive and easy to mould, giving a tangibility and reality to forms and things that can never be obtained by drawing or painting. Then the limitless uses to which clay is put, and, with the development of hygiene, increasingly will be put, have the closest bearing upon the everyday life of the child. They are intimately connected with other studies that cannot fail to be rendered more attractive by working in clay.
But clay work is a branch now so universal that it seems unnecessary to dwell upon its advantages to the kindergartener.
The valuable remedial effects of clay work upon the defective are perhaps less widely known. The manipulation induces a most beneficial concentration and provides a fine discipline without a trace of inimical restraint. Turning to higher grades, the use of clays should foster an interest in the formation, composition, and disintegration of rocks, and in the properties of the products so engendered; in short, a liking for geology.
With the making of simple glazes and colours will awaken an intelligent curiosity concerning the nature of minerals and metals, their actions and reactions in the fire; a lively sympathy only awaiting a touch to turn it into a love for chemistry andphysics. Then as power and ambition and craftsmanship develop, there must needs be a study of the history of ornament. This impinges too closely upon history and geography to fail to increase the student’s attraction towards these more remote but allied fields.
Finally, is it not in the realm of æsthetics that there looms the ultimate reward? The proper pursuit of pottery must eventually lead us “towards that idealization of daily life ... and the road that connects the love of the beautiful with the love of the good is short and smooth” (President Eliot). In the hurried curricula of to-day art plays a rather sorry part. Little time indeed is left for contemplation, for the realization of all that beauty and harmony in our surroundings may mean to us in our everyday work.
The making of a bowl, with the concentration required to shape it in a manner at once beautiful and serviceable, must quicken the perception of beauty and sharpen the quality of judgement, not only for things fictile, but in far wider fields. Thus the things of everyday contact—the tableware, the chairs, the doors, the windows, pictures, ornaments, hangings, and fittings—will all come in for intelligent scrutiny and criticism. This in turn will be carried on and over into matters civic. This must result in a careful estimation, selection, and appreciationof our surroundings, bringing them into harmony with our cultivated thoughts and so enabling us to get through the day’s work with the least amount of useless friction and with the greatest possible measure of enjoyment, well-being, and well-doing.
PLAN OF A SMALL POTTERY.
The Equipment
The divinity that presides over potting is an expensive as well as an exacting mistress. The equipment of even a small pottery is, unfortunately, a matter of considerable expense. Try it from whatever angle we may there is the cost of the kiln to be faced, besides a host of other small but cumulative expenses. The first essential is, of course, a roomy workshop with if possible a top as well as a side light. If the craftsman means business, he should remember that the initial cost of a kiln is often in inverse ratio to its upkeep. If he would aspire to big things, full-bellied pots, plaques, reliefs, and figures,—and every craftsman would,—a brick kiln will be wanted. One holding a dozen saggars could be built, but where some experience has been obtained with materials and processes, a larger one would be more economical. With oil or gas kilns of the ordinary school size the cost of firing and the extra time is proportionately too great to permit of any but comparatively high-priced pots being turned out. This may serve in some cases, but usually it is not practical potting where a livelihood has to be obtained. Where only the painting is to be fired on, an oil or gas kiln is exactly what is wanted.
In this appendix is given a plan of a workshop that has all the equipment necessary for the whole-hearted pursuit of the craft. In such an one a good craftsman, capable ofmodelling and painting decently a figure or a panel, a good thrower, and a handy boy could work wonders. They would be capable of turning out a surprisingly wide range of “pots”: jugs, mugs, pots, bottles, bowls, buttons, dishes, plaques, panels, vases, tiles, and statuettes,—useful and beautiful things. Anything in fact worth doing can be done except fine tableware or those articles that by their nature demand more mechanical accuracy than is possible, or even desirable, for a craftsman to exhibit. Where much plaster turning for moulds was attempted, a lathe would be required; ordinarily the hiring of one should be practicable and expedient. Where only built or cast shapes were attempted, the wheel and its long years of drill might be dispensed with, and it is possible, with strong individual work of high finish and fine quality and the consequently restricted output, that an oil or gas kiln would give economically practicable results. Between the kiln for firing decoration simply painted on the ready-made shape to the full equipment here described will be found several modifications, but to try the craft without a kiln of some sort is an imbecile proceeding.
Most of this equipment has been previously described and needs no further comment.
The pot boards and brackets are simple but indispensable devices. The boards are about six feet long, iron shod or cross battened to prevent warping, and six or nine inches in width. The brackets of any serviceable kind are fixed to the wall at convenient distances. When throwing, turning, or glazing, the pots are stood on one of these boards to dry, and each board as filled is slipped onto the brackets. Thus the pots may be carried about to the kiln, drying cupboard, or glaze tubs without loss of time or frequent handling.
The table must be stout enough to withstand the heavy work of wedging and should have a top of hard wood. Teak or hard-wood glaze tubs have the advantage of not breaking either themselves or pots accidentally knocked against them. Further, some glazes stick badly to porcelain or enamel tubs.
EQUIPMENT FOR A SMALL POTTERY
In the small pottery plotted here, the equipment and arrangement were as follows:
EQUIPMENT FOR SCHOOLS
The teacher with ample funds and a free hand will find the previous chapter all-sufficient, but in many cases the purchase of a kiln will nearly exhaust the allowance and the rest of the equipment becomes sketchy.
The indispensable appliances are as follows:
For a school in the country or where ground is available, a kiln like the one shown at p.164should be practicable. It costs very little to build or to fire. Next comes the question of the clay. This is one of the most abundant of nature’s materials, and almost any river bank or creek will supply clay of some kind. Any sort of clay near to hand should be thoroughly tested before going to other or distant sources.
The clay should be dried, then broken up with a hammer, and mixed with water, and the resultant “slurry” passed through a sieve (No. 80). The slip is allowed to settle and the water siphoned off. The thick slip is then dried on the plaster bats until stiff enough to work up between the hands. From this clay a tile, a plate, and a vase should be made and fired. If the pieces stand a fire of about 1100° (cone .03) without buckling, splitting, or crumbling, the clay should do quite well for school work. Possibly when screened fine enough for working, the clay may be too rich orlongand will split at a moderate fire. Then the screenings might be pounded in the mortar, passed through the sieve, and added to the slip. Again, ground pitchers, fine grog, kaolin, or calcined flint could be tried as stiffening agents. In the unlikely event of the clay being too refractory orshort, a portion of rich, fusible, orfatclay might be added, or the addition of powdered spar tested. (See chapter on Clays.) The colour of the body will hardly matter for schools; indeeda brown, red, or cane-coloured clay will give better results than a staring white paste, when working out simple school problems.
Where necessary, tin glaze could be used for a white ground, or an engobe; that is, a dip of white clay slip over the coloured body. For glazing, a leadless glaze is strongly to be advised. Lead is often indispensable to the craftsman, and with care need not become a danger; but in schools a lead glaze is positively harmful.
A glaze with a borax base, if ground dry and mixed with water and re-ground before sieving, will give little trouble if used immediately. It will answer for all grade work and may be used for spraying, dipping, pouring, or painting, with absolute safety.
The ground pitchers and grog may be obtained by pounding up broken biscuit and pieces of fire tile, respectively. This, and the glaze grinding, is, of course, laborious work, and suggests correlation with the Physical Education Department. The drip pan and the round tins make excellent moulds for casting drying bats and working bats.
For casting purposes plates and shallow bowls may be moulded in one piece as described, p.26. If no lathe be handy, glazed vases may be used as substitutes, the “waste” being added in plasticine to the neck and base.
For tile-making, strips nailed on a stout board will serve in place of tile boxes. The clay is rolled out on cheesecloth with a rolling pin. Various other expedients for drying cupboards, damp-box, etc., will suggest themselves as the course develops.
The above equipment need not be very costly. With it the students should be capable of producing all kinds of tiles, built, pressed, and cast shapes, decorated in relief, with inlays or in colours or glaze.
SIMPLE RAW GLAZES. COLOURLESS
No.MaterialsPartsSieve No.ConeMethod of UsingI GlossyLead oxide, red50100. Mesh.03Applied evenly with a brush to thegreenshapes. Fired very slowly. Earthenware body.China stone30Flint10II GlossyBorax7080. Mesh2Green shapes dipped thick and slowly fired. Stoneware body.China clay10Felspar75Flint20Whiting25III GlossyBorax360100. Mesh.03Ground dry for1⁄2hour. Wet for 11⁄2. Used when fresh on biscuit (earthenware body) for under-glaze painting.Silver sand160China clay120Whiting20Flint10IV GlossyLead carbonate13080. Mesh.04Used with metallic oxides for simple colours on earthenware body; both green and biscuit.Calcined kaolin150Flint50Felspar50Whiting10Zinc oxide10V MattLead carbonate375120. Mesh.04Used thick on hard white earthenware (CC) body.Kaolin210Felspar175Flint120Whiting105Zinc25VI MattLead carbonate120100. Mesh.02Used thick on stoneware body. Coloured with 3 to 7 per cent of glaze stains or U. G. colours. The proportion of lead and whiting may be varied as found expedient.China clay50Felspar80Flint15Whiting45VII EnamelBorax7080. Mesh.07-.05Used with various combinations of cobalt oxide, copper oxide, and iron oxide and copper carbonate, giving wide range of blues and greens. On stoneware body.Lead carbonate300China clay50Felspar120Lynn sand50Tin40
All the above colourless glaze masses may be coloured with combinations of the various metallic oxides, or from 3 to 7 or even 10 per cent of glaze stains or under-glaze colours.