PREPARATION OF THE CLAY

Ingredients and properties.

The making of a pot begins in the clay bed. The clay has to be found, it has to be transported, and above all it has to be tested to see whether it is adapted to the potter’s needs. For there are many different kinds of clay and they are as individual as human beings; so that a thorough understanding of them is essential to the successful potter.

The chief ingredients of clay are silica, alumina, and water. Other possible ingredients are iron oxide, lime (calcium oxide), magnesia, and potash. To the iron compounds are due the different colors of the clay. When potters speak of the color of a clay—red, yellow, white—they refer to the color after burning, not in the raw state. The tones of the color are controlled by heat; for instance, a red clay becomes first pink, then in a higher fire a deeper red, and in a still higher fire a brownish red.

The potter demands three properties of his clay: (1) plasticity, the property which enables the clay to acquire form; (2) porosity, the property which enables the water to escape; and (3) vitrification, the property which enables the clay to be fired. These three properties are due to the three chief component parts of the clay; namely, clay base, quartz, and feldspar. It will be found that some clays are not plastic enough, others not sufficiently porous, and others again not properly vitrifiable; in such cases the addition of certain substances is necessary to make the clay usable. The actual composition of the clay, therefore, is of great importance, as no amount of skilful labor will avail if the clay itself has not the right consistency.

Washing.

When the right composition of the clay has been assured, the next step is to wash it and separate it from the many natural impurities, such as stones, sticks, etc., with which it is mixed. A clay not properly washed is a source of great vexation in the later stages of pottery making. The best method is that of “blunging,” that is, the dry clay is put into water and stirred constantly until it reaches the consistency of cream, technically called “slip,” whereupon it is poured through sieves, coarse or fine according to the desired consistency. The liquid clay or slip must then be dried sufficiently to become plastic and workable. This can be done either in filter presses in which the water is squeezed out in a comparatively short time, or in shallow receptacles in the open air where the water is allowed slowly to evaporate.

Wedging.

But even at this stage the clay is not yet ready for use; it has first to go through the important process of kneading or “wedging.” This consists of cutting a ball of clay in two against a wire (fig. 1), slapping the two parts on a plaster or wooden board, one on top of the other (fig. 2), then lifting up the whole lump, cutting it in two again, and slapping it down as before. The purpose is to remove all air bubbles and to correct irregularities in hardness. The operation has sometimes to be repeated fifteen or twenty times before a good texture is secured.[5]

We learn from the above survey that the fine consistency of the clay in Athenian and in some other Greek wares is not necessarily due to its natural state, but to the careful washing and kneading undergone in its preparation for use. When different particles are found in the fired clay they are due to indifferent washing. And the varying shades of pink and red of Greek vases likewise do not presuppose different kinds of clay, but are due largely to the various temperatures to which the vases were fired. We have too often made our analyses of clays of Greek vases without due cognizance of these facts.

FASHIONING THE VASES

(1) WHEELWORK

There are three principal ways of making vases—fashioning them on the wheel, building them, and making them from moulds. Let us examine first the work on the wheel, the potter’s tool par excellence.

Types of wheel.

There are various types of wheel in general use today. The wheel run by electric power does not concern us here since it cannot have been used by the Greeks. In studio potteries, a kick-wheel is often used. In this the operator stands and kicks with his left foot against a treadle, the weight of his body being supported by the right (fig. 3). Another fairly popular type has a large, heavy disk at the bottom revolving in a horizontal plane, and kept in motion by one foot of the operator (fig. 4). A very simple type of wheel in use some time ago is illustrated in fig. 5. Here the motion is imparted by an assistant turning the handle.

Any one of these three types may have been used by the Greeks. In the representations of ancient potters at work (cf. pp. 64 ff.) the wheel appears to have been propelled either with the foot or by an assistant.

Throwing.

The first task in fashioning a vase on the wheel—or “throwing” it, as it is technically called—is to center the ball of clay on the wheel-head. It is accomplished by pressing the left hand against the ball of clay as it revolves rapidly, care being taken to keep the left forearm absolutely rigid (fig. 6). The right hand is used for keeping the clay wet by sprinkling it with water, and for pulling the clay inward, thus squeezing it up to a cone. The cone is pressed up and down in this manner several times (figs. 7 and 8). When the ball runs perfectly true, it is time to open it by inserting the thumb in the center (fig. 9); then by placing the fingers of one hand inside the hollow, and the fingers of the other on the outside,[6] and by raising both hands gradually several times and squeezing the clay lightly while so doing, a cylinder is formed (fig. 10). The cylinder is the foundation of all other shapes. For to produce a bowl, one need only pull out the cylinder a little at the top (fig. 11); to make a globular jar, pull it out at the bottom and in at the top (fig. 12); to fashion a long-necked vase, pull it out at the bottom and in at the top, leaving enough clay to spin the top into a tall, narrow cylinder which will serve as a neck (fig. 13); and by various other manipulations one can produce almost every variety of shape. To throw a vase to specific measurements, a careful drawing of the shape should first be made and calipers and measuring sticks kept close at hand for checking the work as it proceeds.

The earliest Greek vases are made by hand; but from the Early Minoan III and Middle Helladic I periods (i.e., about 2200 B.C.) in certain places at least, vases were regularly thrown on the wheel. They could not have the regular and symmetrical outlines they have if they were built by hand, and many would show traces of vertical joints if they were made in moulds.

That the processes of throwing were identical with those described as in use today, there is of course no means of determining; but they certainly must have been similar, as clay has not changed its nature from Greek times to ours. The evidence which we glean from representations on Greek vases of potters at work, scanty though it is, bears out this self-evident fact. From the above description it will be noted that in this work of throwing the simultaneous use of both hands is necessary—an important fact to remember when interpreting scenes to be related to the fashioning of vases.

Turning.

After a piece has been thrown on the wheel, it has assumed its general shape, but that is all. The thinning of the walls, the refinements of foot and lip, all such finishing touches must be reserved for the next process. This is known among modern potters as “turning.” In this the clay is no longer in a wet state, but in a “leather-hard” condition, and it is not worked with the hands but with steel cutting tools. A newly shaped vase becomes leather hard after it has been kept in the air and the water allowed to evaporate for about twenty-four hours. Pieces in this state are hard enough to be handled with care and to be cut easily with a knife. They are not so fragile as either in the wet or in the “bone-dry” state, but they are still delicate and exposed to many dangers. Not until a vase has been fired is it safe to handle it freely. The cutting with the steel tools is done on the wheel (or “jigger”[7]), the right hand which grasps the tool being kept steady by letting it rest on a stick held in the left hand; the stick should have a sharpened nail on one end, the point of which is pressed into a wooden board at the height required (fig. 14). By continued cutting off of thin shavings of clay and by adding more clay in slip form when more is needed, the final outline of the shape and the various grooves and mouldings for lip and foot can be obtained. But it is a slow process, requiring time, care, and great patience. For the smoothing of the surface, scrapers, sandpaper, and sponge are useful.

This turning or refining of the shape after throwing, was, as we might expect, not in universal use in ancient times. Prior to the sixth century B.C. it was used occasionally here and there, and often only to a limited extent. But there cannot be the slightest doubt that in the Athenian black-figured and red-figured vases extensive use was made of the turning tools. The grooves and mouldings for lip and foot were produced by this turning process, not, as modern archaeologists tell us, by the use of moulds.[8] For this there is abundant proof. The feet of Athenian vases are almost all turned at the bottom, some with remarkable care and finish (fig. 15), not left flat, as they would be after throwing (fig. 16). The lids of pyxides and similar vases could not have been made to fit so neatly on their ledges without the use of turning. Above all, the wonderful finish and precision of Athenian vases could never have been attained by mere throwing. But there is even more convincing proof. Unless the marks of the turning tools are very carefully obliterated (with scrapers, sandpaper, and sponge), traces of them are always visible. And this is the case also in Athenian vases. The outside surfaces are generally carefully smoothed, but even there the ridges formed by the tools are often discernible (fig. 17); and on the inside of the necks or feet or lids such ridges and concentric or spiral scratches are quite frequent (fig. 18). They are very different, however, from the finishing marks left in handwork (fig. 19). To appreciate the fine, smooth surface which work with the turning tools produces, we need only examine the insides of most Athenian amphorai and hydriai; for these, being more or less concealed, are generally left as thrown, often showing the spiral ridges which rapidly revolving clay will cause (fig. 20). They thus form a striking contrast to the finely smoothed outside surfaces.

The fact that the Athenian potter made use of the turning process shows incidentally that he was able to make his vases to very exact measurements. This is important in connection with Jay Hambidge’s theory that Athenian pottery was carefully designed on certain geometrical principles;[9] for if the Athenian potter had confined himself merely to throwing on the wheel that would not have been possible. It is during the second process of turning that an expert potter can effect many changes in width and height or in details, and thus make his product correspond exactly with his carefully planned design. Modern potters of standing work in the same way today. They first make a drawing of a vase, full size or to scale, and then proceed to follow this drawing in every detail, using rules and calipers for their guidance. Of course it needs a great deal of skill and patience to be able to work so exactly; but Greek potters, we can be quite sure, had a good supply of both of these qualities.

Work in sections.

So far we have spoken only of comparatively small vases, which can be thrown all in one piece. Larger vases are best thrown in sections. To throw large jars in one piece requires great physical strength, and it is very difficult to finish such jars properly on the inside and to prevent them from being unduly heavy. The section work is by no means easy. At first a drawing of the vase has to be made, either full size or to scale, and the heights of the different parts marked off. While throwing the respective pieces use must be made of measuring sticks and calipers, to obtain the right heights and diameters. The measurements should be those of the soft clay, which will of course be slightly larger than those of the final shape. About one-eighth is the average allowance for the shrinkage of the clay in drying and firing. This shrinkage will naturally be proportional; so that the relation of every part to the whole will be the same in the fired vase as in the thrown product. The joining is obtained by applying a thick slip of the same clay as was used for the vase, to act as a binder. When all the sections are in place the outside of the vase can be “turned.” If this and the foregoing processes are done skilfully the final joints will hardly be visible, even before the glaze is applied. Figs. 21, 22, 23 show the three chief stages in the making of a vase in sections.

To obtain good results in this work it is important that it should not be hurried. It is best, for instance, before joining the sections, to let them stand on top of one another for a day or longer, in order that they may mature together. To retain the pieces during this time in leather-hard condition, they must be kept in a “wet cellar,” that is, in a moist place where the water in the clay will not evaporate (fig. 24). With this simple precaution pieces can be kept leather hard practically indefinitely.

Section work was used by the Greeks, as it is now. There would, in fact, be nothing gained in throwing the very large vases, such as some of the kraters and amphorai, all in one piece; and though the joints are, as a rule, skilfully concealed, they are plainly visible on certain examples, especially on the inside. Where possible the joints seem to have been made at the natural angles or “articulations” of the vase (that is, at the neck, the foot, etc.); and further to simplify the work, a thin ridge of clay was often added to conceal the joint.[10]

One of the most difficult things to throw successfully is a flat, wide bowl on a foot; and the larger the diameter of the bowl the more difficult the task, since the overhanging rim almost always sags at the critical moment. The fifth-century kylix has therefore always been rightly admired as one of the greatest feats of the Athenian potter. How did he prevent the bowl from sagging? Did he throw it upside down and hollow it out later with the turning tools? Or did he make the base very thick and then “turn” it down to fit on a slender foot? Both methods would be clumsy, as they would entail lengthy turning work. Or was the Athenian potter so skilful that he somehow prevented the clay from sagging? Not at all. He simply threw his kylix in two sections; the foot with a bowl about half the required diameter in one piece (or possibly two, with the foot separate), and the remaining part of the bowl as a separate section. The joints where the two parts of the bowl were united are clearly visible on many kylikes on the outside (fig. 25)[11]; the inside of the kylix, being the most conspicuous part, is always so carefully turned that no joining can be detected.

Polishing.

To impart a polish, the blade of a knife is applied to the surface while the vase is revolving; for an inward curve a curved tool must be used. The operation is simple and can be accomplished in a few minutes. It is not often employed, however, by the modern potter, whose object is to keep the pores of his vase open for the better adhesion of the glaze with which he intends to cover the surface of his pot.

The Athenian potter, on the other hand, put great stress on giving the surface of his vase a fine polish; probably using the simple method described above. The difference between a polished and an unpolished surface is clearly seen on some vases on which the potter has omitted to repolish the parts round the handles where the slip used for the attachment had spilled over (fig. 26).

Attachment of handles.

The final process in the fashioning of a vase is the attachment of the handles. These can be made either in moulds or by hand. Any one who thinks that the making of handles is a simple or quick process will soon be undeceived. Whether working in plaster, as one would if the handle is made in a mould, or in clay, if it is made by hand, the potter must bestow infinite care on the work, as both clay and plaster are very liable to break; and working on so small a thing as a handle is extremely fussy. The writer personally found nothing so difficult in her whole pottery training as the making of handles. The best method of procedure in handwork is first to shape the handle roughly while the clay is soft and plastic, then wait until it becomes leather hard, and finally refine it to the desired form and finish with modeling tools. In moulded work, the handle has to be cut out in plaster and then used for making the mould. When the handles are finally made, they are joined to the vase by means of slip, in the same way that the sections were (fig. 27). As the handle is pressed into position the superfluous slip will of course spill over the edge, and this has to be carefully removed and the surface smoothed before the vase can be pronounced finished. The vase is then put in the drying room so that all the water in the clay may evaporate. Only when it is perfectly dry can it be fired in the kiln; otherwise it is liable to crack.

The handles of Athenian vases show perhaps better than anything else the great skill and sense of beauty of the Athenian potter; and they will repay detailed study (cf. figs. 28-33). They are never, as so often on modern vases, detached pieces stuck on the vase as a kind of afterthought. Rather, they seem to grow out of the vase like branches from a tree, which gives them a wonderful, living quality. Moreover, the place where they were attached, the size, and the curve have been carefully considered both from a practical and from an aesthetic point of view.

Athenian handles are made by hand, not in moulds. Practically every pair of handles shows perceptible variations such as are unavoidable in handwork and distinguish it from the mechanical products of moulding. The handles were attached to the vase in leather-hard condition, and often the pressure entailed thereby resulted in a slight bulge on the inner side. This is particularly noticeable on kylikes where the walls of the pot were especially thin.

It may be noted that the handles of Athenian vases are not finished off neatly in parts where they were not seen. For instance, the under parts of handles on column kraters are generally left quite rough (fig. 34). This fact, together with that already observed, that the insides of amphorai and hydriai are usually unturned, shows that the Greeks, at least, had no such theories as those often held today that a work should be finished perfectly all over, even in places not ordinarily seen, and were quite willing to save trouble when possible. Many potters today bestow as much care on the inside of a narrow flask as on that of an open bowl. It is characteristic of the sense of proportion of the Greeks that their potters took infinite trouble with what was important—the shapes, the proportions, the decoration—but that they did not spend time and labor where it profited nobody.

(2) BUILDING

Compared to the wheelwork the building appears simple at first, but experience will soon show that it too needs considerable practice. Though the actual process has not the glamor and thrill associated with wheelwork, there is a certain quality in a built vase which gives it a value of its own. Building is generally done nowadays by means of coils of clay (fig. 35), which must be a little thicker than the walls of the vase are to be and should be as uniform as possible. To make the foot of the vase, the end of one of these coils is laid in the center of a plaster bat and the rest coiled round in spiral line. To hide the joints the surface is rubbed over with the fingers on both sides. In making the walls of the vase a coil is used for each round and the superfluous clay pinched off, every new coil being begun at a new point. The whole surface, inside and outside, is again smoothed by rubbing with the fingers, using very little water in the process. Only about three coils should be worked in at a time and then left to harden before new coils are added. In building up a certain shape it is best to use a templet of cardboard or plaster, to be sure that the profile of the vase is followed out correctly. To give the required finish at the end, modeling tools as well as further rubbing with the fingers are required.

With this process in mind it is easy to distinguish between built and wheel-made pottery among the Greek wares. In the built pottery, however careful the work, there is always a certain unevenness of outline—which indeed gives it some of its charm. Unlike the moderns, the Greeks did not continue to build pottery after the invention of the wheel. Naturally the general adoption of the wheel was not synchronous in all ceramic centers. It was used considerably earlier in Crete, for instance, than in Cyprus. But when once its convenience was thoroughly realized, the slower and more monotonous method was entirely dropped. Among Athenian black-figured and red-figured vases there are no built pieces.

(3) MOULDING

The process of moulding vases is the one most in use nowadays, for the simple reason that when once the required mould has been made the production of any number of vases is a rapid and easy task. But though commercially favored, this method is looked down upon by the artistic potter as being purely mechanical, and there is no doubt that a moulded vase has all the characteristics of machine work.

The material used for moulds nowadays is plaster. The clay can either be poured into a mould in slip form or pressed into a mould while soft and plastic. In the former process the mould or moulds are made in two or more pieces, which fit closely together leaving an opening at the top. By pouring the clay slip into the opening, leaving it to harden a little, and then pouring out again what has not hardened, a hollow vase is formed. After due shrinkage the mould is carefully removed from the vase (fig. 36). The same mould can be used indefinitely for making vases of the same shape; it has only to be dried between one use and the next. Handles can be produced in the same way and then attached.

In pressing clay into moulds each part of the mould is used separately, except where only one mould is required, as in the case of an open bowl or tile. When the clay has been carefully pressed into every part of the mould, it is left to harden, and then, upon shrinkage, can be easily separated. If the vase has been pressed in several pieces, the parts must be carefully joined and the seams effaced as neatly as possible.

The Greek potter did not use moulding as a labor-saving device. He employed it only where the work demanded it, as in the Athenian plastic ware. Here we sometimes even find the same mould used several times, as in the group of a negro and a crocodile of which chance has preserved us at least five replicas[12]; but the number of such repetitions is not great and certainly would not indicate mass production.

The material of Greek moulds was burnt clay. That the Athenian plastic vases were pressed into moulds rather than poured can be seen from the fact that the insides of these vases are rough and show finger-marks (cf. fig. 37). The joints of the two parts are clearly visible on many examples (cf. fig. 38). Often the lip was thrown separately on the wheel and attached.

FIRING THE VASES

Production of Temperature.

In the fire the great miracle takes place and the dry clay, most friable and perishable of materials, becomes one of the most durable. This is accomplished by the softening of the feldspar grains which cement the whole together and thus form a dense mass. To produce the temperature at which this phenomenon takes place two things are necessary, fuel and draught, the former supplying the carbon, the latter the oxygen. The liberation of the carbon in the fuel and its union with the oxygen of the air develop combustion, during which heat is generated. Combustion can be complete or incomplete. It is complete when there is an excess of air and the carbon can combine with two molecules of oxygen to form carbon dioxide (CO₂). This condition is called oxidation. It is incomplete when there is not enough air and the carbon can get only one molecule of oxygen, forming carbon monoxide (CO). This condition is called reduction. Carbon monoxide, being very hungry for oxygen, will try to extract it from whatever source it can. If ferric oxide (Fe₂O₃) is present in the clay—which is the case in red clay—the carbon monoxide will take one molecule of oxygen from it and convert it into ferrous oxide (CO + Fe₂O₃ = CO₂ + 2FeO). The important feature in this process is that ferric oxide is red and will make the clay burn red; but ferrous oxide (FeO) is black and will give the clay a blackish color. If no ferric oxide is present in the clay, that is, if the clay is not a red clay, then reduction has no effect on the color of the clay and can be freely used. In Europe potters regularly burn under reducing conditions, while in America the general practice is to burn under oxidizing conditions. When the draught in the kiln is faulty, partial reduction will often occur, and many faults in the burning, especially in the glazes, are attributable to this cause.

We shall see presently how important is a knowledge of these chemical changes during the process of firing when we come to consider the defects on Greek vases caused by injuries in the firing (cf. pp. 44 ff.).

Types of kilns.

There are two chief types of kiln construction in use today: (1) the open kiln, in which the flame passes through the kiln chamber (fig. 39); (2) the muffle kiln, in which the flame passes around the chamber and not through it (fig. 40). In the open kiln the ware either comes in direct contact with the flame, or is stacked in saggers, i.e., boxes made of fire clay fitting one on top of the other (fig. 41). The muffle kiln is, so to speak, one large sagger, and the ware is stacked on shelves. The draught in the kiln can be either an up draught or a down draught; in either case the air supply, as well as the fuel supply, must be under control, so that the combustion shall be as desired. The draught can be regulated by means of dampers, the fuel by attention to the burners. An arched top is an advantage, for it imparts greater strength—an important item considering the strain to which the kiln is subjected—and it facilitates the circulation of the heat. Coal, wood, gas, or kerosene oil can be used for fuel. Of these, oil and gas are now the most popular; coal and wood are rapidly coming into disuse on account of the greater labor they entail.

Packing the kiln.

In packing the kiln the ware is stacked as closely as possible for economical reasons, so that as much as possible shall be accomplished in one firing. In biscuit firing the ware can be placed so that it touches (fig. 40); in glaze firing the pieces must be separated (fig. 42) both from one another and from the bottom of the saggers or shelves on which they stand, since the melted glaze is apt to run. Glazed pieces are therefore generally placed on stilts made of burnt clay, and the marks of these stilts will often show on the bottoms of the vases.

That the chief features of modern and Athenian kilns were similar is clear from an examination of the ancient representations of kilns (cf. figs. 72-81 and pp. 76 ff.). How closely the ware was sometimes stacked is clearly seen in fig. 80. The fuel used by the Greeks was probably wood and charcoal.

Almost all modern pottery is twice fired; once for the conversion of the clay into terracotta or biscuit, and the second time for the glaze. To glaze unbiscuited ware is a delicate business, and the risk of glazing a piece of raw clay is considered larger than the trouble of burning it a second time. It is done occasionally when very tough clay is used, for instance, in kitchen crooks and in stoneware; in that case it is best to apply the glaze when the clay is in leather-hard condition, for then the absorption is less. More than the two regular firings are often used for correcting mistakes in glazing, for additional coats of glaze, and for decorating the ware.

Firing.

Different wares and different glazes require different temperatures. Thus porcelain and stoneware are fired to much higher temperatures than ordinary pottery, and salt and alkaline glazes need a higher fire to mature than the ordinary lead glazes. When the required temperature has been reached—which nowadays is determined either by means of a pyrometer or with the help of pyrometric cones which melt at a given temperature and which are watched through a spy-hole (cf. fig. 40 where the cones are set up opposite the spy-hole in the door, and fig. 42 where the cones have melted)—the fire is gradually extinguished and the kiln left to cool slowly. Twelve hours for the firing and twelve for cooling is a rough estimate for the firing of an ordinary kiln. It is important not to hurry the process of cooling, as a too rapidly cooling fire may crack the ware or affect the glaze injuriously.

The Greeks fired their pottery at a considerably lower temperature than potters do today. It seems to have been about 960° centigrade (corresponding to about cone 010) since any increase over this temperature causes a change in the color of the clay together with an additional contraction. Mr. Tonks has made the ingenious suggestion that, 950° and 1065° being the melting points of silver and gold respectively, the Greeks may have used these metals in the same way as the modern potters use cones, to regulate the heat of the kiln.[13]

When the kiln is finally opened comes the exciting moment of seeing what the fire has done with one’s products. In taking out the contents of the kiln, gloves and sticks are often useful for handling ware that is still too hot to touch. Invariably there will be surprises—what one has expected to be a great success often turns out a failure, and what one thought little of may become a rare thing of beauty. In the biscuit firing the adventures of the pot are comparatively few; it may crack or sag or warp, but as a rule the expected shape is maintained. But in the glaze firing so many elements enter in that even an experienced potter can never be sure of the result. The color may turn out a different shade from that desired; the glaze may unexpectedly be matt (dull) or too glossy; it may blister or peel or crack; it may be too thin or too thick. Such defects are almost invariably due to faulty composition of the clay or the glaze or to the conditions of firing. They can often be remedied by further glazings and firings; but quite often a pot on which much time and labor have been bestowed is hopelessly ruined. A good potter, however, will soon learn to bear such mishaps philosophically; and it is certainly true that one often learns much more from failures than from successes. Moreover, the element of uncertainty lends spice to the craft.

A careful consideration of the modern processes of firing pottery described above will help us to settle the problems connected with the firing of Greek vases—for the action of fire on clay remains the same even though the kilns in use by the Greeks were probably somewhat more primitive than now.

The chief problems which confront us in Athenian pottery are (1) the number of firings, (2) the interpretation of defects on Greek vases as injuries in the firing.