Pottery And Porcelain
clay glaze enamel coloured enamels potter fine silica colour white
POTTERY AND PORCELAIN - the word " pottery " (Fr. poterie) in its widest sense includes all objects made of clay, moulded into form while in a moist plastic state, and then hardened by fire. Clay, the most widely spread and abundant of all mineral substances, consists essentially of a hydrated sili-cate of alumina, (see vol. x. p. 237), admixed, however, in almost all cases with various impurities. Thus it usually contains a considerable proportion of free silica, lime, and oxides of iron, its colour chiefly depending on the last in-gredient. The white kaolin clays (see KAOLIN) used in the manufacture of porcelain are the purest ; they consist of silicate of alumina, with 5 to 7 per cent. of potash, and only traces of lime, iron, and magnesia.
The making of pottery depends on the chemical change that takes place when clay is heated in the fire ; the hydrated silicate of alumina becomes anhydrous, and, though the baked vessel can absorb mechanically a large qua.ntity of water, the chemical state, and with it the hard-ness of the vessel, remains unaltered. A well-baked piece of clay is the most durable of all manufactured subgtances. In preparing clay for the potter it is above all things necessary that it should be worked and beaten, with sufli cient water to make it plastic, into a perfectly homogeneous mass. Any inequalities cause an irregular expansion during the firing, and the pot cracks or flies to pieces. In early times the clay was prepared by being kneaded by the hands or trampled by the feet (see Isa. xli. 25) ; modern manu-facturers prepare it on a larger scale by grinding it between mill-stones, and mixing it in a fluid state with an addi-tional quantity of silica, lime, and other substances.
During the process of firing all clays shrink in volume, partly through the loss of water and partly on account of in-crease of density. What are called "fat" clays - those, that is to say, which are very plastic and unctuous - shrink very much, losing from one-third to one-fourth of their bulk ; they arc also very liable to crack or twist during the firing. "Lean " clays - those that have a large percentage of free silica - shrink but little, and keep their form unaltered under the beat of the kiln ; they are not, however, so easy to mould into the required shape, and thus a certain com-promise is frequently required. Lean and fat clays are mixed together, or silica (sand or ground and calcined flints) is added to a, fat clay in sufficient quantity to enable it to stand the firing. The same result may be attained by the addition of broken pots, crushed or ground, an ex-pedient practised during the earliest stages of the develop-ment of the art of pottery.
Classijication. - Many attempts have been made to classify pottery and porcelain according to their mode of manufacture. The classification of M. Brongmiart (Traite cies Arts Ceramiques, Paris, 1854) has been followed by most later writers. With some modifications it is as follows : - This classification is necessarily imperfect, some pottery coming under two heads, as, for instance, much of the Italian majolica, which is both enamelled and glazed. For this reason in the following article pottery will be treated according to its age and country, not according to its method of manufacture. Porcelain differs from pottery in being whiter, harder, less fusible, and (most essential differeime) in being slightly translucent. The paste of which it is formed is a purer silicate of alumina than the clay of which pottery is made. It will therefore be de-scribed under separate heads (p. 633 sq., infra).
For the sake of clearness it will be well to define the sense in which technical words relating to pottery are used in this article. Body or paste is the clay of which the main bulk of a pot is made. S/ip is clay- finely ground and mixed with water to the consistency of cream. It is usually- applied over the whole surface of a vessel in order to give it a finer face or a different colour from that of the body of the pot. It is also sometimes applied partially, forming ornaments in relief, as in the case of some Roman ware and the coarse 17th-century pottery of Staffordshire described below. Glaze is a, thin coating of glass, evenly fused over the surface of a clay vessel to make it harder, and also to render it impervious to water. Clay simply baked without a vitreous coating is called biscuit ; its surface is dull, and it is more or less porous. The sim-plest and oldest form of glaze is a pure silicate of soda ; the addition of oxide of lead makes the glaze more fusible, but less hard and durable. For decorative purposes glazes may be coloured by various metallic oxides without losing their transparency. Ename/ is a glaze with the addition of some substance to render it opaque. Binoxide of tin has the peculiar property that when even a small quantity is added to a transparent glass it renders it opaque and white without otherwise altering its character. Great con-fusion has been caused in various works on pottery by a careless use of the terms " glaze " and " enamel"; they are both of the nature of glass, but the best distinction to make is to apply the word "enamel" to a vitreous coating that is opaque, and the word " glaze" to one that is trans-parent ; both may be coloured. The method of applying vitreous coatings to clay, whether enamel or glaze, is this. The materials are ground fine and mixed with water to the consistency of cream. The pot is dipped in the inixture, or the fluid is applied with a brush ; it is then set to dry, and finally fired in the kiln, which must be heated sufficiently to fuse the component parts of the glaze or enamel into one smooth vitreous coating, while on the other hand it must not be hot enough to soften or melt the clay body of the vessel. The use of oxide of lead enables a glaze to be applied to a clay body which would not stand the high temperature necessary to combine and fuse a pure silico-alkaline glaze. In order to ,prevent the glaze or enamel from blistering or cracking off there must be a, certain similarity of substance between the clay body and the vitreous coating. A fine silicious glaze or enamel will not adhere to a soft fat clay unless the proportion of silica in the latter is increased either by admixture of a harder, more silicions clay, or by the addition of pure silica either in the form of sand or of ground flint.
The Potter's Wheel. - All pottery, except the rudest and most primitive sorts, is moulded or " thrown " by the aid ' of a very simple contrivance, a small round table fixed on a revolving pivot. Fig. 1, frora a tomb-painting at Thebes, shows its simplest form. The potter at intervals gives a spin to the table, which continues to re-volve for some time without a fresh impulse. This form of wheel, used by the Egyptians (as is shown by existing fragments of pottery) about 4000 B.C., iS still employed without any alteration by the pot-ters of many parts of India. A later improvenient introduced in Egypt under the Ptolemies was to have another larger circular table, fixed lower down on the same axis, which the potter set in inovement with his feet, and thus was able to keep up a regular speed and leave his hands free for the manipulation of the clay (see fig. 2). No process in any handicraft is more beautiful than that of a potter moulding a vessel on the wheel. The ease with which the plastic clay answers to the touch of the hand, and rises or falls, taking a whole succession of symme-trical shapes, and seeming, as it were, instinct with the life and thought of the potter, makes this art beautiful and striking beyond all others, in which the desired form can only be at-_ tained by comparatively slow and laborious methods. Ancient poetry is full of allusions to this. Homer (//., xviii. 600) com-pares the rhythm of a dance to the measured spin of a potter's wheel; and the rapid ease with which a clay vessel is made and remade in a new form is described by Jeremiah (xviii. 3-4) in one of his most forcible similes (compare Horace, A. P., 21-22). Among the Egy-ptians of the Ptolemaic period the potter was used as a type of the Creator. Nouf or Knonm, the divine spirit, and Pthah, the creator of the mundane egg, are symbolized by human figures moulding clay on the potter's whee1.1 The wheel and egg are shown above in fig. 2.
See Rosselliuo, Monumenti dell' E,gitto, pl. xxi. and xxii., 1844.
chamber of brick, with a perforated floor near the bot-tom. The fuel was introduced from an opening on one side, and raked in under the brick floor. The pottery to be baked was piled up in the upper part of the chamber. Fig. 3, from a potter's votive tablet from Corinth, shows an early Greek form of kiln, with a place for the fuel on one side, and a door in the side of the up-per chamber through which the pottery-could be put in and withdrawn. The Cor-inthian kiln differs from the Egy-ptian kiln in being domed over, but it is the same in principle.
Even at the present day kilns shaped almost exactly like this early Greek one are still largely used.
The art of making pottery is one of the rnost extreme antiquity ; with the exception of the cave-dwellers of the Drift or Palteolithic period it was practised by all known prehistoric races from the Neolithic age downwards. The sepulchral barrows of Britain and other European countries have supplied vast stores of this earliest kind of pottery. It is mostly formed of coarse clay, generally- brown in colour, though sometimes grey- or reddish ; some few specimens are fine in texture and have a slightly- glossy surface. The clay, while moist, has been kneaded with some care, and is often mixed with a proportion of gravel, coarse sand, quartz crystals, or pounded pottery. Tbe more carefully made specimens, chiefly those of the bronze and iron ages, are frequently covered with a smooth slip, made of the same clay as the body, but finely pounded and thoroughly mixed. All are alike " hand-made," without any assistance from the potter's wheel; some of the smaller ones are scooped out of a solid ball of clay, while in some cases great skill has been shown in the building up, by the unaided hand, of the thin walls of larger vessels, some of which are so round and neatly formed as to appear at first sight to be wheel-made. This, however, is never the case with the pottery of the three great prehistoric periods.
The shapes found in the sepulchral barrows of Britain, France, Scandinavia, a.nd other countries are usually classified thus - (1) cinerary urns, (2) food vessels, (3) drinking-cups, and (4) the so-called " incense cups " (see fig. 4).
ing-cups, mostly from 6 to 8 inches high, vary but little in form, and are usually completely covered with ornament. They are often rnade with considerable care and skill, and are not ungraceful in shape. The names given to the preceding three classes possibly express their real use, but the name of the fourth class, " incense cups," is purely imaginary. Under this head are comprised a number of small vessels of very varied shape, some with their sides pierced through with square or lozenge-shaped openings, while others, almost globular in shape, have several pierced knob-handles, as if for suspension. Some are quite plain, and others 8,re covered with ornament. Their use is miknown ; one possible suggestion is that they were intended to carry fire from some sacred source to light the funeral pyre. Canon Greenwell, probably the best authority on this subject, believes, contrary to the opinion of many anti-quaries, that none of the above classes of barrow-pottery were intended for domestic use, Mit that they were made solely to be buried with the dead. He considers that a fifth class of pottery, chiefly in the form of bowls, which has occasionally been found, not in barrows but in dwellings, is the only kind that was actually used for domestic purposes by prehistoric man (see Grcenwell, British, Barrows, 1877).
The ornament whic,h is often lavishly applied on prehistoric pottery is of especial interest. It frequently consists of lines of small dots impressed from a notched piece of wood or metal, arranged in various patterns - crosses, chevrons, or zigzags. All the patterns were stamped into the body of the pot before it was hardened by fire. The lines were frequently made by pressing a twisted thong of skin against the moist clay, so that a sort of spiral sunk line was produced. Other bands of ornament were made by wooden stamps ; the end of a hollow round stick was usell to form a row of small circles, or a round stick was used sideways to produce semicircular depressions. In some cases the incised lines or dots have been filled up with a white slip of pipeclay. Con-siderable taste and invention are shown by many of these combined ornaments, and a certain richness of decorative effect is produced on some of the best drinking-cups ; but one thing is to be noted : all the main lines are straight, no wavy lines or circles appearing, except in very rare instances - a fact which points to the very limited artistic development attained by the prehistoric races.
Prehistoric pottery bas sometimes been described as "sun-baked," but this is not the case ; however imperfeetly baked, the pieces have all been permanently hardened by fire, otherwise they would certainly not have lasted to our time. This was done in a very rough and imperfect manner, not in a kiln but in an open fire, so that in some cases tbe pots have received a snperficial black colour from the smoke of the fuel. Great quantities of this pottery have been found in the sepulchral barrows of Great Britain and Ireland ; those from tl:e latter country are nsually very superior in neatness of execution to the British specimens. The British Museum is specially rich in this class of pottery, chiefly the result of excava-tions made in British barrows by Canon Greenwell.
For prehistoric pottery, (7,e Greenwell, British Barrows, 1877 ; Lubbock, Prehistoric Times, 1865 ; Boyd Dawkins, Early Man irt Britarn, 1880 ; Wilson, Prehistoric Man, ad ed., 1876, and Prehistoric Annals of Scotland, 1851n; Keller, Lake.Dwellings in Switzerlawl (tr., by Lee, 1870; Bonstetten, Ream! d'Antiquites Suisses, 1855-57 ; Perrin, Etude PrAistorique, 1870; Tropp. Habitations Lacustres, 1860 ; Borlase, Cornubite, 1872.
But few examples remain which date from the time of the earlier dynasties of Egypt, though from the XVIIIth Dynasty downwards a great quantity of specimens exist. Broken fragments, embedded in the clay bricks of which some of the oldest pyramids are built, supply us with a few imperfect samples whose date can be fixed. The early pottery of Egypt is of many varieties of quality : some is formed of coarse brown clay moulded by hand without the aid of the wheel ; other specimens, thin and carefully wheel-made, are of fine red clay, with a slight surface gloss, something like the " Samian" pottery of the Romans. Some fragments of brown clay have been found, covered with a smooth slip made of a creamy white or yellowish clay. The early use of fine coloured enamels, afterwards brought to such perfection in Egypt, is shown by the enamelled clay plaques in black, white, and greenish blue which decorated the doorway of the great step-pyramid at Sakkara. Each plaque has a pierced projection at the back, so that it could be firmly fixed by means of a wood or metal dowel.
Egypt is rich in materials for pottery, both glazed and enamelled. The finest of clays is washed down and deposited by the Nile ; the sandy deserts supply- pure silica, ; and a great part of the soil is saturated with the alkali necessary for the composition of vitreous enamels and glazes. In spite, however, of this abundance of materials the Egyptians never learned to apply either their enamels or their glazes, both of great beauty, to their larger works in pottery made of the fine Nile clay. The reason probably was that the clay was too fat, and there-fore a vitreous coating would have flaked off during the firing, while they had not discovered the simple expedient of mixing with the native clay an addition of sand (silica), which would have enabled both glazes and enamels to form a firm coating over tbe body of the vessel. The colours used for Egyptian enamels and glazes are very varied, a,nd of great beauty and brilliance. The gla.zes themselves are pure alkaline silicates, free from lead. The enamels are the same, with the addition of oxide of tin. The metallic oxides used to give the colours are these, - various shades of blue and green, protoxide of copper, or more rarely cobalt ; purple and violet, oxide of manganese ; yellow, iron or antimoniate of lead ; red, sub-oxide of copper or iron ; black, magnetic oxide of iron or manganese. The white enamel is simply silicate of soda with oxide of tin. The blues and greens, whether used in transparent glazes or opaque enamels, are often of extreme magnifi-cence of colour, in an endless variety of tints, - turquoise, ultramarine, deep indigo, and all shades of blue passing into green. The most remarkable specimens of Egyptian enamel work are some clay plaques or slabs, about 10 inches high, which were used to decorate the walls of Rarneses II.'s palace at Tel al-Yaluidlya, in the Delta (14th cent. n.c.). These have figures of men and animals executed in many different colours in the most complicated and ingenious manner. They are partly modelled in slight relief, and then covered with coloured enamels ; in other parts a sort of mosaic has been made by mixing fine clay and enamels into soft pastes, the design being fitted together and modelled in these coloured pastes while moist. The slab was then fired, and the enamel pastes were at once vitrified and fixed in their places by- the heat. A third process applied to these elaborate slabs was to fit into cavities left for them certain small pieces of coloured glass or brilliant enamels, giving the effect of precious stones, which were fused into their places by a second firing. The chief figures on the plaques are processions of captives, about 8 inches high ; the enamel flesh is varied according to the nationality of the prisoners : negroes are black, others white, red, or yellow. Some of the dresses are represented with great richness : various embroidered or textile patterns of the most minute scale are shown by enamel inlay of many colours, and even jewel ornaments are shown by the inserted bits of glass; the dress of some Assyrian captives has patterns of great beauty and richness, - the sacred tree betikeen the guardian beasts, and other figures. Besides these elaborate figure-reliefs an enormous number of smaller pieces of clay inlaid with different-coloured pastes were used to form a sort of mosaic wall-decoration in this wonderful palace, the ruins of which have supplied a perfect museum of all kinds and methods of enamelled work as applied to pottery. Tbe British Museum and the Louvre have the finest specimens of these wall-slabs (see Birch, Ancient Pottery, p. 51, 1873).
The term "Egyptian porcelain" has sometimes been given . to the small mummy-figures in brilliant blues and greens. This is a misnomer. The little figures, about 3 to 6 inches high, of which immense numbers bave been found, mostly dating from about the XXth Dynasty downwards, are simply formed of sand (silica) with a little alkali, and only sufficient clay to cement them together, so that they could retain the form given them by the mould into which they- were pressed. The result of analysis is silica 92, alumina 4, and a slight but varying proportion of soda. They are covered with a silicious glaze, brilliantly coloured with copper oxide, and are sometimes painted under the glaze with manganese, a deep purple-violet. A few of these figures, and also small statuettes of deities, have had oxide of tin mixed with the paste; the figure has then been exposed to sufficient heat to fuse the whole into one homogeneous vitreous mass, and thus the statuette has become a solid body of fine blue enamel. A few small objects - such as libation cups, bowls, and chalice-like goblets - were also made of the same sandy paste, covered with blue-green glaze. They are thick and clumsy owing to the very unplastic nature of their paste, which necessitated their being pressed in a mould, not wheel-made. The splendour of their colour, however, makes them objects of great beauty ; they usually have a little painting, lightly executed in outline with manganese purple, generally a circle of fishes swimming or designs taken from the lotus-plant (see fig. 5).
During the XVIIIth and XIXth Dynasties and later pottery was used in many ways for wall-decoration. Bricks or tiles of coarse brown clay were covered with a fine white slip and glazed with brilliant colours. Another method was a sort of in-lay, formed by- stamping incised patterns into slabs of clay and filling up the sinkings with a, semi-fluid clay of some other colour, exactly like the 16th-century Oiron ware. A number of brilliant wall-tiles covered with deep blue glaze, and painted in black outline with figures and hieroglyphs, have been found in many places in. Lower Egypt ; the painting is very simple and decorative in effect, drawn with much skill and precision of touch.
The Canopic vases are an important class and great , quantities have been found in Egyptian tombs. They are generally made of plain brown-red clay, and have a lid in the shape of a human head. On them hieroglyphs are coarsely painted in black or colours (see fig. '6). They contained parts of the viscera of the corpse. The mummies themselves are frequently decked out with pectoral plates, necklaces, and other ornaments, made of clay covered with blue and other coloured enamels. Some of the pectoral plates are very elaborate works of the same class as the figure-reliefs from Tel al-Yalindiya, richly decorated with inlay of diffm-ent-coloured pastes and enamels.
During the Ptolemaic period a quantity of graceful and well -executed pottery was made in fine red and brown clay, mostly without any painted decoration. Some of the vases are of good form, owing to the influenceof Greek taste (see fig. 7); others are coarsely decorated with rude painting in blue, green, red, yellow, and brown, either in simple bands or with lotus and cther flower-patterns (see fig. 8). Both the body of the vases and the colours are usually quite devoid of any gloss. The duller colours a,re various earths, ochre, and white chalk, while the bright blues and greens are produced by mixing powdered enamel of the required colour with light-coloured clay, the depth of the tint de-pending on the proportion of the clay or chalk.
Certain very gaudy and ugly pots were made to imi-tate granite and steatite ves-sels (see fig. 8). They are of brown clay, rudely dabbed aud speckled with brown, red, yellow, and grey colours to represent the markincrs of the stone; others are yelrow, with grey streaks - imitations of marble; most have a painted white tablet, on which are hieroglyphs in black. The pigments arc very shiny in texture, and appear to be unfired. Among the most deli-cate and carefully made kinds of Egyptian pottery are the round flat flasks shaped rather like the mediteval " pil-grim-bottle" (see fig. 9). They are sometimes made of blue paste, fine clay coloured with oxide of copper, and are delicately enriched with im-pressed ornaments, stamped from a mould, in low relief or slightly incised. The orna-ment is often designed like a gold necklace hung round the bottle ; others have tablets with inscriptions. The surface is biscuit ; and the flasks range in colour from light turquoise to deep ultramarine, ' the colour not being superficial but of equal strength all through the paste. Small vases of other forms, made of this same material, also occur, but they are rare.