BEFORE attacking the somewhat complicated subject of the nature and composition of glazes, it will be well to take up again the thread of the mechanical processes that are involved in the making of a piece of porcelain.
The materials that enter into the glaze are reduced to the finest powder in mills similar to those in which the china-stone and flint are ground for the preparation of the paste. If any substance soluble in water, such as borax or salts of the alkalis, enter into the composition of the glaze, these must be first partially fused in combination with the other materials to form afrit, a kind of imperfect glass. These frits, which enter so largely into the composition of soft-paste porcelain, are formed with the object of bringing the soluble constituents into an insoluble form before mixing with water to form the slip. There are indeed other practical reasons that render a preliminary partial fusion desirable.
The finely ground elements of the glaze, mixed in due proportion, are worked up with water to form a creamlike slip into which the vessel to be glazed is now dipped. In China, in many cases, the glaze-slip is blown upon the surface in the form of a spray. This is done by means of a bamboo tube, covered at one end by a piece of silk gauze, through which the liquid is projected by the breath of the operator (French,insufflation); in other cases the glaze may be painted onwith a brush. In China, as we have mentioned, the glaze-slip is generally applied to the raw surface of the thoroughly dried but unbaked ware, but in other countries there is, almost without exception, a preliminary firing of greater or less degree to produce a biscuit.
We shall restrict the use of the word glaze to the vitreous coating applied directly to the surface of the raw paste or of the biscuit to enhance the decorative effect of the ware, and with the more prosaic object of allowing the surface to be easily kept clean. In the case of porcelain this coating is always more or less transparent.[16]There is here no necessity for concealing the natural white colour of the paste. In the case of many kinds of pottery, however, as in the ‘enamelled fayence’ of Delft and Italy, the glaze is rendered opaque by the addition of oxide of tin, so that the ill-favoured ground is concealed by a white shiny surface which may be made to resemble closely the natural surface of porcelain. A glaze of this kind is often called an enamel, but as we are not concerned with such an expedient we shall confine the use of that word to the various forms in which a vitreous decoration, whether translucent or opaque, issuperimposed upon the glazeand fused into it, more or less thoroughly, by a subsequent firing in a muffle furnace.
The English word ‘glaze’ is only another form of the word ‘glass,’ and we may say at once that, in composition at least, there is often little difference between the two substances. The French word for ‘glaze’ iscouverteorvernis; the last term applies well to the thin skin of glaze found on Greek pottery. The Chinese have several expressions, but it is a curious fact that the characters with which most of these terms are written contain the radical for ‘oil,’ and indeed the word ‘oil’itself is often used in the sense of ‘glaze.’
Mr. Rix puts it well when he says that the glaze is to the enameller of porcelain what his canvas is to the painter; while in the case of a decoration ‘sous couverte,’ the glaze corresponds to the varnish which, while protecting his work, gives brilliancy to the colouring (Journal of Society of Arts, vol. xli.). It is, moreover, the vehicle by which the design is harmonised and rendered mellow. The effect is produced at once and endures practically for all time.
The hardness and fusibility of glazes differ widely, and they are conditioned by the nature of the wares that they cover. It is evident that there must be a close relation between the fusing-points of paste and glaze, and that the latter should be the more fusible of the two. The difference of melting-point should, however, not be too great. The melted glaze should rather, by penetrating into the already softened paste or by a chemical action upon its surface, form a more or less uniform mass with it. In cooling, the contraction of the glaze should follow that of the subjacent paste. This is a most important point; any discordance may lead to splitting, cracking, and ‘crazing.’
The beauty of the surface of porcelain depends on the fact that the glaze has become intimately united with the paste during the long exposure of both to a high temperature. We should not be conscious, in regarding a fine specimen of porcelain, of a greater or less thickness of glass covering an opaque substance; we should rather see in it the polished surface of ivory or of some precious marble.
It would seem that it was the beauty of the glassy surface, enhancing the brilliancy of the colouring, rather than any practical advantage connected with its use, that first led to the application of glaze to pottery. The turquoise and green glazes of the Egyptians (the colour is derived from a silicate of copper along with soda and sometimes lime) were known to the men ofthe Early Empire. They were applied to a fritlike mass of sand held together by silicate of soda, to which the name of porcelain has sometimes been very wrongly given. Objects of steatite, of slate, and even of rock crystal were sometimes covered with a coloured glaze of this kind, but it was never applied to the clay vessels in daily use. These were made, then as now, from the unctuous clay of the Nile bank. For this restriction there was a very good reason, namely that a glaze of this nature, composed chiefly of alkaline silicates, will not adhere to a base of ordinary clay. It was not until Ptolemaic and Roman times that, by the discovery or adoption of a glaze containing lead, the ancients were enabled to glaze their pottery. So in Assyria, the employment of glazes was almost confined to the decoration of the surface of brickwork, the bricks being of a loose and somewhat sandy texture.[17]
In these glazes, and indeed in much earlier examples from Babylonia, both tin and lead have been found. The respective virtues of the silicates of these metals were doubtless appreciated, that of tin to form a white opaque enamel hiding the material below, and that of lead to enable the glaze into which it enters to adhere to a paste formed of a plastic clay.
With the Chinese the aim was rather æsthetic than practical. They sought by means of the marvellous glazes that cover their ancient porcelain to imitate the surface of natural stones; their early celadons were in a measure intended to take the place of the precious green jade, so highly esteemed by them.
At the time when the manufacture of porcelain was first introduced from China there were (apart from the salt-glazed stoneware, which lies quite outside our inquiry) three classes of glaze in general use either in Europe or in the nearer East:—
1. Glazes consisting essentially of alkaline silicates without either lead or tin. Such glazes could only be applied to a fritty silicious base, and in India and Persia their employment seems to have been a survival from Egyptian and Assyrian times.[18]
2. Opaque enamel glazes, the opacity being due to the presence of tin; a considerable amount of lead also is generally found in these glazes. We are not concerned here with the obscure origin of this group, but in the sixteenth century this enamelled fayence was in general use for the better class of table-ware. It includes the Italian majolica, the French fayence of Nevers and Rouen, and above all the earthenware of Delft.
3. The oily-looking lead glazes with which the common earthenwares were covered. These were essentially the glazes of the Middle Ages in Europe, and their employment could probably be traced back to the lead-glazed ware sparingly used by the Romans. We have already noticed the use of a similar glaze in Egypt as far back probably as Ptolemaic times.
There were practical objections to all these glazes. It is true that at Delft, by the use of the tin enamel, a ware could be turned out closely resembling, in external aspect, the blue and white porcelain of China, but the enamel was soft and would in time chip off at the edges, showing the dark earthy clay beneath. On the other hand, the alkaline glazes of the East were not much known in Europe; they can only be used upon a very tender and treacherous base. In India and Persia, however, a ware thus glazed still competes with the hard porcelain of the Far East. In spite of the great objections to the glazes of our third class, those containing lead—objections arising fromtheir softness and from the danger of poisoning to those employed in their manufacture—their use has tended rather to increase. Not only is lead the principal constituent of the glazes still universally used for common pottery, but it forms an important element in the glaze of our finer earthenwares as well as in that of those bone pastes which rank with us as porcelain.
The glaze which had been brought to perfection by the Chinese at an early period differs from all those yet mentioned by its hardness, its high fusing-point, and in its chemical composition. Speaking generally, the glaze of porcelain differs in composition from the paste which it covers only sufficiently to allow of its becoming completely liquid at the extreme heat of the furnace; and just as the paste of Chinese porcelain has a wider limit of variability than that made in Europe, but is on the whole of a ‘milder’ type than the latter, so we find that while the glazes of the Chinese are as a whole less refractory and not quite so hard, there is still a wide range of variation in these qualities.
If, then, we theoretically regard porcelain as a compound of a silicate of alumina with an alkaline silicate of the same base, we may say that the glaze of porcelain is formed by the latter body alone, that it is, in fact, merely a fused felspar. But as in the case of the paste, so in the glaze there is generally present an excess of silica, derived from the quartz contained in the petuntse or pegmatite, and this silica enters into combination with some other bases which are present in the constituents of the glaze, thereby increasing its fusibility and modifying the contraction in cooling. The most important of these additional bases is lime, so that the more fusible type may be called a calcareous, as opposed to a more refractory or purely felspathic glaze. As much as 21 per cent. of lime has been found in some Chinese glazes, the amount of alumina being proportionately reduced.
There is more or less lime in the glaze of most kinds of European hard porcelain, but the exceptionally hard and refractory paste made at Sèvres since the time of Brongniart is covered by a glaze of corresponding hardness from which that earth is absent. This hard paste has, however, of late been replaced in part by one of a milder type, and with this latter a calcareous glaze has been adopted even at Sèvres, the object of the change being, as we have said, to allow of a more brilliant decoration.
There is a perceptible difference in the aspect of these two types of glazes after firing. The hard, non-calcareous glaze has a slightly milky look. The softer calcareous type is more brilliant, and approaches in transparence and limpidity to the lead glazes of soft porcelain. A glaze of this last kind was used at Sèvres for a few years after the first introduction of the hard paste, and perhaps also at Dresden in quite early days.
The principal objection to a hard refractory glaze, such as that so long in use at Sèvres, arises from the difficulty of properly incorporating the enamel colours with its body. The restriction of the number of pigments that can be employed, both under and on the surface of the glaze, in consequence of the high temperature at which the latter melts, is another drawback. The dulness, the ‘painted on’ look of so much of the decoration on European hard paste porcelain, is in great measure a consequence of the employment of a glaze that is only softened at a high temperature. As an example of a medium type of glaze we give the composition of that used at Berlin in 1836. This consisted of kaolin, 31 per cent.; quartz, 43 per cent.; gypsum, 14 per cent.; and ground porcelain, 12 per cent. A glaze long in use at Dresden is of a very similar character. Felspar, it will be seen, does not enter into its composition, and such a glaze can contain but little potash or soda. With this we may contrast the hardglaze of Sèvres, composed simply of ground pegmatite, a rock consisting mainly of felspar. This glaze yields on analysis 74 per cent. of silica, 17 per cent. of alumina, and as much as 8 per cent. of potash.
The glaze on Chinese porcelain is prepared by mixing certain special varieties of petuntse with an impure lime, prepared by burning limestone with dry fern as fuel. It contains, as we have seen, from 15 to 21 per cent. of lime, 5 to 6 per cent. of alkalis, 11 per cent. of alumina, and 66 per cent. of silica.
We give these examples to illustrate the principal types of glazes used for hard paste porcelain. It will be noticed that the constituents are drawn from widely different sources.
The glazes of soft paste porcelain always contain a large amount both of lead and of potash or soda, so that they approximate in composition to a flint glass. The alkalis, generally introduced as carbonates, necessitate a previous fritting of part at least of the materials. Boracic acid plays an important part in the glaze of most modern English wares: it is generally introduced in the form of borate of soda or borax. This acid replaces in part the silica, just as in the paste the glassy materials are replaced by bone-earth.
IF we were treating the subject purely from a practical point of view, with the glazing and firing of a piece of porcelain the manufacture might be held to be terminated. This would be strictly true, for instance, of the white porcelain of Berlin, so largely used in the chemical laboratory; a great deal, too, of the china in domestic use receives no decoration of any kind. But for us there remains still to examine the element of colour and the way in which it is applied to the decoration of porcelain.
This is effected in three different ways: by the employment of coloured glazes; by painting on the surface of the paste before the glaze is applied (this is the decorationsous couverte); and finally by coloured enamels applied to the surface of the glaze. These methods may be combined, but as this is rarely the case, such a division forms the basis of a convenient classification, more especially for the wares of China and Japan.
In the case of both the paste and of the glaze, we have been dealing with a restricted group of elements, with alumina, lime, potash and soda; and apart from impurities unintentionally introduced, all the combinations of these bodies are colourless. We have now to consider the effect of introducing certain of the heavy metallic bases which combine with the excess of silica to form coloured silicates.
The metals that give to Oriental porcelain its brilliant hues are few in number. Indeed, in all lands and at all times, iron, copper, cobalt, and manganese have been the principal sources of colour in the decoration not only of porcelain, but of most other kinds of pottery. As equal to these four metals in importance, but not strictly to be classed as colouring materials, we may place tin, the source of most opaque whites, and lead, which is the main fluxing element for our enamels. Next in importance to these metals come antimony, long known to the Chinese as a source of yellow, and finally, but this last only since the beginning of the eighteenth century, gold, as the source of a red pigment.[19]This exhausts the list, not only for the Far East, but for all the pottery of Europe up to the end of the eighteenth century.
It was in a period of artistic decline that the advance of chemical knowledge led to the introduction of other colours, derived both from new metallic bases and from fresh combinations of those already known. By far the most important of these new colours are those derived from the salts of chromium, but uranium and other rare metals have also been called into use. As with the sister art of painting, the beauty and harmony of the effects produced have not kept pace with the enlargement of the palette—the result was rather to accentuate the decline that had already set in from other causes.
There are two metals, iron and copper, that have always been of pre-eminent importance as sources of colour. Each of them forms two series of combinations differing entirely in hue, so that were we confined to the use of these two metals, our palette would still be a fairly complete one.
The protoxide of copper, especially when a certainamount of lime and of soda is present, forms a series of beautiful blue and green silicates. When the proportion of oxygen is decreased, as happens when the surface of the ware is exposed in the kiln to a reducing flame, a suboxide of copper is formed, which gives a deep and more or less opaque red hue to the glaze. So in the case of iron, the so-called sesqui-oxide is perhaps the most abundant source of colouring matter in the mineral kingdom: the colours produced by it range from pale yellow to orange, brown, and full red. When, however, the iron is present as a protoxide, the colour given to the glaze is entirely altered; it ranges from a pale sea-green to a deep olive.
The remaining two elements that have long played an important part in the decoration of pottery are cobalt and manganese. These metals, in the form of silicates, yield the well-known series of blues and purples. One important source of the famous underglaze blue of China and Japan is a black mineral known to us as wad, which occurs in earthy to stony concretions. This wad contains oxides of both cobalt and manganese, and the quality of the blue obtained from it depends in great measure upon the proportion in which the two metals occur.
The employment of antimony is comparatively rare, but, generally in combination with iron, it is an important source of yellow. In spite of the volatile nature of most of its salts, in the presence of silica this metal is able to withstand a high temperature.
But before considering the application of colour to the glaze, we must mention briefly a method of decoration which was in great favour at Sèvres some years ago—I mean the application of colour to the paste itself. This was done long ago by Wedgwood, sometimes to the whole mass of the paste, as was the case with his jasper ware, which some authorities class as a true porcelain. At Sèvres these coloured pasteshave been generally applied to the surface only, in thin layers, or even as mere coats of paint. When laid on in successive coats, as in the so-calledpâte-sur-pâte, the amount of colouring matter need not be large, from 2 to 5 per cent. When larger proportions of coloured oxides are mixed with thepâte, and this is painted on with a brush, the process differs little from the ordinary decoration under the glaze, into which it indeed may be said to pass. Coloured pastes of this description have never been employed by the Chinese, and it is not possible to obtain much brilliancy or decorative effect by their use. They are, indeed, foreign to the nature of porcelain, sacrificing the brilliant white ground which should be the basis of all decorative schemes.
When the colouring matter is subjacent to the glaze it must be of a nature to withstand the full heat of the subsequent firing; we are restricted therefore to colours ‘à grand feu.’ This practically confines us to cobalt and to certain combinations of iron and copper, as far as the ‘old palette’ is concerned. At Sèvres and elsewhere other metals have been made use of whose silicates withstand the extreme temperature of the kiln. By the use of chromium we have command of many shades of green. If to an oxide of tin we add a minute quantity of the sesqui-oxide of chromium, we can obtain, in the presence of lime, many shades from rose to purple; and a mixture of cobalt and chromium produces a fine black. There is, however, as yet no satisfactory yellow pigment known that will withstand thegrand feu. At the best we can get a straw colour from certain ores of tungsten and titanium, and from uranium a yellow deeper in tint but uncertain in application.
The majority of the colours we have mentioned require a more or less oxidising flame for their full development. There are, however, two most important groups of coloured glazes, long the monopoly of the Chinese, but now successfully imitated in France andelsewhere, which require, for a term at least, to be subjected to a reducing flame.
The first of these glazes is the well-knownCeladon, using that term in its proper and restricted sense, for certain shades of greyish green. The celadon of the Chinese is produced by the presence of a small quantity, about two per cent., of protoxide of iron in the glaze. An oxidising flame would change this protoxide to the yellow sesqui-oxide. We may note that a celadon of good tint can only be produced when a considerable quantity of lime is present in the glaze.
The other group, depending also upon a reducing flame, is constituted by the famousSang de bœufandFlambéglazes.
The colour of the first is given by the red sub-oxide of copper, chiefly suspended in the glaze. In the case of theflambéor ‘transmutation’ glazes, the strange caprices of colour have their origin, in part at least, in the contrast of the red sub-oxide and the green silicate of copper. In the case of both these glazes everything depends on the regulation of the draught of the furnace in which they are fired. The French have lately been at great pains to master the difficulties attendant upon the development of the effects sought after, and some success has been attained not only on a porcelain ground as at Sèvres, but these glazes have also been applied to fayence at the Golfe St. Juan and elsewhere. It has been proved by some experiments made at Sèvres, that in the firing, the critical period, during which so much depends upon the regulation of the draught, isjust beforethe melting of the glaze. Once melted the glaze not only forms an impervious cover which prevents the smoky flame from discolouring the paste below, but the glaze itself is no longer sensitive to the action of the gases which surround it. It is therefore only during a short period preceding the moment when the glaze begins to melt,that it is necessary to promote a smoky and reducing flame. This is a point of considerable practical importance.[20]
The application of theDecoration under the Glazeis essentially a Chinese method. To it we owe the important family of ‘blue and white’ ware. The superiority of the Chinese in the management of the blue colour has been attributed to various causes. The result is no doubt influenced not only by the constitution of both paste and glaze, but also by the fact that the colour is painted upon therawpaste.
An important factor also is the care exercised by the Chinese in the selection and preparation of the blue pigment, by which not only the desired intensity but the richness of hue is secured. The quality of the blue depends in great measure upon the presence of a small quantity of manganese in the cobalt ore employed.
The only other colour that the Chinese have succeeded in using under the glaze is the red derived from the sub-oxide of copper. The full development of this colour has for long been a lost art, but a less brilliant red from this source, often little better than a buff colour, is sometimes found in later examples combined with the blue.
In the application of colours under the glaze there is one difficulty that the Chinese have surmounted even in their commonest ware, and this is the tendency of the cobalt blue to dissolve and ‘run’ in the glaze, giving to the design a blurred and indistinct appearance. It would seem that the sharpness of outline depends upon the consistency of the glaze at the moment when it first melts. At that point the glaze should be viscous andnot inclined to flow, and this is what occurs in the case of the highly calcareous glazes of the Chinese.
Before passing to the enamel colours, we must say something of a class of glazes which may be looked upon as to some extent of an intermediate character. These are the glazes associated with the ‘San tsai,’ the ‘three colours’ first used in combination by the Chinese.
These coloured glazes were applied, not, as is usually the case in China, to the raw paste, but they were, it would seem, painted on the surface after a preliminary firing. Being applied with a brush, the whole surface of the biscuit was not necessarily covered, and glazes of all these colours could be used upon the same piece of porcelain. Glazes of this class were rendered more fusible by the addition of a certain quantity of lead, and on this ground, and still more in their historical relation, as we shall see later on, these ‘painted glazes’ may be considered as a link connecting the old refractory glazes of the monochrome and ‘blue and white’ wares on the one hand, with the fusible enamels which were at a later timesuperimposedupon the glaze on the other.
The three colours which are applied in this way by the Chinese are: (1) A turquoise blue derived from copper with the addition of some soda or potash. (2) The manganese purple, often described as aubergine. (3) A yellow prepared from an iron ore containing some amount of antimony. None of these colours would stand the full heat of the furnace, and for a reason which will be explained further on, they are known as the colours of thedemi grand feu.[21]
Coloured Enamels.We have now to describe
PLATE II.CHINESE MING PORCELAIN, BLACK GROUND
PLATE II.CHINESE MING PORCELAIN, BLACK GROUND
PLATE II.CHINESE MING PORCELAIN, BLACK GROUND
the decoration that is applied to the surface of the glaze. In these coloured enamels the colouring matter is dissolved in a flux which contains a large quantity of lead. The comparatively gentle heat at which such enamels fuse allows of the use of a much larger palette than is available for the decoration under the glaze.
It is well to point out at the outset the marked distinction in composition and in appearance between the brilliant enamels of the Chinese and the dull tints of the ‘porcelain colours’ found in the hard pastes of Meissen and Sèvres. To make clear the cause of this difference it will be necessary to enter into some little detail.
The colouring matter in the European enamels may amount to as much as a third part of the total amount of the flux with which they are incorporated. As there is not enough of this flux to dissolve the whole of the oxides, the enamel remains dull and opaque after firing. The flux, in fact, is only used as a vehicle to attach the colour to the surface of the porcelain. The effect in consequence is inferior in brilliancy to that obtained by the Chinese with their transparent enamels in which the metallic oxides, present in much smaller quantity, are thoroughly dissolved to form a glass. There is, unfortunately, a practical obstacle to the application of these glassy enamels to the hard pastes and glazes of Europe. It is impossible to ensure their firm adhesion to the subjacent glaze. The Chinese, however, do not appear to find any difficulty in effecting this. The following explanation has been given to account for the difference of behaviour:—the tendency of the enamel to split off in cooling, as has been proved by experiment, arises from the small amount of contraction at that time of the highly kaolinic paste, compared with that of the superimposed glassy enamel. The more silicious paste used by the Chinese contracts, on the contrary, at the same rate approximately as theenamels that it carries, and these enamels may therefore be laid on in sufficient thickness without any risk of their subsequently splitting off.[22]To appreciate the difference in the decorative value of these two classes of enamels it is only necessary to compare the brilliant effect, say, of a piece of Chinese egg-shell of the time of Kien-lung with the tame surface of a contemporary Meissen plate, elaborately painted with landscapes or flowers.
The glassy enamels used by the Chinese resemble the pastes used for artificial jewellery. They are essentially silicates of lead and an alkali. The composition of the flux has to be modified to ensure the full development of the colour of the different metallic oxides which are either made up with it or added subsequently. But in a general way we may say that the colourless fluxes which form the basis of the coloured enamels are prepared by melting in a crucible a mixture of pure quartz sand and red lead, and adding more or less alkali. In certain cases the lead predominates, as when it is proposed to make an emerald green enamel by means of copper, or when the flux is to serve as a basis for the ruby colour given by a minute quantity of gold. On the other hand, if copper be added to a flux containing an excess of either soda or potash, we obtain a turquoise blue. A fine purple, again, can only be obtained from manganese with an alkaline flux; if too much lead is present only a brown tint is obtainable.
To melt these enamels and to ensure their adherence to the subjacent glaze another firing at a gentler temperature is necessary; indeed in many cases more than one such firing has to be resorted to. The comparatively high temperature required to develop the colour of one enamel may be sufficient to decompose or otherwisedamage another part of the decoration. The lowest temperature of all is that of the muffle-fire in which the gilding is fixed. This is therefore the last decoration to be added.
The oven in which these enamels are melted on to the surface of the already glazed porcelain is called a muffle. The ware in this case is protected from the direct action of the flame by the closed rectangular box of fireclay in which it is placed, like bread in a baker’s oven. The muffle is placed over the fireplace of a rectangular furnace, and the flame plays round the sides in such a way as to ensure the uniform distribution of the heat. For the sake of greater cleanliness and the avoidance of dust, the pieces to be fired are placed upon tiles of porcelain rather than upon biscuit or fireclay supports. The temperature may vary from a dull to a full red heat (600° to 1000°C.), and the firing lasts from four to twelve hours.
We have already mentioned incidentally many of the so-called ‘muffle-colours’ or enamels. Those used in China were carefully studied some years ago by Ebelmen and Salvétat at Sèvres. It would appear that the opaque white of the Chinese is obtained from arsenic—the merits of the use of tin for this purpose appear to be unknown to them. The blacks are made from the already mentioned cobalt-manganese ore (wad), mixed with white lead—when oxide of copper is added a more lustrous black is obtained.[23]For the blue enamel, a very small quantity of cobalt suffices to give a brilliant colour. The various tints of the greens and blues derived from copper depend on the nature of the flux; of this we have already given an instance. Antimony in combination with lead gives a bright yellow, which tends to orange when a little iron is present; by the addition of more iron the colour of old bronze isimitated. Iron in the state of the sesqui-oxide is the source of many shades of red, but as this iron oxide will not readily combine with silica to form a transparent glass, it has to be applied as a more or less opaque paint, and thus differs from the other colours in being in perceptible relief. Hence the importance of the ruby red derived from gold, which was first introduced into China in the early part of the eighteenth century, and soon became the predominating colour in the decoration of the time (thefamille rose).
The palette of the European enameller is a more extensive one, and each large porcelain manufactory has its book of recipes. The composition of the enamels and the relation of the metallic oxides to the fluxes employed have been systematically studied in more than one laboratory. It is only at Sèvres, however, that the results obtained have been made public. It has been the pride of successive generations of chemists—of Brongniart, of Salvétat, of Ebelmen, not to mention living men—to devise fresh sources of colour for the decoration of porcelain. First chromium, then nickel, cadmium, uranium, iridium, and platinum have been added to the list of metals from which enamel pigments have been derived. Among the colours of the muffle-stove the chief gain has perhaps been the discovery of the quality possessed by the oxide of zinc of altering the tints of other metallic oxides with which it is mixed.
‘La porcelaine de la Chine! Cette porcelaine supérieure à toutes les porcelaines de la terre! Cette porcelaine qui a fait depuis des siècles, et sur tout le globe, des passionnés plus fous que dans toutes les autres branches de la curiosité.... Enfin cette matière terreuse façonnée dans les mains d’hommes en un objet de lumière, de doux coloris dans un luisant de pierre précieuse.’—Edmond de Goncourt, ‘La Maison d’un artiste.’
‘La porcelaine de la Chine! Cette porcelaine supérieure à toutes les porcelaines de la terre! Cette porcelaine qui a fait depuis des siècles, et sur tout le globe, des passionnés plus fous que dans toutes les autres branches de la curiosité.... Enfin cette matière terreuse façonnée dans les mains d’hommes en un objet de lumière, de doux coloris dans un luisant de pierre précieuse.’—Edmond de Goncourt, ‘La Maison d’un artiste.’
In any work on porcelain it is something more than the premier place that must be given to the ware of China. We are dealing with an art Chinese in origin, and during a succession of many centuries Chinese in its development. It was only at a comparatively late time that the knowledge of this art spread over the whole civilised world. We in England have, as it were, acknowledged the pre-eminence of that country by adopting the word ‘china’ as an equivalent, more or less, to porcelain.[24]
It was under Imperial patronage that the art was developed in China, and the excellence of the porcelain of that country has in a measure varied with the taste and intelligence with which that patronage was exercised in different reigns. The native scholar and connoisseur has for ages been a collector of choice pieces,and his influence has always been exercised in a conservative direction. There is, indeed, in the whole world no such consistentlaudator temporis acti, and it is this conservative spirit, resulting in a constant ‘returning upon oneself,’ that it is essential to bear in mind if we are to understand the involved relation of the old and the new in the history of the arts of China.
But the Chinese potter was not working only for the court or for the learned connoisseur, or again for the supply of the towns and villages. From the earliest times, or at least for the last thousand years, there has been a demand for his ware, small at first but slowly spreading, from the outer barbarian. Porcelain, or something akin to it, has been exported from China, by one path or another, from the time of the first Arab settlements at Canton and Kinsay in the eighth or ninth century; and thus a countervailing influence, acting in the direction of variety and change, at least as far as the decoration of the ware is concerned, has always been present. To give but two instances of this influence—we shall return to the subject later on: in the intimate connection of the Chinese court with Western Asia, and especially with Persia, in the thirteenth century, we may probably find the occasion of the first introduction into China of the blue decoration under the glaze; and with more certainty—the fact is indeed acknowledged by the Chinese—we may attribute the second great revolution in the decoration of porcelain, the use of enamel colours over the glaze, to European or Arab influence.
On the other hand, the decline that set in at the end of the eighteenth century was not a little hastened by the increased demand for ware decorated to suit the depraved taste of the ‘Western barbarian.’
For in spite of his rigidity and his conservative spirit, the Chinese potter has always understood how to adapt his wares to the changing taste of his customers.Indeed the variation in the decoration, the subtlenuancesin colour and design, that enable us to distinguish between the Chinese porcelain exported to India, to Persia, and to the nations of the Christian west, might be made the basis of a most interesting study.
When we come to consider the various factories of porcelain that sprang up in Europe in the course of the eighteenth century, we shall find that what strikes the inquirer above all (in comparison with the kindred arts of the time) is the little we can observe in the way of development either in the technique or decoration of the wares. The art springs up full-blown; what history there is is concerned rather with an artistic decline. It is only in China that we can hope to trace the steps by which this special branch of the potter’s art attained to the perfection that we find in the products of the eighteenth century, and this alone is a reason for dwelling, even in a treatment of the subject so general and brief as this must needs be, on what may seem to some mere antiquarian detail.
But there is another and perhaps even a more important reason for our trying to form some idea of what the earliest wares of the Chinese were like: unless we make some such endeavour we shall find it impossible to understand the later history of porcelain in that country. One point must be specially borne in mind when we are attempting to follow the order in which fresh styles and designs were introduced in China. When a new method of decoration had been adopted and had come into general use—the introduction of underglaze blue in early Ming times, and that of coloured enamels at a later period, are cases in point—this did not involve the abandonment of the older styles. There was a constant effort to maintain the old methods, and in the most flourishing times of the emperors Kang-he and Kien-lung, the series of great men who had chargeof the imperial works at King-te-chen, some of them practical potters themselves, were constantly occupied with the problems of reproducing the glazes, if not the pastes, of the earliest wares. During the reign of Yung-chêng (1723-1735), perhaps the culminating period in the history of Chinese porcelain, when Nien Hsi-yao was superintendent, a list was drawn up of fifty-seven varieties of porcelain made at King-te-chen. In this list the titles of all the old wares of the Sung dynasty are to be found, and to them the place of honour is evidently awarded (Bushell, chap. xii.). The names of some of these old wares, the Ko yao and the Kuan yao, for instance, are applied to porcelain in common use at the present day, an attribution based on the greater or less resemblance of this modern ware to the Sung porcelain, at least in the matter of the glazes.
It is only quite of late years that we in Europe have been able to make any clear distinction, not only between the different classes of Chinese porcelain, but between what is Chinese and what is not. A few years ago the most characteristic porcelain of Japan was classed as Chinese, while on the other hand Corea and even local English factories were credited with porcelain made and decorated in one or other of the former countries.
It is nearly two hundred years since the famous letters of the Jesuit missionary, the Père D’Entrecolles, were written, and these letters still remain our best source of information for the processes of manufacture at King-te-chen. There was little further information on the subject from the Chinese side[25]until, in 1856,Stanislas Julien translated part of a Chinese work treating chiefly of the same porcelain factory—this is theKing-te-chen Tao Lu, a book which contains in addition some information about the history of the different wares. This translation was for many years the only native source of information available to students of Chinese porcelain, and many were the misconceptions and blunders in which these students were landed. The book was indeed accompanied by a preface and valuable notes by M. Salvétat, the porcelain expert of Sèvres, but Julien himself, though an eminent Chinese scholar, had no practical acquaintance either with the matter in hand or indeed with the country generally.
The beginning of a sounder knowledge of the subject was made when that collector of genius, the late Sir A. Wollaston Franks, published a catalogue of the private collection of Japanese and Chinese porcelain which he afterwards presented to the nation. His marvellous intuition and his vast experience enabled him to seize upon points of resemblance and difference which threw light upon the origin of the various wares, and to expose at the same time the inconsistencies of the arrangements then in vogue. He it was who first pointed out the general worthlessness, as a guide to the date or even the country of any piece of porcelain, of the name of dynasty and emperor which it might bear. His successor, Mr. C. H. Read, has well carried on the tradition. At the present moment the British Museum is one of the few places where an attempt has been made at a systematic arrangement of a representative collection of Chinese and Japanese porcelain.[26]
In the meantime in China itself, both in connection with the embassies at Pekin and among some of the merchants at Shanghai and other treaty ports, much information was being collected, and it was above allthe merit of Franks to keep himself in communication with and to encourage all such research. Dr. Hirth, long in the service of the Chinese at Shanghai and elsewhere, has published a series of learned studies treating of the relation of the Chinese to the Roman empire, of the Arab traders during the Middle Ages, and of the early history of Chinese porcelain generally. But it is to a former member of our embassy at Pekin, to Dr. Bushell, that we are above all indebted for the throwing open of Chinese sources of information upon the history of porcelain. A worthy successor of the Père D’Entrecolles in his intimate acquaintance with the country and its language, Dr. Bushell is well abreast of the chemical and technical knowledge of the day, and his position as physician to our embassy at Pekin has given him access to information from the best Chinese sources, as well as to the treasures of many of the native collections of the capital.
Dr. Bushell has written the text to a sumptuously illustrated work, nominally a catalogue of the collection of porcelain formed by the late Mr. Walters of Philadelphia, and into this text he has woven all the vast wealth of material that he had accumulated during many years of study both at Pekin and in Europe. This work has thus superseded all other sources of information on the history and manufacture of Chinese porcelain. He has, in fact, ransacked all that has been written in China on these subjects, and his translations have this advantage over the works of Julien, that they are made by one who knows thoroughly the subject that the Chinese author is dealing with.
We must not forget the researches on the chemical and technical side of the subject by what we may call the school of Sèvres. To these workers we have made frequent reference in previous chapters. It is to the experiments and analyses of men such as Brongniart, Salvétat, Ebelmen, and Vogt, that we are indebted forour knowledge of the chemical constitution of the paste, the glaze, and the enamels of Chinese porcelain, as well as for a rational exposition of the methods of its manufacture. To sum up, our sources of information of late years are, in the main, English, as far as the history and what I may call the sinology of our subject are concerned; but for the chemistry and technology we must turn to French works. As far as I know, little of value has been published in Germany on the subject of Oriental porcelain. The discussion between Karabacek, Meyer, and Hirth (whose later papers have been published in German) on the early history of celadon and on the Arab traders of the Middle Ages, is perhaps the most notable exception.
We are in the dark even now as to the date and place of origin of more than one class of Oriental porcelain. On the question of the relation of the ceramic wares of China to the contemporary sister arts, there are many points to be cleared up,—I mean especially the question how far the early wares were influenced by the art of the bronze-caster and the carver of jade, and again to what extent the decoration of porcelain in later times was dependent upon the example of the contemporary schools of painting. When we know about the pictorial art of the Chinese even the little that we do already of that of their Japanese neighbours, we shall, to give but one instance, be able to trace the source of the beautiful landscapes and flower designs that we find on the vases and plates of thefamille verteandfamille rose.
There is one source of information which remains as yet almost completely untapped. The Japanese have been for many centuries keen collectors of Chinese porcelain, as of other Chinese objects of art. They have their own views on its history, and some of the finest specimens of the older wares remain still in Japan, in spite of the many pieces that have of lateyears been carried away to Europe and America. As we shall see, they have in their own pottery and porcelain handed on to quite recent days many traditions of Ming and earlier times that have been lost in China. If some Japanese connoisseur or antiquary, strong in Chinese lore, could give us a history of porcelain from his own point of view, I think that European investigators would have cause to be grateful.
Much could be gleaned, as I have already said, by studying the relation of the potters art to that of the jade-carver and the caster of bronze, and this brings us to an important point that perhaps has not been fully appreciated by us in the West. I refer to the comparatively late date of the beginning of porcelain in China compared, for example, to the arts just mentioned. We can hardly carry back the history of true porcelain beyond the great Tang dynasty (618-907A.D.), and even in China there is no existing specimen that can safely be attributed to so early a date. But this same Tang dynasty was the very heyday in that country, not only of military power but also of artistic culture. It would be impossible to enter into this important subject here; it is one that has been strangely ignored by us in Europe. Suffice to say that the great figure-painters of this period were looked back to with veneration in later times, both in China and in Japan, and that the two schools of landscape, the colour school of the North and the black and white ‘literary’ school of the South—schools whose traditions have survived to the present day—were both founded by Tang artists. At that time art critics were known (and even honoured); they already wrote books on the early history of painting, and they have left us descriptions of famous collections.
We may expect, then, to find the influence of these more precocious arts on the early fictile ware of China, and indeed we see the quaint decoration and the nottoo beautiful outlines of the early hieratic bronzes repeated on the rare specimens that survive from the dynasty that after a period of unrest followed that of Tang. This was the Sung dynasty, which lasted till the time of the Mongol invasion in the thirteenth century.[27]
It is difficult for a European to appreciate the charm, or rather superlative excellence, that is found by a Chinaman in a fine specimen of jade. It is, however, a substance that is closely linked with his philosophy, his religion, and above all with his all-important ceremonial. No wonder, then, if from an early time he strove, with the pastes and glazes at his command, to imitate such a material. And numberless references in contemporary writers, as well as the evidence of many of the oldest pieces of porcelain surviving, show that this was the case. We may safely say that in these early specimens the thick glaze, of tints varying from a true celadon to a more pronounced blue or green, was admired in proportion to its resemblance to jade. As for the porcelain itself, all that was looked for in the paste was that it should be hard, and that the vessel when struck should give out a bell-like sound—‘a plaintive note like a cup of jade,’ as one early Chinese writer says of a porcelain cup in his collection.
The Chinese in these times possessed also elaborately carved vessels of rock crystal and of various kinds of chalcedony, and these also it was attempted to imitate with the early glazes. Glass, too, as a material for small objects, was probably known; it seems, however, to have been somewhat of a rarity. It is mentioned by writers of the Tang period in connection with these early wares, and indeed it is possible that there may be some confusion in the literature of the time (or rather perhaps in our interpretation of thelanguage used) between the two materials—the thickly glazed porcelain and the more or less opaque glass.
After these preliminary remarks we shall be in a better position to interpret the somewhat involved and contradictory allusions to our subject found in Chinese books.
We now come to the important question of the classification of Chinese porcelain. A difficulty here arises from the rival claims of two systems. The older and perhaps safer division depends solely on the nature of the ware, its colour, decoration, etc.; but in opposition to this the claim of the more logical, historical classification has, with our increasing knowledge, become of late years more pressing. The result has been an attempt to combine the two systems. Such an attempt must necessarily lead to many compromises, and yet something of the sort is perhaps the only available plan. We may compare the development of the ceramic art in China to what has taken place in the evolution of the animal kingdom: while new and more elaborated forms are evolved, the older ones, or many of them, survive in but slightly modified forms. If this tendency be borne well in mind there will be less danger of confusion between the really old types and the modern representations or even copies which are called, in China, by the same names.
The three classes into which Chinese porcelain is divided—and there is a general agreement among collectors on this head—rest on such an attempt to combine a historical with a technical classification:—
1. Porcelain with single-coloured glazes, including plain white ware. The colour of the glaze is derived from two metals only, iron and copper. Any further decoration depends upon the moulding of the surface or upon patterns incised in the paste. All the wares made up to the end of the Sung period (1279A.D.) may probably be included in this class.
2. Porcelain decorated with colour under the glaze. This division is nearly equivalent to our ‘blue and white’ ware, but in addition to cobalt, copper is at times introduced to give a red colour. This system of decoration was probably introduced during the course of the fourteenth century, and it is associated with the Ming dynasty.
3. Porcelain decorated with enamels over the glaze, necessitating a second firing in a muffle-stove. The use of these fusible enamel colours came in probably during the sixteenth century, but the art was not fully developed till much later.
The glazes of the first and second classes as a rule contained no lead, and to melt them the full heat of the oven, thegrand feu, was required.
There is, however, a class of porcelain which does not fall well into any of the above divisions, but which is historically of great importance. The blue, purple, and yellow glazes of this ware werepaintedon the biscuit after a preliminary baking of the paste, and then fired, not in the hottest part of the furnace, but in what we may call thedemi grand feu. The glaze of this ware contains lead, and this fact and the method of the decoration may be held to give it a position bridging over the interval between our first two classes and the third—that of enamelled porcelain. This ware,painted on the biscuit, dates, however, from an earlier time than the latter class, and must not be confused with it.
As I have pointed out, these types did not entirely replace one another, for the earlier forms continued to be made by the side of the later.
One of our principal difficulties in discussing the early wares of China is to reconcile and co-ordinate the various types described in old Chinese books with the few specimens surviving at the present day. Of these scanty examples we can point to scarcely any in publiccollections; the rare pieces that have been brought from China are in the hands of private collectors in England, France, and America. In the Chinese authorities we find as early as the tenth century references to porcelain which was ‘blue as the sky, brilliant as a mirror, thin as paper, and as sonorous as a piece of jade’; an emperor who reigned just before the accession of the Sung dynasty (960A.D.) demanded that the porcelain made for him should be ‘of the azure tint of the sky after rain, as it appears in the interval between the clouds.’ Compare with these descriptions the thick paste, barely translucent, the heavy irregular glaze, greyish white to celadon or pale blue, of the few specimens of undoubted antiquity that have survived to our day. How can we reconcile the tradition with the material evidence? Two explanations have been given of the discrepancy. According to one theory, all the more delicate and fragile pieces have disappeared ‘under the hands of time’ (or shall we say more definitely under those of endless generations of housemaids?), only the heavy, solid specimens surviving. The other theory is simpler: it is that the writers of the books are apt to fall into exaggeration when speaking of any matter that has the sanction of age—that, not to mince matters, they are as a class great liars; and this is a point of view that commends itself to those who have any acquaintance with Chinese literature.[28]
We have now, however, one source of information for these early wares upon which, although it is in a measure a literary source, we can place greater reliance.This is nothing less than an illustrated list, acatalogue raisonné, of famous specimens of porcelain, drawn up by a distinguished Chinese art connoisseur and collector as long ago as the end of the sixteenth century. In this manuscript there were more than eighty coloured reproductions of pieces, both from the author’s own collection and from those of his friends. The work came from the library of a Chinese prince of high rank, and it was purchased in Pekin by Dr. Bushell some twenty years ago. Since then this valuable document has perished in a fire at a London warehouse, where it had been deposited, but not before the illustrations had been copied by a Chinese artist and its owner had made a careful translation and analysis of its contents.[29]The writer, Hsiang-yuan-pien, better known as Tzu-ching, after giving a brief sketch of the early history of ceramics in his country, exclaims apologetically: ‘I have acquired a morbid taste for pot-sherds. I delight in buying choice specimens of Sung, Yuan, and Ming ware, and exhibiting them in equal rank with the bells, urns, and sacrificial wine-vessels of bronze dating from the three ancient dynasties, from the Chin and the Han’ (2250B.C.to 220A.D.)—that is to say, in placing them in the same rank as antiquities that are acknowledged to be worthy of the attention of the scholar. Porcelain at that time, we see, had hardly established its claim to so dignified a position; hence the apologetic tone. After telling us how with the advice of a few intimate friends he had selected choice specimens, which he then copied in colour and carefully described, Tzu-ching concludes with these words: ‘Say not that my hair is scant and sparse, and yet I make what is only fit for a child’s toy.’ This appeal is evidently addressed to the Lord Macaulays of his day.[30]
The first point to notice in this catalogue is that more than half of the objects described are attributed to the Sung period (960-1279A.D.), that is to say, they were at least three hundred years old at the time when Tzu-ching wrote. The Sung dynasty, we must bear in mind, was above all remembered as a period of great wealth and material prosperity. Less warlike than the Tang which preceded it, the arts were cultivated at the court of the pleasure-loving emperors who had their capital during the earlier time at Kai-feng Fu (in the north of Honan, near to the great bend of the Hoang-ho). When driven south by the advance of the more warlike Mongols they retired to Hangchow, the Kinsay of which Marco Polo has such wonderful tales to relate. In these early days there was no great centre for the manufacture of porcelain; it was made in many widely separated districts, so that the classification of these early wares is, in a measure, a geographical one. At King-te-chen, at least in the later Sung period, they were already making porcelain, but for court use only, it would appear, for at that time the factory was a strict imperial preserve, and its wares did not come into the market.
As to the still older wares, those of Ch’ai and of Ju, which generally hold the place of honour in Chinese lists, it was of the first that the emperor spoke when he commanded that pieces intended for his own use should be clear as the sky after rain; but no specimen of this porcelain was extant even in Ming times. Its place, it would seem, was taken by theJu Yao(the wordyaois about equivalent to our term ‘ware’), which, like the Ch’ai, came from the province of Honan. This ware also is now practically extinct; Tzu-ching, however, claims to have possessed some specimens, and of these he gives more than one illustration. The glaze was thick and like melted lard (a comparison often made by the Chinese), and varied incolour from aclair-de-luneto a brighter tint of blue. The name Ju, we may add, is often applied to more modern glazes which resemble the old ones in colour and thickness.
The nameKuan yao, which means ‘official’ or ‘imperial’ porcelain, has been the cause of much confusion; the term has been applied to any ware made for imperial use. That of the Sung dynasty was made in the immediate neighbourhood of the imperial court, first at Kai-feng Fu and later at Hangchow. In its more strict use the term Kuan yao is applied to pieces generally of archaic form, to censers ornamented with grotesque heads of monstrous animals, and to wares of other shapes copied from old ritual bronzes. The glaze varies in colour from emerald green to greyish green andclair-de-lune, it is generally crackled, the cracks forming large ‘crab-claw’ divisions. Other kinds are described as white and very thin, but of these, perhaps for one of the reasons given above, no examples have survived to our day.
Lung-chuan yaoandKo yao. It will be convenient to class together these two most important types of Chinese porcelain. At the present day these names are applied in China to some comparatively common varieties of porcelain, not necessarily of any great age. But more strictly Lung-chuan yao is the term used by the Chinese for the heavy celadon pieces, whether dating from Sung or from Ming times, which were the first kinds of porcelain to become a regular article of export; while the word Ko yao is used as a general name for many kinds of crackle ware, which may vary in colour from white to a full celadon. In a more restricted sense it includes only the early pieces with a greyish white glaze and well-marked crackles.
Lung-chuan warewas made during Sung times at a town of that name in the province of Chekiang, situated about halfway between the Poyang lake andthe coast. In Ming times the kilns were removed to the adjacent provincial capital, Chu-chou Fu, nearer to the coast. This was probably the ware that Marco Polo saw when passing through the town of Tingui. It was largely exported from the ports of Zaitun and Kinsay. It will, however, be better to defer the discussion of this thorny question to a later chapter, when we shall have something to say about the way in which the knowledge of Chinese porcelain was spread through the Mohammedan and Christian west. It will be enough for the present to mention that the Lung-chuan ware was the original type and always remained one of the principal sources of the Martabani celadon so prized in early Saracen times.
As this is the first time that we come across celadon ware,[31]we may mention that we use the term in the older and narrower sense for a greyish sea-green colour tending at times to blue. The name is, however, sometimes made to cover nearly the whole range of monochrome glazes. It is theChing-tsu[32]of the Chinese and theSei-jiof the Japanese.
The true Lung-chuan celadon of Sung times was, however, of a more pronounced grass-green colour. But we are concerned rather with the later celadon made at Chu-chou Fu during the Ming period. For it is to this time that we must refer most of the heavy dishes and bowls, often fluted or moulded in low relief with a floral design of peony or lotus flowers, or again with plaited patterns surrounding a fish or dragon