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CHAPTER   IV
DECORATION BY MEANS OF COLOUR

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 decoration sous 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 certain amount 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 pastes have 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-called pâte-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 the pâte, 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 the grand 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 and elsewhere, which require, for a term at least, to be subjected to a reducing flame.

The first of these glazes is the well-known Celadon, 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 famous Sang de bœuf and Flambé glazes.

The colour of the first is given by the red sub-oxide of copper, chiefly suspended in the glaze. In the case of the flambé or ‘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, is just before the 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 the Decoration under the Glaze is 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 the raw paste.

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 and not 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 time superimposed upon 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 the demi grand feu.²¹

Coloured Enamels. We have now to describe

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 the enamels 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 otherwise damage 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 is imitated. 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 (the famille 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.

CHAPTER   V
THE PORCELAIN OF CHINA

Introductory—Classification—The Sung Dynasty (960-1279)—The Mongol or Yuan Dynasty (1280-1368)

‘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 consistent laudator 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 subtle nuances in 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 charge of 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 side²⁵ until, in 1856, Stanislas Julien translated part of a Chinese work treating chiefly of the same porcelain factory—this is the King-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 all the 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 for our 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.