PORCELAIN.

Porcelain, in its more general signification, comprehends all kinds of earthen ware, which are white, semitransparent, and have some degree of a vitreous texture· Hence, in this extensive meaning of the term, it includes all kinds of pottery, stoneware, delft ware, &c. But in a more limited sense, the word Porcelain is employed to denote only the finer kinds of earthen ware; and because this kind of ware has been, from time immémorial, manufactured in the greatest degree of perfection in China, it has obtained the name of Chinese Porcelain, or China Ware.

In the Chinese language, porcelain is denoted by the word tse-ki, so that the derivation of the term is not to be sought for in that language; and hence it is supposed to be of European extraction, and to be derived from the Portuguese, in which language the word porcellano signifies a cup or vessel.

The first porcelain which was seen in Europe was brought from Japan and China. Its "whiteness, transparency, and fineness of texture, with its elegance and beautiful colours, soon introduced it as an ornament of the tables of the rich and powerful, whilst, at the same time, it excited the admiration and industry of the European manufacturer. Attempts were accordingly made to imitate this kind of ware, in different countries of Europe. The first European porcelains were made in Saxony. The manufacture was afterwards introduced into France, and successively into England, Germany, and Italy, where it has arrived at various degrees of perfection, according to the nature of the materials which can be obtained, and the industry and ingenuity of the artist who superintends and directs it. But after all, to whatever degree of perfection the manufacture of this ware has attained in Europe, it must still yield, in excellence and perfection, to the porcelain of eastern countries.

Of the antiquity of the manufacture of porcelain in China, little precise information can be expected from a people who have always shown themselves so extremely averse to the freedom of intercourse with other nations. But it is said that the village or town of King-te-ching has furnished the emperors of China with porcelain since the year 442 of the Christian era; and that it is an object of so much attention to the Chinese government, that the manufacture is carried on under the superintendence of one or two mandarins sent from court.

1. History of the Manufacture of Porcelain in China.

The fullest account which has as yet been received in Europe of the manufacture of Chinese porcelain, has been given by Father D’Entrecolles, a Catholic missionary, who lived for some time in the village or town where the principal manufactory was established. The account which has been given by the Jesuit of this village, and of the manufacture of porcelain, is extremely interesting.

This village or town, which is celebrated as producing the best porcelain of China, is in the province of Kiang-si, and is said to be a league and a half in length, containing not less than 1,000,000 of inhabitants. Other manufactories, indeed, have been established in different parts of the Chinese empire, and particularly in those places which are convenient for the European trade, as in the provinces of Fo-kien and Canton; but the porcelain produced at these is said to be held in inferior estimation. A Chinese emperor wishing to have a manufacture of porcelain under his own inspection at Pekin, ordered workmen to be collected for the purpose, with all the necessary materials and implements; but after erecting furnaces and other expensive operations, the attempt failed, so that, in the time of D’Entrc-colles, King-te-tching continued to be the most celebrated place in China for beautiful porcelain; and from this it was transported to all parts of the world.

The chief ingredients which enter into the composition of fine porcelain are petuntse and kaolin, two kinds of earth from the mixture of which the paste is obtained. The petuntse is of a pure white, and, when fully prepared, is in the form of an impalpable powder, so that it is very fine to the touch. The kaolin, he observes, is intermixed with small shining particles. These materials arc carried to the manufactory in the shape of bricks. The petuntse originally consists of the fragments of rock dug out from certain quarries, and reduced to powder; and the colour of the stone which answers the purpose best, according to the Chinese, inclines somewhat to green. The fragments of rock are broken to pieces with a large iron club; they are then put into mortars, and by means of levers headed with hard stone, strongly secured with iron, they are reduced to the state of fine powder. The levers, it is scarcely necessary to observe, are moved either by the labour of men, or by water. The powder, which is afterwards collected, is then thrown into a large vessel full of water, which is strongly agitated with an iron shovel. When this mixture has been allowed to settle for some time, a substance resembling cream rises to the top, which is skimmed off, and poured into another vessel also filled with water. The water in the first vessel is again agitated, and the frothy substance which rises to the surface is collected as before, and the same operation is repeated till it appear that nothing remains but a coarse sediment which falls to the bottom by its own weight. This sediment is then carefully collected, and again subjected to the process of pulverization.

The fluid in the second vessel is allowed to remain at rest till a sediment is produced, forming a kind of crust at the bottom; and when the water above seems to be quite transparent, it is poured off by gently inclining the vessel, that the sediment may not be disturbed. The paste is then put into large moulds, and allowed to dry slowly; but before it becomes quite hard, it is divided into small square cakes, which are sold by the hundred. This is the substance which is called by the Chinese petuntse, and the name is said to be derived from the colour and form of this paste.

The kaolin, the other substance which is employed in the fabrication of porcelain, requires fewer operations in its preparation than the former, as it is found in nature in a state almost ready for the manufacturer. Of this substance it is said, that there are extensive mines in certain mountains, the external strata of which are composed of a kind of red earth. The kaolin is found in these mines in small lumps, and it is formed into bricks by being subjected to a similar process with the petuntse.

The fine porcelain, it has been observed, derives its fabric and texture from the kaolin. It is to this that the qualities which it possesses of resisting the most powerful heat is owing; whilst its strength and consistency is obtained by fusion with the petuntse, which enables it to resist the action of the more powerful agents. D’Entrecolles relates an anecdote which he received from a rich Chinese merchant, that the English and Dutch having purchased a quantity of petuntse, conveyed it to Europe for the purpose of manufacturing[7:18:430] porcelain; but having procured none of the kaolin, the attempt failed. They wanted, added the Chinese with a smile, to form a body, the flesh of which would support itself without bones.

It is said that the Chinese have latterly discovered a new substance which may be employed in the composition of porcelain. This stone is called hoa-chè, the first part of the word signifying glutinous, because it is of a saponaceous quality. Porcelain made with this substance is very rare, and bears a much higher price than any other. The grain is extremely fine, and the painting with which it is ornamented, when compared with that of common porcelain, appears to exceed it as much as vellum surpasses paper. This variety of porcelain, it is added, is also remarkable for its lightness. It is besides much more brittle, and it is found very difficult to hit upon the proper degree of heat for tempering it. This substance, we are farther informed, is but rarely employed in the fabrication of the body of the porcelain; the reason of which perhaps is, the scarcity and high price of this precious article, in consequence of which the workman is contented with making it into a fine size, into which the vessel is immersed when it is dry, that it may receive a coat before.it is painted and glazed; and by this process he finds that he can commmunicate to the ware a very high degree of beauty. The previous processes employed in the preparation of this substance are similar to those which are followed in the preparation of kaolin. When hoa-chè is extracted from the mine, it is washed in rain or river water, for the purpose of separating a yellowish earth with which it is contaminated. It is then reduced to powder, thrown into a vessel filled with water, and then formed into cakes. The hoa-chè prepared in this manner, without the addition of any other earth, is said to be alone sufficient in the fabrication of porcelain. It is employed, as has already been noticed, as a substitute for kaolin; but, on account of its scarcity, it is much dearer. The price of the former is three times that of the latter, and from this circumstance the value of porcelain made with hoa-chè is much higher than that which is manufactured with kaolin.

The principal ingredients in the fabrication of porcelain are petuntse and kaolin; but to these must be added the glaze or varnish, or, as it is called in the account given of Chinese porcelain, the oil, on which depend its splendour and whiteness. This varnish is of a whitish colour, and is obtained from the same kind of stone which yields the petuntse; but for this purpose the whitest stone is always preferred. The glaze is obtained by a process similar to that which is followed in the preparation of petuntse. The stone is first washed and reduced to powder; it is then thrown into a vessel filled with,water, and after being purified, a frothy matter rises to the surface. To 100 pounds of this matter, one pound of a substance called che-kao, is added. This latter is a saline substance, somewhat like alum, which is put into the fire, and allowed to remain till it become red hot, when it is reduced to powder. By the addition of this substance the glaze acquires a greater degree of consistence; but at the same time a proper degree of fluidity-must be preserved. The glaze prepared in this manner is not employed alone. Another glaze is mixed with it, which is obtained from lime and ashes; to 100 pounds weight of which is also added one pound of che-kao, or the aluminous substance mentioned above. When the two substances are mixed, it is necessary to attend that they be nearly of the same consistence, and the workman ascertains this point by,dipping into each of them some cakes of petuntse; and by a close examination of their surfaces after they are drawn out, he is able to judge of the consistence of the fluids. The proportions of the two which are usually employed, are ten parts of the glaze obtained from the stone, to one of that which is prepared from the lime and from ashes.

In the manufacture of the Chinese porcelain, the first process, after the separate preparation of the materials, is a second purification of the petuntse and kaolin; and when these are found to be in a state of sufficient purity, the workmen proceed to mix the two ingredients together. The proportions employed for the finer kinds of porcelain are equal parts of kaolin and petuntse; for an inferior kind, four parts of kaolin to six of petuntse are employed; and in some kinds of porcelain, only one part of the former is added to three of the latter. This is the smallest proportion of kaolin which is employed in the Chinese manufactories. When the proportions are fixed, and the mixture finished, the mass is thrown into a large pit, which is well paved and cemented. It is then trodden upon, and kneaded till it become hard. This is the most fatiguing part of the labour, for it must be continued without intermission. From the mass prepared in this manner the workmen detach different pieces, which they spread out upon large slates, where they knead and roll them in all directions, taking care that no vacuum be left, and that there be no intermixture of any foreign body. The whole work would be entirely spoiled by the addition of a hair, or a particle of sand. W r hen the paste has been properly prepared, the porcelain, when exposed to heat in the furnace, retains its form without becoming soft, or entering into fusion, and becomes semitransparent, without exhibiting cracks or superficial fissures; but when there is any defect in the mixture or preparation, the porcelain cracks, and becomes warped, or melts in the furnace.

The paste being thus prepared, the next operation is to form the vessels for which it is designed. All kinds of plain ware are formed with the wheel. When a cup, for instance, has undergone this operation, the outside of the bottom is quite round. The workman first gives it the requisite height and· diameter, and it comes from his hands almost the moment he has received it. Great dexterity and expedition are absolutely necessary, on account of the low price of labour in these manufactories. A workman, it is said, scarcely receives a farthing per board, each board containing no less than twenty-six pieces. The cup then passes to a second workman, by whom the base is formed; after which it is delivered to a third, who applies it to the mould, and gives it the proper form. When it is taken off the mould, it must be carefully turned,and not pressed more to one side than the other; for without this necessary precaution it would become warped or disfigured. The business of the fourth workman is to polish it with the chisel, especially round the edges, and diminish the thickness, in order to give it the proper degree of transparency. Having at length passed through the different hands from whom it receives its form and various ornaments, it then comes to the last workman, who forms the bottom with a chisel. It is wonderful, we are told, to see with how much dexterity and expedition the workmen convey the vessels from one to another; and it is added, that a single piece of porcelain,' before it is completely finished, must pass through the hands of no fewer than seventy different workmen. It w is indeed, we may observe, to this minute division of labour that its low price is owing; and on the same circumstance depend the remarkable dexterity and expedition which have already been noticed.

In the execution of large works of porcelain, different parts are first formed individually; and when all the pieces are finished, and nearly dry, they are put together and cemented with a paste formed of the same substance, and softened with water. Some time afterwards the seams are polished with a knife on both sides of the vessel, so that when it is covered with a varnish, or glazed, they are so completely concealed, that the least trace of them is not perceptible. It is in this way that spouts, handles, rings, and other parts of a similar nature, are united. And in this way, [7:18:431]particularly are fabricated those pieces which arc formed upon moulds, or by the hand, such as embossed works, grotesque images, idols, figures of trees or animals, and busts. All these are formed of four or five pieces joined together, which are afterwards brought to perfection by means of instruments proper for carving, polishing, and finishing the different traces which the mould has left imperfect. Flowers and ornaments which are not in relief, are either engraved, or the impression is made by means of a stamp; but ornaments in relief are prepared separately, and added to the pieces of porcelain to which they are destined.

The piece of porcelain being prepared according to the operations now described, is next conveyed to the painter; and in this art it is to be observed that the Chinese workmen follow no certain rule, and seem to be unacquainted with any of the principles of perspective. Their knowledge is the effect of practice, guided often by a whimsical imagination. The labour of painting porcelain in the Chinese manufactories is also divided amongst a great number of hands. The business of one man, for instance, is solely limited to the tracing out the first coloured circle with which the brim of the vessel is adorned; another designs the flowers, and a third paints them. One delineates waters’ and mountains, whilst it is the province of another to draw and paint birds and other animals. Of the painting on Chinese porcelain, it has been observed, that the human figure is often most indifferently executed s

A peculiar kind of glaze or varnish, we are informed, is obtained from white flint. This glaze, it is said, has the singular property of making the pieces of porcelain to which it is applied exhibit the appearance of veins distributed in all directions. Vessels glazed with this material seem as if the surface were cracked, without the fragments being separated or displaced. The colour of this glaze is whitish gray; and when it is applied to porcelain having an azure blue ground, it communicates a beautifully-variegated appearance. Vases of Chinese porcelain are sometimes fabricated in a different manner. They are ornamented with a kind of fret-work, which has something of the appearance of fine lace, in the middle of which is placed a cup proper for holding any liquid; which constitutes one body with the surrounding fret-work.

We are informed that the Chinese workmen formerly possessed the secret of fabricating a kind of porcelain of a much more singular nature. On the sides of the vessel thus formed were painted the figures of fishes, insects, and other animals, which could not be seen unless the vessel was filled with water. It is said that this secret is in a great measure lost; but the following is given as part of the process of preparing this kind of porcelain. The vessel which is to be painted, for the purpose of producing this peculiar effect, must be extremely thin and delicate. When it is dry, the colour is laid on, not upon the outside, however, as is usually the case, but upon the inside of the vessel; and it is laid on pretty thickly. The figures which are painted upon it are usually fishes, as being more characteristic of the element in which they live. When the colour is perfectly dry, it is then coated over with a kind of glaze, composed of porcelain earth, so that the azure is thus enclosed between two layers of earthy matter; and when the glaze becomes dry, the workman pours some oil into the vessel, and putting it upon a mould, applies it to the lathe. Porcelain fabricated in this manner, having received its consistence and body within, it is the object of the workmen to make it as thin as possible on the outside, without penetrating to the colour. The external surface is then dipped into a mixture for glazing, and when it is dry it is baked in a common furnace. This kind of porcelain is known by the name of kia-tsing, signifying pressed azure. It is supposed that the Chinese do not at present possess the art of making porcelain of this description, which requires a great deal of dexterity and delicate management; and it isadded,that they have imperfectly succeeded in the attempts which have been occasionally made to discover the secret of this curious process.

The next process in the manufacture of porcelain is baking; but before we describe the method of arranging and managing the furnaces employed for this purpose, we shall give a short account of their construction. The Chinese furnaces for baking porcelain are furnished with a long porch, for the purpose of conveying air, and in some measure as a substitute for bellows. This porch answers the same purpose as the arch of a glass-house; but the furnaces which, as the author from whom the account is taken observes, were formerly only six feet in height, and the same in length, are now constructed upon a much more extensive plan. They are twelve feet in height, and nearly four in breadth; and the roof and sides arc so thick, that the powerful heat which is applied internally does not penetrate to the outside, at least so much as to be inconvenient to bear it on the application of the hand. The dome or roof is in the form of an inverted funnel, having a large aperture at the top by which the smoke escapes. Beside the principal aperture, there are five others of smaller dimensions, which are covered with broken pots in such a manner that the workman can increase or diminish the heat as he finds it necessary. Through these apertures also he is able to see the progress of the baking of the porcelain, and can judge when it is completed. By uncovering the hole which is nearest the principal opening, he opens with a pair of pincers one of the cases containing the pieces of porcelain, and if he perceives a bright fire in the furnace, and all the pieces brought to a red heat, as well as the colours of the porcelain appearing with a full lustre, he concludes that the process is finished. He then diminishes the fire, and entirely shuts up the mouth of the furnace for some time. In the bottom of the furnace there is a deep hearth about two feet in breadth, over which a plank is laid, in order that the workmen may enter to arrange the porcelain. When the fire is kindled on the hearth, the mouth of the furnace is immediately closed up, and an aperture is left only sufficient for the admission of faggots, about a foot in length, but very narrow. The furnace is first heated for a day and a night, after which two men keep continually throwing wood into it, and relieve each other by turns. One hundred and eighty loads are consumed for one baking. As the porcelain is burning hot, the workman employs for the purpose of taking it out, long scarfs or pieces of cloth, which are suspended from his neck.

Having thus given a concise account of the construction of the Chinese furnaces, we procced now to lay before our read ers an account of the method of baking porcelain which is followed in that country. After the porcelain has received its proper form, its colours, and all the intended ornaments, it is transported from the manufactory to the furnace, which is sometimes situated at the other end of the village already mentioned. In a kind of portico which is erected before it, may be seen vast numbers of boxes and cases made of earth, for the purpose of inclosing the porcelain. Each piece, however inconsiderable it may be, has its own case; and the Chinese workman, by means of this procedure, imitates nature, which, in order to bring the fruits of the earth to maturity, clothes them in a covering, to defend them from the excessive heat of the sun during the day, and from the severity of the cold during the night.

A layer of fine sand is put into the bottom of these boxes, which is covered over with the powder of kaolin, to prevent the sand from adhering too closely to the bottom of the vessel. The piece of porcelain is then placed upon this bed of sand, and pressed gently down, in order that the sand may take the form of the bottom of the vessel, which does not touch the sides of its case; but thecase has no cover.
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A second, prepared in the same manner, and containing its vessel, is fitted into the first, so that it entirely shuts it, without touching the porcelain which is bclow; and thus the furnace is filled up with piles of cases, which defend the pieces they contain from the direct action of the fire.

With regard to small pieces of porcelain, such as teacups, they are inclosed in common cases about four inches in height. Each piece is placed upon a saucer of earth about twice as thick as a crown piece, and equal in breadth to its bottom. These small cases are also sprinkled over with the dust of the kaolin. When the cases are large, the porcelain is not placed in the middle, because it would be too far removed from the sides, and consequently from the action of the fire.

These piles of cases are put into the furnace, and placed upon a bed of coarse sand six inches in thickness; those by which the middle space is occupied are at least seven feet in height. The two boxes which are at the bottom of each pile remain empty, because the fire acts too feebly upon them, and because they are partly covered by the sand. For the same reason, the case which is placed at the top of each pile is also allowed to remain empty. The piles containing the finest porcelain are placed in the middle part of the furnace; the coarsest are put at its farthest extremity; and those pieces which have the most body and strongest colouring are near its mouth. These different piles are placed very closely in the furnace; and they materially support each other by pieces of earth, which bind them at the top, bottom, and middle, but in such a manner, that a free passage is left for the flame to insinuate itself everywhere around them.

The Chinese divide their porcelain into several kinds or classes, distinguishing each according to the different degrees of beauty and fineness. The whole of the first or most perfect kind is reserved for the emperor; none of it, we are assured, ever comes into the hands of the public, unless, on account of blemishes or imperfections, it is unworthy of being presented to the sovereign. Many have doubted whether at any time the largest and finest porcelain of China has ever been brought to Europe. None of that kind, at least, is offered for sale at Canton. The Chinese, who are apt to undervalue the productions of other countries, entertain a favourable opinion of the Dresden porcelain, and hold in still higher estimation the porcelain which is produced in the French manufactories.

The following is a short account of the Chinese porcelain manufactures by Sir George Staunton. “From the river,” says he, “were seen several excavations made in extracting from the sides of the adjoining hills, the petuntse useful in the manufacture of porcelain. This material is a species of fine granite, or compound of quartz, feldspar, and mica, in which the quartz seems to bear the largest proportion. It appears from several experiments, that it is the same as the growan stone of the Cornish miners. The micaceous part, in some of this granite from both countries, often contains some particles of iron, in which case it will not answer the pottefs purpose. This material can be calcined and ground much finer by the improved mills of England, than by the very imperfect machinery of the Chinese, and at a cheaper rate than the prepared petuntse of their own country, notwithstanding the cheapness of labour there.

“The kaolin, or principal matter mixed with the petuntse, is the growan clay also of the Cornish miners. The wha-she of the Chinese is the English soap-rock; and the she-kan is asserted to be gypsum. It was related by a Chinese manufacturer of that article, that the asbestos, or incombustible fossil stone, entered also into the composition of porcelain. A village, or unwalled town, called Kin-te-chin, was not very far distant from this part of the present travellers route, in which 3000 furnaces for baking porcelain were said to be lighted at a time, and gave to the place at night the appearance of a town on firc. The genius or spirit of that element is indeed, with some propriety, the principal deity worshipped there. The manufacture of porcelain is said to be precarious, from the want of some precise method of ascertaining and regulating the heat within the furnaces, in consequence of which their whole contents are baked sometimes into one solid and useless mass. Mr. Wedgwood’s thermometer, founded on the quality observed by him, of clay contracting in proportion to the degree of fire to which it is exposed, might certainly be of use to a Chinese potter.”

2. Inquiries of Peaumur into the Nature of Porcelain.

The first scientific investigation which was made into the nature of porcelain, was undertaken by the celebrated Reaumur; and the result of his researches was communicated to the French Academy of Sciences in the years 1727 and 1729. It was not the external form or appearance, nor was it the decorations of painting and gilding, which are by no means essential to porcelain, that constituted the object of his inquiries. His examination was particularly directed to the peculiar texture and fabric of this substance, with the view of ascertaining the nature and proportions of its constituent parts. For this purpose, he broke to pieces some of the Japanese, the Saxon, and the French porcelains, and carfully noted the peculiarities and differences in their texture. The grain or texture of the Japanese porcelain appeared to possess a considerable degree of closeness and compactness, with a smooth and somewhat shining aspect. He found that the Saxon porcelain was still more compact, and that it was smooth, and shining like enamel, but had nothing whatever of the granular texture. In his examination of the French porcelain, he observed that it had much of the shining appearance, and that its grain was not so close and fine as that of the oriental porcelain, having some resemblance to the grain or texture of sugar. Such were the observations which occurred to the French philosopher at the commencement of his inquiries into the nature of porcelains; and hence he justly concluded, that they were characterised by very marked differences.

Proceeding in his investigation, the same philosopher subjected different porcelains to the action of heat; and the result of his experiments with this powerful agent proved, that they might be distinguished by still more decisive characters. It appeared that the porcelain of the East suffered no change from the action of the greatest heat, whereas that of European manufacture underwent fusion at no very high temperature. This remarkable difference between the Chinese and European porcelains, suggested to Reaumur an ingenious thought, which at last led him to the discovery of the true nature of the composition of porcelain. Having observed that all porcelains have some resemblance to glass in some of their general properties, although they are less compact, he considered them as in the state of a semi-vitrified substance. An earthy substance, he observed, may be in a semi-vitrified state in two ways. It may, in the first place, be entirely composed of vitrifiablc or fusible matters; and this being the case, when it is exposed to the action of fire, provided the heat be sufficiently strong and long continued, it will be melted or vitrified. But as this change is not effected instantly, particularly where a violent degree of heat is not applied; and as it passes through different degrees, the progress of which may be more easily observed, according as the heat is managed and regulated, it followed, that by stopping in proper time the application of the heat to porcelain prepared in this way, the ware may be obtained in an intermediate state between those of crude earths and completely vitrified substances; whilst, at the same time, it possesses the semitransparcncy and other distinguishing properties of porcelain. Porcelain of this nature, it is well known, being exposed to a stronger degree of heat, undergoes perfect fusion and complete vitrification. All [7:18:433]the European porcelains which were subjected to experiment by Reaumur, were found to be of this fusible nature.

But on the other hand, porcelain may be composed of fusible or vitrifiable matter, mixed in certain proportions with another matter, which is absolutely infusible in the strongest heat to which it can be exposed in the furnace; and hence, if a mixture of this kind be subjected to a heat sufficient to melt entirely the vitrifiable part of its composition, this will enter into fusion; but being mixed with another matter which is infusible, and which consequently retains its consistency and opacity, the whole will form a compound, partly opaque, and partly transparent, or, in other words, a semitransparent mass; that is, a semivitrified substance, or porcelain, but possessing qualities totally distinct from those of the former. For as the fusible part of the latter has been brought to its utmost degree of fusibility during the process of baking, although the compound may be exposed a second time to a still stronger degree of heat, it will not approach nearer to complete vitrification, that is, it will retain all the qualities of perfect porcelain. Reaumur found that the porcelain of the East was distinguished by the properties now described; and hence he concluded, that its component parts were arranged upon the principle above mentioned. This opinion was afterwards confirmed by incontrovertible facts, deduced from a train of the most satisfactory and well directed experiments.

The ingredients which enter into the composition of the Chinese porcelain, namely, the petuntse and kaolin, were the next object of Reaumur’s inquiries. Having obtained quantities of each, he subjected them separately to a strong heat, and he found that the petuntse entered into fusion, without addition; but it appeared that the kaolin was absolutely infusible. He then mixed the two ingredients, formed into cakes, and exposed them in a furnace to the proper degree of heat; so that by baking they were converted into porcelain exactly similar to that of the Chinese. From these experiments it appeared, that the petuntse of the Chinese was a vitrifiable substance, and that the kaolin was of a different nature, quite refractory, and totally infusible. After this discovery, Reaumur, it would seem, entertained hopes that he might find materials in France, capable of making porcelain, which should possess the same valuable qualities as that of China; but whether hisresearches in the discovery of proper materials in his own country, particularly that which corresponds to the petuntse of the Chinese, were baffled, or whether he was prevented by other avocations from prosecuting his inquiries, does not appear. In his second memoir upon porcelain, however, we find, that he afterwards attempted to compose an artificial petuntse, by mixing vitrifiable stones with such salinebodies aswere capable of rendering them fusible, or even by substituting for this artificial preparation glass ready formed, with the addition of such matters as he supposed might be successfully employed in the place of kaolin. But it would appear that he did not at the time prosecute his inquiries; for the subject was not resumed until the year 1739, when he announced the discovery of a process for converting common glass into a peculiar kind of porcelain, which has been since known by the name of Peaumur’s porcelain.

Although it must appear, from the detail now given, that Reaumur was directed in his researches by the true spirit of philosophical inquiry, he seems to have been misled in certain points. One of his errors was relative to the Saxon porcelain, which he confounded with the other fusible porcelains of European manufacture, unless it be supposed that the porcelain of Saxony was formerly composed of entirely fusible or vitrifiable matters, and that it was porcelain of this description which he examined; for it is now certain, that all the porcelain of that country is capable of resisting the most powerful heat, and is therefore equally infusible with that of China or Japan. The appearance of the in ternal texture of the Saxon porcelain may perhaps have led the philosopher to this erroneous conclusion; for when it is broken, the internal surface does not exhibit a granular texture, but is uniform, smooth, shining, and compact, having a great resemblance to white enamel. This appearance, however, so far from proving that the porcelain of Saxony is a fused or vitrified substance, shews that it is not entirely composed of fusible matters. The internal surface of the most fusible porcelains, it is well known to those who are acquainted with the subject, is also the least dense, and the least compact; for no vitreous matter can be internally smooth and dense, without having been in a state of complete fusion.

The Saxon, like every other porcelain, especially that of China and Japan, contains a fusible substance, which has been in a state of complete fusion during the process of baking. The density and the internal lustre depend chiefly on this fused matter; but it is also certain, that the Saxon porcelain contains a large proportion of a substance which is absolutely infusible, and from which it derives its beautiful white appearance, its firmness and solidity, during the process of baking. It is this infusible substance which is to be considered as the substitute for the kaolin of China, and which possesses the property of contracting its dimensions, whilst it unites with the fusible material. The Saxon porcelain, therefore, is not to be confounded with porcelain manufactured with vitreous and fusible material; for it seems to be equally excellent as that of Japan, and in some of its properties perhaps superior, as will appear from an examination of the qualities which constitute the peculiar excellence of porcelain.

Reaumur seems likewise to have taken an erroneous view of the nature of the Chinese kaolin. According to his account, this matter is a fine talcky powder, from the mixture of which with petuntse, the porcelain of the East is manufactured. It is not impossible, as has been observed, that a porcelain similar to the Chinese might be produced from a talcky substance of this nature mixed with petuntse; but it is well known to those who are at all familiar with the manufacture of any porcelain, that no vessels can be formed, unless the paste of which they are made possess that degree of ductility and tenacity which renders them fit for being worked upon the lathe, or fashioned in the mould. But substances of a talcky nature, to whatever degree of fineness they may be reduced, never acquire the requisite ductility and tenacity which clays of all earthy substances only possess. But as it appears that the Chinese porcelain has been turned upon the lathe, it is obvious that they must have been formed of a very tenacious paste; and hence it is concluded, that kaolin is not purely a talcky matter, but an infusible clay, which, with the petuntse, a fusible material, forms the ingredients which enter into the composition of Chinese porcelain.

3. Peculiar Properties of Porcelain.

It may be worth while now to consider what are the properties which constitute the perfection ofporcelain; and here it is necessary carefully to discriminate between the qualities which are to be regarded as only contributing to the external decoration, and the intrinsic and essential properties in which the fabric and perfection of porcelain consist. Those who have been occupied in experiments upon this subject, have not found itdifficult toform compositions which are very white, beautifully semi-transparent,and covered with a shining glazing, but which are extremely deficient in the more essential properties. It appears, indeed, that they cannot be subjected to the necessary operations in first forming the ware, for want of a proper degree of tenacity, that they are not sufficiently compact, and are quite fusible, subject to break by the sudden application of heat or cold, and from the softness of the glazing, which cracks and becomes rough, are [7:18:434]soon deprived of their lustre. On the other hand, it is by no means difficult to form compositions of pastes, which are very tenacious, and which are capable of being easily worked and well baked, and in the process of bakingwhich acquire the requisite degree of hardness and density; which are infusible, and capable of resisting the effects of sudden changes of heat and cold; and which, in short, possess all the qualities of the most excellent porcelain, excepting its whiteness and transparency. Materials fit for the composition of such porcelains, it will appear, may be found in abundance in most countries; but those fit for the manufacture of the finer and more perfect porcelains, seem to be sparing productions of nature; and therefore the best kind of porcelain, it is presumed, will always be regarded as a valuable and high-priced commodity.

It may be observed that the potteries called stoneware, such as the brown made at Lambeth and some other places, and the white formerly made at Burslem in Staffordshire, which were glazed by salt, or muriate of soda, being thrown into the furnace when in a state of high fusion, possess all the essential qualities of the Japanese porcelain; for, excepting the whiteness,onwhich alone the semitransparency depends, if we compare the properties of the Japmese porcelain with those of our stoneware, little difference is found to exist between them. Both seem to possess the same granular texture; both have the same sonorous quality, when struck with a hard body; both have the same density; they possess also the same hardness, by which they strike fire with steel; they can resist the effects of the heat of boiling liquors without breaking, and are equally infusible when subjected to the most violent heat. Hence it is inferred, that if the earth which enters into the composition of stoneware, were free from foreign colouring matters, which prevent the whiteness and semitransparency, and if the vessels were carefully formed and covered with a very fine glaze, they would not be less per-feetthan the porcelain of the East. (See Pottery.) Earths fit for the production of the more perfect kinds of porcelain are supposed to be more rare in Europe than in Japan and China; and hence probably it has happened, that, from the want of these earths, the first manufacturers of the porcelain in Europe confined themselves to an external imitation, by employing only vitrifiable matters with fusible salts, and small quantity of white earth, of which fusible and vitreous porcelains were composed.

One of the most valuable qualities of porcelain is the property of resisting sudden alternations of heat and cold, in which the European porcelain exceeds that of China or Japan. The quality of porcelain, it is to be observed, is not to be judged of by a slight trial; for as numerous circumstances concur to render a piece of porcelain capable or incapable of resisting the effects of heat or cold, boiling water may be at the same time poured into two vessels, one of which is good porcelain, and the other of an opposite quality, it is not impossible that the former may break, and the latter may remain entire. The true method of discovering what is good porcelain, is to examine several pieces which are in daily use; and it has been found, that in many pieces of porcelain of oriental manufacture, which have been long used, cracks are seen in the direction of their height, which are never perceived in the more perfect porcelains of European manufacture.

It has long been a very general opinion, that the Japanese porcelain is the most perfect; it has indeed continued to be the object of admiration and emulation, and has been held up as a model for the European manufacturer. But the taste of Europeans having required a porcelain possessing the qualities of transparency and whiteness in a greater degree than that of Japan, the attempts to imitate it have been mostly confined to experiments. It has therefore been erroneously contended that an article equal to the Japan porcelain cannot be produced in Europe. The Saxon porcelain has been considered as inferior to the Japanese, on account of its greater smoothness, lustre, and less granular aspect of its internal texture; qualities in which it ought really to be regarded as superior to the porcelain from Japan.

4. Porcelain Maìiufactories in different parts of Europe.

Manufactories of porcelain have been long established in almost every country of Europe, but from the experiments of Reaumur it would appear that the only kind then manufactured was the soft porcelain, ox porcelaine tendre. It has been seen that the Saxon manufacturers charged him with mistake in classing theirs with the soft porcelain; but by admitting that he might have operated upon an article formerly made by them, it is proved that all European porcelain was originally of this kind. Besides that of Saxony, which was the first established in Europe, porcelain is made to a considerable extent at Vienna, at Frankendal, in the neighbourhood of Berlin, and in other places in the German states. The German porcelains are similar to those of Saxony, and are composed of similar materials, although from certain differences in the proportions, or in the modes of managing the manufactories, considerable differences arise in the porcelains manufactured at different places. When Μ. de la Condamine travelled into Italy, he visited a manufacture of porcelain established at Florence by the Marquis de la Ginor, who was at that time governor of Livorno. The French traveller was particularly struck with the large size of some of the pieces of this porcelain. Statues, and even groups of figures half as large as nature, and modelled from some of the finest antiques, were formed of it. The furnaces, he observed, in which the porcelain was subjected to the process of baking, were constructed with a great deal of ingenuity, and were lined with bricks made of the same materials as those which entered into the composition of the porcelain itself; and hence they were able to resist the effects of high degrees of heat. The paste of the porcelain manufactured at Florence appeared to be extremely beautiful, and to possess all the qualities of the best oriental porcelain. The glazing employed in this manufactory seemed to be inferior in whiteness, a circumstance which is supposed to be owing to the desire of using those materials only which are found in the country.

It must be allowed that the labours of the French have been crowned with wonderful success in the improvement and perfection of this manufacture. Some time before even Reaumur communicated the result of his inquiries, porcelain was manufactured at St. Cloud, and also in the suburb of St. Antoine at Paris. This porcelain indeed was of the vitreous or fusible kind, but at the same time it possessed no inconsiderable degree of beauty. Since the period to which we allude, extensive manufactories of porcelain have been established at Villeroy, Chantilly, and Orleans, and at those places the manufacture has been brought to a high degree of perfection. But the great seat of the manufacture is now in the Limousin, where the raw materials are found, and whence the porcelain in a white state is sent to Paris and other places on the continent, to be ornamented. The productions of the celebrated royal porcelain manufactory at Sevres, near Paris, on account of the pure shining white, the fine glazing and coloured grounds, the splendour and magnificence of the gilding, and the elegance and taste displayed in the shape and figures, are universally allowed to surpass every thing of the kind which has yet appeared. It must be remarked, however, that this manufactory at Sèvres, wherein the “ porcelain dure” is produced in so great a degree of perfection, is not carried on with a view to profit, but has received occasional grants of money from the government, as a national concern.

In speaking of the French porcelain, we may notice the result of some researches which were made on this subject [7:18:435]by Guettard, and of which an account appeared in the Memoirs of the Academy of Sciences, for the year 1765. In the neighbourhood of Alençon, Μ. Guettard discovered a whitish argillaceous earth, in which he found that mica considerably predominated. This earth he employed as a substitute for kaolin. The substance which he used instead of the petuntse, he obtained from a hard stone, which is described as a quartzose gritt stone, very abundant in that country, and with which the streets of Alençon are paved. With these materials Guettard instituted a series of experiments on porcelain, previously to the year 1751, and was associated in his inquiries with the Duke of Orleans. For many years the Count de Lauraguais, a member of the Academy of Sciences, was keenly engaged in prosecuting experiments to discover the true nature ofporcelain, and the means by which the manufacture might be improved and perfected. To obtain the object of his researches, which was to produce porcelain that in its essential qualities might be equal to that of eastern countries, he spared no trouble or expense; and it would appear that he was not unsuccessful in his labours; for in the year 1766, when he exhibited some species of porcelain from his manufactory to the members of the Academy of Sciences, the persons who were appointed by that learned body to examine their properties, delivered it as their opinion, that of all the porcelain made in France, that of the Count de Lauraguais approached most nearly in the essential properties of solidity, texture, and infusibility, to that of China and Japan. It is said, however, that it was considerably deficient in whiteness and lustre, when compared with the ancient porcelain of Japan. The great interest, however, created in France in support of this elegant and useful fabric, the continued experiments of the ablest chemists and scientific men, with the discovery of better materials which are abundant in the South of France, gave to that country facilities which enabled her soon to take the lead of the continent and of Britain in the production of this article.

Porcelain manufactories have long been established at Tournay in Flanders. One of these manufactories furnishes all Flanders with blue and white porcelain. At this manufactory they have a particular process in forming cups and other vessels. They are neither turned on the lathe, nor is the clay compressed in a mould; but after being diluted in water, and when the liquid has acquired a proper consistency, the workmen pour it into moulds, two or three hundred of which are arranged together. When they have filled them all, they return to the first in the row. The liquid part is drawn off by a gentle inclination; the surplus adheres to the side of the vessel, and thus forms the piece which it is intended to make. The piece is detached from the mould by means of a slight stroke; and after being sufficiently dried, it is conveyed to the furnace, to undergo the process of baking.

In England but little progress was made in the manufacture of porcelain, until towards the end of the last century. At an earlier period there was a manufactory carried on by some Germans at Chelsea, afterwards removed to Derby, of porcelain of a very superior quality; but whence they derived their materials is now uncertain. The porcelain which was then made at Liverpool, and some other places, was of an inferior kind, and manufactured so thin, in order to procure transparency, as to render it in a great degree unserviceable. This porcelain was made of the clays from Devonshire, to which a frit, described hereafter, was added to improve the colour of the body, and to create that degree of transparency which was required by the public as a principal attribute of porcelain.

About the year 1768, the discovery in Cornwall ofmines of clay and stone similar to those used in France and Germany, and which are believed to be the kaolin and petuntse of the Chinese, soon enabled the English manufacturer to improve his porcelain, by discontinuing the use of frit, or glass, as a component part of the basis or body of the ware, and substituting a mixture of the fusible and infusible earths as the basis of his porcelain, as had been done, at a much earlier period, in Germany and France. And thus the English porcelain, in many of its essential qualities, particularly in the beauty and richness of its paintings and gildings, as well as the elegance of its forms, has become little, if at all inferior, to that of any other country.

There are in England a number of manufactories of porcelain, at Derby, at Worcester, at Coalbrookdale, and at Rotherham, in Yorkshire. But the principal site of this manufacture is now in the Staffordshire Potteries, where it is produced in large quantities, at various manufactories.

5. Different Processes in the Manufacture of Porcelain.

The basis of those porcelains which were respectively known by the name of vitreous, fusible, and soft porcelain, was in part composed of what was called a frit ; that is to say, a mixture of alkalis and siliceous earths, brought into fusion, which, forming an opaque glass, was ground very fine, and mixed with an infusible earth or clay, in quantity sufficient to produce a degree of fusion, and consequent transparency of the whole body, but not so much as to prevent the ductility necessary for the formation of the articles to be made. The basis of the porcelains now generally made is composed of a mixture of infusible and fusible earths, in those proportions which, on the application of intense heat, produce that transparency and semi-vitrification which is required as the distinguishing properties of porcelain.

Up to a certain point, the operations and manipulations are the same in all cases. The clay or infusible earth having been separated by washing from the mass of decomposed granite, of which it forms a part, is mixed with a portion of the fusible earth, finely livigated into aliquid of the consistence of cream, which, after being passed through the finer silk lawns, is placed on kilns to evaporate the superfluous water, until the mass becomes a soft tenacious paste, ready for the operations of the workman. It is then taken to the thrower, to be fashioned on his wheel; and having obtained a sufficient degree ofhardness to preserve its form, is transferred to the lathe to be more correctly shaped, and the surface made even. It next has handles, feet, and other requisites added, and is then ready to receive its first firing. To effect this, it is, when sufficiently dry, put into a case made of earthenware, and placed in the furnace, that it may be subjected to the process of baking. These casesareknown amongst the English potters by the name of seggars or saggars, and they are generally formed of a coarser kind of clay; but this clay must possess the property of resisting the action of heat necessary for the baking of porcelain, without being fused. The porcelain contained in the cases is thus protected from the smoke of the burning fuel. The whiteness of the porcelain depends greatly on the purity of the clay of which the saggars are made, so that being of a more compact texture, the smoke is more effectually excluded. These cases are arranged in the furnace or kiln in piles, one upon the other, to the top of the furnace.

À small fire is first made, that the furnaces may be gradually heated; and it is increased more and more until the process of baking is completed, that is, until the porcelain shall have acquired a proper degree of hardness and transparency. To ascertain this point, much attention is necessary, by taking out of the furnace from time to time, and examining, small pieces of porcelain placed for that purpose in some cases, which have lateral openings in the walls of the furnace to render them accessible. When it appears, from the examination of those pieces, that the porcelain is sufficiently baked, the fire is no longer to be supplied with fuel; the furnace is allowed to cool gradually, and the porcelain is afterwards taken out.

But at this point of the process of baking, or firing, the [7:18:436]modes adopted in France, and on the continent generally, arc materially different from the practice in this country; in fact, are totally reversed. In England the first, or biscuit firing, is employed to produce, by an intense heat, the required degree of transparency and vitrification; whilst in France but a small degree of heat is applied, sufficient only to harden ( dégourdir ) the ware, so that it may bear the manipulation necessary before the glazing, without breaking, the transparency and strength being obtained at the second operation of firing, which, like the English biscuitfiring, requires an intense heat to accomplish that object.

Unglazed porcelain has the appearance of white marble, having nothing of that shining surface which it acquires by covering it with the vitreous composition called glaze, and is said to be in the state of biscuit. For particular purposes, the porcelain is sometimes allowed to remain in this state, and particularly when it is employed in smaller and finer pieces of sculpture, where the fineness of the workmanship and the sharpness of the figures are wished to be preserved, as it is well known that these will be greatly injured by being covered with a coat of glazing. The celebrated manufactory of Sevres has long been distinguished for figures or small statues, and even for larger works, as ornamental vases, &c., which are left in the state of biscuit. The English manufactories are probably not inferior in the delicacy and accuracy of execution of ornamental productions of this kind.

The next operation in the manufacture of porcelain is the process of glazing. This process consists in covering the porcelain with a thin coat of vitreous or fusible matter, which adds greatly to its beauty, by its lustre or shining appearance. In preparing and applying the materials fit for glazing porcelain, it has been found that the same mixture will not admit of general application; for it appears, that what forms a fine glazing for one kind of porcelain, will not answer the same purpose when applied to another. In the former it may have all the necessary requisites, but in the latter it may crack in many places, may have no lustre, and may contain bubbles, or be apt to scale oft’. The first thing, then, is to prepare a glaze which shall be suited to the nature of the porcelain for which it is intended. The glazing must be appropriated to each kind of porcelain, that is, to the ingredients which enter into its composition, or to the degree of hardness or density of the ware. The materials of which the glazing is composed are prepared by previously fusing together all the substances of which they consist, and thus forming a vitreous mass. This mass of vitrified matter must be finely ground in a mill, and the vitreous powder thus obtained be mixed with a sufficient quantity of water, so that the liquor shall have the consistence of cream of milk. The pieces of porcelain are to be covered with a thin coating of this matter, which is done by immersing them hastily in the liquid, and as they greedily imbibe the water, there remains on the surface a uniform covering of the glazing materials. This covering, which, it must be observed, should be very thin, in a short time becomes so dry, that it does not adhere to the fingers when the pieces are handled. When they are sufficiently dry, they are replaced in the fiirnace in the same manner as in preparing the biscuit, and the heat is continued till the glazing be completely fused; but the degree of heat necessary for that purpose is far inferior to that which is requisite in baking the paste. As before noticed, however, this does not apply to the French porcelains, the glazing of which is effected by a higher degree of heat than what is applied to the paste or body.

The glaze used for the soft porcelain possessed great advantages in the execution of the more delicate paintings and decorations, by its property of assisting to flux and fix with more certainty the metallic oxides of which the colours are composed. The old Sèvres chinais of this description. But at that royal manufactory, under the able direction of Μ. Brogniat, the porcelaine dure, now the only kind made there, has been so much improved, as to admit of its being embellished by paintings of the most delicate and brilliant colours and superb grounds, with gilding equal, if not superior, to the old Sevres.

The pieces of porcelain which are intended to remain white are now finished, but those which are to be ornamented with painting and gilding must go through various other operations. The colours which are employed in painting porcelain on the glaze are similar to those which are applied in the painting of enamel. They are all composed of metallic oxides or calces, combined with a very fusible vitreous matter. The different colours are obtained from different metals. The oxides of iron afford a red colour; gold, precipitated by means of tin, furnishes a purple and violet colour; copper, precipitated from its solution in acids by means of an alkali, gives a fine green; cobalt, or when combined with vitreous matter, zaffar, as it is called, yields a fine blue. Earthy matters which are slightly feruginous, produce a yellow colour; and brown and black colours are obtained from iron in different states, and from manganese. The oxide of chrome, which has but lately come into use, has furnished artists with greens and some other colours, of a brilliancy and fixedness in the fire not before known. These colours are applied to the ware by the painters according to the requisite pattern, and it is again conveyed to the furnace, and the colours are vitrified, to give them the proper degree of fixation and lustre. In the common kind of porcelain, once or twice burning is sufficient, but in the finer decorations the colours must be laid on several times, and as often fired before the full effect can be produced. This process is similar to that practised by enamel-lers on copper, &c.; but the blue colour from cobalt is much used for painting on the biscuit ware before glazing.

The discovery of a method of imitating the painted patterns of the Chinese by impressions taken from engraved copper plates, was of great importance, as it enabled the European manufacturers to compete with the cheap labour of the Chinese. This discovery is due to a manufacturer at Liverpool, where porcelain was formerly made. The process is as follows. The pattern being engraved on a copper plate of the size wanted, it is charged with the colour to be used, which is mixed with boiled linseed oil; the plate is then placed on a hot stove, and a piece of thin tissue paper, previously primed with a solution on one side of soft soap, is laid upon the plate, and both passed through the rollars of the press as in ordinary printing. The impression is then taken off, and transferred on to the ware. After being well rubbed with a roller of flannel, to cause the colour and oil to adhere to the ware, the piece is then put into lukewarm water, where the paper, by the action of the soap, leaves the ware and the colour upon it. The ware is next dried, and subjected to a degree of heat, to evaporate the oils, and the ware is then in a condition for the glazing.

But when the pieces of porcelain are to be further decorated with gilding, they are pencilled with a mixture of oil and gold, dissolved or thrown down by quicksilver with the aid of heat, and are again introduced into the furnace. Here the gold returns to its solid state, but comes out with a dull surface; and to recover its lustre and usual brilliancy, it is burnished with blood-stones, and other polishing substances. Much care and attention are necessary in the latter part of the process; for if the gold be not sufficiently burned, it will be apt to separate in thin flakes; and if it have been exposed to too great a heat, it is not susceptible of a fine polish. In this manufactory, when pieces of porcelain are to be finished in the highest style, they are frequently returned to the enamel furnace, where the colours are fluxed six or seven different times; and having gone through the processes now described, the porcelain is fit for the market.
[7:18:437]

The use of platina in porcelain painting has been recommended by Klaproth; and experiments have been made on the subject by that celebrated chemist, with the view of ascertaining its effects for this purpose. In concluding his observations, he says, “The process which I employ in the application of platina to painting on porcelain is simple and easy. I dissolve crude platina in aqua regia, and precipitate it by a saturated solution of sal-ammoniac in water. The red crystalline precipitate thence produced is dried, and being reduced to a very fine powder, is slowly brought to a red heat in a glass retort. As the volatile neutral salt combined with the platina in this precipitate becomes sublimated, the metallic part remains behind in the form of a gray soft powder. This powder is then subjected to the same process as gold; that is to say, it is mixed with a small quantity of the same flux as that used for gold, and being ground with oil of spike, is applied with a brush on the porcelain; after which it is burned-in under the muffle of an enameller’s furnace, and then polished with a burnishing tool.

“The colour of platina burnt into porcelain in this manner is a silver white, inclining a little to a steel gray. If the platina be mixed in different portions with gold, different shades of colour may be obtained; the gradations of which maybe numbered, from the white colour of unmixed platina to the yellow colour of gold. Platina is capable of receiving a considerable addition of gold before the transi-. tion from the white colour to yellow is perceptible. Thus, for example, in a mixture of four parts of gold and one of platina, no signs of the gold were to be observed, and the white colour could scarcely be distinguished from that of unmixed platina: it was only when eight parts of gold to one of platina were employed that the gold colour assumed the superiority.

“I tried in the like manner different mixtures of platina and silver; but the colour produced was dull, and did not seem proper for painting on porcelain.

“Besides this method of burning-in platina in substance on porcelain, it maybe employed also in its dissolved state; in which case it gives a different result both in its colour and splendour. The solution of it in aqua regia is evaporated, and the thickened residuum is then applied several times in succession to the porcelain. The metallic matter thus penetrates into the substance of the porcelain itself, and forms a metallic mirror of the colour and splendour of polished steel.”

General principles of the manufacture of Porcelain and Earthenware.

Convinced that every accurate and scientific investigation into the nature and processes of any important art, will always be deemed of some value to the philosophical observer, or the enlightened manufacturer, we shall introduce the following observations on the principles of the manufacture of porcelain and earthenware.

Observatio7is by Vauquelin.

According to this celebrated chemist, four things may occasion differences in the qualities of earthenware; first, the nature or composition of the matter; second, the mode of preparation; third, the dimensions given to the vessels; fourth, the baking to which they are subjected. By composition of the matter, the author understands the nature and proportions of the elements of which it is formed. These elements in the greater part of earthen ware, either valuable or common, are silex, argil, lime, and sometimes a little oxide of iron. Hence it is evident that it is not so much by the diversity of the elements that good earthenware differs from bad, as by the proportion in which they arc united. Silex or quartz makes always two-thirds at least of earthenware; argil or pure clay, from a fifth to a third; lime from 5 to 20 parts in the hundred; and iron from 0 to 12 or 15 parts in the hundred. Silex gives hardness, infusibility, and unalterability; argil makes the paste pliable, and renders it fit to be kneaded, moulded, and turned at pleasure. It possesses, at the same time, the property of being partially fused by the heat which unites its parts with those of the silex; but it must not be too abundant, or it would render the earthen ware too fusible, and too brittle to be used over the fire.

Hitherto it has not been proved by experience that lime is necessary in the composition of pottery; and if traces of it are constantly found in that substance, it is because it is always mixed with the other earths, from which the washings and other manipulations have not been able to separate it. When this earth, however, does not exceed five or six parts in a hundred, it appears that it is not hurtful to the quality of the pottery; but if more abundant it renders it too fusible· The oxide of iron, besides the inconvenience of communicating a red or brown colour, according to the degree of baking, to the vessels in which it forms a part, has the property of rendering them fusible, and even in a greater degree than lime.

As some kinds of pottery are destined to melt very penetrating substances, such as salts, metallic oxides, glass, &c.] they require a fine kind of paste, which is obtained only by 1 reducing the earths employed to very minute particles. Others destined for melting metals, and substances not very penetrating, and which must be able to support, without breaking, a sudden transition from great heat to great cold, require for their fabrication a mixture of calcined argil with raw argil. By these means you obtain pottery, the coarse paste of which resembles lrreche, or small-grained pudding-stone, and which can endure sudden changes of temperature.

The baking of pottery is likewise an object of great importance. The heat must be capable of expelling humidity, and agglutinating the parts which enter into the composition of the paste, but not strong enough to produce fusion; which, if too far advanced, gives to pottery a homogeneousness that renders it brittle. The same effect takes place in regard to the fine pottery, because the very minute division given to the earths reduces them nearly to the same state as if this matter had been fused. This is the reason why porcelain strongly baked is more or less brittle, and cannot easily endure alternations of temperature. Hence coarse porcelain, in the composition of which a certain quantity of calcined argil is employed, porcelain retorts, crucibles, tubes, and common pottery, the paste of which ψ coarse, are much less brittle than dishes and saucers formed of the same substance, but ground with more labour.

The general and respective dimensions of the different parts of vessels of earthenware, have also considerable influence on their capability to stand the fire. In some cases ' the glazing or covering, especially when too thick, and of a nature different from the body of the pottery, also renders them liable to break. Thus, in making some kinds of pottery, it is always essential, first, to follow the best pro portion in the principles; secondly,to give to the particles of the paste, by grinding, a minuteness suited to the purpose for which it is intended, and to all the parts the same dimensions as far as possible; thirdly, to carry the baking to the highest degree that the matter can bear without being fused; and fourthly, to apply the glazing in thin layers, the fusibility of which ought to approach as near as possible to that of the matter, in order that it may be more intimately united.

Μ. Vauquelin, being persuaded that the quality of good pottery depends chiefly on using proper proportions of the earthy matter, thought it might be of importance to those engaged in this branch of manufacture, to make known the analysis of different natural clays employed for this pur[7:18:438]pose, and of pottery produced by some of them, in order that, when a new earth is discovered, it may be known by a simple analysis whether it will be proper for the same object, and to what kind of pottery already known it bears the greatest resemblance.
[table]

Raw kaolin 100 parts; silex, 74; argil, 16.5; lime, 2; water, 7∙ A hundred parts of this earth gave eight of alum, after being treated with the sulphuric acid.

Washed kaolin, 100 parts; silex, 55; argil, 27; limc, 2; iron, 0.5; water, 14. This kaolin, treated with the sulphuric acid, gave about 45 or 50 per cent, of alum.

Petuntze. Silex, 74; argil, 14.5; lime, 5.5; loss, 6. A hundred parts of this substance, treated with the sulphuric acid, gave seven or eight parts of alum. But this quantity does not equal the loss sustained.

Porcelain of retorts. Silex, 64; argil, 28.8; lime, 4.55; iron, 0.50; loss, 2.77∙ Treated with the sulphuric acid this porcelain gave no alum.

There is a kind of earthen vessels, cal\eåAlcarrezes, which are used in Spain for cooling the water intended to be drunk. These vessels consist of 60 parts of calcareous earth, mixed with alumina and a little oxide of iron, and 36½ of siliceous earth, also mixed with alumina and the same oxide. The quantity of iron may be estimated at almost one hundredth part of the whole. This earth is first kneaded into a tough paste, being for that purpose previously diluted with water; then formed into a cake of about six inches in thickness, and left in that state until it begin to crack. It is then kneaded with the feet, the workman gradually adding to it a quantity of sea-salt, in the proportion of seven pounds to a hundred and fifty; after which it is applied to the lathe, and baked in any kind of furnace used by potters. The alcarrezes, however, are only about half as much baked as the better kinds of common earthenware; and being exceedingly porous, water oozes through them on all sides. Hence the air which comes in contact with it, by causing it to evaporate, carries off the caloric contained in the water in the vessel, which is thus rendered remarkably cool.

Observations of Erongniart on the Colours used for Enamelling.

The art of employing metallic oxides for colouring by fusion different vitreous matters, is of very great antiquity. Every body knows that the ancients manufactured coloured glass and enamel, and that this art was practised in particular by the Egyptians, the first people who in this manner imitated precious stones. The practice of this art in modem times has been carried to a high degree of perfection; but the theory has been neglected. It is almost the only one of the chemical arts in which no attempt has yet been made to apply the new principles of that science. It is well known that all vitrifiable colours have for their basis metallic oxides; but all the metallic oxides are not proper for this purpose; besides, as they are not vitrifiable by themselves, they can scarcely ever be employed alone.

Highly volatile oxides, and those which adhere little to the great quantity of oxygen they contain, either cannot be employed in any manner, as the oxide of mercury and that of arsenic, or are employed only as agents. The colour they present cannot be depended on, since they must lose it in the slightest heat by losing a part of their oxygen. Such are the puce-coloured and red oxides of lead, the yellow oxides of gold, and some others. Oxides in which the proportions of oxygen are susceptible of varying with too much facility, are rarely employed. The oxide of iron, though black, is never employed for producing that colour; and the green oxide of copper is, under many circumstances, very uncertain. We have said that oxides alone are not susceptible of fusion. However, as they are destined to be applied to thin strata upon vitrifiable substances, they may be attached to them by a violent heat. But, excepting the oxides oflead and bismuth, they would give only dull colours. The violent heat, often necessary to fix them, would change or totally destroy the colours. A flux then is added to all metallic oxides.

This flux is glass, lead, and silex; glass of borax, or a mixture of both. Its gene>d effect is to give splendour to the colours after their fusion; to fix them upon the article which is painted, by promoting more or less the softening of its surface; to envelope the metallic oxides, and to preserve their colour, by sheltering them from the contact of the air; in a word, to facilitate the fusion of the colour at a low temperature not capable of destroying it.

But we shall speak here only of the application of metallic colours to vitreous bodies, or to vitreous surfaces. These bodies may be divided into three classes, very distinct by the nature of the substances which compose them, the er- ∙fects produced on them by the colours, and the changes they experience. These crusts are, first, enamel, soft porcelain, and all crusts, enamels, or glass, that contain lead in a notable quantity; secondly, hard porcelain, or porcelain which has a crust of feldspar; thirdly, glass in the composition of which no lead enters, such as common window-glass. We shall here examine in succession the principles of the composition of these colours, and the general phenomena they exhibit on these three kinds of bodies.

It is well known that enamel is glass rendered opaque by the oxide of tin, and exceedingly fusible by the oxide of lead. It is the oxide of lead, in particular, contained in it, that gives it properties very different from those of the other excipients of metallic colours. Thus all glass and glazing that contain lead, will participate in the properties of enamel·; and what we shall say of one may be applied to the rest with very trifling differences. Such are the white and transparent glazing of stoneware, and the glazing of porcelain called soft glazing.

Enamel or soft porcelain colours require muchless flux than others, because the glass upon which they are applied becomes sufficiently soft to be penetrated by them. This flux may be either glass of lead and pure silex, called rocaille, or the same glass mixed with borax. Montamy asserts that glass of lead ought to be banished from among the enamel fluxes; and he employs only borax. He then dilutes his colours in a volatile oil. On the other hand, the painters of the manufactory of Sèvres employ only colours without borax, because they dilute them in gum; and borax does not dilute well in that substance. Brogniart found that both methods were equally good; and it is certain that Montamy was wrong to exclude fluxes of lead, since they are daily employed without any inconvenience, and as they even render the application of colours easier.

We have said that in the baking of these colours, the crust, softened by the fire, suffers itself to be easily penetrated by them. This is the first cause of the change which they experience. By mixing with the crust they become weaker, and the first heat changes a figure which appeared to be finished into a very light sketch.

The two principal causes of the changes which colours on enamel and soft porcelain are susceptible of experiencing do not depend in any manner upon the composition of these colours, but upon the nature of the glass to which they are applied. It follows from what has been said, that pain*
[7:18:439]

ing on soft porcelain has need of being several times retouched, and of several heats, in order that it may be carried to the necessary degree of strength. These paintings have always a certain faintness; but they are constantly more brilliant, and they never are attended with the inconvenience of detaching themselves in scales.

Hard porcelain, according to the division which Brogniart established, is the second sort of excipient of metallic colours. This porcelain, as is well known, has for its base a very white clay called kaolin, mixed with a siliceous and calcareous flux, and for its covering feldspar fused without an atom of lead. The same porcelain, which is that of Saxony, is much newer at Sevres than the soft porcelain. The colours applied to it are of two kinds. The first, destined to represent different objects, are baked in a heat very inferior to that which is necessary for baking porcelain. They arc exceedingly numerous and varied. The others, destined to be fused in the same heat as that which bakes porcelain, lay themselves flat, and are much less numerous. The colours of painting are made nearly like those destined for soft porcelain; they only contain more flux. Their flux is composed of glass of lead and borax. When porcelain is exposed to heat in order to bake the colours, the covering of feldspar dilates itself and opens its pores, but does not become soft; and as the colours do not penetrate it, they experience none of those changes which they undergo on soft porcelain. It must however be said that they lose a little of their intensity by acquiring that transparency which is given to them by fusion.

One of the greatest inconveniences of these colours, especially in the manufactory of Sèvres, is the facility with which they scale off when exposed several times in the fire. To remedy this defect without altering the quality of the paste, Brogniart was of opinion that the crust only ought to be softened by introducing into it more siliceous or calcareous flux, according to the nature of the feldspar. This method succeeded, and being employed, the colours might be exposed two or three times to the fire without scaling, if not overcharged with flux, and laid on too thick.

The third sort of excipient of vitrifiable metallic colours is glass without lead. The application of these colours to glass constitutes painting on glass; an art very much practised some centuries ago, and which was supposed to be lost because out of fashion; but it has too direct a dependence on painting in enamel and porcelain to be entirely lost.

The matters and fluxes which enter into the composition of the colours employed on glass are in general the same as those applied to porcelain. Neither of them differ except in their proportions; but there are a great number of enamel or porcelain colours which cannot be applied to glass, where they are deprived of the white ground that serves to give them relief.

Of Colours in particular.

After collecting the general phenomena exhibited by each class of vitrifiable colours, considered in regard to the body on which they are applied, we shall now make known the most interesting particular phenomena exhibited by each principal kind of colours employed upon soft porcelain and glass in a porcelain furnace.

Feds, Purples, and Violets, made from Gold.

Carmine red is obtained by the purple precipitate of cassius. It is mixed with about six parts of its flux; and this mixture is employed directly, without being fused. It is then of a dirty violet, but by baking it acquires a beautiful red carmine colour. It is, however, exceedingly delicate; but a little too much heat and carbonaceous vapours easily spoil it. On this account it is more beautiful when baked with charcoal than with wood.

This colour and the purple, which is very little different, as well as all the shades obtained from it by mixing it with other colours, really change on all porcelain and in every hand. But it is the only one which changes on hard porcelain. Its place may be supplied by a rose-colour from iron which does not change; so that by suppressing the carmine made with gold, and substituting for it the rose oxide of iron here alluded to, a palette may be exhibited, composed of colours none of which changes in a remarkable manner. This rose-coloured oxide of iron has long been known; but it was not employed on enamel, because on that substance it changed too much. As the painters on enamel, however, have become the painters on porcelain, they have preserved their ancient method.

It might be believed that, by first reducing to a vitreous matter the colour called carmine already mixed with its flux, it might be made to assume its last tint. But the heat necessary to fuse this vitreous mass destroys the red colour. Besides, it is remarked that, to obtain this colour very beautiful, it must be exposed to the fire as few times as possible. The carmine for soft porcelain is made with fulminating gold slowly decomposed, and muriate of silver; no tin enters into it, which proves that the combination of the oxide of this metal with that of gold is not necessary to the existence of the purple colour. Violet is also made with purple oxide of gold. A greater quantity of lead in the flux is what gives it this colour, which is almost the same crude or baked. These three colours totally disappear when exposed to a great porcelain heat.

Carmine and purple give us in glass only tints of a dirty violet. The violet, on the other hand, produces on glass a very beautiful effect, but it is liable to turn blue. We have not been able to discover the cause of this singular change.

Fed, Rose, and Frown Colours, extracted from Iron.

These colours arc made from red oxide of iron prepared with nitric acid. The oxides are further calcined by keeping them exposed to the action of heat; but if heated too much, they pass to brown. Their flux is composed of borax, sand, and minium, in small quantity.

These oxides give rose and red colours capable of supplying the place of the same colours made with oxide of gold. When properly employed upon hard porcelain, they do not change at all. We have caused roses to be painted with these colours, and found no difference between the baked flower and that not baked, except what might be expected to result from the brilliancy given to colours by fusion.

These colours may be employed indiscriminately, either previously fused or not fused. In a great heat they in part disappear, or produce a dull brick ground, which is not agreeable. The composition of them is the same both for soft porcelain and for glass They do not change on the latter; but on soft porcelain they disappear almost entirely on the first exposure to heat, and to make any thing remain they must be employed very deep. This singular effect must be ascribed to the presence of lead in the crust or glazing. We assured ourselves of this by a very simple experiment. We placed this colour on window glass, and having exposed it to a strong baking, it did not change. We covered several parts of it with minium; and on again exposing it to the fire, the colour was totally removed in the places where the red oxide of lead had been applied. By performing this operation on a larger scale in close vessels, a large quantity of oxygen gas was disengaged.

It appears to us that the observation here referred to clearly proves the action of oxidated lead on glass as a destroyer of colour; it is seen that it does not act, as was believed, by burning the combustible bodies, which might tarnish the glass, but by dissolving, discolouring, or volatilizing with it the oxide of iron, which might alter its transparency, [7:18:440]Yellows.

∖ ellows are colours which require a great deal of care in the fabrication, on account of the lead which they contain, and which, approaching sometimes to the metallic state, produces on them dark spots. The yellows for hard and soft porcelain are the same; they are composed of the oxide of lead, white oxide of antimony, and sand.

Oxide of tin is sometimes mixed with them; and when it is required to have them more lively, and nearer the colour du souci, red oxide of iron is added, the too great redness of which is dissipated in the previous fusion to which they are exposed by the action of the lead contained in this yellow. These colours, when once made, never change; they disappear, however, almost entirely when exposed to a porcelain heat.

These yellows cannot be applied to glass, because they are too opaque and dirty. That employed by the old painters on glass has, on the contrary, a beautiful transparency, and is exceedingly brilliant, and of a colour which approaches near to that of gold. The processes which they gave clearly showed that silver formed part of their composition; but, when exactly followed, nothing satisfactory was obtained. Μ. Miraud found means to make as beautiful paintings on glass as the ancients, by employing muriate of silver, oxide of zinc, white argil, and yellow oxide of iron. These colours were applied on glass merely pounded, and without a flux. The oxide of iron brought the yellow to that colour which it ought to have after baking, and contributed with the argil and oxide of zinc to decompose the muriate of silver without deoxidating the silver. After the baking, there remained a dust which had not penetrated into the glass, and which was easily removed.

This yellow, when employed thicker, gives darker shades, and produces a russet colour.

Blues.

It is well known that blues are obtained from the oxide of cobalt. All chemists arc acquainted with the preparation of them. Those of Sèvres, which are justly esteemed for their beauty, are indebted for it solely to the care employed in manufacturing them, and to the quality of the porcelain, which appears more proper for receiving them in proportion to the degree of heat which it can bear.

Respecting the oxide of cobalt, we may remark a fact which is perhaps not known to chemists; namely, its volatility in a violent heat. It is to this property that we must ascribe the bluish tint always assumed by white in the neighbourhood of the blue.

The blue of hard porcelain, destined for what is called the ground of a great heat (les fonds au grand feu) is fused with feldspar; that of soft porcelain has for its flux silex, potash, and lead. It is not volatilized like the preceding; but the heat which it experiences is very inferior to that of hard porcelain. These colours, when previously fused, do not change at all in the application. Blues on glass exhibit the same phenomena as those on soft porcelain.

Greens.

The greens employed in painting are made with green oxide of copper, or sometimes with a mixture of yellow or blue. They must be previously fused with their flux, otherwise they will become black; but after this first fusion they no longer change. They cannot stand a strong heat, as it would make them disappear entirely. Green grounds for a strong heat are composed with the oxides of cobalt and nickel, but a brownish green only is obtained.

Bluish greens, called celestial blues, which were formerly colours very much in vogue, can be applied only upon soft porcelain; on hard porcelain they consequently become scaly, because potash enters into their composition. These greens cannot be applied on glass, because they give a dirty colour. To obtain a green on glass, it is necessary to put yellow on one side, and blue, more or less pale, on the other. This colour may be also made by a mixture of blue with yellow oxide of iron.

Bistres and Russets.

These are obtained by mixtures, in different proportions, of manganese, brown oxide of copper, and oxide of iron from ombre earth. They are also previously fused with their flux, so that they do not in any manner change on soft porcelain, since lead has not the same action on oxide of manganese as on that of iron. This colour fades very speedily on glass.

Russet grounds in a great heat, known under the name of tortoise-shell grounds, are made in the same manner. Their flux is feldspar; and no titanium enters into their composition, though it is so stated in all printed works. Titanium was not known at the manufactory of Sèvres when Brogniart arrived there. He treated this singular metal in various ways, and never obtained any but grounds of a pale dirty yellow, and very variable in tone.

Blacks.

Blacks are the colours the most difficult to be obtained of a very beautiful hue. No metallic oxide alone gives a beautiful black. Manganese is that which approaches nearest to it. Iron gives an opaque, dull, cloudy black, which changes very easily to red; the colour-makers, therefore, to obtain a black which they could not hope for from the best theorist, have united several metallic oxides which separately do not give black, and have obtained a very beautiful colour, which, however, is liable to become sealyand dull. These oxides are those of manganese, the brown oxides of copper, and a little of the oxide of cobalt. The grey is obtained by suppressing the copper, and increasing the dose of the flux.

The manufactory of Sèvres is the only one which has hitherto produced beautiful blacks in a strong heat. This is owing rather to the quality of its paste than to any peculiar processes, since it does not conceal them. It is by darkening the blue by the oxides of manganese and iron that they are able in that manufactory to obtain very brilliant blacks.

Having here made known the principles of the fabrication of each principal colour, it may be readily conceived that by mixing these colours together all the shades possible may be obtained. It is evident also that care in the preparation, choice in the raw materials, and a just proportion of doses, must produce in the result, differences very sensible to an eye accustomed to painting. A mere knowledge of the composition of the colours does not give the talent of executing them well.

From the facts above mentioned, it is therefore seen, 1st, That amongst colours generally employed on hard porcelain one only is susceptible of changing, viz. carmine, and the tints into which it enters; that its place may be supplied by the reds of iron, and that no colour then changes. 2d, That amongst the colours for soft porcelain and enamel, several change in a considerable degree. These are principally the reds of gold and iron, the yellows, the greens, and the browns. They have not been replaced by others, because this kind of painting has been almost abandoned. 3d, That several of the colours on glass change also by acquiring complete transparency. These, in particular, are the yellows and green. 4th, That it is neither by calcining the colours in a higher degree, nor previously fusing them, as supposed by seme, that they are prevented from changing, since these means really alter the changing colours, and produce no effect on the rest. The change which [7:18:441]several colours experience upon soft porcelain and upon glass does not depend on the nature of their composition, but rather on that of the body upon which they are applied.

It follows, then, that, by suppressing from the colours of hard porcelain the carmine of gold, which is by no means indispensably necessary, we shall have a series of colours which do not change, or, in other words, remain unalterable. So much for the colours employed in this manufacture. x. x.