in its more general signification, Nature comprehends all kinds of earthen ware, which are white, porcelain-femitransparent, 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 immemorial, 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 Derivation 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 language; for in this language the word porcelana signifies a cup or vessel.

The first porcelain which was seen in Europe was Porcelain brought from Japan and China. Its whiteness, transparency, fineness of texture, with its elegance and beautiful colours, soon introduced it as an ornament of the tables of the rich and powerful, while at the same time it excited the admiration and industry of the European manufacturer. Accordingly attempts were made to imitate this kind of ware, in different countries of Europe. These attempts have succeeded so well, that the produce of the manufacture has acquired the name of Porcelain. 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 reached 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 Antiquity 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 yet been received in Europe of the manufacture of Chinese porcelain, has been given by Father D'Entrecolles, a Roman missionary, who lived for some time in the village or town where the principal manufactory is established. The account which is given of this village, and of the manufacture of porcelain, by this author, is the following:

This village or town which is celebrated as producing the best porcelain of China, is in the province of Kiang-fu, and it 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 manufactories 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 King-te-tching, in the time of our author, 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 are carried to the manufactory in the shape of bricks. The petuntse is originally 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 petuntse, 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 thrown into a large vessel 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 appears that nothing remains but a coarse sediment which falls to the bottom by its own weight. This sediment is 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. Porcelain. 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 and of the fabrication of porcelain, requires fewer operations in kaolin, 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, &c.

The fine porcelain, it has been observed, derives its Nature of fabric and texture from the kaolin. It is to this that the finer qualities which it possesses of resisting the most powerful agents is owing; and it has been remarked as an extraordinary circumstance, that a soft earth should communicate strength and consistency to the petuntse, which is obtained from some of the hardest rocks. The author 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 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 discovered of late years a new substance which may be employed in the composition of porcelain. This stone is called hoa-chè, the first part of the word signifies 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, seems 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 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 this 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 communicate to the ware a high degree of beauty. The previous processes in the preparation of this substance are similar to those which are followed in the preparation of kaolin. When hoa-chè is dug out 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 been already noticed, as a substitute for kaolin; but, on account of its scarcity, 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 Porcelain. 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. This stone is first washed and reduced to powder; it is then thrown into a vessel 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 becomes 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 10 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 they 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 plates, where they knead and roll them in all directions, taking care that no vacuum be left, and that there be no mixture of any foreign body. The whole work would be entirely spoiled by the addition of a hair, or a particle of sand. When 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, porcelain for instance, has undergone this operation, the outside ware 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 26 pieces. The cup then passes to a second workman, by whom the base is formed; it is then 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 turned carefully, 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, 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, it is said, 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 70 different workmen. It is indeed, we may observe, to this minute division of labour that its low price is owing; and on the same circumstance the remarkable dexterity and expedition which have been noticed, depend.

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 after, 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 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. In this way particularly are fabricated those pieces which are 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 painting, the operations now described, is next conveyed to the painter: and in this art it is 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 among Porcelain among a great number of hands. The business of one man, for instance, is solely limited to 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, while 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.

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 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 on the outside, however, as is usually the case, but on the inside of the vessel, and it is laid on pretty thick. 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 coated over with a kind of glaze, composed of porcelain earth, so that the azure is thus inclosed 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 prefaced 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 is added, 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 12 feet high, and nearly four broad; and the roof and sides are 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 workman 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 proceed now to baking porcelain before our readers 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 factory 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 prefaced 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; the case has no cover. A second, prepared in the same manner, manner, and containing its vessel, is fitted into the first, so that it entirely shuts it, without touching the porcelain which is below; and thus the furnace is filled up with piles of cafes, which defend the pieces they contain from the direct action of the fire.

With regard to small pieces of porcelain, such as tea-cups, 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 cafes are put into the furnace, and placed upon a bed of coarse sand six inches thick; those by which the middle space is occupied are at least seven feet high. 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 farther 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; 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 infuse 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 Dreden 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 grown 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 potter's 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 grown clay also of the Cornish miners. The wha-he of the Chinese is the English soap-rock; and the she-kan is asserted to be gypsum. It was related by a Chinese manufacturer in 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 traveller's 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 fire. 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 Reaumur 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 composition, nor was it the decorations of painting and porcelains, 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 carefully 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 of the granular texture. In his examination of the French porcelain, he observed that it had not much of a 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 characterized by very marked differences.

Proceeding in his investigation, the same philosopher subjected different porcelains to the action of heat; and heat on the result of his experiments with this powerful agent proved, that they might be distinguished by still more decisive characters; for 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 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 semivitrified substance. An earthly substance, he observed, may be in a semivitrified state in two ways. It may, in the first place, be entirely composed of vitrifiable 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, while, at the same time, it possesses the semitransparency 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 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 and 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 on the principle above alluded to. This opinion was afterwards confirmed by the most 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 them 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. Porcelain. After this discovery Reaumur, it would seem, entertained hopes that he might find materials in France, capable of making porcelain, possessing the same valuable qualities as that of China; but whether his researches in the discovery of proper materials in his own country, particularly that which corresponds to the petuntse of the Chinese, or whether he was prevented by other avocations from prosecuting his inquiries, it does not appear. But in his second memoir upon porcelain, we find, that he afterwards attempted to compose an artificial petuntse, by mixing vitrifiable stones with such feline bodies as were 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 till the year 1739, when he announced the discovery of a process for converting common glass to a peculiar kind of porcelain, which has been since known by the name of Reaumur's porcelain.

Although it must appear, from the detail now given, that Reaumur was directed in his researches by the true Reaumur 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 internal texture of the Saxon porcelain may 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 much 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. But if the Saxon density and shining appearance of the porcelain of porcelain, Saxony depended only on the effects of the fusion of a vitreous matter, how is it to be supposed, that vessels formed of that fusible matter should have sustained the necessary degree of heat for producing the density and shining appearance, without having entirely lost their shape?

This peculiar quality of the Saxon porcelain, it is inferred, must then depend on another cause. Like every other porcelain, especially that of China and Japan, it 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 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 considerably contracting its dimensions, while it unites with the fusible material. According to the observation of Macquer, if it be subjected to the most decisive trial, namely, the action of a violent fire, which is capable of melting every porcelain composed only of fusible materials, it appears as the result of numerous experiments, that it remains infusible, unless it be exposed to a heat which is also capable of melting the best and most perfect porcelain of Japan. The Saxon porcelain, therefore, is not to be confounded with porcelain manufactured of vitreous and fusible materials; 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 also to have taken an erroneous view of the nature of the Chinese kaolin. According to his account, this matter is a fine talky powder, from the mixture of which with petuntse, the porcelain of the east is manufactured. It is not impossible, it has been observed, that a porcelain similar to the Chinese might be produced from a talky 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 talky nature, to whatever degree of fineness they may be reduced, never acquire the requisite ductility and tenacity which clays of all earthly 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 talky matter, but mixed with clay, otherwise the petuntse and kaolin, according to the supposition of Reaumur, are not the only ingredients which enter into the composition of Chinese porcelain; but the addition of a certain proportion of some matter of a tenacious quality is absolutely requisite.

3. Peculiar Properties of Porcelain.

It may be worth while now to consider the properties which constitute the perfection of porcelain; 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 on this subject, have not found it difficult to form compositions which are very white, beautifully semi-transparent, and covered with a shining glazing; but which are extremely deficient in the more essential properties, as it appears they cannot be subjected to the necessary operations for want of a proper degree of tenacity; are not sufficiently compact; 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 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 porcelain which are capable of being easily worked and well baked, and in the process of baking, which 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, in short, which possess all the qualities of the most excellent porcelain, excepting its whiteness and beauty. Materials fit for the composition of such porcelains, it will appear, may be found abundantly in most countries; but the difficulty in the manufacture of this ware is to unite beauty and goodness in one composition. The materials 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 stone-ware, possess all the essential qualities of the Japanese porcelain; for, excepting the whiteness, on which alone the semitransparency depends, if we compare the properties of Japanese 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 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 coloured with a fine glaze, they would not be less perfect than the porcelain of the east. 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 a small quantity of white earth, from which fusible and vitreous porcelains were composed. Such might not improperly be denominated false porcelains; but great improvements have taken place since the first introduction of the manufacture of porcelain into Europe. Genuine white porcelains have been long ago produced in Germany, and especially in Saxony. These porcelains are in no respect inferior to those of China or Japan. They are found even to be considerably superior in beauty and whiteness to the productions of the eastern manufactories of modern times; for in these qualities the porcelains of the latter have greatly degenerated. And in one of the most valuable qualities of porcelain, namely, the property of resisting the effects of sudden changes of heat and cold, 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 Porcelaining what is good porcelain, is to examine several pieces of which are in daily use; and it has been found, that in many such pieces of porcelain of oriental manufacture, which have been long used, cracks are always 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; a model which has not yet been equalled, and which, according to the opinion of some, cannot be equalled. In deciding on this subject, the Saxon porcelain is 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. This surface has a near resemblance to that of glass, and it is supposed that this similarity has suggested the opinion; and it would be well founded, if the density and lustre of the European porcelain depended on the fusible and vitreous property of the ingredients of which it is composed; but this not being the case, and the Saxon porcelain being equally fixed and infusible as that of Japan, its superior density must be admitted as a valuable property. For in the comparison of different porcelains which are equal in other properties, that which is most firm and compact certainly claims the superiority. Hence it is that the internal texture of the Japanese porcelain is held in greater estimation, because it possesses a greater degree of density, compactness and lustre, than the European porcelain which is composed only of vitreous sand or frit. For a similar reason the superior density of the Saxon porcelain ought to obtain for it a preference to that which is imported from the east. It is supposed besides, that it would be no difficult matter to communicate to the Saxon porcelain the granular texture of the Japanese, by mixing with the paste a certain proportion of sand or siliceous earth. But in this point, in producing by these means a nearer resemblance to the Japanese porcelain, those who conducted and brought to perfection the Saxon manufactures, were not insensible that their porcelain would sink in its valuable properties.

4. Porcelain Manufactories in different parts of Europe.

Manufactories of porcelain have been long established in almost every country of Europe. Besides that of Saxony, which was the first established in Europe, porcelain is made to a considerable extent at Vienna, at Frankenthal, and in the neighbourhood of Berlin, and in other places of the German states. The German porcelains are similar to those of Saxony, and are composed of similar materials, although from differences in the proportions, or in the modes of managing the manufactories, considerable differences arise in the porcelains manufactured at different places. Italy also is celebrated for its porcelain manufactures, the chief of which, it is said, are carried on at Naples. When M. de la Condamine travelled into Italy, he visited a manufacture of porcelain established at Florence, by the marquis de la Ginor, who was then governor of Leghorn. The French traveller was particularly struck with the large size of some of the pieces of this porcelain. Statues, and even porcelain 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.

In France a greater number of manufactories of porcelain has been established than in any other country; and it must be allowed that the French have had wonderful success in the improvement and perfection of this manufacture. Some time even before Reaumur communicated the result of his inquiries, porcelain was manufactured at St. Cloud, and in the suburb of St. Antoine at Paris. This porcelain indeed was of the vitreous or fusible kind, but at the same time 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 great degree of perfection. But the productions of the celebrated porcelain manufactory at Sevres, 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.

In speaking of the French porcelain, we may notice the result of some researches which were made on this subject 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, Mr. Guettard discovered a whitish argillaceous earth, in which mica considerably predominated. This earth he employed as a substitute for kaolin. The substance which he used in place of the petuntse, he obtained from a hard stone, which is described as a quartzose grittstone, 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, previous 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 of porcelain, 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 manufacture of porcelain has been brought to a great degree of perfection in England. In many of the essential qualities, and particularly in the beauty and richness of the paintings, as well as in the elegance of the forms, the English porcelain is little inferior to that of any other country. Manufactories of this ware have been established in different parts of England. This manufacture was first established at Derby about the year 1750, by a Mr Duesbury, who is said to have been a very ingenious artist. Since his death the manufactories received very considerable improvement, and chiefly in the judicious methods pursued in the preparation of the paste, and increasing the beauty of the ornaments. The ware itself is said not to equal in fineness that which is manufactured in Saxony and France, although it is greatly superior in respect of decoration and workmanship. The paintings in general are rich, and executed with taste, and the gilding and burnishing are extremely beautiful. The body of the semi-vitreous kind, which is formed of a fine white clay, in combination with various proportions of different fusible matters, has obtained the name of porcelain. The best kind is wholly infusible, and is glazed with a vitreous substance which has not a single particle of lead in its composition.

The most famous manufactory of stone-ware, as well as of other kinds of pottery, is at Burslem in Staffordshire. This can be traced with certainty at least two centuries back; but of its first introduction no tradition remains. In 1686, as we learn from Dr Plot's Natural History of Staffordshire published in that year, only the coarse yellow, red, black, and mottled wares, were made in this country; and the only materials employed for them appear to have been the different coloured clays which are found in the neighbourhood, and which form some of the measures or strata of the coal-mines. These clays made the body of the ware, and the glaze was produced by powdered lead-ore, sprinkled on the pieces before firing, with the addition of a little manganese for some particular colours. The quantity of goods manufactured was at that time so inconsiderable, that the chief sale of them, the Doctor says, was "to poor cratchmen, who carried them on their backs all over the country."

About the year 1692, two ingenious artisans from Germany, of the name of Eller, settled near Burslem, and carried on a small work for a little time. They brought into this country the method of glazing stone-ware, by casting salt into the kiln while it is hot, and some other improvements of less importance; but finding they could not keep their secrets to themselves, they left the place rather in disgust. From this time various kinds of stone-ware, glazed by the fumes of salt in the manner above mentioned, were added to the wares before made. The white kind, which afterwards became, and for many succeeding years continued, the staple branch of pottery, is said to have owed its origin to the following accident. A potter, Mr Astbury, travelling to London, perceived something amiss with one of his horse's eyes; an hoffler at Dunstable said he could soon cure him, and for that purpose put a common black flint stone into the fire. The potter observing it, when taken out, to be of a fine white, immediately conceived the idea of improving his ware by the addition of this material to the whitest clay he could procure; accordingly he sent home a quantity of the flint stones of that country, where they are plentiful among the chalk, and by mixing them with tobacco-pipe clay, produced a white stone-ware much superior to any that had been seen before.

Some of the other potters soon discovered the source of this superiority, and did not fail to follow his example. For a long time they pounded the flint stones in private rooms by manual labour in mortars; but many of the poor workmen suffered severely from the dust of the flint getting into their lungs, and producing dreadful coughs, consumptions, and other pulmonary disorders. These disasters, and the increased demand for the flint powder, induced them to try to grind it by mills of various constructions; and this method being found both effectual and safe, has continued in practice ever since. With these improvements, in the beginning of the present century, various articles were produced for tea and coffee equipages. Soon after attempts were made to furnish the dinner table also; and before the middle of the century, utensils for the table were manufactured in quantity as well for exportation as home consumption.

But the salt glaze, the only one then in use for this purpose, is in its own nature so imperfect, and the potters, from an injudicious competition among themselves for cheapness, rather than excellence, had been so impatient to elegance of form and neatness of workmanship, that this ware was rejected from the tables of persons of rank; and about the year 1760, a white ware, much more beautiful and better glazed than ours, began to be imported in considerable quantities from France.

The inundation of a foreign manufacture, so much improved superior to any of our own, must have had very bad effects upon the potteries of this kingdom, if a new one, still more to the public taste, had not appeared soon after. In the year 1763, Mr Josiah Wedgwood, who had already introduced several improvements into this art, invented a species of earthen ware for the table quite new in its appearance, covered with a rich and brilliant glaze, bearing sudden alterations of heat and cold, manufactured with ease and expedition, and consequently cheap, and having every requisite for the purpose intended. To this new manufacture the queen was pleased to give her name and patronage, commanding it to be called Queen's ware, and honouring the inventor by appointing him her majesty's potter.

The common clay of the country is used for the ordinary pots; the finer kinds are made of clay from Devonshire and Dorsetshire, chiefly from Biddeford; but the flints from the Thames are all brought rough by sea, either to Liverpool or Hull, and so by Burton. The convenience of plenty of coals, which abound in that part of the country, is supposed, and with good reason, to be the chief cause of the manufacture having been established here.

The flints are first ground in mills, and the clay prepared by breaking, washing, and sifting, and then they are mixed in the requisite proportions. The flints are bought... Porcelain bought first by the people about the country, and by them burnt and ground, and sold to the manufacturers by the peck.

The mixture is then laid in large quantities in kilns to evaporate the moisture; but this is a nice work, as it must not be too dry: next it is beaten with large wooden hammers, and then is in order for throwing, and is moulded into the forms in which it is to remain; this is the most difficult work in the whole manufacture. A boy turns a perpendicular wheel, which by means of thongs turns a small horizontal one, just before the thrower, with such velocity, that it twirls round the lump of clay he lays on it into any form he directs it with his fingers.

There are 300 houses, which are calculated to employ upon an average twenty hands each, or 6000 in the whole; but of all the variety of people that work in what may be called the preparation for the employment of the immediate manufacturers, the total number cannot be much short of 10,000, and it is increasing every day. Large quantities are exported to Germany, Ireland, Holland, Russia, Spain, the East Indies, and much to America; some of the finest sorts to France.

5. Different Processes in the Manufacture of Porcelain.

Vitreous or fusible porcelain.

The basis of those porcelains which are known by the name of vitreous or fusible, and sometimes false porcelain, is denominated by the workmen a frit. This is a mixture of sand or powdered flints, with a saline substance, capable of bringing it to a state of fusion when the mixture is exposed to a sufficient degree of heat. The frit is then mixed with a proper proportion of clay or argillaceous earth, so that it may have such a degree of tenacity as to make it capable of being worked upon the wheel. The whole mixture is, after being well ground in a mill, to be made into a paste, which is to be formed, either upon the wheel or in moulds, into pieces of such forms or figures as may be required. Each of the pieces, when it is sufficiently dried, is put into a case made of earthen ware, and placed in the furnace, that it may be subjected to the process of baking. These cases are known among the English potters by the name of saggers or saggers, 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 it is 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 very top of the furnace.

The furnaces are chambers or cavities of various forms and sizes, and they are so constructed that the fire-place is situated on the outside, opposite to one or more openings, which have a communication with the furnace internally. The flame of the fuel is drawn within the furnace, the air of which being rarefied, determines a strong current of air to the inside, as is the case in other furnaces. A small fire is first made, that the furnaces may be gradually heated, and it is to be increased more and more, till the process of baking is completed; that is, till the porcelain shall have acquired a proper degree of hardness and transparency. To ascertain this point, a good deal of attention is necessary; and this is done by taking out of the furnace from time to time, and examining, small pieces of porcelain placed for that purpose in the cases, which have lateral openings to render them accessible. When it appears from the examination of these 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. In this state the porcelain has the appearance of white marble, having nothing of that shining surface which it acquires by covering it with a vitreous composition known by the name of glazing, a process which is afterwards to be described; but in the mean time we shall speak of the infusible porcelains.

The materials which enter into the composition of the infusible porcelains, and such as approach to the nature of stone ware, are first to be ground in a mill, and the earths or clays being well washed, are next to be carefully mixed and formed into a paste. The pieces at first receive a rude form from the wheel or lathe of the potter, according to their nature and magnitude. As the wheel and lathe are the principal machines employed in the manufacture of porcelain or pottery, we shall here give a short description of their construction. The potter's wheel, which is used for larger works, consists principally in the nut, which is a beam or axis, whose foot or pivot plays perpendicularly on a free-stone sole or bottom. From the four corners of this beam, which Potter's does not exceed two feet in height, arise four iron bars, wheel-called the spokes of the wheel; which forming diagonal lines with the beam, descend, and are fastened at bottom to the edges of a strong wooden circle, four feet in diameter, perfectly like the fellows of a coach-wheel, except that it has neither axis nor radii, and is only joined to the beam, which serves it as an axis, by the iron bars. The top of the nut is flat, of a circular figure, and a foot in diameter; and on this is laid the clay which is to be turned and fashioned. The wheel thus disposed is encompassed with four sides of four different pieces of wood fastened on a wooden frame; the hind-piece, which is that on which the workman sits, is made a little inclining towards the wheel; on the fore-piece is placed the prepared earth; on the side pieces he rests his feet, and these are made inclining to give him more or less room. Having prepared the earth, the potter lays a round piece of it on the circular head of the nut, and fitting down turns the wheel with his feet till it has got the proper velocity; then, wetting his hands with water, he presses his fist or his fingers-ends into the middle of the lump, and thus forms the cavity of the vessel, continuing to widen it from the middle; and thus turning the inside into form with one hand, while he proportions the outside with the other, the wheel constantly turning all the while, and he wetting his hands from time to time. When the vessel is too thick, he uses a flat piece of iron, somewhat sharp on the edge, to pare off what is redundant; and when it is finished, it is taken off from the circular head by a wire patted under the vessel.

The potter's lathe is also a kind of wheel, but more simple and slight than the former: its three chief members are an iron beam or axis three feet and a half high, and two feet and a half diameter, placed horizontally Porcelain tally at the top of the beam, and serving to form the vessel upon; and another large wooden wheel, all of a piece, three inches thick, and two or three feet broad, fastened to the same beam at the bottom, and parallel to the horizon. The beam or axis turns by a pivot at the bottom of an iron stand. The workman gives the motion to the lathe with his feet, by pushing the great wheel alternately with each foot, still giving it a greater or lesser degree of motion as his work requires. He works with the lathe with the same instruments, and after the same manner, as with the wheel. The mouldings are formed by holding a piece of wood or iron cut in the form of the moulding to the vessel, while the wheel is turning round; but the feet and handles are made by themselves and set on with the hand; and if there be any sculpture in the work, it is usually done in wooden moulds, and stuck on piece by piece on the outside of the vessel. The lathe is employed for smaller works in porcelain.

After the first application of the pieces of porcelain to the wheel or lathe, they are allowed to become nearly dry; and to give the requisite form, or a greater degree of accuracy and perfection, they are again subjected to the same operation. They are afterwards introduced into the furnace, not, however, for the purpose of baking them completely, but only to apply a sufficient heat, to give them that firmness and solidity that they may undergo the various necessary manipulations without being disfigured or broken. In this state they are ready for the process of glazing. As the pieces of porcelain, after being subjected to this moderate degree of heat, are very dry, they readily imbibe water, and it is this property of absorbing water, which greatly assists in the application of the glazing; and having received this covering, the pieces of porcelain are again put into the furnace, to complete the process of baking. The heat is gradually raised, and at last brought to that degree that all the objects within the furnace shall be white, and the cases shall be scarcely distinguished from the flame. To ascertain when the porcelain is sufficiently baked, small pieces are taken out in the manner already described, after which the fire is withdrawn, and the furnace allowed to cool gradually. If the process of baking have succeeded properly, the pieces of porcelain will, after this operation, be porous, compact, having a moderate degree of lustre, and covered externally with a fine coat of glaze. If this porcelain is destined to receive the ornaments of painting and gilding, these operations are performed in the manner to be afterwards described.

After the porcelain has been subjected to the process of baking, and before it is glazed, it is said to be in the state of biscuit, in which it possesses various degrees of beauty and perfection, according to the nature and proportions of the materials employed. 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 porcelain glazing. The celebrated manufactory of Sevres in France has been long 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, and particularly that of Mr Wedgwood, 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 calcine 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 kind of glass will not admit of general application; for it appears that a glass which 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 off. The first thing then is to prepare a glass 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 (A). This mass of vitrified matter is to be finely ground in a mill, and the vitreous powder thus obtained is to 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 is necessary to observe, 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 furnace 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. 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, of which the following is a general account.

The colours which are employed in painting porcelain 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

(A) The proportion of the materials employed for common white pottery-ware are 60 parts of litharge, 10 of clay, and 20 of ground flint. Porcelain or when combined with vitreous matter, zaffar, as it is called, yields a fine blue. Earthy matters which are slightly ferruginous, produce a yellow colour, and brown and black colours are obtained from iron in different states, and from manganese. A coloured glazing has been recommended by O'Reilly *, which may be applied to coarse articles of earthen ware. It is obtained from the residuum after the distillation of oxymuriatic acid. The manganese contained in this residuum is said to communicate a blackish appearance like that of bronze, which, says the author, is far from being disagreeable to the eye. This glazing he employed several times by way of trial, first fusing it with sand in a potter's furnace, throwing it into cold water to facilitate its division, and grinding it in a mill, that it may be more completely diffused in water. This glazing is attended with the advantage of being free from those dangerous qualities so common in all preparations made from the oxides of lead. Whatever colouring matters are employed, they are finely ground with gum water, or with some essential oil, in which state they are fit to be employed for the painting of porcelain with figures of flowers, or any other design with which it is intended to be adorned.

In gilding porcelain, the oxide or calx of gold (B) is employed, and it is applied nearly in the same manner as the coloured enamels. The gold, which is in the state of very minute division, is mixed with gum water and borax, and in this state is applied to the clean surface of the porcelain with a fine camel's hair pencil. The painted and gilded porcelains are then exposed to such a degree of heat in the furnace as is capable of fusing the vitreous matter with which the metallic colours are mixed. The gold is fixed by means of the borax undergoing the process of vitrification, and thus strongly adhering to the porcelain. Most of the metallic colouring matters exhibit all their beauty when the porcelain is taken from the furnace; but to bring out the lustre and beauty of the gold, those parts of the porcelain which have been gilt are afterwards subjected to the operation of burnishing.

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. The following is the conclusion of his observations.

"The process which I employ in the application of platina to painting on porcelain is simple and easy: it is as follows:—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 burnt-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 silvery 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 may be 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 transition 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 may be 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."

The same substance has been applied as a glazing to porcelain in some of the English manufactories, but however valuable and important the application of platina to this purpose may be, the scarcity of that metal, and its consequent high price, must always prevent it from coming into very general use.

We have already noticed the establishment of the manufacture of porcelain in Derby. The following is a short detail of the method of conducting that manufacture. After the paste has been properly prepared, by grinding and other necessary operations, it is delivered to the workmen, by whose dexterity the shapeless mass is converted into various beautiful forms. Vessels of a round form are usually made by a man called a thrower, by whom they are worked on a circular block moving horizontally on a vertical spindle. They are next carried to the lathe; and being fixed on the end of a horizontal spindle, they are reduced to the proper form and thickness.

(B) A powder of gold is prepared for this purpose in other two different ways. By one of these methods a quantity of gold leaf is put into a glass or earthen mortar, with a little honey or thick gum water, and ground till the gold is reduced to very minute particles; a little warm water is then added, which will wash out the honey or gum, and leave the gold behind: but the process by which the finest ground gold is obtained, is by gradually heating a gold amalgam in an open earthen vessel, and continuing the heat till the mercury is entirely evaporated, stirring the mixture with a glass rod, or tobacco pipe, that the particles of gold may be prevented from adhering as the mercury flies off. The gold remaining after the evaporation of the mercury is then ground with a little water in a Wedgwood-ware mortar, and after being dried is fit for use. Porcelain. thicknesses. They are afterwards finished, and handled by other persons, if that should be necessary, and are then introduced into a stove, where the moisture is entirely evaporated, and they become fit for the process of baking. Vessels of an oval figure, such as tea-pots, tureens, &c., acquire their form by being pressed with the hand into moulds of plaster or gypsum. The pieces of porcelain being thus prepared, are put into the fagars or cafes, which are of various sizes and dimensions, and these are set in the kiln or furnace, one upon the other, till they are filled up nearly to the top, in the manner already described. The furnace being full, the ware is baked, and after this first baking, the porcelain is in the state of biscuit.

The next process is the glazing, which, according to the description already given, is performed by dipping the pieces of porcelain in glaze of the consistence of cream. They are then conveyed to the glaze furnace, where they are again baked, but in a degree of heat inferior to that necessary for the first baking.

If the pieces of porcelain are to receive the additional ornaments of painting and gilding, they are next delivered to another set of workmen. The colouring matters, as already noticed, are extracted from mineral bodies, and after proper preparation, they are applied to the ware by the painters, in the form of landscapes or figures, according to the requisite pattern. After this process the ware is again conveyed to the furnace, and the colours are vitrified, to give them the proper degree of fixation and lustre. After every coat or layer of colour, a fresh burning is necessary. In the common kind of porcelain, once or twice is found sufficient for the ornaments it requires; but in the finer decorations, the colours must be laid on several times, and as often subjected to the action of heat, before the full effect can be produced. This completes the process for those articles of porcelain in which glazing and painting only are required.

But when the pieces of porcelain are to be farther 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 to 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 bloodstones, and other polishing substances. Much care and attention are necessary in the latter part of the process; for if the gold be not sufficiently burnt, 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 five or seven different times; and having gone through the processes now described, the porcelain is fit for the market.

White ware, or biscuit figures, are made at this manufactory, which are supposed to be equal in beauty and delicacy to any European productions of a similar kind. In this kind of porcelain, the lathe is of no use, for the figures are cast in moulds of plaster or gypsum. The materials of which they are composed being properly prepared, and previously reduced to a liquid of the appearance and consistence of thick cream, are poured into the moulds, which from the absorbent property of the plaster, imbibe the water contained in the mixture, so that the paste soon becomes sufficiently hard to part freely from the mould. The different parts of figures, as the head, arms, legs, &c., are cast in separate moulds, and after being dried and repaired, they are joined by a paste of the same kind, but of a thinner consistence. The porcelain pieces thus formed are then conveyed to the furnace, and after being subjected for a proper length of time, to a regular and continued heat, they come out extremely white and delicate.

Porcelain manufactories have been long established at Manufac-Tournay in Flanders; one of these manufactories furnishes all Flanders with blue and white porcelain. At Tournay, this manufactory they have a particular process in forming cups and other vessels, which is somewhat similar to that now described. 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 consistence, 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, is conveyed to the furnace, to undergo the process of baking.

In the manufacture of utensils for chemical purposes, where they are to be subjected to the effects of powerful chemical agents, greater attention is necessary. Vessels of this description should be infusible at any degree of heat; possess a sufficient compactness of texture, to retain saline and other fluxes in fusion, without undergoing any change; and should bear sudden changes of temperature, particularly sudden heating, without cracking, or in any degree giving way. It has been found impracticable to have the three requisites now mentioned united in the same ware, so that it becomes necessary to select the kind of ware according to the purpose for which they are intended. For bearing high degrees of heat, Hessian crucibles are found to answer best; they are composed of a very refractory clay, mixed with sand, of which the finest part is separated by a sieve, and thrown away. These vessels are made by mixing the clay with a smaller proportion of water than usual, so that a stiffer mass is obtained, and the vessel brought to the requisite shape by ramming the clay strongly into an iron mould. In this way they are very compact, and for a considerable time retain saline fluxes. Ordinary crucibles, it is found, are rendered more retentive by lining them on the inside, before they are quite dry, with a thin coating of pure clay, without the addition of any other mixture. But the most refractory material known is a mixture of unburnt with burnt clay. Vessels made of this material are found capable of resisting the effects of saline fluxes longer than any other, and hence this material is employed in making large crucibles for glasshouses.

One of the most valuable qualities of porcelain ware, is to bear sudden changes of heat and cold; but in this quality some of the most perfect kinds of ware in other respects are extremely deficient, and can scarcely be subjected, without danger of cracking, to the draught of a wind furnace, even when the heat is slowly and gradually applied. This happens to the celebrated porcelains. Porcelain

lain fire ware invented by an enlightened and philosophical manufacturer, the late Mr Wedgwood. This effect of cracking, on sudden changes of temperature, seems to depend on the hardness and closeness of texture; and the closeness of texture is found to be in proportion to the minute division of the materials before baking. The clay and flint of Wedgwood's ware are brought to a most impalpable powder before mixture, so that the texture is uncommonly hard and close. It may be worth while to mention, that Wedgwood's porcelain resists the effects of sudden heat and cold much better, by being covered with a thin coating of Windsor loam, or of a fine lute composed of coarse sand and clay, and tow or horse-dung. When crucibles are intended merely for the fusion of metals, they are greatly improved by a mixture of black lead. This substance being involved in the clay, is protected from the access of air, and is then incombustible. It has no affinity for the earths at any temperature, and being absolutely infusible, it enables the clay to bear, without melting, the greatest degree of heat. The mixture of this substance, as a material for crucibles, has another advantage, that no part of the melted metal is detained in the crucible, as is the case in the common rough ware. It also bears sudden heating and cooling better than any other.

6. General Principles of the Manufacture of Porcelain.

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 philosophic observer, or the enlightened manufacturer, we shall introduce the following observations on the principles of the manufacture of porcelain.

Observations by Vaquelin.

According to this celebrated chemist, four things may occasion difference in the qualities of earthen-ware: 1st, The nature or composition of the matter; 2nd, The mode of preparation; 3rd, The dimensions given to the vessels; 4th, 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 flint, 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 earthen-ware differs from bad, as by the proportion in which they are united. Silex or quartz makes always two-thirds at least of earthen-ware; 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 flint; but it must not be too abundant, as 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 Mode of penetrating substances, such as salts, metallic oxides, preparations glafts, &c., they require a fine kind of paste, which is obtained only by 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 breche, or small grained pudding-stone, and which can endure sudden changes of temperature.

The baking of pottery is also 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 is coarse, are much less brittle than dishes and saucers formed of the same substance, ground with more labour.

The general and respective dimensions of the different Dimensions parts of vessels of earthen-ware 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, 1st, To follow the best proportion in the principles; 2nd, 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; 3rd, To carry the baking to the highest degree that the matter can bear without being fused; 4th, 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.

C. Vaquelin, being persuaded that the quality of good pottery depends chiefly on using proper proportions of the earthy matters, though 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 purpose, and of pottery produced by some of them, in order that, when a new earth Porcelain 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.

| Hessian Argil | Porcelain Wedgwood's Crucibles | Droux Capsules | Pyrometers | |---------------|-------------------------------|----------------|-----------| | Silex | 69 | 43.5 | 61 | 64.2 | | Argil | 21.5 | 33.2 | 28 | 25 | | Lime | 1 | 3.5 | 6 | 6 | | Oxide of iron | 8 | 1 | 0.5 | 0.2 | | Water | 18 | | | 6.2 |

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, lime 2, iron 0.5, water 14. This kaolin, treated with the sulphuric acid, gave about 45 or 50 per cent. of alum.

Petunzé.—Silex 74, argil 14.5, lime 5.5, lofs 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 lofs sustained.

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

There is a kind of earthen vessels, called Alcarrezes, 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 364 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; formed into a cake of about six inches in thickness, and left in that state till it begins 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 earthen ware; and being exceedingly porous, water oozes through them on all sides. Hence the air, which comes in contact with it, by making it evaporate, carries off the calorific contained in the water in the vessel, which is thus rendered remarkably cool.

Observations of Brongniart.

The author of the following observations is superintendent of the celebrated porcelain manufactory at Sévres in France. The extensive views he has taken of the subject, and the general principles which he has advanced, will, we doubt not, be favourably received by the intelligent manufacturer, and meet with attention and consideration adequate to their importance and utility.

"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 glas 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 modern 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 oxide of gold, &c. 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 that colour; and the green oxide of copper is, under many circumstances, very uncertain. I have said that oxides alone are not susceptible of fusion: however, as they are destined to be applied in thin strata on vitrifiable substances, they may be attached to them by a violent heat. But, except the oxides of lead 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 glas, lead, and silex; glas of borax, or a mixture of both. Its general effect is, to give splendour to the colours after their fusion; to fix them on the article which is painted, by promoting more or less the softening of its surface; to envelop 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.

"I shall speak here only of the application of metallic colours to vitreous bodies or to vitreous surfaces, the substances to which they are applied. These bodies may be divided into three classes, very distinct by the nature of the substances which compose them, the effects produced on them by the colours, and the changes they experience. These classes are: 1st, Enamel, soft porcelain, and all crusts, enamels, or glases, that contain lead in a notable quantity. 2nd, Hard porcelain, or porcelain which has a crust of feldspar. 3rd, Glases in the composition of which no lead enters, such as common window-glas.

"I 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 glas rendered opake 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 glases 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..." Enamel or soft porcelain colours require less flux than others, because the glaze on which they are applied becomes sufficiently soft to be penetrated by them. This flux may be either glaze of lead and pure flux, called rocaille, or the same glaze mixed with borax. Montamy asserts that glaze 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 Sevres employ only colours without borax, because they dilute them in gum; and borax does not dilute well in that substance. I have found that both methods are 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.

I 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 on the composition of these colours, but on the nature of the glaze to which they are applied. It follows from what has been said, that painting 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 I have established, is the second fort 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.

This 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 necessary for baking porcelain. They are 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 glaze 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: 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 Sevres, 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, I was of opinion that the crust only ought to be softened by introducing into it more siliceous or Porcelain calceous flax, according to the nature of the feldspar. This method has succeeded; and for about a year past the colours might be exposed two or three times to the fire without scaling, if not overcharged with flux, and if not laid on too thick.

The third fort of excipient of vitrifiable metallic colours is glaze without lead.

The application of these colours to glaze constitutes and to glaze painting on glaze; 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 glaze are in general the same as those applied to porcelain. Neither of them differ but in their proportions; but there are a great number of enamel or porcelain colours which cannot be applied to glaze, where they are deprived of the white ground which 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, I must make known the most interesting particular phenomena exhibited by each principal kind of colours employed on soft porcelain and glaze in a porcelain furnace.

Of Reds, Purples, and Violets, made from Gold.

Carmine red is obtained by the purple precipitate of caffius; 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; 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 that 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, you may exhibit a palette composed of colours none of which change in a remarkable manner. This rose-coloured oxide of iron has been long known; but it was not employed on enamel, because on that substance it changes too much. As the painters on enamel, however, have become the painters on porcelain, they have preferred 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, as I have experienced. 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. "POR"

"Violet is made also 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 have given us in glass tints only of a dirty violet. The violet, on the other hand, produces on glass a very beautiful effect, but it is liable to turn blue. I have not yet been able to discover the cause of this singular change, which I saw for the first time a few days ago.

"Red, Rose, and Brown Colours, extracted from Iron.

"These colours are made from red oxide of iron prepared with nitric acid. These oxides are further calcined by keeping them exposed to the action of heat. 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 on hard porcelain, they do not change at all. I 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 red 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 anything remain they must be employed very deep.

"This singular effect must be ascribed to the presence of lead in the crust or glazing. I assured myself of this by a very simple experiment. I placed this colour on window glass, and having exposed it to a strong baking, it did not change.

"I covered several parts of it with minium; and 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 clothe vessels, a large quantity of oxygen gas was disengaged.

"It appears to me that this observation 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.

"Yellows.

"Yellows 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 black 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 livelier, and nearer Porcelain, 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: they are too opaque and dirty. That employed by the old painters on glass has, on the contrary, a beautiful transparency, 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. C. Miraud, whom I have already had occasion to mention, has 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 are applied on glass merely pounded, and without a flux. The oxide of iron brings the yellow to that colour which it ought to have after baking, and contributes with the argil and oxide of zinc to decompose the muriate of silver without deoxidating the silver. After the baking, there remains a dust which has not penetrated into the glass, and which is easily removed.

"This yellow, when employed thicker, gives darker shades, and produces a ruffet.

"Blues.

"It is well known that these are obtained from the oxide of cobalt. All chemists are acquainted with the preparation of them. Those of Sevres, which are justly esteemed for their beauty, are indebted for it only 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.

"I remarked respecting the oxide of cobalt a fact which is perhaps not known to chemists: it is volatile in a violent heat: it is to this property we must ascribe the bluish tint always assumed by white in the neighbourhood of the blue. I have placed expressly on purpose, in the same case, a white piece close to a blue one, and found that the side of the white piece next the blue became evidently bluish.

"The blue of hard porcelain, destined for what is called the ground for a great heat (les fonds au grand feu) is fused with feldspar; that of soft porcelain has for its flux silice, potash, and lead: it is not volatilized like the preceding; but the heat 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..." Porcelain heat are composed with the oxides of cobalt and nickel, but a brownish green only is obtained.

"Blueish greens called celestial blues, which were formerly colours very much in vogue, can be applied only upon soft porcelain; on hard porcelain they constantly become scaly, because potash enters into their composition.

"These greens cannot be applied on glaas; they give a dirty colour. To obtain a green on glaas, it is necessary to put yellow on one side, and blue, more or less pale, on the other. This colour may be made also by a mixture of blue with yellow oxide of iron. I hope to obtain from oxide of chrome a direct green colour. The trials I have made give me reason to hope for success. Pure chromate of lead, which I applied to porcelain in a strong heat, gave me a pretty beautiful green of great intensity and very fixed.

Byfres and Ruffets.

"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 change in any manner on soft porcelain, as lead has not the same action on oxide of manganese as on that of iron, as I assured myself by an experiment similar to that already mentioned.

"This colour fades very speedily on glaas.

"Ruffet grounds in a great heat, known under the name of tortoiseshell grounds, are made in the same manner. Their flux is feldspar: no titanium enters into their composition, though said so in all printed works. Titanium was not known at the manufactory of Sevres when I arrived there. I treated this singular metal in various ways, and never obtained but grounds of a pale dirty yellow, and very variable in its tone.

Blacks.

"Blacks are the colours most difficult to be obtained very beautiful. No metallic oxide gives alone a beautiful black. Manganese is that which approaches nearest to it. Iron gives an opake, 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 scaly and dull.

"These oxides are those of manganese, the brown oxides of copper, and a little of the oxide of cobalt. The gray is obtained by suppressing the copper, and increasing the dose of the flux.

"The manufactory of Sevres 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 just proportion of doses, must produce in the results 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.

"In recapitulating the facts above mentioned, to present them under another general point of view, it is seen,

"It, That among colours generally employed on Faits rel. hard porcelain one only is susceptible of changing, viz. tive to carmine, and the tints into which it enters: that its hours rec. may be supplied by the reds of iron, and that no colour then changes.

"I have prefented to the Institute a head not baked, executed according to this method: and the painting of two roses, that of the one baked, and that of the other not baked. It has been seen that there was no difference between them.

"2d, That among 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, 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 glaas change also by acquiring complete transparency. These in particular are the yellows and greens.

"4th, That it is neither by calcinating the colours in a higher degree, nor previously fusing them, as supposed by some, that they are prevented from changing, since these means really alter the changing colours, and produce no effect on the rest. The change which several colours experience on soft porcelain and on glaas does not then depend on the nature of their composition, but rather on that of the body on which they are applied.

"Consequently, by suppressing from the colours of hard porcelain the carmine of gold, which is not indispensably necessary, we shall have a series of colours which do not change."

As it must be of no small importance to the chemical Refuls of manufacturer to be acquainted with the results of experiments on the effects of heat, when applied to different proportions of the materials employed in making certain porcelain, or other analogous ware, we shall insert the important following tables, exhibiting those results. The first table contains the results of the numerous experiments of Achard and Morveau on the vitrification of earths with saline bodies. The mixture of the earths and salts was made in a clay crucible, and, in the experiments of Morveau, the crucible was exposed for two hours to a heat from 22° to 26° of Wedgwood's pyrometer; but in those of Achard, the crucible was kept for three hours in the heat of a strong wind furnace, in which the temperature was probably higher than the former.

The second table presents a view of the effects of the vitrification of earths by means of metallic oxides. The mixtures were exposed in earthen crucibles to the heat of a porcelain furnace during the whole time required to bake porcelain ware.

In the third table are exhibited the curious results of the effects of vitrifying materials on the crucibles in which the vitrification takes place. It is to be observed, that the effects of the same materials, and in the same proportions, are very different, in different vessels; and without attending to this circumstance, very erroneous conclusions will be drawn in estimating the action of vitrifiable substances on each other. This diversity of the effects of the same materials in different crucibles, TABLE I. Shewing the Results of the Vitrification of Earths with Saline Bodies.

| Mixture | Results | |--------------------------|-------------------------------------------------------------------------| | A. Silex | 1. A yellow glass, not hard enough to give sparks with steel. | | Carbonate of potash | 2. A colourless transparent glass, but deliquescent from the excess of alkali. | | M. Silex | 3. A vitriform mass, yellow, hard, and scintillant. | | Carbonate of soda (dry) | | | A. Silex | 4. A beautiful transparent glass, not at all soluble in water. | | Carbonate of potash | | | A. Silex | 5. A white porcellaneous mass, scarcely scintillant. | | Boracic acid | | | A. Silex | 6. A hard transparent glass—scintillant. | | Boracic acid | | | A. Silex | 7. A white opaque melted porous mass—scintillant. | | Boracic acid | | | A. Silex | 8. A transparent glass—hard and scintillant. | | Calcined borax | | | A. Silex | 9. A mass resembling agate—but perfectly fused and scintillant. | | Calcined borax | | | A. Silex | 10. A green scintillant glass. | | Sulphate of soda | | | A. Silex | 11. A soft green transparent glass. | | Nitre | | | A. Silex | 12. Scoria—the crucible entirely destroyed. | | Common salt | | | M. Silex | 13. A white opaque, puffy, vitreous mass, deliquescent, and reddening litmus. | | Phosphate of soda and ammonia | | | M. Lime | 14. A white spongy opaque mass, crumbling between the fingers. | | Carbonate of soda | | | A. Chalk | 15. Partly fused—the rest pulverulent—the crucible strongly corroded. | | Carbonate of potash | | | A. Chalk | 16. A well-fused, polished, black scintillant glass. | | Carbonate of potash | | | A. Chalk | 17. Remained a white powder. | | Carbonate of potash | | | M. Lime | 18. A fine transparent yellowish glass—the crucible strongly corroded. | | Borax | | | A. Chalk | 19. A well-fused, black, scintillant, polished mass. | | Borax | | | A. Chalk | 20. A yellow scintillant glass. | | Borax | | | A. Chalk | 21. A yellow glass—run through the crucible. | | Boracic acid | |

Vol. XVII. Part I. Porcelain.

Mixture.

A. Chalk - Sulphate of soda - 3. A hard yellow scintillant glass. A. Chalk - Sulphate of soda - 1. A hard brown scoria—the crucible totally destroyed. A. Chalk - Nitrate of soda - 1. A hard yellow glass. A. Chalk - Common salt - 1. A yellow scintillant glass—the crucible entirely destroyed. M. Lime - Phosphate of soda and ammonia - 1. A white opake crumbly mass. M. Alumine - Carbonate of soda - 1. A gray opake ill-fused frit, not cohering to the crucible and deliquescent. A. Alumine - Carbonate of soda and potash in all proportions from 1 to 12 - 4. Remained unmelted and uncohering. A. Alumine - Carbonate of potash - 1. Partially melted, but soft and friable. M. Alumine - Borax - 1. A fine transparent clear green glass. A. Alumine - Borax - 1. Remained pulverulent. A. Alumine - Boracic acid - 1. Part unfused and remaining pulverulent, the rest partially melted. M. Alumine - Phosphate of soda and ammonia - 1. A green frit easily friable. M. Magnesia - Carbonate of soda - 1. A white opake uncohering mass. M. Magnesia - Borax - 1. A semi-transparent somewhat milky glass of a gelatinous appearance, but very hard and brilliant on the surface. M. Magnesia - Phosphate of soda and ammonia - 1. A white mass a little agglutinated but not adhering to the crucible. M. Barytes (pure) - Carbonate of soda - 1. A very hard semi-vitrified mass, of a clear green. M. Barytes - Borax - 1. A beautiful transparent glass with a faint yellow tinge, strongly adhering to the crucible. M. Barytes - Phosphate of soda and ammonia - 1. A remarkably fine transparent glass.

Table II. Containing the Results of the Vitrification of Earths by Metallic Oxides.

Mixture.

Silex - Scoria - Black and polished—hard, giving sparks with fleel. Oxide of iron - Not fused - Black and friable. Silex - Oxide of iron - Scoria run through the crucible - Black and hard—scintillant. Silex - Oxide of copper - Not fused. Silex - Oxide of copper - Not fused. | Porcelain | Mixture | Result | Colour and Texture | |-----------|---------|--------|-------------------| | Silex | 1. | A solid mass but not fused | White and hard. | | Oxide of lead | 1. | Fused, porous, and semi-vitrified | Yellow—not scintillant. | | Silex | 2. | Perfect glass | Green—not scintillant. | | Oxide of tin | 1. | A coherent mass | Gray—easily friable. | | Silex | 2. | Vitrified | Greenish yellow—not scintillant. | | Oxide of bismuth | 1. | Remained in powder. | Deep yellow—not scintillant. | | Silex | 4. | Perfect glass | Colourless—scintillant. | | Oxide of antimony | 1. | Glass | Gray and friable. | | Silex | 2. | Not melted | White—hard. | | Oxide of zinc | 1. | Remained in powder. | Gray—scintillant. | | Silex | 2. | Melted only where touching the crucible | Black—scintillant. | | Oxide of zinc | 3. | Perfectly fused | Red—scintillant. | | Lime (carbonated) | 1. | A melted porous mass | The same. | | Oxide of iron | 1. | Melted, polished in the fracture, part of the copper reduced | Gray. | | Lime | 3. | Melted, but porous | Greenish yellow—scintillant. | | Oxide of copper | 1. | Part only melted, the rest pulverulent | Yellow—scintillant. | | Lime | 4. | Glass run through the crucible | Yellow—scintillant. | | Oxide of lead | 1. | Remained in powder. | Yellow—scintillant. | | Lime | 1. | Semi-vitrified | Greenish yellow—scintillant. | | Oxide of tin | 2. | Glass | Gray. | | Lime | 2. | Glass penetrating the crucible | Green. | | Oxide of antimony | 1. | Glass penetrating the crucible | Yellow—scintillant. |

C & 2 Lime Porcelain.

Mixture.

Result.

Porcelain.

Lime - Oxide of antimony

1. Remained in powder.

Lime - Oxide of antimony

2. Glass penetrating the crucible - Deep yellow—scintillant.

Lime - Oxide of antimony

4. A semi-transparent polished mass - Gray yellow—scintillant.

Lime - Oxide of zinc

1. Glass - Deep yellow—scintillant.

Alumine - Oxide of iron

1. Only partially fused.

Alumine - Oxide of iron

3. A melted porous mass - Black—scintillant.

Alumine - Oxide of copper

1. Only partially fused.

Alumine - Oxide of copper

4. The same.

Alumine - Oxide of lead

1. Remained in powder.

Alumine - Oxide of lead

3. The same.

Alumine - Oxide of lead

1. Glass - Deep yellow—scintillant.

Alumine - Oxide of tin

2. A melted porous mass, not polished in the fracture - Gray—scintillant.

Alumine - Oxide of bismuth

2. Partially fused.

Alumine - Oxide of antimony

4. Only partially fused.

Alumine - Oxide of zinc

4. Remained in powder.

Magnesia - Oxide of iron

3. Half fused, but not cohering.

Magnesia - Oxide of copper

3. A porous half-fused mass - Gray—scintillant.

Magnesia - Oxide of lead

3. Not fused.

Magnesia - Oxide of lead

4. A porous melted mass, part of the oxide reduced.

Magnesia - Oxide of antimony

3. Beginning to fuse - Gray—scintillant.

Table III. Shewing the Action of the Vitrifying matters on the Crucibles that contain them.

Substances used.

Result in the Clay crucible (A).

Common flint.

Opake and milk-white, but without fusion.

Marble.

Run into a green glass.

Gypsum.

Run into a radiated green glass.

Result in the Chalk crucible (B).

Opake and white, but with beginning fusion wherein contact with the crucible.

No change.

No change.

Result in the Charcoal crucible (C).

As in A.

No change.

No change. Porcelain clay.

Ditto, another kind.

Reddle.

Jasper.

Muscovy talc.

Spanish chalk.

Basalt.

Result in the Clay crucible (A.)

Melted and ran through the crucible.

Compact, white and no signs of fusion.

A compact mass partially melted.

A black glass covered with a crust of reduced iron.

No fusion, but the colour changed to brown.

A black glass with interspersed grains of iron.

Only hardened.

Brown-yellow glass with a crust of iron.

Result in the Chalk crucible (B.)

Melted down with the crucible to a tough flag.

Run into a hard blue clear glass.

A perfectly black glass.

A semitransparent apple-green glass.

Completely fused in the parts touching the crucible.

The whole crucible was penetrated with a scoria so as not to fall to powder on exposure to air.

A gray semitransparent glass.

A green scoria, also with a crust of iron.

Result in the Charcoal crucible (C.)

Scarcely altered, except slight fusion at the edges.

As in A.

As in A.

As in A.

As in A.

As in A.

As in A.

As in A.

As in A.

For an account of some valuable experiments of a similar nature, which were made by the celebrated Klaproth, in crucibles of clay and charcoal, in which the differences of the results are very striking, the reader is referred to his Analyt. Essays, or to Aikin's Dictionary of Chemistry and Mineralogy.

Porcelain-Shell, a species of Cypraea. See Cypraea, Conchology Index.