Spirit of Discovery.

POTTERY.[³]

(Continued from page 284.)

China.

The name China, by which the ware that I am about to describe is known in England, shows sufficiently the country from which we have received it. The term porcelain, which is applied to it on the continent of Europe, is Italian; porcellana being in that language the name of those univalve shells forming the genus cypraea of the conchologist, which have a high arched back like that of the hog (porco, Ital.), and are remarkable for the white, smooth, vitreous glossiness of the surface about the mouth of the shell, and sometimes, as in the common cowry (Cypraea moneta), over the whole surface.

The introduction of the Chinese porcelain soon excited a strong desire in the various countries of Europe to imitate it; but as the establishment of experimental manufactories for this purpose required the expenditure of considerable sums, and at a risk beyond the means of private persons, it is chiefly to the munificence of the sovereigns of Europe that the public are indebted for the first steps made in this interesting art. In Germany, chemists and mineralogists were set to work; the latter to seek for the most appropriate raw materials, and the former to purify and to combine them in the most advantageous proportions. The French government adopted the very sensible plan of instructing some of the Jesuit missionaries, who at that time had penetrated to the court of China, and into most of the provinces of that empire, to collect on the spot specimens of the materials employed by the Chinese themselves, together with the particulars of the process. The precise result thus obtained is not known; for as a considerable rivalry existed between the different royal manufactories of this ware, the most valuable information would of course be kept as secret as possible.

Of the European manufactories of porcelain, that established at Miessen, near Dresden, by Augustus Elector of Saxony and King of Poland, in the early part of the 17th century, was the first that aspired to a competition with the Chinese. In compactness of texture and infusibility it was reckoned perfect a hundred years ago. It is not quite so white as some of the French and English porcelains, but is inferior to none in its painting, gilding, and other decorations.

The French royal manufactory at Sevrès, near Paris, has been for several years in a gradually advancing state, with regard to the whiteness, compactness, and infusibility of the body, the elegance of the forms, the brilliancy of the colours, the elaborateness of the drawing, and the superb enrichments of the gilding. The private manufactories of porcelain in France imitate and approach more or less near to the royal establishment.

At Berlin and at Vienna are royal porcelain manufactories in high esteem, as well as in some of the smaller states of Germany.

British Porcelain.

The first manufactories of porcelain in England were those at Bow, and at Chelsea, near London. In these, however, nothing but soft porcelain was made. This was a mixture of white clay and fine white sand from Alum bay, in the Isle of Wight, to which such a proportion of pounded glass was added as, without causing the ware to soften so as to lose its form, would give it when exposed to a full red heat a semi-transparency resembling that of the fine porcelain of China. The Chelsea ware, besides bearing a very imperfect similarity in body to the Chinese, admitted only of a very fusible lead glaze; and in the taste of its patterns, and in the style of their execution, stood as low perhaps as any on the list. The china works at Derby come, I believe, the next in date; then those of Worcester, established in 1751: and the most modern are those of Coalport, in Shropshire; of the neighbourhood of Newcastle, in Staffordshire, and in other parts of that county.

The porcelain clay used at present in all the English works is obtained in Cornwall, by pounding and washing over the gray disintegrated granite which occurs in several parts of that county: by this means the quartz and mica are got rid of, and the clay resulting from the decomposition of the felspar is procured in the form of a white, somewhat gritty powder. This clay is not fusible by the highest heat of our furnaces, though the felspar, from the decomposition of which it is derived, forms a spongy milk-white glass, or enamel, at a low white heat. But felspar, when decomposed by the percolation of water, while it forms a constituent of granite, loses the potash, which is one of its ingredients to the amount of about 15 per cent, and with it the fusibility that this latter substance imparts.

The siliceous ingredient is calcined flint; and in some of the porcelain works, (particularly, I believe, those at Worcester,) the soapstone from the Lizard-point, in Cornwall, is employed. These are all the avowed materials; but there is little doubt that the alkalies, or alkaline earths, either pure or in combination, are also used, in order to dispose the other ingredients to assume that state of semi-fusion characteristic of porcelain.

(The principal processes are) the grinding and due mixture of the ingredients, in order to obtain a mass sufficiently plastic; the forming this mass on the wheel; the subsequent drying of the ware; the first firing, by which it is brought to the state of biscuit; the application of the firmer colours occasionally on the surface of the biscuit; the dipping the biscuit in the glaze; the second firing, by which the glaze is vitrified; the pencilling in of the more tender colours on the surface of the glaze; and the third and last firing that is given to the porcelain.

It is not for me to determine which of our English porcelains is the best; probably, indeed, one will be found superior in hardness, another in whiteness, a third in the thinness and evenness of the glaze, a fourth in the form of the articles, a fifth in the design, and a sixth in the colours. In hardness and in fusibility, they are probably all inferior to the Dresden and to the Sevrès porcelain; for pieces in biscuit and in white glaze, from both these manufactories, are imported in considerable quantities, in order to be painted and finished here. But it is equally certain, that the last ten years have seen the commencement, and, in part, the completion, of such improvements in this fabric, as will probably place the English porcelains on an equality with the best of the continental European ones.

Advantage has recently been taken of the semi-transparency of porcelain biscuit to form it into plates, and to delineate upon it some very beautiful copies of landscapes and other drawings, by so adapting the various thicknesses of the plate as to produce, when held between the eye and the light, the effects of light and shadow in common drawings. The invention originated in the ingenuity of our French neighbours.