POTTERY, PORCELAIN. In refer ence to chemical constitution, there are only two genera of baked stoneware. The first consists of a fusible earthy mix ture, along with an infusible, which when combined are susceptible of becoming semi-vitrified and translucent in the kiln. This constitutes porcelain or china-ware ; which is either hard and genuine, or ten der and according to the quali ty and quantity of the fusible ingredient. The second kind consists of an infusible mixture of earths, which is refractory in the kiln, and continues opaque. This is pottery, properly so called ; but it compre hends several sub-species, which gradu ate into each other by imperceptible shades of difference. To this head be long earthenware, stoneware, flintware, fayence, delftware, iron-stone, china, &e.
The earliest attempts to make a com pact stoneware, with a painted glaze, seem to have originated with the Arabi ans in Spain, about the 9t11 century, and to havepassed thence into Majorca, in which island they were carried on with no little success. In the 14th century, these articles, and the art of imitating them were highly prized by the Italians, under the name of Majolica, and porcela na, from the Portuguese word for a cup. The first fabric of stoneware possessed by them was erected at Fayenza, in the ecclesiastical state, whence the French term fayence is derived. The body of the ware was usually a red clay, and the glaze was opaque being formed of the oxydes of lead and tin, along with potash and sand. Bernhard de Palissy, about the middle of the 16th century, manufac tured the first white fayence, at Saintes, in France; and not long afterwards the Dutch produced a similar article, of sub stantial make, under the name of delft ware, and delft porcelain, but destitute of those graceful Ibrms and paintings for which the ware of Fayenza was dis tinguished. Common may be, therefore, regarded as a strong, well burned, but rather coarse-grained kind of stoneware.
It was in the 17th century that a small work for making earthenware of a coarse description, coated with a common lead glaze, was formed at Burslem, in Staf fordshire, which may be considered as the germ of the vast potteries now es tablished in that county. The manufac
ture was improved about the year 1690, by two Dutchmen, the brothers Elers, who intoroduced the mode of glazing ware by the vapor of salt, which they threw by handfuls at a certain period among the ignited goods in the kiln. But these were rude, unscientific, and desultory efforts. It is to the late Josiah Wedgewood, Esq., of England, that the world at large is mainly indebted for the great modern advancement of the ceramic art.
This country contains all the materials for establishing a perfect manufacture ; but as yet little has been done except in the production of coarse articles. The bet ter kind ofpottery, is made of an artificial mixture of alumina and silica ; the for mer obtained in the form of a fine clay:, from Devonshire in England, chiefly ; and the latter consisting of chert or flint, which is heated red-hot, quenched in wa ter, and then reduced to powder. Each material, carefully sifted, is diffused through water, mixed by measure, and brought to a due consistency by evapo ration : it is then highly plastic, and formed upon the potter's wheel and lathe into various circular vessels, or moulded into other forms, which, af ter having been dried in a warm room, are inclosed in baked clay cases re sembling bandboxes, and called eeg gars • these are ranged in the kiln so as near to fill it, leaving only space enough for the fuel ; here the ware is kept red hot for a considerable time, and thus brought to the state of biscuit. This is afterwards glazed, which is done by dip ping the biscuit-ware into a tub contain ing a mixture of about 60 parts of h. tharge, 10 of clay, and 20 of ground flint, diffused in water, to a creamy consist ence ; and when taken out enough ad heres to the piece to give an uniform glazing when again heated. The pieces are then again packed up in the seggars, with small bits of pottery interposed be tween each, and fired in a kiln as before. The glazing mixture fuses at a very moderate heat, and gives an uniform glossy coating, which finishes the pro cess when it is intended for common white ware.