On the operation of baking depend the nature and cha racteristics of the porcelain manufactures. It is not at all difficult to procure earths and other ingredients that will exhibit nearly all the appearances of porcelain, ere it be subjected to the fire; but the great and distinctive pro perty of porcelain is its semi-vitrification, to which it owes its lustre and transparency; a result which has not yet been satisfactorily attained with any other substances, but those of which the Chinese form their celebrated manufacture.
Reaumur was the first who examined this subject scientifically. He analysed the Chinese and European porcelains; lie tried to ascertain their real and inherent qualities by the action of heat; and the result of his ex periments was, that the properties of the two manufac tures were essentially different ; that European porcelain, when subjected to the fire, underwent perfect fusion ; that the eastern porcelain was unaltered by the fire, and was a half-vit•ified substance, in a middle state between the com mon baken earthenware of vulgar manufactures, and true glass. Other philosophers have since made this subject the object of scientific investigation, particularly the late Mr. Wedgewood, though the result of his experiments was riot exactly the same as those of Reaumur. Mr. Wedgewood ascertained the fusibility of most of the Eu ropean porcelains ; that several kinds, manufactured in England underwent perfect vitrification at temperatures from 90° of his scale to 120'; that one kind, manufactur ed at Bristol, showed no symptoms of vitrification at I:35'; and that the Dresden porcelain was still more obstinate in resisting the heat. He also ascertained that common Chinese porcelain did not vitrify completely by any heat, but began to soften at 120', and at 156° became so soft as to lose their shape; that the real King-te-tching porcelain did not soften in any heat that could be applied ; but that, on the contrary, its internal substance, entirely unaltered, still retained its grandular texture.—In a former part of
this article, it was mentioned that earths have recently been discovered in different parts of Europe, possessing similar properties as those of China ; and hence that our Euro pean porcelain has of late attained to very considerable perfection. The true and real porcelain seems to be formed when the fusible part requires the greatest degree of heat for that purpose. This is the case with the pe tuntse of the Chinese, which is allowed to be similar to, if not the same as the feldspar of Cornwall. The other ingredient, to which the porcelain mass owes its ductility, is called porcelain•clay or earth, which is a substance coin posed of alumina and silex, in various proportions, and which corresponds in no inconsiderable degree with the kaolin of the east. In Europe, the substance known by the name of soap.rock or steatite, is employed with the kaolin or porcelain-clay, with the view of giving firmness to the infusible part of the manufacture.—Such being our advantages, we may hope soon to rival the celebrated porcelain manufacture of the east ; though probably, even allowing we have the materials, centuries may elapse ere our workmen attain to that surprising degree of de licacy, ingenuity and accuracy, in conducting the dif ferent steps of the progress, for which the Chinese la bourers have, for time immemorial, been so celebrated; and without which all the other advantages we possess can be of no avail.