Hard Paste.—The impulse of the Western potter had always been to reproduce exactly and chemically the Oriental porcelain. Until the first decade of the eighteenth century this had not been achieved. The news of the great discovery by Johann Fredrich Böttger, in 1709, of a white translucent porcelain, having all the characteristics of the Chinese ware, ran like a flame throughout Europe. Translucent porcelain may be either what is termed hard paste (pâte dure), containing only natural elements in the composition of the body and the glaze; or soft paste (pâte tendre), where the body is an artificial combination of various materials used as a substitute for the natural earths. All Chinese or true porcelain is of the hard-paste variety. The term pâte tendre really applies to the feeble resistance of this artificial porcelain to the action of a high temperature as compared with that offered by true porcelain, and also to the softness of the glaze, which can be scratched by steel.
The body of the true porcelain is essentially of two elements—the white clay or kaolin, the infusible element which may be said to be the skeleton, and petuntse, the felspathic stone, which is fusible at a high temperature, which may be termed the flesh, and gives transparency to the porcelain. Of the two Chinese names, which have become classical since they were adopted in the dictionary of the French Academy, kaolin is the name of a locality where the best porcelain earth is mined, and petuntse, literally "white briquettes," refers to the shape in which the finely pulverized porcelain stone is brought to the Chinese potteries, after it has been submitted to the preliminary processes of pounding and decantation.[1]
[1] Chinese Art, vol. ii. p. 16, 1906, by Stephen W. Bushell, C.M.G. (late Physician to H.M. Legation, Peking).
Soft Paste.—The artificial porcelain, which was difficult of fabrication, was an imitation of the true Chinese porcelain, although its whiteness, its translucency, and its brilliant glaze have all the appearance of true porcelain. Kaolin and petuntse are of little importance in the composition of soft porcelain. Its transparency was obtained by the addition of glass, its plasticity by the use of soapstone, and its glaze by an admixture of silica and lead. Moreover, the composition of artificial porcelain has required researches and combinations much more intricate than those which had led to the discovery of hard porcelain, the latter being produced by two substances already provided by nature.
Imitative porcelain had been made at Florence under the auspices of the Grand Duke of Tuscany as early as from 1568 to 1587, of which fabrique only about thirty pieces are known. France is the most prolific in porcelain factories of the pâte tendre, as it came afterwards to be termed in contradistinction to the pâte dure or true porcelain of Meissen. The factory at St. Cloud lasted from 1695 till 1773. Vincennes was founded in 1740, and was finally transferred to Sèvres in 1756, which factory stands paramount in its porcelain, known to collectors as vieux Sèvres.
At Nove, near Venice, in 1752, Pasqual Antonibon brought from Meissen a potter, Sigismond Fischer, to construct a furnace for making porcelain in the Saxon style. In 1761 there were three furnaces, one for hard paste ad uso Sassonia, and two for soft paste ad uso Francia.[2]
[2] Marks and Monograms on Pottery and Porcelain, by William Chaffers. (Letter from Francesco Antonibon to Lady Charlotte Schreiber.)
It will thus be seen that the two schools had begun to run side by side. The crowning point was in 1768, when the Sèvres factory commenced to make hard paste. Both bodies were simultaneously made until 1804, after which the manufacture of soft porcelain at Sèvres was discontinued by M. Brongniart. In 1847, the old style was revived by his successor, M. Edelman (Report on Pottery at the Paris Exhibition by M. Arnoux, 1867).
In general, it may be said that the manufacture of soft porcelain is beset with difficulties and uncertainties. Its artificial composition renders it capricious in the kiln. In connection therefore with the modern manufacture of Sèvres of the old pâte tendre variety, it is interesting to record that in the late eighties the original formulæ of the early potters were used in an attempt to reproduce the old body, but had, after repeated and costly failures, to be abandoned as hopeless.