436 



REPORT OF NATIONAL MUSEUM, 1888. 



fourteenth century, a sort of transparent glass with a foundation of 

 lead — a glaze still common in country productions. Later, in the fifteenth 

 century the true white enamel, email, a mixture of salt, of lead and 

 tin, the thickness of which concealed the color of the paste, was dis- 

 covered in Italy and gained immortality for Luca della Eobbia of 

 Florence, and Oragio Fontana of Pesaro. In this category also belong 

 the majolicas, faenza, the faiences of Niirnberg, Bernard Palisy's pot- 

 tery, the faiences of Nevers, Eouen, and other places, ancient and 

 modern. The couverte is confined to porcelain proper. 



Crude Chinese kaolin, when cleansed by washing out its impurities, 

 and ready for use in making the paste, gives a very white clay, soft to 

 the touch, possessing a plasticity very similar to that of Saint Yrieix, 

 which is derived from decomposed pegmatite. The residue left by the 

 washing contains a good deal of quartz, crystals of feldspar partially 

 decomposed, and flakes of mica, as would be found in graphic granite. 

 Analysis shows that the fusible portion consists chiefly of petrosilex 

 and, by its composition and density, closely resembles the rock found 

 in abundance at Saint Yrieix, which, without addition, furnishes the 

 glaze for hard porcelain at Sevres. 



The composition of Chinese and of the most celebrated of European 

 l)orcelains may be compared in the following table: 



[Average of six analyses.] 



Thus, generally speaking, Chinese porcelain contains more silica and 

 less alumina than do the products of the manufactories of Sevres, Vi- 

 enna, and Saxony, respectively. The effect of the presence in greater or 

 less degree of these components is well known by the Chinese, who say 

 that to produce fine porcelain the ratio of alumina must be increased; 

 to produce the commoner kinds that of silica must be increased. In 

 Europe experience has taught the same results. The porcelain of com- 

 merce shows much the same composition as do the specimens of Chinese 

 analyzed by M. Salvetat, also i^resumably ordinary ware and not the 

 finest grades intended for Imperial use, while in the three Government 

 establishments mentioned a larger ratio of alumina is introduced, be- 

 cause it resists high temperatures and is therefore necessary to enable 

 the designs painted to maintain their sharpness of outline. In some 

 cases the Chinese also employ ferruginous kaolins, which sensibly di- 

 minish the value of the manufactured article. 



