90 Beginnings of Porcelain 



Analysis of the Glaze 



Silica, SiOj 54-17 



Alumina, AljOt 14.16 



Iron oxide, FeO 4-36 



Lime, CaO 1905 



Magnesia, MgO 2.04 



Soda, NajO 5 . 49 



Potash, K a O 0.00 



99.27 



This is obviously an alkali-lime-iron-alumina silicate glaze. This 

 is so purely a Chinese type, that it is useless to compare it with any but 

 Chinese glazes. Even the Japanese glazes differ materially from those 

 of the Chinese, being intermediate in character between these and the 

 European. Those Chinese porcelain glazes the analyses of which have 

 been examined are all white, and hence free or nearly so from iron. 

 The influence of iron on a glaze is very great, and extends to nearly all 

 its properties. Hence, in modifying a yellow glaze to a white one, 

 there is much to do in the way of readjusting the proportions of all the 

 elements, besides removing the iron. Therefore the close correspond- 

 ence which appeared among the several body analyses will not be found 

 to hold between the yellow and the colorless glazes, even if one has been 

 derived from the other. 



Comparative Table of Chinese Glazes 



ABC 



Silica, SiOj ' 54-17 68 64.1 



Alumina, AljOs 14.16 12 10.2 



Iron oxide, FeO 4-38 traces traces 



Lime, CaO 1905 x 4 2I 



Magnesia, MgO 2.04 not determined 



Alkali, Na 2 0, K,0 5.49 6 5 



Explanation of Table 

 A. — Ancient Chinese pottery glaze, analysis by H. W. Nichols. 

 B and C. — Modern Chinese porcelain glazes, analyses by A. Salv£tat {I. c, p. 132). 



The glaze on porcelain is thin, and Salv6tat evidently had difficulty 

 in securing enough material for a thorough analysis. The examples 

 given in the table are sufficient to show that all these glazes are of the 

 same character. 



$| A comparison of the compositions of glaze and body suggests that 

 the glaze has been prepared by mixing the material of the body with 

 pulverized limestone. A brief calculation of the quantitative relations 

 between the several elements of body and glaze confirms this impression 

 in such a manner that there can remain no doubt as to the mode of 



