92 Beginnings of Porcelain 



It is of course possible that the potters had learned to adjust the 

 qualities of the glaze by small additions of alkali and iron oxide. Slight 

 variations in the quantity of either of these substances greatly influence 

 the physical properties of the glaze. 



This table cannot give more than a rough approximation of the 

 quantities of the two ingredients of the mixture, as the losses of volatile 

 matter in both limestone and clay during burning cannot be computed 

 with accuracy. The table suggests that not far from one part of lime- 

 stone to two parts of clay were employed. We may safely conclude 

 that this glaze was made by adding pulverized limestone, lime, or 

 milk of lime to the material from which the body of the pottery 

 was made. The modern Chinese glaze for porcelain is made by mixing 

 lime with one of the two ingredients of which they make the body. 

 This process seems to be peculiar to China. 



Conclusions. — At the time this ware was made, the potters had 

 already acquired a high degree of dexterity. Many of the things that 

 they accomplished in the fabrication of this pottery required technical 

 skill of no mean order. The engobe coat, without which no satisfactory 

 glaze could be made upon so porous a ware, was used. The expansion 

 of the glaze has been very accurately adjusted to that of the body. 

 The glaze is remarkably b-tlliant for one free from lead. The glaze 

 has no large bubbles, nor are small bubbles numerous enough to cloud 

 the ware. On the other hand, they made the glaze too thick, and they 

 could not prevent it from running during the firing. 



With potters as skilful as these, the discovery of methods of over- 

 coming the porosity of the ware, and thus making it a true porcelain, 

 should be only a matter of time. As the engobe coat is porcelain, it 

 is quite possible that the knowledge was not lacking even at that time. 

 They may not have realized that a dense ware would be worth the 

 great expense involved in grinding the materials to the necessary 

 fineness by the crude methods then available, and in the control of the 

 drying and firing methods to prevent distortion of the ware. 



II. Analysis of a Green Glaze from a Bowl of Han Pottery 



This is a brilliant glassy glaze of a bottle-green color from a Han 

 pottery bowl (Cat. No. 1 18578). It is thickly applied over a red 

 porous body. 



It is believed that the material selected for analysis correctly 

 represents the original unaltered glaze. The glaze with its red backing 

 was crushed to fragments of about a millimetre average size, and clear 

 unaltered fragments were selected after scrutiny under a powerful 



