Technical Investigation of Chinese Pottery 89 



Its average thickness is one-quarter millimetre, but this thickness is 

 very variable. Although it is not pure white in color, it is of a dis- 

 tinctly lighter gray than the body; also it differs from the body, in 

 that it is compact and free from pores. When examined under a 

 hand magnifying-glass, it seems to be very sharply and distinctly sep- 

 arated from the body. When examined as a thin section under the 

 microscope, the sharp line of demarcation disappears, as well as 

 the difference in color. It then seems to be of the same material as the 

 body freed from ferruginous particles and from coarse grains, so that 

 it has vitrified into a dense non-porous body. The object of such a 

 coating as this is twofold: it provides a light-colored background for 

 the transparent glaze, whereby its brilliancy is enhanced; and it provides 

 an impervious support for the glaze, which otherwise might be absorbed 

 into the pores of the body during the firing. The appearance of the 

 material, when viewed in the form of a micro-section, suggests that 

 this coat is merely the result of floating the finer particles of the mix 

 to the surface during the process of forming the vessel. This would 

 ordinarily be accomplished by the friction of the hand or of some tool. 

 But the coating under the more fusible glaze, where its presence is 

 imperative, is much thicker than that under the less fusible glaze, 

 where the necessity for it is much less. The way the coarse particles 

 of the body project through the red glaze is difficult to understand on 

 the theory of a floated surface; and there are no signs of dragging along 

 the surface of those coarse particles which lie immediately under the 

 surface; also it would be difficult to float so much fine material when the 

 deficiency of this matter is such as to leave so many voids in the interior. 

 The preponderance of evidence indicates that this material is an engobe 

 coat put on possibly by dipping, but more probably by spraying. In 

 both its physical and chemical aspect, this coat is a true porcelain. 



The glaze is a greenish-yellow glass, brown in the thicker places. 

 It is of variable thickness, as it ran badly during firing. Aside from 

 this serious deficiency, it is a remarkably good glaze. It still adheres 

 firmly to the body, and there has been no chipping or scaling. The 

 crazing takes the form of a fine and uniform network of cracks. 

 The brilliancy is very great, and there is no sign of devitrification. The 

 attainment of these qualities, especially the continued perfect adhesion, 

 which necessitates a very nice adjustment of the coefficients of expan- 

 sion of body and glaze, indicates that the potters had already attained 

 a high degree of skill. Running of a glaze of this type during firing is 

 a condition unusually difficult to contend with. The color almost 

 certainly identifies this glaze as a lime-alumina-iron silicate, and this 

 is verified by an analysis made in the Museum laboratories. 



