Technical Investigation of Chinese Pottery 93 



glass. These fragments were freed from the adhering films of red 

 earthy matter by use of forceps and a fine file. As finally prepared, 

 the glass showed no altered material, nor any but a few unweighable 

 traces of earthy matter. 

 The analysis gives: 



Silica, Si0 2 29.91 



Lead oxide, PbO 65.45 



Iron oxide, FeO 0.81 



Copper oxide, CuO 2 . 60 



Lime, CaO 0.94 



Alkalies, Na»0, K 2 0.00 



99 5i 

 This gives the molecular formula: 



1 RO : 1.4 Si0 2 or nearly 5 RO. 7 SiOj. 

 The traces of iron and lime are obviously impurities. 



This is a simple lead silicate colored by copper, and is utterly unlike 

 any glaze of which I have any analysis, the nearest approach to it being 

 the alkali-lead silicate which seems to have been an ordinary glaze in 

 all countries. The omission of alkali places this glaze in a very differ- 

 ent class. It could be easily and simply compounded, as there are but 

 three ingredients, — some lead salt (perhaps red lead or white lead), a 

 pure white sand, and a small quantity of some copper compound for 

 coloring. 



Professor R. T. Stull, Acting Director of the Ceramic Department 

 of the University of Illinois, has been good enough to supply the fol- 

 lowing additional information on the preceding analysis: 



"I am very much interested in the data you present on the early 

 Chinese glaze. I have calculated an approximate empirical formula 

 from the analysis, which gives: 



.827 PbO 



.093 CuO 1.408 SiO s 

 .049 CaO 

 .031 FeO 

 "This approximates closely the theoretical formula: 



iiCuo} I -5SiO I = 2 R0. 3 Si0 1 



A glaze can be made by mixing the following materials, which would 

 be very similar to the Chinese glaze when first made: 



Red lead 205 



Copper oxide 8 



Potter's flint 90 



1 



