Was bone used in the glaze of the ancient Qiong kilns for the production of tang dynasty opaque glaze celadon?

Being an important source of primary celadon in ancient China, the Qiong kiln is one of the few kilns that can skillfully produce opaque glaze celadon, which is of great significance in the history of Chinese ceramics. In this study, the chemical composition, microstructure, and crystalline phase of sixteen pieces of opaque glaze celadon excavated from the site of Qiong kiln Shifangtang dated at the Tang Dynasty were investigated by using ultra depth of field microscopy, scanning electron microscopy, energy spectrometry, and micro confocal Raman spectrometry. The findings indicate that Fe is the predominant coloring element in the ceramic glaze, and Cu is sometimes a secondary coloring element. During porcelain firing, washed plant ash was used to increase the phosphorus content of the glaze, while some wares incorporated animal ashes as a flux to improve glaze emulsification.