Fundamental Study Of Copper Glaze And Copper Color Decoration Of Changsha Kiln

The Changsha Kiln is located in the area of Shizhuhu,Wangcheng district,Changsha.It arised after Anshi's Rebellion,thrived in the Middle and Late Tang and decayed in the Five Dynasties.The Changsha Kiln is a kiln mainly for export production,which attracts people with its unique and exotic decoration.The state of"southern blue and northern white" was broken by Changsha Kiln,leaving the situation in a state of "southern blue,northern white and Changsha color".High temperature copper red glaze was initially produced and underglaze color was invented in the Changsha Kiln,while a foundation for the development of other copper glazes was also established.This article takes 42 Changsha Kiln's samples as main research objects,upon which synthesized methods are employed to study scientific meanings of copper glaze and copper color of products in the kiln.These results provide significant information for further study in the ancient decoration technique and reference for the improvement of modern copper glaze crafts.Polarizing Microscope,X-Ray Fluorescence(XRF),X-Ray Diffraction(XRD)and Thermal Dilatometer were employed to observe the mineral composition,to measure the major and minor elements,and to test the phase structure,firing temperature and water absorption.Colorimeter,X-ray Photoelectron Spectrometer(XPS),and Scanning Electron Microscope(SEM)were used to observe the glaze color and the microstructure of the samples,and to study the valence of state of color elements.The paper investigated the color mechanism of the copper glaze and the influence of the copper valence on glaze color,and made comparative study of the relationship between the copper glaze of the porcelain unearthed from Changsha Kiln and those of the later ages.Besides,our study tested the element distribution among the body and glaze by XRF and the digital microscope to observe the features of color decoration,and compared the coloring technique of the porcelain of Changsha Kiln with that of "Underglaze-Red" porcelain in Yuan dynasty.The results indicated that samples of Changsha Kiln had a fairly coarse texture,and the body mineral composition matched the typical recipe of the southern porcelain.The glaze composition of Changsha Kiln belongs to the typical type of calcium glaze with a moderate firing temperature,and the main coloring elements in glaze were Cu and Fe.Changsha Kiln may be the pioneer of the "glazing red"technique.In the glaze colorized by Cu,copper red mostly exists in Cu0 and Cu+ and copper green mostly exists in Cu0,Cu2+.Based on the test results,the color-causing mechanism of the copper glaze conformed with the metal-alkali ion exchange theory.Besides,the fractal structure was found in all samples of copper glaze.The fractal particle size results from Rayleigh scattering,so the glaze presents opalescent.Moreover,the opacification effect of glaze was enhanced by the existence of the bubbles,Sn and crystallization in the glaze.The technique of color decoration of Changsha Kiln is mainly overglaze,without any finds of underglaze color or in-glaze decoration.