Coloring Mechanism and Manufacturing Techniques of the Song Dynasty Tea Bowls from the Jizhou Kiln

Author:Xu Zuo Song

Supervisor:li wei dong


Degree Year:2018





The Jizhou kiln is a famous ancient folk kiln in Southern China that is located in present-day Ji’an county of Jiangxi Province.This kiln began firing porcelain in the Tang dynasty(618-907 A.D.),became prosperous in the Southern Song dynasty(1127-1279 A.D.)and closed down at the end of the Yuan dynasty(1271-1368 A.D.).The black-glazed tea bowls produced for tea tasting and competition in the Southern Song dynasty are the most attractive wares among the products from Jizhou kiln.In recent years,the development of analysis method,the further study of material science and the archaeological excavation in Jizhou kiln site give us an opportunity to further study the Jizhou kiln.It plays a key role in reconstructing the technique of treasured Jizhou tea bowls and inheriting the tradition of Jizhou kiln.In this study,OM,EDXRF,XRD,SEM-EDS,TEM-SAD-EDS,ICP-OES,TIMS,Raman and UV-Vis-NIR spectrometer were applied to the tea bowls and raw materials excavated from Jizhou kiln site,in order to study the chemical composition,microstructure,technique and coloring mechanism of Jizhou tea bowls thoroughly.(1)According to the OM observation of the cross section and the natural surface of glaze,a white opaque glazed surface covers a black lower layer,indicating that two-layer glazing technique was used in making Jizhou tea bowls.Interactions between white cover glaze and black ground glaze at high temperature lead to the opaque light brown region and bluish violet region on the tea bowls.With the contribution of the"boiling effect"of the ground glaze and the surface precipitation,diverse appearance can be found in Jizhou tea bowls.(2)The chemical composition of the cover glazes was obtained by analyzing the underfired tea bowl samples.The cover glaze and ground glaze are both calcia-alkali glaze,while the ground glaze has high Fe2O3 content and the cover glaze has high CaO,MnO and P2O5 contents.Using multi-variable factor-loading analysis,the low-iron glazes of tea bowls,white,greenish-white and white-rim black porcelains have quite different chemical compositions.Plant ash was used as the flux in recipe of the cover glaze to promote the opacification of the glaze.(3)SEM and TEM were used to identify the different microstructures in different color regions and the physicochemical foundation of the glaze is also discussed.With the help of reflectance spectra of the glaze,the influence of the microstructure upon coloring and the coloring mechanism of the bluish violet structural color in Jizhou tea bowls have been studied.The liquid-liquid phase separation structure resulting from the immiscibility between CaO and SiO2 is widely observed in Jizhou tea bowl glazes,which is vital to glaze coloring.With the different chemical compositions,white region and bluish violet region have different characteristic sizes of the phase separation structure.A large-scale interconnected phase separation structure is formed in the unreacted portion of the cover glaze,and the characteristic size of the phase separation structure is approximately 217-355 nm.All wavelengths of the incident visible light are scattered by the structure,resulting in the opacification effect of the glaze.A small-sized interconnected phase separation structure is formed under the influence of the ground glaze,with a characteristic size of approximately 117-170 nm.The blue light range of the incident visible light is selectively scattered by the structure,causing the special bluish violet structural color on the glaze surface.Therefore,bluish violet streaks usually appear at the edge of the white streaks.(4)According to Sr isotope composition and chemical composition of the raw materials excavated from Jizhou kiln site,plant ash was introduced into the glaze recipe of Jizhou tea bowls.The black glaze recipe is composed of over 50%by weight of washed high-silica botanic ash with the remainder being the local sericite-type clay and a little iron-bearing mineral.Straw ash and fern ash were probably used in the recipe.And the local sericite-type clay serves as the unitary body material of the Jizhou tea bowls.Low-quality porcelain stone was used to make the body of Jizhou tea bowls,while high-quality porcelain stone was mainly used to make the body of white,greenish-white and white-rim black porcelains.(5)Thermal history as well as the thickness of the cover glaze greatly influences the exterior appearance of the tea bowls.Chemical composition of the tea bowls provides the thermodynamic basis for the formation of phase separation structure,while the thermal history determines the formation of phase separation structure in kinetics.In a word,both chemical composition and thermal history have impact upon the formation of phase separation structure and its characteristic size,which is vital to glaze coloring.