Research Of The Glaze Technology In Jingdezhen From Tang To Yuan Dynasty

It is very important to fully understand the development of Jingdezhen ceramics and the formation of its central position in Chinese ceramic history,to clarify the technical context of Jingdezhen ceramics development,to understand and trace the real beginning of Jingdezhen ceramics,especially the early development,evolution and influence of glaze technology.Based on the unearthed materials from latest archaeological excavations of Leping Nan kiln,Xianghu Lantian kiln and Tongluoshan kiln,Fenghuangshan kiln,Hutian kiln,Luomaqiao kiln and Yuyaochang,this work studied various chemical and physical nature of early Jingdezhen ceramics using energy dispersive X-ray fluorescence spectrometry,strontium isotope analysis,scanning electron microscopy,X-ray diffraction and other modern analytical techniques.Glaze samples of different historical periods and their possible raw materials for production were systematically analyzed.Simulation experiment and literature records were also applied in this study to discuss the key problems such as the technical characteristics,evolution rules,raw material formula and technical source of representative glaze in Jingdezhen of different periods,annotated the scientific connotation of "no grey,no glaze".The chemical characteristics of Jingdezhen Tang Dynasty glaze are similar to Yue Kiln green glaze,in which the content of CaO,P2O5 was about 15%and 0.5%separately and the strontium was almost above 500 ppm,that were both high calcium and high strontium plant ash glaze.The Five Dynasties period explored technological experiments based on northern white glaze formula.A new glaze based on the mixture of plant ash and limestone as the flux and Youguo as siliceous material was developed for greyish-green wares and white wares of the Five Dynasties period.In this glaze,the content of CaO was remained around 15%,but the P2O5 was sharply decreased to less than 0.25%and the Sr was just about 100ppm which could attribute to the use of the new flux,meanwhile,the content of TiO2 was reduced to below 0.15%and even reached 0.03%in the white glaze of the Five Dynasties from the amount of above 0.4%in the glaze of the Tang Dynasty which could attribute to the use of the Youguo.This glaze recipe laid the foundation for the subsequent emergence of bluish-white porcelain.After the Southern Song Dynasty,the preparation of glaze raw materials became mature and consistent,and the amount of glaze ash added in the mixture gradually decreased.Microstructural analyses show that there were a large number of worm-like droplets in the green glaze of the Jingdezhen Tang Dynasty and Five Dynasties,and a certain number of spherical droplets were found inside the worm-like structure among a few samples.The similar phase separation structure weren't be found obviously in the white glaze of the Five Dynasties,the bluish-white glaze of the Song Dynasty,the blue and white glaze and the Shufu glaze of the Yuan Dynasty.The amount of bubbles in the bluish-white glaze of the Song Dynasty increased obviously and became larger than in the previous glazes,and a certain amount of short columnar or needle-like crystals were found in the Shufu glaze of the Yuan Dynasty.The phase separation structure in the green glaze of the Tang and Five Dynasties formed mainly because of its high phosphorus and high calcium in the chemical composition.Both the P2O5 and SiO2 are the glass network former,and there will generate[PO4]3-and[SiO4]4-two different forms of network structure at the high temperature which would induce phase separation in the glaze during cooling process.Simulation experiments and analysis of glaze materials show that bracken,which is a commonly available plants in Jingdezhen,is ideal to be used as the fuel during plant ash preparation.It is ease to collect and has large annual output.Dry bracken is also a fuel with low initial decomposition temperature and two continuous exothermic peaks,which are very good qualities for the transformation of Ca(OH)2 to CaCO3 in slaked lime during the process of glaze ash simmering.As an indicating plant of acid soil,the high content of Fe2O3 in bracken's chemical composition promotes the "Bluish-white" feature of Jingdezhen porcelain glaze.These features of bracken are the reasons why it has been used as the sole raw material for the firing of glaze ash for a long time.In addition,the process of calcination,digestion,simmer and urine retting used in the preparation of glaze ash are also effective steps to pulverize and purify this calcareous raw material.Moreover,the content of CaCO3 in glaze ash can reach 91%and the average particle size of glaze ash is only 13.45?m after three simmering processes and four months long of urine treatment which indicates that the series of process methods,such as calcination,digestion,simmering and urine treatment,used in the preparation of glaze ash,is an effective process of fine pulverization and high purification of ancient limestone raw materials.The research shows that Jingdezhen completed the transition from calcium glaze to calcium alkali glaze and alkali calcium glaze between the Tang Dynasty and the Ming Dynasty,and this process can be roughly divided into three stages.The Tang Dynasty was the initial stage when this evolution began.The Five Dynasties to the Northern Song Dynasty was a highly experimental period when lots of new recipes and techniques were put in trial.The period of maturity and promotion From the Southern Song Dynasty onward,it was the period Jingdezhen ceramic technology took off and came into maturity.The transformation from calcium glazes to calcium alkali glazes in Jingdezhen during the Yuan,the Ming and the Qing dynasty provided better technical conditions for the performance of underglaze painting fine lines due to the later glaze had higher high temperature fluidity,which may also be an important technical reason for the sudden maturity and rise of blue and white porcelain in Jingdezhen Yuan Dynasty.In addition,the characteristics of Jingdezhen glaze technology evolution fully reflect the cultural characteristics of openness,inclusiveness and innovation of Jingdezhen,which is also an important reason for Jingdezhen to become the porcelain capital of the millennium.