The colouring mechanism of the Brown glaze porcelain of the Yaozhou Kiln in the Northern Song Dynasty
Introduction
Yaozhou Kiln is located in present day in Huangbu Town, Tongchuan City, Shaanxi Province. The area was part of Yaozhou district during the Song Dynasty, it was called Yaozhou Kiln, and its products were known as YaoCi (Yao porcelain) [1]. The site of the ancient kiln is distributed along the banks of the Qishui River and is about 5 km long. In ancient times, it was known as “the Shili Kiln Area” [2]. Yaozhou Kiln was created in the Tang Dynasty (618–907 A.D). After the development of porcelain technology and firing tools in The Five Dynasties period (907–960 A.D), Yaozhou kiln reached its peak during the Northern Song Dynasty (960–1127 A.D), and then began to produce brown glaze porcelain. The colour is similar to that of sesame paste so was called brown glaze porcelain [3]. It is also known as “persimmon glaze” or “purple gold glaze”. Both the Northern Song (960–1127 A.D) and Southern Song (1127–1279 A.D) Dynasties were golden period for the development of brown glaze porcelain; this type of porcelain was produced in many kilns such as Ding, Jiexiu, Cizhou, Jizhou, Jian and others. However, their quality did not surpassed that of the products from Dangyangyu and Yaozhou kiln [4,5].
The iron oxide acts as the colour agent for the brown glaze [6,7], but the microstructure of the glaze is quite special. When observing the cross-section, it can be seen that there is a clear delamination of the brown glaze, the surface glaze is brown, and the underlying glaze is black. Orvar Karlbeck noticed this feature in the 1930s, when he discovered several pieces of brown glaze porcelain during excavations of the Dangyangyu kiln site in Henan. He believed that the difference in colour was the result of the use of different colour glaze during the second glazing [8]. Yang Junyan's research on brown glaze porcelain from Dangyangyu Kiln revealed that, in addition to the large amount of hematite in the surface glaze, there was a large amount of magnetite in the sample. The crystals were well developed, dendritic or palm leaf-shaped, and the brown glaze was mainly determined by the crystallization of this layer [9]. Wang Fen mentioned the phenomenon of stratification [10]. Hu Yonggang replicated the process of porcelain production and observed that the glaze layer delamination was mainly caused by concentration of a large amount of Fe2O3 crystals on the surface of the glaze [5]. Pan Guoping analyzed brown glaze porcelain from BangKong kiln of Kampuchea. The analysis of the glaze from that site showed that the colour was related to iron oxide, however, the content of titanium was also an important factor affecting the colour of the glaze [11]. Previous studies have basically revealed the relationship between the surface of the brown glaze and the crystallization of Fe2O3, but there is still a lack of in-depth studies on the types of crystals and crystallization process. Based on the previous research, this paper will further explore the colouring mechanism and firing process of brown glaze porcelain from the Yaozhou kiln.
Section snippets
Information about the samples
Seven brown glaze samples provided by Yaozhou Kiln Museum (YZSJ-01 to YZSJ-07) were analyzed. The basic information of the samples are shown in Fig. 1 and Table 1.
Optical microscopy and scanning electron microscopy (SEM)
The surface of the samples were cleaned by ethyl alcohol before all the experiments. The optical microscopy observation was carried out in School of Cultural Heritage, Northwest University. The instrument is KH-7700 of HIROX Company. Lens model is MX-5040RZF. The metal halogen cold light source is used. The sample were observed on 50 times magnification. The scanning electron microscope was performed by TESCAN Company; the test voltage is 20 kV and 15 kV, and the sample were observed on 8000
Optical microscopy and scanning electron microscopy (SEM)
As shown on Fig. 2, the microscope analysis confirmed that the double glaze layers covered the ceramic body; the surface glaze is brown with an average thickness of 90 μm and a thicker layer of black glaze exists between the surface glaze and the body, which average thickness is 380 μm, reaching more than 1000 μm on some parts of the samples. On the surface of YZS J −07, there are many holes caused by the air bubbles trapped in the glaze during the firing process. Most of Yaozhou Kiln brown
Comparative analysis of black glaze porcelain
The brown glaze and black glaze both produced in Yaozhou kiln were compared to investigate the difference of their recipe. The chemical composition of black glazed was shown in Table 3 [21,22].
The result showed that the compositions of the two kinds of glaze are basically similar except for Fe2O3 and TiO2. The content of Fe2O3 in the brown glaze porcelain is higher than in the black glaze porcelain. The highest content of Fe2O3 is in the upper layer of the brown glaze porcelain. Even though
Conclusions
The Yaozhou kiln was set up in the Tang dynasty (618–907 A.D), and the kiln reached its peak in the Northern Song (960–1127 A.D). It innovated many new types of porcelain during its prime time. The brown glaze porcelain was one of its innovations. The glaze of brown colour was produced as early as Eastern Han dynasty (25–220 A.D), however, the colour trended to brownish black and the hue was dull. The brown glaze of the Yaozhou appeared reddish brown and the hue was bright. The scientific
Acknowledgement
This study was sponsored by the National Natural Science Foundation of China (grant number: 11575142) Special thanks go to the Shanghai Synchrotron Radiation Facility for helping us finish the analysis and Yaozhou kiln museum which kindly provided us with the brown glaze samples in this study.
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