Comparative Study of Black and Gray Body Celadon Shards Excavated from Wayaoyang Kiln in Longquan, China

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Microchemical Journal 126 (2016) 274–279

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Microchemical Journal

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Comparative study of black and gray body celadon shards excavated from Wayaoyang kiln in Longquan, China

Hongying Duan a,b,⁎, Dongge Ji a,b, Yinzhong Ding a,b, Guangyao Wang c, Jianming Zheng d, Guanggui Zhou e, Jianmin Miao a,b a Key Scientiﬁc Research Base of Ancient Ceramics (the Palace Museum), State Administration of Cultural Heritage, Beijing 100009, China b Conservation Department, the Palace Museum, Beijing 100009, China c Department of Objects and Decorative Arts, the Palace Museum, Beijing 100009, China d Zhejiang Provincial Cultural Relics Archaeological Research Institute, Hangzhou, Zhejiang 310014, China e The Museum of Longquan City, Longquan, Zhejiang 323700, China article info abstract

Article history: Longquan celadon is one of the most valuable treasures in Chinese ceramic history. Representative products are Received 8 August 2015 Ge ware (Ge meaning elder brother, black body celadon) and Di ware (Di meaning younger brother, gray body Received in revised form 12 December 2015 celadon) of the Song Dynasty (960–1279 A.D.). In this study, Ge and Di ware shards excavated from Wayaoyang Accepted 12 December 2015 kiln site in Longquan were collected and studied. Chemical and crystallite composition, microstructure, body and Available online 19 December 2015 glaze thickness, ﬁring temperature and glaze reﬂectance spectrum were observed and examined. Differences in Keywords: raw materials and manufacturing technology between Ge and Di ware were studied. Based on the results and Longquan Ge ware historical background, it was speculated that some Ge wares from Wayaoyang kiln site might be the test products Longquan Di ware of jade-like black body celadon for the imperial court. Combined analytical methods © 2015 Elsevier B.V. All rights reserved. Comparative analysis Jade-like glaze

1. Introduction Di ware was manufactured over a longer period than Ge ware which was mainly produced during the Southern Song Dynasty Celadon is the earliest porcelain in China and has been deeply appre- (1127–1279 A.D.). Approximately 90% of shards found or excavated ciated by Chinese and foreign collectors for its simple but refined aesthet- in the Longquan kilns are Di wares whilst Ge wares have been found ically pleasing appearance. Longquan kiln is one of the most famous and to be fired together with Di wares in only small part of the kilns [6]. representative celadon kilns in China with up to sixteen hundred years Since the 1960s, significant research has been performed into the re- production history [1]. The plum green and light greenish-blue color production of top quality Longquan celadon investigating raw mate- glazes from this kiln are the most familiar and attractive products rials [7], manufacture procedures [8,9,10] and technology recovery representing highlights of artistic achievement in Chinese celadon [2]. [11,12]. Other papers related to provenance [13], chemical composi- Longquan is rich in mineral resources necessary for porcelain production, tion [14,15] and comparison with other celadon [16] have also been such as porcelain stone, purple clay and limestone. Its manufacturing published. However most of these studies were focused on Di wares, prowess reached its peak during the Song Dynasty and to date over five problems such as the origin, development and disappearance of Ge hundred kiln sites have already been found [1]. ware, similarity and difference between Ge and Di ware from the GewareandDiwarearethemostfamousLongquanproductswhich same provenance and period, still remained to be convincingly have been recorded in numerous ancient literature sources [3].Thetypi- answered. cal visual appearance features of Ge ware are a thin black body, thick jade- Since 2010, archaeologists have carried out large scale excavations in like glaze, light greenish-blue (regarded as the best quality color) glaze, Longquan. In Wayaoyang kiln site, two kilns and a large quantity of black and yellow stained cracks on glaze, purple rim and dark circular celadon shards consisting of both Ge and Di wares have been found foot. Di ware features a gray or white body, preferably a plum green and (Fig. 2). Fired in the same kilns, these samples provide an excellent light greenish-blue glaze with few or no cracks on glaze. Fig. 1 shows opportunity to increase the understanding of Ge ware and for a compar- typical Ge ware [4] and Di ware [5] of Longquan. ative study between Ge and Di ware. In this paper, Ge and Di ware shards from Wayaoyang kiln site were ⁎ Corresponding author: 4 Jingshanqianjie, the Palace Museum, Beijing, China, 100009. analyzed using various analytical methods, the similarities and dif- E-mail address: [email protected] (H. Duan). ferences between them are summarized herein. Combined with the

Fig. 1. Typical Longquan Ge ware (left) and Di ware (right).

Fig. 2. Two kilns and excavated shards of Wayaoyang kiln site. historical background, the origin and products characteristics of Ge 2.2. Instruments and methods ware, and the factors which made Ge ware different from Di ware are discussed. Chemical composition was measured with energy-dispersive X-ray fluorescence spectrometer [17] (EDAX Eagle III XXL, United States). Glaze surface and cross section of the shards were taken for glaze and 2. Materials and methods body measurement, respectively. Before measurement, samples were ultrasonic cleaned with distilled water twice and then ethanol once. 2.1. Archaeological samples X-ray diffractometer (Rigaku D/max 2550PC, Japan) was employed to identify the crystalline phases in shard body and glaze. Powder samples Thirty-five Ge ware shards and thirty-six Di ware shards excavated were measured with Si plate sample holder to minimize the back- from Wayaoyang kiln site were provided by Zhejiang Provincial Cultural ground. Microstructure was observed using polarizing microscope Relics Archaeological Research Institute and the Museum of Longquan (Leica DM4000M, Germany) and field emission scan electron micro- City. Archaeological evidence assigned these shards to the Southern scope (Hitachi S4800, Japan). FESEM samples were obtained by etching Song Dynasty. The description of these samples is presented in polished cross sections of glazes in 1% HF solution for 10 s. Shards sur- Table 1. face and cross section were placed under microscopes (Leica MZ16A,

Table 1 Appearance and description of the samples.

Sample Vessel shape Glaze Body

Translucent, jade-like; thick glaze; light greenish-blue, Black, gray, dark gray color; thin body; Ge ware shards Vase, plate, bowl, dish, Xi, jar gray green color; many cracks on surface middle ﬁne, porous Di ware shards Ewer, vase, jar, cup, burner, Less translucent and more vitreous; plum green, light greenish-blue, Gray, gray white, white color; ﬁne dish, Xi, bowl, box gray green color; few or no cracks on surface

Table 2 Chemical composition of bodies and glazes (wt%).

Sample Results Na2O MgO Al2O3 SiO2 K2O CaO TiO2 MnO Fe2O3 Ge ware body Mean 0.45 0.84 28.46 60.74 4.35 0.19 0.30 0.03 3.65 Standard deviation 0.13 0.11 2.06 2.10 0.35 0.10 0.13 0.01 0.42 Standard error 0.02 0.02 0.35 0.35 0.06 0.02 0.02 0.00 0.07 Di ware body Mean 0.49 0.43 18.81 73.41 3.27 0.10 0.28 0.03 2.17 Standard deviation 0.14 0.08 1.14 1.40 0.29 0.04 0.08 0.01 0.21 Standard error 0.02 0.01 0.19 0.23 0.05 0.01 0.01 0.00 0.03 Ge ware glaze Mean 0.46 1.16 12.97 70.23 4.09 9.11 0.06 0.09 0.83 Standard deviation 0.17 0.38 0.80 2.01 0.51 1.66 0.01 0.03 0.21 Standard error 0.03 0.06 0.13 0.34 0.09 0.28 0.00 0.01 0.03 Di ware glaze Mean 0.60 0.94 13.01 70.90 4.00 8.10 0.09 0.10 1.26 Standard deviation 0.27 0.29 0.84 1.69 0.67 1.91 0.03 0.04 0.29 Standard error 0.05 0.05 0.14 0.28 0.11 0.32 0.00 0.01 0.05 276 H. Duan et al. / Microchemical Journal 126 (2016) 274–279

Fig. 3. Factor analysis based on body chemical composition. Fig. 5. Factor analysis based on glaze chemical composition.

fl Germany) for micromorphology observation. Re ectance curve of glaze F2 ¼ 0:864TiO2 þ 0:673CaO þ 0:573MnO was obtained by integrating sphere spectrophotometer (X-Rite SP60, United States). Firing temperature of body was examined by dilatome- As shown in Fig. 4, the main crystalline phases present in Ge and Di ter (NETZSCH DIL 402C, Germany). Glaze maturing range was estimated ware bodies were quartz and mullite. The mullite content is similar in according to the temperature interval between HP (hemisphere point) both samples while the quartz content is significantly different. Ge fl and FP ( owing point) measured by high temperature microscope ware bodies contain relatively less quartz, which is consistent with silica (GX-III, China). content results in Table 2. When observed under microscope, heteroge- neous size quartz crystallites can be clearly seen in both Ge and Di ware 3. Results and discussion bodies. There were some continuous large pores in Ge ware bodies, an indication of under-firing bodies [18] due to high alumina (28.46 wt%) 3.1. Comparative analysis content.

3.1.1. Body raw materials 3.1.2. Glaze raw materials

As shown in Table 2, relative amounts of SiO2,Al2O3, MgO and Fe2O3 components were different in Ge and Di ware bodies. Multivariable sta- ¼ − : þ : þ : − : þ : tistical analysis was utilized to compare the body chemical composition F1 0 937CaO 0 826SiO2 0 621K2O 0 608MgO 0 496Fe2O3 þ 0:449Na O of Ge and Di ware shards. Fig. 3 illustrates factor analysis utilizing all 2 body chemical components listed in Table 2. It is clear that the samples ¼ : þ : divide into two distinctive groups, indicating different raw material F2 0 773MnO 0 689TiO2 were used for Ge and Di ware bodies. To investigate the relationship and difference of glaze composition, factor analysis was applied to the glaze data in Table 2 and the result F1 ¼ −0:985SiO2 þ 0:964Al2O3 þ 0:951MgO þ 0:9330Fe2O3 was shown in Fig. 5. It can be seen that Ge and Di ware glazes are partly þ : 0 906K 2O overlapped and cannot be completely separated, indicating close

Fig. 4. XRD spectra for bodies. Fig. 6. XRD spectra for glazes. H. Duan et al. / Microchemical Journal 126 (2016) 274–279 277

Fig. 7. Microstructure images of Di ware glaze (a: plane polarization; b and c: FESEM). chemical composition between the two types of glaze, which may be interconnected structure (Fig. 8c). The scale of phase diameters due to similar raw materials. It was recorded in ancient literature that ranged from 60 nm to 100 nm, most of which were about 70 nm, the glaze was manufactured with a three-component recipe of plant which was within the range of Rayleigh scattering. ash, limestone and porcelain stone as raw materials [19].InTable 2,it The scattering source in glaze such as micro-scale anorthite crys- is apparent that CaO and Fe2O3 content is slightly different in the two tallite, unmelted quartz, bubbles and nano-scale phase separation glaze groups. CaO was obtained from plant ash and limestone, while will refract the incident light and increase the light path, making

Fe2O3 was mainly from porcelain stone. Therefore the small difference the glaze translucent. That was the reason why Ge ware glaze possesses in CaO and Fe2O3 contents may be caused by different proportion of a jade-like appearance and Di ware glaze has a slightly more glassy the three raw materials in glaze preparation. appearance. From the XRD results shown in Fig. 6, Ge ware glaze contains a certain amount of anorthite and unmelted quartz crystallites, while Di ware glaze 3.1.4. Manufacture technology contains little anorthite and quartz crystallites but a higher content of amorphous phase material. The content and shape of anorthite crystal- 3.1.4.1. Firing temperature. Due to the small size and thin body of our lites can provide information about the glaze firing process. Anorthite samples, only two pieces of Di ware body samples were successfully crystallites generate in the glaze during the firing process, with the tem- tested by dilatometer at approximately 1270 °C. The same two Di perature increasing, anorthite crystallites continue to grow and develop, ware glaze samples and two Ge ware glaze samples were studied with however, they will re-melt if the temperature is too high. Therefore, firing high temperature microscope to obtain the glaze melting temperature at an appropriate temperature for a long time promotes the growth of an- range. Heating behavior measurement shows that HP (hemisphere orthite crystallites. point) and FP (flowing point) of Di and Ge ware glazes are 1200 ± 10 °C and 1310 ± 10 °C, 1240 ± 10 °C and 1320 ± 10 °C, respectively. 3.1.3. Glaze microstructure Glaze maturing range is in the temperature interval between HP and Fig. 7 and Fig. 8 illustrate the microstructure images of Di and Ge FP. Unfortunately we could not get the body firing temperature of Ge ware glazes, respectively. As shown in Fig. 7a, Di ware glaze contains ware, however, from the point view of glaze maturing range, it was less anorthite and quartz but large bubbles, indicating a small number speculated that the firing temperature of Ge ware was close to, or slight- of light scattering particles. In Fig. 8a, a larger number of anorthite crys- ly higher than Di ware, which could be achieved by being placed and tallites in forms of cluster or stripe shape, quartz and smaller bubbles fired at different kiln positions, since the kiln temperatures are different present in Ge ware glaze. FESEM images of Fig. 7 and 8 show nano- at different positions in the dragon kiln [23]. scale liquid–liquid phase separation structure within the peripheral re- Although the four glazes were correctly fired, yet the two black Ge gions around anorthite crystallites or in the interspaces of anorthite ware bodies were porous, indicating under-firing of the Ge bodies due clusters. Crystallization phase separation structure of China celadon to its high Al2O3 concentrations. glaze determined by the chemical heterogeneity of surrounding glass matrix caused by anorthite crystallization has been reported [20,21, 3.1.4.2. Glazing technique. As shown in Fig. 9, a multilayer glaze structure, 22]. The shape and distribution of phase separation structure were usually two to three layers, was observed in Ge ware glaze while this closely associated with the density of anorthite crystallites. Therefore, kind of phenomenon was not observed in Di ware glaze, indicating Ge phase separation mainly distributed only around the crystallite clusters ware had been repeatedly glazed. Body and glaze thickness of our sam- in Di ware glaze, while phase separation with various forms could be ples were measured under microscope and the data are illustrated with identified in most regions of Ge ware glaze, such as the spherical the box-plot Fig. 10. In comparison, Ge ware belongs to the porcelain or strip isolated form droplet (Fig. 8b) and three-dimensional group characterized with thick glaze and thin body. The characteristic

Fig. 8. Microstructure images of Ge ware glaze (a: plane polarization; b and c: FESEM). 278 H. Duan et al. / Microchemical Journal 126 (2016) 274–279

Fig. 9. Multilayer structure of Ge ware glaze. features of Ge wares, such as black thin body, thick and multi-layer material for celadon bodies in Zhejiang province and the whole of glaze, typical anorthite crystallization phase separation structure [24] south China and the bodies were of gray or light brown color depending can also be observed in Guan wares of Laohudong kiln site, the imperial on the kiln atmosphere. It is postulated that those celadon products kiln of the South Song Dynasty in Hangzhou. Such similarity between Ge with thick gray body might not satisfy the new Southern Song emperor and Guan ware suggest there was some link and technology exchange who deeply appreciated and preferred uncomplicated jade-like celadon. between Longquan and Hangzhou at that time. It is envisaged that experimentation such as addition of purple clay with high iron, titanium and aluminum content into the body raw materials 3.1.5. Glaze reflectance curve to make the body darker and thinner, applying glaze several times to In the glaze reflectance curve spectra shown in Fig. 11, the dominant obtain a thick glaze followed by firing at a suitable temperature obtain- wavelength of Ge and Di ware glazes ranges from 520 nm to 580 nm, ed the desired translucent jade-like appearance. As Longquan is not far indicating both glazes are mainly green in color. Color due to iron in from Hangzhou, to save cost and time, it is reasonable to speculate that celadon glaze is mainly influenced by the ratio of Fe2+/Fe3+.Itwas when the new court tried in the imperial kilns in Hangzhou, they also concluded that Ge and Di ware were fired under reductive atmosphere. might select and command Longquan potters (Longquan was already The reflectance curve intensity of Ge and Di ware glaze is different, being a prosperous celadon production center at this point) to produce which could be caused by different scattering degree of crystallites porcelain wares in the desired imperial style and quality. and separated phase. In Longquan, over twenty kilns were found to have fired Ge wares, Through above analysis, it is concluded that although fired in the maybe these kilns were outstanding so as to be selected by the court same kiln, there are many differences between Ge and Di ware, such at that time. In addition, from the viewpoint of ware-type, some Ge as body raw material, body and glaze microstructure, and glazing tech- wares excavated from Wayaoyang kiln site have typical “imperial nique. Difference in raw materials, manufacture technology, and struc- characteristics”, it is widely accepted that those Ge wares were fired ture result in a different external appearance for the two wares. As the according to “the standard” provided by the court. This is very impor- differences are significant, we believe that all of these were not acciden- tant evidence supporting our point of view that some Ge wares in tal but intentional by the potters. Wayaoyang kiln site might be the test products of jade-like black body celadon for the imperial court. 3.2. Historic background and speculation Based on the above analytical data and historical background, it was speculated that Di wares were ordinary products for daily usage of local During the last years of the Northern Song Dynasty (960–1127 A.D.), people while Ge wares were specially developed products to satisfy the the invasion of the ethnic group-Jin pushed the court of Northern Song demands from the imperial court. The potters selected special body raw Dynasty southward and as a result setup a new capital in Hangzhou, materials and changed glazing technology for Ge ware. Furthermore the Zhejiang. The urgent need for sacrificial and daily-used ceramics led potters may have selected special kiln positions for the Ge wares to en- the new Southern Song Dynasty court to establish imperial kilns in sure suitable firing temperature leading to the desired jade-like glaze Hangzhou. Before the 12th century, porcelain stone was the main raw appearance.

Fig. 10. Thickness of body and glaze (ceramics group includes some Chinese yellow glaze, transparent glaze, blue and white porcelain samples). H. Duan et al. / Microchemical Journal 126 (2016) 274–279 279

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