- Email: [email protected]
The relationship between the use of Zijin clay and glaze crackles for Chinese celadon with black body
Ceramics International xxx (xxxx) xxx–xxx
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
The relationship between the use of Zijin clay and glaze crackles for Chinese celadon with black body Lingtong Yan, Heyang Sun, Li Li, Xiangqian Feng∗ Institute of high energy physics, Chinese academy of sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Celadon with black body Glaze crackle Song dynasty Zhejiang province Zijin clay
The celadon with black body is a famous type of ceramic product in ancient China due to its appearance features, black body and crazing glaze, different from regular. For this type of ware, the crazing glaze is a kind of artificial decoration, not production defect. How the glaze crackles were made by ancient potter has always attracted many people's attention. And it has been studied mainly based on chemical composition. In this paper, we aim to provide our discussion and explanation for its sophisticated combinations of crazing glaze and black body. Based on analysis of ancient and modern celadon products, we thought that the difference in quartz content of the fired body is the reason why the celadon with black body is more likely to have crazing glaze than regular. And, the potter could control the expansion coefficient of the body by using Zijin clay with low quartz content as raw material.
1. Introduction Celadon as a famous category of ceramic artifact is appreciated for its magnificent jade-like glaze covered on the surface of the ware. It began to be produced since Shang dynasty (ca. 1600-1027 BC), and became one kind of the most popular and long-lived ceramic product in ancient China [1]. In history, there is a well-known type of ware named as celadon with black body. It has some special appearance features that are very different from regular celadon. This type of ware used thin darker body that supplied the famous “purple rims and iron-feet” [2,3]. And, it has a typological appearance characteristic of crazing glaze that is generally seen as an undesirable coating for ceramic ware. For celadon with black body, the crazing glaze is not one kind of production happening defect, but man-made artistic decoration. Due to the thin body and crazing glaze, this type of ware is unsuitable for daily use. It is mainly used as a work of art and has always been regarded as collector's item. The representatives of this type of celadon are Southern Song Guan and Ge wares that are generally considered as the most famous ceramic products during Song dynasty (AD 960–1279). They were mainly produced in Hangzhou, Longquan and Cixi, Zhejiang Province (southeastern China), an important celadon producing area in history. In addition, there are some imitations produced in other regions after Song dynasty (AD 960–1279). At present, a small number of surviving Song wares in China are preserved in a few museums, such as The Palace Museum (Beijing) and National Palace Museum (Taibei).
∗
Scholars thought that crackles as glaze decoration for celadon with black body were originally inspired by Ru ware with light-body and finely crazing glaze, a type of classic official artifact (Northern Song dynasty, AD 960–1127) produced in northern China [1]. The difference is that their glaze crackles are more obvious than that of Ru ware. The Ru celadon is sometimes described as the first Chinese ceramic product that exploited glaze crackles for decoration effect. How crazing glaze were made by ancient potters has always attracted many people's attention. For celadon with black body, the cause of the crazing phenomenon has been studied mainly based on chemical composition [4–7]. In this paper, we aim to provide our explanation for the relationship between crazing glaze and odd black body or the use of Zijin clay. 2. Materials and methods 2.1. Materials For comparative study, we collected both types of shards unearthed from three kiln sites (Longquan, southern Zhejiang). According to the excavation, all the celadon shards were fired during Southern Song dynasty (AD 1127–1279). Archaeologists believe that Xiaomeizhen mainly produced celadon with black body, while the samples from Jincun are regular celadon. Wayaoyang produced both types of wares [8]. All samples were grouped according to the site location, while the
Corresponding author. E-mail address: [email protected] (X. Feng).
https://doi.org/10.1016/j.ceramint.2019.11.192 Received 4 November 2019; Received in revised form 19 November 2019; Accepted 21 November 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Lingtong Yan, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.11.192
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Table 1 Chemical composition of samples unearthed from Longquan. Mean results (wt%) and standard deviation of element oxides are reported here, and full results for all the samples are provided in supplementary Table s1 and s2. Site Location
Amount
Measurement
Na2O
MgO
Al2O3
SiO2
P2O5
K2O
CaO
TiO2
MnO
Fe2O3
Xiaomeizhen (Group 1)
20
Body
0.6 ± 0.17 0.52 ± 0.16 0.65 ± 0.16 0.53 ± 0.19 0.68 ± 0.18 0.55 ± 0.2 0.49 ± 0.1 0.34 ± 0.08
0.52 ± 0.09 0.52 ± 0.11 0.59 ± 0.08 0.56 ± 0.1 0.51 ± 0.06 0.52 ± 0.14 0.37 ± 0.05 0.69 ± 0.16
22.67 ± 1.43 14 ± 0.97 26.65 ± 2.04 13.45 ± 1.05 20.21 ± 1.2 13.42 ± 0.76 19.62 ± 0.99 13.75 ± 0.96
66.02 ± 2.2 67.77 ± 3.3 62.02 ± 2.43 69.08 ± 2.09 71.43 ± 1.6 70.51 ± 1.73 73.55 ± 1.52 66.86 ± 2.79
0.06 ± 0.01 0.17 ± 0.03 0.05 ± 0.01 0.16 ± 0.04 0.06 ± 0.01 0.14 ± 0.02 0.05 ± 0.01 0.2 ± 0.04
4.41 ± 0.61 4.17 ± 0.46 4.69 ± 0.42 4.87 ± 0.65 3.98 ± 0.48 4.7 ± 0.76 3.37 ± 0.52 3.62 ± 0.63
0.41 ± 0.3 11.17 ± 0.3 0.31 ± 0.22 9.88 ± 1.44 0.13 ± 0.07 8.13 ± 1.65 0.1 ± 0.03 12.6 ± 2.47
0.8 ± 0.22 0.16 ± 0.05 0.52 ± 0.11 0.12 ± 0.03 0.37 ± 0.08 0.15 ± 0.04 0.33 ± 0.05 0.17 ± 0.1
0.05 ± 0.01 0.13 ± 0.08 0.03 ± 0.01 0.13 ± 0.06 0.03 ± 0.01 0.14 ± 0.09 0.02 ± 0.01 0.37 ± 0.1
4.39 ± 0.82 1.27 ± 0.48 4.21 ± 0.44 1.09 ± 0.22 2.53 ± 0.29 1.62 ± 0.5 2.05 ± 0.49 1.25 ± 0.37
Glaze Wayaoyang (Group 2)
26
Body Glaze
Wayaoyang (Group 3)
36
Body Glaze
Jincun (Group 4)
15
Body Glaze
Fig. 1. Images of fragment samples unearthed from Longquan. (They were grouped according to the origin or iron content in the body. a: Xiaomeizhen; b: Wayaoyang sample with high content of iron; c: Wayaoyang sample with low content of iron; d: Jincun).
(EDXRF, Eagle III μProbe). The spectrometer was equipped with a Mo tube and a 125 μm Be window. It worked at a voltage of 40 kV, current 250 μA. The X-ray beam spot was selected to be Ф = 1 mm. The spectrum of each sample was measured with a live time of 300s. The detector is a liquid-nitrogen-cooled Si (Li) crystal with a 160.3 eV at Mn Kα. The analysis was carried out in a vacuum environment. To calibrate the substance effects and improve the accuracy of the data, we used a set of house ceramic reference materials for EDXRF. The software employed for analysis is the program VISION32 associated with the instrument. The X-ray diffraction (XRD) patterns were obtained on a X-ray diffractometer (D8 Advance, Bruker, Germany) with Cu-Kα radiation
samples from Wayaoyang were divided into two groups based on the difference in iron level of the body (Table 1). It is difficult to distinguish the type of body by visual observation, because most of them are not particularly noticeable in color, and only a small amount of samples have an obvious black body. Some images of typical shards are in Fig. 1.
2.2. Analysis experiment The measurement area of bodies was polished to remove the surface layer that may be contaminated. Then the samples were washed three times in an ultrasonic cleaner with deionized water and dried at 95 °C. The elemental composition was analyzed by the Energy Dispersive XRF 2
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
(λ = 1.5406 Å). To prepare the sample, the bodies were ground into powder. Operating conditions for the XRD was 40 kV of voltage and 40 mA of current. The samples were continuously scanned from 10o-60o (2θ), with a step size of 0.02o and a time per step of 1.0s. The minerals were identified using the ICDD (International Center for Diffraction Data) database. The result of firing temperature was based on measurement of thermal expansion. The bodies were cut into pieces with size 25 × 5 × 5 mm. Then they were washed in the ultrasonic cleaning machine and dried in oven at 95 °C. The dilatometer used for this research was a DIL402PC (NETSCH, Germany) thermal expansion instrument. Samples were heat at a rate of 5 °C/min in N2 atmosphere during measurement.
Most of the ancient glazes in this paper are characterized by a relatively large thickness based on method of multi-layer glazing [3,8]. The reason for use of thick glaze is still unclear, but it is widely applied to regular celadon in Longquan area, not only wares with black body. We speculate that the thick glaze layer may affect the appearance of cracks, but it should not be the main means for generating crazing glaze for celadon with black body. The purpose of this approach is more likely to reduce the effect of the fired body on the color appearance of partly translucent celadon glaze, especially for the wares with black body. 3) Adjusting the composition of glaze or body. It is the most practical method to control glaze crackles, because different physical properties that can affect the crazing, such as the expansion coefficient, strength and elastic modulus, are mainly determined by different compositions of glaze and body [7,13]. In order to control the crazing, modern potters usually adjust the concentration of some oxides in the glaze to change its thermal expansion and contraction, because used raw materials for body cannot conveniently be changed [15]. However, for ancient potter, they could adjust both the composition of raw material for body and glaze recipe to influence the appearance of crazing glaze.
3. Results and discussion 3.1. Method to generate the crazing glaze The reasons for glaze crackles were studied by many researches. They could be divided into instant and delayed. The delayed crack is caused by the moisture expansion of the porous body, and it occurs over a period of time after firing [9,10]. The crackles of the celadon with black body should be instant glaze cracks generated in manufacturing process. During high-temperature firing, the clay body is matured and becomes more vitreous, and the glaze is melted into a liquid state. In this stage, the substance has good fluidity and large elasticity modulus, and there is no obvious stress between body and glaze layer. After hightemperature firing, the mineralogical transformation has completed. During the low-temperature stage, the body and glaze begin to contract during the cooling process, and the Young's modulus becomes smaller. If the contraction of glaze is different from the body, there will be residual stress existing between them [11]. The coefficient of expansion of material is often used to characterize the relative tendency to expand and contract when heated and cooled. When the glaze layer is subjected to a large stress overcoming its resistance, the force is liable to cause cracks in the glaze. The glaze deformation can be divided into two categories, crazing and shivering. Crazing happens when the glaze is under extreme tension. On the other hand, Shivering occurs when a glaze is under too much compression. The probability of crazing occurring is somewhat complex. Because the thermal expansion mismatch between body and glaze and their resistance to stress vary with the composition of the material and the temperature. Researchers thought that three artificial methods in the practical production process could be used to influence the appearance of glaze crackles [7,12–14]:
Based on above discussion, we speculated that compared to the first two methods, ancient Chinese potters are most likely to adjust the composition of ceramic ware to purposefully produce crazing glaze in large quantities. And many previous related researches on celadon with black body were also focused on this method. 3.2. Raw materials for different types of bodies In ancient China, celadon wares with black and regular body were produced at the same time. A compositional comparison of two types of celadon products may be of great help in understanding how ancient potter made crazing glaze. So we collected and analyzed some typical celadon shards from Longquan, Zhejiang. Based on the compositional comparison of bodies (Table 1), we found that all the samples in this paper can be divided into two groups according to the iron content (Fig. 2). This is also in line with the classification of the black and regular body from archaeologists, and especially the Wayaoyang site produced two types of wares at the same time (group 2 and 3). Apart from this, it is interesting that another important result is the difference in the ratio SiO2/Al2O3 for all the samples (Fig. 2). The samples of Group 3 from Wayaoyang and Jincun have relatively low, while for Group 2 is higher and the samples from Xiaomeizhen are in the middle. Similarly, we have reported that samples from Jiaotanxia (alter
1) Designed firing process. In the simulation experiments, Lahlil et al. [7] found that if the temperature and atmosphere can be controlled during the firing process, the thermal contract of body and glaze and the effect of the crack in the glaze can be affected. However, for ancient celadon production in Zhejiang, the firing process was carried out in the dragon kiln that is essentially a tunnel built on a gentle slope (usually along with hillside), and could be very long, up to several tens of meters [2]. This type of kiln has a very large internal space, and the temperature varies greatly from location to location. In addition, some scholars thought that the celadon with black and regular wares might be fired together in the same kiln. When firing a large number of ceramic products in this type of kiln, it seems more difficult to apply different precisely designed firing surrounding for separate category of wares. This may be a less practical way for ancient potters to produce crazing glaze in large quantities. 2) The relative glaze-body thickness. People can optimize the relative glaze-body thickness to obtain a controlled appearance of crackles [7,12,13]. The thickness could influence stress between body and glaze, and glaze resistance under the same compression or tension.
Fig. 2. Scatterplots showing the ratio SiO2/Al2O3 and Fe2O3 content in the bodies. 3
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Table 2 The summarized compositional data (wt%) of Zijin clays from references and result (wt%) of raw material in this paper (’-‘ means the data was not found). Type of clay
Origin
Na2O
MgO
Al2O3
SiO2
P2O5
K2 O
CaO
TiO2
MnO
Fe2O3
Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay** Zijin clay*** Porcelain clay* Porcelain clay* Porcelain clay* Porcelain clay* Porcelain clay** Porcelain clay***
Jingdezhen, Jiangxi Wuguishan, Zhejiang Wuguishan, Zhejiang Dayao, Zhejiang Dayao, Zhejiang Baoxi, Zhejiang Mudai, Zhejiang Hangzhou, Zhejiang Longquan, Zhejiang Guishan,Zhejiang Dayao, Zhejiang Shangyu, Zhejiang Shangyu, Zhejiang Hangzhou, Zhejiang Longquan, Zhejiang
0.21 0.34 0.23 0.45 0.53 0.31 0.34 0.3 0.51 0.17 0.16 0.71 0.19 0.2 0.45
0.42 0.07 0.18 0.51 0.86 0.97 0.89 0.2 0.59 0.14 0.22 0.38 0.41 0.2 0.70
20.53 34.61 17.44 18.01 24.77 20.57 16.3 22 33.73 13.3 17.96 18.07 16.94 17.0 22.08
62.7 56.19 61.1 66.93 45.92 59.41 70.26 62.6 41.51 78.97 71.66 68.07 73.11 73.6 69.37
0.17 0.29 0.19 0.07 0.13 0.12 0.05
2.33 0.98 1.06 5.23 1.53 4.93 3.09 0.6 0.2 4.0 2.13 7.17 5.56 1.8 4.01
0.23 0.09 0.096 1.23 0.46
0.73 0.92 0.76 0.45 2 0.99 0.56 1.1 4.09 0.07 0.11 0.08 0.9 0.4
0.01 0.01 0.08 0.11 0.17 0.02 0.02 0.04 0.02 < 0.01 0.06
6.23 9.17 13.44 3.11 13.85 5.93 3.62 7.8 19.08 0.65 1.45 0.99 0.5 1.0 2.65
0.14 0.8 0.01 0.04 0.01 0.11 0.03 0.13 0.15
*Reference [18]. * Reference [3]. ***This paper.
crystalline glass [15,20], and the chemical composition has a linear influence on its thermal expansion and strength [21]. So, people could adjust the expansion coefficient and other properties by changing the content of some oxides in the glassy substance, such as alkali metals, silicon and aluminum [13,22–24]. In this paper, we didn't find obvious difference in such elements between different groups (Fig. 3). Although there were no experimentally measurements of the expansion coefficient and mechanical properties (elastic modulus and resistance to stress) of glazes, we roughly speculate that they are close in these properties based on their similar chemical composition. And the difference in the expansion coefficient of the body may be the main reason for crazing glaze of celadon with black body.
Southern Song Guan) also can be roughly divided into two groups based on the content of iron and titanium, and the black body has a relatively lower ratio SiO2/Al2O3 [16]. The ancient potter used porcelain clay (or called as porcelain stone), a kind of high-grade clay rich in silicon, as the single raw material for body production in southern China [2,17]. However, the celadon with black body used porcelain clay mixing with a kind of clay named as Zijin [2]. It appears red due to rich in iron, and the potter is easy to distinguish it from porcelain clay by color. In addition, this method of mixing has been recorded in the ancient literature, and is also widely applied in modern production of celadon with black body. What influence does the addition of Zijin clay have on the body? Some researchers analyzed the chemical composition of Zijin and porcelain clay from many regions (Table 2) [3,18]. They found that there are some differences between them. First, the contents of iron and titanium in Zijin are higher than that of porcelain clay, which is accepted by scholars. And except for two samples, most Zijin clays have a common and outstanding feature, lower silicon content or ratio SiO2/Al2O3 than that of porcelain clay. We also analyzed both types of clay that are currently used in Longquan, and found the same compositional characteristics as above (Table 2). So, it is certain that the mixing of Zijin clay is likely to objectively result in a lower ratio SiO2/Al2O3 for the black body compared to regular made only of porcelain clay.
3.4. The differences in expansion coefficient between black and regular bodies
3.3. Chemical composition of celadon glaze
It seems that investigating the thermal expansion of the fired body is the key to understanding the crazing glaze. For celadon with black body, the reason for the appearance of glaze crackles is considered to be that the body and glaze have different shrinkage during the last 300 °C of cooling [3]. However, it is difficult to estimate the expansion of the body based on chemical composition alone, because it is mainly dependent on the internal structure of the body, such as phase composition, the size and distribution of grains or pores. And phase composition is the most important factor that affects the thermal performance of substance. Different types of phase in the fired body (amorphous phase
We analyzed elemental composition of all the glazes in this paper. The result indicated that most glazes have a similar characteristic, higher level of calcium (Table 1). It should be lime-rich glaze that is often a mixture of refined body raw material and ash or limestone [3]. However, regardless of whether the samples were grouped based on origin or body type, we found that there is almost no significant difference in concentration of several major elements, as they had a relatively large distribution range. We thought that this was completely understandable. These kiln sites are located in Longquan, and they were likely to use the similar materials, such as raw clay and wood ash flux, which makes their difference in glaze less obvious. In addition, we also used the same method to analyze the composition of glaze from celadon with black body unearthed in Zhejiang [19]. No obvious difference was found between Southern Song Guan wares from Laohudong (Hangzhou) and some shards from Wayaoyang and Xiaomenzhen (Longquan). This suggests that in Zhejiang, it is possible that potters used glaze with similar composition for celadon production in a wider area and for a long time during Song Dynasty. The fired glaze is a glassy state hardly with crystals mixed. This type of material should have a steady or straight-line expansion like non-
Fig. 3. Scatterplots showing the ratio SiO2/Al2O3 and R2O (R = Na, K) content in the glazes. 4
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Fig. 4. X-ray powder diffraction patterns of typical samples (a: ancient regular body; b: ancient black body; c: porcelain clay; d: Zijin clay; e: modern regular body; f: modern black body).
and amorphous glass are the main phases in both types of the body (Fig. 4a and b). Even without quantitative analysis based on diffraction spectra, it can be concluded that the black bodies have significantly lower quartz and higher mullite than regulars, which is the most obvious difference between the two types of the body. In addition, we also collected porcelain and Zijin clay that are currently used in Longquan, and analyzed their phase composition. The results show that the
and crystalline minerals) will undergo volume changes as temperature changes, and their contractions determine the shrinkage of the substance during cooling process [15]. In order to understand the difference in the expansion coefficient between two types of the body, we analyzed the phase composition of some typical samples by X-ray diffraction method (XRD). The diffraction patterns suggest that quartz (an important form of silica), mullite 5
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
3.6. Comparison of expansion coefficients based on experimental analysis
porcelain clay contains quartz and orthoclase that is a common mineral of the feldspar group and used as fluxes in the manufacture of ceramic product. For Zijin clay, it contains quartz, kaolinite-montmorillonite and goethite. The kaolinite and montmorillonite are both alumina-silicate clay minerals and will react to form mullite during high temperature firing. Goethite is a widespread iron oxide mineral, and its high content in the raw material will make the body appear black even in reduction conditions of firing. The Zijin clay should be a lateritic deposit in southern China. Previous research indicated that after undergoing chemical weathering over geologic time scales, it tends to be silica-poor and rich in aluminum and iron oxides [25]. It is important that the content of quartz in porcelain clay is significantly higher than that of Zijin clay (Fig. 4c and d). Therefore, we inferred that compared with regular, the low level of undissolved quartz in the black body is mainly due to the incorporation of Zijin clay with low quartz content, although the quartz contained in raw material will decrease during high-temperature firing. The thermal expansion coefficient (called as α) of phases mentioned in this paper can be found in literature for reference [15,20]. The quartz abruptly contracts on cooling due to crystal transformation over a narrower range around 573 °C. And, it has a relatively higher thermal expansion coefficient below 573 °C than other phases in the fired body [20,26]. Mullite is present in a kaolinitic clay body at a firing temperature higher than 1100 °C [27]. Its presence indicated that these shards had higher temperature and enough holding time during firing [28]. It has a relatively lower α (5.1 ppm/°C during 25–1000 °C). The amorphous phase is made up of a silicate glass, originated from fusible mineral, such as feldspar; it has a coefficient of expansion (0.55 ppm/°C during 25–1000 °C) higher than mullite but lower than quartz [15,22]. Two forms of silica, quartz and cristobalite, can significantly affect the contraction of the ceramic body during cooling process, because they have a larger expansion coefficient than other common materials in the fired body [15], as some experiments have shown [29,30]. For two types of the body, it can be concluded that during cooling process, the expansion coefficient of the black body is smaller than that of regular because of the difference in quartz content.
In above discussion, the reason of crazing glaze for celadon with black body is that its body has lower quartz content than regular, while the two types of wares have glazes with similar thermal expansion coefficients. The effective way to verify it is to compare the thermal expansion coefficients of the two types of body. However, the experimental comparison has some practical problems. First, the bodies of ancient celadon shards collected in this work were so thin that they cannot meet the size requirement for expansion coefficient measurement. Second, it is impossible to accurately fire two kinds of bodies according to the traditional method by relying only on the composition and phase information. Fortunately, modern ceramic manufacture produces celadon with black body and regular. The porcelain and Zijin clay are still used as raw material and feldspars are the most commonly used fluxes in ceramic products, which may be different from ancient wares. The XRD patterns (Fig. 4e and f) indicate that modern body has the same characteristics in phase composition. We compared the content ratio of quartz vs. mullite by using the analysis software associated with the instrument. Although the accuracy of the quantitative results is not very good, they still clearly indicated that like ancient products, black bodies have a lower content of undissolved quartz (61:39, 60:40, 62:38) than regulars (76:24, 73:27, 77:23). We believe that this difference is caused by using Zijin clay with low content of quartz too. In addition, these products were manufactured in the same process, such as firing and preparation of clay material, and have a more compact body than ancient wares, which greatly reduces the influence from other factors (excluding phase composition) on thermal expansion. Based on the above considerations, we believe that they are suitable for demonstrating the relationship between the use of Zijin clay and expansion coefficient. We collected some modern celadon products that can meet the size requirement for experimental measurement. The thermal expansion curves were obtained in temperature range 25–950 °C. We measured six samples for both two types of products. According to the patterns (Fig. 6), there is an obvious fluctuation at 570 °C for all the samples due to the phase change of quartz. And below this temperature, there is no phase transformation but only the change in lattice volume. In this stage, the linear expansion of the black body is lower than that of regular. Therefore, the black body will contract less during cooling process, which is in line with our assumption. Thus, the lower shrinkage is due to the lower amount of undissolved quartz with a relatively high expansion coefficient. So, the incorporation of Zijin clay is an effective method to control the thermal expansion of the body, and is the reason why celadon with black body is more prone to have crazing glaze compared to regular.
3.5. Glaze crackles in different types of celadon A generally accepted view is that celadon with black body is known as crazing glaze and people have a variety of specific names for crackles according to their type and quantity. It can be seen from Fig. 1 that the glaze crackles of Group 2 (Wayaoyang) and 1 (Xiaomeizhen) seems to be more common and purposely wonted. The glazes of Group 3 (Wayaoyang) also have crackles, but they do not look clearly pursued. Only a few samples from Group 4 (Jincun) have small amount crackles in glaze. The statistical result of appearance observation indicated that the celadon with black body is more likely to have crazing glaze than regular. Although the number of samples collected in this article is small, we believe that the distribution of glaze crackles is in line with people's view about two types of celadon ware. Fig. 5 shows typical micrographs of crackles in glaze of celadon with black body and regular. We can clearly see that the cracks are so deep that they penetrate the thick glaze layer (about 1000 μm) and reach the body. Based on this, it could be inferred that the glaze contracts more than the body as they cool from their maturation temperature in the kiln. This causes the glaze crackles for both types of ware. Based on analysis results, we assumed that for two types of celadon, their expansion coefficients of glaze are not much different because of the similar chemical composition, and the black body mixed with Zijin clay has a lower expansion coefficient than regular during cooling process due to lower content of quartz. The mismatch of contraction between the glaze and support is greater in black body celadon than in regular celadon. So, the black body is more likely to cause the glaze to be subjected to great tension. The distribution of glaze crackles for different groups is consistent with our assumptions.
4. Conclusion We collected Song celadon shards unearthed in Longquan. These samples can be divided into black and regular according to the type of body. Based on the experimental analysis results, the following conclusions were obtained: 1. There is no significant difference in chemical composition of glaze between two types of product. And it is speculated that their properties, such as expansion coefficient and elastic modulus, are not much different. 2. The black body has lower content of quartz than regular due to the use of Zijin clay, which results in their difference in the expansion coefficient. We think this is the reason why the glaze crackles of celadon with black body are pursued as a distinguishing mark. 3. The result of expansion measurement of modern wares also proved that black body contracts less than regular due to a lower content of quartz. We thought that for the ancient potter lack of modern scientific knowledge, the use of Zijin clay is a very practical method to control the expansion coefficient of the body. The ancient potter may also use other 6
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Fig. 5. Microphotographs of glaze crackles for celadon with black body (a) and regular (b) and schematic diagram of contraction for ceramic ware during cooling stage (c).
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.ceramint.2019.11.192. References [1] X.M. Feng (Ed.), History of Chinese Ceramics, Cultural Relics Press, Beijing, 1982(In Chinese). [2] J.Z. Li (Ed.), History of Science and Technology in China-Porcelain, Science Press, Beijing, 1998(In Chinese). [3] N. Wood, Chines Glaze-Their Origins, Chemistry and Recreation, A&C Black, London, 1999. [4] H.M. Ye, F.S. Lao, G.Z. Li, L.Z. Ji, G.Z. Ye, An investigation on southern Song Guan celadon ware, J. Chin. Ceram. Soc. 11 (1983) 19–32 (In Chinese). [5] H.W.M. Hodges, The formation of crazing in some early Chinese glazed wares, Stud. Conserv. 33 (1988) 155–157, https://doi.org/10.1179/SIC.1988.33.S1.036. [6] J.E. Zhou, D. Liang, J. Wu, Q.J. Li, M.L. Zhang, J.M. Wu, Study on the formation mechanism and preparation of ice crackle celadon, J. Synth. Cryst. 40 (2011) 1076–1082 (In chinese). [7] S. Lahlil, J.M. Xu, W.D. Li, Influence of manufacturing parameters on the crakling process of ancient Chinese glazed ceramics, J. Cult. Herit. 16 (2015) 401–412, https://doi.org/10.1016/j.culher.2014.10.003. [8] Y.M. Shen, Collection of Ge Wares in the Palace Museum: Archaeological Discovery and Understanding of the Longquan Celadon with Black Body, Palace Museum Press, Beijing, 2017 (In Chinese). [9] L. Mattyasovszky-Zsolnay, Delayed thermal contraction and crazing of ceramic glazes, J. Am. Ceram. Soc. 29 (1946) 200–203, https://doi.org/10.1111/j.11512916.1946.tb11580.x. [10] A. Hamilton, C. Hall, The mechanics of moisture-expansion cracking in fired-clay ceramics, J. Phys. D Appl. Phys. 46 (2013) 092003, https://doi.org/10.1088/00223727/46/9/092003. [11] M. Kavanová, A. Kloužková, J. Kloužek, Characterization of the interaction between glazes and ceramic bodies, Ceram-Silikáty 61 (2017) 267–275, https://doi.org/10. 13168/cs.2017.0025. [12] H.G. Schurecht, D.H. Fuller, Some effects of thermal shock in causing crazing of glazed ceramic ware, J. Am. Ceram. Soc. 48 (1931) 565–571, https://doi.org/10. 1111/j.1151-2916.1931.tb16660.x. [13] N.N. Stasevich, Cause of hair cracks in ceramic glazes, Glass. Ceram. 14 (1957) 196–201, https://doi.org/10.1007/BF00668285. [14] H.G. Schurecht, Methods for testing crazing of glazes caused by increases in size of ceramic bodies, J. Am. Ceram. Soc. 11 (1928) 271–277, https://doi.org/10.1111/j. 1151-2916.1928.tb16178.x. [15] W.G. Lawrence, R.R. West, Ceramic Science for the Potter, Chilton Book Company, Pennsylvania, 1982. [16] Y. Huang, L.T. Yan, H.Y. Sun, X.Q. Feng, A study on black-body celadon excavated in the alter Guan and literature Ge (Longquan Ge) kilns by EDXRF, Archaeometry 60 (2018) 54–75, https://doi.org/10.1111/arcm.12302. [17] M.S. Tite, Ceramic production, Provenance and use- A review, Archaeometry 50 (2008) 216–231, https://doi.org/10.1111/j.1475-4754.2008.00391.x. [18] Y.Y. Guo, Preliminary study on Ge wares, China Ceram. 34 (1998) 21–25 (in Chinese). [19] L.T. Yan, H.Y. Sun, L. Li, X.Q. Feng, Characterization of early Chinese northern celadon with lead glaze from Caocun kiln within Yecheng site, J. Archaeol. Sci.: Rep. 19 (2018) 643–650, https://doi.org/10.1016/j.jasrep.2018.04.004.
Fig. 6. Comparison of expansion curves of two types of modern body measured by dilatometer.
methods, such as increasing the thickness of the glaze, to affect the appearance of glaze crackles. This also can explain the sophisticated combinations of crazing glaze and black body that has a contrast effect on the appearance of greenish glazes. In addition, it should be noted that previous studies have shown that the Zijin clays from different sources vary in composition. So, the potter might adjust the type or percentage of Zijin clay incorporated into the raw material of the body to control the crack effect based on experimental results. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment The project was supported by National Natural Science Foundation of China (NSFC, grant numbers 11775237, 11875056 and U1732106). The authors greatly appreciate researcher Zheng Jianmin from Zhejiang Provincial Institute of Cultural Relics Archaeology who provided all the samples. We thank Jiang Peng from Jingdezhen for his help in collecting of modern samples. 7
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
division of red soil in southern China, Quat. Sci. 28 (2008) 1–13 (In chinese). [26] J.L. Rosenholtz, D.T. Smith, Linear thermal expansion and inversions of quartz, var. rock crystal, Am. Mineral. 26 (1941) 103–109. [27] M.P. Rice, Pottery Analysis, The university of Chicago Press, London, 2015. [28] W.M. Carty, U. Senapati, Porcelain-raw materials, processing, phase evolution, and mechanical behavior, J. Am. Ceram. Soc. 81 (1998) 3–20, https://doi.org/10.1111/ j.1151-2916.1998.tb02290.x. [29] W.R. Morgan, Relation between uncombined quartz and thermal expansion of ceramic bodies, J. Am. Ceram. Soc. 17 (1–12) (1934) 117–121, https://doi.org/10. 1111/j.1151-2916.1934.tb19292.x. [30] A. Upali, T.J. Sanjeewani, Thermal compatibility studies of variable body and glaze compositions for glazed clay based cookware applications, Suranaree, J. Sci. Technol. 20 (2013) 51–57.
[20] C.B. Carter, M.G. Norton, Ceramic Materials-Science and Engineering, Springer Science + Business Media, New York, 2007. [21] J.L. Benson, Effect of Glaze Variables of the Mechanical Strength of White Wares, Master Thesis, Alfred University, 2003. [22] A.K. Varshneya, Fundamentals of Inorganic Glasses, Academic Press, San Diego, 1994. [23] W.D. Kingery, Factors affecting thermal stress resistance of ceramic materials, J. Am. Ceram. Soc. 38 (1955) 3–15, https://doi.org/10.1111/j.1151-2916.1955. tb14545.x. [24] D.V. Van Gordon, W.C. Spangenberg, Adjustment of thermal expansion of cone 8 glazes, J. Am. Ceram. Soc. 38 (1955) 331–335, https://doi.org/10.1111/j.11512916.1955.tb14956.x. [25] B.Y. Yuan, Z.K. Xia, B.S. Li, Y.S. Qiao, et al., Chrono-stratigraphy and stratigraphic
8
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
The relationship between the use of Zijin clay and glaze crackles for Chinese celadon with black body Lingtong Yan, Heyang Sun, Li Li, Xiangqian Feng∗ Institute of high energy physics, Chinese academy of sciences, Beijing, 100049, China
A R T I C LE I N FO
A B S T R A C T
Keywords: Celadon with black body Glaze crackle Song dynasty Zhejiang province Zijin clay
The celadon with black body is a famous type of ceramic product in ancient China due to its appearance features, black body and crazing glaze, different from regular. For this type of ware, the crazing glaze is a kind of artificial decoration, not production defect. How the glaze crackles were made by ancient potter has always attracted many people's attention. And it has been studied mainly based on chemical composition. In this paper, we aim to provide our discussion and explanation for its sophisticated combinations of crazing glaze and black body. Based on analysis of ancient and modern celadon products, we thought that the difference in quartz content of the fired body is the reason why the celadon with black body is more likely to have crazing glaze than regular. And, the potter could control the expansion coefficient of the body by using Zijin clay with low quartz content as raw material.
1. Introduction Celadon as a famous category of ceramic artifact is appreciated for its magnificent jade-like glaze covered on the surface of the ware. It began to be produced since Shang dynasty (ca. 1600-1027 BC), and became one kind of the most popular and long-lived ceramic product in ancient China [1]. In history, there is a well-known type of ware named as celadon with black body. It has some special appearance features that are very different from regular celadon. This type of ware used thin darker body that supplied the famous “purple rims and iron-feet” [2,3]. And, it has a typological appearance characteristic of crazing glaze that is generally seen as an undesirable coating for ceramic ware. For celadon with black body, the crazing glaze is not one kind of production happening defect, but man-made artistic decoration. Due to the thin body and crazing glaze, this type of ware is unsuitable for daily use. It is mainly used as a work of art and has always been regarded as collector's item. The representatives of this type of celadon are Southern Song Guan and Ge wares that are generally considered as the most famous ceramic products during Song dynasty (AD 960–1279). They were mainly produced in Hangzhou, Longquan and Cixi, Zhejiang Province (southeastern China), an important celadon producing area in history. In addition, there are some imitations produced in other regions after Song dynasty (AD 960–1279). At present, a small number of surviving Song wares in China are preserved in a few museums, such as The Palace Museum (Beijing) and National Palace Museum (Taibei).
∗
Scholars thought that crackles as glaze decoration for celadon with black body were originally inspired by Ru ware with light-body and finely crazing glaze, a type of classic official artifact (Northern Song dynasty, AD 960–1127) produced in northern China [1]. The difference is that their glaze crackles are more obvious than that of Ru ware. The Ru celadon is sometimes described as the first Chinese ceramic product that exploited glaze crackles for decoration effect. How crazing glaze were made by ancient potters has always attracted many people's attention. For celadon with black body, the cause of the crazing phenomenon has been studied mainly based on chemical composition [4–7]. In this paper, we aim to provide our explanation for the relationship between crazing glaze and odd black body or the use of Zijin clay. 2. Materials and methods 2.1. Materials For comparative study, we collected both types of shards unearthed from three kiln sites (Longquan, southern Zhejiang). According to the excavation, all the celadon shards were fired during Southern Song dynasty (AD 1127–1279). Archaeologists believe that Xiaomeizhen mainly produced celadon with black body, while the samples from Jincun are regular celadon. Wayaoyang produced both types of wares [8]. All samples were grouped according to the site location, while the
Corresponding author. E-mail address: [email protected] (X. Feng).
https://doi.org/10.1016/j.ceramint.2019.11.192 Received 4 November 2019; Received in revised form 19 November 2019; Accepted 21 November 2019 0272-8842/ © 2019 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: Lingtong Yan, et al., Ceramics International, https://doi.org/10.1016/j.ceramint.2019.11.192
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Table 1 Chemical composition of samples unearthed from Longquan. Mean results (wt%) and standard deviation of element oxides are reported here, and full results for all the samples are provided in supplementary Table s1 and s2. Site Location
Amount
Measurement
Na2O
MgO
Al2O3
SiO2
P2O5
K2O
CaO
TiO2
MnO
Fe2O3
Xiaomeizhen (Group 1)
20
Body
0.6 ± 0.17 0.52 ± 0.16 0.65 ± 0.16 0.53 ± 0.19 0.68 ± 0.18 0.55 ± 0.2 0.49 ± 0.1 0.34 ± 0.08
0.52 ± 0.09 0.52 ± 0.11 0.59 ± 0.08 0.56 ± 0.1 0.51 ± 0.06 0.52 ± 0.14 0.37 ± 0.05 0.69 ± 0.16
22.67 ± 1.43 14 ± 0.97 26.65 ± 2.04 13.45 ± 1.05 20.21 ± 1.2 13.42 ± 0.76 19.62 ± 0.99 13.75 ± 0.96
66.02 ± 2.2 67.77 ± 3.3 62.02 ± 2.43 69.08 ± 2.09 71.43 ± 1.6 70.51 ± 1.73 73.55 ± 1.52 66.86 ± 2.79
0.06 ± 0.01 0.17 ± 0.03 0.05 ± 0.01 0.16 ± 0.04 0.06 ± 0.01 0.14 ± 0.02 0.05 ± 0.01 0.2 ± 0.04
4.41 ± 0.61 4.17 ± 0.46 4.69 ± 0.42 4.87 ± 0.65 3.98 ± 0.48 4.7 ± 0.76 3.37 ± 0.52 3.62 ± 0.63
0.41 ± 0.3 11.17 ± 0.3 0.31 ± 0.22 9.88 ± 1.44 0.13 ± 0.07 8.13 ± 1.65 0.1 ± 0.03 12.6 ± 2.47
0.8 ± 0.22 0.16 ± 0.05 0.52 ± 0.11 0.12 ± 0.03 0.37 ± 0.08 0.15 ± 0.04 0.33 ± 0.05 0.17 ± 0.1
0.05 ± 0.01 0.13 ± 0.08 0.03 ± 0.01 0.13 ± 0.06 0.03 ± 0.01 0.14 ± 0.09 0.02 ± 0.01 0.37 ± 0.1
4.39 ± 0.82 1.27 ± 0.48 4.21 ± 0.44 1.09 ± 0.22 2.53 ± 0.29 1.62 ± 0.5 2.05 ± 0.49 1.25 ± 0.37
Glaze Wayaoyang (Group 2)
26
Body Glaze
Wayaoyang (Group 3)
36
Body Glaze
Jincun (Group 4)
15
Body Glaze
Fig. 1. Images of fragment samples unearthed from Longquan. (They were grouped according to the origin or iron content in the body. a: Xiaomeizhen; b: Wayaoyang sample with high content of iron; c: Wayaoyang sample with low content of iron; d: Jincun).
(EDXRF, Eagle III μProbe). The spectrometer was equipped with a Mo tube and a 125 μm Be window. It worked at a voltage of 40 kV, current 250 μA. The X-ray beam spot was selected to be Ф = 1 mm. The spectrum of each sample was measured with a live time of 300s. The detector is a liquid-nitrogen-cooled Si (Li) crystal with a 160.3 eV at Mn Kα. The analysis was carried out in a vacuum environment. To calibrate the substance effects and improve the accuracy of the data, we used a set of house ceramic reference materials for EDXRF. The software employed for analysis is the program VISION32 associated with the instrument. The X-ray diffraction (XRD) patterns were obtained on a X-ray diffractometer (D8 Advance, Bruker, Germany) with Cu-Kα radiation
samples from Wayaoyang were divided into two groups based on the difference in iron level of the body (Table 1). It is difficult to distinguish the type of body by visual observation, because most of them are not particularly noticeable in color, and only a small amount of samples have an obvious black body. Some images of typical shards are in Fig. 1.
2.2. Analysis experiment The measurement area of bodies was polished to remove the surface layer that may be contaminated. Then the samples were washed three times in an ultrasonic cleaner with deionized water and dried at 95 °C. The elemental composition was analyzed by the Energy Dispersive XRF 2
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
(λ = 1.5406 Å). To prepare the sample, the bodies were ground into powder. Operating conditions for the XRD was 40 kV of voltage and 40 mA of current. The samples were continuously scanned from 10o-60o (2θ), with a step size of 0.02o and a time per step of 1.0s. The minerals were identified using the ICDD (International Center for Diffraction Data) database. The result of firing temperature was based on measurement of thermal expansion. The bodies were cut into pieces with size 25 × 5 × 5 mm. Then they were washed in the ultrasonic cleaning machine and dried in oven at 95 °C. The dilatometer used for this research was a DIL402PC (NETSCH, Germany) thermal expansion instrument. Samples were heat at a rate of 5 °C/min in N2 atmosphere during measurement.
Most of the ancient glazes in this paper are characterized by a relatively large thickness based on method of multi-layer glazing [3,8]. The reason for use of thick glaze is still unclear, but it is widely applied to regular celadon in Longquan area, not only wares with black body. We speculate that the thick glaze layer may affect the appearance of cracks, but it should not be the main means for generating crazing glaze for celadon with black body. The purpose of this approach is more likely to reduce the effect of the fired body on the color appearance of partly translucent celadon glaze, especially for the wares with black body. 3) Adjusting the composition of glaze or body. It is the most practical method to control glaze crackles, because different physical properties that can affect the crazing, such as the expansion coefficient, strength and elastic modulus, are mainly determined by different compositions of glaze and body [7,13]. In order to control the crazing, modern potters usually adjust the concentration of some oxides in the glaze to change its thermal expansion and contraction, because used raw materials for body cannot conveniently be changed [15]. However, for ancient potter, they could adjust both the composition of raw material for body and glaze recipe to influence the appearance of crazing glaze.
3. Results and discussion 3.1. Method to generate the crazing glaze The reasons for glaze crackles were studied by many researches. They could be divided into instant and delayed. The delayed crack is caused by the moisture expansion of the porous body, and it occurs over a period of time after firing [9,10]. The crackles of the celadon with black body should be instant glaze cracks generated in manufacturing process. During high-temperature firing, the clay body is matured and becomes more vitreous, and the glaze is melted into a liquid state. In this stage, the substance has good fluidity and large elasticity modulus, and there is no obvious stress between body and glaze layer. After hightemperature firing, the mineralogical transformation has completed. During the low-temperature stage, the body and glaze begin to contract during the cooling process, and the Young's modulus becomes smaller. If the contraction of glaze is different from the body, there will be residual stress existing between them [11]. The coefficient of expansion of material is often used to characterize the relative tendency to expand and contract when heated and cooled. When the glaze layer is subjected to a large stress overcoming its resistance, the force is liable to cause cracks in the glaze. The glaze deformation can be divided into two categories, crazing and shivering. Crazing happens when the glaze is under extreme tension. On the other hand, Shivering occurs when a glaze is under too much compression. The probability of crazing occurring is somewhat complex. Because the thermal expansion mismatch between body and glaze and their resistance to stress vary with the composition of the material and the temperature. Researchers thought that three artificial methods in the practical production process could be used to influence the appearance of glaze crackles [7,12–14]:
Based on above discussion, we speculated that compared to the first two methods, ancient Chinese potters are most likely to adjust the composition of ceramic ware to purposefully produce crazing glaze in large quantities. And many previous related researches on celadon with black body were also focused on this method. 3.2. Raw materials for different types of bodies In ancient China, celadon wares with black and regular body were produced at the same time. A compositional comparison of two types of celadon products may be of great help in understanding how ancient potter made crazing glaze. So we collected and analyzed some typical celadon shards from Longquan, Zhejiang. Based on the compositional comparison of bodies (Table 1), we found that all the samples in this paper can be divided into two groups according to the iron content (Fig. 2). This is also in line with the classification of the black and regular body from archaeologists, and especially the Wayaoyang site produced two types of wares at the same time (group 2 and 3). Apart from this, it is interesting that another important result is the difference in the ratio SiO2/Al2O3 for all the samples (Fig. 2). The samples of Group 3 from Wayaoyang and Jincun have relatively low, while for Group 2 is higher and the samples from Xiaomeizhen are in the middle. Similarly, we have reported that samples from Jiaotanxia (alter
1) Designed firing process. In the simulation experiments, Lahlil et al. [7] found that if the temperature and atmosphere can be controlled during the firing process, the thermal contract of body and glaze and the effect of the crack in the glaze can be affected. However, for ancient celadon production in Zhejiang, the firing process was carried out in the dragon kiln that is essentially a tunnel built on a gentle slope (usually along with hillside), and could be very long, up to several tens of meters [2]. This type of kiln has a very large internal space, and the temperature varies greatly from location to location. In addition, some scholars thought that the celadon with black and regular wares might be fired together in the same kiln. When firing a large number of ceramic products in this type of kiln, it seems more difficult to apply different precisely designed firing surrounding for separate category of wares. This may be a less practical way for ancient potters to produce crazing glaze in large quantities. 2) The relative glaze-body thickness. People can optimize the relative glaze-body thickness to obtain a controlled appearance of crackles [7,12,13]. The thickness could influence stress between body and glaze, and glaze resistance under the same compression or tension.
Fig. 2. Scatterplots showing the ratio SiO2/Al2O3 and Fe2O3 content in the bodies. 3
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Table 2 The summarized compositional data (wt%) of Zijin clays from references and result (wt%) of raw material in this paper (’-‘ means the data was not found). Type of clay
Origin
Na2O
MgO
Al2O3
SiO2
P2O5
K2 O
CaO
TiO2
MnO
Fe2O3
Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay* Zijin clay** Zijin clay*** Porcelain clay* Porcelain clay* Porcelain clay* Porcelain clay* Porcelain clay** Porcelain clay***
Jingdezhen, Jiangxi Wuguishan, Zhejiang Wuguishan, Zhejiang Dayao, Zhejiang Dayao, Zhejiang Baoxi, Zhejiang Mudai, Zhejiang Hangzhou, Zhejiang Longquan, Zhejiang Guishan,Zhejiang Dayao, Zhejiang Shangyu, Zhejiang Shangyu, Zhejiang Hangzhou, Zhejiang Longquan, Zhejiang
0.21 0.34 0.23 0.45 0.53 0.31 0.34 0.3 0.51 0.17 0.16 0.71 0.19 0.2 0.45
0.42 0.07 0.18 0.51 0.86 0.97 0.89 0.2 0.59 0.14 0.22 0.38 0.41 0.2 0.70
20.53 34.61 17.44 18.01 24.77 20.57 16.3 22 33.73 13.3 17.96 18.07 16.94 17.0 22.08
62.7 56.19 61.1 66.93 45.92 59.41 70.26 62.6 41.51 78.97 71.66 68.07 73.11 73.6 69.37
0.17 0.29 0.19 0.07 0.13 0.12 0.05
2.33 0.98 1.06 5.23 1.53 4.93 3.09 0.6 0.2 4.0 2.13 7.17 5.56 1.8 4.01
0.23 0.09 0.096 1.23 0.46
0.73 0.92 0.76 0.45 2 0.99 0.56 1.1 4.09 0.07 0.11 0.08 0.9 0.4
0.01 0.01 0.08 0.11 0.17 0.02 0.02 0.04 0.02 < 0.01 0.06
6.23 9.17 13.44 3.11 13.85 5.93 3.62 7.8 19.08 0.65 1.45 0.99 0.5 1.0 2.65
0.14 0.8 0.01 0.04 0.01 0.11 0.03 0.13 0.15
*Reference [18]. * Reference [3]. ***This paper.
crystalline glass [15,20], and the chemical composition has a linear influence on its thermal expansion and strength [21]. So, people could adjust the expansion coefficient and other properties by changing the content of some oxides in the glassy substance, such as alkali metals, silicon and aluminum [13,22–24]. In this paper, we didn't find obvious difference in such elements between different groups (Fig. 3). Although there were no experimentally measurements of the expansion coefficient and mechanical properties (elastic modulus and resistance to stress) of glazes, we roughly speculate that they are close in these properties based on their similar chemical composition. And the difference in the expansion coefficient of the body may be the main reason for crazing glaze of celadon with black body.
Southern Song Guan) also can be roughly divided into two groups based on the content of iron and titanium, and the black body has a relatively lower ratio SiO2/Al2O3 [16]. The ancient potter used porcelain clay (or called as porcelain stone), a kind of high-grade clay rich in silicon, as the single raw material for body production in southern China [2,17]. However, the celadon with black body used porcelain clay mixing with a kind of clay named as Zijin [2]. It appears red due to rich in iron, and the potter is easy to distinguish it from porcelain clay by color. In addition, this method of mixing has been recorded in the ancient literature, and is also widely applied in modern production of celadon with black body. What influence does the addition of Zijin clay have on the body? Some researchers analyzed the chemical composition of Zijin and porcelain clay from many regions (Table 2) [3,18]. They found that there are some differences between them. First, the contents of iron and titanium in Zijin are higher than that of porcelain clay, which is accepted by scholars. And except for two samples, most Zijin clays have a common and outstanding feature, lower silicon content or ratio SiO2/Al2O3 than that of porcelain clay. We also analyzed both types of clay that are currently used in Longquan, and found the same compositional characteristics as above (Table 2). So, it is certain that the mixing of Zijin clay is likely to objectively result in a lower ratio SiO2/Al2O3 for the black body compared to regular made only of porcelain clay.
3.4. The differences in expansion coefficient between black and regular bodies
3.3. Chemical composition of celadon glaze
It seems that investigating the thermal expansion of the fired body is the key to understanding the crazing glaze. For celadon with black body, the reason for the appearance of glaze crackles is considered to be that the body and glaze have different shrinkage during the last 300 °C of cooling [3]. However, it is difficult to estimate the expansion of the body based on chemical composition alone, because it is mainly dependent on the internal structure of the body, such as phase composition, the size and distribution of grains or pores. And phase composition is the most important factor that affects the thermal performance of substance. Different types of phase in the fired body (amorphous phase
We analyzed elemental composition of all the glazes in this paper. The result indicated that most glazes have a similar characteristic, higher level of calcium (Table 1). It should be lime-rich glaze that is often a mixture of refined body raw material and ash or limestone [3]. However, regardless of whether the samples were grouped based on origin or body type, we found that there is almost no significant difference in concentration of several major elements, as they had a relatively large distribution range. We thought that this was completely understandable. These kiln sites are located in Longquan, and they were likely to use the similar materials, such as raw clay and wood ash flux, which makes their difference in glaze less obvious. In addition, we also used the same method to analyze the composition of glaze from celadon with black body unearthed in Zhejiang [19]. No obvious difference was found between Southern Song Guan wares from Laohudong (Hangzhou) and some shards from Wayaoyang and Xiaomenzhen (Longquan). This suggests that in Zhejiang, it is possible that potters used glaze with similar composition for celadon production in a wider area and for a long time during Song Dynasty. The fired glaze is a glassy state hardly with crystals mixed. This type of material should have a steady or straight-line expansion like non-
Fig. 3. Scatterplots showing the ratio SiO2/Al2O3 and R2O (R = Na, K) content in the glazes. 4
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Fig. 4. X-ray powder diffraction patterns of typical samples (a: ancient regular body; b: ancient black body; c: porcelain clay; d: Zijin clay; e: modern regular body; f: modern black body).
and amorphous glass are the main phases in both types of the body (Fig. 4a and b). Even without quantitative analysis based on diffraction spectra, it can be concluded that the black bodies have significantly lower quartz and higher mullite than regulars, which is the most obvious difference between the two types of the body. In addition, we also collected porcelain and Zijin clay that are currently used in Longquan, and analyzed their phase composition. The results show that the
and crystalline minerals) will undergo volume changes as temperature changes, and their contractions determine the shrinkage of the substance during cooling process [15]. In order to understand the difference in the expansion coefficient between two types of the body, we analyzed the phase composition of some typical samples by X-ray diffraction method (XRD). The diffraction patterns suggest that quartz (an important form of silica), mullite 5
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
3.6. Comparison of expansion coefficients based on experimental analysis
porcelain clay contains quartz and orthoclase that is a common mineral of the feldspar group and used as fluxes in the manufacture of ceramic product. For Zijin clay, it contains quartz, kaolinite-montmorillonite and goethite. The kaolinite and montmorillonite are both alumina-silicate clay minerals and will react to form mullite during high temperature firing. Goethite is a widespread iron oxide mineral, and its high content in the raw material will make the body appear black even in reduction conditions of firing. The Zijin clay should be a lateritic deposit in southern China. Previous research indicated that after undergoing chemical weathering over geologic time scales, it tends to be silica-poor and rich in aluminum and iron oxides [25]. It is important that the content of quartz in porcelain clay is significantly higher than that of Zijin clay (Fig. 4c and d). Therefore, we inferred that compared with regular, the low level of undissolved quartz in the black body is mainly due to the incorporation of Zijin clay with low quartz content, although the quartz contained in raw material will decrease during high-temperature firing. The thermal expansion coefficient (called as α) of phases mentioned in this paper can be found in literature for reference [15,20]. The quartz abruptly contracts on cooling due to crystal transformation over a narrower range around 573 °C. And, it has a relatively higher thermal expansion coefficient below 573 °C than other phases in the fired body [20,26]. Mullite is present in a kaolinitic clay body at a firing temperature higher than 1100 °C [27]. Its presence indicated that these shards had higher temperature and enough holding time during firing [28]. It has a relatively lower α (5.1 ppm/°C during 25–1000 °C). The amorphous phase is made up of a silicate glass, originated from fusible mineral, such as feldspar; it has a coefficient of expansion (0.55 ppm/°C during 25–1000 °C) higher than mullite but lower than quartz [15,22]. Two forms of silica, quartz and cristobalite, can significantly affect the contraction of the ceramic body during cooling process, because they have a larger expansion coefficient than other common materials in the fired body [15], as some experiments have shown [29,30]. For two types of the body, it can be concluded that during cooling process, the expansion coefficient of the black body is smaller than that of regular because of the difference in quartz content.
In above discussion, the reason of crazing glaze for celadon with black body is that its body has lower quartz content than regular, while the two types of wares have glazes with similar thermal expansion coefficients. The effective way to verify it is to compare the thermal expansion coefficients of the two types of body. However, the experimental comparison has some practical problems. First, the bodies of ancient celadon shards collected in this work were so thin that they cannot meet the size requirement for expansion coefficient measurement. Second, it is impossible to accurately fire two kinds of bodies according to the traditional method by relying only on the composition and phase information. Fortunately, modern ceramic manufacture produces celadon with black body and regular. The porcelain and Zijin clay are still used as raw material and feldspars are the most commonly used fluxes in ceramic products, which may be different from ancient wares. The XRD patterns (Fig. 4e and f) indicate that modern body has the same characteristics in phase composition. We compared the content ratio of quartz vs. mullite by using the analysis software associated with the instrument. Although the accuracy of the quantitative results is not very good, they still clearly indicated that like ancient products, black bodies have a lower content of undissolved quartz (61:39, 60:40, 62:38) than regulars (76:24, 73:27, 77:23). We believe that this difference is caused by using Zijin clay with low content of quartz too. In addition, these products were manufactured in the same process, such as firing and preparation of clay material, and have a more compact body than ancient wares, which greatly reduces the influence from other factors (excluding phase composition) on thermal expansion. Based on the above considerations, we believe that they are suitable for demonstrating the relationship between the use of Zijin clay and expansion coefficient. We collected some modern celadon products that can meet the size requirement for experimental measurement. The thermal expansion curves were obtained in temperature range 25–950 °C. We measured six samples for both two types of products. According to the patterns (Fig. 6), there is an obvious fluctuation at 570 °C for all the samples due to the phase change of quartz. And below this temperature, there is no phase transformation but only the change in lattice volume. In this stage, the linear expansion of the black body is lower than that of regular. Therefore, the black body will contract less during cooling process, which is in line with our assumption. Thus, the lower shrinkage is due to the lower amount of undissolved quartz with a relatively high expansion coefficient. So, the incorporation of Zijin clay is an effective method to control the thermal expansion of the body, and is the reason why celadon with black body is more prone to have crazing glaze compared to regular.
3.5. Glaze crackles in different types of celadon A generally accepted view is that celadon with black body is known as crazing glaze and people have a variety of specific names for crackles according to their type and quantity. It can be seen from Fig. 1 that the glaze crackles of Group 2 (Wayaoyang) and 1 (Xiaomeizhen) seems to be more common and purposely wonted. The glazes of Group 3 (Wayaoyang) also have crackles, but they do not look clearly pursued. Only a few samples from Group 4 (Jincun) have small amount crackles in glaze. The statistical result of appearance observation indicated that the celadon with black body is more likely to have crazing glaze than regular. Although the number of samples collected in this article is small, we believe that the distribution of glaze crackles is in line with people's view about two types of celadon ware. Fig. 5 shows typical micrographs of crackles in glaze of celadon with black body and regular. We can clearly see that the cracks are so deep that they penetrate the thick glaze layer (about 1000 μm) and reach the body. Based on this, it could be inferred that the glaze contracts more than the body as they cool from their maturation temperature in the kiln. This causes the glaze crackles for both types of ware. Based on analysis results, we assumed that for two types of celadon, their expansion coefficients of glaze are not much different because of the similar chemical composition, and the black body mixed with Zijin clay has a lower expansion coefficient than regular during cooling process due to lower content of quartz. The mismatch of contraction between the glaze and support is greater in black body celadon than in regular celadon. So, the black body is more likely to cause the glaze to be subjected to great tension. The distribution of glaze crackles for different groups is consistent with our assumptions.
4. Conclusion We collected Song celadon shards unearthed in Longquan. These samples can be divided into black and regular according to the type of body. Based on the experimental analysis results, the following conclusions were obtained: 1. There is no significant difference in chemical composition of glaze between two types of product. And it is speculated that their properties, such as expansion coefficient and elastic modulus, are not much different. 2. The black body has lower content of quartz than regular due to the use of Zijin clay, which results in their difference in the expansion coefficient. We think this is the reason why the glaze crackles of celadon with black body are pursued as a distinguishing mark. 3. The result of expansion measurement of modern wares also proved that black body contracts less than regular due to a lower content of quartz. We thought that for the ancient potter lack of modern scientific knowledge, the use of Zijin clay is a very practical method to control the expansion coefficient of the body. The ancient potter may also use other 6
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
Fig. 5. Microphotographs of glaze crackles for celadon with black body (a) and regular (b) and schematic diagram of contraction for ceramic ware during cooling stage (c).
Appendix A. Supplementary data Supplementary data to this article can be found online at https:// doi.org/10.1016/j.ceramint.2019.11.192. References [1] X.M. Feng (Ed.), History of Chinese Ceramics, Cultural Relics Press, Beijing, 1982(In Chinese). [2] J.Z. Li (Ed.), History of Science and Technology in China-Porcelain, Science Press, Beijing, 1998(In Chinese). [3] N. Wood, Chines Glaze-Their Origins, Chemistry and Recreation, A&C Black, London, 1999. [4] H.M. Ye, F.S. Lao, G.Z. Li, L.Z. Ji, G.Z. Ye, An investigation on southern Song Guan celadon ware, J. Chin. Ceram. Soc. 11 (1983) 19–32 (In Chinese). [5] H.W.M. Hodges, The formation of crazing in some early Chinese glazed wares, Stud. Conserv. 33 (1988) 155–157, https://doi.org/10.1179/SIC.1988.33.S1.036. [6] J.E. Zhou, D. Liang, J. Wu, Q.J. Li, M.L. Zhang, J.M. Wu, Study on the formation mechanism and preparation of ice crackle celadon, J. Synth. Cryst. 40 (2011) 1076–1082 (In chinese). [7] S. Lahlil, J.M. Xu, W.D. Li, Influence of manufacturing parameters on the crakling process of ancient Chinese glazed ceramics, J. Cult. Herit. 16 (2015) 401–412, https://doi.org/10.1016/j.culher.2014.10.003. [8] Y.M. Shen, Collection of Ge Wares in the Palace Museum: Archaeological Discovery and Understanding of the Longquan Celadon with Black Body, Palace Museum Press, Beijing, 2017 (In Chinese). [9] L. Mattyasovszky-Zsolnay, Delayed thermal contraction and crazing of ceramic glazes, J. Am. Ceram. Soc. 29 (1946) 200–203, https://doi.org/10.1111/j.11512916.1946.tb11580.x. [10] A. Hamilton, C. Hall, The mechanics of moisture-expansion cracking in fired-clay ceramics, J. Phys. D Appl. Phys. 46 (2013) 092003, https://doi.org/10.1088/00223727/46/9/092003. [11] M. Kavanová, A. Kloužková, J. Kloužek, Characterization of the interaction between glazes and ceramic bodies, Ceram-Silikáty 61 (2017) 267–275, https://doi.org/10. 13168/cs.2017.0025. [12] H.G. Schurecht, D.H. Fuller, Some effects of thermal shock in causing crazing of glazed ceramic ware, J. Am. Ceram. Soc. 48 (1931) 565–571, https://doi.org/10. 1111/j.1151-2916.1931.tb16660.x. [13] N.N. Stasevich, Cause of hair cracks in ceramic glazes, Glass. Ceram. 14 (1957) 196–201, https://doi.org/10.1007/BF00668285. [14] H.G. Schurecht, Methods for testing crazing of glazes caused by increases in size of ceramic bodies, J. Am. Ceram. Soc. 11 (1928) 271–277, https://doi.org/10.1111/j. 1151-2916.1928.tb16178.x. [15] W.G. Lawrence, R.R. West, Ceramic Science for the Potter, Chilton Book Company, Pennsylvania, 1982. [16] Y. Huang, L.T. Yan, H.Y. Sun, X.Q. Feng, A study on black-body celadon excavated in the alter Guan and literature Ge (Longquan Ge) kilns by EDXRF, Archaeometry 60 (2018) 54–75, https://doi.org/10.1111/arcm.12302. [17] M.S. Tite, Ceramic production, Provenance and use- A review, Archaeometry 50 (2008) 216–231, https://doi.org/10.1111/j.1475-4754.2008.00391.x. [18] Y.Y. Guo, Preliminary study on Ge wares, China Ceram. 34 (1998) 21–25 (in Chinese). [19] L.T. Yan, H.Y. Sun, L. Li, X.Q. Feng, Characterization of early Chinese northern celadon with lead glaze from Caocun kiln within Yecheng site, J. Archaeol. Sci.: Rep. 19 (2018) 643–650, https://doi.org/10.1016/j.jasrep.2018.04.004.
Fig. 6. Comparison of expansion curves of two types of modern body measured by dilatometer.
methods, such as increasing the thickness of the glaze, to affect the appearance of glaze crackles. This also can explain the sophisticated combinations of crazing glaze and black body that has a contrast effect on the appearance of greenish glazes. In addition, it should be noted that previous studies have shown that the Zijin clays from different sources vary in composition. So, the potter might adjust the type or percentage of Zijin clay incorporated into the raw material of the body to control the crack effect based on experimental results. Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper. Acknowledgment The project was supported by National Natural Science Foundation of China (NSFC, grant numbers 11775237, 11875056 and U1732106). The authors greatly appreciate researcher Zheng Jianmin from Zhejiang Provincial Institute of Cultural Relics Archaeology who provided all the samples. We thank Jiang Peng from Jingdezhen for his help in collecting of modern samples. 7
Ceramics International xxx (xxxx) xxx–xxx
L. Yan, et al.
division of red soil in southern China, Quat. Sci. 28 (2008) 1–13 (In chinese). [26] J.L. Rosenholtz, D.T. Smith, Linear thermal expansion and inversions of quartz, var. rock crystal, Am. Mineral. 26 (1941) 103–109. [27] M.P. Rice, Pottery Analysis, The university of Chicago Press, London, 2015. [28] W.M. Carty, U. Senapati, Porcelain-raw materials, processing, phase evolution, and mechanical behavior, J. Am. Ceram. Soc. 81 (1998) 3–20, https://doi.org/10.1111/ j.1151-2916.1998.tb02290.x. [29] W.R. Morgan, Relation between uncombined quartz and thermal expansion of ceramic bodies, J. Am. Ceram. Soc. 17 (1–12) (1934) 117–121, https://doi.org/10. 1111/j.1151-2916.1934.tb19292.x. [30] A. Upali, T.J. Sanjeewani, Thermal compatibility studies of variable body and glaze compositions for glazed clay based cookware applications, Suranaree, J. Sci. Technol. 20 (2013) 51–57.
[20] C.B. Carter, M.G. Norton, Ceramic Materials-Science and Engineering, Springer Science + Business Media, New York, 2007. [21] J.L. Benson, Effect of Glaze Variables of the Mechanical Strength of White Wares, Master Thesis, Alfred University, 2003. [22] A.K. Varshneya, Fundamentals of Inorganic Glasses, Academic Press, San Diego, 1994. [23] W.D. Kingery, Factors affecting thermal stress resistance of ceramic materials, J. Am. Ceram. Soc. 38 (1955) 3–15, https://doi.org/10.1111/j.1151-2916.1955. tb14545.x. [24] D.V. Van Gordon, W.C. Spangenberg, Adjustment of thermal expansion of cone 8 glazes, J. Am. Ceram. Soc. 38 (1955) 331–335, https://doi.org/10.1111/j.11512916.1955.tb14956.x. [25] B.Y. Yuan, Z.K. Xia, B.S. Li, Y.S. Qiao, et al., Chrono-stratigraphy and stratigraphic
8