Creating Wusetu (“Five-Coloured Clay”): Chronological Changes in Zisha Ware Clay Recipes and the Complexity of Potters’ Technological Choices

Creating Wusetu (“Five-Coloured Clay”): Chronological Changes in Zisha Ware Clay Recipes and the Complexity of Potters’ Technological Choices | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Research Article Creating Wusetu (“Five-Coloured Clay”): Chronological Changes in Zisha Ware Clay Recipes and the Complexity of Potters’ Technological Choices Xuyang Gao, Anke Hein, Tao Hang, Xingnan Huang This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6945795/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 29 Nov, 2025 Read the published version in Archaeological and Anthropological Sciences → Version 1 posted 9 You are reading this latest preprint version Abstract Technological choices in pottery production, particularly the selection of raw materials, are much discussed for prehistoric periods but have received little scholarly attention in the case of Late Imperial China. In this paper, zisha teapots, which became China’s main tea preparation vessels over the course of the 15th–20th century, are presented as a case study to explore the complexity underlying potters’ raw material selection in historic periods. A total of 187 excavated zisha sherds was analysed using optical microscopy, semi-quantitative chemical analysis via scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) spectroscopy, and ImageJ analysis of SEM backscatter spectrum images. These zisha sherds date from the Ming dynasty to the Republican period (1368–1949) and were recovered from Shushan kiln site. SEM-EDX analysis combined with image manipulation in ImageJ revealed changes in the clay recipe over time, including an increase in iron oxide variation and increasing fineness of clay particle sizes, suggesting an expanded colour range and refinement of the clay paste. Combining these findings with an examination of the geological setting of the mining locations, the clay procurement sequence, the clay-processing techniques used by the potters, and texts discussing clay colour and texture appreciation, this study demonstrates the complexity of the potters’ raw material choices in Late Imperial China and illustrates how these factors can be elucidated through a combination of scientific analysis of archaeological material, examination of geological samples, visual analysis, and reference to historical sources. Potters’ technological choice zisha clay Shushan site Ming and Qing dynasties colourant oxides particle sizes Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 Figure 14 Figure 15 Figure 16 Figure 17 Figure 18 Figure 19 1. Introduction This study explores the complexity of potters’ technological choices, particularly raw material choice in Late Imperial China, focusing on zisha teapot clay recipe changes. Zisha teapots, produced in Yixing, China, are unglazed tea-making vessels that started to gain popularity during the Late Ming period (Cai 2019; Liu 2013; Fig. 1) and became internationally renowned in the 17th and 18th centuries, as they were exported across Asian and European markets (Li 2009; Teng 2017; Valfre 2000). “Potters’ technological choices” refers to a series of interrelated decisions, including the selection of raw materials (such as clay sources and recipes), tools and equipment for shaping pottery, energy sources (e.g., hydro-powered clay mills and fuels for firing), and processing and shaping techniques(Hunt 2016 pp. 104–106; Lemonnier 1993, pp. 6–12; Schiffer and Skibo 1997; Sillar and Tite 2000). These decisions also intersect with broader cultural, economic, and social dynamics (Kudelić and Neral 2025). Potters’ raw material selection is shaped by various factors, including the properties and availability of raw materials (Cumberpatch et al. 2001; Martineau et al. 2007; Sillar and Tite 2000), cultural values and community preferences (Arnold et al. 2007; Mahias 1993), mechanical performance (e.g., resistance to thermal shock and overall durability) (Bronitsky and Hamer 1986; Kilikoglou et al. 1998; Tite et al. 2001; Vekinis and Kilikoglou 1998), and regional crafting traditions (Dietler and Herbich 1989). The study of raw material choice in Chinese ceramic production has largely focused on the Neolithic period and especially on Majiayao and Yangshao ceramics (Dammer, Hein, and Spataro 2024; Li et al. 2025; Spataro and Hein 2025; Womack et al. 2019). For instance, Dammer, Hein, and Spataro (2024) demonstrated through geological surveying and experimental firing combined with petrographic and geochemical analyses on excavated sherds and experimental material that Majiayao potters intentionally selected clays with certain calcium contents and that they added granitic fragments or river sand as temper, demonstrating a nuanced understanding of raw material behaviour and environmental constraints. Less attention has been given to raw material choice in Late Imperial China ceramic production. Most studies of Late Imperial ceramics have focused on analysing the chemical and mineralogical properties of clay recipes, including several studies on Jingdezhen (He, Zhang, and Zhang 2016; Wood 2021; Yap and Hua 1992) and Dehua wares (Li et al. 2011; Wu et al. 2014), none of them considering the underlying decision-making strategies behind material use and processing techniques. For instance, Li (2011) examined porcelain samples from five Dehua kiln sites, and published detailed data on Song, Yuan, and Ming dynasty Dehua wares, concluding that their Fe 2 O 3 and K 2 O compositions varied. However, the author did not discuss potential reasons for the clay recipe changes. Thus, although compositional analyses are abundant, the decision-making processes of Late Imperial potters—why they chose certain clay sources over others—remain underexplored. We argue that zisha teapots offer a rare and valuable lens through which to examine the complexity of these clay choices in Late Imperial China. First, zisha wares were and continue to be produced in Yixing, China (Jiangsusheng 1992; Jiangsusheng dituji 2004) (Fig. 1), one of the main regional ceramic production centres in China during the Ming and Qing dynasties, comparable to Dehua and Shiwan (Keer and Wood 2004; Liang 1991; Xu 2000). These wares, like the ones produced in Jingdezhen and Dehua, were exported to Asian and European countries like Japan, Thailand, Spain, Holland, and England during the 17 th and 18 th century (Valfre 2000). Second, in contrast to glazed wares, the clay body is of particular importance in zisha wares, as users and consumers can directly observe the colour and texture of the fired clay which is neither fully vitrified nor covered by a glaze that would obscure these properties. Their final appearance and texture are determined largely by the composition and treatment of the clay and the firing conditions (temperature and atmosphere). This unglazed feature makes zisha an ideal case study for investigations into how potters negotiated geological settings and procurement, clay processing, and technological and aesthetic preferences. Third, clay properties and origins are particularly important in zisha making and consumption. Zisha teapots are crafted from zisha clay, which is procured from different mining locations in Yixing. Certain mining locations, including the Huanglongshan 黄龙山 and Zhaozhuangshan 赵庄山 mines, are known for their “authentic” zisha clay (for a detailed discussion of zisha clay authenticity, see Hou et al. 2016; Xu 2009; Zhao and Lu 2013). The three main clay types are Zini (紫泥, “clay with purplish colour”), Hongni (红泥, “clay with reddish colour”), and Lüni (绿泥, “clay with greenish colour”) (Han et al 1981; He 1988; Zhu 2009, p. 38). Local potters call this clay Wusetu (五色土, “five-coloured clay”), due to its diverse colours (Wu 2014 [1786], p. 871; Zhou 2014 [ca. 1640], p. 514). Ming and Qing dynasty texts document specific clay mining locations and make it clear that connoisseurship of clay sources added cultural significance to these zisha clay sources (Cai 2019; Li 2006; Yan 2016). As zisha ware from Yixing represents a well-known regional ceramic tradition in Late Imperial China, its specific mining locations, diverse clay colours, and rich cultural background present a unique opportunity to investigate diachronic changes in raw material use—an area that remains underexplored in the archaeological literature despite the prominence of zisha in Chinese ceramic production. 2. Previous studies and research gaps Most existing zisha clay studies focus on its chemical and mineralogical composition (Cao et al. 2016; Hou et al. 2016; Jiang 2011; Wu 1991; Zhu et al. 2019) and its uniqueness (Chen, Lu, and Zhan 2019; Luo 2016; Luo and Leng 2017; Ouyang et al. 2011; Wang et al. 2016a, b; Zhang 2020). Change in the clay recipe over time, however, is less frequently discussed. For example, the analysis of zisha sherds from the Yangjiaoshan site (a zisha kiln site investigated in 1976; see Section 3.1) does not include a discussion of zisha clay recipe changes (Gu et al. 1984, p. 2); instead, the main focus is on a comparison of the chemical compositions of Yangjiaoshan zisha sherds with modern zisha pieces. Regarding colourant oxides and changes to their proportions, multiple studies have concluded that the main colourant oxides in zisha are Fe 2 O 3 , and that their proportion increased from the Late Ming to the Republican period (Wu et al. 2013; Zhang et al. 2016). These studies did not examine other factors resulting in fired piece colour changes, such as titanium oxide content (Wood 2021) or firing atmosphere (Wakamatsu et al. 1985). If the results of these studies—which indicate an increasing proportion of Fe₂O₃ over the examined period—are correct, then, under consistent firing conditions, the differing clay compositions would likely lead to a greater prevalence of reddish hues in later periods compared to earlier ones. However, the Yangxian shahu tukao 陽羨砂壺圖考, composed in 1937, lists over 27 types of clay sources used by Yixing potters (Gao 2025, p. 123; Zhang and Li (1998 [1937]). The list includes clays described as bai (白; “white”) and lengjin (冷金; “cold golden”) in colour. The literature reflects a diversification in the colour of fired pieces in the early 20 th century and the appearance of lighter colours (presumably clays with a lower iron content). These texts contradict earlier findings that point to an increase in iron content in the later period. This discrepancy between chemical analyses and written sources calls for a re-examination of the colour changes in the zisha clay recipe. The mineralogical properties and microstructures of zisha clay and fired pieces have been the subject of heated discussions in previous research, but changes in particle size have so far remained unexplored. This is where the present study sets in. It is commonly believed that zisha clay consists mainly of quartz, mica, feldspar, hematite, and kaolinite (Gao 2025; Li 2018; Han et al. 1981; Yang et al. 2021; Zhu et al. 2019). The pore structure and microstructure of fired zisha pieces have been the focus of previous studies, and most researchers believe that zisha ’s layered pores are one of the key factors leading to its superior tea-making qualities (Gao 2025; Han et al. 1981; Jiang 2011, pp. 29–52). For instance, Jiang (2011) observed the layered pore structure in zisha cross-sections, with fewer pores on the exterior surface layers and more pores on the interior layers, concluding that this pore structure provides improved mechanical strength and thermal resistance. Previous research has also investigated a variety of factors that may affect potters’ raw material choices, including local geological conditions (De Binus et al 2017, Gliozzo et al 2008), mining locations (Arnold 1991, p. 15; Arnold 2000; Kudelić and Neral 2025), mining and clay deposit sequences (Hein and Kilikoglou 2020), clay-processing techniques (Eramo 2020; Gosselain and Livingstone Smith 2005; Spataro and Hein 2025), and various social and cultural factors (Sillar and Tite 2000). For instance, Eramo (2020) examined common clay-processing techniques (e.g. crushing, pounding, ageing) and their relationship to the properties of the clay sources, such as plasticity and workability. Hein and Kilikoglou (2020) observed that ceramic raw materials are a mixture of sedimentary rocks and that the composition of clay is related to its source rock as well as the weathering sequences of the clay deposit. Although these factors have been covered in some previous research, how sedimentary sequences and clay exploitation sequences relate to clay colours has rarely been discussed. Moreover, the appreciation of clay colour and texture is seldom addressed in studies concerning raw material selection. As an unglazed ware, zisha teapots provide an ideal case for examining the valuation of unglazed clay surfaces and their relationship to the choice of raw materials. The inner complexity of the potters’ raw material choice has been highlighted previous, and researchers have explored holistic methods for understanding potters’ choices (Gualtieri 2020; Santacreu 2017; Van der Leeuw 1993). Santacreu (2017) considered environmental parameters (e.g. proximity and accessibility), use of energy, and the physical properties of the clay paste as well as its qualities and functional constraints to explain clay recipe changes. Adding to this discussion, this study further explores the correlations between geological conditions, exploitation sequences, clay-processing techniques, and the appreciation of the clay colour and texture. This study also reinforces the complexity of these factors and considers them not in isolation but jointly to investigate their effect on the potters’ material choice and the changes to the clay recipe. From the review of previous literature provided above, three primary research gaps require further examination: 1) whether there are chronological changes in the visual colour of the fired zisha pieces from the Shushan site and if so, what the main colourant oxides causing this are, 2) whether paste coarseness (the size and quantity of particles) changed over time and if so how exactly, and 3) what factors may have led the potters in Yixing to alter their clay recipes. To address these research gaps, this study focuses on 187 sherds excavated from the Shushan site ( zisha kiln sites excavated in 2005–2007; see Section 3.1). This larger sample size allows a more comprehensive overview of chronological changes. Colourant oxides are re-examined to address the discrepancies discovered between previous chemical analyses and the written sources. In this analysis of colourant oxides, additional factors, including titanium oxides and firing atmosphere, are taken into consideration. Particle size changes in the zisha clay recipe are also examined here for the first time. This study explores the complex negotiations behind the clay recipe and its changes, addressing geological conditions, clay mining sequences, clay processing, and the appreciation of clay, as associated with changes in the zisha clay recipe from the Late Ming to the Republican period in terms of its colour and particle size. 3. The Shushan site, sampling, and methods of analysis 3.1 The Shushan site The Yangjiaoshan and Shushan sites are the only two known zisha kiln sites. Dating at the Yangjiaoshan site, investigated in 1976, is problematic, as zisha sherds were erroneously dated to the Song dynasty (Yixing Taoci Gongsi 1984). The dating is based on limited archaeological evidence and ambiguous literary references to Zi’ou 紫甌 (“purple-coloured bowl”) in Song dynasty literature. Compared with the Yangjiaoshan site, the Shushan site, excavated in 2005–2007, provides precise archaeological dating based on stratigraphy (Hang 2008, 2009). In addition, the Shushan site yielded over 30,000 ceramic sherds, most of which were identified as zisha ware (Fig. 2). The large quantities of zisha sherds found here which dated from the Late Ming to the Republican period, enable the reconstruction of changes to the zisha clay recipe over time. Therefore, this study is based on data and sherds from the Shushan site. Between 2019 and 2022, author Gao documented, photographed, and sampled zisha sherds from Shushan. The meticulous documentation of the site’s archaeological excavation allowed precise dating of artefacts across six distinct zones (A–F), spanning from the Late Ming dynasty to the Republican period. Zone A predominantly contained zisha ware dating from the Qianlong (1736–1796) to the Republican period, whereas Zone B held ceramics (including zisha teapots and glazed daily-ware sherds) dating to the Late Ming dynasty. Ceramic sherd accumulations in Zones C and D were dated to the Late Qing dynasty, while Zone E encompassed ceramic sherds spanning several centuries, from the Late Ming dynasty to the Republican period. Zone F contained daily-ware sherds, including a reddish-brown bowl and basin that were dated to the Late Qing dynasty. 3.2 Sampling Sampling was conducted in collaboration with officers and archaeologists from the Office of the Yixing Municipal Cultural Relics Management Committee (宜興市文物管理委员会办公室) and Nanjing Museum (南京博物院). Following the sampling strategies described in existing ceramics studies (Orton 2000, pp. 142–147; Richardson and Gajewski 2003), 187 sherds were randomly selected for this study from different excavation layers, based on accessibility and preservation conditions. Sherds with limescale contaminations were avoided because limescale contains high levels of calcium carbonate, resulting in elevated calcium content in these samples. 3.3 Methods To investigate changes in clay colour and coarseness, the sherds’ chemical composition, the particle area within the cross-section of scanned sherds, and the average individual particle size were examined. Low-magnification optical quantitative analysis was used to characterize optical attributes, including colour and clay texture (Ballirano et al. 2014; De Bonis et al. 2017). Following that analysis, the colour and coarseness (particle size and area in cross-sections of the samples) were assessed using optical and qualitative methods, referencing the Munsell Soil Color Chart as well as percentage diagrams for estimating composition by volume (Compton 1985; Munsell Color (Firm) 2018). The resultant data were compared with the findings from scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) to identify the main colourant oxides. SEM-EDS analysis provided semi-quantitative chemical data on sherd composition, while SEM backscatter images facilitated particle and microstructure analysis, identifying for instance mineral crystals and pores (Freestone and Middleton 1987; Palanivel and Meyvel 2010; Tite et al. 1982). ImageJ (bundled with 64-bit Java 8) was used to statistically calculate the SEM backscattered imagery sources and quantify particle area and size (Marcomini and Souza 2011; Sheikhattar et al. 2016; Venkataraman et al. 2007). ImageJ analysis of the backscattered images was first tested for accuracy and then used to compute particle area and particle size in the scanned areas. This analysis was conducted at the University of Oxford Research Laboratory for Archaeology and History of Art (RLAHA), with Hitachi TM 4000Plus and Jeol JSM-5910 SEMs. To investigate the geological and cultural factors that may have influenced Yixing potters’ raw material choices, this study analyses geographical information, data collected during a research trip to local mining sites, and texts written during the Ming and Qing dynasties. Geological data gathered around Yixing is used to determine the nature of the geological formations and the distribution of clay deposits. Observations of present-day Yixing potters and their clay-processing practices—such as grinding, sieving, washing—also provides insight into possible changes in the clay recipe over time. In addition, historical texts from the Ming and Qing periods, including the earliest known monograph on zisha teapots, Yangxian minghuxi (陽羨茗壺系, Renowned Teapots in Yangxian) by Zhou Gaoqi (周高起) (Zhou 2014 [ca. 1640]), were consulted. The aim of examining these written sources was to understand contemporaneous appreciation of zisha clay colour and fired texture, which is connected to shifts in clay selection and processing practices. 4. Chronological changes in clay colour 4.1 Optical analysis of clay colour The zisha samples were sorted into six colour groups based on visual analysis. A Munsell Soil Chart was used to assign sherds to the different colour categories: red, reddish brown, pale brown, dark reddish brown, dark grey, and reddish grey. The results of the optical quantitative analysis data are provided in Appendix 1. The number of clay colour categories increased from four during the Ming dynasty to five during the Early Qing dynasty and to six during the Mid-Qing and Late Qing/Republican period (Fig. 3). Shannon entropy is a statistical quantifier extensively used for the characterization of complex processes and to measure uncertainty regarding the occurrence of a particular event (Karaca and Moonis 2022; Shannon, 1948). In the present study, it was used to measure colour diversity by calculating the unpredictability of the distribution, with higher values indicating more diverse and evenly distributed colours. The Simpson index quantifies diversity by focusing on the probability of two randomly selected items belonging to different categories (Gorelick 2006), with values closer to 1 representing greater diversity. In the ceramic colour analysis of the Shushan site samples, both metrics increase from the Ming dynasty (Shannon=1.75, Simpson=0.67) to the Late Qing/Republican period (Shannon=2.35, Simpson=0.79), scientifically confirming that ceramic colours became more diverse and evenly distributed over time, shifting from a red-dominated palette to a more balanced one that included a greater variety of colours. Several factors, including the composition and proportion of colourant oxides in the clay paste, firing atmosphere, calcium content, and firing temperature, influence the optical colour of the fired pieces (De Bonis et al. 2017; Maniatis et al. 1983). Therefore, further chemical analysis may be able to determine whether the colour changes in the zisha clay recipe were caused by changes in chemical composition. 4.2 SEM-EDS chemical analysis SEM-EDS analysis was conducted at a fixed 200× magnification for 15 seconds per area on each sample. To ensure sample representation by SEM mapping area, three areas were chosen on each sample, and the average was computed to obtain its EDS profile. One sample from each historical period and colour group was randomly selected for SEM-EDS analysis. The results of the SEM-EDS analysis are presented in Appendix 2. The SEM chemical-composition data shows an increasing variation in iron composition from the Ming to the Late Qing period (Fig. 4). The iron composition of the Late Qing samples ranged from 2.1 to 7.59%, while that of the Ming dynasty samples exhibited less diversity, ranging from 5.03 to 6.87%. Iron oxides significantly affect the body colour of ceramic vessels (De Bonis et al 2017; Hradil et al. 2003). In oxidising firing environments (oxygen-rich environments), iron forms ferric oxide, yielding red tones. In reducing conditions (oxygen-poor environments), iron forms ferrous oxide, resulting in darker grey and black tones (Molera 1998). Under identical firing oxidation–reduction conditions, the broad range of iron oxides observed in the pieces belonging to the Mid- and Late Qing dynasty periods indicates a wider spectrum of body colours among sherds from these periods than those from earlier periods. Thus, the findings corroborate the optical analysis results and suggest that iron composition is the principal contributor to colour diversity in zisha clay. Furthermore, the standard deviation in iron percentages across each period reveals a notable increase in iron content from the Early Qing to the Mid- and Late Qing dynasty/Republican period (Fig. 5). The materials from the Ming dynasty exhibit a standard deviation similar to that of the Early Qing period, differing by only 0.05. This elevated standard deviation suggests greater internal diversity in iron content in later periods. These findings support the expansion of colour categories identified through optical analysis in Section 4.1. Previous studies have discussed titanium as one of the chemical components affecting Fe–Ti reaction, as titanium oxides can transform iron-blue glazes into green by oxidising certain Fe2+ ions to Fe3+ when exposed to the high temperatures of a kiln (Wood 2011, 2021). However, according to SEM backscatter imaging, titanium oxides in the zisha sherds manifested as particles suspended in the clay paste rather than dissolved in it (Fig. 6). Thus, the particles could not actively interact with iron oxides to alter the colour of zisha ware. Additionally, colourant oxides, including calcium oxide, could potentially influence optical colour under similar firing conditions (Maniatis et al. 1981). Given that the calcium percentage of the zisha sherds was below 1%, no significant contribution from calcium oxidation to the zisha sherd colour took place. SEM backscatter analysis showed that the iron oxides in the zisha clay paste come from iron oxide minerals (e.g. haematite, goethite) and iron-rich rock fragments. For example, sample 05BG1(4)_48 contained a sub-rounded rock fragment with a high concentration of iron, (Fig. 7) suggesting that in addition to pure minerals, iron-rich rock fragments also contributed significantly to the iron variability in the clay, potentially affecting its coloration. 5. Chronological changes in clay particle size 5.1 Optical analysis of sample coarseness Optical quantitative analysis was conducted on cross-sections of the zisha sherds. The resultant data are presented in Appendix 1. Using percentage diagrams to estimate composition by volume, the coarseness of the cross-sections was categorized into five groups, ranging from very fine (group 1) to coarse (group 5). In contrast with the Early Qing–Late Qing/Republican sherds, a larger percentage of the Ming dynasty zisha sherds belong to the coarse group (Fig. 8). The mean coarseness is calculated as the arithmetic average of the coarseness values of all samples within each time period. A pronounced decreasing trend can be observed from the Ming dynasty (approximately 2.68) to the Mid-Qing period (approximately 1.68), followed by a slight increase during the Late Qing/Republican period (approximately 1.88) (Fig. 9). The superimposed linear regression (y = -0.246x + 2.61) indicates an overall declining trajectory, suggesting a general improvement in surface smoothness across these periods. Furthermore, SEM spectrum mapping using a HITACHI TM4000II at a fixed 200× magnification with a count ranging between 16,000 and 25,000 cps was performed on 18 randomly chosen samples from three SEM coarseness categories (fine, medium, and coarse clay; see Appendices 1 and 3). The obtained mapping images were processed with ImageJ. 5.2 ImageJ calculation of particle size ImageJ is widely used for processing images and converting them into quantifiable data (Collins 2007; Dal Sasso et al. 2014), for instance to determine particle shapes and sizes. Igathianathane and colleagues used ImageJ to calculate the dimensions of particles of various geometric shapes and concluded that particle shape does not affect dimension calculation in ImageJ (Igathianathane et al. 2008). Lormand and colleagues used ImageJ to analyse backscattered electron images of crystals in volcanic rock, providing a case study for the application of ImageJ in rock crystal analysis (Lormand et al. 2018). ImageJ has also been used in petrography; Berrezueta and colleagues used it to calculate pore size in microscopic images (Berrezueta et al. 2019). Based on these previous successful studies, this study uses ImageJ to calculate particle size in backscattered SEM images. Beyond following the previous research, the accuracy of ImageJ in calculating particle size was validated in the context of the present study. To do this, two black squares, each consisting of 16 units (16 + 16 = 32 units), were generated on a white canvas measuring 324 grid units (18 × 18 units; Fig. 10). Mathematically, these black squares encompass 9.87% of the white canvas. The ImageJ threshold function (which converts a grayscale image into a binary, black-and-white image) and area calculation function determined that the black area occupied 10% of the total area, reflecting a 0.13% error margin compared to the mathematical calculations. Additionally, two black circles on an identical white canvas were tested, revealing a 0.02% error margin between the areas determined via ImageJ and mathematical calculations. These results confirm that ImageJ’s area calculation function provides reliable measurements and can thus accurately reflect particle areas in image analysis. A limitation of the use of Image J to calculate particle area is that the particle area calculation in this study only accounts for particles that exceed 10 pixels in fineness on SEM backscatter images, which corresponds to particles larger than 10µm in diameter. This was taken into account when evaluating the data. 5.3 Changes in clay particle size over time 5.3.1 Calculation of quartz particle size The size of quartz particles in zisha clay serves as an ideal indicator for assessing clay paste coarseness. The primary reason for this is that quartz can be readily distinguished from other mineral crystals in SEM spectrum mapping due to its consistently high silicon content. Quartz is prominent component of zisha clay paste in the examined periods (Fig. 11). Therefore, although several other particles, including clay clumps, feldspar crystals, also contribute to the clay paste coarseness, quartz is analysed in this study as a representative particle. In the analysis below, the word “particle” in later discussion refers to quartz particles. On the SEM, three silicon spectrum mapping images were captured from each sample and subjected to thresholding, binary conversion, and particle analysis processes in ImageJ to distinctly outline individual particles (Figs. 12–14) and calculate the area of all outlined particles or individual outlined particles. The total area of quartz particles in examined thin section reflects the size of all quartz particles and also provides insights into the coarseness of the sample. A comparison of the area of all outlined particles in samples from the Late Ming to the Late Qing/Republican period shows a decreasing trend in particle area size, ranging from 53,507–63,548 µm² in the Ming dynasty to 29,802–34,059 µm² in the Late Qing/Republican period (Fig. 15; Appendix 4). These findings indicate that fewer quartz particles or smaller quartz particles appeared in the later samples. Zisha potters in later periods clearly opted for finer clay than their predecessors. To determine whether the decrease in quartz particle area was caused by a reduction in individual particle size or a reduction in particle quantity, the size of the average quartz particle and the standard deviation of particles in each sample were calculated in ImageJ. According to the ImageJ calculations, the average individual particle size during the Ming dynasty was within the range of 129–183 µm², while particles in pieces from the Mid-Qing and Late Qing/Republican periods measured between 77–122 µm² and 79–109 µm², respectively (Appendix 5; Fig. 16). Notably, Early Qing dynasty zisha clay exhibited the largest individual particle size, ranging from 206.39 to 169.37 µm². The Early Qing period was characterized by dynastic changes and warfare, which may have affected ceramic production during this period. An examination of the standard deviation confirmed a reduction in size variation among quartz particles over time. Specifically, the range diminished from 630–1,665 µm² during the Ming dynasty, to 225–511 µm² during the Late Qing period (Appendix 6; Fig. 17). These findings suggest that the zisha paste used in the earlier periods was poorly sorted, with particles displaying substantial size disparities, while the paste used in later periods shows evidence of improved sorting, as the quartz particles had a more consistent appearance and were relatively homogeneous in size. In previous research on ceramic production, homogeneous size of particles in clay pastes has generally been attributed to the use of certain clay-processing techniques (Eramo 2020; Gosselain & Livingstone Smith 2005). For instance, crushing clay rock and sieving clay paste breaks down or removes larger mineral particles, resulting in a more homogeneous particle sizes. Zisha clay-processing techniques and their relationship to the homogeneity of the clay paste are discussed in Section 6.3. 6. Factors that may have influenced potters’ raw material choices The following discussion of zisha teapot recipe changes focuses on the complexity of raw material choices and discuss the correlations between geological formations, clay exploration sequences, and clay-processing techniques, as well as cultural factors that may have led to the clay recipe changes—the growing diversity of colour, decrease in the number of quartz particles, and increasing homogeneity in particle size. 6.1 Geological formation and clay mining sequence Geologically, z isha clay forms through sedimentary processes involving weathering, transportation, and deposition of silicate materials (Guggenheim and Martin 1995, p. 255; Rice 2015, p. 202). Like other sedimentary rocks, it develops when weathered fragments are carried by wind, rivers, or ocean currents to deposition sites, creating layers with varying grain sizes and textures (Allen 1970; Tucker 2001, p. 1). The characteristic reddish colouration of zisha clay stems primarily from the presence of iron oxide minerals—hematite, goethite, and limonite—whose different oxidation states produce colours ranging from black to red (McBride 1974; Rothwell 1989, p. 139). During formation, amorphous ferric hydroxide appears as the main weathering product and may recrystallize into goethite, yielding yellow to orange hues (Schmalz 1968, p. 277). Hematite’s red colour can be modified through interactions with ferric oxy-hydroxide or goethite. In 2005 and 2010, Gao conducted field studies in Yixing, which confirmed the sedimentary deposit of the clay sources in Yixing. At the open-air clay mining site in Hufu town[1] (Fig. 18), southwest of Yixing, a clear cross-section from surface level to deeper clay bedding formation could be observed. Five clay layers with distinguishable colours can be identified in the stratigraphic cross-section of the mine (Fig. 19). Visual examination of the geological bedding revealed distinct belt-like sedimentary structures with diverse colour gradations. From top to bottom, the layers display pale brown, brownish yellow, yellow, brown, and greyish brown hues. This variation in colour within a single clay mine may be caused by differences in iron oxides between layers (e.g. variations in the presence and distribution of haematite, goethite, and limonite). The presence of hematite results in black to red colours (Torrent & Schwertmann 1987). Both amorphous ferric hydroxide and goethite produce a colour range that includes yellow, yellowish brown and orange (Schwertmann 1993). This variation of oxides is one of the key factors contributing to the colour differences observed in the fired clay pieces from the Shushan site. Due to the clay’s layered sedimentary structure, with different iron compositions in each layer, access to clay containing various iron oxides depended heavily on the sequence in which Yixing potters or clay dealers extracted the clay deposit. In earlier periods, they extracted clay from surface layers only, as the deeper strata did not become accessible until later periods. Ming dynasty potters accessed the clay in the uppermost quarry layers while subsequent potters and clay merchants gained access to both surface layers and deeper deposits (Fig. 19). As mining activities reached deeper levels, more sedimentary layers became accessible to later potters and clay dealers. Craftspeople in later periods, who had access to a greater number of geological strata, naturally had a wider range of clay colours available to them. The clay exploration sequences could thus partly explain the increase in clay colour diversity. Therefore, the increasing diversity in clay colour and the expanding range of iron oxides in the zisha clay recipe (as concluded in Section 3) can be attributed to the layered sedimentary geological structure of the deposit, as well as clay mining sequences. 6.2 Clay processing and selection The physical properties of a clay paste correlate with raw material processing techniques and selection criteria (Arnold 1985, p. 20; Eramo 2020; Gosselain 1994, p. 102; Velde & Druc 1999). During field research in 2016, author Gao conducted systematic observations of the clay classification and processing methods used by contemporary potters and clay dealers (Gao 2016). Zisha clay dealers evaluate the colour and texture of the clay rocks and categorize raw clay materials with the same chromatic gradation and texture into a group destined for pottery making. During the clay weathering process, the clay dealers’ classification is predominantly based on two parameters: chromatic gradation and textural properties. The textural assessment, locally termed cuci (粗次, grade of coarseness), is based on the macroscopically observable granularity of the clay rock’s cross-sectional surface. Dealers with substantial experience demonstrate the capacity to differentiate nuanced variations in both parameters (Gao 2016, p. 18). Therefore, the colour of the clay used for pottery making is ultimately determined by the clay dealers’ classification, probably combined with their own experience with one or other of these types of clays and/or what they were told by their own teachers. These experiences and debates were not part of the present research, however, but would need to be the subject of further research on knowledge transmission both among potters and between dealers and potters and vice versa. The 2016 field research also made clear that traditional zisha clay-processing includes grinding, siving and levigation. After grinding, a preliminary sieving process takes place, and a stone mill is used for clay-grinding. The weathered clay powder is placed in water, stirred with bamboo sticks, and washed to remove impurities and rock fragments (Gao 2016, p. 18–20). When the clay sediments, potters pour out the water on the upper level and add more clear water to wash the clay, repeating the previous steps. The clay is aged inside vessels, submerged in water for years or even decades, before it is dehydrated to create a clay paste ready for pottery making. Techniques involving grinding, sieving, and levigation are used to alter dry consolidated clay rocks into pastes ready for use, a process that refines the clay by removing or crushing larger particles and homogenizing the clay paste (Eramo 2020; Quinn 2013, p. 154–155; Roux 2016). Therefore, the decreasing average particle size and increasing homogeneity of the clay paste reflect potters’ deliberate efforts to refine and perfect their clay-processing techniques. 6.3 Appreciation of clay colours and textures Zisha clay colours and textures are frequently mentioned in Ming and Qing dynasty texts such as Jingxi shu (荊溪疏, Annotated Commentary on Jingxi), Yangxian minghuxi (阳羡名壶系, Renowned Teapots in Yangxian), Minghu tulu (茗壶图录, Teapot Catalogue), Yangxian mingtaolu (阳羡名陶录, A Record of Renowned Teapots in Yangxian), and Yixing taoqi gaiyao (宜興陶器概要, An Overview of Yixing Pottery) (Ao 1998 [1874]; Siku Jinhuishu 2000 [unknown];Wu 2014 [1786]; Zhou 2014 [ca.1640]; Zhou and Zhou 1932). To better understand the literati appreciation criteria of zisha teapots, the Yangxian minghuxi , a text known as the first zisha monograph, is examined here in some detail (Chen 2016, 2018; Li 2008). This text was written by Zhou Gaoqi (周高起) in the late 17 th century. Although he did not serve as an official at court, Zhou was a literatus and diligent writer. In addition to the Yangxian minghuxi , he also wrote texts for the local gazetteer Jiangyin Xianzhi (江阴县志, Gazetteer of Jiangyin County) (Feng, Xu, and Zhou 2003 [ca. 1640]) as well as a book on tea plants titled Dongshan jiechaxi (洞山岕茶系, Jie tea in Dongshan) (Zhou 2014 [ca.1639]). Him writing the texts Yangxian minghuxi and Dongshan jiechaxi makes it clear that Zhou was an enthusiastic tea connoisseur who appreciated zisha teapot artisanship. His knowledge of zisha teapots was influenced by Wu Honghua 吳洪化, a zisha teapot collector from a prominent Yixing family. The details of Zhou’s connection with Wu Honghua are analysed in an article by Gao and Hein (2024). The Yangxian minghuxi focuses on documenting renowned potters, clay sources, mining locations, and the artistic styles and designs of teapots. The clay used to make zisha wares, and particularly its colour, is described in detail in the text, as shown in the passage quoted below. Original text: 嫩泥出趙莊山，以和一切色， 上乃黏脂可築蓋陶壺之丞弼也。 石黃泥出趙莊山，即未觸風日之石骨也。陶之乃變朱（硃）砂色。天青泥出蠡墅。陶之變黯肝色。又其夾支，有梨皮泥。陶現梨凍色。淡紅泥， 陶現鬆花色。淺黃泥，陶現豆碧綠色蜜。泥陶現輕赭色。梨皮和白砂，陶現淡墨綠色。山靈腠絡，陶冶變化，尚露種種光怪雲。老泥出團山。陶則白砂星星。按若珠琲。以天青石黃和之成淺深古色。白泥出大潮山，陶缾盎缸用之。 (Zhou 2014 [ca.1640], p. 514) Translation: Nen (嫩, “soft”)-textured clay is extracted from the Zhaozhuang Mountain and can be mixed with zisha of different colours to produce various categories of ceramic products from teapots to food containers. Shihuang (石黃, “rocky yellow”) clay is found in the Zhaozhuang mountains, and is an unweathered clay rock. Fired pots made with shihuang clay are zhusha (硃砂, “cinnabar”) coloured. Tianqing (天青, “bluish green”) clay is sourced from the Lishu 蠡墅 area. Fired pots made with tianqing clay are angan (黯, “dark liver”) coloured. Different types of zisha clay are collected from the tianqing clay layer(s), such as lipi (梨皮, “pear peel”)-coloured clay. Fired pieces made from lipi clay are dongli (凍梨, “chilled pear peel”) coloured, while those made from danhong (淡紅, “light red”) clay are songhua (松花, “pine tree flower”) coloured. Fired pieces made from qianhuang (淺黃, “light yellow”)-coloured clay result in a doubi (豆碧, “bean green”) colour, while unfired pieces are qingzhe (輕赭, “light reddish brown”) coloured. When lipi clay is mixed with baisha (白砂, “white sand”) clay, a greyish-green-coloured clay is produced. These strange phenomena of clays and changes in pots’ colours are attributed to the spirits in the mountains. Lao (老, “aged”)-textured clay is procured from the Tuanshan 團山 mine. The pots have star-like white spots. The surfaces of the pots resemble pearls. When tianqing and shihuang clays are mixed, two kinds of clays of a dark brown colour are produced. bai (白, “white”) clay is excavated from Dachaoshan 大潮山 and is used to produce vessels, bowls, and jars. This section underscores the importance of mining locations in the classification of zisha clay. It reveals that clay types were named according to both their chromatic or textural properties after firing. Sites such as Zhaozhuang Mountain (赵庄山), Lishu (蠡墅), Tuanshan (团山), and Dachaoshan (大潮山) are associated with at least eight distinct clay types— nen (嫩, “soft”) , shihuang (石黃, “rocky yellow”), tianqing (天青, “bluish green”), lipi (梨皮, “pear peel”), danhong (淡紅, “light red”), danhuang (淡紅, “light red”), lao (老, “aged”), and bai (白, “white”)—each bearing distinct colours and textures. For example, shihuang clay produces a vivid cinnabar red when fired, while tianqing yields a dark liver hue; lipi and danhong result in surface colours likened to chilled pear skin and pine pollen, respectively (Zhou 2014 [ca. 1640], p. 514). In the section titled Mingjia (名家, “renowned potters”), Zhou Gaoqi offers a critical appraisal of the teapots produced by Xu Youquan (徐友泉), framing the diversity of clay colours as both a marker of technical expertise and a vehicle for artistic expression. Zhou describes Xu as a distinguished artisan who deliberately selected clay bodies of varied hues to enhance the visual and material qualities of his ceramic works, as evidenced by the quoted text below. Original text: 泥色有海棠红、朱砂紫、定窑白、冷金黄、淡墨、沉香、水碧、榴皮、葵黄、闪色、梨皮诸名。种种变异，妙出心裁。 (Zhou 2014 [ca.1640], p. 513) Translation: The clay colours include crab apple red, cinnabar purple, ding-ware white, pale golden yellow, pale ink, agarwood, greenish water, pomegranate skin, sunflower yellow, shan (a mixture of contrasting colour tones), pear peel, etc. The colour changes form an exceptional and ingenious design. The colours employed by Xu include haitanghong (海棠红, “crab apple red”), zhushazi (朱砂紫, “cinnabar purple”), dingyaobai (定窑白, “Ding-ware white”), lengjinhuang (冷金黄, “pale golden yellow”), danmo (淡墨, “pale ink”), chenxiang (沉香, “agarwood”), shuibi (水碧, “greenish water”), liupi (榴皮, “pomegranate skin”), kuihuang (葵黄, “sunflower yellow”), shanse (闪色, referring to variegated or iridescent colouration), and lipi (梨皮, “pear peel”). This wide chromatic range—encompassing shades of red, purple, yellow, and white—demonstrates an advanced level of material literacy and aesthetic refinement. Zhou’s use of the phrase miaochu xincai (妙出心裁), which connotes ingenuity and originality, further underscores the degree to which these colour variations were not incidental but rather the result of deliberate artistic design. In this context, clay colour selection functions as a key index of craftsmanship, creativity, and cultivated taste (Zhou 2014 [ca. 1640], p. 513). Zhou Gaoqi argues that the distinctive smooth and naturally matte finish of zisha teapots makes them particularly well-suited as refined objects for scholarly appreciation (Zhou 2014 [ca. 1640], p. 515), which could be evident from the text as below. Original text: 壺入用久，滌拭日加自發闇然之光，入手可鑒。 此為書房雅供。 Translation: With prolonged use, the teapot gradually accumulates a natural patina through daily cleaning, emitting a subdued radiance when held. This is an elegant addition to the study. (Zhou 2014 [ca.1640], p. 515) This view underscores the central role of surface texture in the aesthetic evaluation of teapots, as the matte quality—achieved through the use of fine-textured clay—embodies both visual restraint and tactile subtlety. Zhou further notes that with prolonged use and regular cleaning, zisha teapots develop a subdued, lustrous patina that enhances their visual appeal, describing this glow as “a subdued radiance” ( anran zhiguang , 闇然之光) that becomes evident when the teapot is held. Such a transformation is not only a result of material properties but also a sign of cultivated interaction between object and user over time. In this way, the teapot becomes more than a functional vessel—it evolves into a scholar’s object, appropriate for the refined atmosphere of the study ( shufang yagong , 書房雅供). The frequent references to clay colour and surface finish in historical texts thus reflect more than technical concerns; they reveal an enduring cultural valuation of subtle material and colour variation aesthetics in zisha craftsmanship. [1] The Hufu mine was the only mining site examined in this study, as parts of the Huanglong mining area were flooded at the time and closed to public access (Gao 2016; Zhao 2010). 7. Discussion This study set out to explore the complexity of potters’ raw material choices in Late Imperial China, with a particular focus on changes in the clay recipe for zisha teapots excavated from the Shushan site. Through a combination of archaeometric analysis, geological data, observation of contemporary practitioners, and written texts, this discussion synthesizes how geological formations, clay mining sequences, clay-processing practices, and aesthetic preferences intersected to shape technological choices. Rather than attributing material selection to any singular factor, this study frames raw material choice as the outcome of the interplay between environmental, technological, and cultural variables. The geological origin of zisha clay as a sedimentary deposit—composed of stratified layers with varying iron oxide content—provides a foundational explanation for the observable increase in colour diversity over time. The results from SEM-EDS analysis demonstrate a broader range of iron oxide percentages from the Ming to the Late Qing period, while optical data reveal an expansion in the diversity of clay colours used to make zisha teapots. Field observations from the Hufu mine confirmed stratified beds of clay exhibiting chromatic gradations, suggesting that access to deeper deposits in later periods enabled potters to exploit layers with differing iron compositions. This progressive vertical mining strategy aligns with expansion of clay colours during the examined period, supporting the hypothesis that the mining sequence, determined by the local geological structure, influenced the composition of the clay recipe. Clay processing techniques, particularly grinding, sieving, and washing, played a significant role in clay paste changes. The analysis result demonstrates a marked reduction in particle size and variability from the Ming to the Republican periods. This refinement of texture aligns with field observations of present-day Yixing clay-processing methods, which aim to remove impurities and produce more homogenous pastes. The historical shift toward finer, more uniformly processed clays suggests increasing control over the mechanical and visual properties of the final product, reflecting potters’ growing technical proficiency and awareness of consumer preferences. A key contribution of this study lies in highlighting the cultural valuation of clay appreciation as a driver of technological change. Unlike glazed wares, where surface decoration can obscure the clay body, zisha teapots rely entirely on the visual and tactile qualities of their clay. Historical texts from the Ming and Qing periods—particularly Zhou Gaoqi’s Yangxian Minghuxi —emphasized appreciation of subtle colour tones and surface textures and catalogued the vocabulary of named clay types. These written texts provide evidence of the emphasis on clay colour and texture during the Ming and Qing dynasties. Therefore, the increased chromatic and textural variation can be seen, in part, as a result of clay appreciation shaped by literati taste and artisanal reputation. Potters such as Xu Youquan, praised for their innovative use of diverse clays, exemplify how aesthetic connoisseurship shaped production decisions. The increasing homogeneity and colour diversity of clay bodies must therefore be read as both technological and cultural responses to elite consumption practices. Rather than treating geological conditions, clay processing, and cultural aesthetics as isolated determinants, this study proposes that it is their interaction which best explains the observed changes in zisha clay recipes. The expansion of mining activity into deeper strata offered the potters a broader palette of clays, while increasingly sophisticated processing methods enabled them to tailor their materials to meet changing aesthetic demands. Meanwhile, the enduring cultural emphasis on matte, fine-textured surfaces and nuanced hues motivated the continual refinement of clay selection. This integrated analysis aligns with broader discussions in ceramic studies that conceptualize technological choices as embedded within social, economic, and environmental contexts (Arnold 1985 ; Lemonnier 1993 ; Santacreu 2017 ). 8. Conclusion This analysis of Shushan-site zisha sherds dating from the Ming dynasty to the Republican period reveals significant insights into the complex factors that influenced potters’ raw material choices in Late Imperial China. Our multi-method investigation, combining SEM-EDS analysis, optical examination, and analysis of textual materials, demonstrates that the alteration of the zisha clay recipe was shaped by an intricate interplay of geological factors, clay-processing techniques, and clay appreciation. The scientific analysis revealed two key chronological trends: an increasing diversity in clay colours and a shift toward finer clay textures. SEM-EDS analysis showed a growing variation in iron oxide composition (from 5.03–6.87% in Ming samples to 2.1–7.59% in Late Qing samples), while particle analysis demonstrated a reduction in average particle size (from 129–183 µm² in Ming samples to 79–109 µm² in the Late Qing/Republican period samples) and improvements in particle sorting techniques in clay processing. While geological factors, mining sequences, and clay-processing techniques partially explain these trends, our research indicates that the appreciation of clay colour significantly influenced potters’ raw material choices. Historical texts written during this period explicitly connect clay colour diversity and fine texture with artistic excellence, suggesting that potters actively selected and modified clay recipes to meet these aesthetic preferences. This study thus enriches our theoretical framework for understanding the complexity of technological choice, particularly when it concerns Late Imperial Chinese ceramic production. This study suggests that future research on ceramic technologies should consider not only the physical properties and functional requirements of materials but also the cultural context of appreciation and connoisseurship that may influence technical decisions. More broadly, this research illustrates the value of integrating scientific analysis with geological data, field trip observations, written texts to understand the potters’ technological choice. Declarations Acknowledgements We would like to express our sincere gratitude to Hang Tao 杭涛 from the Nanjing Museum and Huang Xingnan 黄兴南 from the Office of the Yixing Municipal Cultural Relics Management Committee along with his team members, for kindly providing the samples from Shushan site and offering invaluable technical assistance during the sample collection and photography process. Special thanks go to Zhou Xiaodong 周晓东, former head of the China Yixing Ceramics Museum, for kindly granting access to the material from the Yangjiaoshan 羊角山 site for comparative study with the Shushan materials. We are especially indebted to Professor Christopher Doherty for his unwavering support during the laboratory work at Oxford. His expertise in geology, guidance with SEM sample preparation, and detailed instruction on laboratory procedures were instrumental to this research. This article could not have been completed without his generous help and mentorship. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6945795","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Research Article","associatedPublications":[],"authors":[{"id":478172021,"identity":"8831c863-d4ca-44fe-9322-323ee1c9d275","order_by":0,"name":"Xuyang Gao","email":"","orcid":"","institution":"Hong Kong Palace Museum","correspondingAuthor":false,"prefix":"","firstName":"Xuyang","middleName":"","lastName":"Gao","suffix":""},{"id":478172022,"identity":"7be20b1a-e3ec-42da-8ed8-8f414e870fb0","order_by":1,"name":"Anke Hein","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA+ElEQVRIie2RsUoDQRCG/+UgaQZs90DOV9iwoAhBX2WPg02TLiCWB4FJFVJLnkJsUh4Ecs1hvaKFIlivCGIqTQLBamPsUuxXTTEf8/8MEIkcJC1AlCC0y82wxeyhUPVPBZBmT+VoyvmzmHWPz9LXN7+cIVNV8uIF26AinxZzJRpL51Orb8YNdFq2tBTcD+dyPV4tzEk9Gp0IRj4BTiH4OmicuN7oS/A3qYf6Y6Mw2p87FeXsYrVQkXK0vULrK+FgHWcLmXNBqukPxJilToc0kOY+XD9ztuPf+eJS1fUdltzNVD269f6qCNdfY35HCSTY/chIJBKJ/M0PJW9M3SpD9Q8AAAAASUVORK5CYII=","orcid":"","institution":"University of Oxford","correspondingAuthor":true,"prefix":"","firstName":"Anke","middleName":"","lastName":"Hein","suffix":""},{"id":478172023,"identity":"4d7efcf7-7dfa-408b-9ae6-8aedfa1e3e67","order_by":2,"name":"Tao Hang","email":"","orcid":"","institution":"Nanjing Museum","correspondingAuthor":false,"prefix":"","firstName":"Tao","middleName":"","lastName":"Hang","suffix":""},{"id":478172024,"identity":"fcd02bc2-940f-4708-9ce2-5f9e1d03797b","order_by":3,"name":"Xingnan Huang","email":"","orcid":"","institution":"Yixing Centre for Archaeology and Cultural Heritage Preservation","correspondingAuthor":false,"prefix":"","firstName":"Xingnan","middleName":"","lastName":"Huang","suffix":""}],"badges":[],"createdAt":"2025-06-21 15:23:16","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6945795/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6945795/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1007/s12520-025-02335-y","type":"published","date":"2025-11-29T15:57:04+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":85835691,"identity":"bee42eaa-0250-42ef-a434-bfde865bc1da","added_by":"auto","created_at":"2025-07-02 08:17:24","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":370173,"visible":true,"origin":"","legend":"\u003cp\u003eTop left: the location of Yixing in China. Bottom left: Yixing zisha teapots with Yang Pengnian (楊彭年) inscriptions (a Ming dynasty potter), held by the Victoria \u0026amp; Albert Museum. Right: the location of the Zhaozhuangshan 趙莊山mine, the Huanglongshan 黃龍山mine, and the Shushan site 蜀山in Yixing.\u003c/p\u003e","description":"","filename":"1.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/57d324b1fdc2e6332fc52889.png"},{"id":85835658,"identity":"04c0e944-2b15-4803-81fe-8b2c24c808c1","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":286859,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cem\u003eZisha\u003c/em\u003esherds from the Shushan site. All photographs taken by Xuyang Gao at Yixing Cultural Relic Committee (YCRC). Fig. 2 (a) Ming dynasty teapot spout from the Shushan site. Fig. 2 (b) Early Qing dynasty teapot lid. Fig. 2 (c) Mid-Qing dynasty teapot body with handle. Fig. 2 (d) Late Qing dynasty teapot lid.\u003c/p\u003e","description":"","filename":"2.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/e13354b4d148a71b2203d93b.png"},{"id":85835665,"identity":"39ff8367-0d6b-4bbd-a8a8-959fad0b314d","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":117633,"visible":true,"origin":"","legend":"\u003cp\u003eThe colours of the analysed fired pieces from Shushan. Colours marked 1–6 represent red, reddish brown, pale brown, dark reddish brown, dark grey, and reddish grey. Shannon entropy and Simpson index calculations quantify colour diversity.\u003c/p\u003e","description":"","filename":"3.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/de17b7d5f6b2d4baae2f0ff7.png"},{"id":85837259,"identity":"b33eb247-42ee-4f75-a936-7c71b857ceb5","added_by":"auto","created_at":"2025-07-02 08:25:22","extension":"png","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":186585,"visible":true,"origin":"","legend":"\u003cp\u003eIron percentage of samples from the Ming to Late Qing dynasties.\u003c/p\u003e","description":"","filename":"4.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/9ae4ec17623cd3299d73e87e.png"},{"id":85835676,"identity":"724b2ee0-ebd2-46d6-8133-7b0a52c255b8","added_by":"auto","created_at":"2025-07-02 08:17:23","extension":"png","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":344172,"visible":true,"origin":"","legend":"\u003cp\u003eIron composition standard deviation in the examined samples from Shushan.\u003c/p\u003e","description":"","filename":"5.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/eff1199964b39960c5d35e07.png"},{"id":85835660,"identity":"641ff853-2111-4704-9ce2-fe6fea18f571","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":5713,"visible":true,"origin":"","legend":"\u003cp\u003eTitanium particle in an SEM backscatter image of sample 05BG1(4)_80.\u003c/p\u003e","description":"","filename":"6.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/19d4637aa9f11615a54f3c31.png"},{"id":85837264,"identity":"3573ed61-fefc-499e-aada-d0178a72d444","added_by":"auto","created_at":"2025-07-02 08:25:23","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":228870,"visible":true,"origin":"","legend":"\u003cp\u003eIron-rich rock fragments in SEM-EDS iron distribution mapping, from sample 05BG1(4)_48. The lighter grey colour suggests concentrated iron, demonstrating that the rock fragment has a high iron content.\u003c/p\u003e","description":"","filename":"7.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/c4b832cb2046755b5e0f97f0.png"},{"id":85835661,"identity":"8e120928-d130-4c8e-9e9c-d569f4b0022e","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":90635,"visible":true,"origin":"","legend":"\u003cp\u003eCoarseness of fired pieces from Shushan. Coarseness was defined by optical analysis and categories are labelled 1 to 5, representing fine, fine-to-medium, medium, medium-to-coarse, and coarse.\u003c/p\u003e","description":"","filename":"8.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/dc23c6adf3b9198bdaddebcf.png"},{"id":85835693,"identity":"d228441b-9195-462a-9035-55b81db73643","added_by":"auto","created_at":"2025-07-02 08:17:24","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":75644,"visible":true,"origin":"","legend":"\u003cp\u003eMean coarseness values of fired pieces from the Shushan site dating from the Late Ming to the Late Qing/Republican period.\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/8e8d3e5510fc86a7fb04c474.png"},{"id":85835681,"identity":"2970ee4a-e476-425e-9619-b03941acfbb3","added_by":"auto","created_at":"2025-07-02 08:17:23","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":30745,"visible":true,"origin":"","legend":"\u003cp\u003eTwo 16-unit black squares on a 324-unit background canvas.\u003c/p\u003e","description":"","filename":"10.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/420f9c34fdfe85965dbfb333.png"},{"id":85837287,"identity":"17e34120-9233-4b27-beb0-c3d3ac7a43c7","added_by":"auto","created_at":"2025-07-02 08:25:26","extension":"png","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":199080,"visible":true,"origin":"","legend":"\u003cp\u003eQuartz particles in a fired\u003cem\u003e zisha\u003c/em\u003e sherd. Sample 05BG1(4)_48.\u003c/p\u003e","description":"","filename":"11.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/7b4bf3218d5e41d1f912fd07.png"},{"id":85835670,"identity":"4e760add-afe3-4e19-9fae-aeae4e67a155","added_by":"auto","created_at":"2025-07-02 08:17:23","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":257851,"visible":true,"origin":"","legend":"\u003cp\u003eSEM silicon map of sample 06ET1K2(14)_24. The bright area shows the silicon distribution.\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/fb3cc8b74604fa2d7bb1890b.png"},{"id":85837266,"identity":"186d90bf-a9b2-4be3-994a-522d84c7c00e","added_by":"auto","created_at":"2025-07-02 08:25:23","extension":"png","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":131032,"visible":true,"origin":"","legend":"\u003cp\u003eSEM silicon map of sample 06ET1K2(14)_24 after application of the threshold function. The black area represents the silicon-rich area.\u003c/p\u003e","description":"","filename":"13.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/6df717cb733a52a77423a671.png"},{"id":85835739,"identity":"140a84a8-2c48-4ee3-83ac-0723acac428b","added_by":"auto","created_at":"2025-07-02 08:17:26","extension":"png","order_by":14,"title":"Figure 14","display":"","copyAsset":false,"role":"figure","size":304645,"visible":true,"origin":"","legend":"\u003cp\u003eSEM silicon map of sample 06ET1K2(14)_24 after application of the threshold function, binary (converts to black and white images based on the current threshold settings), and particle analysis, showing the outlines of particles and the number of counted particles.\u003c/p\u003e","description":"","filename":"14.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/e299806c9484cc6b143f07fb.png"},{"id":85835683,"identity":"c3d39da5-30dd-4f9e-bdf4-7a13215efa78","added_by":"auto","created_at":"2025-07-02 08:17:23","extension":"png","order_by":15,"title":"Figure 15","display":"","copyAsset":false,"role":"figure","size":132723,"visible":true,"origin":"","legend":"\u003cp\u003eQuartz particle area of ceramic pieces dating from the Ming to the Late Qing/Republican period.\u003c/p\u003e","description":"","filename":"15.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/d40fc91436107739a4fa4fcc.png"},{"id":85835720,"identity":"fa048e01-cbcd-4d90-b6ad-8bead932af09","added_by":"auto","created_at":"2025-07-02 08:17:25","extension":"png","order_by":16,"title":"Figure 16","display":"","copyAsset":false,"role":"figure","size":91483,"visible":true,"origin":"","legend":"\u003cp\u003eAverage quartz particle size in samples from the Ming to the Late Qing/Republican periods.\u003c/p\u003e","description":"","filename":"16.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/c9dfdee528f00a3778dbf3f0.png"},{"id":85835687,"identity":"df6946c5-7f27-4fab-bace-d6c8b7b5fa5c","added_by":"auto","created_at":"2025-07-02 08:17:23","extension":"png","order_by":17,"title":"Figure 17","display":"","copyAsset":false,"role":"figure","size":137786,"visible":true,"origin":"","legend":"\u003cp\u003eStandard deviation of quartz particle size in samples from the Ming to the Late Qing periods.\u003c/p\u003e","description":"","filename":"17.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/de74db5251c8bcc3b73795b2.png"},{"id":85835669,"identity":"9fc9d206-5627-46c4-bd91-e6a84e287b63","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":18,"title":"Figure 18","display":"","copyAsset":false,"role":"figure","size":269891,"visible":true,"origin":"","legend":"\u003cp\u003eLocation of the Hufu mine in the southwestern mountains of Yixing, situated west of Dingshu village and the Huanglong mine.\u003c/p\u003e","description":"","filename":"18.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/1779ab6e0602f88876dd58e1.png"},{"id":85835664,"identity":"28b50a9a-2efa-4183-bbd1-58a13c55080b","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"png","order_by":19,"title":"Figure 19","display":"","copyAsset":false,"role":"figure","size":259735,"visible":true,"origin":"","legend":"\u003cp\u003eThe working face of a mining area at Hufu mine, showing all clay layers\u003c/p\u003e","description":"","filename":"19.png","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/a9f1286ee70d50ecbc0a8084.png"},{"id":97178376,"identity":"f68f9adf-7f22-4df9-8e0f-c2c13625d373","added_by":"auto","created_at":"2025-12-01 16:09:21","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":4190610,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/b2959100-37c1-4915-b327-21e3f7213440.pdf"},{"id":85835657,"identity":"59ceccfd-a25e-408a-b844-d1f5a5aa0411","added_by":"auto","created_at":"2025-07-02 08:17:22","extension":"docx","order_by":0,"title":"","display":"","copyAsset":false,"role":"supplement","size":2741616,"visible":true,"origin":"","legend":"","description":"","filename":"CreatingWusetuappendices21062025.docx","url":"https://assets-eu.researchsquare.com/files/rs-6945795/v1/b73e411fe4fb386e474ef3fd.docx"}],"financialInterests":"Competing interest reported. This research was supported by the Meyerstein and School Research Awards for Archaeological Research (2019–2020) and the St Cross College Academic Travel and Research Fund (2020).","formattedTitle":"Creating Wusetu (“Five-Coloured Clay”): Chronological Changes in Zisha Ware Clay Recipes and the Complexity of Potters’ Technological Choices","fulltext":[{"header":"1. Introduction","content":"\u003cp\u003eThis study explores the complexity of potters’ technological choices, particularly raw material choice in Late Imperial China, focusing on \u003cem\u003ezisha\u003c/em\u003e teapot clay recipe changes. \u003cem\u003eZisha\u003c/em\u003e teapots, produced in Yixing, China, are unglazed tea-making vessels that started to gain popularity during the Late Ming period (Cai 2019; Liu 2013; Fig. 1) and became internationally renowned in the 17th and 18th centuries, as they were exported across Asian and European markets (Li 2009; Teng 2017; Valfre 2000). “Potters’ technological choices” refers to a series of interrelated decisions, including the selection of raw materials (such as clay sources and recipes), tools and equipment for shaping pottery, energy sources (e.g., hydro-powered clay mills and fuels for firing), and processing and shaping techniques(Hunt 2016 pp. 104–106; Lemonnier 1993, pp. 6–12; Schiffer and Skibo 1997; Sillar and Tite 2000). These decisions also intersect with broader cultural, economic, and social dynamics (Kudelić and Neral 2025).\u003c/p\u003e\n\u003cp\u003ePotters’ raw material selection is shaped by various factors, including the properties and availability of raw materials (Cumberpatch et al. 2001; Martineau et al. 2007; Sillar and Tite 2000), cultural values and community preferences (Arnold et al. 2007; Mahias 1993), mechanical performance (e.g., resistance to thermal shock and overall durability) (Bronitsky and Hamer 1986; Kilikoglou et al. 1998; Tite et al. 2001; Vekinis and Kilikoglou 1998), and regional crafting traditions (Dietler and Herbich 1989). The study of raw material choice in Chinese ceramic production has largely focused on the\u0026nbsp;Neolithic period and especially on Majiayao and Yangshao ceramics (Dammer, Hein, and Spataro 2024; Li et al. 2025; Spataro and Hein 2025; Womack et al. 2019). For instance, Dammer, Hein, and Spataro (2024) demonstrated through geological surveying and experimental firing combined with petrographic and geochemical analyses on excavated sherds and experimental material that Majiayao potters intentionally selected clays with certain calcium contents and that they added granitic fragments or river sand as temper, demonstrating a nuanced understanding of raw material behaviour and environmental constraints.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eLess attention has been given to raw material choice in Late Imperial China ceramic production. Most studies of Late Imperial ceramics have focused on analysing the chemical and mineralogical properties of clay recipes, including several studies on Jingdezhen (He, Zhang, and Zhang 2016; Wood 2021; Yap and Hua 1992) and Dehua wares (Li et al. 2011; Wu et al. 2014), none of them considering the underlying decision-making strategies behind material use and processing techniques. For instance, Li (2011) examined porcelain samples from five Dehua kiln sites, and published detailed data on Song, Yuan, and Ming dynasty Dehua wares, concluding that their Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e and K\u003csub\u003e2\u003c/sub\u003eO compositions varied. However, the author did not discuss potential reasons for the clay recipe changes. Thus, although compositional analyses are abundant, the decision-making processes of Late Imperial potters—why they chose certain clay sources over others—remain underexplored.\u003c/p\u003e\n\u003cp\u003eWe argue that \u003cem\u003ezisha\u003c/em\u003e teapots offer a rare and valuable lens through which to examine the complexity of these clay choices in Late Imperial China. First, \u003cem\u003ezisha\u003c/em\u003e wares were and continue to be produced in Yixing, China (Jiangsusheng 1992; Jiangsusheng dituji 2004) (Fig. 1), one of the main regional ceramic production centres in China during the Ming and Qing dynasties, comparable to Dehua and Shiwan (Keer and Wood 2004; Liang 1991; Xu 2000). These wares, like the ones produced in Jingdezhen and Dehua, were exported to Asian and European countries like Japan, Thailand, Spain, Holland, and England during the 17\u003csup\u003eth\u003c/sup\u003e and 18\u003csup\u003eth\u003c/sup\u003e century (Valfre 2000). Second, in contrast to glazed wares, the clay body is of particular importance in \u003cem\u003ezisha\u003c/em\u003e wares, as users and consumers can directly observe the colour and texture of the fired clay which is neither fully vitrified nor covered by a glaze that would obscure these properties. Their final appearance and texture are determined largely by the composition and treatment of the clay and the firing conditions (temperature and atmosphere). This unglazed feature makes \u003cem\u003ezisha\u003c/em\u003e an ideal case study for investigations into how potters negotiated geological settings and procurement, clay processing, and technological and aesthetic preferences. Third, clay properties and origins are particularly important in\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e making and consumption. \u003cem\u003eZisha\u003c/em\u003e teapots are crafted from \u003cem\u003ezisha\u0026nbsp;\u003c/em\u003eclay, which is procured from different mining locations in Yixing. Certain mining locations, including the Huanglongshan\u0026nbsp;黄龙山\u0026nbsp;and Zhaozhuangshan\u0026nbsp;赵庄山\u0026nbsp;mines, are known for their “authentic” \u003cem\u003ezisha\u003c/em\u003e clay (for a detailed discussion of \u003cem\u003ezisha\u003c/em\u003e clay authenticity, see Hou et al. 2016; Xu 2009; Zhao and Lu 2013). The three main clay types are \u003cem\u003eZini\u003c/em\u003e (紫泥, “clay with purplish colour”), \u003cem\u003eHongni\u003c/em\u003e (红泥, “clay with reddish colour”), and \u003cem\u003eLüni\u003c/em\u003e (绿泥, “clay with greenish colour”) (Han et al 1981; He 1988; Zhu 2009, p. 38). Local potters call this clay \u003cem\u003eWusetu\u0026nbsp;\u003c/em\u003e(五色土, “five-coloured clay”), due to its diverse colours (Wu 2014 [1786], p. 871; Zhou 2014 [ca. 1640], p. 514). Ming and Qing dynasty texts document specific clay mining locations and make it clear that connoisseurship of clay sources added cultural significance to these \u003cem\u003ezisha\u003c/em\u003e clay sources (Cai 2019; Li 2006; Yan 2016). As \u003cem\u003ezisha\u003c/em\u003e ware from Yixing represents a well-known regional ceramic tradition in Late Imperial China, its specific mining locations, diverse clay colours, and rich cultural background present a unique opportunity to investigate diachronic changes in raw material use—an area that remains underexplored in the archaeological literature despite the prominence of \u003cem\u003ezisha\u003c/em\u003e in Chinese ceramic production.\u003c/p\u003e"},{"header":"2. Previous studies and research gaps","content":"\u003cp\u003eMost existing \u003cem\u003ezisha\u003c/em\u003e clay studies focus on its chemical and mineralogical composition (Cao et al. 2016; Hou et al. 2016; Jiang 2011; Wu 1991; Zhu et al. 2019) and its uniqueness (Chen, Lu, and Zhan 2019; Luo 2016; Luo and Leng 2017; Ouyang et al. 2011; Wang et al. 2016a, b; Zhang 2020). Change in the clay recipe over time, however, is less frequently discussed. For example, the analysis of \u003cem\u003ezisha\u003c/em\u003e sherds from the Yangjiaoshan site (a \u003cem\u003ezisha\u003c/em\u003e kiln site investigated in 1976; see Section 3.1) does not include a discussion of \u003cem\u003ezisha\u003c/em\u003e clay recipe changes (Gu et al. 1984, p. 2); instead, the main focus is on a comparison of the chemical compositions of Yangjiaoshan \u003cem\u003ezisha\u003c/em\u003e sherds with modern \u003cem\u003ezisha\u003c/em\u003e pieces.\u003c/p\u003e\n\u003cp\u003eRegarding colourant oxides and changes to their proportions, multiple studies have concluded that the main colourant oxides in \u003cem\u003ezisha\u003c/em\u003e are Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e, and that their proportion increased from the Late Ming to the Republican period (Wu et al. 2013; Zhang et al. 2016). These studies did not examine other factors resulting in fired piece colour changes, such as titanium oxide content (Wood 2021) or firing atmosphere (Wakamatsu et al. 1985). If the results of these studies—which indicate an increasing proportion of Fe₂O₃ over the examined period—are correct, then, under consistent firing conditions, the differing clay compositions would likely lead to a greater prevalence of reddish hues in later periods compared to earlier ones. However, the \u003cem\u003eYangxian shahu tukao\u003c/em\u003e 陽羨砂壺圖考, composed in 1937, lists over 27 types of clay sources used by Yixing potters (Gao 2025, p. 123; Zhang and Li (1998 [1937]). The list includes clays described as \u003cem\u003ebai\u0026nbsp;\u003c/em\u003e(白; “white”) and \u003cem\u003elengjin\u003c/em\u003e (冷金; “cold golden”) in colour. The literature reflects a diversification in the colour of fired pieces in the early 20\u003csup\u003eth\u003c/sup\u003e century and the appearance of lighter colours (presumably clays with a lower iron content). These texts contradict earlier findings that point to an increase in iron content in the later period. This discrepancy between chemical analyses and written sources calls for a re-examination of the colour changes in the\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e clay recipe.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe mineralogical properties and microstructures of \u003cem\u003ezisha\u003c/em\u003e clay and fired pieces have been the subject of heated discussions in previous research, but changes in particle size have so far remained unexplored. This is where the present study sets in. It is commonly believed that \u003cem\u003ezisha\u003c/em\u003e clay consists mainly of quartz, mica, feldspar, hematite, and kaolinite (Gao 2025; Li 2018; Han et al. 1981; Yang et al. 2021; Zhu et al. 2019). The pore structure and microstructure of fired \u003cem\u003ezisha\u003c/em\u003e pieces have been the focus of previous studies, and most researchers believe that \u003cem\u003ezisha\u003c/em\u003e’s layered pores are one of the key factors leading to its superior tea-making qualities (Gao 2025; Han et al. 1981; Jiang 2011, pp. 29–52). For instance, Jiang (2011) observed the layered pore structure in\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e cross-sections, with fewer pores on the exterior surface layers and more pores on the interior layers, concluding that this pore structure provides improved mechanical strength and thermal resistance.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003ePrevious research has also investigated a variety of factors that may affect potters’ raw material choices, including local geological conditions (De Binus et al 2017, Gliozzo et al 2008), mining locations (Arnold 1991, p. 15; Arnold 2000;\u0026nbsp;Kudelić\u0026nbsp;and Neral 2025), mining and clay deposit sequences (Hein and Kilikoglou 2020), clay-processing techniques (Eramo 2020; Gosselain and Livingstone Smith 2005; Spataro and Hein 2025), and various social and cultural factors (Sillar and Tite 2000). For instance, Eramo (2020) examined common clay-processing techniques (e.g. crushing, pounding, ageing) and their relationship to the properties of the clay sources, such as plasticity and workability. Hein and Kilikoglou (2020) observed that ceramic raw materials are a mixture of sedimentary rocks and that the composition of clay is related to its source rock as well as the weathering sequences of the clay deposit. Although these factors have been covered in some previous research, how sedimentary sequences and clay exploitation sequences relate to clay colours has rarely been discussed. Moreover, the appreciation of clay colour and texture is seldom addressed in studies concerning raw material selection. As an unglazed ware, \u003cem\u003ezisha\u003c/em\u003e teapots provide an ideal case for examining the valuation of unglazed clay surfaces and their relationship to the choice of raw materials.\u003c/p\u003e\n\u003cp\u003eThe inner complexity of the potters’ raw material choice has been highlighted previous, and researchers have explored holistic methods for understanding potters’ choices (Gualtieri 2020; Santacreu 2017; Van der Leeuw 1993). Santacreu (2017) considered environmental parameters (e.g. proximity and accessibility), use of energy, and the physical properties of the clay paste as well as its qualities and functional constraints to explain clay recipe changes. Adding to this discussion, this study further explores the correlations between geological conditions, exploitation sequences, clay-processing techniques, and the appreciation of the clay colour and texture. This study also reinforces the complexity of these factors and considers them not in isolation but jointly to investigate their effect on the potters’ material choice and the changes to the clay recipe.\u003c/p\u003e\n\u003cp\u003eFrom the review of previous literature provided above, three primary research gaps require further examination: 1) whether there are chronological changes in the visual colour of the fired \u003cem\u003ezisha\u003c/em\u003e pieces from the Shushan site and if so, what the main colourant oxides causing this are, 2) whether paste coarseness (the size and quantity of particles) changed over time and if so how exactly, and 3) what factors may have led the potters in Yixing to alter their clay recipes. To address these research gaps, this study focuses on 187 sherds excavated from the Shushan site (\u003cem\u003ezisha\u003c/em\u003e kiln sites excavated in 2005–2007; see Section 3.1). This larger sample size allows a more comprehensive overview of chronological changes. Colourant oxides are re-examined to address the discrepancies discovered between previous chemical analyses and the written sources. In this analysis of colourant oxides, additional factors, including titanium oxides and firing atmosphere, are taken into consideration. Particle size changes in the \u003cem\u003ezisha\u003c/em\u003e clay recipe are also examined here for the first time. This study explores the complex negotiations behind the clay recipe and its changes, addressing geological conditions, clay mining sequences, clay processing, and the appreciation of clay, as associated with changes in the \u003cem\u003ezisha\u003c/em\u003e clay recipe from the Late Ming to the Republican period in terms of its colour and particle size.\u003c/p\u003e"},{"header":"3. The Shushan site, sampling, and methods of analysis","content":"\u003ch3\u003e3.1 The Shushan site\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThe Yangjiaoshan and Shushan sites are the only two known \u003cem\u003ezisha\u003c/em\u003e kiln sites. Dating at the Yangjiaoshan site, investigated in 1976, is problematic, as \u003cem\u003ezisha\u003c/em\u003e sherds were erroneously dated to the Song dynasty (Yixing Taoci Gongsi 1984). The dating is based on limited archaeological evidence and ambiguous literary references to \u003cem\u003eZi\u0026rsquo;ou\u003c/em\u003e 紫甌 (\u0026ldquo;purple-coloured bowl\u0026rdquo;) in Song dynasty literature. Compared with the Yangjiaoshan site, the Shushan site, excavated in 2005\u0026ndash;2007, provides precise archaeological dating based on stratigraphy (Hang 2008, 2009). In addition, the Shushan site yielded over 30,000 ceramic sherds, most of which were identified as \u003cem\u003ezisha\u003c/em\u003e ware (Fig. 2). The large quantities of \u003cem\u003ezisha\u0026nbsp;\u003c/em\u003esherds found here which dated from the Late Ming to the Republican period, enable the reconstruction of changes to the \u003cem\u003ezisha\u0026nbsp;\u003c/em\u003eclay recipe over time. Therefore, this study is based on data and sherds from the Shushan site.\u003c/p\u003e\n\u003cp\u003eBetween 2019 and 2022, author Gao documented, photographed, and sampled \u003cem\u003ezisha\u003c/em\u003e sherds from Shushan. The meticulous documentation of the site\u0026rsquo;s archaeological excavation allowed precise dating of artefacts across six distinct zones (A\u0026ndash;F), spanning from the Late Ming dynasty to the Republican period. Zone A predominantly contained \u003cem\u003ezisha\u003c/em\u003e ware dating from the Qianlong (1736\u0026ndash;1796) to the Republican period, whereas Zone B held ceramics (including \u003cem\u003ezisha\u003c/em\u003e teapots and glazed daily-ware sherds) dating to the Late Ming dynasty. Ceramic sherd accumulations in Zones C and D were dated to the Late Qing dynasty, while Zone E encompassed ceramic sherds spanning several centuries, from the Late Ming dynasty to the Republican period. Zone F contained daily-ware sherds, including a reddish-brown bowl and basin that were dated to the Late Qing dynasty.\u003c/p\u003e\n\u003ch3\u003e3.2 Sampling\u003c/h3\u003e\n\u003cp\u003eSampling was conducted in collaboration with officers and archaeologists from the Office of the Yixing Municipal Cultural Relics Management Committee (宜興市文物管理委员会办公室) and Nanjing Museum (南京博物院). Following the sampling strategies described in existing ceramics studies (Orton 2000, pp. 142\u0026ndash;147; Richardson and Gajewski 2003), 187 sherds were randomly selected for this study from different excavation layers, based on accessibility and preservation conditions. Sherds with limescale contaminations were avoided because limescale contains high levels of calcium carbonate, resulting in elevated calcium content in these samples.\u003c/p\u003e\n\u003ch3\u003e3.3 Methods\u003c/h3\u003e\n\u003cp\u003eTo investigate changes in clay colour and coarseness, the sherds\u0026rsquo; chemical composition, the particle area within the cross-section of scanned sherds, and the average individual particle size were examined. Low-magnification optical quantitative analysis was used to characterize optical attributes, including colour and clay texture (Ballirano et al. 2014; De Bonis et al. 2017). Following that analysis, the colour and coarseness (particle size and area in cross-sections of the samples) were assessed using optical and qualitative methods, referencing the \u003cem\u003eMunsell Soil Color Chart\u003c/em\u003e as well as percentage diagrams for estimating composition by volume (Compton 1985; Munsell Color (Firm) 2018). The resultant data were compared with the findings from scanning electron microscopy combined with energy-dispersive X-ray spectroscopy (SEM-EDS) to identify the main colourant oxides. SEM-EDS analysis provided semi-quantitative chemical data on sherd composition, while SEM backscatter images facilitated particle and microstructure analysis, identifying for instance mineral crystals and pores (Freestone and Middleton 1987; Palanivel and Meyvel 2010; Tite et al. 1982). ImageJ (bundled with 64-bit Java 8) was used to statistically calculate the SEM backscattered imagery sources and quantify particle area and size (Marcomini and Souza 2011; Sheikhattar et al. 2016; Venkataraman et al. 2007). ImageJ analysis of the backscattered images was first tested for accuracy and then used to compute particle area and particle size in the scanned areas. This analysis was conducted at the University of Oxford Research Laboratory for Archaeology and History of Art (RLAHA), with Hitachi TM 4000Plus and Jeol JSM-5910 SEMs.\u003c/p\u003e\n\u003cp\u003eTo investigate the geological and cultural factors that may have influenced Yixing potters\u0026rsquo; raw material choices, this study analyses geographical information, data collected during a research trip to local mining sites, and texts written during the Ming and Qing dynasties. Geological data gathered around Yixing is used to determine the nature of the geological formations and the distribution of clay deposits. Observations of present-day Yixing potters and their clay-processing practices\u0026mdash;such as grinding, sieving, washing\u0026mdash;also provides insight into possible changes in the clay recipe over time. In addition, historical texts from the Ming and Qing periods, including the earliest known monograph on \u003cem\u003ezisha\u003c/em\u003e teapots, \u003cem\u003eYangxian minghuxi\u003c/em\u003e (陽羨茗壺系, Renowned Teapots in Yangxian) by Zhou Gaoqi (周高起) (Zhou 2014 [ca. 1640]), were consulted. The aim of examining these written sources was to understand contemporaneous appreciation of\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e clay colour and fired texture, which is connected to shifts in clay selection and processing practices.\u003c/p\u003e"},{"header":"4. Chronological changes in clay colour","content":"\u003ch3\u003e4.1 Optical analysis of clay colour\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThe \u003cem\u003ezisha\u003c/em\u003e samples were sorted into six colour groups based on visual analysis. A Munsell Soil Chart was used to assign sherds to the different colour categories: red, reddish brown, pale brown, dark reddish brown, dark grey, and reddish grey. The results of the optical quantitative analysis data are provided in Appendix 1. The number of clay colour categories increased from four during the Ming dynasty to five during the Early Qing dynasty and to six during the Mid-Qing and Late Qing/Republican period (Fig. 3). Shannon entropy is a statistical quantifier extensively used for the characterization of complex processes and to measure uncertainty regarding the occurrence of a particular event (Karaca and Moonis 2022; Shannon, 1948). In the present study, it was used to measure colour diversity by calculating the unpredictability of the distribution, with higher values indicating more diverse and evenly distributed colours. The Simpson index quantifies diversity by focusing on the probability of two randomly selected items belonging to different categories (Gorelick 2006), with values closer to 1 representing greater diversity. In the ceramic colour analysis of the Shushan site samples, both metrics increase from the Ming dynasty (Shannon=1.75, Simpson=0.67) to the Late Qing/Republican period (Shannon=2.35, Simpson=0.79), scientifically confirming that ceramic colours became more diverse and evenly distributed over time, shifting from a red-dominated palette to a more balanced one that included a greater variety of colours.\u003c/p\u003e\n\u003cp\u003eSeveral factors, including the composition and proportion of colourant oxides in the clay paste, firing atmosphere, calcium content, and firing temperature, influence the optical colour of the fired\u0026nbsp;pieces (De Bonis et al. 2017; Maniatis et al. 1983). Therefore, further chemical analysis may be able to determine whether the colour changes in the\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e clay recipe were caused by changes in chemical composition.\u003c/p\u003e\n\u003ch3\u003e4.2 SEM-EDS chemical analysis\u003c/h3\u003e\n\u003cp\u003eSEM-EDS analysis was conducted at a fixed 200\u0026times; magnification for 15 seconds per area on each sample. To ensure sample representation by SEM mapping area, three areas were chosen on each sample, and the average was computed to obtain its EDS profile. One sample from each historical period and colour group was randomly selected for SEM-EDS analysis. The results of the SEM-EDS analysis are presented in Appendix 2.\u003c/p\u003e\n\u003cp\u003eThe SEM chemical-composition data shows an increasing variation in iron composition from the Ming to the Late Qing period (Fig. 4). The iron composition of the Late Qing samples ranged from 2.1 to 7.59%, while that of the Ming dynasty samples exhibited less diversity, ranging from 5.03 to 6.87%. Iron oxides significantly affect the body colour of ceramic vessels (De Bonis et al 2017; Hradil et al. 2003). In oxidising firing environments (oxygen-rich environments), iron forms ferric oxide, yielding red tones. In reducing conditions (oxygen-poor environments), iron forms ferrous oxide, resulting in darker grey and black tones (Molera 1998). Under identical firing oxidation\u0026ndash;reduction conditions, the broad range of iron oxides observed in the pieces belonging to the Mid- and Late Qing dynasty periods indicates a wider spectrum of body colours among sherds from these periods than those from earlier periods. Thus, the findings corroborate the optical analysis results and suggest that iron composition is the principal contributor to colour diversity in \u003cem\u003ezisha\u003c/em\u003e clay.\u003c/p\u003e\n\u003cp\u003eFurthermore, the standard deviation in iron percentages across each period reveals a notable increase in iron content from the Early Qing to the Mid- and Late Qing dynasty/Republican period (Fig. 5). The materials from the Ming dynasty exhibit a standard deviation similar to that of the Early Qing period, differing by only 0.05. This elevated standard deviation suggests greater internal diversity in iron content in later periods. These findings support the expansion of colour categories identified through optical analysis in Section 4.1.\u003c/p\u003e\n\u003cp\u003ePrevious studies have discussed titanium as one of the chemical components affecting Fe\u0026ndash;Ti reaction, as titanium oxides can transform iron-blue glazes into green by\u0026nbsp;oxidising certain Fe2+ ions to Fe3+ when exposed to the high temperatures of a kiln (Wood 2011, 2021). However, according to SEM backscatter imaging, titanium oxides in the \u003cem\u003ezisha\u003c/em\u003e sherds manifested as particles suspended in the clay paste rather than dissolved in it (Fig. 6). Thus, the particles could not actively interact with iron oxides to alter the colour of\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e ware. Additionally, colourant oxides, including calcium oxide, could potentially influence optical colour under similar firing conditions (Maniatis et al. 1981). Given that the calcium percentage of the\u003cem\u003e\u0026nbsp;zisha\u003c/em\u003e sherds was below 1%, no significant contribution from calcium oxidation to the \u003cem\u003ezisha\u003c/em\u003e sherd colour took place.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;SEM backscatter analysis showed that the iron oxides in the zisha clay paste come from iron oxide minerals (e.g. haematite, goethite) and iron-rich rock fragments. For example, sample 05BG1(4)_48 contained a sub-rounded rock fragment with a high concentration of iron, (Fig. 7) suggesting that in addition to pure minerals, iron-rich rock fragments also contributed significantly to the iron variability in the clay, potentially affecting its coloration.\u003c/p\u003e"},{"header":"5. Chronological changes in clay particle size","content":"\u003ch3\u003e5.1 Optical analysis of sample coarseness\u003c/h3\u003e\n\u003cp\u003eOptical quantitative analysis was conducted on cross-sections of the \u003cem\u003ezisha\u003c/em\u003e sherds. The resultant data are presented in Appendix 1. Using percentage diagrams to estimate composition by volume, the coarseness of the cross-sections was categorized into five groups, ranging from very fine (group 1) to coarse (group 5). In contrast with the Early Qing\u0026ndash;Late Qing/Republican sherds, a larger percentage of the Ming dynasty \u003cem\u003ezisha\u003c/em\u003e sherds belong to the coarse group (Fig. 8).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe mean coarseness is calculated as the arithmetic average of the coarseness values of all samples within each time period. A pronounced decreasing trend can be observed from the Ming dynasty (approximately 2.68) to the Mid-Qing period (approximately 1.68), followed by a slight increase during the Late Qing/Republican period (approximately 1.88) (Fig. 9). The superimposed linear regression (y = -0.246x + 2.61) indicates an overall declining trajectory, suggesting a general improvement in surface smoothness across these periods.\u003c/p\u003e\n\u003cp\u003eFurthermore, SEM spectrum mapping using a HITACHI TM4000II at a fixed 200\u0026times; magnification with a count ranging between 16,000 and 25,000 cps was performed on 18 randomly chosen samples from three SEM coarseness categories (fine, medium, and coarse clay; see Appendices 1 and 3). The obtained mapping images were processed with ImageJ.\u003c/p\u003e\n\u003ch3\u003e5.2 ImageJ calculation of particle size\u003c/h3\u003e\n\u003cp\u003eImageJ is widely used for processing images and converting them into quantifiable data (Collins 2007; Dal Sasso et al. 2014), for instance to determine particle shapes and sizes. Igathianathane and colleagues used ImageJ to calculate the dimensions of particles of various geometric shapes and concluded that particle shape does not affect dimension calculation in ImageJ (Igathianathane et al. 2008). Lormand and colleagues used ImageJ to analyse backscattered electron images of crystals in volcanic rock, providing a case study for the application of ImageJ in rock crystal analysis (Lormand et al. 2018). ImageJ has also been used in petrography; Berrezueta and colleagues used it to calculate pore size in microscopic images (Berrezueta et al. 2019). Based on these previous successful studies, this study uses ImageJ to calculate particle size in backscattered SEM images.\u003c/p\u003e\n\u003cp\u003eBeyond following the previous research, the accuracy of ImageJ in calculating particle size was validated in the context of the present study. To do this, two black squares, each consisting of 16 units (16 + 16 = 32 units), were generated on a white canvas measuring 324 grid units (18 \u0026times; 18 units; Fig. 10). Mathematically, these black squares encompass 9.87% of the white canvas. The ImageJ threshold function (which converts a grayscale image into a binary, black-and-white image) and area calculation function determined that the black area occupied 10% of the total area, reflecting a 0.13% error margin compared to the mathematical calculations. Additionally, two black circles on an identical white canvas were tested, revealing a 0.02% error margin between the areas determined via ImageJ and mathematical calculations. These results confirm that ImageJ\u0026rsquo;s area calculation function provides reliable measurements and can thus accurately reflect particle areas in image analysis. A limitation of the use of Image J to calculate particle area is that the particle area calculation in this study only accounts for particles that exceed 10 pixels in fineness on SEM backscatter images, which corresponds to particles larger than 10\u0026micro;m in diameter. This was taken into account when evaluating the data.\u003c/p\u003e\n\u003ch3\u003e5.3 Changes in clay particle size over time\u003c/h3\u003e\n\u003ch4\u003e5.3.1 Calculation of quartz particle size\u0026nbsp;\u003c/h4\u003e\n\u003cp\u003eThe size of quartz particles in \u003cem\u003ezisha\u0026nbsp;\u003c/em\u003eclay serves as an ideal indicator for assessing clay paste coarseness. The primary reason for this is that quartz can be readily distinguished from other mineral crystals in SEM spectrum mapping due to its consistently high silicon content. Quartz is prominent component of \u003cem\u003ezisha\u003c/em\u003e clay paste in the examined periods (Fig. 11). Therefore, although several other particles, including clay clumps, feldspar crystals, also contribute to the clay paste coarseness, quartz is analysed in this study as a representative particle. In the analysis below, the word \u0026ldquo;particle\u0026rdquo; in later discussion refers to quartz particles.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eOn the SEM, three silicon spectrum mapping images were captured from each sample and subjected to thresholding, binary conversion, and particle analysis processes in ImageJ to distinctly outline individual particles (Figs. 12\u0026ndash;14) and calculate the area of all outlined particles or individual outlined particles.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe total area of quartz particles in examined thin section reflects the size of all quartz particles and also provides insights into the coarseness of the sample. A comparison of the area of all outlined particles in samples from the Late Ming to the Late Qing/Republican period shows a decreasing trend in particle area size, ranging from 53,507\u0026ndash;63,548 \u0026micro;m\u0026sup2; in the Ming dynasty to 29,802\u0026ndash;34,059 \u0026micro;m\u0026sup2; in the Late Qing/Republican period (Fig. 15; Appendix 4). These findings indicate that fewer quartz particles or smaller quartz particles appeared in the later samples. \u003cem\u003eZisha\u003c/em\u003e potters in later periods clearly opted for finer clay than their predecessors.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo determine whether the decrease in quartz particle area was caused by a reduction in individual particle size or a reduction in particle quantity, the size of the average quartz particle and the standard deviation of particles in each sample were calculated in ImageJ. According to the ImageJ calculations, the average individual particle size during the Ming dynasty was within the range of 129\u0026ndash;183 \u0026micro;m\u0026sup2;, while particles in pieces from the Mid-Qing and Late Qing/Republican periods measured between 77\u0026ndash;122 \u0026micro;m\u0026sup2; and 79\u0026ndash;109 \u0026micro;m\u0026sup2;, respectively (Appendix 5; Fig. 16). Notably, Early Qing dynasty \u003cem\u003ezisha\u003c/em\u003e clay exhibited the largest individual particle size, ranging from 206.39 to 169.37 \u0026micro;m\u0026sup2;. The Early Qing period was characterized by dynastic changes and warfare, which may have affected ceramic production during this period.\u003c/p\u003e\n\u003cp\u003eAn examination of the standard deviation confirmed a reduction in size variation among quartz particles over time. Specifically, the range diminished from 630\u0026ndash;1,665 \u0026micro;m\u0026sup2; during the Ming dynasty, to 225\u0026ndash;511 \u0026micro;m\u0026sup2; during the Late Qing period (Appendix 6; Fig. 17). These findings suggest that the \u003cem\u003ezisha\u003c/em\u003e paste used in the earlier periods was poorly sorted, with particles displaying substantial size disparities, while the paste used in later periods shows evidence of improved sorting, as the quartz particles had a more consistent appearance and were relatively homogeneous in size. In previous research on ceramic production, homogeneous size of particles in clay pastes has generally been attributed to the use of certain clay-processing techniques (Eramo 2020; Gosselain \u0026amp; Livingstone Smith 2005). For instance, crushing clay rock and sieving clay paste breaks down or removes larger mineral particles, resulting in a more homogeneous particle sizes. \u003cem\u003eZisha\u003c/em\u003e clay-processing techniques and their relationship to the homogeneity of the clay paste are discussed in Section 6.3.\u003c/p\u003e"},{"header":"6. Factors that may have influenced potters’ raw material choices","content":"\u003cp\u003eThe following discussion of \u003cem\u003ezisha\u003c/em\u003e teapot recipe changes focuses on the complexity of raw material choices and discuss the correlations between geological formations, clay exploration sequences, and clay-processing techniques, as well as cultural factors that may have led to the clay recipe changes\u0026mdash;the growing diversity of colour, decrease in the number of quartz particles, and increasing homogeneity in particle size.\u003c/p\u003e\n\u003ch3\u003e6.1 Geological formation and clay mining sequence\u003c/h3\u003e\n\u003cp\u003eGeologically, \u003cem\u003ez\u003c/em\u003e\u003cem\u003eisha\u003c/em\u003e clay forms through sedimentary processes involving weathering, transportation, and deposition of silicate materials (Guggenheim and Martin 1995, p. 255; Rice 2015, p. 202). Like other sedimentary rocks, it develops when weathered fragments are carried by wind, rivers, or ocean currents to deposition sites, creating layers with varying grain sizes and textures (Allen 1970; Tucker 2001, p. 1). The characteristic reddish colouration of \u003cem\u003ezisha\u003c/em\u003e clay stems primarily from the presence of iron oxide minerals\u0026mdash;hematite, goethite, and limonite\u0026mdash;whose different oxidation states produce colours ranging from black to red (McBride 1974; Rothwell 1989, p. 139). During formation, amorphous ferric hydroxide appears as the main weathering product and may recrystallize into goethite, yielding yellow to orange hues (Schmalz 1968, p. 277). Hematite\u0026rsquo;s red colour can be modified through interactions with ferric oxy-hydroxide or goethite.\u003c/p\u003e\n\u003cp\u003eIn 2005 and 2010, Gao conducted field studies in Yixing, which confirmed the sedimentary deposit of the clay sources in Yixing. At the open-air clay mining site in Hufu town[1] (Fig. 18), southwest of Yixing, a clear cross-section from surface level to deeper clay bedding formation could be observed. Five clay layers with distinguishable colours can be identified in the stratigraphic cross-section of the mine (Fig. 19). Visual examination of the geological bedding revealed distinct belt-like sedimentary structures with diverse colour gradations. From top to bottom, the layers display pale brown, brownish yellow, yellow, brown, and greyish brown hues. This variation in colour within a single clay mine may be caused by differences in iron oxides between layers (e.g. variations in the presence and distribution of haematite, goethite, and limonite). The presence of hematite results in black to red colours (Torrent \u0026amp; Schwertmann 1987). Both amorphous ferric hydroxide and goethite produce a colour range that includes yellow, yellowish brown and orange (Schwertmann 1993). This variation of oxides is one of the key factors contributing to the colour differences observed in the fired clay pieces from the Shushan site.\u003c/p\u003e\n\u003cp\u003eDue to the clay\u0026rsquo;s layered sedimentary structure, with different iron compositions in each layer, access to clay containing various iron oxides depended heavily on the sequence in which Yixing potters or clay dealers extracted the clay deposit. In earlier periods, they extracted clay from surface layers only, as the deeper strata did not become accessible until later periods. Ming dynasty potters accessed the clay in the uppermost quarry layers while subsequent potters and clay merchants gained access to both surface layers and deeper deposits (Fig. 19). As mining activities reached deeper levels, more sedimentary layers became accessible to later potters and clay dealers. Craftspeople in later periods, who had access to a greater number of geological strata, naturally had a wider range of clay colours available to them. The clay exploration sequences could thus partly explain the increase in clay colour diversity. Therefore, the increasing diversity in clay colour and the expanding range of iron oxides in the \u003cem\u003ezisha\u003c/em\u003e clay recipe (as concluded in Section 3) can be attributed to the layered sedimentary geological structure of the deposit, as well as clay mining sequences.\u0026nbsp;\u003c/p\u003e\n\u003ch3\u003e6.2 Clay processing and selection\u0026nbsp;\u003c/h3\u003e\n\u003cp\u003eThe physical properties of a clay paste correlate with raw material processing techniques and selection criteria (Arnold 1985, p. 20; Eramo 2020; Gosselain 1994, p. 102; Velde \u0026amp; Druc 1999). During field research in 2016, author Gao conducted systematic observations of the clay classification and processing methods used by contemporary potters and clay dealers (Gao 2016). \u003cem\u003eZisha\u003c/em\u003e clay dealers evaluate the colour and texture of the clay rocks and categorize raw clay materials with the same chromatic gradation and texture into a group destined for pottery making. During the clay weathering process, the clay dealers\u0026rsquo; classification is predominantly based on two parameters: chromatic gradation and textural properties. The textural assessment, locally termed \u003cem\u003ecuci\u003c/em\u003e (粗次, grade of coarseness), is based on the macroscopically observable granularity of the clay rock\u0026rsquo;s cross-sectional surface. Dealers with substantial experience demonstrate the capacity to differentiate nuanced variations in both parameters\u0026nbsp;(Gao 2016, p. 18).\u0026nbsp;Therefore, the colour of the clay used for pottery making is\u0026nbsp;ultimately determined by\u0026nbsp;the\u0026nbsp;clay dealers\u0026rsquo; classification, probably combined with their own experience with one or other of these types of clays and/or what they were told by their own teachers. These experiences and debates were not part of the present research, however, but would need to be the subject of further research on knowledge transmission both among potters and between dealers and potters and vice versa.\u003c/p\u003e\n\u003cp\u003eThe 2016 field research also made clear that traditional \u003cem\u003ezisha\u003c/em\u003e clay-processing\u003cem\u003e\u0026nbsp;\u003c/em\u003eincludes grinding, siving and levigation. After grinding, a preliminary sieving process takes place, and a stone mill is used for clay-grinding. The weathered clay powder is placed in water, stirred with bamboo sticks, and washed to remove impurities and rock fragments (Gao 2016, p. 18\u0026ndash;20). When the clay sediments, potters pour out the water on the upper level and add more clear water to wash the clay, repeating the previous steps. The clay is aged inside vessels, submerged in water for years or even decades, before it is dehydrated to create a clay paste ready for pottery making.\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTechniques involving grinding, sieving, and levigation are used to alter dry consolidated clay rocks into pastes ready for use, a process that refines the clay by removing or crushing larger particles and homogenizing the clay paste (Eramo 2020; Quinn 2013, p. 154\u0026ndash;155; Roux 2016). Therefore, the decreasing average particle size and increasing homogeneity of the clay paste reflect potters\u0026rsquo; deliberate efforts to refine and perfect their clay-processing techniques.\u003c/p\u003e\n\u003ch3\u003e6.3 Appreciation of clay colours and textures\u003c/h3\u003e\n\u003cp\u003e\u003cem\u003eZisha\u003c/em\u003e clay colours and textures are frequently mentioned in Ming and Qing dynasty texts such as \u003cem\u003eJingxi shu\u0026nbsp;\u003c/em\u003e(荊溪疏, Annotated Commentary on Jingxi), \u003cem\u003eYangxian minghuxi\u0026nbsp;\u003c/em\u003e(阳羡名壶系,\u0026nbsp;Renowned Teapots in Yangxian), \u003cem\u003eMinghu tulu\u003c/em\u003e (茗壶图录,\u0026nbsp;Teapot Catalogue), \u003cem\u003eYangxian mingtaolu\u0026nbsp;\u003c/em\u003e(阳羡名陶录,\u0026nbsp;A Record of Renowned Teapots in Yangxian), and \u003cem\u003eYixing taoqi gaiyao\u0026nbsp;\u003c/em\u003e(宜興陶器概要, An Overview of Yixing Pottery) (Ao 1998 [1874]; Siku Jinhuishu 2000 [unknown];Wu 2014 [1786]; Zhou 2014 [ca.1640]; Zhou and Zhou 1932).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eTo better understand the literati appreciation criteria of \u003cem\u003ezisha\u003c/em\u003e teapots, the \u003cem\u003eYangxian minghuxi\u003c/em\u003e, a text known as the first \u003cem\u003ezisha\u003c/em\u003e monograph, is examined here in some detail (Chen 2016, 2018; Li 2008). This text was written by Zhou Gaoqi (周高起) in the late 17\u003csup\u003eth\u003c/sup\u003e century. Although he did not serve as an official at court, Zhou was a literatus and diligent writer. In addition to the \u003cem\u003eYangxian minghuxi\u003c/em\u003e, he also wrote texts for the local gazetteer \u003cem\u003eJiangyin Xianzhi\u003c/em\u003e (江阴县志, Gazetteer of Jiangyin County) (Feng, Xu, and Zhou 2003 [ca. 1640]) as well as a book on tea plants titled \u003cem\u003eDongshan jiechaxi\u003c/em\u003e (洞山岕茶系, Jie tea in Dongshan) (Zhou 2014 [ca.1639]). Him writing the texts \u003cem\u003eYangxian minghuxi\u003c/em\u003e and \u003cem\u003eDongshan jiechaxi\u003c/em\u003e makes it clear that Zhou was an enthusiastic tea connoisseur who appreciated \u003cem\u003ezisha\u003c/em\u003e teapot artisanship. His knowledge of \u003cem\u003ezisha\u003c/em\u003e teapots was influenced by Wu Honghua 吳洪化, a \u003cem\u003ezisha\u003c/em\u003e teapot collector from a prominent Yixing family. The details of Zhou\u0026rsquo;s connection with Wu Honghua are analysed in an article by Gao and Hein (2024).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe \u003cem\u003eYangxian minghuxi\u003c/em\u003e focuses on documenting renowned potters, clay sources, mining locations, and the artistic styles and designs of teapots. The clay used to make \u003cem\u003ezisha\u003c/em\u003e wares, and particularly its colour, is described in detail in the text, as shown in the passage quoted below.\u003c/p\u003e\n\u003cp\u003eOriginal text:\u0026nbsp;嫩泥出趙莊山，以和一切色，\u0026nbsp;上乃黏脂可築蓋陶壺之丞弼也。\u0026nbsp;石黃泥出趙莊山，即未觸風日之石骨也。陶之乃變朱（硃）砂色。天青泥出蠡墅。陶之變黯肝色。又其夾支，有梨皮泥。陶現梨凍色。淡紅泥，\u0026nbsp;陶現鬆花色。淺黃泥，陶現豆碧綠色蜜。泥陶現輕赭色。梨皮和白砂，陶現淡墨綠色。山靈腠絡，陶冶變化，尚露種種光怪雲。老泥出團山。陶則白砂星星。按若珠琲。以天青石黃和之成淺深古色。白泥出大潮山，陶缾盎缸用之。\u003c/p\u003e\n\u003cp\u003e(Zhou 2014 [ca.1640], p. 514)\u003c/p\u003e\n\u003cp\u003eTranslation: Nen (嫩, \u0026ldquo;soft\u0026rdquo;)-textured clay is extracted from the Zhaozhuang Mountain and can be mixed with \u003cem\u003ezisha\u003c/em\u003e of different colours to produce various categories of ceramic products from teapots to food containers. \u003cem\u003eShihuang\u003c/em\u003e (石黃, \u0026ldquo;rocky yellow\u0026rdquo;) clay is found in the Zhaozhuang mountains, and is an unweathered clay rock. Fired pots made with shihuang clay are \u003cem\u003ezhusha\u003c/em\u003e (硃砂, \u0026ldquo;cinnabar\u0026rdquo;) coloured. \u003cem\u003eTianqing\u0026nbsp;\u003c/em\u003e(天青, \u0026ldquo;bluish green\u0026rdquo;) clay is sourced from the Lishu 蠡墅 area. Fired pots made with \u003cem\u003etianqing\u003c/em\u003e clay are \u003cem\u003eangan\u003c/em\u003e (黯, \u0026ldquo;dark liver\u0026rdquo;) coloured. Different types of \u003cem\u003ezisha\u003c/em\u003e clay are collected from the \u003cem\u003etianqing\u0026nbsp;\u003c/em\u003eclay layer(s), such as \u003cem\u003elipi\u0026nbsp;\u003c/em\u003e(梨皮, \u0026ldquo;pear peel\u0026rdquo;)-coloured clay. Fired pieces made from \u003cem\u003elipi\u003c/em\u003e clay are \u003cem\u003edongli\u003c/em\u003e (凍梨, \u0026ldquo;chilled pear peel\u0026rdquo;) coloured, while those made from \u003cem\u003edanhong\u0026nbsp;\u003c/em\u003e(淡紅, \u0026ldquo;light red\u0026rdquo;) clay are \u003cem\u003esonghua\u0026nbsp;\u003c/em\u003e(松花, \u0026ldquo;pine tree flower\u0026rdquo;) coloured. Fired pieces made from \u003cem\u003eqianhuang\u003c/em\u003e (淺黃, \u0026ldquo;light yellow\u0026rdquo;)-coloured clay result in a \u003cem\u003edoubi\u0026nbsp;\u003c/em\u003e(豆碧, \u0026ldquo;bean green\u0026rdquo;) colour, while unfired pieces are \u003cem\u003eqingzhe\u003c/em\u003e (輕赭, \u0026ldquo;light reddish brown\u0026rdquo;) coloured. When \u003cem\u003elipi\u003c/em\u003e clay is mixed with \u003cem\u003ebaisha\u0026nbsp;\u003c/em\u003e(白砂, \u0026ldquo;white sand\u0026rdquo;) clay, a greyish-green-coloured clay is produced. These strange phenomena of clays and changes in pots\u0026rsquo; colours are attributed to the spirits in the mountains. \u003cem\u003eLao\u003c/em\u003e (老, \u0026ldquo;aged\u0026rdquo;)-textured clay is procured from the Tuanshan 團山 mine. The pots have star-like white spots. The surfaces of the pots resemble pearls. When \u003cem\u003etianqing\u003c/em\u003e and \u003cem\u003eshihuang\u003c/em\u003e clays are mixed, two kinds of clays of a dark brown colour are produced. \u003cem\u003ebai\u003c/em\u003e (白, \u0026ldquo;white\u0026rdquo;) clay is excavated from Dachaoshan 大潮山 and is used to produce vessels, bowls, and jars.\u003c/p\u003e\n\u003cp\u003eThis section underscores the importance of mining locations in the classification of \u003cem\u003ezisha\u003c/em\u003e clay. It reveals that clay types were named according to both their chromatic or textural properties after firing. Sites such as Zhaozhuang Mountain (赵庄山), Lishu (蠡墅), Tuanshan (团山), and Dachaoshan (大潮山) are associated with at least eight distinct clay types\u0026mdash;\u003cem\u003enen\u0026nbsp;\u003c/em\u003e(嫩, \u0026ldquo;soft\u0026rdquo;) , \u003cem\u003eshihuang\u003c/em\u003e (石黃, \u0026ldquo;rocky yellow\u0026rdquo;), \u003cem\u003etianqing\u0026nbsp;\u003c/em\u003e(天青, \u0026ldquo;bluish green\u0026rdquo;), \u003cem\u003elipi\u0026nbsp;\u003c/em\u003e(梨皮, \u0026ldquo;pear peel\u0026rdquo;), \u003cem\u003edanhong\u0026nbsp;\u003c/em\u003e(淡紅, \u0026ldquo;light red\u0026rdquo;), \u003cem\u003edanhuang\u0026nbsp;\u003c/em\u003e(淡紅, \u0026ldquo;light red\u0026rdquo;), \u003cem\u003elao\u0026nbsp;\u003c/em\u003e(老, \u0026ldquo;aged\u0026rdquo;), and \u003cem\u003ebai\u0026nbsp;\u003c/em\u003e(白, \u0026ldquo;white\u0026rdquo;)\u0026mdash;each bearing distinct colours and textures. For example, \u003cem\u003eshihuang\u003c/em\u003e clay produces a vivid cinnabar red when fired, while \u003cem\u003etianqing\u003c/em\u003e yields a dark liver hue; \u003cem\u003elipi\u003c/em\u003e and \u003cem\u003edanhong\u003c/em\u003e result in surface colours likened to chilled pear skin and pine pollen, respectively (Zhou 2014 [ca. 1640], p. 514).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eIn the section titled \u003cem\u003eMingjia\u003c/em\u003e (名家, \u0026ldquo;renowned potters\u0026rdquo;), Zhou Gaoqi offers a critical appraisal of the teapots produced by Xu Youquan (徐友泉), framing the diversity of clay colours as both a marker of technical expertise and a vehicle for artistic expression. Zhou describes Xu as a distinguished artisan who deliberately selected clay bodies of varied hues to enhance the visual and material qualities of his ceramic works, as evidenced by the quoted text below.\u003c/p\u003e\n\u003cp\u003eOriginal text:\u0026nbsp;泥色有海棠红、朱砂紫、定窑白、冷金黄、淡墨、沉香、水碧、榴皮、葵黄、闪色、梨皮诸名。种种变异，妙出心裁。\u0026nbsp;(Zhou 2014 [ca.1640], p. 513)\u003c/p\u003e\n\u003cp\u003eTranslation: The clay colours include crab apple red, cinnabar purple, ding-ware white, pale golden yellow, pale ink, agarwood, greenish water, pomegranate skin, sunflower yellow, \u003cem\u003eshan\u003c/em\u003e (a mixture of contrasting colour tones), pear peel, etc. The colour changes form an exceptional and ingenious design.\u003c/p\u003e\n\u003cp\u003eThe colours employed by Xu include \u003cem\u003ehaitanghong\u003c/em\u003e (海棠红, \u0026ldquo;crab apple red\u0026rdquo;), \u003cem\u003ezhushazi\u003c/em\u003e (朱砂紫, \u0026ldquo;cinnabar purple\u0026rdquo;), \u003cem\u003edingyaobai\u003c/em\u003e (定窑白, \u0026ldquo;Ding-ware white\u0026rdquo;), \u003cem\u003elengjinhuang\u003c/em\u003e (冷金黄, \u0026ldquo;pale golden yellow\u0026rdquo;), \u003cem\u003edanmo\u003c/em\u003e (淡墨, \u0026ldquo;pale ink\u0026rdquo;), \u003cem\u003echenxiang\u003c/em\u003e (沉香, \u0026ldquo;agarwood\u0026rdquo;), \u003cem\u003eshuibi\u003c/em\u003e (水碧, \u0026ldquo;greenish water\u0026rdquo;), \u003cem\u003eliupi\u003c/em\u003e (榴皮, \u0026ldquo;pomegranate skin\u0026rdquo;), \u003cem\u003ekuihuang\u003c/em\u003e (葵黄, \u0026ldquo;sunflower yellow\u0026rdquo;), \u003cem\u003eshanse\u003c/em\u003e (闪色, referring to variegated or iridescent colouration), and \u003cem\u003elipi\u003c/em\u003e (梨皮, \u0026ldquo;pear peel\u0026rdquo;). This wide chromatic range\u0026mdash;encompassing shades of red, purple, yellow, and white\u0026mdash;demonstrates an advanced level of material literacy and aesthetic refinement. Zhou\u0026rsquo;s use of the phrase \u003cem\u003emiaochu xincai\u003c/em\u003e (妙出心裁), which connotes ingenuity and originality, further underscores the degree to which these colour variations were not incidental but rather the result of deliberate artistic design. In this context, clay colour selection functions as a key index of craftsmanship, creativity, and cultivated taste (Zhou 2014 [ca. 1640], p. 513).\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eZhou Gaoqi argues that the distinctive smooth and naturally matte finish of \u003cem\u003ezisha\u003c/em\u003e teapots makes them particularly well-suited as refined objects for scholarly appreciation (Zhou 2014 [ca. 1640], p. 515), which could be evident from the text as below.\u003c/p\u003e\n\u003cp\u003eOriginal text: 壺入用久，滌拭日加自發闇然之光，入手可鑒。 此為書房雅供。 Translation: With prolonged use, the teapot gradually accumulates a natural patina through daily cleaning, emitting a subdued radiance when held. This is an elegant addition to the study. (Zhou 2014 [ca.1640], p. 515)\u003c/p\u003e\n\u003cp\u003eThis view underscores the central role of surface texture in the aesthetic evaluation of teapots, as the matte quality\u0026mdash;achieved through the use of fine-textured clay\u0026mdash;embodies both visual restraint and tactile subtlety. Zhou further notes that with prolonged use and regular cleaning, \u003cem\u003ezisha\u003c/em\u003e teapots develop a subdued, lustrous patina that enhances their visual appeal, describing this glow as \u0026ldquo;a subdued radiance\u0026rdquo; (\u003cem\u003eanran zhiguang\u003c/em\u003e,\u0026nbsp;闇然之光) that becomes evident when the teapot is held. Such a transformation is not only a result of material properties but also a sign of cultivated interaction between object and user over time. In this way, the teapot becomes more than a functional vessel\u0026mdash;it evolves into a scholar\u0026rsquo;s object, appropriate for the refined atmosphere of the study (\u003cem\u003eshufang yagong\u003c/em\u003e, 書房雅供). The frequent references to clay colour and surface finish in historical texts thus reflect more than technical concerns; they reveal an enduring cultural valuation of subtle material and colour variation aesthetics in \u003cem\u003ezisha\u003c/em\u003e craftsmanship.\u003c/p\u003e\n\u003cp\u003e[1] The Hufu mine was the only mining site examined in this study, as parts of the Huanglong mining area were flooded at the time and closed to public access (Gao 2016; Zhao 2010).\u003c/p\u003e"},{"header":"7. Discussion","content":"\u003cp\u003eThis study set out to explore the complexity of potters\u0026rsquo; raw material choices in Late Imperial China, with a particular focus on changes in the clay recipe for \u003cem\u003ezisha\u003c/em\u003e teapots excavated from the Shushan site. Through a combination of archaeometric analysis, geological data, observation of contemporary practitioners, and written texts, this discussion synthesizes how geological formations, clay mining sequences, clay-processing practices, and aesthetic preferences intersected to shape technological choices. Rather than attributing material selection to any singular factor, this study frames raw material choice as the outcome of the interplay between environmental, technological, and cultural variables.\u003c/p\u003e \u003cp\u003eThe geological origin of \u003cem\u003ezisha\u003c/em\u003e clay as a sedimentary deposit\u0026mdash;composed of stratified layers with varying iron oxide content\u0026mdash;provides a foundational explanation for the observable increase in colour diversity over time. The results from SEM-EDS analysis demonstrate a broader range of iron oxide percentages from the Ming to the Late Qing period, while optical data reveal an expansion in the diversity of clay colours used to make \u003cem\u003ezisha\u003c/em\u003e teapots. Field observations from the Hufu mine confirmed stratified beds of clay exhibiting chromatic gradations, suggesting that access to deeper deposits in later periods enabled potters to exploit layers with differing iron compositions. This progressive vertical mining strategy aligns with expansion of clay colours during the examined period, supporting the hypothesis that the mining sequence, determined by the local geological structure, influenced the composition of the clay recipe.\u003c/p\u003e \u003cp\u003eClay processing techniques, particularly grinding, sieving, and washing, played a significant role in clay paste changes. The analysis result demonstrates a marked reduction in particle size and variability from the Ming to the Republican periods. This refinement of texture aligns with field observations of present-day Yixing clay-processing methods, which aim to remove impurities and produce more homogenous pastes. The historical shift toward finer, more uniformly processed clays suggests increasing control over the mechanical and visual properties of the final product, reflecting potters\u0026rsquo; growing technical proficiency and awareness of consumer preferences.\u003c/p\u003e \u003cp\u003eA key contribution of this study lies in highlighting the cultural valuation of clay appreciation as a driver of technological change. Unlike glazed wares, where surface decoration can obscure the clay body, \u003cem\u003ezisha\u003c/em\u003e teapots rely entirely on the visual and tactile qualities of their clay. Historical texts from the Ming and Qing periods\u0026mdash;particularly Zhou Gaoqi\u0026rsquo;s \u003cem\u003eYangxian Minghuxi\u003c/em\u003e\u0026mdash;emphasized appreciation of subtle colour tones and surface textures and catalogued the vocabulary of named clay types. These written texts provide evidence of the emphasis on clay colour and texture during the Ming and Qing dynasties. Therefore, the increased chromatic and textural variation can be seen, in part, as a result of clay appreciation shaped by literati taste and artisanal reputation. Potters such as Xu Youquan, praised for their innovative use of diverse clays, exemplify how aesthetic connoisseurship shaped production decisions. The increasing homogeneity and colour diversity of clay bodies must therefore be read as both technological and cultural responses to elite consumption practices.\u003c/p\u003e \u003cp\u003eRather than treating geological conditions, clay processing, and cultural aesthetics as isolated determinants, this study proposes that it is their interaction which best explains the observed changes in \u003cem\u003ezisha\u003c/em\u003e clay recipes. The expansion of mining activity into deeper strata offered the potters a broader palette of clays, while increasingly sophisticated processing methods enabled them to tailor their materials to meet changing aesthetic demands. Meanwhile, the enduring cultural emphasis on matte, fine-textured surfaces and nuanced hues motivated the continual refinement of clay selection. This integrated analysis aligns with broader discussions in ceramic studies that conceptualize technological choices as embedded within social, economic, and environmental contexts (Arnold \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e1985\u003c/span\u003e; Lemonnier \u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e1993\u003c/span\u003e; Santacreu \u003cspan citationid=\"CR88\" class=\"CitationRef\"\u003e2017\u003c/span\u003e).\u003c/p\u003e"},{"header":"8. Conclusion","content":"\u003cp\u003eThis analysis of Shushan-site \u003cem\u003ezisha\u003c/em\u003e sherds dating from the Ming dynasty to the Republican period reveals significant insights into the complex factors that influenced potters\u0026rsquo; raw material choices in Late Imperial China. Our multi-method investigation, combining SEM-EDS analysis, optical examination, and analysis of textual materials, demonstrates that the alteration of the \u003cem\u003ezisha\u003c/em\u003e clay recipe was shaped by an intricate interplay of geological factors, clay-processing techniques, and clay appreciation.\u003c/p\u003e \u003cp\u003eThe scientific analysis revealed two key chronological trends: an increasing diversity in clay colours and a shift toward finer clay textures. SEM-EDS analysis showed a growing variation in iron oxide composition (from 5.03\u0026ndash;6.87% in Ming samples to 2.1\u0026ndash;7.59% in Late Qing samples), while particle analysis demonstrated a reduction in average particle size (from 129\u0026ndash;183 \u0026micro;m\u0026sup2; in Ming samples to 79\u0026ndash;109 \u0026micro;m\u0026sup2; in the Late Qing/Republican period samples) and improvements in particle sorting techniques in clay processing.\u003c/p\u003e \u003cp\u003eWhile geological factors, mining sequences, and clay-processing techniques partially explain these trends, our research indicates that the appreciation of clay colour significantly influenced potters\u0026rsquo; raw material choices. Historical texts written during this period explicitly connect clay colour diversity and fine texture with artistic excellence, suggesting that potters actively selected and modified clay recipes to meet these aesthetic preferences. This study thus enriches our theoretical framework for understanding the complexity of technological choice, particularly when it concerns Late Imperial Chinese ceramic production.\u003c/p\u003e \u003cp\u003eThis study suggests that future research on ceramic technologies should consider not only the physical properties and functional requirements of materials but also the cultural context of appreciation and connoisseurship that may influence technical decisions. More broadly, this research illustrates the value of integrating scientific analysis with geological data, field trip observations, written texts to understand the potters\u0026rsquo; technological choice.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eWe would like to express our sincere gratitude to Hang Tao\u0026nbsp;杭涛\u0026nbsp;from the Nanjing Museum and Huang Xingnan\u0026nbsp;黄兴南\u0026nbsp;from the Office of the Yixing Municipal Cultural Relics Management Committee along with his team members, for kindly providing the samples from Shushan site and offering invaluable technical assistance during the sample collection and photography process. Special thanks go to Zhou Xiaodong\u0026nbsp;周晓东, former head of the China Yixing Ceramics Museum, for kindly granting access to the material from the Yangjiaoshan\u0026nbsp;羊角山\u0026nbsp;site for comparative study with the Shushan materials.\u003c/p\u003e\n\u003cp\u003eWe are especially indebted to Professor Christopher Doherty for his unwavering support during the laboratory work at Oxford. His expertise in geology, guidance with SEM sample preparation, and detailed instruction on laboratory procedures were instrumental to this research. This article could not have been completed without his generous help and mentorship.\u003c/p\u003e\n\u003cp\u003eWe are also deeply grateful to Professor Lin Liugen\u0026nbsp;林旒根, former head of the Nanjing Museum, Professor Gao Dalin\u0026nbsp;高大伦, and Professor Xu Tianjin\u0026nbsp;徐天进\u0026nbsp;for their generous support in facilitating communication and offering insightful guidance on the research direction.\u003c/p\u003e\n\u003cp\u003eWe would like to thank the Meyerstein Foundation and St Cross College for their financial support of this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding declaration\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Meyerstein and School Research Awards for Archaeological Research (2019\u0026ndash;2020) and the St Cross College Academic Travel and Research Fund (2020).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n \u003cli\u003eAllen JRL (1970) Studies in fluviatile sedimentation: a comparison of fining-upwards cyclothems, with special reference to coarse-member composition and interpretation. 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In: Zheng PK 鄭培凱 Zhu ZZ 朱自振 (eds) Zhongguo lidai chashu huibian jiaozhuben\u0026nbsp;中國歷代茶書彙編校注本, Shangwu Yinshuguan 商務印書館, Xianggang, pp. 520\u0026ndash;523\u003c/li\u003e\n \u003cli\u003eZhou RS 周潤生, Zhou YD 周幽東 (1932) Yixing taoqi gaiyao 宜興陶器概要. Yixing taoqi canjia zhijiage bolanhui choubei Weuyuanhui 宜興陶器參加芝加哥博覽會籌備委員會, Yixing\u0026nbsp;\u003c/li\u003e\n \u003cli\u003eZhu J, MacDonald BL, Hang T et al (2019) Compositional chracterization of Zisha clay from the Yixing area (Jiangsu, China) by neutron activation analysis. Microchem J 147:1117\u0026ndash;1122. https://doi.org/10.1016/j.microc.2019.04.031\u003c/li\u003e\n \u003cli\u003eZhu ZW 朱澤偉 (2009) Yixing zisha kuangliao\u003cem\u003e\u0026nbsp;\u003c/em\u003e宜興紫砂礦料. Dizhi Chubanshe 地質出版社, Beijing\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"archaeological-and-anthropological-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aasc","sideBox":"Learn more about [Archaeological and Anthropological Sciences](http://link.springer.com/journal/12517)","snPcode":"12520","submissionUrl":"https://submission.nature.com/new-submission/12520/3","title":"Archaeological and Anthropological Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false},"keywords":"Potters’ technological choice, zisha clay, Shushan site, Ming and Qing dynasties, colourant oxides, particle sizes","lastPublishedDoi":"10.21203/rs.3.rs-6945795/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6945795/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eTechnological choices in pottery production, particularly the selection of raw materials, are much discussed for prehistoric periods but have received little scholarly attention in the case of Late Imperial China. In this paper, \u003cem\u003ezisha\u003c/em\u003e teapots, which became China\u0026rsquo;s main tea preparation vessels over the course of the 15th\u0026ndash;20th century, are presented as a case study to explore the complexity underlying potters\u0026rsquo; raw material selection in historic periods. A total of 187 excavated \u003cem\u003ezisha\u003c/em\u003e sherds was analysed using optical microscopy, semi-quantitative chemical analysis via scanning electron microscopy (SEM) combined with energy-dispersive X-ray (EDX) spectroscopy, and ImageJ analysis of SEM backscatter spectrum images. These \u003cem\u003ezisha\u003c/em\u003e sherds date from the Ming dynasty to the Republican period (1368\u0026ndash;1949) and were recovered from Shushan kiln site. SEM-EDX analysis combined with image manipulation in ImageJ revealed changes in the clay recipe over time, including an increase in iron oxide variation and increasing fineness of clay particle sizes, suggesting an expanded colour range and refinement of the clay paste. Combining these findings with an examination of the geological setting of the mining locations, the clay procurement sequence, the clay-processing techniques used by the potters, and texts discussing clay colour and texture appreciation, this study demonstrates the complexity of the potters\u0026rsquo; raw material choices in Late Imperial China and illustrates how these factors can be elucidated through a combination of scientific analysis of archaeological material, examination of geological samples, visual analysis, and reference to historical sources.\u003c/p\u003e","manuscriptTitle":"Creating Wusetu (“Five-Coloured Clay”): Chronological Changes in Zisha Ware Clay Recipes and the Complexity of Potters’ Technological Choices","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-07-02 08:17:16","doi":"10.21203/rs.3.rs-6945795/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-30T05:31:37+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-29T08:03:12+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"283203861411266800459803973181225048168","date":"2025-07-22T12:02:17+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-21T20:56:52+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"69614748542676120631863497444343164974","date":"2025-06-29T06:38:36+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-26T16:49:51+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-06-25T05:24:08+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-06-24T06:48:38+00:00","index":"","fulltext":""},{"type":"submitted","content":"Archaeological and Anthropological Sciences","date":"2025-06-21T15:16:27+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"archaeological-and-anthropological-sciences","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"aasc","sideBox":"Learn more about [Archaeological and Anthropological Sciences](http://link.springer.com/journal/12517)","snPcode":"12520","submissionUrl":"https://submission.nature.com/new-submission/12520/3","title":"Archaeological and Anthropological Sciences","twitterHandle":"","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"Springer Hybrid","inReviewEnabled":true,"inReviewRevisionsEnabled":false}}],"origin":"","ownerIdentity":"83639cf9-e259-4f1f-92f4-3fde769c787f","owner":[],"postedDate":"July 2nd, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-01T16:01:22+00:00","versionOfRecord":{"articleIdentity":"rs-6945795","link":"https://doi.org/10.1007/s12520-025-02335-y","journal":{"identity":"archaeological-and-anthropological-sciences","isVorOnly":false,"title":"Archaeological and Anthropological Sciences"},"publishedOn":"2025-11-29 15:57:04","publishedOnDateReadable":"November 29th, 2025"},"versionCreatedAt":"2025-07-02 08:17:16","video":"","vorDoi":"10.1007/s12520-025-02335-y","vorDoiUrl":"https://doi.org/10.1007/s12520-025-02335-y","workflowStages":[]},"version":"v1","identity":"rs-6945795","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6945795","identity":"rs-6945795","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}