1 Introduction
Bohai glazed pottery refers to low-temperature lead-glazed ceramics found in Bohai cultural sites. They are mainly distributed in northeastern China, as well as parts of the Russian Far East and the Korean Peninsula, and date to the 8th–10th centuries CE. By function, they can be divided into architectural ceramics (e.g., arc tiles, flat tiles, eave-end tiles, and roof ornaments such as chiwen) and utilitarian vessels (e.g., bowls, jars, and pots). The former are concentrated in the three capitals—Shangjing, Zhongjing, and Dongjing—while the latter are more commonly found in elite burials and sites in the Russian Primorye region.
Research has largely followed two approaches: typology and archaeometry. Typological studies, based on form, body, and glaze appearance, generally suggest that architectural glazed pottery was produced locally, whereas utilitarian vessels include both local products and imports from the Central Plains. At Shangjing, eave-end tiles and arc tiles typically have dense red bodies, while sculptural elements such as animal-head ornaments and chiwei show grayish-white bodies similar to those of utilitarian vessels (
IACASS, 1997). Based on the large quantity of architectural components and the presence of distinctive forms such as glazed inverted-basin-shaped column bases—absent in the Central Plains (
Feng 1999;
Peng 2006;
Wang 2006)—some scholars argue for local production. For utilitarian wares, the white-bodied high-quality vessels are interpreted as imported from the Central Plains and sand-tempered coarse-bodied vessels are deemed local (
IACASS 1997).
However, typological study has clear limitations. It relies heavily on visual assessment and often overlooks the possibility that bodies and glazes were made from different raw materials and recipes, potentially sourced from multiple regions. Archaeometric methods like chemical analysis of bodies and glazes, and lead isotope analysis provide new evidence. Existing research indicates that the lead materials used in Bohai glazed ceramics originated from diverse sources, including multiple regions such as the Central Plains and Japan (
Furihata et al. 2015). Furthermore, variations in the provenance of lead materials are observed across different capital cities during distinct periods (
Chang et al. 2023).
The current issues are that architectural glazed ceramics are predominantly surface-collected, lacking stratigraphic information, which complicates dating; furthermore, no definitive glazed ceramic kiln sites have been identified, leaving the question of local production unresolved. This study integrates documentary evidence with scientific analysis to reconstruct the spatiotemporal framework of glaze material sources and examine the production models of architectural glazed ceramics.
2 Archaeological Context and Chronology
2.1 Chronological Framework
Due to the predominantly surface-collected and fragmented nature of architectural glazed ceramics excavated from the Bohai capital, direct typological dating is challenging; this study therefore establishes a chronological framework primarily through integration of historical records concerning the four relocations of the capital and archaeological chronology.
(1) Mid to late 8th century: During the reign of Da Qinmao relocated the capital successively to Zhongjing (c. 755 CE) and Dongjing (785–794 CE), corresponding to the production periods of architectural glazed ceramics from Xigucheng at Zhongjing and Baliancheng at Dongjing.
(2) Mid-9th century: Although palatial structures at Shangjing had already existed in the 8th century, archaeological excavations by scholars including Liu Xiaodong indicate that major palace complexes such as Palaces 1 and 2, along with the main gate of the imperial enclosure (
Liu and Wei 1991), were primarily constructed during the reigns of Great King Da Renxiu and Da Yizhen in the 9th century (
Tuotuo 1974).
(3)9–10th century: Artifacts recovered from the Kraskino site possess well-defined stratigraphic contexts, with radiocarbon and contextual evidence indicating a primary date range of c. 810–930 CE.
2.2 Archeological context
To date, no specialized kilns for glazed pottery production have been identified in the Bohai region. However, several official brick and tile kilns have been discovered in close proximity to the capitals, including the Xingshan kiln complex (located approximately 30 km from Shangjing), which comprises around a dozen kiln structures (Heilongjiang Provincial Institute of Cultural Relics and Archaeology, 1986), and the Shuaiwanzi kiln site near Dongjing (Heilongjiang Provincial Institute of Cultural Relics and Archaeology, 2009). The plan and side views of Kiln 4 in the Xingshan kiln complex are shown in Fig. 1.
Typological comparisons reveal that the unglazed patterned bricks excavated from the Xingshan kiln are virtually identical in form and decoration to those found at the Shangjing palace site (Fig. 2), suggesting its status as an "official kiln" dedicated to capital construction. Given the low firing temperatures required for lead glazes, production would not have necessitated complex, specialized kiln structures. Therefore, these official brick and tile kilns provided the readily available infrastructure for firing the locally sourced clay bodies of the architectural glazed ceramic.
3 Methods and data
As this study focuses on a macro-regional synthesis of glazed pottery production networks, the analytical dataset was compiled from previously published literature.
This study compiles data on architectural glazes from major Bohai sites—Shangjing, Zhongjing Xigu, and Dongjing Baliancheng (
Chang et al. 2021;
Chang et al. 2023)—as well as vessels from the Kraskino site (
Furihata et al. 2015), establishing a lead isotope database of lead glazed pottery. To trace the provenance of lead materials, reference datasets include
sancai ceramics from Tang dynasty kilns at Huangye and Huangpu in China (
Cui et al. 2010), and lead-glazed and lead-glass artifacts from eighth-century Japanese contexts (Fukakusa workshop, Nara-Asuka, and Heijō-kyō) (
Tatsumi et al. 2011). Also, chemical composition data of architectural glazed pottery and plain ceramic roof tiles from the Shangjing site were collated to assess clay provenance (
Chang 2019).
To re-evaluate the production models, bivariate scatter plots (207Pb/204Pb vs. 206Pb/204Pb and 208Pb/206Pb vs. 207Pb/206Pb) were generated to compare the Bohai artifacts against the established isotopic fields of the reference regions. Furthermore, to examine the relationship between clay body categories and glaze provenance at the Kraskino site, a Fisher’s Exact Test was conducted, as the small sample sizes within certain categories precluded the use of standard Chi-square testing.
4 Results
4.1 Ceramic Bodies
Architectural ceramic fragments excavated from the Shangjing site primarily comprise roof tiles, tile ends, and ridge ornaments, characterised by red-fired bodies coated with green or yellow lead glazes. The red body is associated with a low-temperature lead-glazing technique involving two-stage firing: initial high-temperature biscuit firing followed by subsequent low-temperature glaze application.
Typologically, glazed architectural elements and plain tiles exhibit largely consistent forms, with unglazed red-fired components clearly corresponding to their glazed counterparts. These observations suggest that both types likely originated from a shared production system.
Chemical compositional analysis further supports this conclusion: the levels of SiO2, Al2O3, and Fe2O3 in the glazed ceramics are highly consistent with those of unglazed bricks and tiles, yet distinctly different from those of Tang dynasty capital site glazes (Fig. 3), indicating the use of locally sourced clay for the ceramic bodies.
4.2 Lead Isotope Provenance of Glazes
Through scatter plots of 207Pb/204Pb–206Pb/204Pb and 208Pb/206Pb–207Pb/206Pb (Fig. 4, 5), the following sourcing results were obtained:
(1) Shangjing: The lead isotope ratios of the vast majority of architectural glazes (excluding SJC:8) closely align with those from the Tang dynasty Huangye kilns, indicating that the lead ore was sourced from central China.
(2) Zhongjing and Dongjing: The lead isotope characteristics of architectural glazes (excluding XGC:5) are highly consistent with those from the Nara region of Japan, indicating the importation of lead materials from Japan.
(3) Kraskino Site (Yanzhou): The lead sources for 21 examples of utilitarian glazed ceramics exhibit complex origins. Eight are comparable to those from Japan, twelve align with materials from Tang dynasty kiln sites in central China (eight from Huangye and four from Huangpu), while one (K:4) remains unclassified.
5 Discussion
Previously, traditional archaeology frequently conflated the body, glaze, and kiln sites of glazed pottery, broadly regarding the glazed pottery used in the capital’s architecture as "completely locally produced". Although no dedicated ceramic glaze kilns have been identified, the low firing temperatures required for lead glazing suggest production could occur within conventional brick and tile kilns. Therefore, production likely involved the use of local clay, imported high-grade lead from overseas, and took place in official kilns surrounding the capital.
5.1 Glazed tiles in Bohai capitals
5.1.1 8th Century: Japanese Glaze in Zhongjing and Dongjing
Architectural glazed pottery from Zhongjing (n=12) and Dongjing (n=10) features high-iron, low-aluminum bodies consistent with local clay. Supported by nearby brick and tile kilns such as Shuaiwanzi, this confirms the hypothesis of local production and firing. However, lead isotopes indicate their glazes were mainly imported from Japan.
This raw material supply chain closely aligns with the frequent diplomatic interactions between Bohai and Japan during the mid-to-late 8th century. Historical texts record numerous Bohai missions to Japan during the reigns of Kings Wu and Wen (e.g., 12 missions under Da Qinmao), while wooden slips from Heijō Palace verify bilateral trade (
Sakayori 2002a,
2002b). It is highly possible that Dongjing Longyuanfu—the overland starting point of the "Japan Route" (
Ouyang and Song 1975)—imported Japanese lead via maritime networks for capital construction.
5.1.2 9th Century: Central Plains Glaze in Shangjing
Excluding one outlier, five of the six architectural glazed pottery samples from Shangjing exhibit lead isotope signatures identical to those of the Tang dynasty Huangye kilns. Historically, this shift from Japanese to Central Plains glaze sources likely occurred during Shangjing's large-scale expansion in the 9th century, rather than its initial mid-8th century establishment. This is because when An Lushan rebelled against the Tang Dynasty, the Bohai Kingdom adopted a neutral stance and severed official ties with the Tang Dynasty for five years (
Sun and Miao 2014). Meanwhile, Bohai and Japan maintained closer relations during this period in order to jointly resist Silla, which likely involved close material exchanges.
By the 9th century, Bohai's foreign relations shifted significantly. Economically strained, Japan restricted Bohai missions (extending intervals from six to twelve years(
Sun 1990)), cooling bilateral trade. Conversely, Sino-Bohai relations flourished. During the reigns of Da Renxiu and Da Yizhen, over 20 tributary missions were sent to the Tang (
Liu 1975;
Cheng 2013), and Bohai comprehensively adopted Tang administrative and cultural systems. To accommodate booming mutual trade, the Tang established a Bohai Hostel in Dengzhou (
Sun 1990). The abundance of Xing and Changsha kiln-style ceramics unearthed at Shangjing further substantiates the large-scale influx of Tang material culture and handicraft raw materials—including Huangye lead—into Bohai during this period (
Peng and Wang 2021).
5.2 Glazed Vessels: Transregional exchange at Kraskino
As the crucial late-Bohai (9th–10th centuries) port of Yanzhou, Kraskino yielded 21 utilitarian glazed vessels (e.g., bowls, lids) (
Yang and Song 2022)displaying characteristics distinct from the capital's architectural ceramics.
Previous macroscopic observations by Japanese scholars classified these bodies into Types A, B, and C (
Furihata et al. 2015). A Fisher's Exact Test assessing the relationship between glaze provenance (Japan/Huangye/Huangpu) and body type revealed a highly significant statistical correlation (p<0.001) (Table 1.). For instance, all samples utilizing Japanese lead belong to Type A, whereas those with Huangye lead predominantly correspond to Type B.
This strong correlation indicates an absence of cross-combination between clay and glaze types. It strongly implies that the utilitarian glazed vessels at Yanzhou were imported directly as finished products from the Central Plains or Japan, rather than being locally potted and glazed.
Chronologically, vessels with Japanese lead are concentrated in the late 9th century, while those with Central Plains lead mostly date to the late 9th and early 10th centuries. This demonstrates that even after Bohai's late-stage southward shift of its political center, the "Japan Route" remained active. As a trade hub, Yanzhou continued to amass ceramic commodities from both the Tang dynasty and Japan.
6 Conclusion
This study demonstrates that glazed ceramic production in the Bohai was characterized by a dual system combining local manufacture and long-distance material procurement. Architectural ceramics in the capitals were produced locally using indigenous clay resources, but relied on imported lead-based glazes, reflecting technological constraints and selective adaptation. In contrast, utilitarian glazed wares recovered from the port site of Kraskino were primarily imported as finished products, indicating a different mode of supply shaped by maritime trade networks.
A significant temporal shift in glaze provenance is identified. During the 8th century, glaze materials used in Zhongjing and Dongjing were predominantly derived from Japanese sources, while in the 9th century, Shangjing relied increasingly on Tang Chinese sources. This transition corresponds closely with broader geopolitical changes, including the decline of Bohai–Japan relations and the strengthening of Bohai–Tang interactions.
These findings suggest that the Bohai glazed pottery industry operated within a framework of regional specialization, in which raw materials, technologies, and finished products circulated across political boundaries. The study not only refines previous assumptions of local production but also highlights the importance of interregional exchange in shaping technological practices. More broadly, it contributes to our understanding of economic organization and cultural connectivity in the 8-10 century Northeast Asia.
The Author(s) 2026. This article is available under open access at journal.hep.com.cn.
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