In 2022, the Shaanxi Academy of Archaeology conducted archaeological excavations on the Chang'an Campus of Shaanxi Normal University, uncovering a total of 10 Han Dynasty (206 BCE–220 CE) tombs, 6 Tang Dynasty (618–907 CE) tombs, 5 Song Dynasty (960–1279 CE) tombs, 1 Ming-Qing Dynasty (1368–1912 CE, covering both the Ming and Qing dynasties) tomb, and 2 trenches. A variety of funerary objects, including pottery and bronze artifacts, were unearthed. Notably, based on the epitaphs discovered in five of the Song Dynasty tombs, it was determined that these tombs belonged to three successive generations of the Fan clan from Gaoping during the Northern Song period (960–1127 CE). The site selection and arrangement of these tombs adhered to the prevalent " Five Tones Corresponding to Surnames (五音姓利) " theory of the Northern Song era, representing a typical family cemetery laid out in accordance with this principle. The well-preserved cemetery, with its complete array of artifacts, offers valuable insights for studying burial practices and funerary artifact assemblages of the time.

A total of 72 Go stones were unearthed from Tomb M22, the grave of Fan Xiaocun, all positioned to the left of the tomb occupant's skull, as illustrated in Fig. 1a. Among them, there were 37 white stones, measuring 1.5 to 2 centimeters in diameter and 0.4 to 0.5 centimeters in thickness; 33 black stones, with diameters ranging from 1.7 to 2 centimeters and thicknesses from 0.5 to 0.7 centimeters; and 2 patterned stones, each 1.85 centimeters in diameter and 0.46 centimeters thick, as shown in Fig. 1b.

Three representative Go stones were selected for research: a white stone, a black stone, and a patterned stone, as depicted in Fig. 1c. All three stones share similar characteristics, featuring a rounded shape, circular edges, and flat surfaces on both sides, with comparable dimensions. They exhibit minor indentations and chipping along the edges. The white stone displays uneven coloring with visible streaks that possess a pearlescent luster; the black stone is plain, uniformly black throughout; and the patterned stone has a white base with a slightly rough texture, adorned with identical carved floral motifs on both sides—specifically, two chrysanthemum flowers enclosed within a circular border.

The super-depth-of-field micrographs of the three stones are shown in Fig. 2. The white stone has uniform lamellar patterns and a pearlescent luster on its surface; the black stone has a relatively uniform and fine texture; and the patterned stone has a slightly rough surface with soil stains and engraved marks on the edges of the patterns.

The results of X-ray diffraction analysis of the three stones are shown in Fig. 3. The main component of the white stone is aragonite [CaCO₃], the main components of the black stone are kaolinite [Al₂(Si₂O₅)(OH)₄] and quartz [SiO₂], and the main components of the patterned stone are quartz [SiO₂], cristobalite [SiO₂], and mullite [Al₆Si₂O₁₃].

Given the unique characteristics of Go stones and their significance in heritage conservation, damaging methods like thermal expansion analysis are not suitable. Thus, we indirectly infer their firing temperatures from XRD results¹⁶. Kaolinite dehydrates to form metakaolin at temperatures between 550°C and 650°C, with no structural changes¹⁷. When the temperature is raised to 950°C to 1000°C, metakaolin gradually transforms into aluminosilicate spinel. At temperatures approaching 1050°C, aluminosilicate spinel converts into mullite. After 1200°C, mullite gradually develops fully¹⁸. Quartz converts from β-quartz to α-quartz at 573°C. After maintaining this state for a considerable time above 1200°C, α-quartz may convert to cristobalite^19,20. From this, it can be inferred that the firing temperature for black stone was below 950°C, while that for patterned stone was above 1200°C.

To determine the phase of the black substance on the surface of the black stone, a Raman microscope was employed for surface analysis, revealing that the substance was carbon²¹, as illustrated in Fig. 4. The vibrational modes observed at 1382 cm⁻¹ and 1603 cm⁻¹ correspond to the D and G normal modes characteristic of carbon, respectively²².

The production of black ceramic involves various fields such as ceramic materials science, the history of science and technology, and art history, making it an important research topic in both the ceramic and archaeological communities in China. Experts and scholars have proposed various interpretations of its craftsmanship characteristics and technical features, primarily including "carbonized plant admixture", "black slip or clay coating", and "carburization"²³. The "carbonized plant admixture" refers to intentionally incorporating carbonized plant branches, stems, leaves, and rice husks into the clay²⁴. Black ceramic produced using this technique exhibits visible carbon particles from burnt plant stems, leaves, and rice husk fragments under both naked eye observation and microscopic examination. Microscopic examination of the black stone revealed a smooth surface without charred plant stems, leaves, or rice husk fragments, indicating that the stone was not produced using the "carbonized plant admixture" technique. The "black slip or clay coating" refers to a surface colored black by clay glaze, where the coloring element is iron^25,26, or a black ceramic coating applied, primarily made from clay rich in aluminum, potassium, and iron²⁷; Upon observation, the black stone's surface shows no traces of black slip, and XRF analysis results indicate that its iron content does not meet the required level for iron to serve as the coloring element in this technique. This confirms that the stone was not produced using either of these techniques.

Based on the analysis results, it is speculated that the black stone was made using the "carburization" technique^28,29—at temperatures between 400–600°C, the ceramic body undergoes moisture evaporation and organic decomposition, creating a near-vacuum state internally with strong adsorption properties. At this point, within the sealed kiln, plants burn in an oxygen-deprived environment, producing black smoke rich in carbon. The microscopic carbon particles in the smoke gradually penetrate the surface of the ceramic, causing it to turn black and become more dense. The depth of the carbonization layer primarily depends on the duration of the carbonization and insulation process; longer carbonization times result in the core turning black, while shorter times only blacken the surface, leaving the core its original color. Observation shows that the core of the black stone has turned black, indicating a longer carbonization and insulation time.

The analysis results indicate that the primary component of the white stone is aragonite (CaCO₃). Aragonite is a low-temperature mineral that primarily forms through exogenous processes, occurring in modern seabed sediments, clays, and limestone caves. It can also develop via endogenous processes, such as in hot spring deposits and fractures or vesicles within volcanic rocks. Additionally, aragonite can be biologically formed in the shell layers of cephalopods and the nacreous layers of mollusk shells, among other biological settings³⁰. The micrograph of the white stone reveals patterns and luster resembling those of a mollusk shell's nacreous layer, leading to the conclusion that this piece is a shell-derived artifact.

Modern shell Go stones are considered top-tier when produced in Kokura Hama, Hyuga City, Miyazaki Prefecture, Japan, which is currently the only region in the world where shell Go stones are manufactured. However, shell Go stones trace their origins back to the Tang Dynasty (618–907 CE) in China. In the poem "Thanking Someone for Ten Colored Flowered Paper and Go Stones(谢人惠十色花笺并棋子)" by Tang Dynasty poet Qi Ji, the line "Shells carved into stars(海蚌琢成星落落)" indicates that the Go stones were made from shells. A batch of shell pieces with drilled holes, remnants from the production of Go stones during the Tang (618–907 CE) and Song (960–1279 CE) Dynasties, was unearthed in the Old City of Luoyang, Henan Province. One of these shell stones and the original shell mold with drilled holes are housed in the Luoyang Go Museum, as shown in Fig. 5a. Information on well-documented official archaeological finds of shell-made Go stones is presented in Table 2. The discovery of these Go stones and their original shell molds sufficiently demonstrates that Chinese had already mastered the technique of making Go stones from shells as early as the Tang and Song Dynasties.

The analysis results show that the black Go stone is ceramic fired using a carburization process, with no glaze or patterns on the surface. Unglazed ceramic Go stones were the standard style for Go during the Song Dynasty (960–1279 CE), spreading widely due to the development and expansion of ceramic kilns across the country. They were also commonly found in the territories ruled by the Liao Dynasty (907–1125 CE), Western Xia (1038–1227 CE), and Jin Dynasty (1115–1234 CE). This was also the traditional style of Go stones, with most stones from the Pre-Qin period (before 221 BCE) to the Tang Dynasty (618–907 CE) being made of polished stone, featuring solid colors without patterns, a design that continued into the Song Dynasty.

The patterned stone is high-temperature ceramic pieces made from clay containing kaolinite, with patterns created using engraving techniques. The production techniques for patterns primarily fall into two categories: molding and engraving. Engraving involves using a chisel to directly carve intricate lines on the surface of the clay body, while molding uses pre-made clay molds to imprint patterns onto the surface of the clay body, resulting in patterns that resemble relief sculptures. It is worth noting that the origin and evolution of clay molds have a unique cultural context: they were formed through the long-term fusion of foreign religious culture and Chinese folk culture, and were initially used in sacrificial or blessing ceremonies, embodying beliefs in fertility, prosperity, and protection from evil. With the prosperity of the commodity economy and the growth of the urban middle class during the Song Dynasty, the functions of ceramic molds gradually expanded beyond religious contexts, extending into everyday life, commerce, and even entertainment, forming a culturally diverse ecosystem with multiple functions³⁴. This transformation promoted the widespread adoption of mold-printing techniques in the production of Go stones. Compared to the high reliance on craftsmen's skills in engraved Go stones, mold-printing techniques enabled mass production through standardized molds, reducing costs while ensuring the uniformity of patterns. As a result, it became the mainstream choice for producing patterned Go stones at major kiln sites during the Song Dynasty. This chrysanthemum-patterned Go stone has numerous identical or similar counterparts in publicly available materials, as shown in Fig. 6, indicating it was a popular pattern at the time. A batch of Go stones from the Song Dynasty (960–1279 CE) was unearthed at the Hutian Kiln site in Jingdezhen, divided into plain and patterned types, with diameters ranging from 1.3 to 2.1 centimeters and thicknesses from 0.4 to 0.8 centimeters. Additionally, 11 Go stone molds were unearthed, featuring a circular plan view, concave top surface, straight side walls, and flat bottom. These molds also come in plain and patterned varieties, with patterns including gardenia, chrysanthemum, and coin motifs. Some patterned stones correspond with their respective molds, as shown in Fig. 6a and 6b³⁵. Over 220 Go stones were unearthed from the site of Dongjing City of the Northern Song Dynasty (960–1127 CE). All of them are made of porcelain and come in two shapes: flat and round. They are black and white in color, and some of the flat stones are engraved with floral patterns, coin patterns, and dot patterns. They have a diameter of 1 to 2 centimeters, and one of the chrysanthemum pattern stones is shown in Fig. 6c³⁶. The Luoyang Go Museum houses 38 types of clay Go stones and 1 type of porcelain Go stone, with a diameter of 1.5 to 2 centimeters and a thickness of 0.5 to 0.9 centimeters, all circular and uniformly shaped. The Go stones feature a variety of patterns, including plants and flowers, birds, inscriptions, and coins. 2 Go stones with chrysanthemum patterns are shown in Fig. 6d and 6e³⁷.

Based on research into ancient texts, the author has made two speculations about the function of patterned Go stones. The first is that they were used as gifts or betting chips. Since its inception, Go has been closely intertwined with the mundane affairs of life, and the practice of betting in Go games has persisted throughout history. From imperial court games between emperors and generals, to literary gatherings among scholars, to street-corner gambling among commoners, Go gambling has been a common occurrence, with stakes taking various forms: gold and silver to symbolize wealth³⁸; calligraphy and art to express refined tastes; or even intangible items like official positions or poems as stakes, hinting at hidden strategies³⁹. These stakes not only represent the competition between winners and losers, but also reflect the love and cultural pursuits of different social classes towards Go. In this context, it is reasonable to speculate that patterned Go stones were also used as stakes. They are not only carriers of material wealth, but also symbols of cultural taste and social status, making them an excellent choice for showcasing identity and expressing refined tastes in gambling games. The second use is as tactical markers in the game. In the history of Go, the tradition of marking "critical moves" has a long and storied heritage. The Dunhuang Go Classic employs rules as metaphors for strategic key points⁴⁰. The Song Dynasty Go treatise "Thirteen Chapters on the Art of Weiqi" explicitly identifies the core of strategy through concepts like "winning through unconventional yet appropriate moves(奇胜正合)", while its discussions on "sacrificing stones to gain positional advantage(弃子取势)" and "prioritizing initiative over immediate gains(先机后势)" directly highlight the disruptive impact of "critical moves" on the game's dynamics⁴¹. In Japanese classics such as the Xuanxuan Classic of Weiqi, symbols such as " momentum (势)", "urgent(急)", and "slow(缓)" are often used alongside game records to mark key points of attack and defense⁴². These practices reveal that, since ancient times, Go players have isolated and reinforced memory of decisive moves by using symbols, text, or naming conventions, distinguishing them from the broader game context. Extending this logic to patterned Go stones, their physical attributes—such as decorative motifs, contrasting colors, or engraved symbols—could similarly fulfill this marking function. Specific patterns might denote the "divine move" (a brilliantly insightful play), while differently colored stones could flag "game-deciding moves," ensuring that "critical moves" are preserved not only in game records but also materialized within the stones themselves. This method of "embodying strategy in objects" aligns with the Go philosophy that "a single stone can determine the fate of the game(一子定乾坤)", while also providing historical justification for the evolution of patterned stones from mere decorative items into meaningful symbols of strategic mastery.

The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.