A Study of the Technological Features of Bronze Anthropomorphic Sculpture Production from the Jin Dynasty (1115–1234 AD) from the Collection of the IHAE FEB RAS

Abstract

This paper presents the results of a comprehensive technological study of three bronze sculptures from the Jin Empire period (1115–1234 AD) from the collection of the Museum of Archaeology and Ethnography at the Institute of History, Archaeology and Ethnography of the Peoples of the Far East, Far Eastern Branch of the Russian Academy of Sciences (IHAE FEB RAS). Using photon-counting computed tomography (PCCT) and energy-dispersive X-ray spectroscopy (EDS), the production techniques were reconstructed, differences in alloy composition were identified, and specific features of the casting processes were determined. Tomographic analysis revealed two fundamentally different manufacturing approaches: a multi-stage technology involving the use of different alloys and the assembly of separately cast elements, and a single-cast technology with a homogeneous structure. Elemental analysis of the three sculptures using EDS demonstrated significant compositional variability—from 21% to 67% copper and from 9% to 69% tin in different parts of the objects—confirming the complexity of the technological processes. An expanded study of 20 bronze sculptures using portable X-ray fluorescence analysis (pXRF) allowed for the identification of four typological alloy groups: classic balanced lead–tin bronzes (Cu 30–58%, Sn 16–23%, Pb 16–28%), high-lead bronzes (Pb up to 52%), high-tin bronzes (Sn up to 30%), and low-tin alloys (Sn less than 11%). The morphological features of the sculptures suggest one of their possible interpretations as ancestor spirits used in ritual practices. The research findings contribute to the study of Jurchen metallurgical traditions and demonstrate the potential of interdisciplinary, non-destructive analytical methods for reconstructing the technological, social, and cultural aspects of medieval Far Eastern societies.

1. Introduction

Bronze artifacts from the Jin Empire period (1115–1234 AD) are of significant interest for reconstructing the technological traditions of bronze casting and the cultural connections among medieval states of the Far East [1,2]. The collection of the Museum of Archaeology and Ethnography at the Institute of History, Archaeology and Ethnography of the Peoples of the Far East (IHAE), Far Eastern Branch of the Russian Academy of Sciences (FEB RAS), contains a series of unique sculptural images discovered during archaeological investigations of Jurchen culture sites in the territory of modern Primorsky Krai (Figure 1).

The sculptures under consideration belong to the category of prestige goods, accessible only to elite members of society, who used these bronze depictions as a symbol of social status and as cult objects. The production of such sculptures required a high level of skill and knowledge of complex metallurgical technologies, making their study particularly valuable for understanding the level of craft development in medieval Primorye. According to the classification by E.V. Astashenkova [1], Jurchen anthropomorphic depictions are divided into three main groups: (1) shamanic cult images, (2) images associated with Buddhist and Daoist mythology, and (3) images of real historical persons.

Shamanic cult images include figurines of ancestor spirits, which were particularly popular among the Jurchens. To date, 40 such figurines have been discovered in the territories of Primorye and the Amur region. They are cast from bronze, and their height ranges from 3.1 to 6.5 cm. These figurines are characterized by a distinctive body disproportion: a large, massive head constitutes approximately one-third of the entire body, while the legs are rendered in a miniature form (Figure 2).

During casting, the artisans sought to imbue the depictions with a portrait likeness to the deceased ancestor and to denote their social status. All figurines possess distinctly Mongoloid facial features, with elements of clothing and hairstyles rendered with particular care, providing a wealth of factual material for characterizing the people’s material culture. The sculptural images can be categorized into three main types: warriors, officials, and commoners. All figurines depict men and feature a loop on the head for suspension, indicating they were worn on the chest or belt.

The iconographic features of the depictions, including the presence of a vessel in the hands of most figures, allow for their interpretation as ancestor spirits. The vessels are clan lamps, indicating to which clan a particular ancestor spirit belongs and whom it will protect. E.V. Shavkunov notes shared characteristics between Jurchen ancestor spirits and Turkic “babas” and concludes that this cult was borrowed from the ancient Turks, evidencing complex ethnocultural interactions in the region [2].

The study of Jurchen bronze anthropomorphic depictions has a considerable history. A fundamental contribution to the research of Jurchen material culture was made by E.V. Shavkunov, who in 1975 published a work [3], dedicated to bronze anthropomorphic pendant figurines and the ancestor cult among the Jurchens. The researcher conducted a detailed analysis of the sculptures’ iconography, identified their typological features, and established their connection to shamanistic beliefs.

Specific aspects related to the purpose of these figurines and detailed descriptions of their appearance are contained in articles by L.N. Guseva [4,5,6], Artemyeva [7], Kolzunov [8], and Astashenkova [1]. It should be noted that such statuettes are also known in the territory of Manchuria.

Despite a significant body of research devoted to the stylistic, iconographic, and cultural aspects of the bronze sculptures, the technological features of their manufacture have remained insufficiently studied until now. Traditional methods of archaeological analysis do not allow for obtaining detailed information about the internal structure of the artifacts, the sequence of technological operations, and the variability of alloy recipes without compromising the integrity of the objects. In this regard, the application of modern non-destructive methods of physicochemical analysis opens new perspectives for an in-depth study of Jurchen metallurgical traditions.

Within the framework of this study, a technological profile of the bronze sculptures from the Jin Empire period in the IHAE collection was reconstructed through the comprehensive application of non-destructive analytical methods. In recent decades, computed tomography (CT) [9,10,11,12,13,14] have seen widespread use in archaeological studies of metal artifacts worldwide. The recent adoption of advanced Photon-Counting Computed Tomography (PCCT) is pushing this frontier even further. Initially emerged to support medical diagnostics [15], PCCT has enabled researchers and imaging specialists from many areas of science and industry to obtain non-destructively not only detailed three-dimensional data on the internal structure of their objects but also crucial information about the spatial distribution of elements within their composition [16,17,18]. This method can provide unprecedented insights into ancient materials, manufacturing techniques, craftsmanship, and provenance. Energy Dispersive X-ray Fluorescence (EDXRF) analysis is a cornerstone non-destructive technique in modern archaeometry, enabling in situ, multi-elemental characterization of metal artifacts without compromising their integrity. Its utility extends from the study of iconic classical bronzes [19,20,21,22,23,24,25,26].

However, their combined application to the study of bronze sculptures from the Jin Empire period is being undertaken for the first time, which constitutes the scientific novelty of the present research.

2. Materials and Methods

2.1. Research Objects

The objects of this study are bronze sculptures recovered during archaeological expeditions in the Primorsky Krai territory. For detailed analysis using photon-counting computed tomography (PCCT), three representative figurines demonstrating diverse morphological, stylistic, and presumed technological features were selected.

Sculpture No. 1 depicts a person in a traditional long robe, holding a vessel. The figurine was discovered in Dwelling No. 43, located in the central part of the Ananyevskoye settlement in the Nadezhdinsky District of Primorsky Krai [5,27,28].

The figurine’s height is approximately 5.5 cm. A characteristic feature of this artifact is the visually distinct metal composition and an intense green patina. The formation of such a patina, primarily consisting of copper carbonates like malachite (Cu₂CO₃(OH)₂), is a well-documented phenomenon indicative of prolonged burial in soil environments and active corrosion processes [29].

The figurine exhibits iconographic features characteristic of ancestor spirits: a large head with meticulously rendered facial features, including a Mongoloid anthropological type, an elaborately executed hairstyle, and detailed elements of the costume. A suspension loop is present on the head. The clothing consists of a long robe with detailed collar and cuffs. The figure holds a vessel in its hands—a characteristic attribute of ancestor spirits, identified as a clan lamp according to E.V. Shavkunov [2]. Visual inspection reveals a noticeable difference in the surface quality of the left and right halves of the object: one side features a smooth surface with clearly legible relief, while the other exhibits a lumpy texture with multiple imperfections and poorly discernible details (Figure 3).

Sculpture No. 2 depicts an anthropomorphic figure in a reclining position with arms crossed over the chest. The sculpture’s height is approximately 4.8 cm. This figurine is characterized by concise forms and schematically rendered anatomical details, typical of a specific category of Jurchen anthropomorphic depictions. The sculpture is executed in a more schematic manner compared to the first object but retains the primary iconographic attributes, including Mongoloid facial features and the characteristic hairstyle. It was found in Dwelling No. 178 of the Shaigin settlement in the Partizansky District of Primorsky Krai.

The patina on the surface of this object has a darker shade compared to the first sculpture, which may indicate different depositional conditions or a slightly different alloy composition. A suspension loop is present on the head. Visually, the sculpture gives the impression of being a single-cast object without clear signs of assembly from separate elements. The surface is characterized by relative smoothness and homogeneity, although minor defects typical of ancient castings are present (Figure 4).

Sculpture No. 3 is distinguished by its particular morphological complexity and dynamic composition. It is a unique depiction of a winged human in a dynamic flying posture. The height of the sculpture is approximately 5.2 cm. The figurine is depicted with closely joined, slightly bent legs, a head tilted backwards, and a tensed abdomen, creating a sense of movement and flight. This sculpture represents a rare type of anthropomorphic depiction (Figure 5).

Decorative elements include a characteristic rhomboid mesh on the back, vertical grooves on the wings and the surviving arm. The figure is clad in a shirt with narrow sleeves. A wide sash is indicated just above the waist; straps descend from the shoulders to its middle in a V-shape. Below the sash, two bindings are discernible. The figure’s left arm is broken off, as is clearly evident from the nature of the fracture. The right arm, extended to the side, contains a through-hole which could have served a functional purpose, although the suspension loop characteristic of most ancestor spirits was not found on this sculpture. It was discovered incidentally near the village of Novo-Nikolsk, but according to E.V. Shavkunov [2], it also dates to the Jurchen period.

The selection of these three specific sculptures for PCCT examination was based on several factors. Firstly, all three objects fit within the size constraints of the tomographic system used in the present study. Their average dimensions do not exceed 6 × 5 cm. Furthermore, Sculpture No. 1 is morphologically close to a cylindrical shape, which is optimal for X-ray tomography (tomographic studies of high-density objects with more complex shapes can be complicated by reconstruction artifacts associated with uneven absorption of X-ray radiation in different projections). Secondly, these sculptures demonstrate varying degrees of morphological complexity and presumably different technological approaches to manufacture, allowing for a comparative analysis of production traditions. Thirdly, the visual characteristics of the first sculpture’s surface suggest potential technological anomalies requiring detailed investigation.

Description of Sculptures for Elemental Analysis

To obtain a comprehensive overview and reconstruct the alloy recipes used for manufacturing bronze sculptures in the Jin Empire, an additional 17 similar ancestor spirit figurines from the same collection were included in the study. These were investigated using portable X-ray fluorescence analysis (pXRF) Olympus Delta Professional DP 4000 (Tokyo, Japan) to determine the elemental characteristics of their alloys. Consequently, the total sample for elemental analysis comprised 20 bronze sculptures. This sample size ensures the statistical representativeness of the results and allows for the identification of both general patterns in metallurgical traditions and individual features of specific artifacts.

The state of preservation of the objects varies: some figurines are almost undamaged and retain all structural elements, including suspension loops, while others exhibit mechanical damage, loss of specific parts (arms, legs, headgear), and varying degrees of surface corrosion. The patina on the surface of the sculptures ranges in color from light green to dark brown, which may reflect differences in alloy composition as well as varying soil deposition conditions.

2.2. Research Methods

2.2.1. Photon-Counting Computed Tomography (PCCT): Equipment and Research Parameters

Tomographic reconstructions of the three bronze sculptures were performed at Lomonosov Moscow State University. The investigation was conducted using a photon-counting computed tomography scanner manufactured by MARS Bioimaging Ltd. (Christchurch, New Zealand).

The scanner is equipped with hybrid semiconductor Medipix 3RX Spectroscopic detectors [An introduction to the Medipix family ASICs—[30]] with 1 mm thick CdZnTe sensors, developed by the international Medipix 3 collaboration under the auspices of CERN (Geneva, Switzerland). The use of such detectors enables not only the registration of the overall intensity of X-ray radiation after its transmission through an object but also the assessment of its spectrum, i.e., determining the dependence of the X-ray attenuation coefficient on the energy of the X-ray photons. This allows for tomographic reconstructions that account for both X-ray density and the chemical composition of the object’s structures.

The geometric resolution of the detector is 110 µm, enabling tomographic reconstructions with a voxel size of up to 60 µm and providing detailed visualization of the internal structure of small archaeological artifacts. The energy resolution of the detector is approximately 7%, allowing for the differentiation of structures dominated by chemical elements whose K-absorption edges differ by approximately 5 keV. The actual energy resolution for reconstructions of high-density objects, particularly metal artifacts composed predominantly of elements with Z > 50 (Sn), is lower due to noise associated with the detection of scattered photons. Nevertheless, it is sufficient for identifying characteristic features of the absorption spectra of the main components of bronze alloys (Cu, Sn, Pb) and for differentiating the metal matrix from non-metallic inclusions.

Scanning was performed with a tube voltage of 120 kV and a current of 20 µA. The exposure time varied from 150 to 200 ms. The combination of tube voltage, current, and exposure time was selected to ensure that the number of detector pixels registering more than 4095 events per exposure time for one or several thresholds in flat-field mode (without an object) did not exceed 20%. The geometric magnification of the system was 1.76. Overview scans were performed using a single energy threshold of 30 keV; for scans assessing the absorption spectra of the samples, thresholds of 30, 45, 60, 75, and 90 keV were used. The projection step was 0.5° or 1° (720 or 360 projections per rotation), depending on the object’s size. The full scanning cycle for one object, including flat-field projection registration, took between 1.5 and 2.5 h. Reconstruction was performed using the scanner’s built-in software with a voxel size of 60 µm and energy windows of 7–30, 30–45, 45–60, and 60–75 keV. Energy-integrative reconstruction was performed for overview scans. Visualization and analysis of the tomographic reconstructions were conducted using the MARS Vision 2.0 software (MARS Bioimaging Ltd., Christchurch, New Zealand).

Due to the strict time constraints imposed by the museum status of the specimens, the entire tomographic research program—including scanning, reconstruction, analysis, and additional work—had to be completed within a single work week. This is why it was necessary to conduct preliminary testing of the scanning protocols on more readily available objects.

Preliminary Studies. Preparation for the tomographic study involved several critical stages aimed at optimizing the scanning parameters and ensuring the correctness of the obtained results, considering the limited time available for working with the primary samples.

The preparation was conducted using a set of four bronze buckles of varying configurations from the archaeological collection of IHAE FEB RAS. The selection of these samples was driven by the need to approximate the scanning conditions as closely as possible to those of the main objects under investigation.

Conducting preliminary studies without using the primary artifacts was possible due to the identical or highly similar metallurgical composition of the buckles and the studied sculptures. Preliminary express analysis using XRF showed that all objects were made of tin-lead bronzes with similar ratios of the main components, ensuring comparable characteristics of interaction with X-ray radiation. This allowed for the configuration of the PCCT parameters (X-ray tube voltage and current, detector energy channel thresholds, exposure time) to ensure optimal image quality for metallic objects of this specific composition and size range.

2.2.2. Energy-Dispersive X-Ray Spectroscopy (EDS)

Surface elemental composition was determined using EDS on a Shimadzu EDX-7000 spectrometer (Tokyo, Japan), equipped with a Rhodium-anode X-ray tube capable of generating radiation with energy up to 50 keV. This enables the excitation of characteristic X-ray emission from elements ranging from sodium (Z = 11) to uranium (Z = 92). The diameter of the analyzed area was approximately 1–3 mm, allowing for local analysis of individual morphological elements of the sculptures (face, clothing, limbs, fastening elements).

EDS analysis was performed under atmospheric conditions. The spectrum accumulation time for each point was 60 s. To minimize errors associated with sample geometry, objects were securely fixed on the stage, and their orientation was adjusted to achieve the greatest possible normality of the analyzed micro-area relative to the detector axis. The employed collimator aperture width (~1–3 mm) contributed to averaging data across the micro-relief of the selected zones.

Selection of Measurement Points. A critical aspect of EDS analysis of archaeological metal objects is the correct selection of measurement areas. The prolonged burial of bronze artifacts in soil leads to the formation of a layer of corrosion products—patina—on their surface. This patina can have a complex, multi-layered composition and differ significantly in elemental composition from the original alloy. The patina is typically enriched with elements from the surrounding soil (Si, Al, Fe, Ca) and depleted in the most mobile components of the alloy. Furthermore, selective leaching of individual alloy components can occur during corrosion, altering the ratio of the main elements in the surface layer. The surface topography, which is far from a polished state, is also of considerable importance.

To minimize the influence of corrosion processes on the results, measurements were preferably conducted on flat surface areas with minimal patina coverage, as well as in recesses of the relief where the patina might have been mechanically removed during archaeological excavation or subsequent handling of the find.

The total number of measurement points for the three sculptures was 36. This provided a detailed characterization of the spatial distribution of the elemental composition and allowed for the identification of both local heterogeneities related to manufacturing techniques and general patterns in the recipes of the alloys used.

2.2.3. Portable X-Ray Fluorescence Analysis (pXRF)

To obtain a comprehensive overview of the variability in the elemental composition of the bronze sculptures from the collection and to reconstruct the typical alloy recipes used by the Jin Empire for manufacturing such items, X-ray fluorescence analysis was performed on an expanded sample set comprising 20 sculptures (the three objects studied by PCCT and EDS, plus 17 additional artifacts).

The analysis was carried out using an Olympus Delta Professional DP 4000 portable X-ray fluorescence analyzer (Tokyo, Japan), equipped with a miniature X-ray tube with a voltage of up to 40 kV and a silicon drift detector (SDD) providing an energy resolution of approximately 140–150 eV. The diameter of the analyzed spot is approximately 3–5 mm, depending on the distance from the detector to the object’s surface. The analyzer allows for the determination of elemental composition in the range from magnesium (Z = 12) to uranium (Z = 92), with detection limits for most elements at the level of 0.01–0.1 weight percent, depending on the sample matrix and measurement time [31]. Portable XRF analysis has a penetration depth of tens of microns and reflects the composition of the surface layer. Therefore, for archaeometallurgical objects, the data are interpreted as semi-quantitative indicators of general technological trends, not as the precise composition of the original alloy.

For pXRF analysis, the portable analyzer was used in handheld mode. The measurement window of the device, surrounded by its protective cap, was manually pressed firmly against the selected area of the sculpture’s surface, ensuring a constant working distance. Measurements were performed with the object securely placed on a laboratory table, allowing the operator to reliably hold the instrument’s position to minimize errors.

For each sculpture, one to three measurements were taken on different areas of the surface, with subsequent averaging of the results. The spectrum acquisition time was 40 s, ensuring sufficient accuracy for determining the main components of bronze alloys (copper, tin, lead) and major impurity elements. Measurements were conducted in the “Alloy” analysis mode, optimized for determining the composition of copper and other metal alloys.

Quantitative analysis was performed using factory calibrations based on an extensive database of certified reference materials.

The determination of major and impurity components, along with the comparison of their concentration ratios, was performed by visualizing the pXRF data through the construction of box-and-whisker plots using descriptive statistics. These plots display (1) central statistical values (median and mean); (2) range statistics (lower and upper quartiles); (3) minimum and maximum sample values; (4) the lower (25%) and upper (75%) quartile points, which contain 50% of the concentration values (interquartile range) for each chemical element; and (5) outliers—values significantly different from the rest in the sample. This type of diagram is well-established for analyzing large datasets, as it is one of the simplest and most accessible methods for identifying variance and asymmetry in a statistical sample [32].

3. Results

3.1. Results of PCCT Analysis of the Three Sculptures

The process of interpreting the obtained PCCT tomograms involved correlating the virtual reconstructions with the original objects to verify the results and identify correlations between the internal structure and external morphological features.

3.1.1. Sculpture No. 1

Internal Structure and Defects. The first research object represents the most technologically complex among the three studied sculptures (Figure 6). PCCT analysis revealed pronounced material heterogeneity, with the presence of multiple cavities of varying sizes and areas of the object exhibiting uneven X-ray density. The internal structure is characterized by the presence of air bubbles distributed unevenly throughout the volume of the sculpture, indicating insufficient degassing of the melt during casting or the entrapment of gas during mold filling.

Of particular interest are inclusions with X-ray density differing from the metallic matrix. Based on their characteristics, these can be interpreted as foreign non-metallic particles.

The use of PCCT made it possible to distinguish air bubbles, characterized by a complete absence of X-ray absorption, from inclusions with low but finite density, whose absorption spectrum differs from the base material by a sharp decrease in the attenuation coefficient at high X-ray photon energies, indicating their likely nature as particles of molding material—sand or clay—used in the manufacture of the casting mold (Figure 7).

The presence of such inclusions indicates that during the casting process, the inner surface of the mold partially deteriorated, allowing individual particles to enter the melt. This is a characteristic sign of the use of disposable clay or sand molds, which was typical for small-scale bronze casting in various pre-modern societies, including the medieval period in East Asia [33].

The distribution of defects throughout the sculpture’s volume is uneven: the highest concentration of porosity and inclusions is observed in the upper part of the torso and in the transition area from the torso to the head. This may be related to the specifics of how the mold was filled with the melt and its subsequent solidification.

Casting Features and Indications of Process Interruption. One of the most significant features identified by the PCCT of the first sculpture is the indistinct boundaries between different sections of the object, which is attributed to the specificities of the casting technology. A detailed analysis of the reconstructions established that casting occurred with the mold in a horizontal position, as evidenced by the pattern of defect distribution and the orientation of air inclusions.

An important observation is the presence of a clearly defined density boundary running vertically through the central part of the figurine, dividing it into left and right halves. The nature of this boundary, manifesting as a gradual transition of a low-density zone between two areas of higher density, indicates an interruption in the pouring process followed by its resumption.

The mechanism for the formation of such a structure can be reconstructed as follows. The casting mold was positioned horizontally, likely with the left side facing down. Initially, approximately half of the mold’s volume was filled, after which the pouring process was interrupted for an undetermined reason (possibly due to an insufficient volume of prepared melt, technical issues with the crucible or ladle, or other factors). During the pause, the surface of the already poured metal began to crystallize, forming a thin crust of solid alloy. When pouring resumed, the new portion of the melt partially remelted this crust, but complete homogenization of the two metal portions did not occur, leading to the formation of a low-density zone at their interface.

This interpretation is supported by visual observations of the sculpture’s surface: the left half of the figurine has a relatively smooth surface with clearly legible relief, well-defined details of clothing and anatomical elements, while the right half is characterized by a lumpy texture with multiple surface defects, blurred relief, and poorly executed details. Such a difference in surface quality is typical for situations where the first portion of the melt has partially solidified before the second portion arrives, leading to the formation of a defective structure in the latter part of the casting.

In the lower part of the figurine, near the pouring layer boundary, an inclusion with a complex S-shape is also identified (shown in Figure 6). It is located in the same plane as the layer boundary and exhibits a lower X-ray density than the base material. This inclusion was only visualized on energy-integrating reconstructions, making analysis of its absorption spectra impossible. However, based on a combination of features (location, shape, X-ray density), it can be hypothesized that this inclusion represents a metallic structure (wire) made of an alloy similar to the base material but with a reduced content of “heavy” metals (Sn, Pb). It is assumed that this inclusion was intentionally introduced during casting to improve contact between the pouring layers. Additional research, such as neutron tomography, is required to clarify the nature of this inclusion.

Structural Elements and Post-Casting Processing. PCCT analysis revealed that Sculpture No. 1 is a composite object, whose individual elements were manufactured separately and subsequently joined during post-casting processing. The most obvious evidence of this construction is the figurine’s head, which was determined to have been fabricated independently.

A double line is detected across the entire surface of the head—an artifact that can be interpreted as a seam from the mold used for the separate manufacture of this element. Such a double line forms when a part is cast in a composite mold consisting of two halves, the joining line of which leaves a characteristic mark on the casting’s surface.

Additional hairstyle elements located on the head were also attached after the main casting process. The PCCT data show that these elements have a different internal structure compared to the main volume of the head and are characterized by zones of altered density at the boundary with the main part, which is typical for soldered joints (Figure 8).

The nature of the joint indicates poor workmanship: the loop shows a poor fit to the head’s surface, with significant gaps visible between the loop and the head. PCCT data reveal these gaps are filled with a material of lower X-ray density compared to the base alloy. This observation, combined with the statistically significant difference in the elemental composition (particularly the elevated lead content) of the loop (

Table 1. Elemental composition of the bronze sculptures’ surfaces at local measurement areas (wt. %). The measurement points correspond to the designations in Figure 9.

Measurement Point (Figure 9)	Measurement Area	Concentration, wt.%
		Cu	Sn	Pb	Si	Zn	Fe	Ag	Ni	P	Ca
Bronze Sculpture No. 1
A1	Suspension Loop	45.7	17.3	27.7		5.9	3.4
A2	Suspension Loop	36.7	31.5	14.2	9.1	6.6	1.6	0.3
A3	Face	36.3	38.1	13.1	8.4	2.3	1.5	0.3
A4	Right Ear	30.9	37.9	16.5	8.3	3.9	2	0.5
A5	Left Ear	33.1	38.9	13.9	9.8	2.3	1.6	0.4
A6	Front Side, 1	38.5	26.2	19.7	10.4	3.2	1.6	0.4
A7	Front Side, 2	40.4	20.8	24	8.8	5.7		0.3
A8	Back of Head	37.3	34.2	12.9	10.2	3.2	1.8	0.4
A9	Reverse Side, 1	34.8	27.4	24.3	8.2	3.5	1.5	0.3
A10	Reverse Side, 2	40	24.9	21.9	8.9	2.8	1.2	0.3
A11	Left Side	67.5	9.7	12.4		10.1	0.3
A12	Right Side	32.7	37.7	16.9	7.2	3.1	2.1	0.3
A13	Leg	21	68.8	6.1		1.2	2.2	0.7
Bronze Sculpture No. 2
B1	Hair	46.2	25.4	14	13.3		0.8	0.2	0.1
B2	Face	31.4	21.7	16.3	26.3		4.3
B3	Left Arm	38.7	38.9	21.3	0.5		0.2	0.3	0.1
B4	Right Arm	39.9	29.6	20.2	9.7		0.2	0.3	0.1
B5	Back of Head	39.7	27.4	24	8.4		0.2	0.2	0.1
B6	Back, 1	34.8	29.4	20.9	10.6		0.2	0.2	0.1	3.8
B7	Back, 2	48.8	24.5	13.3	10.7		0.1	0.2	0.1	2.3
B8	Right Leg	41.4	34.2	23.6	0.1		0.3	0.3	0.1
B9	Left Leg	36.1	29.2	25.1	9.2		0.1	0.2	0.1
Bronze Sculpture No. 3
C1	Head	38.3	28.9	28.9		0.6	3.3
C2	Chest	25.5	30.1	23.2	17	0.4	3.4				0.4
C3	Abdomen,1	44.7	35.2	18.1	0.6	0.4	0.8	0.2
C4	Abdomen, 2	36.7	28.4	17.7	12.7	0.3	1	0.1		3.1
C5	Right Leg	32.4	32.8	22	10.2	0.4	2	0.2
C6	Left Leg	23.1	32.4	31.4	10.5	0.3	2.3
C7	Ear	43.8	21	17.8	13.1	1.1	2.9	0.3
C8	Hair	30.5	35.2	22.5	10.1	0.3	1.2	0.2
C9	Back of Head	37.2	28.2	18.4	11.4	0.3	1.2	0.2		3.1
C10	Back, 1	34.8	33.5	19.9	9.8	0.4	1.4	0.2
C11	Back, 2	33.3	32.5	17.3	14.5	0.4	1.8	0.2
C12	Left Leg, Reverse Side	27.7	33.7	18.2	14.7	0.4	2			3.3
C13	Right Leg, Reverse Side	24.3	32.3	29.2	12.2	0.3	1	0.2			0.5
C14	Left Wing	25.6	43.8	27.5		0.3	2.5	0.3

, points A1, A2) compared to the head, allows this material to be identified as solder or its corrosion products. Visually and based on the ECT images, it is evident that the attachment was made unprofessionally, possibly in haste or using suboptimal technical methods (Figure 9).

A separate question concerns the collar of the figurine’s garment, which in the PCCT reconstructions shows a substantially higher X-ray density compared to the surrounding areas. This could point to one of several scenarios. The first scenario suggests post-processing of this area using an additional material—possibly the application of a decorative coating made from an alloy with a higher content of heavy elements, or inlay work. The second scenario relates to the possibility of mechanical working of this area (chasing, engraving), which could have led to compaction of the surface metal layer. However, it should be noted that the final interpretation of this observation is complicated by the high X-ray density of the figurine’s material and the specific geometry of the neck area (circular thinning), which can lead to reconstruction artifacts in the form of a false increase in the calculated attenuation coefficients (Figure 10).

This issue requires further investigation using optical and electron microscopy of a surface cross-section, which is not permissible as it would lead to the destruction of the sample.

3.1.2. Sculpture No. 2

Structural Characteristics. The second research object (Figure 11) demonstrates a fundamentally different technological approach to manufacture.

The object represents a uniform and solid casting, whose internal structure shows no signs of assembly from separate elements or the joining of different parts. A homogeneous X-ray density is observed throughout the volume of the sculpture, without sharp boundaries or zones with anomalous characteristics, indicating a single-pour process of filling the mold with melt, without technological pauses or interruptions. The item was apparently cast horizontally on one of its sides, as suggested by the distribution pattern of minor defects, which tend to concentrate in the upper part of the casting. At the same time, no clear boundary between different portions of metal, similar to that observed in the first sculpture, is visualized.

The overall level of porosity in the second sculpture is significantly lower than in the first, indicating more thorough melt preparation, possibly including holding at temperature for degassing, or the use of a more advanced mold-filling technique that minimized gas entrapment. Non-metallic inclusions, if present, are significantly fewer in number and smaller in size, suggesting better quality of the casting mold or more meticulous preparation.

Manufacturing and Use-Related Defects. The most significant manufacturing defect is an elongated air bubble discovered inside the sculpture’s right arm (Figure 11). The bubble has a characteristic elongated shape oriented along the axis of the arm, measuring approximately 3–4 mm in length and about 0.5–0.8 mm in width. The morphology of this defect is not typical for ordinary gas bubbles formed by the release of gases dissolved in the melt during crystallization, which usually have a near-spherical shape. The elongated form and specific localization of this inclusion allow it to be interpreted as a shrinkage defect.

The mechanism for the formation of such a defect is related to the decrease in metal volume during crystallization (for typical bronzes, shrinkage is 3–5% by volume). If the casting configuration creates isolated volumes of melt that solidify last and lack effective feeding of liquid metal from other parts of the mold, shrinkage cavities form within them. The thin, elongated shape of the arm creates precisely such conditions, leading to the formation of this characteristic linear defect. It is important to note that such a defect is an inevitable consequence of the part’s geometry and does not indicate low-quality workmanship by the artisan, but rather reflects the limitations of the casting technology of that time.

A second identified defect is localized in the area of the suspension loop on the head of the figurine. The loop exhibits a deformation of its hole, which in its nature differs from manufacturing defects and should be classified as use-related damage. The hole of the loop, which initially probably had a round or oval shape, has become stretched and deformed in one direction. Such deformation is characteristic of damage resulting from prolonged wearing of the item on a cord or strap: under the weight of the figurine and the constant tilting during wear, the relatively soft bronze metal of the loop gradually stretches, leading to a change in the hole’s shape.

Based on the PCCT data, it is difficult to determine how the hole in the loop was initially made—whether it was cast along with the loop, or whether the loop was cast solid and the hole was formed after casting by drilling or piercing. This question requires further investigation with higher spatial resolution, possibly using microfocus X-ray tomography or direct microscopic examination of the hole’s internal surface, which might retain traces of the tool used to form it.

3.1.3. Sculpture No. 3: Morphologically Complex Composition

Internal Structure. The third object, due to its greatest morphological complexity and the presence of protruding elements, required more time and specialized algorithms for correcting the PCCT study compared to the other sculptures (Figure 12).

The PCCT results demonstrate that the sculpture is a single-cast object with high density and homogeneity of its internal structure. The object itself is characterized as a dense, solid pour without significant internal cavities or inclusions. The X-ray density is distributed uniformly throughout the volume of the object, except for several specific zones which will be discussed below.

The level of internal porosity is minimal and does not exceed values typical for high-quality ancient bronze castings. Individual small gas bubbles less than 0.5 mm in size are visualized sporadically; their distribution shows no specific pattern and does not concentrate in certain areas, indicating good degassing of the melt and efficient filling of the mold (Figure 13).

Zones of Reduced Density and Their Interpretation. In the transition area where the wings meet the body of the figurine, symmetrically located zones with reduced X-ray density are detected. These zones have a characteristic localization—at the junction of the wing with the torso. The extent of each zone is approximately 2–3 mm; they are symmetrical relative to the figurine’s longitudinal axis and have similar morphology.

The reduction in X-ray density in these zones is approximately 10–15% relative to the density of the surrounding metal, which is significant and cannot be explained by measurement noise or reconstruction artifacts. The boundaries of the low-density zones are relatively diffuse, without a sharp transition, which distinguishes them from boundaries characteristic of joining separately made parts by hard soldering.

An alternative interpretation links these zones not to post-processing, but to specific features of the casting process itself. When filling a complex mold with thin protruding elements, a situation can arise where different parts of the mold are filled with melt with a slight time delay. The wings, being thin, flat projections, might have been filled last with already partially cooled metal. In this case, an area with a slightly altered microstructure could form at the junction of the metal flows that filled the main body and the wings, which manifests as a zone of reduced density in the tomograms. It is important to note that in this scenario, the object remains a single casting, and the observed zones are not the junctions of separate parts but rather artifacts of the complex mold-filling process.

Crucial for distinguishing between these two scenarios is the absence, in the tomograms, of evidence suggesting the wings were initially cast separately. No separate casting shells characteristic of independently manufactured parts are visualized, nor are there traces of mechanical processing on the wing ends, which would have been necessary to prepare them for subsequent soldering. These observations favor the interpretation of the second scenario—single casting with a complex mold-filling process.

An interesting feature of the third sculpture is the presence of a through-hole in the preserved right hand of the figurine. The hole has a rounded shape, approximately 1.5–2 mm in diameter, and passes through the entire thickness of the arm. Based on its morphology and location, this hole could have been used for suspending the object. However, a detailed tomographic analysis of the hole’s internal surface and the surrounding areas did not reveal traces of wear or deformation, which would be inevitable if the figurine had been worn for a prolonged period on a cord threaded through this hole. The absence of such traces suggests that the object was not used as a pendant. Similar figurines with holes in their hands are found among Jurchen-period artifacts discovered in China. However, these also do not show clear evidence of the holes being used for suspension and lack the suspension loops on the head characteristic of ancestor spirits. This suggests that sculptures of this type might have had a different functional purpose or mode of display compared to standard depictions of ancestor spirits.

3.2. Results of Elemental Analysis by EDS

The results of the elemental composition analysis of surface areas at the local points marked in Figure 14 are presented in Table 1. To simplify the analysis process, these results are visualized as box-and-whisker plots in Figure 15.

Qualitative analysis of the obtained spectra confirmed that all three investigated objects belong to the Cu-Sn-Pb (copper-tin-lead) alloy system, representing tin-lead bronze. This is one of the most common types of alloys in Far Eastern archaeological contexts, appearing in the region from approximately the 7th century AD and continuing in active use throughout the existence of the Jin Empire in Primorsky Krai and the Eastern Xia state in the Amur region.

All obtained spectra show the presence of significant amounts of silicon (Si), iron (Fe), and in some cases also aluminum (Al), calcium (Ca), phosphorus (P), and other elements that are not typical alloying components of ancient bronzes. As noted in the methodology section, the presence of these elements is in most cases associated with residual corrosion products on the analyzed surface, soil particles, or other surface contaminants. In the quantitative interpretation of the alloy composition, these elements were considered impurities. Primary attention was paid to the content and ratio of the three main bronze components—copper, tin, and lead.

3.2.1. Sculpture No. 1: Heterogeneity of Elemental Composition

Analysis of the elemental composition of the first sculpture revealed pronounced heterogeneity, which correlates well with the internal structural features identified by PCCT and confirms the hypothesis of a complex, multi-stage manufacturing process for this artifact.

Analysis of the Suspension Loop and Fastening Elements. The results from two points located on the suspension loop demonstrated a substantial difference in the elemental composition of this part compared to the main body of the sculpture. This confirms the PCCT finding that it was manufactured separately and attached subsequently.

At the first point on the loop (Spectrum No. 1), high copper content (45.68%), significant lead content (27.74%), and relatively low tin content (17.33%) were observed. Additionally, the presence of zinc (5.89%) and iron (3.36%) was recorded. The second point on the loop (Spectrum No. 2) shows a somewhat different composition: copper 36.51%, tin 31.53%, lead 14.24%, along with a high silicon content (9.10%), likely due to the local presence of corrosion products or residual molding material on the surface.

The average composition of the loop (excluding the anomalously high silicon value in the second point) is characterized by approximately 41% copper, 24% tin, and 21% lead. In comparison, the main body of the sculpture demonstrates significantly different ratios of these elements (discussed in detail below), confirming the use of different alloys for manufacturing the loop and the main part of the object.

The comparison of tin content is particularly indicative: in the loop, it averages 17–32% (depending on the measurement point), whereas in the main body, the tin content varies in the range of 20–39%, with a predominance of higher values. The lead content in the loop (14–28%) also differs from its content in most points on the main body. Such differences cannot be explained solely by the influence of corrosion or surface contamination and indicate real differences in metallurgical composition.

Differences Between the Left and Right Halves. The most significant differences in elemental composition were found when comparing the left and right halves of the sculpture.

Measurement point No. 11, located on the left side of the figurine in the area of the shoulder or upper arm, demonstrated the following composition: copper 67.52%, tin 9.67%, lead 12.44%, zinc 10.09%. This composition sharply differs from that typical for bronzes of this period and is characterized by an anomalously high copper content with very low tin content. For comparison, measurement point No. 12, located symmetrically on the right side of the figurine relative to point No. 11, showed a completely different composition: copper 32.71%, tin 37.72%, lead 16.86%. The tin content here is almost four times higher than on the left side, while the copper content is, conversely, two times lower. These results align well with the assumption of a technological pause during the casting process. An alternative explanation could be related to processes occurring within the melt itself during the pause. It is known that in ternary Cu-Sn-Pb alloys, liquation—gravitational segregation of components with different densities—can occur. Lead, having the highest density among the bronze components, tends to sink, while lighter components concentrate in the upper parts of the melt. If the technological pause was sufficiently long and the melt temperature was not high enough for effective stirring, such liquation could have resulted in the second portion of metal poured into the mold having a composition enriched in copper due to the settling of lead and partial crystallization of the tin-based eutectic.

Additional confirmation for the interrupted casting interpretation comes from the analysis of the surface appearance in these areas. The left half of the figurine has a smooth, high-quality surface with clear relief, while the right half is characterized by numerous surface defects. This difference can be explained by the fact that the left half, poured first, crystallized under favorable conditions with direct contact between the melt and the mold, whereas the right half formed under conditions involving the partially solidified metal of the first portion, leading to the formation of a defective structure.

Analysis of several other points on the torso confirms the overall picture of lateral heterogeneity. Points on the front and reverse sides of the torso (Spectra Nos. 6, 7, 9, 10) show intermediate values for copper (34–40%), tin (21–27%), and lead (19–24%) content. This may reflect the mixing of two different metal portions in the central part of the object or a gradient distribution of components due to diffusion processes.

Composition of the Leg Area. The result from point No. 13, located in the area of the figurine’s legs, deserves special attention. The recorded composition is unique and has no analogues among all other investigated points: copper 20.98%, tin 68.79%, lead 6.12%. The tin content here is anomalously high—nearly 69%, which is more than double the typical values for ancient tin bronzes and approaches the composition of intermetallic compounds in the Cu-Sn system.

Such a high tin content cannot be explained by random variations within a single alloy and indicates that this structural element was made from a fundamentally different material. Tomographic data also demonstrate a difference in X-ray density in the leg area, which correlates with the difference in elemental composition. The high tin content provides higher X-ray density (tin has an atomic number of 50, significantly higher than copper’s atomic number of 29), which is manifested in the tomograms.

Interpretation of this observation suggests that the sculpture’s legs were manufactured separately from the main body.

The composition of the head area (Spectra Nos. 3, 4, 5, 8) demonstrates a relatively homogeneous composition with copper content of 30–37%, tin 34–39%, and lead 13–17%. This composition differs from both the loop and the left side of the torso but is close to the composition of the right side of the torso. This may indicate that the head was made from the same alloy used for the second portion poured into the torso, or that the head was attached to the torso at a stage when the second half of the torso had already been formed.

3.2.2. Sculpture No. 2: Relative Homogeneity of Composition

The sculpture is cast from a tin-lead bronze (Cu 36–42%, Sn 29–39%, Pb 20–25%), where the high lead content provided excellent casting properties due to increased fluidity and better mold filling.

Point No. 2, located on the face of the figurine, showed significantly lower copper (31.43%) and tin (21.67%) content alongside high silicon content (26.28%). Given that the face is one of the most protruding parts of the sculpture, the high silicon content here is likely related to more intensive corrosion processes and the formation of silicate-containing corrosion products on the surface. This explanation is also supported by the elevated iron content (4.30%) at this point, which may be associated with the incorporation of iron-containing minerals from the soil into the corrosion layer.

Two points on the back of the figurine (Spectra Nos. 6 and 7) demonstrate an interesting feature—the presence of phosphorus in concentrations of 3.84% and 2.34%, respectively. The localization of phosphorus specifically in the back area might indicate that this part of the sculpture was filled with melt to which a phosphorus-containing deoxidizer had been added, whereas this was not done for other parts. Alternatively, the uneven distribution of phosphorus could be related to liquation processes in the melt—phosphorus, which forms specific intermetallic phases with copper, can redistribute during crystallization, concentrating in certain areas of the casting.

The small amounts of iron (Fe), silver (Ag), and nickel (Ni), recorded in all points at concentrations from hundredths to several tenths of a percent, represent typical impurities in ancient bronzes, associated with the characteristics of the original ores and smelting technology. These elements are usually not added intentionally but are present as natural impurities in copper and tin ores and transfer into the alloy during metallurgical operations.

3.2.3. Sculpture No. 3: Variability in Component Distribution

The object is made of tin-lead bronze, whose composition generally corresponds to the typical metallurgical traditions of this period (copper from 23.08% to 44.73%, tin from 21.00% to 43.76%, lead from 17.34% to 31.39%).

Point No. 1, located on the head, showed the composition: copper 38.32%, tin 28.89%, lead 28.92%, iron 3.29%. The high and almost equal content of tin and lead, with moderate copper content, characterizes this as a balanced casting bronze. Point No. 7, located on the ear, demonstrates a substantially different composition: copper 43.82%, tin 21.00%, lead 17.75%, silicon 13.12%. The higher copper content with reduced tin and lead may reflect local liquation processes or specific solidification conditions in this thin, protruding detail.

Two points on the abdomen (Spectra Nos. 3 and 4) show significant differences between them, despite being located on the same morphological element. Point No. 3 showed: copper 44.73%, tin 35.19%, lead 18.11%, while point No. 4 showed: copper 36.60%, tin 28.40%, lead 17.71%, silicon 12.70%. The difference in copper content is over 8%, which is substantial and cannot be fully explained by analytical errors or the influence of corrosion.

Of particular interest is the composition of the left wing (Spectrum No. 14): copper 25.58%, tin 43.76%, lead 27.53%. This is the only point in the entire sample of three sculptures where the tin content exceeds 43%, approaching the composition of high-tin bronzes. Such a composition provides increased hardness and a specific silvery surface color characteristic of high-tin alloys. It is interesting to correlate this observation with the results of the tomographic study, which revealed zones of reduced X-ray density at the junction of the wings with the body.

Both legs of the sculpture (right—Spectrum No. 5, left—Spectrum No. 6, and their reverse sides—Spectra No. 12 and 13) demonstrate a relatively homogeneous composition with some variations, likely related to different degrees of surface corrosion at the analyzed points. The average composition for this area is: copper 25–32%, tin 32–33%, lead 22–31%. The relatively low copper content with high tin content characterizes this as a tin-rich lead bronze.

Points on the back (Spectra Nos. 10 and 11) showed compositions: No. 10—copper 34.83%, tin 33.51%, lead 19.93%; No. 11—copper 33.29%, tin 32.50%, lead 17.34%, silicon 14.51%. The closeness of these values indicates relative homogeneity of composition in this area. The elevated silicon content in point No. 11, as in similar cases on other sculptures, is likely related to surface corrosion processes.

3.3. Results of X-Ray Fluorescence Analysis of the Collection (20 Items)

The study of an expanded sample of 20 bronze sculptures using pXRF provided a generalized overview of the variability in metallurgical recipes used by the Jin Empire for manufacturing such items (

Table 2. Elemental composition data obtained by pXRF for 20 bronze sculptures from the IHAE FEB RAS collection. Statistical processing based on this data has been performed, and typological alloy groups have been identified.

No.	Concentration, wt%
	Cu	Sn	Pb	Si	P	Al	Fe	Bi	Zn	Ni	Sb	Zr	Ti	Mn	Ag	Au
9 (center)	32.280	28.300	25.160	8.410	3.290	1.760	0.440	0.190	0.130	0.040
9 (legs)	40.360	27.890	21.450	4.000	3.150	2.410	0.650		0.050	0.040
10 (center)	34.260	23.240	23.660	10.520	3.040	4.090	0.530	0.180	0.210	0.070	0.200
10 (legs)	31.900	19.980	28.080	12.920	2.020	3.770	0.940		0.130	0.064	0.180	0.016
11 (center)	30.040	23.020	35.510	5.780	3.150	1.150	0.940		0.360	0.032		0.018
11 (legs)	35.050	14.960	32.900	9.350	4.370	1.740	1.300		0.290	0.021		0.019
12 (center)	30.350	29.500	27.400	7.060	3.950	1.360	0.190		0.130	0.045		0.015
12 (legs)	45.550	14.660	21.370	10.350	3.230	3.490	0.940		0.160	0.030			0.220
13 (center)	20.570	21.330	49.510	4.790	2.750	0.740	0.290					0.020
13 (legs)	29.730	10.820	51.510	4.290	2.240	0.910	0.490					0.010
14 (center)	29.530	30.350	24.370	9.530	3.240	1.770	0.570	0.190	0.160	0.070	0.200	0.020
15 (center)	38.440	14.650	28.960	11.400	2.350	2.450	1.400		0.290			0.020		0.040
16 (center)	45.810	21.860	22.190	5.310	1.190	1.540	1.220		0.880
17 (center)	40.550	22.740	22.350	6.630	2.840	1.840	2.670	0.180	0.140	0.046		0.014
18 (center)	28.520	30.250	28.520	7.060	2.670	1.420	0.840	0.290		0.036			0.394
18 (head)	30.740	27.070	29.940	7.390	2.840	1.380	0.580			0.060
19 (center)	66.430	10.380	14.360		1.730	1.040	1.560	1.280	2.070						0.790	0.360
20 (center)	50.330	17.790	21.390	6.880	2.620		0.760			0.050	0.180
21 (center)	37.060	29.270	26.020	4.710	1.520		0.650	0.240	0.460	0.050		0.020
22 (center)	29.630	7.020	10.360	7.410	0.940	2.610	4.170		0.320			0.010
23 (center)	57.630	16.160	16.110	6.220	1.750		0.330		1.780	0.020
24 (center)	36.230	27.690	20.600	8.690	0.680	1.360	1.760	0.430	2.560
25 (center)	25.000	29.160	32.000	9.910	1.100	1.790	0.910		0.130
26 (center)	54.740	19.010	17.830	5.870	2.060		0.300		0.190

, Figure 16). It should be emphasized that pXRF, applied to analyze the surface of artifacts with a macroscopic irradiation area (3–5 mm), provides semi-quantitative results significantly influenced by the surface condition, the presence of patina, and corrosion products. Therefore, the obtained data should be considered primarily as a qualitative characterization of compositional variability, rather than as precise quantitative measurements.

3.3.1. General Characterization of the Elemental Composition

All studied sculptures were made from ternary Cu-Sn-Pb alloys. The copper content in the sample varies from 20.57% to 66.43% (median ~33%, mean ~36.5%), demonstrating a wide range of recipes. The tin content ranges from 7.02% to 30.35% (median ~23%, mean ~22%), with the majority of specimens concentrated in the 15–30% range. The lead content varies from 10.36% to 51.51% (median ~24%, mean ~25.5%), showing the greatest variability among the major components.

The box-and-whisker plot (Figure 16) clearly demonstrates that copper is the predominant component in most samples, with statistical outliers present both towards very low values (around 20–25%) and high values (above 55–60%). The distribution of tin is relatively more compact with fewer outliers. The lead content shows a broad distribution with several outliers in the extremely high value range (~50%), indicating the existence of a specific group of high-lead alloys.

Silicon was detected in practically all samples within the range of 4–12.9%, primarily associated with surface corrosion products and soil residues. Phosphorus is present in concentrations of 0.68–4.37% (median ~2.5%), and its distribution is relatively uniform, which may indicate either natural impurities in the ores or intentional addition as a deoxidizer in some specimens. Aluminum was detected in concentrations up to 4.09%, also predominantly linked to surface contamination.

Among the minor elements (Figure 16), Fe is present in concentrations of 0.19–2.67% (excluding the anomalous sample No. 22 with 41.7% content, which is clearly related to surface contamination). Zinc was recorded in most samples in concentrations from trace amounts up to 2.56%, which is characteristic of natural impurities in copper ores. Bi, Sb, Zr, and Ti are present in trace amounts (<0.5%). Silver (Ag) was detected in only one sample (No. 19) at a concentration of 0.79%, and gold (Au) in the same sample at 0.36%, which may indicate the use of reminted coin metal or copper from a unique deposit.

3.3.2. Typological Alloy Groups

Based on the distribution of the main components (Cu, Sn, Pb) within the sample, four primary typological alloy groups can be distinguished.

Group 1. Classic Balanced Lead–Tin Bronzes (Samples Nos. 12, 16, 17, 20, 23, 26). These are characterized by a copper content of 30–58%, tin 16–23%, and lead 16–28%. This group forms the core of the sample and represents typical casting bronzes with an optimal balance of mechanical and technological properties. Samples in this group demonstrate relatively low impurity levels and align well with known regional metallurgical traditions.

Group 2. High-Lead Bronzes (Samples Nos. 9, 10, 11, 13, 25). The lead content in this group significantly exceeds typical values, reaching 25–52%. Sample No. 13 represents an extreme case with a lead content of approximately 50% (center: 49.51%, legs: 51.51%), approaching the composition of a lead-bronze eutectoid. Such high lead concentrations drastically reduce mechanical strength but provide excellent fluidity and ease of casting. Samples Nos. 9, 10, and 11 demonstrate an interesting feature: analysis of different points (center and legs) on a single object reveals compositional variability, which may indicate alloy heterogeneity or differing surface conditions in these areas.

Group 3. High-Tin Bronzes (Samples Nos. 14, 18, 21, 24). These are characterized by a tin content of approximately 27–30%, which is comparable to or exceeds typical values. Sample No. 18 demonstrates a unique balance with nearly equal content of copper (28.52–30.74%), tin (27.07–30.25%), and lead (28.52–29.94%). Such a composition provides specific properties–increased hardness, a characteristic color, and good fluidity. Analysis of two points on sample No. 18 (center and head) shows relative compositional homogeneity.

Group 4. Low-Tin Alloys (Samples Nos. 19, 22). These are characterized by a tin deficit with content < 11%. Sample No. 19 (copper 66.43%, tin 10.38%) represents a high-copper alloy with minimal alloying. Sample No. 22 demonstrates an extremely low tin content (7.02%) alongside an anomalously high iron content (41.7%), which clearly indicates severe surface contamination and makes this result largely unsuitable for metallurgical interpretation.

3.3.3. Specific Compositions and Local Heterogeneity

For several samples (Nos. 9, 10, 11, 12, 13, 18), analysis was conducted at two different points—in the central part of the figurine and in the area of the legs or head. The results revealed significant local compositional variability, exceeding the analytical error of the method.

Sample No. 9 shows differences: center (Cu 32.28%, Sn 28.30%, Pb 25.16%) and legs (Cu 40.36%, Sn 27.89%, Pb 21.45%). The most noticeable change is an 8% increase in copper content in the leg area.

Sample No. 11 shows even more significant differences: center (Cu 30.04%, Sn 23.02%, Pb 35.51%) and legs (Cu 35.05%, Sn 14.96%, Pb 32.90%). The tin content in the leg area is nearly 8% lower than in the center, accompanied by an increase in copper content.

Sample No. 13, with its high lead content, demonstrates: center (Pb 49.51%, Sn 21.33%) and legs (Pb 51.51%, Sn 10.82%). In the leg area, the lead content is even higher, while the tin content is nearly halved.

This local heterogeneity can be explained by several factors: (1) varying surface conditions and thickness of the corrosion layer at different points; (2) real metal heterogeneity due to liquation processes during crystallization; (3) the use of different alloys for individual elements in the case of composite objects. Given the semi-quantitative nature of the pXRF method and its high sensitivity to surface condition, the first explanation appears most likely for the majority of cases.

3.3.4. Generalized Characterization of Metallurgical Traditions

The box-and-whisker plots (Figure 16) clearly show the presence of numerous outliers, reflecting specific recipes or production conditions.

The predominance of classic balanced bronzes in the sample indicates an established metallurgical tradition with a good understanding of the relationship between alloy composition and properties. Simultaneously, the presence of high-lead, high-tin, and low-tin alloys testifies to a flexible production capability, able to adapt to varying conditions of raw material availability and functional requirements.

The wide range of lead content (from ~10% to 52%) likely reflects different production strategies: from a focus on mechanical strength (low lead content) to a priority on technological efficiency and ease of casting (high lead content).

The detection of trace noble metals (Ag, Au) in sample No. 19, although an isolated case, is of interest as possible evidence for the use of remelted metal or copper from specific deposits. This finding may hold significance for reconstructing economic connections and raw material sources.

4. Discussion

4.1. Technological Features of Manufacture

4.1.1. Two Production Approaches

The analysis of the results has enabled the identification of two distinct production approaches during the Jin Empire period.

The first approach, represented by Sculpture No. 1, is characterized by a complex, multi-stage technology involving the use of different alloys and the joining of separately manufactured elements. PCCT data demonstrate pronounced heterogeneity of the internal structure, the presence of a clear density boundary between the left and right halves of the figurine, multiple casting defects (air inclusions, particles of molding mixture), as well as soldering zones indicating the attachment of the head and suspension loop after the main casting process. Elemental analysis confirms these observations, revealing compositional differences between various parts of the object: the left half (Cu ~67%, Sn ~9%, Pb ~12%), the right half (Cu ~32%, Sn ~37%, Pb ~17%), the suspension loop (Cu ~45%, Sn ~17%, Pb ~28%), and the leg area (Cu ~21%, Sn ~69%, Pb ~6%).

This complexity in the technological process can be interpreted in several ways. One interpretation suggests an experimental or low-skill level of production, where the artisan, lacking sufficient experience or working under suboptimal conditions, was forced to interrupt the casting process and use different batches of metal available at hand. An alternative interpretation posits that this object could be the result of repair or modification of an existing sculpture, to which new elements were added.

The second approach, represented by Sculptures No. 2 and No. 3, is distinguished by the single-cast nature of the objects, with a relatively homogeneous alloy composition and minimal production defects. The elemental composition does not reveal systematic differences between major morphological elements. For Sculpture No. 2, the copper content varies within the range of 31–49%, tin 22–39%, and lead 13–25%, which can be explained by local liquation processes during crystallization and the influence of varying degrees of surface corrosion. Sculpture No. 3 demonstrates somewhat greater compositional variability (Cu 23–45%, Sn 21–44%, Pb 17–31%), which may be associated with the object’s more complex morphology and specific mold-filling characteristics.

The artisans employing this approach possessed sufficient expertise to correctly calculate the required volume of metal, maintain the optimal melt temperature and mold-filling rate, and to produce high-quality casting molds that minimized defects.

4.1.2. Casting and Assembly Techniques

Mold Orientation during Casting. Tomographic data for all three sculptures indicate the use of a horizontal mold position during the pouring process. This is evidenced by the pattern of defect distribution (air inclusions predominantly concentrate in the upper parts of the casting), the orientation of elongated bubbles (in Sculpture No. 2, the bubble in the right arm is oriented vertically, consistent with the direction of gas buoyancy in a horizontally positioned mold), and the specific nature of the boundary between the left and right halves of Sculpture No. 1 (a vertical boundary is characteristic of horizontal pouring with a side-mounted gate).

Technological Pauses in the Casting Process. The case of Sculpture No. 1 is of particular interest as an example of an unintentional interruption in the casting process. The combination of data—a clear density boundary in the tomograms, a sharp difference in elemental composition between the left and right halves, and visual differences in surface quality—convincingly indicates that the metal pour was interrupted, likely for technical reasons, and then resumed using an alloy of a different composition.

This case demonstrates the technological challenges faced by ancient artisans and indicates that not all objects were produced under ideal conditions. It is possible that this sculpture was made by a craftsman with limited experience, under conditions of inadequate workshop equipment, or under metal scarcity, necessitating the use of different available batches of alloy.

Composite Construction and Joining Techniques. The head of sculpture No. 1 was likely manufactured separately from the torso, as evidenced by the double line on the head’s surface, characteristic of casting in a composite mold.

The suspension loop was added during the final stage of post-processing, likely by soldering, with the quality of the joint being low—tomography reveals significant gaps between the loop and the head’s surface. The leg area also exhibits a sharply different elemental composition with an extremely high tin content (69%), indicating their separate manufacture.

The technique for joining elements, judging by the nature of the soldering zones in the tomograms, involved hard soldering—using a copper-based alloy with a reduced melting point achieved by adding significant amounts of lead or tin. The soldering quality varies: the loop attachment shows obvious defects, while other soldered areas are executed with sufficient quality.

4.1.3. Post-Processing of the Objects

Mechanical Working. All three sculptures show traces of surface mechanical working aimed at removing casting defects, cleaning seams from composite molds, and final detailing. The most obvious traces of mechanical working are observed on Sculpture No. 3, where all technological refinements (the rhomboid mesh incisions on the back, vertical grooves on the wings) were executed on the finished casting through engraving or chasing. The character of these elements (clear, straight-line boundaries, uniform depth) indicates the use of metal gravers or burins.

Addition of Functional Elements. For Sculpture No. 1, the suspension loop was clearly added after the main casting via soldering. For other sculptures in the collection, the attachment method (integral casting, post-cast drilling, or soldering) could not be definitively determined without invasive examination. Tomographic data demonstrate that the loop has a different elemental composition and internal structure compared to the head to which it is attached. The attachment method was likely soldering, although in the case of Sculpture No. 1, the quality of this operation was poor. For Sculpture No. 2, it is impossible to definitively determine whether the loop was cast integrally with the main body or added later.

4.2. Metallurgical Traditions

4.2.1. Alloy Recipes and Their Functional Purpose

Analysis of the expanded sample of 20 bronze sculptures, using portable XRF data interpreted with necessary caution, revealed four main typological alloy groups. The method’s fundamental limitation—its sensitivity to surface condition and shallow analysis depth, which captures the altered patina layer—means the results are treated as semi-quantitative. They are thus valued primarily for comparative purposes and for delineating broad groups within the assemblage.

Classic balanced lead–tin bronzes (approximately 30% of the sample), with copper content of 30–58%, tin 16–23%, and lead 16–28%, represent an optimal compromise between casting properties and mechanical strength. This composition provides sufficient fluidity to fill fine mold details and reproduce small features, a low melting point facilitating the casting process, and acceptable mechanical strength and hardness of the finished product. The presence of phosphorus in concentrations of 2–4% in some samples of this group indicates its intentional use as a deoxidizer.

High-lead bronzes (approximately 20% of the sample), with lead content of 25–50%, represent the opposite strategy, where manufacturability is prioritized at the expense of mechanical properties. Extremely high lead content (up to 50% in sample No. 13) drastically reduces the material’s strength and hardness, making it soft and easily deformable, but simultaneously provides exceptional fluidity and a very low melting point.

It is interesting to note that within this group, a continuum of compositions is observed–from moderately high lead content (25–30%) to extreme values (around 50%)–which may reflect the gradual adaptation of recipes to changing economic conditions or different quality levels of products for various market segments.

High-tin bronzes (approximately 10% of the sample), with tin content of 27–30%, comparable to or exceeding the copper content, represent specialized alloys. High tin content provides increased hardness, a characteristic silvery-white surface color, and a specific metallic luster. At the same time, significant lead content (26–29%) compensates for the increase in melting point associated with high tin content and ensures acceptable fluidity.

The use of such expensive alloys (tin was one of the most scarce and expensive bronze components in the region) indicates a special functional purpose or a prestigious status for these items.

Low-tin alloys (approximately 10% of the sample), with tin content less than 11%, represent products manufactured under conditions of resource scarcity. Such low tin content deprives the material of most characteristics typical of bronze—it becomes similar in properties to pure copper with minor additions. The presence of such alloys in a collection of ancestor spirit sculptures, which are usually associated with prestigious ritual objects, is somewhat unexpected and may indicate production during periods of economic hardship when access to tin raw materials was limited.

The detection of trace noble metals (Ag, Au) in one sample points to a unique compositional feature of that specific artifact, the origin of which (ore source, contamination, or recycling) remains an open question for future research.

4.2.2. Regional Specifics of Metalworking

All studied sculptures were made from ternary Cu-Sn-Pb alloys. The range of main component content (Cu 20–66%, Sn 7–44%, Pb 10–52%) is significantly wider than that usually observed for earlier periods or neighboring cultural complexes, which may reflect several factors. Firstly, the greater variability could be related to the increasing complexity of the socio-economic structure of society and the emergence of demand for products of varying quality and price ranges—from cheap high-lead bronzes for the general populace to prestigious high-tin alloys for the elite. Secondly, the variability may reflect instability in access to raw materials during different periods or in different production centers, forcing artisans to adapt recipes to available resources.

The high phosphorus content recorded (up to 7.73%), which likely indicates its intentional use as a deoxidizer and reflects advanced metallurgical knowledge, must be considered with caution. This is because the available data cannot definitively exclude its origin from specific ores or potential post-depositional contamination.

The presence of zinc in concentrations up to 2% in some samples may indicate either the use of copper ores with natural zinc content or the remelting of items containing brass. Brass (a copper-zinc alloy) was known in China and used for manufacturing various objects; therefore, the presence of zinc in bronze alloys could be related to the practice of remelting mixed scrap metal, which is common in metallurgy with a developed metal recycling system.

Comparison with data on metalworking from the preceding Bohai period (698–926 AD) shows a certain continuity in the use of tin-lead bronzes, but also some differences. Bohai metallurgy, according to available data, was characterized by a narrower range of compositions and rare use of high-lead alloys. In contrast, the Jin Empire period demonstrates greater flexibility and adaptability in metallurgical practices, which may be associated with a more complex socio-economic situation or the integration of metallurgical traditions from various ethnic groups within a multi-ethnic state.

4.3. Interpretation of Compositional Variability

Technological Factors

The variability in elemental composition, observed both between different sculptures in the sample and between different parts of individual objects, can be explained by a complex of technological factors related to the specifics of ancient metallurgical processes.

Liquation Processes during Crystallization. In ternary Cu-Sn-Pb alloys, characterized by a complex phase diagram and a wide solidification range, liquation processes—gravitational and dendritic segregation of components with different physicochemical properties—inevitably occur. Lead, having the highest density (11.34 g/cm³) among bronze components and being virtually insoluble in solid copper and tin, tends to separate into discrete inclusions that, under gravity, can redistribute to the lower parts of the casting. Tin, which forms intermetallic compounds with copper having different melting points, can be unevenly distributed between the primarily crystallizing copper dendrites and the eutectic phases forming later.

These processes result in some compositional heterogeneity in the final casting, even with ideal melt stirring before pouring. The degree of this heterogeneity depends on the cooling rate (rapid cooling “freezes” the structure, minimizing liquation; slow cooling allows segregation processes to develop more fully), the casting’s massiveness (liquation is more pronounced in thick-walled objects), and the initial alloy composition (high-lead alloys are more prone to liquation).

In the context of the studied sculptures, liquation processes can explain the moderate compositional variability (on the order of 5–10% for the main components) between different points on Sculptures No. 2 and No. 3, which were identified as single-cast objects.

Oxidation and Loss of Components during Smelting. When bronze alloys are heated to the temperatures required for casting (typically 1000–1200 °C depending on composition), partial oxidation of the melt components by atmospheric oxygen occurs. Different bronze components have varying susceptibilities to oxidation: tin oxidizes relatively easily, forming tin oxide (SnO₂), which transitions into slag and is removed from the melt surface; copper oxidizes more slowly; lead occupies an intermediate position. The duration the melt is held at high temperature, the presence or absence of a protective atmosphere or fluxes preventing oxidation, and the intensity of melt stirring significantly affect the degree of component loss.

With repeated remelting of secondary metal or prolonged holding of the melt (for instance, if an artisan prepared several sequential castings from one crucible), the composition can gradually shift towards lower tin content. This may partially explain the presence of low-tin alloys in the sample, which could have formed from initially balanced bronzes as a result of multiple remelting cycles.

Heterogeneity of Raw Materials. Ancient metallurgical processes did not achieve the degree of purity and homogeneity of raw materials characteristic of modern production. Copper and tin were smelted from ores with variable compositions containing various impurities depending on the specific deposit or even the section of the ore body. Lead, although added intentionally, could also have varying impurity compositions. Mixing metals from different sources when preparing the charge for casting could lead to some heterogeneity in the final alloy.

Furthermore, the practice of remelting old objects (secondary metal), which was widespread in antiquity due to the high cost of metals, led to the mixing of alloys of different origins and compositions.

5. Conclusions

The conducted study of three bronze sculptures from the Jin Empire period (1115–1234 AD) using photon-counting computed tomography and energy-dispersive X-ray spectroscopy has demonstrated the efficacy of an interdisciplinary approach for reconstructing the technological features of ancient metal artifact production.

The PCCT method revealed internal structural features of the objects, established their internal architecture, and detected cavities, heterogeneities, and inclusions of various natures. The non-destructive EDS method determined the surface elemental composition of the bronze alloys, enabling the establishment of the component ratios in the Cu-Sn-Pb system, the identification of heterogeneity in their spatial distribution, and the characterization of the impurity profile. Synthesizing the results from PCCT and EDS allowed for the determination of the production specifics of the objects: the nature of casting (single-cast or composite objects, single-pour or multi-stage process) was established, casting defects and methods for joining separate elements were identified, and the sequence of technological operations was reconstructed.

The research enabled the identification of two fundamentally different production approaches. The first, represented by Sculpture No. 1, is characterized by a complex, multi-stage technology involving the use of different alloys (copper content varying from 21% to 67%, tin from 9% to 69% in different elements), an interruption in the casting process, and subsequent assembly from separately manufactured parts. The second approach, represented by Sculptures No. 2 and No. 3, is distinguished by the single-cast nature of the objects with a relatively homogeneous alloy composition and indicates a more mature production tradition. The stylistic and technological similarity of these two sculptures suggests they may originate from a single production center.

The expanded analysis of 20 bronze sculptures using portable X-ray fluorescence analysis revealed significant diversity in metallurgical recipes while maintaining general technological principles. Four main typological alloy groups were distinguished: classic balanced lead–tin bronzes (Cu 30–58%, Sn 16–23%, Pb 16–28%), high-lead bronzes (Pb up to 52%), high-tin bronzes (Sn up to 30%), and low-tin alloys (Sn less than 11%). This diversity reflects the flexibility of metallurgical practices, adaptation to varying economic conditions and functional requirements, as well as the social differentiation of the clientele.

The use of phosphorus as a deoxidizer (recorded in concentrations up to 7.73%) testifies to the advanced metallurgical knowledge of Jurchen artisans. The detection of trace amounts of noble metals (Ag, Au) in one sample, recorded by surface-sensitive pXRF, requires cautious interpretation. While one possibility is the use of specific ore or recycled metal, an equally plausible explanation is surface contamination from contact with other objects in the burial context or the degradation of a now-invisible surface coating. This isolated finding does not indicate a general practice.

The morphological and iconographic features of the sculptures (portrait likeness, detailed rendering of clothing elements, presence of suspension loops) confirm their interpretation as ongons (ancestor spirits) used within the framework of Jurchen shamanistic ritual practices. The unique winged figure (Sculpture No. 3) may represent a special category of helper spirits with a different functional purpose.

The results of the study make a substantial contribution to understanding the metallurgical traditions of the Jurchen during the Jin Empire period and demonstrate a developed metalworking culture with a sound understanding of the relationship between alloy composition and properties. The identified variability in technological approaches and alloy recipes reflects the complex socio-economic structure of Jurchen society and the existence of both specialized, high-level urban workshops and less skilled production centers.

Prospects for further research include expanding the sample of artifacts for statistically significant analysis of regional and chronological variability in metallurgical traditions, applying additional analytical methods (scanning electron microscopy, optical metallography) to detail the microstructural features of the alloys, and experimental modeling of ancient casting processes to verify the proposed technological reconstructions.

The methodological approach implemented in this work demonstrates the potential of the comprehensive application of modern physicochemical analysis methods to the study of archaeological metal artifacts. The integration of non-destructive research methods (computed tomography, X-ray fluorescence spectroscopy) with traditional archaeological and art historical approaches opens new possibilities for reconstructing not only technological processes but also the cultural, economic, and social aspects of medieval societies. Each artifact emerges as a complex system of informational codes, reflecting the knowledge and skills of ancient artisans, resource availability, social relations, and ritual practices, which can be decoded given an adequate methodological toolkit.