Introduction

Lianying Han Tomb is located in Lianying Village, about 16 kilometers southwest of Yizheng City and 11 kilometers east of Yangzhou City in Jiangsu Province. It is not far from the Miaoshan Han Tomb which has been confirmed to be the tomb of King Guangling in the early Western Han Dynasty (Fig. 1a). Lianying Han tomb dated back to the Western Han Dynasty (202 BC-8 AD) and it is speculated to be an auxiliary tomb to the main tomb of Miaoshan. A total of 136 tombs and sacrificial pits have been discovered (Fig. 1b). In M59, the red-painted inner coffin was divided into four compartments and placed within the black-painted outer coffin (Fig. 1c). The inner coffin was decorated with cloud dragon patterns, indicating that the tomb occupant held a high social status. A large number of burial objects were unearthed from M59, including lacquer ware, jade, glazed pottery, and bronze weapons. The name of the tomb owner can be confirmed from the words “Fan Xuqi” engraved on the jade seal. Judging from the weapons buried with him, Fan Xuqi should have been a senior general of King Guangling1. Of particular note is the rare lacquered gauze discovered in M59. The total area of the unearthed lacquered gauze fragments was approximately 500 cm2, with the largest fragment measuring 13 × 6 cm. It is speculated that these fragments could have been from the lacquered gauze headgear. One of the fragments looked like an ear flap with a hole at the end for a string to be tied (Fig. 1d). This type of lacquered gauze headgear was a headdress worn by military officers in the Han Dynasty2.

Fig. 1: Location and features of the Lianying Han Tomb.
Fig. 1: Location and features of the Lianying Han Tomb.
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a geographical location, b tomb M59, c burial chambers of M59, d unearthed lacquered gauze fragments from M59.

The lacquered gauze appeared as early as the Warring States Period (475–221 BC) and reached its peak in the Han Dynasty (202 BC-220 AD). The earliest lacquered gauze fragments were found in a Western Zhou tomb dating back more than 3000 years3. In documents, murals, and portrait bricks of the Qin and Han dynasties, many written records and images of ancient people wearing lacquered gauze headgear have been found4,5. During the Han Dynasty, lacquered gauze became a symbol of aristocratic status, and the upper classes favored its use for making headgear. According to published archeological excavation reports, some lacquered gauze objects have been unearthed from Han tombs in Hubei, Hunan, Jiangsu, Shandong, Guangxi, Gansu, etc. Unfortunately, most unearthed lacquered gauze objects are fragmentary and in a poor state of preservation due to environmental factors and inherent material decay. Only the lacquered gauze headgear from the Mawangdui Han Tomb was well preserved6. The use of lacquered gauze continued into the Ming and Qing Dynasties, where it was employed in clothing, headdresses, and architectural decoration. For example, the black gauze hats worn by Ming Dynasty officials and the gilded lacquered gauze in the collection of the Palace Museum are both extremely precious and exquisite cultural relics7.

The lacquered gauze is a special textile fabric treated with raw lacquer, including an outer layer of lacquer film and an inner layer of silk or bast fibers (hemp or ramie) fabric. Raw lacquer is a natural polymer, mainly composed of 60–65% urushiol, 20–25% water, 5–7% polysaccharides and 1% laccase. The polymeric lacquer film is very stable and has waterproof, corrosion-resistant and antibacterial properties. For these reasons, raw lacquer was used as the surface finishing material for wood, textiles, pottery and other materials in ancient China. The emergence of lacquered gauze craftsmanship can be attributed to the practical needs of ancient people for shaping and reinforcing fabrics. It is an innovation of traditional Chinese handicrafts, perfectly combining the strength of fabrics with the protective properties of raw lacquer. By painting a layer of lacquer film on the fabric surface, the lacquered fabric becomes waterproof and its hardness, durability and toughness can be enhanced. Therefore, the identification and characterization of the making materials and the lacquering technique used in the lacquered gauze are critical for its scientific conservation and restoration. However, there is little research on the materials and techniques used in making lacquered gauze. The previous studies mainly focused on the shape of lacquered gauze headgear and the weaving method of the lacquered fabric8,9,10. A few studies have applied nondestructive analytical techniques, such as optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), Raman spectroscopy, Fourier transform infrared spectroscopy (FTIR) to observe the weaving structure of the lacquered gauze and identify the characteristics of the lacquer film11,12. However, the identification of the base fabric material has traditionally relied on historical records and researcher experience. Therefore, it is necessary to develop additional effective analytical methods for in-depth research on the fabric weaving materials and lacquering techniques in order to provide more scientific information for the conservation and restoration of Han Dynasty lacquered gauze.

This study aimed to investigate the materials and techniques of the lacquered gauze excavated from Lianying Han Tomb M59 using multi-analytical methods, including digital microscopy, SEM, FTIR and thermally assisted hydrolysis-methylation pyrolysis-gas chromatography/mass spectrometry (THM-Py-GC/MS). The structural characteristics and weaving techniques of ancient lacquered gauze were analyzed using OM, and the morphology of the inner fabric fibers was further examined and compared with that of modern ramie fibers using scanning electron microscopy. FTIR and THM-Py-GC/MS were employed to identify the organic components including lacquer, drying oils and fabric fibers. The research results not only help clarify the craftsmanship of the lacquered gauze of the Han Dynasty, but also provide scientific support for its conservation and restoration, laying a foundation for the reconstruction of lacquered gauze headgear.

Methods

Samples

The experimental samples included both ancient and modern reference materials. The ancient sample was taken from a lacquered gauze fragment excavated from the Lianying Han Tomb M59. It was cleaned with deionized water and a soft brush to remove surface contaminants, then dried in a constant-temperature room at 20 °C for 48 h.

Modern reference samples consisted of a cured lacquer film and a ramie fabric. The raw lacquer, obtained from a lacquerware workshop in Enshi, Hubei Province, was dried and cured at room temperature to produce a modern lacquer film. The modern ramie sample was sourced from a textile supplier in Jingdezhen, Jiangxi Province.

Optical microscope and scanning electron microscopy (SEM)

A VHX-600K ultra-depth three-dimensional microscope was used to observe the surface morphological characteristics and weaving structure of the ancient sample.

A Schottky field emission scanning electron microscope (ZEISS, Germany) was used to obtain longitudinal and cross-sectional images of the ancient sample and modern ramie sample at an accelerating voltage 3.0 kV.

Fourier transform infrared spectroscopy (FTIR)

Fourier-transform infrared (FTIR) spectra of the ancient sample were acquired using a Nicolet iN10 spectrometer. Spectra were recorded at room temperature from 16 scans at a resolution of 4 cm⁻¹ over the wavenumber range of 4000–400 cm⁻¹. The collected data was processed using Origin 8.0 software and the spectra were baseline-corrected before analysis.

Pyrolysis gas chromatography and mass spectrometry with thermally assisted hydrolysis and methylation (THM-Py-GC/MS)

THM-Py-GC–MS analyses were performed on a CDS Pyroprobe 6200 (CDS Analytical, Oxford, PA, USA) coupled with a Thermo Scientific TRACE 1610 gas chromatograph/ISQ 7610 single quadrupole mass spectrometer (Thermo Scientific, USA). A TG-624SilMS capillary column (30 m × 0.25 mm × 1.4 μm) was used with helium flow set to 1.0 mL per minute. The mass spectrometer was equipped with an electron ionization (EI) source operating at 70 eV.

Samples were treated with 5 μL of 25% TMAH in methanol and pyrolyzed at 600 °C for 40 s. The GC inlet temperature was set to 320 °C and the split ratio was 20:1. The GC column temperature was maintained at 50 °C for 2 min, then increased to 280 °C at 5 °C per min for 1 min, and increased to 300 °C at 25 °C per min for 6 min. The ion source temperature was 250 °C, and the transfer line temperature was 300 °C. The data were acquired in full-scan mode with a scan range of m/z 35–600. The compounds were identified by matching spectra to the NIST mass spectral database.

Results and Discussion

Microscopic observation of the lacquered gauze structure

Optical microscope is a simple and effective method for examining the surface morphological characteristics and weaving structures. Fig. 2 shows the structural images of the ancient lacquered gauze sample obtained using an ultra-depth three-dimensional microscope. Fig. 2a presents the rhomboid network structure of the lacquered gauze. Each weaving thread is of uniform thickness with a diameter of about 0.3 mm. The weaving density in the lacquered gauze is about 12 × 14 strands/cm2, reflecting the advanced level of weaving technology in the Han Dynasty. Fig. 2b shows the image of the fracture surface of the lacquered gauze, indicating that the lacquered gauze consists of an inner fabric layer and an outer lacquer film. After being painted with raw lacquer, the fabric becomes more durable and elastic and the lacquer film also has a waterproof function, demonstrating the wisdom of the ancient craftsmen.

Fig. 2: Microscope images of the lacquered gauze surface morphology and weaving structure.
Fig. 2: Microscope images of the lacquered gauze surface morphology and weaving structure.
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a surface morphology, b inner layer morphology, c cross section, d schematic diagram of the weaving structure.

Fig. 2c, d show a cross-sectional image and a schematic diagram of the weaving structure, respectively. Two threads form a group, and four threads constitute a weaving unit. Two sets of criss-cross threads are intersected and interwoven with each other. This weaving method differs from the shuttle weaving method and the mesh structure woven in this way could be adjusted and deformed. Consequently, this weaving method was commonly used to weave the inner fabric of lacquered gauze during the Han Dynasty. The lacquered gauze objects unearthed from Dayunshan Han Tomb, Mawangdui Han Tomb, Haiqu Han Tomb and Haihunhou Tomb all used the weaving method6,9,10,11.

Identification of the fabric fibers using SEM

Scanning electron microscopy (SEM) enables clear observation of the morphology features of fabric fibers. The ancient lacquered gauze sample and a modern ramie sample were examined by SEM to compare their fiber morphological characteristics. Fig. 3 presents SEM images of the longitudinal and cross-section morphology of fibers from the ancient sample (a, c) and modern ramie fibers (b, d), respectively.

Fig. 3: SEM images of fiber morphologies.
Fig. 3: SEM images of fiber morphologies.
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a longitudinal view of the ancient sample, b longitudinal view of modern ramie, c cross-section of the ancient sample, d cross-section of modern ramie.

As shown in Fig. 3a, the fibers in the ancient sample are straight in the longitudinal direction. The diameter of a single fiber is about 20 μm. Multiple fibers are bundled together and arranged in order. The SEM images reveal fiber breakage and discontinuity, indicating that the ancient fibers were severely degraded due to being buried underground for thousands of years. The reference ramie fiber in Fig. 3b has a diameter of approximately 27 µm, which is larger than that of the ancient fibers. This size difference may be attributed to the decay of the ancient fibers, which can result in the formation of hollow structures that subsequently collapse.

The cross-sectional image in Fig. 3c shows that the most of the fibers are elliptical or polygonal. These characteristics are consistent with those of the modern ramie in Fig. 3d, supporting the identification of the ancient fibers as ramie13. Ramie is an excellent textile fiber and one of the earliest textile raw materials used by humans. It was widely used as a textile material in ancient China. As early as the Neolithic age, the ancient Chinese people had already mastered ramie weaving technology. Ramie artifacts, such as ramie ropes, ramie cloth, and ramie leaves, have been unearthed at the Hemudu site and Qianshanyang Neolithic site in Zhejiang Province14. The ramie square-hole yarn was unearthed from the Eastern Zhou tomb in Jiangxi, and ramie fabrics were unearthed from Chu tomb15. Although previous studies showed that most of the lacquered gauze objects unearthed from the Han tombs were made from silk fabrics, the lacquered gauze made from the bast fibers was also found in the Luobowan Han Tomb16. Historical records suggest that the practice of lacquering ramie fabric predates that of silk fabric. When silk became available, silk fibers replaced hemp or ramie fibers as the material for making the lacquered gauze17. Based on archeological evidence, historical documents, and morphological analysis, it is inferred that the ancient sample was woven from ramie fibers.

Characterization of the outer layer of the ancient sample using FTIR

FTIR is a non-destructive analysis technique used to identify the functional groups in the lacquer film of ancient lacquerware. Fig. 4 compares the infrared spectra of the raw lacquer film and the ancient sample. The spectra of the two samples are very similar. For the ancient sample, the broad absorption peak near 3413 cm⁻¹ corresponds to the O-H stretching vibration of the hydroxyl group on the benzene ring of urushiol18. The peak at 1360 cm-1 is also related to the O-H stretching vibration of hydroxyl group19. The two sharp peaks at 2925 cm-1 and 2854 cm-1 are assigned to the -CH2 stretching vibration absorption peaks, corresponding to the methylene vibration on the side chain of urushiol20. The peak at 1623 cm-1 is attributed to the C = C bond stretching vibration absorption peak of the side chain of the benzene ring of urushiol21. The peak at 1442 cm-1 is attributed to the -CH2 and -CH3 asymmetric bending or deformation in phenyl groups22. The peaks at 1276 cm-1, 1076 cm-1 and 1037 cm-1 are the C-O stretching vibrations in phenol hydroxyl groups and lacquer polysaccharide23. In addition, the peak at 1709 cm-1 is indicative of the C = O stretching in the carbonyl group, which is related to the oxidation of urushiol and the drying oil added during lacquering24. All of these characteristic peaks are consistent with the characteristic peaks of raw lacquer. Therefore, it can be concluded that the outer layer of the ancient lacquered gauze is composed of raw lacquer.

Fig. 4
Fig. 4
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FTIR spectra of modern raw lacquer film (black) and the outer layer of the lacquered gauze (red)

Characterization of the lacquered gauze using THM-Py-GC/MS

Thermally assisted hydrolysis and methylation pyrolysis-gas chromatography/mass spectrometry (THM-Py-GC/MS) is an excellent analytical technique for characterizing mixed organic compounds, such as natural resins, drying oils, proteins, and colorants. The operation is simple and rapid, and the technique requires only a small amount of sample with no pretreatment, making it highly suitable for analyzing cultural relic samples. In order to further clarify the composition of the lacquered gauze, THM-Py-GC/MS was used to analyze the ancient lacquered gauze, raw lacquer and modern ramie samples. The total ion chromatogram obtained by THM-Py-GC/MS is shown in Fig. 5. The detailed spectrum and the identified compounds of the samples are listed in Table 1.

Fig. 5: THM-Py-GC/MS analysis.
Fig. 5: THM-Py-GC/MS analysis.
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Pyrograms obtained by THM-Py-GC/MS analysis for a modern ramie fiber, b raw lacquer film, and c the ancient lacquered gauze sample.

Table 1 Compounds identified in the ancient lacquered gauze sample by THM-Py-GC/MS in comparison with reference materials (modern ramie and raw lacquer)
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Fig. 5 shows that compounds, such as catechol derivatives (#14), phenol (#8), alkylbenzenes (#2, #5, #13, #18, #22), benzoic acid derivatives (#21), alkanes (#10, #15, #20, #24, #26) and alkenes (#19, #23) were detected in the mass spectrum of the ancient lacquered gauze sample, which are consistent with the thermal degradation characteristics of raw lacquer25,26. The main component of raw lacquer is Urushiol, which can form the lacquer film through oxidation and polymerization. Urushiol is a catechol derivative with an unsaturated C15 aliphatic side chain27. At high temperature, the pyrolysis products of raw lacquer include catechols, alkylbenzenes, carboxybenzenes, phenols, alkenes and alkanes28. Alkanes, alkenes, and alkylbenzenes are generated through thermal decomposition. This process preferentially cleaves bonds at the α- and β-positions which are relative to both the double bond in the olefin side chain and the benzene ring of the lacquer phenol, thereby disrupting the structures of raw lacquer25,29. Especially, the catechol derivatives extracted from urushiol can be used as characteristic markers for the qualitative analysis of lacquer by Py-GC/MS. Since the methylating agent TMAH was added to the sample, the catechol containing hydroxyl groups underwent methylation reaction and converted into methyl ether derivatives30. For instance, catechol derivatives were converted into 2,3-dimethoxytoluene (#14). In addition, 1-methoxy-3-pentadecylbenzene (#35) was found in the ancient sample, which was attributed to the pyrolysis of 3-pentadecylcatechol derived from urushiol at high temperature after methylation31. From these pyrolysis products detected by THM-Py-GC/MS, it can be conclusively determined that the ancient sample is composed of raw lacquer.

The peak areas of the pyrolysis products from the ancient lacquered gauze and the raw lacquer reference were normalized. A correlation plot of the normalized peak areas exhibits a linear relationship, described by the regression equation y = 0.68x + 1.98 (R² = 0.64). However, the correlation coefficient (R² = 0.64) is relatively low, which can be attributed to severe degradation and changes in the chemical composition of the ancient lacquered gauze due to long-term aging. Fig. 6 shows the linear correlation of relative peak areas of shared markers between the ancient sample and raw lacquer. The correlation shown in Fig. 6 indicates a consistent relative distribution of these compounds, further supporting the conclusion that the ancient sample was composed of raw lacquer.

Fig. 6
Fig. 6
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Linear correlation of the relative peak areas of shared markers between the raw lacquer and the ancient lacquered gauze.

Another group of compounds was also detected in the ancient sample, including monocarboxylic fatty acid methyl esters (#7, #11, #16, #29, #31, #32, #34, #36), dicarboxylic fatty acids methyl esters (#12, #17, #25, #27, #28) and glycerol analogs (#4). All of these are characteristic pyrolysis products of the drying oil. Drying oils, such as linseed oil and tung oil are mainly composed of triglycerides and contain a large amount of unsaturated fatty acids. Their pyrolysis products are monocarboxylic and dicarboxylic fatty acids. In the presence of the methylating agent TMAH, these fatty acids are converted into fatty acid methyl esters32,33. At the same time, dimethyl azelate (#27), a characteristic marker of drying oil, was detected in the ancient sample, suggesting that drying oil was added as additive during the lacquering process34. Additionally, studies have shown that the saturated fatty acid components, such as palmitic acid and stearic acid do not participate in oxidative degradation process, and the ratio of palmitic acid to stearic acid (P/S) remains stable over time35. Therefore, the P/S value of methyl palmitate (#31) to methyl stearate (#33) in the ancient sample can be used to identify the type of drying oil36. The P/S value of the ancient sample is 1.87, which is consistent with that of linseed oil32. Based on these characteristics, the results indicated that the drying oil used in the lacquered gauze was linseed oil. During the Han Dynasty, lacquering technique gradually matured, and drying oil was often used to modify raw lacquer to increase the gloss and elasticity of the lacquer film.

Furthermore, the THM-Py-GC/MS analysis (Fig.5) showed that compounds, such as 2-cyclopenten-1-one (#1), 1,2-cyclopentanedione (#3), 5-methyl-2-furancarboxaldehyde (#6) and guaiacol (#9) were detected in both the ancient sample and the modern ramie sample. Ramie is a natural bast fiber composed of cellulose, hemicellulose and lignin. Cellulose is the main component, accounting for about 65-85% of the total. It has been reported that furan derivatives (#6) and cyclopentanone compounds (#1, #3) are pyrolysis products of cellulose during thermal decomposition37,38, while guaiacol is a characteristic pyrolysis product of lignin39,40. This indicated that the ancient sample contains cellulose and lignin. Combined with the SEM analysis results, this confirms that these compounds were thermal decomposition products of the plant fabrics in the lacquered gauze.

Three groups of compounds derived from raw lacquer, drying oil and ramie were identified through THM-Py-GC/MS analysis, elucidating the production materials and process of the ancient lacquered gauze were explored. The lacquered gauze was made by using strong and breathable ramie fabric as the base material, which was then painted with raw lacquer. This treatment not only made the lacquered gauze waterproof but also enhanced its hardness, durability and toughness. During the lacquering process, linseed oil was added to modify the raw lacquer, improving the flexibility and gloss of the resulting lacquer film.

In summary, the lacquered gauze excavated from the Lianying Han tomb in Jiangsu Province was characterized and identified in this paper through OM, SEM, FTIR and THM-Py-GC/MS, by focusing on the weaving method, fabric fiber identification and lacquering technique. Microscopic analysis revealed that the lacquered gauze consisted of an outer layer of lacquer film and an inner layer of the fabrics. From the cross-section of the ancient sample, it can be seen that the inner fabric was twisted into square or diamond-shaped grid holes with two sets of criss-cross weaving warp threads, reflecting the exquisite hand-weaving skills of ancient craftsmen. By comparing the modern ramie with the ancient sample using SEM, it was found that the inner fabric was woven from ramie fibers. THM-Py-GC/MS analysis detected characteristic pyrolysis products derived from urushiol derivatives and linseed oil, suggesting that linseed oil was added as an oxidation catalyst to accelerate the cross-linking of urushiol and enhance the flexibility and adhesion of the lacquer film. At the same time, the marker compounds of cellulose and lignin were also identified, which confirmed that the lacquered gauze contained ramie fibers combing with SEM analysis results. The lacquered gauze craftsmanship perfectly blended the strength of fabrics with the protective properties of lacquer, embodying the advanced skills of ancient craftsmen and their wisdom in applying natural materials. The research results not only provide scientific support for the conservation and restoration of unearthed lacquered gauze, but also offer methodological guidance for the analysis of similar artifacts.