Abstract:For the detection of the weathering of stone relics, both gel-coupled and contact ultrasonic testing (without couplant) techniques are prevalently employed. However, these techniques harbor inherent challenges, such as potential contamination from couplants and the risk of relic damage during ultrasonic testing contact. The advent of air-coupled ultrasonic testing presents a safer alternative for weathering detection of stone relics, though its stability and applicability to weathering degree detection still require further validation. In this research, using sandstone samples from Yungang Grottoes, we conducted simulated weathering tests under freeze-thaw cycles and acid soaking conditions, where an air-coupled ultrasonic detection system was set up, and the ultrasonic velocity of sandstone samples was calculated based on the obtained original waveforms. Meanwhile, the samples of sandstone with different degrees of weathering were detected by gel-coupled and contact ultrasonic testing. The value of ultrasonic wave velocity and its variational trend with the weathering process were analyzed by means of the least squares regression model and oscillation coefficient calculation. As revealed by the results:1) the wave velocity dispersion of air-coupled ultrasound in repeated detection was significantly lower than that of the other two traditional ultrasonic detection techniques; 2) the obtained wave velocity was more consistent with the variational trend of weathering degree, featuring high applicability to the weathering degree detection of stone relics. In summary, presenting more accurate, safer and more effective weathering detection data, and having strong applicability and broad application prospects in the detection of stone relics, the air-coupled ultrasonic testing technique could provide important support for the conservation of stone relics.

Abstract:The Avalokiteshvara Bodhisattva statue on the south wall outside Wanfodong Cave in Longmen Grottoes is praised as “the most beautiful Avalokiteshvara Bodhisattva in Longmen” on the basis of its exquisite carving skill and graceful shape. However, affected by human and natural factors, the statue face has become incomplete and the paint has almost disappeared. Therefore, making virtual restoration to reshow its complete appearance is important for the relevant archaeological research and exhibition. Based on a historical picture, we used a method combining 3D digitalization and sculpture repair to realize the virtual restoration of the shape and stony texture. A virtually restored physical model was made by high-precision SLA 3D printing. The remaining paint components were determined using X-ray fluorescence spectrometry and Raman spectrometry. On this basis and according to its remaining paint distribution and the color style of statues of the same period in Longmen Grottoes, the virtual color restoration of the Avalokiteshvara Bodhisattva statue was finished. In this scientific research practice, an entire technological process for the virtual shape and color restoration of incomplete cultural relics was designed and its feasibility was verified. The coloring of the physical model and utilization in exhibitions were also realized.

Abstract:Scientific environmental conservation and management strategies for grottoes are essential for the safety of artifacts inside caves. This study began by focusing on the adverse effects of cave door activities on the artifacts inside caves. The current large number and great scale of caves in China place demands on automated management and conservation. It was observed that the water vapor activity in the inner and outer cave environments in two different states—the grotto doors being open and being closed—exhibited great differences in the monitoring data. Therefore, this study attempted to introduce a method for automated conservation and management of grottoes by combining environmental monitoring with machine learning, thus avoiding the labor-intensive and error-prone manual operations of the past. The study utilized environmental data collected over a three-year period from two single open caves (Cave 133 and Cave 127) in Maijishan Grottoes. Based on the characteristics of the water vapor content profiles inside and outside the caves in both open and closed states of the cave doors, the following two steps were established to identify the activity of the cave doors:1) the doors were dichotomized as being open or closed; 2) then the transient entry and exit activities of the people were detected from the period when the doors were closed. Three key parameters were established, including the correlation coefficient, the Euclidean distance and the short-term fluctuation difference. Subsequently, machine learning models were used to classify these features and detect the behavior of personnel momentarily entering and exiting the cave through outlier diagnosis. Different machine learning models including k-nearest neighbors (k-NN), decision trees, and support vector machines (SVMs) and their performances under the corresponding parameters were evaluated separately. The results show that SVMs were more accurate with a recognition rate of 97.7%. For detecting transient entry and exit activities, making the first-order differences of the curves and setting thresholds to acquire outlier detection achieved an accuracy of 94.9% under optimal conditions. Despite its merits, the study acknowledges certain limitations. Environmental data analysis relied on a daily time window, which limited the resolution of door state identification and might affect the fineness of response to environmental mutations. In addition, expanding the dataset to include a more diverse range of grotto structures and environmental contexts could enhance the robustness and generalizability of the system. In conclusion, this study provides new ideas for integrating machine learning into cultural heritage conservation, and also gives new technological support for preventive conservation practices.

Abstract:The ancient building complex of Wudang Mountain is located in the Wudang Mountain Tourism Special Economic Zone, Shiyan City, Hubei Province, China. These royal Taoist buildings of the Ming Dynasty (1368 CE-1644 CE) served as the highest level of Taoist architecture and the center of Taoist activities at that time. Wulonggong Palace was one of the nine palaces in the ancient building complex. Today, the surviving architecture of Wulonggong Palace was mostly constructed in 1412 CE during the reign of Yongle of the Ming Dynasty. Archaeological excavations performed by the Hubei Provincial Institute of Cultural Relics and Archaeology commenced on September 8th, 2020. The entire site includes the north palace, the middle palace, the south palace, and a 180-meter-long walkway, covering a total area of approximately 50 000 m². Although Wulonggong Palace has endured over 600 years of weathering and erosion, some structures still remain remarkably well-preserved. This good preservation condition is closely related to the excellent performance of the historical mortar used in construction. From the perspective of principles for cultural relic restoration and environmental protection, research and application of original materials for restoration as much as possible has become a consensus within the academic community, aiming to guarantee compatibility with ancient masonry and weathered surfaces. The performance of historical lime mortar used for Wulonggong Palace has been proven through its long-term practice, making in-depth investigation into its material characteristics and manufacturing techniques crucial and necessary. During archaeological excavations at the Wulonggong Palace site, a large number of well-preserved mortar samples were found. In this study, multiple analytical methods, including polarized light microscopy (PLM), X-ray diffraction (XRD), thermogravimetric-differential scanning calorimetry (TG-DSC), X-ray fluorescence (XRF) spectrometry, filler analysis, chemical analysis, Fourier transform infrared (FTIR) spectrometry and scanning electron microscopy (SEM), were utilized on five bonding mortar samples carefully selected from different walls in Wulonggong Palace. The comprehensive analytical results reveal that these mortar samples were magnesium lime, originating from the calcination of associated-magnesite limestone. The magnesium oxide contents in the five mortar samples ranged from 3.49% to 17.76%. In China, the raw materials for magnesium lime are widely distributed, especially in Hubei and the northeast and southwest regions. Such abundant mineral resources provided both geographical accessibility and material feasibility for ancient builders to systematically produce magnesium lime mortar used for Wulonggong Palace. The contents of filler in the mortar samples were 4.7%-17.7%, with the particle size being medium (0.154-0.9 mm) or fine sand (＜0.154 mm) levels. The content and particle size of fillers are strongly related to the mortar performance. Fillers with similar particle size in the lime mortar samples indicated that the fillers had been screened by the craftsman, reflecting the maturity of historical mortar techniques. Moreover, sticky rice was found in all samples. Unlike pure calcite crystals with distinct edges and regular shapes, the mortar samples from Wulonggong Palace were composed of nano-sized and irregularly shaped calcite particles. The significant change in microstructure was the regulating effect of sticky rice ingredients on the carbonation process of lime mortar, making the sample structure denser and improving the overall performance. Also, the alkaline environment created by lime inhibited microbial growth, providing a guarantee for the long-term preservation of sticky rice ingredients. Fiber was observed in one mortar sample. As shown in SEM, the fibers in Sample WLH-5 penetrated through the mortar, serving for reinforcement and as a skeletal structure. Besides, the cavity structure of the fibers could store moisture during the carbonation process of the mortar, reducing early-stage shrinkage and the risk of cracking. In the historical lime mortar craft of ancient China, which has a long history, there was a technique of incorporating plant fibers and animal hair into lime mortar to enhance its toughness and prevent crack formation. Modern research has shown that the addition of fibers can significantly improve the mechanical properties and freeze-thaw resistance of mortar, effectively remedying the shortcomings of traditional Chinese air hardening mortar such as high shrinkage and low early curing hardness. Although fibers were not detected in all samples, this finding at least confirmed the application of the fiber blending technique to the mortar production process for Wulonggong Palace. Compared to calcium lime, magnesium lime has higher strength, crisp knocking sound, and some better properties, but it is prone to reacting with sulfides in the air, causing the mortar to become brittle and lose strength. Therefore, intensified observation and regular testing should be carried out in future conservation to avoid adverse effects of environmental factors on the mortar performance. The in-depth study of the mortar used for Wulonggong Palace is an interpretation of the history of imperial architectural engineering in the Ming Dynasty from a micro perspective. In addition, research on material characteristics and manufacturing techniques for historical mortar could provide important reference for the selection of restoration materials used for ancient buildings in the future.

Abstract:The weapons and ammunition from the shipwrecks of Zhiyuan and Jingyuan are physical evidence of the weaponry that the Northern Fleet of the Imperial Chinese Navy forces were equipped with during the First Sino-Japanese War. The gunpowder samples inside the cultural relics are of great significance to the study of gunpowder history. Instruments such as the Fourier infrared spectrometer, gas chromatograph-mass spectrometer, inductively coupled plasma emission spectrometer, scanning electron microscope-energy spectrometer, elemental analyzer, optical microscope, and ultra depth-of-field microscope were used to deeply study the internal gunpowder of five cultural relics from the shipwrecks of Zhiyuan and Jingyuan. The results show that black powder was used to fill the shells, guncotton was used as the filling agent in the shells and torpedo fuses, and the guncotton made into small-size powder was loaded into the ammunition. This preliminary study of gunpowder samples provides physical evidence for the weaponry of the Northern Fleet of the Imperial Chinese Navy during the First Sino-Japanese War (1894-1895), and also has significant importance for the advancement of research on the historiography of gunpowder technology.

Abstract:The Spring and Autumn and Warring States Periods were an important stage in the development of metal smelting and casting techniques in China; the main decorative crafts of this period included gold and silver inlaying. In recent years, a number of important Xirong remains have been discovered in Gansu, with the Shijia and Yucun site in Ningxian County and the Majiayuan site in Zhangjiachuan Hui Autonomous County as representatives. The metallic relics unearthed at these sites provide us with precious physical evidence, which can more objectively reflect the craftsmanship standard of this historical stage. In our work, we took “S”-shaped gold, silver and iron ornaments unearthed at the Shijia cemetery and the Majiayuan site as the study objects, and used modern analytical techniques such as super depth-of-field microscopy, X-ray fluorescence spectrometry, and scanning electron microscopy, in combination with the artifacts unearthed at related Qin tombs, to conduct an in-depth exploration and discussion. Through the analysis of two “S”-shaped gold, silver and iron ornaments, it was found that the “amalgamated mercury” technique was adopted in the production process, and that the ornaments were finely polished after engraving. This discovery not only reveals the techniques for gold, silver and iron ornament production in this period, but also provides important historical reference for subsequent research, which further enriches the understanding of the material culture of gold, silver and iron ornaments and the development of its production process.

Abstract:In 1985, Yangzhou Museum excavated a lacquer mask with cloud and auspicious animal patterns from the female coffin of the M102 Han tomb at Yaozhuang, Yangzhou. The lacquer mask was made using a Mujiazhu core-making method. The process includes making the core with Cotinus coggygria, plastering, applying two layers of primer, applying black brown and red finish on the surface, and depicting the decorative layer. According to the result of pyrolysis-gas chromatography/mass spectrometry, both sides of the lacquer film contained Chinese lacquer and dry oil. Using near-infrared spectrometry combined with chemical stoichiometry, it was determined that the dry weight ratio of lacquer to dry oil was 71.5%∶28.5% for the outer black brown lacquer film, and that for the inner red lacquer film was 66.7%∶33.3%. The nails embedded on the lacquer mask were made of a bronze alloy, and their surface was gilt. However, due to the influence of the burial environment, the Au contents of copper ornaments at different parts were different. Based on scientific understanding of the material, process, and diseases of the lacquer mask, a scientific conservation and restoration route was formulated. After comprehensive cleaning, traditional materials and techniques were used for core, lacquer film and paint restoration, to recover the integrity of this lacquer mask to the greatest extent and to achieve satisfactory results. The lacquer mask has been put into exhibition, and the overall effect is good.

Abstract:The surface finishing and treatment process is an important part of the production techniques for traditional wooden furniture and is also an important basis for its conservation and restoration. In this study, surface finishing and repairing materials for three typical pieces of furniture collected in the Palace Museum were analyzed using pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS). A variety of organic components were identified based on their characteristic pyrolysis products, and their treatment techniques were further revealed. The results show that waxing was the main technique, and the type of wax used was mainly beeswax. The treatment process included hot wax (Tangla) and rubbing wax techniques, etc. In particular, the characterization of the heating markers of beeswax could provide scientific evidence for the identification of the traditional Tangla technique. Unrefined shellac was also used in the refinishing treatment for furniture surfaces. In addition, various plant resins were also added to furniture finishes, such as commonly used pine resin, as well as benzoin and sandarac. This study contributes to the understanding of the materials and techniques of surface finishing and treatment for traditional wooden furniture, and the results could be applied to the restoration of wooden furniture.

Abstract:The tomb of Murong Zhong, from the Tuyuhun royal family tomb complex, represents the highest grade of the tombs discovered in this site to date. Among the exquisite artifacts unearthed were painted pottery artifacts, including standing human figurines, horse-riding figurines, notable for their intricate shapes and vibrant colors. In this work, we analyzed the structures, pigments, and adhesive materials for these relics, employing methods such as super depth-of-field microscopy, X-ray fluorescence spectrometry, X-ray diffraction, Raman spectrometry, and pyrolysis gas chromatography-mass spectrometry. Our findings reveal that:1) two distinct painting processes were used for the pottery artifacts:clay body-pigment layer, and clay body-primer layer-pigment layer; 2) the mineral pigments identified included miniumite, malachite, indigo, cinnabar, calcite, etc.; 3) the binding materials were found to be the animal glue. The analytical results not only provide methodological reference for investigating the production materials and techniques for ancient painted pottery relics, but also offer vital information in terms of the restoration of the related artifacts. This study is of significant importance for the conservation of painted pottery relics.

Abstract:The Chenghua Doucai porcelain has a significant position in the history of Chinese colored porcelain. Inheriting previous craftsmanship, its Doucai technique was developed and improved upon to reach an extraordinary realm, and also laid an important foundation for the Qing Dynasty overglaze pastel technique. In order to explore the red, yellow and green-firing techniques for the Ming Dynasty Chenghua Doucai porcelain and other related technical issues, we conducted a number of firing tests using a modern electric furnace and an ancient red furnace, and analyzed and inferred the suitable firing temperature and duration, heating curve, atmosphere, etc. for the Doucai porcelain from both macroscopic and microscopic perspectives. Considering the various firing defects observed during the tests, it seems that for Chenghua Doucai, its overglaze colors were developed best when fired for more than 6 hours at 780-800℃ in a pure oxidizing atmosphere.

Abstract:The precious collection of books in the Qing Dynasty palace, known as Tianlu Linlang, has been famous for a long time. For some of these books, a kind of coated paper was used for the cover. In this study, the coated paper was analyzed using multiple scientific approaches. The surface characteristics of the paper were understood through visual observation. The coating on this paper was observed and the fiber composition of the base paper was analyzed using optical microscopy, which led to the conclusion that the paper fiber was from wingceltis bark. The paper was scanned using Fourier transform infrared spectrometry, leading to the speculation that the main component of the powdery substance on the paper surface was kaolin. The paper surface was scanned using X-ray fluorescence spectrometry, which revealed that the coating mainly contained elements such as Si and Al, similar in composition to kaolin. Adhesive and pigment components in the coating were analyzed using pyrolysis gas chromatography-mass spectrometry, which revealed the existence of bone glue or animal skin glue, and indigo. The possibility of wax on the surface of the front coating of this paper was tested using differential scanning calorimetry. Based on the above results, we attempted to find approximate materials to imitate this coated paper in order to apply it to the restoration of relevant ancient books.

Abstract:At present, it is generally found that there are calcium and magnesium carbonate deposit crusts on the surface of unearthed stone relics. The deposit crusts will affect the safety of their surface decorations, especially for polychrome or gilt stone relics, so the cleaning method must be targeted and controlled. Scanning electron microscopy-energy dispersive spectrometry and Fourier transform infrared spectrometry were used for the analysis of simulation samples in order to investigate the cleaning mechanism of polyvinylamine (PVAm) gel. The results show that the PVAm gel could slowly release an acidic cleaning agent, thus controlling its penetration and diffusion, so that the cleaning effect occurred evenly on the surface of deposit crusts. The absorption and porosity of the samples before and after cleaning were also tested. The results show that stone relics themselves, especially the carbonate stone and painting or gilding layer, could avoid being damaged by the PVAm gel, and thus the safety of cleaning was evaluated. In addition, the results of cleaning on small pieces of cultural relics show that it was a safe and effective cleaning method, which could provide a new idea for research on the cleaning materials for unearthed stone relics.

Abstract:Samye Monastery is known as the first temple in Xizang, and a large number of murals are preserved therein. In this study, X-ray diffraction, scanning electron microscopy and optical microscopy were used to analyze the structure and material composition of the mural plaster layer of Samye Monastery. The results show that the main components of the mural plaster layer were Aga soil, sand and charcoal, with a mass ratio of about 24∶75∶1. Charcoal is not a necessary material for making Tibetan murals, but why was the charcoal added to the murals in Samye Monastery? Through infrared thermographic inspection, it was found that the mural dado was wet, and the addition of charcoal into the plaster layer could play a moisture-proof effect. This study could provide reference for the conservation and restoration of the murals in Samye Monastery.

Abstract:To uncover the craftsmanship and materials for painted warrior figurines and to gain insights into their rich scientific and unique artistic significance, a variety of analytical techniques, including microscopic observation, laser Raman spectrometry, scanning electron microscopy-energy dispersive spectrometry, X-ray diffraction, Fourier transform infrared spectrometry and pyrolysis gas chromatography-mass spectrometry, were employed to examine a sample excavated from Murong Zhi’s tomb of the Tang Dynasty in Wuwei, Gansu. The findings reveal that the warrior figurine was constructed with separate parts. A ground layer was applied to the wood components using a “one hemp layer, one mortar layer” technique prior to painting. From the innermost to the outermost, the structure was comprised of a hemp layer, a mortar layer, a base color layer, and a pigment layer. Animal glue was used as a binder in the pigment layer, and flour may have been added into the ground layer. The pigments used included carbon black for black, iron red for red, miniumite for orange, azurite for blue, and malachite for green, with the ground color layer predominantly consisting of lead white. The selection of wood as the primary material for this segmented wooden figurine may reflect a long-standing funeral tradition of the Hexi region. The application of a hemp ground layer on wood surfaces was a practice that could be traced back to the Tang Dynasty and might have a profound impact on the “one hemp layer, five mortar layers” technique used in ancient Chinese architecture during the Ming and Qing Dynasties. The analysis and interpretation of the craftsmanship for this painted warrior figurine offer new scientific insights into the painted woodcraft of the Tang Dynasty and provide strong physical evidence for investigating the multicultural influences within the Tuyuhun region.

Abstract:Hepu, as the starting port of the Han Dynasty Maritime Silk Road, has witnessed a large number of precious bronzes unearthed at its Han tomb group. However, most of the bronzes are fragile, and seriously corroded and mineralized. In order to study their preservation status, corrosion characteristics, and the causes of corrosion and mineralization, and provide a scientific basis for the conservation and restoration of the typical fragile ones, Ultra depth-of-field microscopy, X-radiography, metallographic microscopy, X-ray fluorescence spectrometry, and scanning electron microscopy-energy dispersive spectrometry were used to detect and analyze the microstructures, corrosion products and compositions of nine bronze wares unearthed at the Hepu Han tomb group. The results show that the objects were made of a copper, tin and lead ternary alloy, mainly low-tin bronze, and had a thin matrix. They also featured serious copper loss and a high content of oxygen, and arsenic might have come from the burial environment, and no chlorine was found. In addition, corrosion mineralization was serious, and its main causes might be due to the low-tin alloy, thin matrix, acidic soil and other internal and external reasons. Therefore, the traditional conservation technology for bronzes is no longer applicable, and it is urgent to explore the conservation technology suitable for such objects. Also, immediate conservation work should be carried out at archaeological excavation sites.

Abstract:After the restoration of ceramic relics, their restoration materials often undergo aging and yellowing during exhibition and transportation or due to human interaction. This significantly lowers the display quality of cultural relics and subsequently affects audience satisfaction. Therefore, it is imperative to gain a thorough understanding of the mechanisms of yellowing shown by different restoration materials and fillers upon mixing. In this study, we selected several adhesives commonly used for porcelain restoration:Hezhong AAA standard adhesive, Hezhong AAA anti-yellowing adhesive, Hongxing 509, Araldite 2020, and Hxtal NYL-1. Furthermore, several commonly used fillers were also chosen, including talcum powder, kaolin, titanium dioxide, UV absorbent and glass beads. Taking into account the climatic characteristics of the northwest arid region, we conducted aging tests of dry heat, UV exposure, salt spray, and freeze-thaw cycling on these materials. Colorimetry, hardness testing, scanning electron microscopy and X-ray diffraction were used for characterization. Accordingly, then the yellowing mechanisms of various materials after aging were discussed, and the impact of climate environment on these restoration materials was investigated. The findings revealed that the Hxtal NYL-1-mixed restoration materials exhibited excellent color stability in UV aging and dry heat aging, and the Hongxing 509-mixed ones maintain hardness admirably in salt spray aging and freeze-thaw cycling. Additionally, among the fillers, the results show that talcum powder and titanium dioxide exhibited remarkable color stability, while kaolin showed exceptional hardness stability. These could help restorers select suitable restoration materials, ensuring better preservation and exhibition of ceramic relics. By combining basic research and current research hot spots, this study offers both exploratory and comprehensive insights, carrying significant application value.

Abstract:i>Professor Gladys Yang is a double-sided oil painting collected by the National Museum of China. Due to the influence of the preservation environment and aging of materials, the work has shown deformation of the support body and cracking, warping and peeling of the pigment layer on the back. In this study, we surveyed the basic condition of the oil painting, analyzed the materials used to make the work, and assessed the diseases. In addition, according to the basic principles of conservation and restoration, we formulated and carried out restoration objectives and programs, and also solved the problem of selecting reinforcement solvents, which is one of the difficulties in restoration technology. The oil painting has been restored to a stable state following an effective restoration technology route in this work, which provides a study case for the restoration of double-sided oil paintings in China.

Abstract:For over a century, a huge number of bamboo and wooden slips have been unearthed from ancient wells (cellars) in China. The burial conditions of these slips were complex, and they were all saturated with water when excavated, often piled up chaotically, with poor preservation conditions, severe material corrosion, and low strength. Scientific and standardized on-site conservation work for bamboo and wooden slips holds significant academic value and is characterized by its technical implementation, which is highly time-sensitive and specialized. However, there are still issues such as weak research foundations and an incomplete theoretical system in this field, necessitating deeper systematic research and standardization efforts. This study, after summarizing practical experience from on-site conservation and collecting conservation materials, has organized and generalized the on-site conservation technology for ancient well (cellar) bamboo and wooden slips and represents a collaboration of cultural heritage conservation and archaeological work. The on-site conservation technology mainly includes:investigating the burial conditions upon discovery; controlling the on-site environment through methods like constructing protective shelters; reinforcing the walls of ancient wells (cellars) to ensure the safety of both personnel and slips themselves; cleaning silt and contained objects; sampling soil and slips without characters; extracting slips based on their individual, bundled, clustered, or scattered burial conditions; screening and cleaning the excavated fill soil; applying moisture-retaining and mold-preventing treatments to the extracted slips; and promptly packaging and transporting them back indoors for storage. The principle is to maximize the integrity and safety of slips while preserving and extracting as much archaeological information as possible. This review of the on-site conservation technology for ancient well (cellar) bamboo and wooden slips could serve as reference for the conservation work at similar archaeological sites in the future.