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Abstract Ancient Chinese bronzes, particularly bronze mirrors, often develop a fatty, oily, or greasy film on their surface, known as patina. This film can appear silvery, green, or black. Bronze mirror samples from the Spring and Autumn Period (770–476/403 BCE) to the Ming Dynasty (1368–1644 CE) were analyzed using a systematic approach that included super depth of field three-dimensional microscopy, scanning electron microscopy/energy dispersive X-ray spectroscopy (SEM–EDS), Raman spectroscopy, and THM-Py-GC/MS. The analysis indicates the presence of advanced organic acid lead in the matrix of ancient bronze mirrors. The ancient existence of the lost wax method combined with the mould method of bronze casting technology is verified through simulation experiments and ancient literature. Ancient bronze mirrors may have utilized this technique, with advanced organic acid lead remaining in the mirror mould that entered the bronze mirror matrix during pouring. The Lead organic acids in bronze mirrors readily precipitate on the surface and cover the mirror. The change in the greasy sheen on the surface of the bronze mirror may be related to the degree of corrosion. If the mirror's corrosion level is low, the organic acid lead film remains transparent. If the level of corrosion is significant, the organic acid lead film may darken in color due to oxidation, aging, hydrolysis, or microbial activity.

Abstract The “Nanhai I” shipwreck is an important discovery in the underwater archaeology of China, and many ceramics have been unearthed. These ceramics are important material artifacts of China’s “Maritime Silk Road” and have considerable significance for the study of foreign trade in the Southern Song Dynasty (1127–1279 A.D.). However, these ceramics have been buried in a marine environment for approximately 800 years and have all been corroded to varying degrees, with green-glazed pottery being the most severely corroded. In this study, the chemical compositions of five samples of green-glazed pottery and the corrosion morphology and mechanism of a representative sample were analyzed by optical microscopy, scanning electron microscopy-energy dispersive X‐ray spectrometry (SEM–EDS), Raman spectroscopy, and X-ray diffraction (XRD). Results: The green glaze is a low-temperature silica-aluminum oxide-lead oxide (SiO2-Al2O3-PbO) glaze with copper ions (Cu2+) as the main colorant. The corrosion morphology is characterized by alternating silicon (Si)- and lead (Pb)-rich layers, a sharp reaction interface between the Si-rich layer and the pristine glaze, and a relatively high porosity of the Si-rich gel layer, which is formed by the accumulation of spherical hydrated silica colloidal particles. These features suggest that the glaze was corroded through an interface-coupled dissolution–precipitation mechanism and that the properties of the gel pores controlled the reaction kinetics. Fluctuations in the solution properties at the reaction interface produced the complex morphology of the gel layer, whereas changes in the dryness and humidity of the environment are not essential factors. The samples have been corroding in the marine environment for nearly a thousand years, and explorations of the corrosion morphology and mechanism could provide reference information on the corrosion of various ancient ceramics and glasses and a basis for scientific conservation of these objects.

Abstract This work proposes the virtual restoration of the Bodhidharma polychrome sculpture from the Lingyan Temple in China. Based on scientific analyses and simulation experiments, exterior colours and textures were virtually restored by combining 3D scanning and multi-view 3D reconstruction. At the same time, an efficient cultural relics high-fidelity information 3D modelling method was proposed. Colours and textures are essential for polychrome cultural relics, reflecting the historical appearance and technology. Due to long periods of natural ageing and the destruction of environmental factors, the colours and textures of polychrome sculptures are often altered or radically changed, making it difficult for people to appreciate the initial appearance. With the rapid development of digital technology and high-fidelity 3D modelling, virtual reality technology allows us to restore the appearance of cultural relics. This study expands the dimension of cultural relics exhibition, provides new perspectives for archaeology, art history and cultural heritage research, and provides a reference for the virtual restoration and digitalised archive of other cultural relics.

Abstract Nanhai I shipwreck was a large wooden merchant ship (22.15 m in length and 9.85 m in width) built in the Southern Song Dynasty (1127–1279 A.D.) of China, which was heavily loaded with a large number of porcelain and iron artifacts. In the South China Sea, it was found in 1987 and lifted as a whole in 2007. Its excavation provides a precious opportunity to reveal the preservation status of Nanhai I shipwreck. Iron compounds give rise to challenges in conservation procedures and the long-term stability of Nanhai I shipwreck. In this paper, the degradation of the wood and the iron deposits in the wood structure are investigated from the aspects of microscopic morphology, composition, and distribution to evaluate the preservation state of the waterlogged wood. Physical parameters, chemical composition, and the results of elemental analysis, and FTIR analysis suggest that the cellulose of wood is degraded, and the relative concentration of lignin increases. The ash content varies greatly among different samples, and the element of the highest content in ash is iron. The study on transverse and longitudinal sections from samples indicate that the deposits are unevenly concentrated in the cell lumen, middle lamella, rays, and pits of the cell wall. The cell lumen is filled with deposits in areas close to the surface of the samples. The XRD analysis demonstrates that the deposits in wood are mainly iron deposits, containing compounds pyrite (FeS2), siderite (FeCO3), iron oxyhydroxides (FeOOH), and magnetite (Fe3O4). The micro-X-ray Fluorescence mapping analysis suggests that the content of iron is relatively richer while containing less sulfur on the exterior of the sample. The presence of iron deposits accelerates wood degradation and increases the safety hazards of shipwrecks in the preservation process. We hope that our findings can make a modest contribution to iron removal from waterlogged archeological wood and shipwreck conservation.

Abstract As non-renewable cultural heritage, wall paintings play an important role in society. To reveal the trends in the scientific analysis of mural paintings, 845 relevant research articles published from 2011 to 2021 were collected from the Web of Science database and analyzed. The VOSviewer software was adopted to map the network data of scientific publications, so that relationships among authors, countries, institutions can be displayed, and the co-occurrence of keywords and co-citation can be analyzed. The results revealed close and strong interconnections between the top authors, suggesting a considerable strong research link in this field. The cooperation between research institutions was relatively close. The most productive country of relevant publications was Italy. The leading journals for the scientific analysis of wall paintings were Journal of Raman Spectroscopy and Journal of Cultural Heritage. At present, the hotspots of scientific analysis and research on wall painting are revealing the composition, distribution, origin, and deterioration mechanism of pigments, alongside with evaluating the effects and mechanism of conservation materials and techniques. On the one hand, a possible development direction in this field is introducing more cutting-edge analysis and data processing methods. On the other hand, scientific analysis is increasingly adopted to guide the research and development of mural conservation materials.

Abstract Scientific analysis revealed the materials and techniques used in the process of making polychrome sculptures providing a solid foundation for the protection and restoration of the painted statues. In addition, the analyses revealed changes in colour schemes applied to the sculptures can provide the basis for the virtual restoration of the painted statues. In order to carry out scientifically-informed protection and restoration of the Bodhidharma statue from the Lingyan Temple, Changqinq, Shandong, several analytical methods such as optical microscope (OM), Micro-Raman spectroscopy (μ-RS), scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDS) and Fourier transform infrared spectroscopy (FTIR) were employed. Analyses clearly reveal the information including the stratigraphic structure and the composition of pigment. The use of silver foils and golden yellow pyrophyllite mineral to replace gold foils were found in the gilding paint layer in the later repainting after the Song Dynasty. This work reports the coexistence of emerald green (Cu(C2H3O2)2·3Cu(AsO2)2) and the degradation product lavendulan (NaCaCu5(AsO4)4Cl·5H2O) in large areas of the paint stratigraphy and on the surface confirming that the degradation of emerald green is related to the thickness of the paint layer; in thinner paint layers emerald green is transformed in lavendulan, while thicker layers of contain both lavendulan and emerald green, suggesting an environmental source of chlorides.

Abstract For conservation and restoration purposes, the precious historical rubbings preserved in Wuyuan Museum were studied by multi-analytical techniques including 14C radiocarbon dating, scanning electron microscopy (SEM), Pyrolysis–Gas Chromatography/Mass Spectrometry (Py-GC/MS) and Herzberg staining method. The results showed that the Py-GC/MS method is an efficient method for identifying the raw materials of paper and ink in historical rubbings simultaneously. Through Py-GC/MS analysis, five types of constituents could be detected: (1) polycyclic aromatic hydrocarbons (PAHs) from soot; (2) compounds related to tar of conifer wood: retene and methyl dehydroabietate; (3) marker compounds from the whole egg; (4) additive compounds: menthol and curcumene, which were found for the first time in ink; (5) biochemical compounds from bark paper: β-amyrin and α-amyrin. Based on the above results, the ink type, binding media and additives in ink, as well as the fiber origin of the rubbing paper could be concluded. This study could not only provide scientific support for conservation and restoration of the historical rubbings preserved in Wuyuan museum, but also give method guidance for analysis of the uncharacterized rubbings from different origins.

Abstract The spontaneous degradation of pigments in painting may occur depending on environment, especially the surrounding condition of high humidity and soluble salts. Even some of these are well studied, more investigations are still in need for heritage science. Paint cross sections from Vairocana Statue in Dazu Rock Carvings, one of World Cultural Heritage, Chongqing, China are studied by optical microscopy (OM), Raman spectroscopy (Raman) and mapping, and scanning electron microscopy coupled with energy dispersive X-ray analysis (SEM–EDS). Ultramarine blue, emerald green, synthetic atacamite, vermilion, red lead, gold foil, orpiment, cerussite, gypsum and barite are identified as pigments. Moreover, lavendulan (NaCaCu5(AsO4)4Cl·5H2O) and mimetite (Pb5(AsO4)3Cl) are degradation products of emerald green (Cu(C2H3O2)2·3Cu(AsO2)2) and cerussite(PbCO3) originally used as green pigment with mixture. These secondary products are formed via multistep progresses as degradation of emerald green and cerussite, oxidation of arsenite ((AsO2)−), migration of arsenate ((AsO4)3−) and precipitation reaction of these ions with other necessary ions from environmental conditions. Based on the pigment and paint layer stratigraphy analysis, the paintings of the statue have been executed at least four times and the most recent may be after 1850s. The formation of lavendulan give rise to a highlight for identification of green copper-arsenic containing pigments and characterization of degradation in complex conditions.

Abstract Red discolorations are an effloresce phenomenon detect on the surface of stone objects and considered as damage factor in both esthetic and conservation points of view. It is very difficult to remove and seldom report about their weathering mechanism. Recently, numerous of red discolorations have affected the limestone objects of Lingyan Temple in Shandong province, one of the most important building materials in China. In order to set up the appropriate conservation remedy, it is essential to identify the origin, characteristics, composition, and the formation process of red discolorations. Several analytical and investigation techniques, such as X-ray fluorescence spectroscopy (XRF), X-ray diffraction (XRD), Micro-Raman spectroscopy (Raman), Fourier transform infrared spectroscopy (FTIR), scanning electron microscopy (SEM) equipped with energy dispersive spectrometer (EDS) were used to better understand the red discolorations. The results demonstrated that the discolorations on limestone surface have been caused by carbonic acid weathering process. The red discolorations consisted mainly of kutnohorite (Ca(Fe,Mg,Mn)CO3) and iron oxides. They showed tabular, lamellar, and granular morphologies, which originated from the in situ carbonic acid weathering of kutnohorite. After rainfall, the Ca, Mg, Mn ions with relatively high solubility were primarily leached from carbonatite phases. It was resulting in the sedimentation of red iron oxides through a chemical reaction and physical adhesion. Based on those analyses, a chelating agent (ethylenediamine tetraacetic acid disodium salt) was chosen to remove theses red discolorations on the stone object.

Abstract The ancient Chinese Jun Porcelain has of typical high fired calcium silicate glaze. After observation of Jun porcelain shards excavated from Juntai Kiln in Yuzhou, Henan Province, China, two pieces with light greenish blue glaze and reddish purple glaze are selected for study as special corrosion samples buried in soil environment. Taking the corrosion of each phase of the overall glaze into consideration, the chemistry compositional and morphological structural features of the earthworm-walking patterns and their surrounding white area (corroded zone) in the glazes are compared and studied with optical microscopy (OM), scanning electron microscopy with energy dispersive X-ray analysis (SEM–EDS), Raman spectroscopy (Raman) and electron microprobe (EPMA): during the firing of Jun Porcelain, the dendritic and columnar crystals coming out of the glaze and mostly in surrounding corroded areas are identified as wollastonite (CaSiO3), which provides active sites for localized corrosion. The wollastonite crystalline phases have preferential corrosion initiated by pitting corrosion relative to glassy phase, leaving dendritic or columnar pits and craters to dissolve into calcium ions and silicic acid and losing into the burial environment. Some calcium ions in the surface pits react with dissolved inorganic carbon (DIC) from the soil to form calcium carbonate (CaCO3) precipitated on the surface of the glazes. The cracks formed during the cooling process and the interconnected craters caused by crystals dissolution can provide channels to facilitate the progression of the corrosion. This research is of great significance to the study of the corrosion mechanism of ancient porcelain and the conservation of its cultural relics. It has changed the traditional view that porcelain is corrosion-resistant. At the same time, the study of the corrosion process and characteristics of ancient porcelain can provide reference for modern ceramic research and corrosion protection.

Abstract Man-made ancient Chinese barium copper silicate pigments: Chinese (Han) Purple, BaCuSi2O6; Chinese (Han) Blue, BaCuSi4O10; Chinese Dark Blue, BaCu2Si2O7 (in summary called Chinese blues), and platelet-like crystals of BaSnSi3O9 were detected on mural paintings of a tomb in Luoyang City, Henan Province, China, dated to Western Han Dynasty (206 BC–8 AD). The pigments of the LY01 and LY02 samples were analyzed by archaeometrical methods: powder X-ray diffractometry (XRD), scanning electron microscopy (SEM–EDX) and micro-Raman spectroscopy. While the artificial nature of the ancient barium copper silicates was undoubted, the synthetic or mineral origin of BaSnSi3O9 of these murals had to be clarified. Involvement of the rare mineral pabstite Ba(Sn,Ti,Zr)Si3O9 from the Tian Shan mountains could be ruled out due to absence of Ti and Zr in the elemental composition. Tin compounds as admixtures to the lead minerals—the latter required as flux additive for the preparation of the Chinese blues—or tin admixtures to pristine barium starting minerals could be excluded, as well as the use of tin containing mineral mushistonite (CuSn(OH)6), primarily intended to be applied as copper source. Related to the findings for the production of Egyptian Blue (CaCuSi4O10), bronze or bronze scrap including also corroded material was used intending copper recycling. For the synthesis of the Luoyang Chinese blues only low amounts of bronze or bronze scrap were required providing the additional advantage to form in presence of air a tin/lead oxide flux with lowered vitrification temperatures and viscosities. This marked the advent of an ‘innovative production technology’ avoiding addition of large amounts of lead minerals as an effective lead-only flux. Despite of the chemical similarity to production of Egyptian Blue, the tin/lead based developments for the Chinese blues were anticipated to be independent excluding technology transfer from ancient Egypt. For further substantiation of the appearance of pabstite in the Luoyang Chinese blues a contemporary independent synthesis was sought, carried out under conditions similar to those of the barium copper silicate syntheses (1000 °C, but absence of a flux) starting from cassiterite (SnO2), quartz (SiO2) and witherite (BaCO3).