Corrosion mechanisms of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty excavated from the Nanhai No. 1 shipwreck

Corrosion mechanisms of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty excavated from the Nanhai No. 1 shipwreck | Research Square window.SnipcartSettings = { analytics: { enabled: false } }; (function() { var accessVector = localStorage.getItem('access_vector') || ''; window.dataLayer = window.dataLayer || []; if (accessVector) { window.dataLayer.push({ user: { profile: { profileInfo: { snid: accessVector } } } }); } })(); (function(w,d,s,l,i){w[l]=w[l]||[];w[l].push({'gtm.start':new Date().getTime(),event:'gtm.js'});var f=d.getElementsByTagName(s)[0],j=d.createElement(s),dl=l!='dataLayer'?'&l='+l:'';j.async=true;j.src='https://www.googletagmanager.com/gtm.js?id='+i+dl;f.parentNode.insertBefore(j,f);})(window,document,'script','dataLayer','GTM-K279D39R'); Browse Preprints In Review Journals COVID-19 Preprints AJE Video Bytes Research Tools Research Promotion AJE Professional Editing AJE Rubriq About Preprint Platform In Review Editorial Policies Our Team Advisory Board Help Center Sign In Submit a Preprint Cite Share Download PDF Article Corrosion mechanisms of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty excavated from the Nanhai No. 1 shipwreck Yanzi Wang, Yongbin Yu, Naisheng Li, Qiang Wu, Xiaolin Cheng This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-6289041/v1 This work is licensed under a CC BY 4.0 License Status: Published Journal Publication published 23 Jul, 2025 Read the published version in npj Heritage Science → Version 1 posted 13 You are reading this latest preprint version Abstract Understanding the influence of marine-organism attachment on the corrosion of ancient porcelains is crucial for the conservation of underwater cultural heritage. In this study, the mutually beneficial relationship between siliceous sponges and ancient silicate ceramics was elucidated for the first time. The complex interactions between the sponges’ secondary metabolites (nitrogen-containing alkaloids and carbon-containing organic mucus) and corrosion products were studied in detail, along with their filtration and purification effects. We comprehensively analysed the morphological structures and chemical compositions of the surface concretions and glaze surface of bluish-white porcelains excavated from the Nanhai No. 1 shipwreck. The results indicated that the concretions consisted of sponge remains, with the skeleton primarily composed of silicon carbonate. The main corrosion products were iron(III) oxide-hydroxide and iron(III) oxide. The sponge-secreted alkaloids formed secondary corrosion products which bonded with the primary corrosion products in the surface alteration layer, resulting in significant differences in corrosion morphology across the glaze surface depending on concretion detachment. This study demonstrates the presence of an inorganic/organic silicon cycle and elucidates the complex interactions therein. Our findings serve as an important reference for research on the conservation of excavated underwater ancient ceramics, marine palaeontology, and geochemistry. Nanhai No. 1 shipwreck Southern Song Dynasty bluish-white porcelain of Hutian kiln corrosion mechanisms sponges Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Figure 13 1 Introduction Nanhai No. 1 was a Chinese merchant ship that sank in the South China Sea along the Maritime Silk Road during the Southern Song Dynasty (1127–1279). The ship was discovered in 1987, buried in seafloor sediments at a depth of 25 m, ten nautical miles southwest of Xiachuan Island, Guangdong Province, off the south coast of China. [ ] Its cargo included significant quantities of ceramics as well as ironware. [ 2 ] The ceramics excavated from the shipwreck included bluish-white porcelains from the renowned Hutian kiln in Jingdezhen. These porcelains possess several distinct characteristics of Southern Song Dynasty pottery: (1) a whitish and thin body with a delicate texture; (2) a lustrous and smooth glaze with a bluish-white colour and glass-like texture; and (3) decorative motifs produced by incision, carving, or impression. [ 3 ] The porcelains also have an unglazed rim, as the ceramics were formed by inverted firing (i.e., with the rim facing down). The excavated artefacts have great artistic, historical, and scientific value. However, submersion in seawater for nearly a millennium has led to varying degrees of corrosion and damage. Several samples have large concretions attached to the unglazed rim and neighbouring glaze surface or an altered gel layer covering the glaze. Understanding the influence of marine-organism attachment on the corrosion of ceramic artefacts is therefore crucial for the conservation of this underwater cultural heritage. Since the 1980s, materials scientists, marine chemists, and physicists have sought to elucidate the corrosion mechanisms of ancient ceramics. Studies have focused on the corrosion of the glass phase, [ 4 ],[ 5 ] crystalline regions, [ 6 ],[ 7 ] and other phase structures [ 8 ],[ 9 ],[ 10 ] in the glaze layer; the formation of surface concretions and corrosion products and their interactions with the artefact body; [ 11 ] microbial corrosion; [ 12 ],[ 13 ],[ 14 ],[ 15 ],[ 16 ],[ 17 ] and other factors. [ 18 ],[ 19 ],[ 20 ] However, few studies have investigated the effects of voids and entrained bubbles, which are highly prevalent in ancient ceramics and considerably influence the corrosion process, despite their isolation from the external environment. Pertinent studies have found that bubbles in glaze can affect the direction in which corrosion structures arrange on the artefact surface, [14] influence the chemical composition of the local glaze surface, [6] create rapid corrosion pathways and deposition sites for aqueous solutions and foreign contaminants, [7],[9],[13] and provide space for the growth of corrosion products. [12] In addition, despite several investigations into the effects of calcium-rich marine-organism attachment on the corrosion of ancient ceramics, including the influence of coralline algae, [12] bryozoans, and oysters, [17] few reports have explored the influence of sponges with siliceous spicules on ancient ceramics. Consequently, further research is required to elucidate how bubbles in glaze participate in the corrosion of ancient ceramics and the unique corrosion pathways of ceramics with attached siliceous sponges. In this study, we investigated the morphological evolution of bubbles in ancient ceramic glazes and the complex interactions between siliceous sponges and ancient ceramics, intending to elucidate the mechanisms of bluish-white porcelain corrosion in marine environments and identify methods for the conservation of such porcelain wares. Bluish-white porcelains from the Nanhai No. 1 shipwreck—submerged in a marine environment for approximately 800 years—were subjected to technical analyses to explore the formation mechanisms and morphologies of the corrosion products. The findings not only enhance our understanding of the corrosion mechanisms of ancient bluish-white porcelain wares in marine environments but also serve as a key reference for future research on the long-term corrosion mechanisms of modern silicate glasses. 2 Materials and methods 2.1 Materials Porcelain fragments (Figs. 1a and 1b) from the Nanhai No. 1 shipwreck were desalinated at the Maritime Silk Road Museum, Guangdong Province, China, for 12 weeks prior to their use in the present study. The unglazed rim and neighbouring glaze surface of the ceramics were covered by black–brown concretions. Yellowing was observed on certain parts of the glaze surface, and both the inner and outer walls were densely covered with dark spots. Samples were cut from the porcelain fragments, and the cross-sections were ground and polished using 1500-mesh boron carbide powder. The samples were sequentially washed with deionised water (2 × 15 min) and ethanol (1 × 15 min) in an ultrasonic bath and dried in an oven at 110°C for 3 h. 2.2 Analytical methods 2.2.1 Energy dispersive X-ray fluorescence (ED-XRF) spectroscopy The chemical compositions of the glaze and concretions were quantitatively analysed by energy dispersive X-ray fluorescence (ED-XRF) spectroscopy (Eagle III, EDAX Inc., USA). Testing was performed on the natural surface of the glaze and concretions and the attachment layer of the concretions (where they attached to the glaze surface). The ED-XRF spectrometer had the following specifications: side-window rhodium target, 50 W X-ray tube, downward irradiation, and lithium-drifted silicon (Si(Li)) detector. Samples were tested with an X-ray tube voltage of 50 kV, tube current of 200 µA, vacuum optical path, incident X-ray beam spot diameter of 300 µm, and measurement duration of 200 s. For quantitative analysis, calibration curves were created using a series of 13 standard reference materials for non-destructive ancient ceramics testing, developed by the Shanghai Institute of Ceramics of the Chinese Academy of Sciences (Shanghai, China). 2.2.2 Microscopy The macromorphology of the natural surface and polished cross-sections of the samples were examined under a three-dimensional (3D) ultra-depth microscope (VHX-6000; Keyence). The micro-morphology and chemical composition were characterised using cold-field-emission scanning electron microscopy (SEM; SU8100, Hitachi, Japan) and energy dispersive X-ray spectroscopy (EDS; Xplore 30, Oxford Instruments, UK). SEM analyses were performed in a low-vacuum environment (10 − 3 Pa) at an accelerating voltage of 5 kV, with EDS spectra acquisition lasting for 60 s at a working distance of 15 mm. To examine the cross-sectional microstructures, 1 × 1 × 1 cm pieces were cut from the edges of the samples using a diamond saw blade, embedded in epoxy resin, and polished with silicon carbide sandpaper and diamond polishing pastes (3 and 1 µm). 2.2.3 Micro-Raman spectroscopy and X-ray diffraction (XRD) The phase compositions of the glaze and concretions were characterised by micro-Raman (µ-Raman) spectroscopy (WITec alpha300 R, Oxford Instruments, UK) with a 100× optical lens and 532 nm laser. Baseline removal was performed with LabSpec software (Horiba, Japan), and the spectra were smoothed and deconvolved using Origin software (OriginLab, USA). The phase composition of the concretions was further analysed using X-ray diffraction (XRD; D8 Discover, Bruker, Germany) with Cu Kα radiation (40 kV, 40 mA) in the 2 θ range of 5°–80°. The spot diameter and step size were 20 µm and 6°/min, respectively. 3 Results 3.1 Chemical composition of glaze The transparent regions of the glaze surface were analysed by ED-XRF spectroscopy (Table 1 ). The chemical composition was consistent with those of bluish-white porcelains produced by Hutian kiln in Jingdezhen during the Southern Song Dynasty. The glaze comprised a quaternary CaO-MgO-Al 2 O 3 -SiO 2 system, with CaO being the primary fluxing agent. The glaze also contained Fe in the form of Fe 2 O 3 ; however, because this oxide is sensitive to the kiln atmosphere, Fe also existed in the reduced form Fe 2+ . This produced a blue–green colour [ 21 ] that manifested as a bluish-green tint on thicker parts of the glaze. In addition, MnO and P 2 O 5 were present in the porcelain glaze, indicating that glaze ash or plant ash may have been introduced into the glaze formulation. The glaze coefficient b (calculated as b = RO/(RO + R 2 O), where RO represents the content of alkaline earth metal oxides and R 2 O represents the content of alkali metal oxides [ 22 ] ) had a value of b > 0.76, which is consistent with typical Ca-based glazes. Table 1 Major and minor components of the glaze (average values) Region wt% µg/g Na 2 O MgO Al 2 O 3 SiO 2 K 2 O CaO TiO 2 Fe 2 O 3 MnO P 2 O 5 Glaze surface 0.63 1.02 16.71 70.12 2.78 7.46 0.05 0.23 623 333 Table 2 lists the elemental composition of the natural surface and polished cross-section of the glaze, as determined by EDS. The cross-section was free of corrosion and therefore considered to be representative of the chemical composition of the original glaze. [4],[5],[9],[12] The Fe content of the glaze surface (0.6 wt%) was higher than that of the cross-section (0.3 wt%), which was ascribed to the gradual deposition of Fe from ironware on the same ship and other external contaminants (e.g., rust) carried by seawater. The K, Ca, and Zr contents of the glaze surface (2.52, 8.51, and 3.07 wt%, respectively) were lower than those of the cross-section (3.06, 9.24, and 9.50 wt%, respectively). This was attributed to cation leaching and ion exchange between the glaze surface and seawater. The Mg content was higher in the glaze surface (0.33 wt%) than in the cross-section (0.30 wt%), which was associated with the abundance of Mg 2+ in seawater. Table 2 Elemental composition of natural glaze surface and polished cross-section (wt%) Region O Mg Al Si K Ca Mn Fe Zr Glaze surface 43.51 0.33 9.58 31.85 2.52 8.51 / 0.62 3.07 Cross-section 33.83 0.30 10.59 32.95 3.06 9.24 0.26 0.27 9.50 3.2 Analysis of concretions 3.2.1 Morphology The surface and cross-sections of the concretions attached to the sample surface were examined under a 3D ultra-depth optical microscope (Figs. 2a–2d). The concretions had a complex morphology with significant heterogeneity. Porous mesh-like sponge remains with translucent white granules embedded within them were observed at the rim of the artefact and on the neighbouring glaze surface. The mesh-like sponge remains also had irregular polygonal pore structures with diameters ranging from approximately 3 to 300 µm. The pores were filled with black–brown material. Notably, bored pits of various depths were observed on the artefact surface beneath the concretions. Furthermore, the interface between the concretions and porcelain body was filled by an approximately 30 µm-thick corrosion product layer. 3.2.2 ED-XRF analysis The natural surface and attachment layer of the concretions (where they attached to the glaze) were analysed by ED-XRF (Table 3 ). The yellow skeleton, brown concretions, and black–brown material filling the pores were analysed separately. The attachment layer did not exhibit black regions; therefore, only yellow and brown areas were analysed. The yellow skeleton at the attachment layer would have been isolated from seawater as the concretion layer grew; therefore, its data were assumed to be representative of the original sponge struts. The results revealed that the yellow skeleton was siliceous, with that near the attachment layer (assumed to be the original chemical composition) having a Si content of 47.37 wt% and Ca content of only 0.37 wt%, indicating an extremely low possibility of a calcareous skeleton. In contrast, Fe was the predominant component of the black–brown filler (73.49 wt%), while the Si content (16.22 wt%) was significantly lower than that of the skeleton. Therefore, these regions were ascribed to Fe-rich contaminants and sea-sand deposition. The chemical composition of the brown concretions was similar to that of the yellow skeleton, but with a higher Fe content and lower Si content. All regions also contained S, which likely originated from sulphate salts from sea mud on the seafloor. Table 3 ED-XRF analysis of the concretions wt% Al Si S K Ca Ti Fe Natural surface Yellow skeleton 9.91 41.49 3.32 1.36 0.60 0.54 42.78 Brown concretions 7.76 38.26 4.14 1.58 0.39 0.61 47.26 Black–brown filler 4.73 16.22 3.49 1.15 0.29 0.62 73.49 Attachment layer Yellow skeleton 8.78 47.37 2.05 1.32 0.37 0.42 39.7 Brown region 7.15 37.97 7.85 1.13 0.99 0.68 44.23 3.2.3 Microstructure and chemical composition SEM images, EDS elemental maps, and EDS point analyses of the surface and cross-section of the concretions showed significant heterogeneity in the chemical composition. In general, the concretions consisted of a siliceous skeleton, Fe-rich deposits, corrosion products such as rust, and seafloor sediment, which were consistent with the ED-XRF results. The black–brown filler mainly comprised Fe, with the ratio of Fe at the surface to that in the cross-section being approximately 2:1. EDS point analysis of the black–brown filler on the concretion surface (P1 in Fig. 3a, Table 4 ) revealed a high Fe content of 90.0 wt%. An interwoven radial skeletal structure was visible within the black–brown region near the surface (box in Fig. 3a, enlarged in Fig. 3b). The corresponding EDS data (P4 and P5 in Fig. 3b, Table 4 ) showed that this region was severely contaminated with Fe-rich compounds but did not contain Ca. The chemical composition of the black–brown filler cross-section (P6 and P7 in Fig. 3c, Table 4 ) was generally consistent with that at the surface; however, the Fe content decreased significantly to 34.7 wt% with an increase in the acquisition depth (P6 → P7). This indicates that the mesh-like structure of deposits attached to the artefact surface obstructed the penetration of Fe-rich contaminants, leading to their deposition in the pores. The original porous skeleton mainly comprised O, Si, and C, whereas Ca was not detected. Figures 3d and 3e show the porous structure within a pit on the porcelain body beneath the concretions. Given that the position was isolated from the marine environment, the composition of the skeleton here was considered to be representative of the original sponge skeleton. The EDS point data of this area (P13 in Fig. 3e, Table 4 ), compared with the elemental map of the skeleton (Fig. 4a), indicated that it comprised silicon carbonate spicules. Micro-cracks within the skeleton (Fig. 3a), which may have been caused by external mechanical forces, provided sites for the deposition of external contaminants such as fine sea sand (Fig. 4b). Notably, a translucent crystalline phase with a diameter of > 200 µm was found in the centre of a pore (Supplementary Fig. 1). EDS analysis (P10 in Table 4 ) revealed that this crystal primarily comprised O, Si, C, and a small amount of N. Figure 4c shows an elemental map of the cross-section of the concretions. The main elements in the brown deposits were Fe, O, and C (P3, P9, and P11–P13 in Figs. 3a, 3c, 3d, and 3e, Table 4 ). These deposits were located in the outermost and bottommost layers of the concretions and had thicknesses of approximately 20–50 µm. EDS point analysis (P9 in Fig. 3c, Table 4 ) revealed that the local C content reached 71.6 wt% in the outermost layer, while the elemental map (Fig. 4d) and point analysis data (P11 in Fig. 3d, Table 4 ) jointly indicated that the light brown corrosion layer that filled the gap at the concretion/body interface contained Fe, O, C, Al, Si, and small amounts of S and N. Further elaboration is provided in the Discussion (Section 4 ). Table 4 EDS point analysis of different regions (wt%) Position C N O Na Al Si S Cl K Mn Ca Fe Zr Surface P1 (black–brown filler) 5.3 / 2.5 / 0.3 1.7 / / / / 0.3 90.0 / P2 (yellow skeleton) 18.1 / 25.4 0.4 2.4 12.2 0.6 0.2 0.3 / 0.2 40.2 / P3 (brown concretion) 6.4 / 28.6 / 3.0 7.7 0.5 / 2.4 / / 51.5 / P4 (black–brown skeleton) 6.9 / 26.2 / 0.7 2.1 0.7 0.3 / / / 63.2 / P5 (black–brown filler) 6.8 / 13.2 0.4 0.1 1.5 / 0.1 / / / 74.1 3.9 Cross-section P6 (black–brown filler near surface) 24.2 / 18.1 / 0.3 0.7 17.5 / 0.2 1.2 / 34.7 3.2 P7 (black–brown filler further from surface) 21.5 / 26.8 / / 1.1 / / / / / 45.9 3.2 P8 (yellow skeleton) 27.0 / 35.1 / 0.3 18.9 / / / / / 14.0 4.8 P9 (brown concretion) 71.7 / 10.1 1.3 1.3 2.2 0.8 1.1 0.4 / 0.1 0.4 / P10 (translucent crystals) 13.3 2.4 40.6 / / 38.1 / / / / / 0.3 / P11 (deposits at interface) 11.0 1.7 31.1 / 9.2 3.4 1.7 / / / / 41.8 / P12 (brown deposits) 6.8 / 11.3 / 3.9 6.8 / / 0.3 / / 67.5 3.3 P13 (yellow skeleton) 17.2 / 39.8 / 7.7 26.3 / / 2.9 / / 1.2 1.0 P14 (filler in the pore) 8.8 / 22.2 / 15.1 8.6 / / 0.9 / / 34.2 10.3 P15 (sheet-like sediment in pits) 60.5 / 13.7 / 5.8 5.3 0.5 / 0.5 / 0.3 8.9 / When the microstructures and EDS data of the concretions and underlying porcelain surface were analysed in combination with previously reported electron micrographs of spicules and images of in situ spicule growth, it was deduced that the concretions attached to the unglazed rim and neighbouring glaze surface comprised the remains of sponges ( Demospongiae ). Such organisms possess siliceous spicules and/or fibre-like structures composed of spongin, and their cells mainly contain silicon carbonate and an abundance of collagen. [ 23 ] Clionid sponges are capable of dissolving and boring into Ca-containing substances. Their larvae attach to these substances and metamorphosise into adults while boring galleries. Figures 3d and 3f show cross-sectional SEM images of the concretion/body (and glaze) interface. Bored pits of various depths were observed in both images, with well-preserved mesh-like porous structures visible in certain pits. We hypothesised that sponges colonised the surface of the bluish-white porcelain through these pits and contributed to its preservation, corrosion, and purification. As illustrated in Fig. 3d, two bored pits with depths exceeding 100 µm were present on the body surface, with pale-yellow mesh-like porous structures (box 3 in Fig. 2c). Compared with the skeleton exposed to the marine environment (P2 and P4 in Table 4 ), the porous skeleton at this position had a significantly higher Si content and lower Fe content. As illustrated in Fig. 3f, two open pores with a depth of approximately 20 µm that had been contaminated with Fe-rich corrosion products were present on the surface of the glaze (box 1 in Fig. 2d, Fig. 3f and 4e). The bottom parts of these pores were connected to two large bubbles in the glaze. We hypothesised that physical and chemical damage to the glaze surface had transformed closed bubbles in the glaze into open ones, thereby forming a 3D interconnecting network throughout the glaze layer. These bubble channels provided a pathway for the growth of sponges within the artefact itself. Sponges are filter-feeders that absorb and decompose large amounts of suspended organic matter in seawater (e.g., plant and animal debris, algae, and bacteria), thereby serving as an important organic carbon sink. [ 24 ] In addition, sponges are primitive animals capable of bio-mineralisation. With the ability to form siliceous spicules through the absorption and fixation of silicate ions, they are the earliest animals on earth to participate in the silicon cycle. [ 25 ] A random distribution of translucent crystals with diameters of > 100 µm were observed in the cross-sectional images of the concretion pores (Fig. 2). These crystals are siliceous particles that had been stored in sponge organelles for conversion into skeletal structures. The N content (2.4 wt%) may be related to the nitrogenous alkaloids secreted by sponges. Waste-containing mucus is slowly ejected from the ostia of sponges and expelled into the surrounding seawater to ensure it does not obstruct the internal filtration system. Notably, this provides a purification effect on the deposits at the glaze surface and within the porcelain (via bubble channels and cracks). The organic mucus moves continuously and accumulates on sponge surfaces, which sufficiently explains the overall abundance of C in the concretions and the extremely high C content in the outermost layer. EDS elemental line scans of the concretion cross-section (Fig. 5 ) showed that the C content peaked in the outermost layer and declined sharply with depth, which was consistent with the EDS point analyses. The C content was also high at the concretion/porcelain interface. The Fe content followed a similar trend to the S and O contents, whereas the Si content exhibited the opposite trend. The Mg, Al, K, and Ca contents decreased gradually at the glaze surface, which may be ascribed to the high degree of de-alkalinisation of the glaze. During submergence, contact with seawater facilitated ion exchange between cations in the bluish-white glaze and H 3 O + and H + in solution, resulting in cation leaching from the glaze. Notably, the S content remained at approximately 50 cps within the glaze itself, with a gradual reduction at depths of 50 µm and below in the glaze layer. This phenomenon was closely associated with contamination and alteration of the glaze. The results described above demonstrate that sponges colonised the artefact surface. As living organisms, they contributed to the ecological preservation of the bluish-white porcelain by purifying the surface. As skeletal remains, they impacted the corrosion process and shielded the porcelain from subsequent external contamination. 3.2.4 Mineral phases Figure 6 shows the XRD spectrum of the concretion surface. The concretions comprised quartz, muscovite, albite, and microcline, which corroborated the ED-XRF and EDS results. Characteristic regions of the concretions, including the natural surface and attachment layer, were also analysed by µ-Raman spectroscopy. As shown in Fig. 7, several mineral phases were identified, including Fe 3 O 4 (from the filler), α-FeOOH, β-FeOOH, and γ-FeOOH (from the corrosion layer at the interface), and quartz (from P10). These findings corroborated the ED-XRF, EDS, and XRD results. 3.3 Analysis of glaze corrosion 3.3.1 Morphology We examined the natural glaze surface and polished cross-section of the ceramics under a 3D ultra-depth optical microscope (Fig. 8). The corrosion products on the bluish-white glaze surface exhibited a typical lamellar structure (Fig. 8a), which is believed to form via pH oscillations in the local solution during the corrosion process. [ 26 ] Much of the glaze surface was covered with a corrosion layer that was accompanied by scratches and pits. The glaze surface also contained a dense distribution of dark spots (Fig. 8b), a clear and transparent glaze layer, and bubbles of various sizes. Bubbles at the glaze/body interface served as a pathway that allowed deposits to reach the porcelain body (Figs. 8c and 8d). Notably, a matte texture was observed in certain parts of the corrosion morphology, which was closely associated with the selective attachment of sponges. The glaze surface, and particularly the textural characteristics, was analysed at the same positions before and after carefully detaching the concretions (Supplementary Fig. 2). The glaze surface was divided into three layers: inner layer (translucent matte region), intermediate layer (pale-yellow matte region and brown reflective region), and outer layer (brown matte region and black–brown shell-like substance). Figure 8a shows the transition zone at the interlayer boundary. Several spots were observed on the glaze surface (Fig. 8b). These spots were distributed individually or in groups and were of a similar size to the bubbles in the glaze. The spots were generally circular or annular. During the Southern Song Dynasty, glazes with bubbles were an aesthetic feature of traditional porcelains made in Jingdezhen. T’ao Ya (Pottery Refinements), a monograph on Chinese ceramics published during the Qing Dynasty, states the following: “Foam in the glaze is known as ‘spittle’ if bubbles exhibit a beaded appearance. A rim that has an absence of foam bubbles but appears like a tear-filled eye is known as a ‘water eye’.” [ 27 ] Notably, the morphology of these circular or annular micro-bubbles makes them preferential corrosion sites in marine environments and provides suitable conditions for the selective attachment of sponges. The evolution of the bubble morphology during submergence is discussed in Section 3.3.2 . 3.3.2 Microstructure and chemical composition As shown in Fig. 9, the overall corrosion morphology of the bluish-white glaze surface exhibited randomly arranged amorphous silica nanoparticles with various accumulation densities. EDS point analyses (Table 5 ) revealed the elemental evolution across different corrosion layers and regions of the glaze surface. The Fe content increased progressively across the layers; the Si, K, Ca, and Zr contents peaked in the translucent matte region and declined thereafter; and C and S were only detected in the intermediate and outer layers, with the C content peaking in the pale-yellow matte region next to the inner layer and the black–brown substances in the outer layer. These findings were consistent with the elemental line scans of the concretion cross-section (Fig. 5 ). The inner corrosion layer in contact with the original glaze (i.e., the corrosion front) (Fig. 9a) had a translucent and matte appearance (Fig. 9b). The high-magnification SEM image (Fig. 9c) and EDS data revealed that this region comprised particulate aggregates with a high Si content. Based on a unifying refined mechanistic glass corrosion model, when silicate glass is in contact with water, many coupled processes such as hydration, hydrolysis, dissolution, diffusion, ion exchange, adsorption, crystal nucleation, and growth begin to operate at the solid/water interface to reach a new equilibrium or steady state. [ 28 ],[ 29 ],[ 30 ],[ 31 ],[ 32 ] The sea mud around the Nanhai No. 1 shipwreck had a pH of 7.74 and water content of 32.8%. [ 33 ] The interactions between the bluish-white glaze of the ancient ceramics and seawater, therefore, involved congruent dissolution of the glaze due to the low silica content in the liquid phase. The dissolution reactions were spatially and temporally coupled to the precipitation of amorphous silica, causing the dissolution/precipitation interface to migrate into the glaze layer. [28],[29],[30],[31] These complex interactions and reactions led to the formation of a porous surface alteration layer, as shown in Fig. 9c. It is worth noting that Mg 2+ and Ca 2+ both existed in the glaze, but their contents exhibited opposite trends. This may be because, for ions with the same charge, the diffusion of larger ions (e.g., Ca 2+ ) is energetically unfavourable, whereas smaller ions (e.g., Mg 2+ ) can pass through the glass network more easily. [ 34 ] We speculated that the leaching of Fe ions from the glaze surface was the primary cause of blue–green colour fading. Table 5 EDS analysis of corrosion layers on the glaze surface (wt%) C O Mg Al Si S Cl K Ca Fe Zr Relatively well-preserved glaze surface / 43.5 0.3 9.6 31.9 / / 2.5 8.5 0.6 3.1 Inner layer Translucent matte region / 27.5 / 9.7 35.5 / / 4.8 15.3 1.8 5.3 Intermediate layer Pale-yellow matte region 12.3 39.0 / 5.4 10.4 0.4 / 0.9 2.3 26.5 2.8 Brown reflective region 4.7 33.8 / 5.9 13.2 0.4 0.2 0.6 0.6 40.6 / Outer layer Brown matte region 4.9 25.5 / 1.3 0.9 0.4 / / / 67.1 / Black–brown shell-like substance 10.9 8.4 / 0.8 1.3 0.3 / 0.1 0.2 78.3 / The pale-yellow matte region in the intermediate layer corresponded to the glaze surface after concretion detachment (Fig. 9d), whereas the brown reflective region corresponded to the surface alteration layer with excessive growth of Fe-rich corrosion products (Fig. 9e). Detachment of the concretions attached to the brown corrosion layer by mechanical force also caused detachment of the interfacial corrosion layer attached to the bottom of the concretions, exposing the glaze surface with a pale-yellow matte appearance. SEM-EDS results of this region were vastly different from those of the inner corrosion layer, with the main components being Fe, C (12.3 wt%), and a small amount of S. EDS point analysis of the brown reflective region indicated a high Fe content of 40.6 wt%. This indicates that the pores arising from the formation of spherical precipitates from amorphous silica served as open channels, thereby providing space for infiltration of the Si-rich gel layer by Fe-rich contaminants. Multiple micro-cracks were present in this region, as shown in Figs. 8a and 9e. Micro-cracking likely occurred due to volume contraction following ion exchange between the alkali metal and alkaline earth metal ions in the glaze with H + and H 3 O + in seawater; [ 35 ] H + ions have a smaller radius than the original cations in the glaze, leading to local volume contraction that culminated in micro-cracking. [ 36 ] Micro-cracking may also have occurred due to shrinkage caused by dehydration upon removing the ceramics from seawater. The Fe content peaked at 78.3 wt% in the outermost corrosion layer (Figs. 9f and 9g). Spherical micro-organisms were also found on the surface of the condensate (Fig. 9h), which is discussed further in Section 4 . To explore the state of corrosion within the bubbles in the glaze, four representative spots were selected from regions with an absence of concretions. The results demonstrated that even bubbles enclosed deep in the glaze layer provided preferential sites for corrosion, with external contaminants being deposited within the space in the bubbles. For instance, an open indentation formed by the connection of several circular pits appeared brown under an optical microscope, whereas the corresponding SEM-EDS results (Figs. 10a and 11a) were indicative of a closed glaze surface at this position. Under higher magnification (Supplementary Fig. 3), multiple micro-cracks were observed on the inner walls of the pits. In another bubble, a pore was observed on the bottom surface (Fig. 10b), which connected it to another bubble via a bubble channel. These micro-cracks and pore channels provide pathways and deposition sites for external contaminants (e.g., rust) to penetrate deep within the glaze layer. Box 1 in Fig. 10c shows an annular pit with severe corrosion, its elemental map is shown in Fig. 11b. To elucidate its corrosion mechanism, a cross-section of the pit was also analysed (Figs. 10d and 11c). As shown in Fig. 10d, a piece of residual glaze with an upturned crescent shape was suspended above the pit. A semi-circular gap between this piece of suspended glaze and the glaze layer was filled with external contaminants such as rust. The other side of the residual glaze was partially connected to the surrounding glaze surface (box 2 in Fig. 10c) and had not yet become detached. The fragile connection with the glaze surface may be gradually broken due to further corrosion or mechanical forces, causing the residual glaze to become detached. This would transform the annular morphology to a circular one. 3.3.3 µ-Raman analysis µ-Raman spectroscopy indicated that α-FeOOH, β-FeOOH, and γ-FeOOH were detected in both the brown regions of the glaze surface and the black–brown shell-like substances, which was consistent with the µ-Raman spectroscopy results for the attachment layer of the concretions. The main corrosion product in the brown reflective regions was β-FeOOH, whereas the brown matte region comprised both α-FeOOH and β-FeOOH. γ-FeOOH may have formed from spongin fibres through bio-mineralisation. [ 37 ] 4 Discussion The corrosion of the bluish-white porcelain from the Nanhai No. 1 shipwreck in seawater followed a typical ecological process involving marine animals and micro-organisms. In this process, micro-organisms served as pioneer organisms (Fig. 9h), forming a biofilm on the artefact surface. With gradual hydrolysis of the glass phase in the glaze layer, Fe ions in the environment were deposited onto the Si-rich gel layer through ion exchange. Fe(OH) 3 was formed under the action of Fe-oxidising bacteria, and subsequently converted to FeOOH through redox reactions by seawater. At this point, the glaze surface had lost its smoothness owing to mechanical collisions with marine debris and microstructural reorganisation. This provided suitable conditions for the selective attachment of sponges. The unglazed rim of the artefact, caused by inverted firing (i.e., firing with the rim facing down) during fabrication, attracted sponge larvae to settle along the rim and neighbouring glaze surface. Continuous reactions at the solid/liquid interface led to gradual hydrolysis of the glass framework, releasing large amounts of silicic acid (H 4 SiO 4 ). [29] As long as the concentration of silicic acid in the environment does not exceed its solubility limit (< 2 mmol/L), it diffuses to the external environment and is taken up by the cells or compartments of micro-organisms, which accumulate and deposit silica in the form of amorphous hydrated silica through a process known as bio-silification. [ 38 ] Sponges actively absorb, accumulate, and deposit silica. [ 39 ],[ 40 ],[ 41 ],[ 42 ],[ 43 ] Their osteoblasts absorb silicic acid through Na + /HCO 3 − [Si(OH) 4 ] transporters and store it in specific organelles, thereby forming immature siliceous spicules. [44] Consequently, the silicate-based bluish-white porcelain and siliceous sponges co-existed through a silicon cycle. Si enhances the structural stability and damage resistance of sponges and promotes their adsorption of bacteria, redox reactions, and glucose metabolism. [ 44 ],[ 45 ] Alkaloids (nitrogen-containing basic organic compounds) were secreted by the sponges as secondary metabolites and subsequently dissolved in the local aqueous solution. The binding of N to H + led to the release of free OH − ions that subsequently reacted with Fe 2+ /Fe 3+ in seawater. This contributed to the formation of Fe(OH) 3 species on the artefact surface beneath the attached sponges, which were then expelled from the sponges through the respiratory and filtration system. When a sponge reached its end of life, Fe(OH) 3 species that had not been expelled were deposited at the interface between the concretion and artefact, and were subsequently converted to α-FeOOH (brown matte regions) through redox reactions. Through molecular cohesion, the α-FeOOH species bound to the β-FeOOH species (brown reflective regions) that had formed initially in the surface alteration layer; thus, these two species jointly constituted the interfacial corrosion layer. Negatively charged functional groups in the organic mucus secreted by sponges (e.g., –C–O–C and –OH) exerted strong adsorption effects on positively charged metal ions, [ 46 ][ 47 ] facilitating the chemical adsorption of corrosion products onto the sponge remains. When the concretions were gently peeled from the artefact surface, the corrosion products that had formed on the surface alteration layer of the glaze prior to sponge attachment also detached. This demonstrates that the attached sponges aided in the bio-preservation of the bluish-white porcelain. However, irregular shapes with a matte texture, outlined by corrosion products, remained on the bluish-white porcelain glaze surface, resulting in a “map” of past sponge attachment. This provides methodological insight into removing insoluble salt deposits from the surfaces of ancient ceramics: identical compounds can be cultivated on the difficult-to-remove deposits on artefact surfaces. When the accumulated material reaches a certain thickness, removal may be achieved through mutual attraction between adjacent parts and molecules of the same material. Further investigation of this approach will be conducted through simulated experiments. When the artefacts were removed from seawater, dehydration led to the loss of H 2 O molecules from the FeOOH species, which contributed to the formation of Fe 2 O 3 . Subsequently, unstable biogenic silica (e.g., siliceous spicules of sponges) underwent dissolution and re-precipitation (opal-A → opal-CT → authigenic quartz) to form biogenic quartz in the form of crypto-crystals, micro-crystals, and micro-crystalline aggregates. [ 48 ],[ 49 ] This explains the presence of translucent crystalline granules with diameters exceeding 300 µm within the pores. With regard to the circular pits on the glaze surface, some formed from the rupture or hydrolysis of thin glaze layers covering bubbles, whereas others formed by corrosion of annular micro-bubbles. Based on the above discussion, a schematic of the corrosion process of bluish-white porcelain in seawater and its complex interactions with siliceous sponges is shown in Fig. 13. 5 Conclusion In this study, we analysed the corrosion morphologies of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty following their excavation from the Nanhai No. 1 shipwreck, with the aim of investigating the corrosion mechanisms of ancient ceramics in marine environments and the complex interactions of these ceramics with siliceous sponges. The following conclusions were drawn: (1) Bluish-white porcelains with unglazed rims were subjected to wear from debris carried by seawater and corrosion of the glass phase in the glaze. This led to scratches, pits, and micro-cracks, as well as the deposition of corrosion products (e.g., FeOOH) on the rough surfaces. These sites provided suitable conditions for the selective attachment of sponges. Leaching of Fe ions from the glaze layer resulted in fading of the blue–green colour of the porcelain. (2) Sponge larvae colonised the artefacts, resulting in a mutually beneficial relationship between the attached sponges and porcelain. The larvae absorbed, fixed, and converted large amounts of H 4 SiO 4 that had been released through hydrolysis of the glass network. This benefitted the skeletal system of the larvae, while the soft sponges protected the porcelain surface from mechanical forces. Meanwhile, the organic mucus secreted by sponges encapsulated deposits on the artefact surface, and Fe(OH) 3 precipitates formed under the action of alkaloids. These substances were expelled into the seawater through the sponges’ respiratory and filtration system, which provided a purification effect to the glaze surface. (3) Upon reaching their end of life, the interwoven skeletal remains of the sponges served as deposition sites and filters for external contaminants, trapping contaminants within their mesh-like structure while continuing to provide resistance against external mechanical forces. Corrosion products that formed under the action of alkaloids bonded with the initial corrosion products in the surface alteration layer of the glaze surface through molecular cohesion, leading to the formation of an interfacial corrosion layer. Ultimately, insoluble salts could be removed from the excavated artefacts by gently peeling the sponge remains from the artefact surfaces. Declarations Acknowledgements The authors wish to express their gratitude to Dr. Wen Zou of the Ceramic Research Institute of Light Industry, China, and Dr. Shuimiao Yu and Yuan Xu of WITec for their kind support and assistance with this research. Author contributions YY provided support and guidance for this study, provided the samples; YW designed and performed all experiments, interpreted the data, and wrote and revised the manuscript; XC assisted with the Raman spectroscopy and XRD; NL acquired funding; and QW provided assistance. All authors have read and approved the final version of the manuscript. Funding This research was supported by the Key Technologies and Application Demonstrations for the Protection of Marine Ceramic Cultural Relics (2023YFF0906400), the National Archaeological Talent Revitalization Plan Project (2024-276), and Key Project 1 of the National Social Science Foundation of China (23FKGA002). Availability of data and materials Data sharing is not applicable. 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Supplementary Files Supplementarymaterial.doc Cite Share Download PDF Status: Published Journal Publication published 23 Jul, 2025 Read the published version in npj Heritage Science → Version 1 posted Editorial decision: Revision requested 29 Apr, 2025 Reviews received at journal 28 Apr, 2025 Reviews received at journal 12 Apr, 2025 Reviewers agreed at journal 09 Apr, 2025 Reviews received at journal 07 Apr, 2025 Reviewers agreed at journal 03 Apr, 2025 Reviews received at journal 01 Apr, 2025 Reviewers agreed at journal 27 Mar, 2025 Reviewers agreed at journal 27 Mar, 2025 Reviewers invited by journal 27 Mar, 2025 Editor assigned by journal 26 Mar, 2025 Submission checks completed at journal 26 Mar, 2025 First submitted to journal 23 Mar, 2025 You are reading this latest preprint version Research Square lets you share your work early, gain feedback from the community, and start making changes to your manuscript prior to peer review in a journal. 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6289041","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":442099240,"identity":"8f24040e-17be-4f4d-9289-eee80ea759b2","order_by":0,"name":"Yanzi Wang","email":"","orcid":"","institution":"Jingdezhen Ceramic University","correspondingAuthor":false,"prefix":"","firstName":"Yanzi","middleName":"","lastName":"Wang","suffix":""},{"id":442099241,"identity":"1e65e335-0530-49ed-8153-d0388f6b0833","order_by":1,"name":"Yongbin Yu","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAAwklEQVRIiWNgGAWjYJACZgYDGzn7442NDz8Qr6UgzZjhzOFmYwnitXw4nNhwI71NgIcY5QY3EtikCwwOGzPOfNjGIMFgJ6fbQIyWGQbpcszSiW0PChiSjc0OEKOFx8DamE06sd1AguFA4jYitTAn9kgebJPgIUGLc+IMCUYitUieecBsPcMgzdiAJxEYyAZE+IXveALj7YI/NnIG7McfPvxQYSdHUIvCAf4vSBFoQEA5CMg3MDATnUxGwSgYBaNghAIAT1dAH4pcEa4AAAAASUVORK5CYII=","orcid":"","institution":"Archaeological Research Center of National Cultural Heritage Administration","correspondingAuthor":true,"prefix":"","firstName":"Yongbin","middleName":"","lastName":"Yu","suffix":""},{"id":442099242,"identity":"d40d5f28-5b1f-4ca4-a362-0d0d1a77debb","order_by":2,"name":"Naisheng Li","email":"","orcid":"","institution":"Archaeological Research Center of National Cultural Heritage Administration","correspondingAuthor":false,"prefix":"","firstName":"Naisheng","middleName":"","lastName":"Li","suffix":""},{"id":442099243,"identity":"26e46900-5fb4-48e6-86a7-7b9c37eba0aa","order_by":3,"name":"Qiang Wu","email":"","orcid":"","institution":"Institute of Antient Ceramic","correspondingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Wu","suffix":""},{"id":442099244,"identity":"a6f4c1d9-da44-49b6-ba47-03f427dbe091","order_by":4,"name":"Xiaolin Cheng","email":"","orcid":"","institution":"National Museum of China","correspondingAuthor":false,"prefix":"","firstName":"Xiaolin","middleName":"","lastName":"Cheng","suffix":""}],"badges":[],"createdAt":"2025-03-23 15:08:22","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6289041/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6289041/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s40494-025-01945-y","type":"published","date":"2025-07-23T15:57:19+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":80569369,"identity":"93aba0ed-dea3-40b6-b0cd-c71cb6c25041","added_by":"auto","created_at":"2025-04-14 18:55:29","extension":"png","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":1773741,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003ePorcelain fragment from the Nanhai No. 1 shipwreck\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Inner and (b) outer surface. The unglazed rim is located at the top \u0026nbsp;\u0026nbsp;of the fragment\u003c/p\u003e","description":"","filename":"Figure1.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/ad02c694f505b0974a780e39.png"},{"id":80569372,"identity":"565a401f-27d8-4b76-b6e4-461c2d10e377","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":5323121,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSurface and cross-sectional optical micrographs of concretions \u0026nbsp;\u0026nbsp;attached to the outer surface of the porcelain fragment\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Surface of concretions on the exposed body at \u0026nbsp;\u0026nbsp;the rim of the artefact. A longitudinal crack was observed at the rim (box 1). \u0026nbsp;\u0026nbsp;To the left of the crack, a brown concretion covers the outermost layer, and to \u0026nbsp;\u0026nbsp;the right, the pores in the yellow skeleton are filled with black–brown material. \u0026nbsp;\u0026nbsp;(b) Surface of concretions on neighbouring glaze surface. Several pores were \u0026nbsp;\u0026nbsp;observed, the smallest of which had a diameter of 3 μm (indicated by the red arrow) \u0026nbsp;\u0026nbsp;which represents the minimum bubble size. (c) Cross-section of concretions on \u0026nbsp;\u0026nbsp;the exposed body at the rim of the artefact. Box 1 shows the top area of the \u0026nbsp;\u0026nbsp;concretions, with the outermost brown coating visible. Box 2 shows translucent \u0026nbsp;\u0026nbsp;crystals embedded within the yellow skeleton. Box 3 shows a brown interface \u0026nbsp;\u0026nbsp;layer (approximately 30 μm thick) between the \u0026nbsp;\u0026nbsp;concretions and porcelain body, with bored pits on the body. (d) Cross-section \u0026nbsp;\u0026nbsp;of concretions. The red line marks a large translucent crystal embedded in \u0026nbsp;\u0026nbsp;the centre of the yellow skeleton pore, with a diameter of about 300 μm, which represents the maximum pore size. Box 1 \u0026nbsp;\u0026nbsp;shows the presence of pits on the glaze covered by the concretions. The red \u0026nbsp;\u0026nbsp;boxes mark the locations of the SEM images in Figure 3\u003c/p\u003e","description":"","filename":"Figure2.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/3ee629bf3c920fbe8d672043.png"},{"id":80569387,"identity":"b4c90de7-46cb-42a2-9ed7-adf0b00119fe","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":1795673,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSEM images of surface and cross-section of the concretions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) \u0026nbsp;\u0026nbsp;Region near the surface (box 1 in Figure 2a). P1: \u0026nbsp;\u0026nbsp;black–brown filler, P2: yellow skeleton, and P3: brown concretions. (b) Black–brown \u0026nbsp;\u0026nbsp;region near the surface (box in Figure 3a). P4: sponge skeleton and P5: \u0026nbsp;\u0026nbsp;filler. (c) Cross-section near the \u0026nbsp;\u0026nbsp;surface (box 1 in Figure 2c). P6: black–brown \u0026nbsp;\u0026nbsp;filler close to the surface, P7: black–brown filler further from the surface, \u0026nbsp;\u0026nbsp;P8: yellow skeleton, and P9: brown concretions. (d) Cross-section of concretion/body \u0026nbsp;interface (box 3 in Figure 2c). P11: brown corrosion \u0026nbsp;\u0026nbsp;interlayer and P12: sediment within the pore structure in the pit. (e) Porous structure within a pit on the porcelain body. P13: yellow porous skeleton, P14: filler in the pores, and P15: \u0026nbsp;\u0026nbsp;sheet-like sediment in pits. (f) Cross-section of concretion/glaze \u0026nbsp;interface (box 1 in Figure 2d)\u003c/p\u003e","description":"","filename":"Figure3.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/04068a3ca9798953dee9eb3e.png"},{"id":80570126,"identity":"ed4a5cd7-7f56-421e-a564-c2afa30f289b","added_by":"auto","created_at":"2025-04-14 19:11:30","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":814713,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eElemental mapping images of the concretion cross-section\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Area \u0026nbsp;\u0026nbsp;in Figure 3b; (b) Area in Figure 3a; (c) Area in Figure 3c; (d) Area in Figure 3d with partial \u0026nbsp;\u0026nbsp;magnification; (e) Area in Figure 3f\u003c/p\u003e","description":"","filename":"Figure4.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/6440b365402ab924859920bc.jpg"},{"id":80569520,"identity":"e97c8616-fa3d-4650-83fb-9848a662bc8a","added_by":"auto","created_at":"2025-04-14 19:03:30","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":1250866,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEDS elemental line scans of the concretion cross-section\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure5.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/5b3ad52d1cb0972964ea286e.jpg"},{"id":80569523,"identity":"012399a3-f8f7-40db-8e05-881f947e7e7c","added_by":"auto","created_at":"2025-04-14 19:03:30","extension":"png","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":1999833,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eXRD spectrum of concretion surface\u003c/strong\u003e\u003c/p\u003e","description":"","filename":"Figure6.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/6dcaee958659fc368c23f0ee.png"},{"id":80569380,"identity":"9395b28e-34d6-4808-8102-8660c81bd00e","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":118880,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eμ-Raman spectra of characteristic regions on the concretions\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(1) Black filler within the pores on the natural surface of the \u0026nbsp;\u0026nbsp;concretions; (2) Brown interface layer at the bottom of the concretions; (3) Translucent \u0026nbsp;\u0026nbsp;granules on the natural surface of the concretions\u003c/p\u003e","description":"","filename":"Figure7.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/6436349aa5ad0d5cb68a8383.png"},{"id":80569383,"identity":"dc3492eb-c1c6-4b09-805a-3bdc49139826","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":4876794,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCorrosion morphologies of the bluish-white glaze surface and \u0026nbsp;\u0026nbsp;cross-section\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Typical lamellar structure and transition zone \u0026nbsp;\u0026nbsp;at the interlayer boundary on glaze surface; (b) Dense spots distributed on \u0026nbsp;\u0026nbsp;the glaze surface; (c) Clear and transparent \u0026nbsp;\u0026nbsp;glaze layer, and bubbles of various sizes; (d) Foreign material at the glaze/body interface.\u003c/p\u003e","description":"","filename":"Figure8.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/5d69989695bfaf43d247ed8f.png"},{"id":80569375,"identity":"26f2f840-367a-49e8-b93a-3b3cd5c132c1","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":2206223,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSEM images of different regions of the glaze surface\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Original glaze; (b) Relatively well-preserved glaze surface; (c) Inner layer (translucent matte \u0026nbsp;\u0026nbsp;region); (d) Intermediate \u0026nbsp;\u0026nbsp;layer (pale-yellow matte region); (e) Intermediate layer (brown reflective region); (f) Outer layer (brown matte region); (g) Outer \u0026nbsp;\u0026nbsp;layer (black–brown shell-like substance); (h) Spherical micro-organisms \u0026nbsp;\u0026nbsp;on glazed surface\u003c/p\u003e","description":"","filename":"Figure9.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/1127132bfa63091fd95f6857.png"},{"id":80569409,"identity":"e1e0f33c-8db5-46e9-879a-ad7703c5105f","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"png","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":1149117,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eSEM images of corrosion features in bubbles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Open \u0026nbsp;\u0026nbsp;indentation formed by the connection of several circular pits. The area in the box \u0026nbsp;\u0026nbsp;shows multiple micro-cracks on the inner walls of the pits (Supplementary \u0026nbsp;\u0026nbsp;Figure 3); (b) A pore on the bottom surface; (c) Box 1 shows a \u0026nbsp;\u0026nbsp;severely corroded annular pit; Box 2 shows the area where the residual glaze \u0026nbsp;\u0026nbsp;in the annular pit is partially connected to the surrounding glaze surface; \u0026nbsp;\u0026nbsp;(d) Cross section of an annular pit\u003c/p\u003e","description":"","filename":"Figure10.png","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/3b7d8ee0a640a0d2b797aa95.png"},{"id":80569526,"identity":"d885612b-205e-423b-aa18-d32b2c9ba688","added_by":"auto","created_at":"2025-04-14 19:03:30","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":4525800,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eEDS elemental maps of corrosion features in bubbles\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Region in Figure 10a; (b) Region in Figure 10c; \u0026nbsp;\u0026nbsp;(c) Region in Figure 10d\u003c/p\u003e","description":"","filename":"Figure11.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/c4f3f300a42454cfbd90bc7b.jpg"},{"id":80569391,"identity":"a04d8ba3-363a-4a8d-9710-8bb60075e993","added_by":"auto","created_at":"2025-04-14 18:55:30","extension":"jpg","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":961921,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eRaman spectra of corrosion layers \u0026nbsp;\u0026nbsp;of the glaze surface\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(1) Brown reflective region; (2) Brown matte region; (3) and (4) Black–brown shell-like \u0026nbsp;\u0026nbsp;substance; and (5) Standard spectra (for reference)\u003c/p\u003e","description":"","filename":"Figure12.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/62177b7830ab602740f5f93d.jpg"},{"id":80569528,"identity":"2ed85304-a0e5-492c-8c42-0404843c859c","added_by":"auto","created_at":"2025-04-14 19:03:30","extension":"jpg","order_by":13,"title":"Figure 13","display":"","copyAsset":false,"role":"figure","size":2706554,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eCorrosion process of bluish-white \u0026nbsp;\u0026nbsp;porcelain and its complex interactions with sponges\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e(a) Before the sponge adheres to the bluish white porcelain, \u0026nbsp;\u0026nbsp;the artefact surface begins to undergo physical damage and chemical corrosion; \u0026nbsp;\u0026nbsp;(b) Sponge adheres to rough surface, and glaze corrosion continues; (c) Sponge \u0026nbsp;\u0026nbsp;continues to function in the form of remains after death, and glaze corrosion \u0026nbsp;\u0026nbsp;continues; (d) Corrosion morphology of the surface of bluish-white porcelain after \u0026nbsp;\u0026nbsp;sponge peeling\u003c/p\u003e","description":"","filename":"Figure13.jpg","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/ae793c9dfe136a3e885d4f19.jpg"},{"id":87756854,"identity":"194b89e0-78af-4cc3-b58b-663350f77510","added_by":"auto","created_at":"2025-07-28 16:09:42","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":30249773,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/3ad4cc9b-40e1-435c-a82c-d00af9d6505b.pdf"},{"id":80569521,"identity":"01e1e729-1eba-4d74-932b-3d1ed090e2d3","added_by":"auto","created_at":"2025-04-14 19:03:30","extension":"doc","order_by":1,"title":"","display":"","copyAsset":false,"role":"supplement","size":1271144,"visible":true,"origin":"","legend":"","description":"","filename":"Supplementarymaterial.doc","url":"https://assets-eu.researchsquare.com/files/rs-6289041/v1/6466ef795c04a8549417df70.doc"}],"financialInterests":"No competing interests reported.","formattedTitle":"Corrosion mechanisms of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty excavated from the Nanhai No. 1 shipwreck","fulltext":[{"header":"1 Introduction","content":"\u003cp\u003eNanhai No. 1 was a Chinese merchant ship that sank in the South China Sea along the Maritime Silk Road during the Southern Song Dynasty (1127\u0026ndash;1279). The ship was discovered in 1987, buried in seafloor sediments at a depth of 25 m, ten nautical miles southwest of Xiachuan Island, Guangdong Province, off the south coast of China.\u003csup\u003e[\u003c/sup\u003e\u003ca class=\"FNLink\" href=\"#Fn1\" id=\"#FNLinkFn1\"\u003e\u003c/a\u003e\u003csup\u003e]\u003c/sup\u003e Its cargo included significant quantities of ceramics as well as ironware.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e2\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e The ceramics excavated from the shipwreck included bluish-white porcelains from the renowned Hutian kiln in Jingdezhen. These porcelains possess several distinct characteristics of Southern Song Dynasty pottery: (1) a whitish and thin body with a delicate texture; (2) a lustrous and smooth glaze with a bluish-white colour and glass-like texture; and (3) decorative motifs produced by incision, carving, or impression.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e3\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e The porcelains also have an unglazed rim, as the ceramics were formed by inverted firing (i.e., with the rim facing down). The excavated artefacts have great artistic, historical, and scientific value. However, submersion in seawater for nearly a millennium has led to varying degrees of corrosion and damage. Several samples have large concretions attached to the unglazed rim and neighbouring glaze surface or an altered gel layer covering the glaze. Understanding the influence of marine-organism attachment on the corrosion of ceramic artefacts is therefore crucial for the conservation of this underwater cultural heritage.\u003c/p\u003e \u003cp\u003eSince the 1980s, materials scientists, marine chemists, and physicists have sought to elucidate the corrosion mechanisms of ancient ceramics. Studies have focused on the corrosion of the glass phase,\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e4\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e5\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e crystalline regions,\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e6\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e7\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e and other phase structures\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e8\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e9\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e10\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e in the glaze layer; the formation of surface concretions and corrosion products and their interactions with the artefact body;\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e11\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e microbial corrosion;\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e12\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e13\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e14\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e15\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e16\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e17\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e and other factors.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e18\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e19\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e20\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e However, few studies have investigated the effects of voids and entrained bubbles, which are highly prevalent in ancient ceramics and considerably influence the corrosion process, despite their isolation from the external environment. Pertinent studies have found that bubbles in glaze can affect the direction in which corrosion structures arrange on the artefact surface,\u003csup\u003e[14]\u003c/sup\u003e influence the chemical composition of the local glaze surface,\u003csup\u003e[6]\u003c/sup\u003e create rapid corrosion pathways and deposition sites for aqueous solutions and foreign contaminants,\u003csup\u003e[7],[9],[13]\u003c/sup\u003e and provide space for the growth of corrosion products.\u003csup\u003e[12]\u003c/sup\u003e In addition, despite several investigations into the effects of calcium-rich marine-organism attachment on the corrosion of ancient ceramics, including the influence of coralline algae,\u003csup\u003e[12]\u003c/sup\u003e bryozoans, and oysters,\u003csup\u003e[17]\u003c/sup\u003e few reports have explored the influence of sponges with siliceous spicules on ancient ceramics. Consequently, further research is required to elucidate how bubbles in glaze participate in the corrosion of ancient ceramics and the unique corrosion pathways of ceramics with attached siliceous sponges.\u003c/p\u003e \u003cp\u003eIn this study, we investigated the morphological evolution of bubbles in ancient ceramic glazes and the complex interactions between siliceous sponges and ancient ceramics, intending to elucidate the mechanisms of bluish-white porcelain corrosion in marine environments and identify methods for the conservation of such porcelain wares. Bluish-white porcelains from the Nanhai No. 1 shipwreck\u0026mdash;submerged in a marine environment for approximately 800 years\u0026mdash;were subjected to technical analyses to explore the formation mechanisms and morphologies of the corrosion products. The findings not only enhance our understanding of the corrosion mechanisms of ancient bluish-white porcelain wares in marine environments but also serve as a key reference for future research on the long-term corrosion mechanisms of modern silicate glasses.\u003c/p\u003e"},{"header":"2 Materials and methods","content":"\u003cdiv id=\"Sec3\" class=\"Section2\"\u003e\n\u003ch2\u003e2.1 Materials\u003c/h2\u003e\n\u003cp\u003ePorcelain fragments (Figs.\u0026nbsp;1a and 1b) from the Nanhai No. 1 shipwreck were desalinated at the Maritime Silk Road Museum, Guangdong Province, China, for 12 weeks prior to their use in the present study.\u003c/p\u003e\n\u003cp\u003eThe unglazed rim and neighbouring glaze surface of the ceramics were covered by black\u0026ndash;brown concretions. Yellowing was observed on certain parts of the glaze surface, and both the inner and outer walls were densely covered with dark spots. Samples were cut from the porcelain fragments, and the cross-sections were ground and polished using 1500-mesh boron carbide powder. The samples were sequentially washed with deionised water (2 \u0026times; 15 min) and ethanol (1 \u0026times; 15 min) in an ultrasonic bath and dried in an oven at 110\u0026deg;C for 3 h.\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec4\" class=\"Section2\"\u003e\n\u003ch2\u003e2.2 Analytical methods\u003c/h2\u003e\n\u003cdiv id=\"Sec5\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.1 Energy dispersive X-ray fluorescence (ED-XRF) spectroscopy\u003c/h2\u003e\n\u003cp\u003eThe chemical compositions of the glaze and concretions were quantitatively analysed by energy dispersive X-ray fluorescence (ED-XRF) spectroscopy (Eagle III, EDAX Inc., USA). Testing was performed on the natural surface of the glaze and concretions and the attachment layer of the concretions (where they attached to the glaze surface). The ED-XRF spectrometer had the following specifications: side-window rhodium target, 50 W X-ray tube, downward irradiation, and lithium-drifted silicon (Si(Li)) detector. Samples were tested with an X-ray tube voltage of 50 kV, tube current of 200 \u0026micro;A, vacuum optical path, incident X-ray beam spot diameter of 300 \u0026micro;m, and measurement duration of 200 s. For quantitative analysis, calibration curves were created using a series of 13 standard reference materials for non-destructive ancient ceramics testing, developed by the Shanghai Institute of Ceramics of the Chinese Academy of Sciences (Shanghai, China).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec6\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.2 Microscopy\u003c/h2\u003e\n\u003cp\u003eThe macromorphology of the natural surface and polished cross-sections of the samples were examined under a three-dimensional (3D) ultra-depth microscope (VHX-6000; Keyence). The micro-morphology and chemical composition were characterised using cold-field-emission scanning electron microscopy (SEM; SU8100, Hitachi, Japan) and energy dispersive X-ray spectroscopy (EDS; Xplore 30, Oxford Instruments, UK). SEM analyses were performed in a low-vacuum environment (10\u003csup\u003e\u0026minus;\u0026thinsp;3\u003c/sup\u003e Pa) at an accelerating voltage of 5 kV, with EDS spectra acquisition lasting for 60 s at a working distance of 15 mm. To examine the cross-sectional microstructures, 1 \u0026times; 1 \u0026times; 1 cm pieces were cut from the edges of the samples using a diamond saw blade, embedded in epoxy resin, and polished with silicon carbide sandpaper and diamond polishing pastes (3 and 1 \u0026micro;m).\u003c/p\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec7\" class=\"Section3\"\u003e\n\u003ch2\u003e2.2.3 \u003cstrong\u003eMicro-Raman spectroscopy and X-ray diffraction (XRD)\u003c/strong\u003e\u003c/h2\u003e\n\u003cp\u003eThe phase compositions of the glaze and concretions were characterised by micro-Raman (\u0026micro;-Raman) spectroscopy (WITec alpha300 R, Oxford Instruments, UK) with a 100\u0026times; optical lens and 532 nm laser. Baseline removal was performed with LabSpec software (Horiba, Japan), and the spectra were smoothed and deconvolved using Origin software (OriginLab, USA). The phase composition of the concretions was further analysed using X-ray diffraction (XRD; D8 Discover, Bruker, Germany) with Cu K\u0026alpha; radiation (40 kV, 40 mA) in the 2\u003cem\u003e\u0026theta;\u003c/em\u003e range of 5\u0026deg;\u0026ndash;80\u0026deg;. The spot diameter and step size were 20 \u0026micro;m and 6\u0026deg;/min, respectively.\u003c/p\u003e\n\u003c/div\u003e\n\u003c/div\u003e"},{"header":"3 Results","content":"\u003cdiv id=\"Sec9\" class=\"Section2\"\u003e\n \u003ch2\u003e3.1 Chemical composition of glaze\u003c/h2\u003e\n \u003cp\u003eThe transparent regions of the glaze surface were analysed by ED-XRF spectroscopy (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e1\u003c/span\u003e). The chemical composition was consistent with those of bluish-white porcelains produced by Hutian kiln in Jingdezhen during the Southern Song Dynasty. The glaze comprised a quaternary CaO-MgO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e system, with CaO being the primary fluxing agent. The glaze also contained Fe in the form of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e; however, because this oxide is sensitive to the kiln atmosphere, Fe also existed in the reduced form Fe\u003csup\u003e2+\u003c/sup\u003e. This produced a blue\u0026ndash;green colour\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e21\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e that manifested as a bluish-green tint on thicker parts of the glaze. In addition, MnO and P\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e were present in the porcelain glaze, indicating that glaze ash or plant ash may have been introduced into the glaze formulation. The glaze coefficient \u003cem\u003eb\u003c/em\u003e (calculated as \u003cem\u003eb\u003c/em\u003e\u0026thinsp;=\u0026thinsp;RO/(RO\u0026thinsp;+\u0026thinsp;R\u003csub\u003e2\u003c/sub\u003eO), where RO represents the content of alkaline earth metal oxides and R\u003csub\u003e2\u003c/sub\u003eO represents the content of alkali metal oxides\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e22\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e) had a value of \u003cem\u003eb\u003c/em\u003e\u0026thinsp;\u0026gt;\u0026thinsp;0.76, which is consistent with typical Ca-based glazes.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab1\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eMajor and minor components of the glaze (average values)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eRegion\u003c/p\u003e\n \u003c/th\u003e\n \u003cth colspan=\"8\" align=\"left\"\u003e\n \u003cp\u003ewt%\u003c/p\u003e\n \u003c/th\u003e\n \u003cth colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003e\u0026micro;g/g\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNa\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMgO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK\u003csub\u003e2\u003c/sub\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCaO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eTiO\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMnO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eP\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGlaze surface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.63\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.02\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e16.71\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e70.12\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.46\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.23\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e623\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e333\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eTable\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e2\u003c/span\u003e lists the elemental composition of the natural surface and polished cross-section of the glaze, as determined by EDS. The cross-section was free of corrosion and therefore considered to be representative of the chemical composition of the original glaze.\u003csup\u003e[4],[5],[9],[12]\u003c/sup\u003e The Fe content of the glaze surface (0.6 wt%) was higher than that of the cross-section (0.3 wt%), which was ascribed to the gradual deposition of Fe from ironware on the same ship and other external contaminants (e.g., rust) carried by seawater. The K, Ca, and Zr contents of the glaze surface (2.52, 8.51, and 3.07 wt%, respectively) were lower than those of the cross-section (3.06, 9.24, and 9.50 wt%, respectively). This was attributed to cation leaching and ion exchange between the glaze surface and seawater. The Mg content was higher in the glaze surface (0.33 wt%) than in the cross-section (0.30 wt%), which was associated with the abundance of Mg\u003csup\u003e2+\u003c/sup\u003e in seawater.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003ctable id=\"Tab2\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 2\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eElemental composition of natural glaze surface and polished cross-section (wt%)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eRegion\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eGlaze surface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e43.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.33\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.52\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.51\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.07\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCross-section\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.83\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.30\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.59\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e32.95\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.06\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.24\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.27\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.50\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec10\" class=\"Section2\"\u003e\n \u003ch2\u003e3.2 Analysis of concretions\u003c/h2\u003e\n \u003cdiv id=\"Sec11\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.1 Morphology\u003c/h2\u003e\n \u003cp\u003eThe surface and cross-sections of the concretions attached to the sample surface were examined under a 3D ultra-depth optical microscope (Figs.\u0026nbsp;2a\u0026ndash;2d). The concretions had a complex morphology with significant heterogeneity. Porous mesh-like sponge remains with translucent white granules embedded within them were observed at the rim of the artefact and on the neighbouring glaze surface. The mesh-like sponge remains also had irregular polygonal pore structures with diameters ranging from approximately 3 to 300 \u0026micro;m. The pores were filled with black\u0026ndash;brown material. Notably, bored pits of various depths were observed on the artefact surface beneath the concretions. Furthermore, the interface between the concretions and porcelain body was filled by an approximately 30 \u0026micro;m-thick corrosion product layer.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec12\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.2 ED-XRF analysis\u003c/h2\u003e\n \u003cp\u003eThe natural surface and attachment layer of the concretions (where they attached to the glaze) were analysed by ED-XRF (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e3\u003c/span\u003e). The yellow skeleton, brown concretions, and black\u0026ndash;brown material filling the pores were analysed separately. The attachment layer did not exhibit black regions; therefore, only yellow and brown areas were analysed. The yellow skeleton at the attachment layer would have been isolated from seawater as the concretion layer grew; therefore, its data were assumed to be representative of the original sponge struts. The results revealed that the yellow skeleton was siliceous, with that near the attachment layer (assumed to be the original chemical composition) having a Si content of 47.37 wt% and Ca content of only 0.37 wt%, indicating an extremely low possibility of a calcareous skeleton. In contrast, Fe was the predominant component of the black\u0026ndash;brown filler (73.49 wt%), while the Si content (16.22 wt%) was significantly lower than that of the skeleton. Therefore, these regions were ascribed to Fe-rich contaminants and sea-sand deposition. The chemical composition of the brown concretions was similar to that of the yellow skeleton, but with a higher Fe content and lower Si content. All regions also contained S, which likely originated from sulphate salts from sea mud on the seafloor.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab3\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 3\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eED-XRF analysis of the concretions\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" rowspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/td\u003e\n \u003ctd colspan=\"7\" align=\"left\"\u003e\n \u003cp\u003ewt%\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTi\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"3\" align=\"left\"\u003e\n \u003cp\u003eNatural surface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eYellow skeleton\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.91\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e41.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.36\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.60\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.54\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e42.78\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBrown concretions\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.76\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e38.26\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.14\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.58\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.39\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.61\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e47.26\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBlack\u0026ndash;brown filler\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.73\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e16.22\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.49\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.29\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.62\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e73.49\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eAttachment layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eYellow skeleton\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.78\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e47.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.05\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.32\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.37\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.42\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.7\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBrown region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.15\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e37.97\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.85\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.13\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.99\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.68\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e44.23\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec13\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.3 Microstructure and chemical composition\u003c/h2\u003e\n \u003cp\u003eSEM images, EDS elemental maps, and EDS point analyses of the surface and cross-section of the concretions showed significant heterogeneity in the chemical composition. In general, the concretions consisted of a siliceous skeleton, Fe-rich deposits, corrosion products such as rust, and seafloor sediment, which were consistent with the ED-XRF results.\u003c/p\u003e\n \u003cp\u003eThe black\u0026ndash;brown filler mainly comprised Fe, with the ratio of Fe at the surface to that in the cross-section being approximately 2:1. EDS point analysis of the black\u0026ndash;brown filler on the concretion surface (P1 in Fig.\u0026nbsp;3a, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) revealed a high Fe content of 90.0 wt%. An interwoven radial skeletal structure was visible within the black\u0026ndash;brown region near the surface (box in Fig.\u0026nbsp;3a, enlarged in Fig.\u0026nbsp;3b). The corresponding EDS data (P4 and P5 in Fig.\u0026nbsp;3b, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) showed that this region was severely contaminated with Fe-rich compounds but did not contain Ca. The chemical composition of the black\u0026ndash;brown filler cross-section (P6 and P7 in Fig.\u0026nbsp;3c, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) was generally consistent with that at the surface; however, the Fe content decreased significantly to 34.7 wt% with an increase in the acquisition depth (P6 \u0026rarr; P7). This indicates that the mesh-like structure of deposits attached to the artefact surface obstructed the penetration of Fe-rich contaminants, leading to their deposition in the pores.\u003c/p\u003e\n \u003cp\u003eThe original porous skeleton mainly comprised O, Si, and C, whereas Ca was not detected. Figures\u0026nbsp;3d and 3e show the porous structure within a pit on the porcelain body beneath the concretions. Given that the position was isolated from the marine environment, the composition of the skeleton here was considered to be representative of the original sponge skeleton. The EDS point data of this area (P13 in Fig.\u0026nbsp;3e, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e), compared with the elemental map of the skeleton (Fig.\u0026nbsp;4a), indicated that it comprised silicon carbonate spicules. Micro-cracks within the skeleton (Fig.\u0026nbsp;3a), which may have been caused by external mechanical forces, provided sites for the deposition of external contaminants such as fine sea sand (Fig.\u0026nbsp;4b). Notably, a translucent crystalline phase with a diameter of \u0026gt;\u0026thinsp;200 \u0026micro;m was found in the centre of a pore (Supplementary Fig.\u0026nbsp;1). EDS analysis (P10 in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) revealed that this crystal primarily comprised O, Si, C, and a small amount of N. Figure\u0026nbsp;4c shows an elemental map of the cross-section of the concretions.\u003c/p\u003e\n \u003cp\u003eThe main elements in the brown deposits were Fe, O, and C (P3, P9, and P11\u0026ndash;P13 in Figs.\u0026nbsp;3a, 3c, 3d, and 3e, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e). These deposits were located in the outermost and bottommost layers of the concretions and had thicknesses of approximately 20\u0026ndash;50 \u0026micro;m. EDS point analysis (P9 in Fig.\u0026nbsp;3c, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) revealed that the local C content reached 71.6 wt% in the outermost layer, while the elemental map (Fig.\u0026nbsp;4d) and point analysis data (P11 in Fig.\u0026nbsp;3d, Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e) jointly indicated that the light brown corrosion layer that filled the gap at the concretion/body interface contained Fe, O, C, Al, Si, and small amounts of S and N. Further elaboration is provided in the Discussion (Section \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e).\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab4\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 4\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEDS point analysis of different regions (wt%)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003ePosition\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eN\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eNa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMn\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"5\" align=\"left\"\u003e\n \u003cp\u003eSurface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP1 (black\u0026ndash;brown filler)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e90.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP2 (yellow skeleton)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e12.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP3 (brown concretion)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e28.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e7.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e51.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP4 (black\u0026ndash;brown skeleton)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e63.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP5 (black\u0026ndash;brown filler)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e74.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"10\" align=\"left\"\u003e\n \u003cp\u003eCross-section\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP6 (black\u0026ndash;brown filler near surface)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e24.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e17.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP7 (black\u0026ndash;brown filler further from surface)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e21.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e45.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.2\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP8 (yellow skeleton)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e35.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e18.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e14.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP9 (brown concretion)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e71.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e10.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e2.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP10 (translucent crystals)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e38.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP11 (deposits at interface)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e41.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP12 (brown deposits)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e11.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e6.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e3.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP13 (yellow skeleton)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e17.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e7.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.0\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP14 (filler in the pore)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e22.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e34.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eP15 (sheet-like sediment in pits)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e60.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e13.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cp\u003eWhen the microstructures and EDS data of the concretions and underlying porcelain surface were analysed in combination with previously reported electron micrographs of spicules and images of \u003cem\u003ein situ\u003c/em\u003e spicule growth, it was deduced that the concretions attached to the unglazed rim and neighbouring glaze surface comprised the remains of sponges (\u003cem\u003eDemospongiae\u003c/em\u003e). Such organisms possess siliceous spicules and/or fibre-like structures composed of spongin, and their cells mainly contain silicon carbonate and an abundance of collagen.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e23\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Clionid sponges are capable of dissolving and boring into Ca-containing substances. Their larvae attach to these substances and metamorphosise into adults while boring galleries. Figures\u0026nbsp;3d and 3f show cross-sectional SEM images of the concretion/body (and glaze) interface. Bored pits of various depths were observed in both images, with well-preserved mesh-like porous structures visible in certain pits. We hypothesised that sponges colonised the surface of the bluish-white porcelain through these pits and contributed to its preservation, corrosion, and purification.\u003c/p\u003e\n \u003cp\u003eAs illustrated in Fig.\u0026nbsp;3d, two bored pits with depths exceeding 100 \u0026micro;m were present on the body surface, with pale-yellow mesh-like porous structures (box 3 in Fig.\u0026nbsp;2c). Compared with the skeleton exposed to the marine environment (P2 and P4 in Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e), the porous skeleton at this position had a significantly higher Si content and lower Fe content. As illustrated in Fig.\u0026nbsp;3f, two open pores with a depth of approximately 20 \u0026micro;m that had been contaminated with Fe-rich corrosion products were present on the surface of the glaze (box 1 in Fig.\u0026nbsp;2d, Fig.\u0026nbsp;3f and 4e). The bottom parts of these pores were connected to two large bubbles in the glaze. We hypothesised that physical and chemical damage to the glaze surface had transformed closed bubbles in the glaze into open ones, thereby forming a 3D interconnecting network throughout the glaze layer. These bubble channels provided a pathway for the growth of sponges within the artefact itself.\u003c/p\u003e\n \u003cp\u003eSponges are filter-feeders that absorb and decompose large amounts of suspended organic matter in seawater (e.g., plant and animal debris, algae, and bacteria), thereby serving as an important organic carbon sink.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e24\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e In addition, sponges are primitive animals capable of bio-mineralisation. With the ability to form siliceous spicules through the absorption and fixation of silicate ions, they are the earliest animals on earth to participate in the silicon cycle.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e25\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e A random distribution of translucent crystals with diameters of \u0026gt;\u0026thinsp;100 \u0026micro;m were observed in the cross-sectional images of the concretion pores (Fig.\u0026nbsp;2). These crystals are siliceous particles that had been stored in sponge organelles for conversion into skeletal structures. The N content (2.4 wt%) may be related to the nitrogenous alkaloids secreted by sponges. Waste-containing mucus is slowly ejected from the ostia of sponges and expelled into the surrounding seawater to ensure it does not obstruct the internal filtration system. Notably, this provides a purification effect on the deposits at the glaze surface and within the porcelain (via bubble channels and cracks). The organic mucus moves continuously and accumulates on sponge surfaces, which sufficiently explains the overall abundance of C in the concretions and the extremely high C content in the outermost layer.\u003c/p\u003e\n \u003cp\u003eEDS elemental line scans of the concretion cross-section (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e) showed that the C content peaked in the outermost layer and declined sharply with depth, which was consistent with the EDS point analyses. The C content was also high at the concretion/porcelain interface. The Fe content followed a similar trend to the S and O contents, whereas the Si content exhibited the opposite trend. The Mg, Al, K, and Ca contents decreased gradually at the glaze surface, which may be ascribed to the high degree of de-alkalinisation of the glaze. During submergence, contact with seawater facilitated ion exchange between cations in the bluish-white glaze and H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e and H\u003csup\u003e+\u003c/sup\u003e in solution, resulting in cation leaching from the glaze. Notably, the S content remained at approximately 50 cps within the glaze itself, with a gradual reduction at depths of 50 \u0026micro;m and below in the glaze layer. This phenomenon was closely associated with contamination and alteration of the glaze.\u003c/p\u003e\n \u003cp\u003e\u0026nbsp;\u003c/p\u003e\n \u003cp\u003eThe results described above demonstrate that sponges colonised the artefact surface. As living organisms, they contributed to the ecological preservation of the bluish-white porcelain by purifying the surface. As skeletal remains, they impacted the corrosion process and shielded the porcelain from subsequent external contamination.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec14\" class=\"Section3\"\u003e\n \u003ch2\u003e3.2.4 Mineral phases\u003c/h2\u003e\n \u003cp\u003eFigure 6 shows the XRD spectrum of the concretion surface. The concretions comprised quartz, muscovite, albite, and microcline, which corroborated the ED-XRF and EDS results. Characteristic regions of the concretions, including the natural surface and attachment layer, were also analysed by \u0026micro;-Raman spectroscopy. As shown in Fig.\u0026nbsp;7, several mineral phases were identified, including Fe\u003csub\u003e3\u003c/sub\u003eO\u003csub\u003e4\u003c/sub\u003e (from the filler), \u0026alpha;-FeOOH, \u0026beta;-FeOOH, and \u0026gamma;-FeOOH (from the corrosion layer at the interface), and quartz (from P10). These findings corroborated the ED-XRF, EDS, and XRD results.\u003c/p\u003e\n \u003c/div\u003e\n\u003c/div\u003e\n\u003cdiv id=\"Sec15\" class=\"Section2\"\u003e\n \u003ch2\u003e3.3 Analysis of glaze corrosion\u003c/h2\u003e\n \u003cdiv id=\"Sec16\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.1 Morphology\u003c/h2\u003e\n \u003cp\u003eWe examined the natural glaze surface and polished cross-section of the ceramics under a 3D ultra-depth optical microscope (Fig.\u0026nbsp;8). The corrosion products on the bluish-white glaze surface exhibited a typical lamellar structure (Fig.\u0026nbsp;8a), which is believed to form via pH oscillations in the local solution during the corrosion process.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e26\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Much of the glaze surface was covered with a corrosion layer that was accompanied by scratches and pits. The glaze surface also contained a dense distribution of dark spots (Fig.\u0026nbsp;8b), a clear and transparent glaze layer, and bubbles of various sizes. Bubbles at the glaze/body interface served as a pathway that allowed deposits to reach the porcelain body (Figs.\u0026nbsp;8c and 8d). Notably, a matte texture was observed in certain parts of the corrosion morphology, which was closely associated with the selective attachment of sponges.\u003c/p\u003e\n \u003cp\u003eThe glaze surface, and particularly the textural characteristics, was analysed at the same positions before and after carefully detaching the concretions (Supplementary Fig.\u0026nbsp;2). The glaze surface was divided into three layers: inner layer (translucent matte region), intermediate layer (pale-yellow matte region and brown reflective region), and outer layer (brown matte region and black\u0026ndash;brown shell-like substance). Figure\u0026nbsp;8a shows the transition zone at the interlayer boundary.\u003c/p\u003e\n \u003cp\u003eSeveral spots were observed on the glaze surface (Fig.\u0026nbsp;8b). These spots were distributed individually or in groups and were of a similar size to the bubbles in the glaze. The spots were generally circular or annular. During the Southern Song Dynasty, glazes with bubbles were an aesthetic feature of traditional porcelains made in Jingdezhen. T\u0026rsquo;ao Ya (Pottery Refinements), a monograph on Chinese ceramics published during the Qing Dynasty, states the following: \u0026ldquo;Foam in the glaze is known as \u0026lsquo;spittle\u0026rsquo; if bubbles exhibit a beaded appearance. A rim that has an absence of foam bubbles but appears like a tear-filled eye is known as a \u0026lsquo;water eye\u0026rsquo;.\u0026rdquo;\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e27\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Notably, the morphology of these circular or annular micro-bubbles makes them preferential corrosion sites in marine environments and provides suitable conditions for the selective attachment of sponges. The evolution of the bubble morphology during submergence is discussed in Section \u003cspan class=\"InternalRef\"\u003e3.3.2\u003c/span\u003e.\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec17\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.2 Microstructure and chemical composition\u003c/h2\u003e\n \u003cp\u003eAs shown in Fig.\u0026nbsp;9, the overall corrosion morphology of the bluish-white glaze surface exhibited randomly arranged amorphous silica nanoparticles with various accumulation densities. EDS point analyses (Table\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e) revealed the elemental evolution across different corrosion layers and regions of the glaze surface. The Fe content increased progressively across the layers; the Si, K, Ca, and Zr contents peaked in the translucent matte region and declined thereafter; and C and S were only detected in the intermediate and outer layers, with the C content peaking in the pale-yellow matte region next to the inner layer and the black\u0026ndash;brown substances in the outer layer. These findings were consistent with the elemental line scans of the concretion cross-section (Fig.\u0026nbsp;\u003cspan class=\"InternalRef\"\u003e5\u003c/span\u003e).\u003c/p\u003e\n \u003cp\u003eThe inner corrosion layer in contact with the original glaze (i.e., the corrosion front) (Fig.\u0026nbsp;9a) had a translucent and matte appearance (Fig.\u0026nbsp;9b). The high-magnification SEM image (Fig.\u0026nbsp;9c) and EDS data revealed that this region comprised particulate aggregates with a high Si content. Based on a unifying refined mechanistic glass corrosion model, when silicate glass is in contact with water, many coupled processes such as hydration, hydrolysis, dissolution, diffusion, ion exchange, adsorption, crystal nucleation, and growth begin to operate at the solid/water interface to reach a new equilibrium or steady state.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e28\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e29\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e30\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e31\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e32\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e The sea mud around the Nanhai No. 1 shipwreck had a pH of 7.74 and water content of 32.8%.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e33\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e The interactions between the bluish-white glaze of the ancient ceramics and seawater, therefore, involved congruent dissolution of the glaze due to the low silica content in the liquid phase. The dissolution reactions were spatially and temporally coupled to the precipitation of amorphous silica, causing the dissolution/precipitation interface to migrate into the glaze layer.\u003csup\u003e[28],[29],[30],[31]\u003c/sup\u003e These complex interactions and reactions led to the formation of a porous surface alteration layer, as shown in Fig.\u0026nbsp;9c. It is worth noting that Mg\u003csup\u003e2+\u003c/sup\u003e and Ca\u003csup\u003e2+\u003c/sup\u003e both existed in the glaze, but their contents exhibited opposite trends. This may be because, for ions with the same charge, the diffusion of larger ions (e.g., Ca\u003csup\u003e2+\u003c/sup\u003e) is energetically unfavourable, whereas smaller ions (e.g., Mg\u003csup\u003e2+\u003c/sup\u003e) can pass through the glass network more easily.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e34\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e We speculated that the leaching of Fe ions from the glaze surface was the primary cause of blue\u0026ndash;green colour fading.\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003ctable id=\"Tab5\" border=\"1\"\u003e\n \u003ccaption\u003e\n \u003cdiv class=\"CaptionNumber\"\u003eTable 5\u003c/div\u003e\n \u003cdiv class=\"CaptionContent\"\u003e\n \u003cp\u003eEDS analysis of corrosion layers on the glaze surface (wt%)\u003c/p\u003e\n \u003c/div\u003e\n \u003c/caption\u003e\n \u003cthead\u003e\n \u003ctr\u003e\n \u003cth colspan=\"2\" align=\"left\"\u003e\u0026nbsp;\u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eC\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eO\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eMg\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eAl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eSi\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eS\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCl\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eK\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eCa\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eFe\u003c/p\u003e\n \u003c/th\u003e\n \u003cth align=\"left\"\u003e\n \u003cp\u003eZr\u003c/p\u003e\n \u003c/th\u003e\n \u003c/tr\u003e\n \u003c/thead\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd colspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eRelatively well-preserved glaze surface\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e43.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e9.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e31.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e8.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e3.1\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eInner layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eTranslucent matte region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e27.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e9.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e35.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e15.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e5.3\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eIntermediate layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003ePale-yellow matte region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e12.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e39.0\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e26.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e2.8\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBrown reflective region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.7\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e33.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e5.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e13.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e40.6\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd rowspan=\"2\" align=\"left\"\u003e\n \u003cp\u003eOuter layer\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBrown matte region\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e4.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e25.5\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e67.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003eBlack\u0026ndash;brown shell-like substance\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e10.9\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e8.4\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e0.8\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e1.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.1\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e0.2\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"char\"\u003e\n \u003cp\u003e78.3\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd align=\"left\"\u003e\n \u003cp\u003e/\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n \u003c/table\u003e\n \u003c/div\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n \u003c/div\u003e\n \u003cp\u003eThe pale-yellow matte region in the intermediate layer corresponded to the glaze surface after concretion detachment (Fig.\u0026nbsp;9d), whereas the brown reflective region corresponded to the surface alteration layer with excessive growth of Fe-rich corrosion products (Fig.\u0026nbsp;9e). Detachment of the concretions attached to the brown corrosion layer by mechanical force also caused detachment of the interfacial corrosion layer attached to the bottom of the concretions, exposing the glaze surface with a pale-yellow matte appearance. SEM-EDS results of this region were vastly different from those of the inner corrosion layer, with the main components being Fe, C (12.3 wt%), and a small amount of S. EDS point analysis of the brown reflective region indicated a high Fe content of 40.6 wt%. This indicates that the pores arising from the formation of spherical precipitates from amorphous silica served as open channels, thereby providing space for infiltration of the Si-rich gel layer by Fe-rich contaminants. Multiple micro-cracks were present in this region, as shown in Figs.\u0026nbsp;8a and 9e. Micro-cracking likely occurred due to volume contraction following ion exchange between the alkali metal and alkaline earth metal ions in the glaze with H\u003csup\u003e+\u003c/sup\u003e and H\u003csub\u003e3\u003c/sub\u003eO\u003csup\u003e+\u003c/sup\u003e in seawater;\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e35\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e H\u003csup\u003e+\u003c/sup\u003e ions have a smaller radius than the original cations in the glaze, leading to local volume contraction that culminated in micro-cracking.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e36\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Micro-cracking may also have occurred due to shrinkage caused by dehydration upon removing the ceramics from seawater. The Fe content peaked at 78.3 wt% in the outermost corrosion layer (Figs. 9f and 9g). Spherical micro-organisms were also found on the surface of the condensate (Fig. 9h), which is discussed further in Section \u003cspan class=\"InternalRef\"\u003e4\u003c/span\u003e.\u003c/p\u003e\n \u003cp\u003eTo explore the state of corrosion within the bubbles in the glaze, four representative spots were selected from regions with an absence of concretions. The results demonstrated that even bubbles enclosed deep in the glaze layer provided preferential sites for corrosion, with external contaminants being deposited within the space in the bubbles. For instance, an open indentation formed by the connection of several circular pits appeared brown under an optical microscope, whereas the corresponding SEM-EDS results (Figs. 10a and 11a) were indicative of a closed glaze surface at this position. Under higher magnification (Supplementary Fig. 3), multiple micro-cracks were observed on the inner walls of the pits. In another bubble, a pore was observed on the bottom surface (Fig. 10b), which connected it to another bubble via a bubble channel. These micro-cracks and pore channels provide pathways and deposition sites for external contaminants (e.g., rust) to penetrate deep within the glaze layer. Box 1 in Fig. 10c shows an annular pit with severe corrosion, its elemental map is shown in Fig. 11b. To elucidate its corrosion mechanism, a cross-section of the pit was also analysed (Figs. 10d and 11c). As shown in Fig. 10d, a piece of residual glaze with an upturned crescent shape was suspended above the pit. A semi-circular gap between this piece of suspended glaze and the glaze layer was filled with external contaminants such as rust. The other side of the residual glaze was partially connected to the surrounding glaze surface (box 2 in Fig. 10c) and had not yet become detached. The fragile connection with the glaze surface may be gradually broken due to further corrosion or mechanical forces, causing the residual glaze to become detached. This would transform the annular morphology to a circular one.\u0026nbsp;\u003c/p\u003e\n \u003c/div\u003e\n \u003cdiv id=\"Sec18\" class=\"Section3\"\u003e\n \u003ch2\u003e3.3.3 \u0026micro;-Raman analysis\u003c/h2\u003e\n \u003cp\u003e\u0026micro;-Raman spectroscopy indicated that \u0026alpha;-FeOOH, \u0026beta;-FeOOH, and \u0026gamma;-FeOOH were detected in both the brown regions of the glaze surface and the black\u0026ndash;brown shell-like substances, which was consistent with the \u0026micro;-Raman spectroscopy results for the attachment layer of the concretions. The main corrosion product in the brown reflective regions was \u0026beta;-FeOOH, whereas the brown matte region comprised both \u0026alpha;-FeOOH and \u0026beta;-FeOOH. \u0026gamma;-FeOOH may have formed from spongin fibres through bio-mineralisation.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e37\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e\u003c/p\u003e\n \u003cdiv class=\"gridtable\"\u003e\n \u003cdiv class=\"colspec\" align=\"left\"\u003e\u003cbr\u003e\u003c/div\u003e\n \u003c/div\u003e\n \u003c/div\u003e\n\u003c/div\u003e"},{"header":"4 Discussion","content":"\u003cp\u003eThe corrosion of the bluish-white porcelain from the Nanhai No. 1 shipwreck in seawater followed a typical ecological process involving marine animals and micro-organisms. In this process, micro-organisms served as pioneer organisms (Fig.\u0026nbsp;9h), forming a biofilm on the artefact surface. With gradual hydrolysis of the glass phase in the glaze layer, Fe ions in the environment were deposited onto the Si-rich gel layer through ion exchange. Fe(OH)\u003csub\u003e3\u003c/sub\u003e was formed under the action of Fe-oxidising bacteria, and subsequently converted to FeOOH through redox reactions by seawater. At this point, the glaze surface had lost its smoothness owing to mechanical collisions with marine debris and microstructural reorganisation. This provided suitable conditions for the selective attachment of sponges. The unglazed rim of the artefact, caused by inverted firing (i.e., firing with the rim facing down) during fabrication, attracted sponge larvae to settle along the rim and neighbouring glaze surface.\u003c/p\u003e\n\u003cp\u003eContinuous reactions at the solid/liquid interface led to gradual hydrolysis of the glass framework, releasing large amounts of silicic acid (H\u003csub\u003e4\u003c/sub\u003eSiO\u003csub\u003e4\u003c/sub\u003e).\u003csup\u003e[29]\u003c/sup\u003e As long as the concentration of silicic acid in the environment does not exceed its solubility limit (\u0026lt;\u0026thinsp;2 mmol/L), it diffuses to the external environment and is taken up by the cells or compartments of micro-organisms, which accumulate and deposit silica in the form of amorphous hydrated silica through a process known as bio-silification.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e38\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Sponges actively absorb, accumulate, and deposit silica.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e39\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e40\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e41\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e42\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e43\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e Their osteoblasts absorb silicic acid through Na\u003csup\u003e+\u003c/sup\u003e/HCO\u003csub\u003e3\u003c/sub\u003e\u003csup\u003e\u0026minus;\u003c/sup\u003e[Si(OH)\u003csub\u003e4\u003c/sub\u003e] transporters and store it in specific organelles, thereby forming immature siliceous spicules.\u003csup\u003e[44]\u003c/sup\u003e Consequently, the silicate-based bluish-white porcelain and siliceous sponges co-existed through a silicon cycle. Si enhances the structural stability and damage resistance of sponges and promotes their adsorption of bacteria, redox reactions, and glucose metabolism.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e44\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e45\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e\u003c/p\u003e\n\u003cp\u003eAlkaloids (nitrogen-containing basic organic compounds) were secreted by the sponges as secondary metabolites and subsequently dissolved in the local aqueous solution. The binding of N to H\u003csup\u003e+\u003c/sup\u003e led to the release of free OH\u003csup\u003e\u0026minus;\u003c/sup\u003e ions that subsequently reacted with Fe\u003csup\u003e2+\u003c/sup\u003e/Fe\u003csup\u003e3+\u003c/sup\u003e in seawater. This contributed to the formation of Fe(OH)\u003csub\u003e3\u003c/sub\u003e species on the artefact surface beneath the attached sponges, which were then expelled from the sponges through the respiratory and filtration system. When a sponge reached its end of life, Fe(OH)\u003csub\u003e3\u003c/sub\u003e species that had not been expelled were deposited at the interface between the concretion and artefact, and were subsequently converted to \u0026alpha;-FeOOH (brown matte regions) through redox reactions. Through molecular cohesion, the \u0026alpha;-FeOOH species bound to the \u0026beta;-FeOOH species (brown reflective regions) that had formed initially in the surface alteration layer; thus, these two species jointly constituted the interfacial corrosion layer. Negatively charged functional groups in the organic mucus secreted by sponges (e.g., \u0026ndash;C\u0026ndash;O\u0026ndash;C and \u0026ndash;OH) exerted strong adsorption effects on positively charged metal ions,\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e46\u003c/sup\u003e\u003csup\u003e][\u003c/sup\u003e\u003csup\u003e47\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e facilitating the chemical adsorption of corrosion products onto the sponge remains.\u003c/p\u003e\n\u003cp\u003eWhen the concretions were gently peeled from the artefact surface, the corrosion products that had formed on the surface alteration layer of the glaze prior to sponge attachment also detached. This demonstrates that the attached sponges aided in the bio-preservation of the bluish-white porcelain. However, irregular shapes with a matte texture, outlined by corrosion products, remained on the bluish-white porcelain glaze surface, resulting in a \u0026ldquo;map\u0026rdquo; of past sponge attachment. This provides methodological insight into removing insoluble salt deposits from the surfaces of ancient ceramics: identical compounds can be cultivated on the difficult-to-remove deposits on artefact surfaces. When the accumulated material reaches a certain thickness, removal may be achieved through mutual attraction between adjacent parts and molecules of the same material. Further investigation of this approach will be conducted through simulated experiments.\u003c/p\u003e\n\u003cp\u003eWhen the artefacts were removed from seawater, dehydration led to the loss of H\u003csub\u003e2\u003c/sub\u003eO molecules from the FeOOH species, which contributed to the formation of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e. Subsequently, unstable biogenic silica (e.g., siliceous spicules of sponges) underwent dissolution and re-precipitation (opal-A \u0026rarr; opal-CT \u0026rarr; authigenic quartz) to form biogenic quartz in the form of crypto-crystals, micro-crystals, and micro-crystalline aggregates.\u003csup\u003e[\u003c/sup\u003e\u003csup\u003e48\u003c/sup\u003e\u003csup\u003e],[\u003c/sup\u003e\u003csup\u003e49\u003c/sup\u003e\u003csup\u003e]\u003c/sup\u003e This explains the presence of translucent crystalline granules with diameters exceeding 300 \u0026micro;m within the pores. With regard to the circular pits on the glaze surface, some formed from the rupture or hydrolysis of thin glaze layers covering bubbles, whereas others formed by corrosion of annular micro-bubbles.\u003c/p\u003e\n\u003cp\u003eBased on the above discussion, a schematic of the corrosion process of bluish-white porcelain in seawater and its complex interactions with siliceous sponges is shown in Fig.\u0026nbsp;13.\u003c/p\u003e\n\u003cdiv class=\"gridtable\"\u003e\n\u003cdiv class=\"colspec\" align=\"left\"\u003e\u0026nbsp;\u003c/div\u003e\n\u003c/div\u003e"},{"header":"5 Conclusion","content":"\u003cp\u003eIn this study, we analysed the corrosion morphologies of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty following their excavation from the Nanhai No. 1 shipwreck, with the aim of investigating the corrosion mechanisms of ancient ceramics in marine environments and the complex interactions of these ceramics with siliceous sponges. The following conclusions were drawn:\u003c/p\u003e \u003cp\u003e(1) Bluish-white porcelains with unglazed rims were subjected to wear from debris carried by seawater and corrosion of the glass phase in the glaze. This led to scratches, pits, and micro-cracks, as well as the deposition of corrosion products (e.g., FeOOH) on the rough surfaces. These sites provided suitable conditions for the selective attachment of sponges. Leaching of Fe ions from the glaze layer resulted in fading of the blue\u0026ndash;green colour of the porcelain.\u003c/p\u003e \u003cp\u003e(2) Sponge larvae colonised the artefacts, resulting in a mutually beneficial relationship between the attached sponges and porcelain. The larvae absorbed, fixed, and converted large amounts of H\u003csub\u003e4\u003c/sub\u003eSiO\u003csub\u003e4\u003c/sub\u003e that had been released through hydrolysis of the glass network. This benefitted the skeletal system of the larvae, while the soft sponges protected the porcelain surface from mechanical forces. Meanwhile, the organic mucus secreted by sponges encapsulated deposits on the artefact surface, and Fe(OH)\u003csub\u003e3\u003c/sub\u003e precipitates formed under the action of alkaloids. These substances were expelled into the seawater through the sponges\u0026rsquo; respiratory and filtration system, which provided a purification effect to the glaze surface.\u003c/p\u003e \u003cp\u003e(3) Upon reaching their end of life, the interwoven skeletal remains of the sponges served as deposition sites and filters for external contaminants, trapping contaminants within their mesh-like structure while continuing to provide resistance against external mechanical forces. Corrosion products that formed under the action of alkaloids bonded with the initial corrosion products in the surface alteration layer of the glaze surface through molecular cohesion, leading to the formation of an interfacial corrosion layer. Ultimately, insoluble salts could be removed from the excavated artefacts by gently peeling the sponge remains from the artefact surfaces.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors wish to express their gratitude to Dr. Wen Zou of the\u0026nbsp;Ceramic Research Institute of Light Industry, China, and\u0026nbsp;Dr. Shuimiao Yu and Yuan Xu of WITec for their kind support and assistance with this research.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;Author\u003c/strong\u003e\u003cstrong\u003econtributions\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eYY provided support and guidance for this study, provided the samples; YW designed and performed all experiments, interpreted the data, and wrote and revised the manuscript; XC assisted with the Raman spectroscopy and XRD; NL acquired funding; and QW provided assistance. All authors have read and approved the final version of the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eFunding\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThis research was supported by the Key Technologies and Application Demonstrations for the Protection of Marine Ceramic Cultural Relics (2023YFF0906400), the National Archaeological Talent Revitalization Plan Project (2024-276), and Key Project 1 of the National Social Science Foundation of China (23FKGA002).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAvailability of data and materials\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eData sharing is not applicable.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDeclaration of competing interests\u003c/strong\u003e\u0026nbsp;\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAppendix A. Supplementary data\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eSupplementary data to this article can be found online .\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eWei, J. Archaeology of the shipwreck \u0026ldquo;Nanhai I\u0026rdquo; and protection of underwater cultural heritage. \u003cem\u003eCult. Heritage\u003c/em\u003e\u003cstrong\u003e1\u003c/strong\u003e, 148-153 (2008).\u003c/li\u003e\n\u003cli\u003eGuangdong Institute of Cultural Relics and Archaeology, State Administration of Cultural Heritage Protection Center for Underwater Cultural Heritage. Underwater Archaeology Project of the Southern Song Dynasty Shipwreck \u0026ldquo;Nanhai I\u0026rdquo; in Guangdong. 2022.\u003c/li\u003e\n\u003cli\u003eLiu, D. Research on Jingdezhen kiln bluish-white porcelain from the shipwreck \u0026ldquo;Nanhai I\u0026rdquo;. \u003cem\u003eJ. Cult. Hist. 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Gas Geosci.\u003c/em\u003e\u003cstrong\u003e27\u003c/strong\u003e, 377-386 (2016).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"Nanhai No. 1 shipwreck, Southern Song Dynasty, bluish-white porcelain of Hutian kiln, corrosion mechanisms, sponges","lastPublishedDoi":"10.21203/rs.3.rs-6289041/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6289041/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eUnderstanding the influence of marine-organism attachment on the corrosion of ancient porcelains is crucial for the conservation of underwater cultural heritage. In this study, the mutually beneficial relationship between siliceous sponges and ancient silicate ceramics was elucidated for the first time. The complex interactions between the sponges\u0026rsquo; secondary metabolites (nitrogen-containing alkaloids and carbon-containing organic mucus) and corrosion products were studied in detail, along with their filtration and purification effects. We comprehensively analysed the morphological structures and chemical compositions of the surface concretions and glaze surface of bluish-white porcelains excavated from the Nanhai No. 1 shipwreck. The results indicated that the concretions consisted of sponge remains, with the skeleton primarily composed of silicon carbonate. The main corrosion products were iron(III) oxide-hydroxide and iron(III) oxide. The sponge-secreted alkaloids formed secondary corrosion products which bonded with the primary corrosion products in the surface alteration layer, resulting in significant differences in corrosion morphology across the glaze surface depending on concretion detachment. This study demonstrates the presence of an inorganic/organic silicon cycle and elucidates the complex interactions therein. Our findings serve as an important reference for research on the conservation of excavated underwater ancient ceramics, marine palaeontology, and geochemistry.\u003c/p\u003e","manuscriptTitle":"Corrosion mechanisms of bluish-white porcelains of Hutian kiln of the Southern Song Dynasty excavated from the Nanhai No. 1 shipwreck","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-04-14 18:55:25","doi":"10.21203/rs.3.rs-6289041/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-04-29T14:00:23+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-28T23:54:45+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-12T16:33:17+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"64984086860936406539806929217842652338","date":"2025-04-09T11:36:18+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-07T12:14:31+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"197974313505790358385091498818519609633","date":"2025-04-03T16:12:41+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-04-01T04:33:14+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"191573523514010351995344248511992039347","date":"2025-03-28T01:22:16+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"84982438631639985751463334286912403012","date":"2025-03-27T10:25:25+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-03-27T05:31:23+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-03-26T11:52:06+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-03-26T11:51:17+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj heritage science","date":"2025-03-23T15:02:59+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"5030ecd4-62dd-45c1-a593-4e39fa2338b9","owner":[],"postedDate":"April 14th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-07-28T16:05:02+00:00","versionOfRecord":{"articleIdentity":"rs-6289041","link":"https://doi.org/10.1038/s40494-025-01945-y","journal":{"identity":"npj-heritage-science","isVorOnly":false,"title":"npj Heritage Science"},"publishedOn":"2025-07-23 15:57:19","publishedOnDateReadable":"July 23rd, 2025"},"versionCreatedAt":"2025-04-14 18:55:25","video":"","vorDoi":"10.1038/s40494-025-01945-y","vorDoiUrl":"https://doi.org/10.1038/s40494-025-01945-y","workflowStages":[]},"version":"v1","identity":"rs-6289041","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6289041","identity":"rs-6289041","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}