Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago

Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago | 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 Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago Xuesong Yin, Berta Mañas Alcaide, Christel Pesme, Qiang Li, Jingyi Zhang, and 8 more This is a preprint; it has not been peer reviewed by a journal. https://doi.org/ 10.21203/rs.3.rs-2540579/v1 This work is licensed under a CC BY 4.0 License Status: Posted Version 1 posted You are reading this latest preprint version Abstract Ancient ceramics have profound influences on the living habits of human beings. The emergence of high-fired polychromic glazes during Tang period (618–907 AD) highlights a significant advancement in ceramic history that reflected inter-civilizational communications more than 1000 years ago. However, the understanding of colouration mechanisms in Tang glazes are still not satisfactory. In this work, we unravel the mysteries of colourful Tang glazes through a comparative study of Tang Sancai and Changsha kiln samples. Multiple chemical and structural factors, including colourants in varied concentrations and oxidation states as well as microstructures resulted from phase separation, impurity and corrosion, are found responsible for the glaze appearance. More importantly, the combination of different coloration ingredients brings about additional colours and optical effects that any individual factor can hardly generate. These fresh observations and comprehensive analyses provide an insightful assessment of the diversity of Tang glazes and promote the perception of ancient ceramics in a more scientific manner. The knowledge and methodology revealed here are expected to inspire more studies of heritage materials. Physical sciences/Chemistry Physical sciences/Materials science Ancient ceramics coloration Tang Sancai Changsha kiln polychromic structural colour Figures Figure 1 Figure 2 Figure 3 Figure 4 Introduction The advent of ceramics has provided human beings vessels to store, cook and preserve goods and largely shaped the way people lived since 20000 years ago. 1 , 2 , 3 In history, Tang Empire (618–907 AD) has been esteemed as one of the most prosperous and influential periods. 4 Accompanied by frequent transcontinental trades along silk roads (by land and sea, Fig. 1 a), tremendous cultural exchange and fusion took place between western and eastern civilizations. 5 , 6 Innovative decoration styles involving various colours applied on different artefacts were developed during this period. 7 Ceramics, as a popular trading product, always took along the new fashions timely and played a critical role in the global commerce. 8 , 9 , 10 Due to the heavy and fragile nature of ceramic products, water transportation is a preferred way for ceramics trading. Ceramic artefacts in Tang dynasty have been discovered in many ancient city sites, such as Yangzhou and Guangzhou in China, Mantai in Sri Lanka, Samarra in Iraq, Fostat in Egypt, etc in Fig. 1 (a). 11 , 12 It is not surprising that numerous Tang wares were also salvaged from some shipwrecks. Two famous Tang shipwrecks are the Belitung ship from Indonesia (exhibited in Asian Civilizations Museum of Singapore) and the Chau Tan ship from central Vietnam. 8 , 13 , 14 , 15 Thanks to the plentiful ceramic relics, a vivid picture of trading routes along the maritime silk roads over ten centuries ago can be manifested today. 9 , 16 , 17 In addition to the historical values, there are significant developments in ceramic technologies in Tang dynasty, especially the appearance of varied colours and glaze effects. The most famous example is the low-fired tri-colour (Sancai) wares. 12 Since a considerable amount of Sancai wares excavated in 1920s, they have been praised as the crown of Tang ceramic arts. 11 More recently, several kiln sites that produced Sancai wares, such as Gongxian kiln in Henan, Yaozhou kiln and Liquanfang kiln in Shaanxi, Qiong kiln in Sichuan and Xing kiln in Hebei, were identified and studied. 12 , 18 , 19 , 20 For high-fired polychromic wares, the Changsha kiln in Hunan province attracts more and more interests after several excavations and studies of kiln/city/port sites and shipwrecks. The colourful and freehand decoration signifies a pioneering role of Changsha kiln in calcium-based polychromic glazes. 13 , 14 , 21 , 22 Although there are a few technical reports on Tang glazes, it is still far from satisfactory to recognize such an important category of heritage materials. A better understanding of the colouration mechanisms in different Tang glazes is necessary and valuable. Therefore, we present this study to explore the colourful glazes of Tang ceramics through a comparative study of Sancai and Changsha kiln glazes. Comprehensive characterizations and analyses reveal multiple factors that contribute to the appearance of Tang ceramics, including types of glaze, colorants, oxidation states, glaze microstructures, impurities and even corrosion. More interestingly, these chemical and structural colouring elements synergize and create more hues and glaze effects. The cooperation of colourants Fe and Cu gives rise to diverse colours covering a wide spectrum from light yellow to dark brown and various greens. The mixture of liquid-liquid (L-L) phase separation and copper red/green generates special opaque effects and colours ranging from milky white to bluish green to purplish red. Glaze corrosions add silvery iridescence and frosted appearances on some aged Sancai and Changsha wares, respectively. Close investigations on phase diagrams and residual materials in glaze also provide more indications on Tang ceramic technologies in terms of firing conditions and raw pigments. The knowledge obtained in this study not only extends the recognition of Tang ceramics from a scientific perspective but will also benefit studies of many other ancient ceramics. Results Samples. Figure 1 (c) and (d) show twelve ceramic samples, six Tang Sancai (T 1 -T 6 ) and six Changsha kiln (C 1 -C 6 ), studied in this work. The conditions of glaze, clay, their interface and provenance are presented in Table 1 . A more detailed summary of the samples is provided in Supplementary Table S1. In Fig. 1 (b), four kilns producing Sancai wares, Gongxian kiln in Henan province, Yaozhou kiln in Shaanxi province, Xing kiln in Hebei province and Qiong kiln in Sichuan province, and Changsha kiln in Hunan province are indicated with some major cities nearby. It is worth noting that the cities were normally accessible and connected by water networks shown in Fig. 1 (b). For instance, both Sancai (T 6 ) and Changsha (C 2 ) samples were found from Yangzhou city, which was an important port linking inland waters and sea during Tang dynasty. In Fig. 1 (c), a light-yellow translucent glossy glaze is applied to both sides of sample T 1 . T 2 has a dark brown exterior glaze and a light greenish interior glaze. T 3 has a mixture of light brown and green glazes. Some dark spots on the brown glaze and a white-silvery layer on the green glaze are also found on T 3 . T 4 -T 6 samples have transparent/white base glazes with coloured patches applied on the surface. The variegated colours include dark green on T 4 and T 5 , and dark blue and brown on T 6 . For the Changsha pieces in Fig. 1 (d), a transparent/yellowish base glaze with dark brown and opaque green dotted patterns is applied on C 1 . C 2 has a translucent light-green glaze with decorations in brown and purple red. Exterior surface of C 3 is covered by a brown glaze. Meanwhile, a transparent glaze is applied on its interior surface. C 4 and C 5 have green coloured patchy decorations. But the base glaze of C 4 is opaque light green, while C 5 has a creamy opaque base glaze. C 6 is fully covered by a dark green opaque glaze. Some black dots are found on the dark green surface of C 4 and C 6 . Tang Sancai samples T 1 -T 3 and T 5 have a layer of white slip in between the clay body and glaze. No slips are observed in T 4 and T 6 . Changsha samples C 1 and C 3 -C 5 have a well-developed white interphase layer between their clays and glazes (Table 1 and Supplementary Table S1). In C 2 and C 6 , this interphase layer is not so obvious. Bubbles in glaze and air pockets in clay are often observed in both the Tang Sancai and Changsha glazes. The clays of Tang Sancai and Changsha samples are mostly in pink/red and grey/brown, respectively. Table 1 Sample information. Sample ID Glaze colour Glaze crazing Bubble Glaze/clay interface Clay body Provenance T 1 Light yellow translucent glossy glaze (interior and exterior) Crazing with different shapes and dimensions Small bubbles, not visible White slip (interior and exterior) Red stoneware clay with few small air pockets Qiong kiln, Sichuan city site T 2 Dark brown glaze (exterior) Light greenish glaze (interior) Very thin crazing at different levels No visible bubbles White slip (exterior) Compact pinkish stoneware clay Gongxian kiln, Henan city site T 3 Light brown and green translucent glossy glazes (exterior) with dark spots on brown glaze and a white-silvery layer Very fine crazing, almost not visible No visible bubbles White slip Pinkish stoneware clay with small fine cracks Gongxian kiln, Kiln site T 4 Transparent and dark green translucent glossy glazes (exterior) Extremely fine crazing Many bubbles Not visible Light pinkish stoneware clay with very small air pockets Gongxian kiln, Henan city site T 5 Transparent and dark green glossy glaze (exterior) Very fine crazing No visible bubbles White slip (interior and exterior) Pinkish stoneware clay with many small air pockets Xing kiln, Shandong, Liaocheng city site T 6 Dark blue, brown and transparent glazes (exterior) Very fine crazing Some bubbles Not visible White stoneware clay Unknown kiln, Yangzhou city site C 1 Transparent/yellowish base decorated with dark brown and green dots. (exterior) Fine crazing Some bubbles White interphase or slip Light grey stoneware clay Changsha kiln, Changsha city site C 2 Transparent-light green glaze with decorations in brown and purple red (exterior) Very fine crazing Many bubbles Not visible Grey and pinkish stone ware clay with localized air pockets Changsha kiln, Yangzhou city site C 3 Brown glaze (exterior) and transparent glaze (interior) Fine crazing Fine bubbles White interphase or slip (exterior) Salmon and dark grey stoneware clay with fine cracks Changsha kiln, Changsha city site C 4 Dark and light green glaze with yellow depositions and black spots (exterior) Not visible Some bubbles White interphase or slip Grey stoneware clay with small and large air pockets Changsha kiln, Unknown site C 5 Green glaze applied on creamy opaque glaze (exterior) Fine crazing Bursts in circular shape White interphase or slip Light brown stoneware clay with many large air pockets Changsha kiln, Unknown site C 6 Dark green opaque glossy and transparent glaze with black spots Fine crazing Not visible Not visible Grey stoneware clay with small air pockets Changsha kiln, Changsha city site Glaze compositions. A survey of Tang Sancai and Changsha glazes is conducted with their chemical compositions summarized. The glaze compositions of the samples in Fig. 1 (c) and (d) are also analysed and presented in Supplementary Tables S2 and S3. In Supplementary Table S2, PbO, SiO 2 and Al 2 O 3 are three major components in Sancai glazes, in which alkali PbO serves as the flux agent to reduce melting temperature of the glaze. Alternatively, CaO is the flux agent and forms the majority of Changsha glaze together with SiO 2 and Al 2 O 3 in Supplementary Table S3. In both Sancai and Changsha samples, the top three components take about 90% of the overall weight of the glaze, which determine the glaze properties to a large extent. Other minor elements, like Mg, K, Na, Fe, Ti, are also detected in both Sancai and Changsha glazes. Cu is observed in some green coloured Sancai and Changsha glazes. Comparing with non-detectable phosphorus in Sancai glazes, Changsha glazes often contain a small amount of phosphorus. These minor elements also play important roles as colorants and/or flux agents. 11 , 23 Discussion The varieties in glazing effects of Tang Sancai and Changsha samples presented above are of great interests in understanding the development of early polychromic ceramics. Modern analytical methods have been used as a powerful tool to study heritage materials. 24 , 25 , 26 , 27 For the case of Tang ceramics, F.K. Zhang et al. published compositional characterizations of several Sancai glazes from Gongxian kiln in 1980s. 28 , 29 N. Wood compiled testing results of Tang Sancai samples from Henan, Shaanxi and ancient city sites in Egypt, Iraq and Sri Lanka. 11 B.P. Li et al. analysed trace elements in Sancai wares from Gongxian and Yaozhou kilns. 18 Q.Q. Jiang did a survey of Sancai wares from several kiln sites. 12 J.F. Cui studied Sancai glazes from the Liquanfang site with a focus on the compositions of ceramic bodies. 19 J.Y. Shen conducted a comparative study of Sancai wares from Northern China and Mid-East through chemical analysis. 30 For Changsha wares, Z.G. Zhang et al. examined the compositions of several Changsha samples. 31 In 1986, F.K. Zhang provided more testing results and explanation of colouration in Changsha wares. 32 X.Q. Chen et al. reported the phenomenon of phase-separation in Changsha samples. 33 Y.Q. Li et al. studied the coloration of Changsha copper-red glaze. 34 B. Shen et al. also explored the micro-structures of several Changsha wares and discussed the roles of colorants. 35 From the previous studies, it is noted that Tang Sancai and Changsha glazes belong to two glaze systems, PbO-Al 2 O 3 -SiO 2 and CaO-Al 2 O 3 -SiO 2 , respectively. The different flux agents (Pb in Sancai and Ca in Changsha) result in distinctive glaze properties. The lead-glazed Sancai wares are relatively weaker in mechanical strength, so they were used as burial or worship objects. 12 , 36 In contrast, the more durable Changsha wares were mainly for daily use or trading purposes. 13 , 37 , 38 Generally, Sancai colours are bright and alluring, and Changsha glazes often have soft and warm hues. Sancai and Changsha wares share a common feature of variegated glazes. In spite of these observations, a comprehensive study is necessary to deal with the varieties of Tang glazes and explore the coloration mechanisms. In addition to the individual factors, like glaze chemistry, corrosion effect, colorants, phase structure and even impurity, their synergistic effects also need to be taken into account to elaborate the complicated Tang glazes. Glaze chemistry and corrosion. The ternary phase diagrams of PbO-Al 2 O 3 -SiO 2 and CaO-Al 2 O 3 -SiO 2 are shown in Fig. 2 (a) and (b) with isothermal contour curves, indicating solid-liquid transition temperatures with respect to compositional variations. 39 , 40 The Sancai and Changsha samples are mapped in the diagrams according to their compositions (see Supplementary Tables S2 and S3). It is found that Sancai glazes have a high PbO content of 50–75%, a SiO 2 content around 25–35% and an Al 2 O 3 content of 6–8%. In contrast, the flux CaO content in Changsha glaze is around 12–20%, and the SiO 2 and Al 2 O 3 contents are about 55–65% and 8–15%, respectively. It is interesting to find that the sample compositions are just around the regions with the lowest melting temperature for both Sancai (PbO-Al 2 O 3 -SiO 2 ) and Changsha (CaO-Al 2 O 3 -SiO 2 ) glaze systems. The results indicate ancient potters had engineered their glaze recipes quite well so only a minimized temperature was required. Such optimized firing conditions could benefit the ceramic industry by saving cost and improving yields. In Fig. 2 (c), the Changsha glaze (C 4 ) has a Raman shift profile similar with 0.2CaO-0.8SiO 2 glass, which has major peaks around 960 cm − 1 and 1030 cm − 1 for Si-O-Si bond Q 2 and Q 3 vibrations. 41 , 42 The peaks around 460 cm − 1 and 600 cm − 1 are attributed to Si-O-Si D 1 and D 2 vibration modes. 42 , 43 , 44 The peak at 1385 cm − 1 is related to P-O bond vibration. 45 For the Sancai glaze (T 5 ), the Raman peak around 460–550 cm − 1 and 950 cm − 1 are assigned to various Si-O-Si bonds in Pb rich glasses. 46 , 47 , 48 The high frequency peaks at 1360 cm − 1 and 1600 cm − 1 could be associated with vibrations of slip/body materials. 49 In addition, no characteristic diffraction peaks were observed in the XRD patterns of Sancai or Changsha glazes in Supplementary Fig. S1(a). From the XRD and Raman results, it can be concluded that both Sancai and Changsha glazes exhibit a long-range disordered but short-range ordered glass structure. Corrosion is an inevitable process that affects the appearance of ancient ceramics. 50 The famous silvery iridescence of “Han green glaze” has been well studied with the decomposed structure and corrosion mechanisms established. 29 , 51 Similar corrosion effects are detected on Tang Sancai wares as well. 18 , 20 , 23 , 30 Among the Sancai samples examined in this work (Fig. 1 c), the dual-coloured specimen C 3 has a much degraded glaze with pearly lustre, and the corrosion is more severe on the green part in contrast to the yellow part. Close SEM examination and comparison of this degraded piece (T 3 ) and a high-fired Changsha counterpart (C 1 ) are provided in Supplementary Fig. S1. In Fig. 2 (d), distinctive crystal grains are found in the corroded area of T 3 . The XRD pattern in Fig. 2 (f) further confirmed the crystal structures of 3PbCO 3 ·2Pb(OH) 2 ·2H 2 O (PDF #09-0356), Al 2 Ca(SiO 4 ) 2 (PDF #02-0537) and PbSiO 3 (PDF #29–0782) in the area (ii) of T 3 . It indicates a separation of Pb and Si near the corroded surface, which is resulted from Pb leaching. 51 , 52 This also explains the compositional shift of T 3 to a relatively Si rich and Pb poor position in Fig. 2 (a). Comparatively, the Changsha sample C 1 is less corroded with a disintegrated pitting-like structure in Fig. 2 (e). Its XRD pattern in Fig. 2 (f) suggests an amorphous nature of the weathered area (II) of C 1 . Overall, a drastic corrosion involving glaze disintegration and re-construction brings about a silvery lustre on the Sancai green glaze. The Changsha glaze has a frosted appearance due to its corroded structures. Colorants and phase separation. The samples in Fig. 1 (c) and (d) are mapped on a standard colour wheel chart in Fig. 3 (a) according to their individual colours. These samples cover a wide spectrum from yellow to brown, red to purple and green to blue with various hues. The colorants and microstructures of the glazes need to be identified to access their colouring effects. First, a new colorant, cobalt (Co), should be pointed out, as it brought chemical blue in Tang glazes. It even turned to be a signature of Tang ceramics when several high-fired dishes with blue painted patterns were salvaged from the Belitung cargo. Actually, there are even more cases in low-fired Sancai wares that have blue glazes attributing to the colorant of Co. In Fig. 1 (c), the sample T 6 has a painted blue glaze and its composition in Supplementary Table S2 confirms the existence of Co. The pursuit of blue and application of Co pigment are believed to be influenced by Islamic customs. 53 , 54 Nevertheless, Fe and Cu still remain as two dominant colouring elements in Tang ceramics, complying with earlier traditions of Chinese glazes. 23 The finely potted Yue kiln wares represented one of glorious periods of Fe coloured celadon glazes. Meanwhile, the application of copper in high-fired glazes became a new fashion. Changsha potters were masters of the technique and proficiently practised polychromic decorations on their products. Following the yellow arrow in Fig. 3 (a), a colour changing from light yellow to dark brown with increasing Fe content is demonstrated in Fig. 3 (b). The mixing of Fe and Cu also generates different colouring effects. The relative ratios of Fe and Cu in the samples distributed across yellow to green spectrum are plotted in Fig. 3 (c). The various colours from yellow to olive green, bean green and light green along the green arrow in Fig. 3 (a) indicate synergistic effects of the mixed Fe and Cu colorants. 11 More importantly, the unique copper red glaze also appeared in this period. The effects of copper are further investigated here by a comparison of the Sancai sample T 5 and Changsha sample C 4 . In Fig. 3 (d), optical cross-section image of T 5 shows a uniform green glaze (~ 0.10 mm) on top of a white slip layer (~ 0.15 mm). The glaze is also very smooth as revealed by its SEM image in Fig. 3 (e). In contrast, a thicker glaze (~ 0.20 mm) is directly applied on the body of C 4 (Fig. 3 f). The C 4 glaze manifests a layered structure with a milky greenish top layer and a red/purple bottom layer. Comparing with the amorphous nature of T 5 and C 4 green glaze (Supplementary Fig. S1; Fig. 3 g and i), diffraction peaks of metallic Cu (PDF #02-9026) are revealed in the red area of C 4 glaze (Fig. 3 g). The results agree well with the reported coloration of copper red and green glazes. 10 , 55 , 56 , 57 Synthetic studies also demonstrated a consistent correlation between the green/red colours and the oxidation states of copper. 58 , 59 Interestingly, the C 4 glaze contains many small particles as shown in the image of a thin FIB sample in Fig. 3 (h). The TEM image in Fig. 3 (j) revealed that the particle size is about 100 nm. This type of nanostructures is resulted from liquid-liquid (L-L) phase separation during glaze formation, which gives rise to a milky blueish colour due to light scattering. 60 , 61 , 62 The compositional differences between two liquid phases are further analysed by EDX mapping and quantified in Fig. 3 (j) and (k) and Supplementary Fig. S2. It shows that the particle-like phase (Phase 1) is rich in Si, K and O, and the matrix-like phase (Phase 2) is rich in Ca and Mg. The contents of Al are similar in both phases. The colorants Fe and Cu are slightly more concentrated in Phase 2 (Fig. 3 k and Fig. S2). 61 Herein, four colouring factors, i.e. yellow from oxidized Fe, green from oxidized Cu, red from reduced Cu and opaque white/blue from L-L separation, are figured out and labelled in Fig. 3 (a). How these colouring factors cooperate and generate more effects can be described as follows. Different concentrations of oxidized Fe give rise to colours from light yellow to dark brown. The mixture of oxidized Fe and Cu brings about a wide range of yellow-green colours. Moreover, when the reduced copper red is mixed with L-L separation (C 4 ), the colours ranging from red to purple are created as shown in Fig. 3 (a). The thickness of glaze also matters, as more purplish tint is observed when the glaze goes thicker in Fig. 3 (f). The opaque blueish green colour on the painted surface can be attributed to a mixed effect of oxidized copper green with L-L separation in Fig. 3 (a). Impurity. The Changsha sample C 4 has shown rich glaze effects with various colours and structures. Another interesting feature is discovered when having a close look at the glaze surface. Figure 4 (a) presents a magnified image of the squared area of C 4 in Fig. 1 (d). In addition to the opaque light blue/green glaze, deep green/blue paints and their purplish boundary, some black dots are scattered on the surface of painted area. Similar black dots can also be found along cracks on the sample C 6 (see Supplementary Table S1). In order to find out their origins, an EDX scan (Fig. 4 b) is performed on one black dot with the scanned area indicated in the inset SEM image. A cross-section sample near a black spot is also prepared and shown in Fig. 4 (c). Further EDX elemental mappings (Fig. 4 f) are carried out on the marked area in Fig. 4 (c). The elemental analyses (Figs. 4 b and f) suggest different chemical compositions of the black material from the surrounding glaze. The black substance is rich in S, Fe and Cu, and the ratio of Cu: Fe: S is around 1.2: 1.0: 2.0. The XRD (Fig. 4 d) and Raman (Fig. 4 e) measurements indicate the existence of crystal phases of CuFeS 2 (PDF #35–0752) and CuS 2 (PDF #19–0381). 63 , 64 , 65 Regarding the source of the chemicals, the fuels of Changsha kilns were woods instead of coals used in northern kilns in Tang period, 13 so there should not be significant sulphur from the fuels for Changsha wares. Also considering the black dots only appear on the painted areas, it is highly possible that the material comes from the Cu and S contained mineral pigments for green/red decorations. 55 In summary, to unravel the mysteries of colourful Tang glazes, we carried out a comprehensive study on glaze chemistry, corrosion, colorants, microstructure of some Sancai and Changsha samples. Their optical effects and colouring mechanisms are discussed with fresh experimental observations. A collective exhibition of compositions in Sancai and Changsha glazes and their corresponding phase diagrams provide chemical insights on the distinctive features of base glazes in terms of firing temperature, crystal structure and corrosion resistance. As for colouring effects, in spite of the newly introduced colorant Co, Fe and Cu remain as the dominant colouring agents in Tang glazes. The concentration, oxidation state and relative ratio of Fe and Cu in glazes bring about a wide range of colours. More importantly, the structural colours resulted from L-L phase separations start to play important roles in Tang ceramics. The mixed effects of copper-red, copper-green and structural blue and milky white are of particular interests, which create more rich and pleasant hues. In addition, some black dots found on Changsha samples help reveal the raw pigment materials used in the copper glazes. The chemical insights and understanding of colouration mechanisms obtained in this work will shed new lights on the studies of historical ceramic glazes. Methods Sample preparation. Original samples without any treatment were observed for sample descriptions in Tables 1 and Supplementary Table S1. Testing specimens with various colours were obtained from the shards in Fig. 1 (c) and (d). A portable electric grinder was used to cut the samples and remove excess body clays. To remove residual accretions and small particles, the specimens were cleaned in DI-water and ethanol by an ultra-sonic bath for 15 min. Then, they were dried by using a nitrogen gas spray gun before any chemical or microstructural analyses. The deep green/blue specimen from Changsha sample C 4 is polished to remove the surface layer so that the red part underneath is uncovered for easy access. Dual beam focused ion beam (FIB) technique (FEI, DB Helios 600 Nanolab) was applied to prepare an ultra-thin sample (100 nm) for transmission electron microscopy (TEM) measurements. Instrumental analyses. Digital Microscope (Keyence VHX-6000) with VH-ZST dual objective zoom lens (20x to 200x) was used to observe morphological and optical features of the samples. The magnified microstructures were characterized by using a field-emission scanning electron microscopy (FESEM) (JEOL, JSM 7600F). An energy dispersive X-ray (EDX) analyser, which is equipped in the FESEM system, was applied to analyse the elemental compositions and areal distributions. The crystalline structures of the glazes were determined by X-ray diffraction (Bruker, 2D Micro XRD). Further chemical structure and bonding of the glaze samples were also studied by a Raman microscope (Renishaw inVia confocal Raman system). The high-magnification morphologies and phase separations were analysed by a TEM system (FEI, Tecnai G2 TF20) with EDX analyser and selected area electron diffraction (SAED). Declarations Data availability The authors declare that all data supporting the findings of this study are available within the paper and supplementary information. Author contributions: X.Y., C.P. and Q.L. conceived the concept and planed the study. B.M.A. conducted sample observation and description. X.Y., B.M.A., H.K.H, Y.Y.K.H., P.C.L, N.D. and N.N.T performed the experiments. X.Y. and Q.L. did data analysis. X.Y., B.M.A. C.P., Q.L., J.Z. Q.Z., H.L. and S.Y.C. contributed in paper writing. All authors reviewed the manuscript. Acknowledgement The authors thank Dr. Kevin Lam from Asian Civilizations Museum for reviewing the manuscript. X.Y. acknowledges support from MRCA project (RGOV221031aIMRCOL) and A*STAR career development fund (CDF) SC25/21-811812 (grant no. C210812038). Q.L. and H.L acknowledge support from National Science Foundation of China (No. 51732008). References Boaretto, E., et al . Radiocarbon dating of charcoal and bone collagen associated with early pottery at Yuchanyan Cave, Hunan Province, China. Proc. Natl Acad. Sci. USA 106 , 9595-9600 (2009). Hendy, J., et al. Ancient proteins from ceramic vessels at Catalhoyuk West reveal the hidden cuisine of early farmers. Nat. Commun. 9 , 4064 (2018). Liu, L., et al. The origins of specialized pottery and diverse alcohol fermentation techniques in early neolithic China. Proc. Natl Acad. Sci. USA 116 , 12767-12774 (2019). Benn, C.D. & Benn, C. China's Golden Age: Everyday Life in the Tang Dynasty. (Oxford University Press, 2004). Ye, L., Fei, Z. & Wang, T. China: Five thousand years of history and civilization. (City University of HK Press, 2007). Garver, J.W. China and Iran: Ancient Partners in a Post-imperial World. (University of Washington Press, 2011). Lei, Z., Tantcheva-Burdge, E. & Cheung, V. Investigation into the colours of the DunHuang murals from the Tang Dynasty: Proceedings of the 14th International Colour Association (AIC) Congress, 2021 , 1059-1064 (International Colour Association, 2021). Mikami, T. 9th-10th Century Chinese Ceramics Found in Southeast Asia. (Ceramics and Kiln Technology, Centre of Asian Studies, University of Hong kong, 1990). Mikami, T. Road of Ceramics (Chinese translation). (Tianjin People's Publishing House, 1983). Jiang, X., et al. Early globalized industrial chain revealed by residual submicron pigment particles in Chinese imperial blue-and-white porcelains. Proc. Natl Acad. Sci. USA 117 , 6446-6452 (2020). Wood, N. Chinese glazes: Their origins, chemistry, and recreation. (University of Pennsylvania Press, 1999). Jiang, Q. Tang Sancai. (PhD thesis, University of Oxford, 2009). Yang, L. Tang Dynasty Changsha Ceramics: Shipwrecked, 145-159 (Singapore: Arthur M Sackler Gallery, Smithsonian Institution, 2011). Giang, D.T. Diplomacy, trade and networks: Champa in the Asian commercial context (7th-10th Centuries). Moussons Recherche en sciences humaines sur l’Asie du Sud-Est 27, 59-82 (2016). Nishino, N., et al. Nishimura project: the oldest shipwreck found in Vietnam–testimony to the maritime ceramic route: The international symposium on underwater archaeology in Vietnam and Southeast Asia: Co-operation for the development of Quang Ngai Province, 2014 , 14-15 (2014). Li, Q. Maritime Silk Road . (China Intercontinental Press, 2006). Miksic, J. Chinese ceramic production and trade. In Oxford Research Encyclopedia of Asian History (2017). Li, B.P., et al. Characterisation of Chinese Tang sancai from Gongxian and Yaozhou kilns using ICP-MS trace element and TIMS Sr–Nd isotopic analysis. J. Archaeol. Sci. 33, 56-62 (2006). Cui, J.F., Lei, Y., Jin, Z.B., Huang, B.L. & Wu, X.H. Lead isotope analysis of Tang Sancai pottery glazes from Gongyi kiln, Henan Province and Huangbao kiln, Shaanxi Province. Archaeometry 52, 597-604 (2009). Cui, J., et al. Western technical traditions of pottery making in Tang Dynasty China: chemical evidence from the Liquanfang kiln site, Xi'an city. J. Archaeol. Sci. 37, 1502-1509 (2010). Huang, P.H. Excavation bulletin (1999) of Changsha kiln at Wangchen county of Hunan province (in Chinese). Archaeology 5, 49-62 (2003). Rogers, A. Full spectrum: how the science of color made us modern . (Houghton Mifflin, 2021). Hetherington, A.L. Chinese ceramic glazes . (PD and I. Perkins, 1948). Pollard, A.M., Batt, C.M., Stern, B., Young, S.M. & Young, S. Analytical chemistry in archaeology . (Cambridge University Press, 2007). Bleasdale, M., et al. Ancient proteins provide evidence of dairy consumption in eastern Africa. Nat. Commun. 12, 632 (2021). Zavala, E.I., et al. Pleistocene sediment DNA reveals hominin and faunal turnovers at Denisova Cave. Nature 595 , 399-403 (2021). Dambrogio, J., et al. Unlocking history through automated virtual unfolding of sealed documents imaged by X-ray microtomography. Nat. Commun. 12, 1-10 (2021). Zhang, F.K. & Zhang, Z.G. Low-temperature colored glazes of successive dynasties in ancient China. J. Chin. Ceram. Soc. 8, 9-19 (1980). Zhang, F.K. The science of Chinese ancient ceramics. (Shanghai People's Fine Arts Publishing House, Shanghai, 2000). Shen, J. Chemical and Isotopic Analysis in the Investigation of Glazes from Northern China and the Middle East, 7th-14th Centuries AD. (University of Nottingham, 2017). Zhang, Z.G. & Guo, Y.Y. Study of coloured glazes of Changsha Tongguan kiln (in Chinese). J. Jingdezhen Univ. 1, 6 (1985). Zhang, F.K. Study of Changsha ware. J. Chin. Ceram. Soc. 14, 339-346 (1986). Chen, X.Q., Zhang, Z.G. & Huang, R.F. Opaque glaze of the Changsha Tongguan ware-Another Tang Dynasty's phase separated glaze. J. Chin. Ceram. Soc. 19, 234-240 (1991). Li, Y., et al. Colour-generating mechanism of copper-red porcelain from Changsha Kiln (A.D. 7th–10th century), China. Ceram. Int. 42, 8495-8500 (2016). Shen, B., et al. Micro-structural study of colored porcelains of Changsha kiln using imaging and spectroscopic techniques. Ceram. Int. 44, 18528-18534 (2018). Rawson, J., Tite, M. & Hughes, M. The export of Tang sancai wares: some recent research. Trans. Orient. Ceram. Soc. 52, 39-61 (1989). Ho, C., Charoenwongsa, P. & Bronson, B. Newly identified Chinese ceramic wares from ninth century trading ports in southern Thailand. SPAFA Digest (1980-1990) 11, 12 (1990). Flecker, M. A ninth-century AD Arab or Indian shipwreck in Indonesia: first evidence for direct trade with China. World Archaeol. 32, 335-354 (2001). Chen, S., Zhao, B., Hayes, P. & Jak, E. Experimental study of phase equilibria in the PbO-Al 2 O 3 -SiO 2 system. Metall. Mater. Trans. B 32, 997-1005 (2001). Harada, Y., Saito, N. & Nakashima, K. Crystallinity of supercooled oxide melts quantified by electrical capacitance measurements. ISIJ Int. 57, 23-30 (2017). Retsinas, A., Kalampounias, A.G. & Papatheodorou, G.N. Glass formation and Raman spectra of CaO-SiO 2 glasses towards the orthosilicate limit. J. Phys. Chem. Solids 99, 19-24 (2016). Kucharczyk, S., Sitarz, M., Zajac, M. & Deja, J. The effect of CaO/SiO 2 molar ratio of CaO-Al 2 O 3 -SiO 2 glasses on their structure and reactivity in alkali activated system. Spectrochim. Acta A Mol. Biomol. Spectrosc. 194, 163-171 (2018). Kalampounias, A.G. IR and Raman spectroscopic studies of sol-gel derived alkaline-earth silicate glasses. Bull. Mater. Sci. 34, 299-303 (2011). Robinet, L., et al. Raman spectrometry, a non-destructive solution to the study of glass and its alteration. ICOM Committee for Conservation 15th triennial meeting, I, 190 (2008). Yadav, A.K. & Singh, P. A review of the structures of oxide glasses by Raman spectroscopy. RSC Adv. 5, 67583-67609 (2015). Colomban, P. & Prinsloo, L.C. Optical spectroscopy of silicates and glasses. In Spectroscopic Properties of Inorganic and Organometallic Compounds, 128-149 (2009). Colomban, P., Simsek Franci, G. & Koleini, F. On-site raman spectroscopic study of beads from the Necropolis of Vohemar, northern Madagascar (>13th C.). Heritage 4, 524-540 (2021). Silva, D.C., et al. Synthesis of PbO·SiO 2 glass by CO 2 laser melting method. J. Non-Cryst. Solids 522, 119572 (2019). Colomban, P., Sagon, G.R. & Faurel, X. Differentiation of antique ceramics from the Raman spectra of their coloured glazes and paintings. J. Raman Spectrosc. 32, 351-360 (2001). He, Y., Li, W., Li, J., Xu, C. & Lu, X. Research on the degradation of ancient Longquan celadons in the Dalian Island shipwreck. npj Mater. Degrad. 6, 1-10 (2022). Yin, X., Huang, T.J. & Gong, H. Chemical evolution of lead in ancient artifacts-A case study of early Chinese lead-silicate glaze. J. Eur. Ceram. Soc. 40, 2222-2228 (2020). Zhu, T.Q., Wang, C.S., Mao, Z.W., Li, L.X. & Huang, H. Identification of different corrosion covering the surface of Chinese ancient lead glazed potteries. Spectrosc. Spect. Anal. 30, 266-269 (2010). Wood, N. & Priestman, S. New light on Chinese Tang Dynasty and Iraqi Blue and White in the ninth century: the material from Siraf, Iran. Bull. Chin. Ceram. Art Archaeol. 7, 47-60 (2016). Spataro, M., Wood, N., Meeks, N., Meek, A., & Priestman, S. Pottery technology in the Tang dynasty (ninth century AD): archaeometric analyses of a Gongyi sherd found at Siraf, Iran. Archaeometry 61, 574-587 (2019). Jia, C., et al. A short but glorious porcelain glaze of Early Ming Dynasty: New finding of raw material and colorants in the copper red glaze. J. Eur. Ceram. Soc. 41, 3809-3815 (2021). Brown, S. & Norton, F. Constitution of copper-red glazes. J. Am. Ceram. Soc. 42, 499-503 (1959). Jackson, S.H. A monograph on the copper-red glazes. Trans. Orient. Ceram. Soc. 2, 22-32 (1922). Cuvelier, P.A., Andraud, C., Chaudanson, D., Lafait, J. & Nitsche, S. Copper red glazes: a coating with two families of particles. Appl. Phys. A 106, 915-929 (2012). Turner, T. Chemically reduced copper reds in oxidation. Ceram. Technical 35, 94-101 (2012). Kingery, W., Vandiver, P.B., Huang, I.W. & Chiang, Y.M. Liquid-liquid immiscibility and phase separation in the quaternary systems K 2 O-Al 2 O 3 -CaO-SiO 2 and Na 2 O-Al 2 O 3 -CaO-SiO 2 . J. Non-Cryst. Solids 54, 163-171 (1983). Li, W., Li, J., Wu, J. & Guo, J. Study on the phase-separated opaque glaze in ancient China from Qionglai kiln. Ceram. Int. 29, 933-937 (2003). Shi, P., et al. Amorphous photonic crystals and structural colors in the phase separation glaze. J. Eur. Ceram. Soc. 38, 2228-2233 (2018). Aliyev, Y., et al. The structural and vibrational properties of Ni-doped chalcopyrite CuFeS 2 . J. Ovonic Res. 14, 165-169 (2018). Munce, C.G., Parker, G.K., Holt, S.A. & Hope, G.A. A Raman spectroelectrochemical investigation of chemical bath deposited Cu x S thin films and their modification. Colloids Surf. A: Physicochem. Eng. Asp. 295, 152-158 (2007). Urbano, G., et al. Electrochemical and spectroscopic study of interfacial interactions between chalcopyrite and typical flotation process reagents. International Journal of Minerals, Metallurgy, and Materials 23, 127-136 (2016). Additional Declarations No competing interests reported. Supplementary Files SupplementaryInformation.pdf Cite Share Download PDF Status: Posted Version 1 posted 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. As a division of Research Square Company, we’re committed to making research communication faster, fairer, and more useful. We do this by developing innovative software and high quality services for the global research community. Our growing team is made up of researchers and industry professionals working together to solve the most critical problems facing scientific publishing. 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-2540579","acceptedTermsAndConditions":true,"allowDirectSubmit":true,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":174086432,"identity":"d935e428-cd09-4e90-9006-9fcaed552b0a","order_by":0,"name":"Xuesong Yin","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAABC0lEQVRIie3RwWrCMBjA8S8E6iV11xTB7hFSAuoY0wfxYsnZu4dRAoP6CjmUPcbOlYC7FHYVdnF49bDTUOhg6QYFYd/wODB/ShPa/PgKBfD5/mO0uS346UP+28lTUrVnxBmkieTt9gwinsN1dHwcTYdLTd6hruOhpqtXBtlYY8R2lQyf+LyoSspJLpKiDNQtA6twwpIdccTwGfQ+tSAG2KDHoFToh1kmVsfCkXhLD1CLiYGrD0eyv0iyDXUzBQJ3idRNCRyhY4xElknJ1o6wNB+RXCpDA3lTCDvDSPelGkSH+2xuOtZuoO7fmc7D22a/yCYYuS7bLdE/6/fPFZBqhMTYC0Cn+Hw+38X1BR8ISmPQfet/AAAAAElFTkSuQmCC","orcid":"","institution":"Institute of Materials Research and Engineering","correspondingAuthor":true,"submittingAuthor":false,"prefix":"","firstName":"Xuesong","middleName":"","lastName":"Yin","suffix":""},{"id":174086434,"identity":"4e47f3d9-cb42-4f4c-846c-c8b9bf206205","order_by":1,"name":"Berta Mañas Alcaide","email":"","orcid":"","institution":"Heritage Conservation Centre, National Heritage Board","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Berta","middleName":"Mañas","lastName":"Alcaide","suffix":""},{"id":174086437,"identity":"ba19e66b-7aed-4a45-93f9-d62e2ef53d9a","order_by":2,"name":"Christel Pesme","email":"","orcid":"","institution":"Heritage Conservation Centre, National Heritage Board","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Christel","middleName":"","lastName":"Pesme","suffix":""},{"id":174086438,"identity":"f0a3f4ac-111f-49e3-96a1-30247d503451","order_by":3,"name":"Qiang Li","email":"","orcid":"","institution":"Shanghai Institute of Ceramics, Chinese Academy of Sciences, Shanghai, 200050 China","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Li","suffix":""},{"id":174086439,"identity":"b8dbb2da-d312-4cea-8035-59f07ccbcdb0","order_by":4,"name":"Jingyi Zhang","email":"","orcid":"","institution":"Heritage Conservation Centre, National Heritage Board","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Jingyi","middleName":"","lastName":"Zhang","suffix":""},{"id":174086440,"identity":"ea83714b-4be2-482e-9514-01b47572cbe6","order_by":5,"name":"Hui Kim HUI","email":"","orcid":"","institution":"Institute of Materials Research and Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hui","middleName":"Kim","lastName":"HUI","suffix":""},{"id":174086441,"identity":"5a4962d8-7c88-47ca-ac12-f9da6ffa51e3","order_by":6,"name":"Yu Yu Ko Hnin","email":"","orcid":"","institution":"Institute of Materials Research and Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Yu","middleName":"Yu Ko","lastName":"Hnin","suffix":""},{"id":174086442,"identity":"e32b0c4b-2fc2-4bd4-9569-5554750c38d4","order_by":7,"name":"Poh Chong Lim","email":"","orcid":"","institution":"Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research)","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Poh","middleName":"Chong","lastName":"Lim","suffix":""},{"id":174086443,"identity":"8de90139-0420-4ee1-a599-bb4ee2ead461","order_by":8,"name":"Ning Ding","email":"","orcid":"","institution":"Institute of Materials Research and Engineering (IMRE), A*STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Innovis #08-03, Singapore 138634, Republic of Singapore","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Ning","middleName":"","lastName":"Ding","suffix":""},{"id":174086444,"identity":"9d6ba27c-b0b4-4512-b5c6-d1788715b1c9","order_by":9,"name":"Qiang Zhu","email":"","orcid":"","institution":"IMRE","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Qiang","middleName":"","lastName":"Zhu","suffix":""},{"id":174086445,"identity":"09d5a656-c8ea-4a7c-b6ba-f950a12de1e0","order_by":10,"name":"Nguk Neng Tham","email":"","orcid":"","institution":"Institute of Materials Research and Engineering","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Nguk","middleName":"Neng","lastName":"Tham","suffix":""},{"id":174086446,"identity":"34aeebd5-3bbe-4039-a0c9-e62c34744531","order_by":11,"name":"Sing Yang Chiam","email":"","orcid":"","institution":"Institute of Materials Research \u0026 Engineering (IMRE), Agency for Science, Technology and Research (A*STAR)","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Sing","middleName":"Yang","lastName":"Chiam","suffix":""},{"id":174086447,"identity":"3a143d52-7d0b-4c22-8a48-3d7460d2a905","order_by":12,"name":"Hongjie Luo","email":"","orcid":"","institution":"Shanghai University","correspondingAuthor":false,"submittingAuthor":false,"prefix":"","firstName":"Hongjie","middleName":"","lastName":"Luo","suffix":""}],"badges":[],"createdAt":"2023-02-02 01:14:13","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-2540579/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-2540579/v1","draftVersion":[],"editorialEvents":[],"editorialNote":"","failedWorkflow":false,"files":[{"id":32668890,"identity":"175104f6-9af1-4632-b83f-70b85fa4a6c4","added_by":"auto","created_at":"2023-02-08 20:31:33","extension":"jpeg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":481812,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eTrading routes, major cities, kiln sites and ceramic samples in Tang dynasty.\u003c/strong\u003e (a) Transcontinental trading/transporting routes by both land and sea, and location of some city sites and shipwrecks along the silk roads. (b) Location of kiln and city sites where the Sancai and Changsha samples are originated and some important inland waterways in Tang dynasty. (c) Photos of Lead-glazed Sancai samples T\u003csub\u003e1\u003c/sub\u003e-T\u003csub\u003e6\u003c/sub\u003e and (d) Photos of Calcium-glazed Changsha samples C\u003csub\u003e1\u003c/sub\u003e-C\u003csub\u003e6\u003c/sub\u003e. Scale bar in (c) and (d): 1 cm.\u003c/p\u003e","description":"","filename":"floatimage1.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/f6a37ad737a85678b53fff35.jpeg"},{"id":32668891,"identity":"b08d16a1-1ab5-4776-a927-7f656762a5c9","added_by":"auto","created_at":"2023-02-08 20:31:33","extension":"jpeg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":365335,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eComparison of base glazes of Tang Sancai and Changsha samples. \u003c/strong\u003eContour phase diagrams of (a) PbO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e and (b) CaO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e ternary systems. The tested Sancai and Changsha ceramic specimens in Supplementary Tables S2 and S3 are positioned in the diagrams accordingly. (c) Raman shift profiles of Sancai (T\u003csub\u003e5\u003c/sub\u003e) and Changsha (C\u003csub\u003e4\u003c/sub\u003e) glazes. SEM images of corroded areas (ii and II in Fig. 1) in (d) T\u003csub\u003e3\u003c/sub\u003e and (e) C\u003csub\u003e1\u003c/sub\u003e, and (f) XRD patterns of corroded area in T\u003csub\u003e3\u003c/sub\u003e and C\u003csub\u003e1\u003c/sub\u003e.\u003c/p\u003e","description":"","filename":"floatimage2.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/b7d801c08d20f5d375ef1233.jpeg"},{"id":32668892,"identity":"fd345287-8014-4567-b624-49a92b6c2959","added_by":"auto","created_at":"2023-02-08 20:31:33","extension":"jpeg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":554054,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eColoration of Tang Sancai and Changsha samples. \u003c/strong\u003e(a) Standard colour wheel chart with the samples located in the respective regions according to their colours, (b) Content (wt%) of Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in a series of yellow-brown specimens, (c) Colour change with relative content (wt%) of CuO/(CuO+Fe\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e) in the yellow-green specimens, (d) Optical microscopic cross-section image and (e) SEM image of Sancai sample T\u003csub\u003e5\u003c/sub\u003e, (f) Optical microscopic cross-section image of Changsha sample C\u003csub\u003e4\u003c/sub\u003e, (g) XRD patterns of the green and red areas of Changsha glaze C\u003csub\u003e4\u003c/sub\u003e, (h) TEM image and (i) SAED of Changsha sample C\u003csub\u003e4\u003c/sub\u003e, (j) TEM image with overlay elemental mapping of Changsha sample C\u003csub\u003e4\u003c/sub\u003e and (k) Quantified elemental contents (wt%) in Phases 1 and 2 in (j).\u003c/p\u003e","description":"","filename":"floatimage3.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/c7726f0b18b5e0dcc9f97ef4.jpeg"},{"id":32668893,"identity":"9174c9fb-3984-42d5-8386-a1e735484435","added_by":"auto","created_at":"2023-02-08 20:31:34","extension":"jpeg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":500892,"visible":true,"origin":"","legend":"\u003cp\u003e\u003cstrong\u003eAnalysis of black impurity in the Changsha sample.\u003c/strong\u003e (a) ­­­­Optical microscopic surface image of the painted area of Changsha sample C\u003csub\u003e4\u003c/sub\u003e, (b) EDX spectrum of the black dot with measured location and elemental content (at%) indicated in the insets, (c) Optical microscopic cross-section image of a black dot in C\u003csub\u003e4\u003c/sub\u003e, (d) XRD and (e) Raman profiles of the C\u003csub\u003e4\u003c/sub\u003e glaze near areas with black dots, and (f) SEM image and EDX elemental mappings of the selected area in (c).\u003c/p\u003e","description":"","filename":"floatimage4.jpeg","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/22b8645e48cefa0778501848.jpeg"},{"id":38343797,"identity":"3a296765-ffa7-465b-8866-3d5b6ab0f2d7","added_by":"auto","created_at":"2023-06-11 04:14:38","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":1147854,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/ff6817f3-c9a7-42aa-848c-51d10d6fda91.pdf"},{"id":32668894,"identity":"98225143-c9f3-4e30-95f0-d63f66727d9f","added_by":"auto","created_at":"2023-02-08 20:31:34","extension":"pdf","order_by":2,"title":"","display":"","copyAsset":false,"role":"supplement","size":4127865,"visible":true,"origin":"","legend":"","description":"","filename":"SupplementaryInformation.pdf","url":"https://assets-eu.researchsquare.com/files/rs-2540579/v1/75b845fa55e2b28303bd94e5.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago","fulltext":[{"header":"Introduction","content":"\u003cp\u003eThe advent of ceramics has provided human beings vessels to store, cook and preserve goods and largely shaped the way people lived since 20000 years ago.\u003csup\u003e\u003cspan citationid=\"CR1\" class=\"CitationRef\"\u003e1\u003c/span\u003e, \u003cspan citationid=\"CR2\" class=\"CitationRef\"\u003e2\u003c/span\u003e, \u003cspan citationid=\"CR3\" class=\"CitationRef\"\u003e3\u003c/span\u003e\u003c/sup\u003e In history, Tang Empire (618\u0026ndash;907 AD) has been esteemed as one of the most prosperous and influential periods.\u003csup\u003e\u003cspan citationid=\"CR4\" class=\"CitationRef\"\u003e4\u003c/span\u003e\u003c/sup\u003e Accompanied by frequent transcontinental trades along silk roads (by land and sea, Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ea), tremendous cultural exchange and fusion took place between western and eastern civilizations.\u003csup\u003e\u003cspan citationid=\"CR5\" class=\"CitationRef\"\u003e5\u003c/span\u003e, \u003cspan citationid=\"CR6\" class=\"CitationRef\"\u003e6\u003c/span\u003e\u003c/sup\u003e Innovative decoration styles involving various colours applied on different artefacts were developed during this period.\u003csup\u003e\u003cspan citationid=\"CR7\" class=\"CitationRef\"\u003e7\u003c/span\u003e\u003c/sup\u003e Ceramics, as a popular trading product, always took along the new fashions timely and played a critical role in the global commerce.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e\u003c/sup\u003e Due to the heavy and fragile nature of ceramic products, water transportation is a preferred way for ceramics trading. Ceramic artefacts in Tang dynasty have been discovered in many ancient city sites, such as Yangzhou and Guangzhou in China, Mantai in Sri Lanka, Samarra in Iraq, Fostat in Egypt, etc in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(a).\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e It is not surprising that numerous Tang wares were also salvaged from some shipwrecks. Two famous Tang shipwrecks are the Belitung ship from Indonesia (exhibited in Asian Civilizations Museum of Singapore) and the Chau Tan ship from central Vietnam.\u003csup\u003e\u003cspan citationid=\"CR8\" class=\"CitationRef\"\u003e8\u003c/span\u003e, \u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR15\" class=\"CitationRef\"\u003e15\u003c/span\u003e\u003c/sup\u003e Thanks to the plentiful ceramic relics, a vivid picture of trading routes along the maritime silk roads over ten centuries ago can be manifested today.\u003csup\u003e\u003cspan citationid=\"CR9\" class=\"CitationRef\"\u003e9\u003c/span\u003e, \u003cspan citationid=\"CR16\" class=\"CitationRef\"\u003e16\u003c/span\u003e, \u003cspan citationid=\"CR17\" class=\"CitationRef\"\u003e17\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn addition to the historical values, there are significant developments in ceramic technologies in Tang dynasty, especially the appearance of varied colours and glaze effects. The most famous example is the low-fired tri-colour (Sancai) wares.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e Since a considerable amount of Sancai wares excavated in 1920s, they have been praised as the crown of Tang ceramic arts.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e More recently, several kiln sites that produced Sancai wares, such as Gongxian kiln in Henan, Yaozhou kiln and Liquanfang kiln in Shaanxi, Qiong kiln in Sichuan and Xing kiln in Hebei, were identified and studied.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e\u003c/sup\u003e For high-fired polychromic wares, the Changsha kiln in Hunan province attracts more and more interests after several excavations and studies of kiln/city/port sites and shipwrecks. The colourful and freehand decoration signifies a pioneering role of Changsha kiln in calcium-based polychromic glazes.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR14\" class=\"CitationRef\"\u003e14\u003c/span\u003e, \u003cspan citationid=\"CR21\" class=\"CitationRef\"\u003e21\u003c/span\u003e, \u003cspan citationid=\"CR22\" class=\"CitationRef\"\u003e22\u003c/span\u003e\u003c/sup\u003e Although there are a few technical reports on Tang glazes, it is still far from satisfactory to recognize such an important category of heritage materials. A better understanding of the colouration mechanisms in different Tang glazes is necessary and valuable.\u003c/p\u003e \u003cp\u003eTherefore, we present this study to explore the colourful glazes of Tang ceramics through a comparative study of Sancai and Changsha kiln glazes. Comprehensive characterizations and analyses reveal multiple factors that contribute to the appearance of Tang ceramics, including types of glaze, colorants, oxidation states, glaze microstructures, impurities and even corrosion. More interestingly, these chemical and structural colouring elements synergize and create more hues and glaze effects. The cooperation of colourants Fe and Cu gives rise to diverse colours covering a wide spectrum from light yellow to dark brown and various greens. The mixture of liquid-liquid (L-L) phase separation and copper red/green generates special opaque effects and colours ranging from milky white to bluish green to purplish red. Glaze corrosions add silvery iridescence and frosted appearances on some aged Sancai and Changsha wares, respectively. Close investigations on phase diagrams and residual materials in glaze also provide more indications on Tang ceramic technologies in terms of firing conditions and raw pigments. The knowledge obtained in this study not only extends the recognition of Tang ceramics from a scientific perspective but will also benefit studies of many other ancient ceramics.\u003c/p\u003e \u003cp\u003e \u003c/p\u003e"},{"header":"Results","content":"\u003cp\u003e \u003cb\u003eSamples.\u003c/b\u003e Figure\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) and (d) show twelve ceramic samples, six Tang Sancai (T\u003csub\u003e1\u003c/sub\u003e-T\u003csub\u003e6\u003c/sub\u003e) and six Changsha kiln (C\u003csub\u003e1\u003c/sub\u003e-C\u003csub\u003e6\u003c/sub\u003e), studied in this work. The conditions of glaze, clay, their interface and provenance are presented in Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e. A more detailed summary of the samples is provided in Supplementary Table S1. In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b), four kilns producing Sancai wares, Gongxian kiln in Henan province, Yaozhou kiln in Shaanxi province, Xing kiln in Hebei province and Qiong kiln in Sichuan province, and Changsha kiln in Hunan province are indicated with some major cities nearby. It is worth noting that the cities were normally accessible and connected by water networks shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(b). For instance, both Sancai (T\u003csub\u003e6\u003c/sub\u003e) and Changsha (C\u003csub\u003e2\u003c/sub\u003e) samples were found from Yangzhou city, which was an important port linking inland waters and sea during Tang dynasty.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c), a light-yellow translucent glossy glaze is applied to both sides of sample T\u003csub\u003e1\u003c/sub\u003e. T\u003csub\u003e2\u003c/sub\u003e has a dark brown exterior glaze and a light greenish interior glaze. T\u003csub\u003e3\u003c/sub\u003e has a mixture of light brown and green glazes. Some dark spots on the brown glaze and a white-silvery layer on the green glaze are also found on T\u003csub\u003e3\u003c/sub\u003e. T\u003csub\u003e4\u003c/sub\u003e-T\u003csub\u003e6\u003c/sub\u003e samples have transparent/white base glazes with coloured patches applied on the surface. The variegated colours include dark green on T\u003csub\u003e4\u003c/sub\u003e and T\u003csub\u003e5\u003c/sub\u003e, and dark blue and brown on T\u003csub\u003e6\u003c/sub\u003e. For the Changsha pieces in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d), a transparent/yellowish base glaze with dark brown and opaque green dotted patterns is applied on C\u003csub\u003e1\u003c/sub\u003e. C\u003csub\u003e2\u003c/sub\u003e has a translucent light-green glaze with decorations in brown and purple red. Exterior surface of C\u003csub\u003e3\u003c/sub\u003e is covered by a brown glaze. Meanwhile, a transparent glaze is applied on its interior surface. C\u003csub\u003e4\u003c/sub\u003e and C\u003csub\u003e5\u003c/sub\u003e have green coloured patchy decorations. But the base glaze of C\u003csub\u003e4\u003c/sub\u003e is opaque light green, while C\u003csub\u003e5\u003c/sub\u003e has a creamy opaque base glaze. C\u003csub\u003e6\u003c/sub\u003e is fully covered by a dark green opaque glaze. Some black dots are found on the dark green surface of C\u003csub\u003e4\u003c/sub\u003e and C\u003csub\u003e6\u003c/sub\u003e. Tang Sancai samples T\u003csub\u003e1\u003c/sub\u003e-T\u003csub\u003e3\u003c/sub\u003e and T\u003csub\u003e5\u003c/sub\u003e have a layer of white slip in between the clay body and glaze. No slips are observed in T\u003csub\u003e4\u003c/sub\u003e and T\u003csub\u003e6\u003c/sub\u003e. Changsha samples C\u003csub\u003e1\u003c/sub\u003e and C\u003csub\u003e3\u003c/sub\u003e-C\u003csub\u003e5\u003c/sub\u003e have a well-developed white interphase layer between their clays and glazes (Table\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Supplementary Table S1). In C\u003csub\u003e2\u003c/sub\u003e and C\u003csub\u003e6\u003c/sub\u003e, this interphase layer is not so obvious. Bubbles in glaze and air pockets in clay are often observed in both the Tang Sancai and Changsha glazes. The clays of Tang Sancai and Changsha samples are mostly in pink/red and grey/brown, respectively.\u003c/p\u003e \u003cp\u003e \u003cdiv class=\"gridtable\"\u003e\u003ctable float=\"Yes\" id=\"Tab1\" border=\"1\"\u003e \u003ccaption language=\"En\"\u003e \u003cdiv class=\"CaptionNumber\"\u003eTable 1\u003c/div\u003e \u003cdiv class=\"CaptionContent\"\u003e \u003cp\u003eSample information.\u003c/p\u003e \u003c/div\u003e \u003c/caption\u003e \u003ccolgroup cols=\"7\"\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c1\" colnum=\"1\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c2\" colnum=\"2\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c3\" colnum=\"3\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c4\" colnum=\"4\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c5\" colnum=\"5\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c6\" colnum=\"6\"\u003e\u003c/div\u003e \u003cdiv align=\"left\" class=\"colspec\" colname=\"c7\" colnum=\"7\"\u003e\u003c/div\u003e \u003cthead\u003e \u003ctr\u003e \u003cth align=\"left\" colname=\"c1\"\u003e \u003cp\u003eSample ID\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGlaze colour\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c3\"\u003e \u003cp\u003eGlaze crazing\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBubble\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c5\"\u003e \u003cp\u003eGlaze/clay interface\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c6\"\u003e \u003cp\u003eClay body\u003c/p\u003e \u003c/th\u003e \u003cth align=\"left\" colname=\"c7\"\u003e \u003cp\u003eProvenance\u003c/p\u003e \u003c/th\u003e \u003c/tr\u003e \u003c/thead\u003e \u003ctbody\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLight yellow translucent glossy glaze (interior and exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eCrazing with different shapes and dimensions\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSmall bubbles, not visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite slip (interior and exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eRed stoneware clay with few small air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eQiong kiln, Sichuan city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDark brown glaze (exterior)\u003c/p\u003e \u003cp\u003eLight greenish glaze (interior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVery thin crazing at different levels\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo visible bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite slip (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eCompact pinkish stoneware clay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGongxian kiln, Henan city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eLight brown and green translucent glossy glazes (exterior) with dark spots on brown glaze and a white-silvery layer\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVery fine crazing, almost not visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo visible bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite slip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePinkish stoneware clay with small fine cracks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGongxian kiln, Kiln site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTransparent and dark green translucent glossy glazes (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eExtremely fine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMany bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLight pinkish stoneware clay with very small air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eGongxian kiln, Henan city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTransparent and dark green glossy glaze (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVery fine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNo visible bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite slip (interior and exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003ePinkish stoneware clay with many small air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eXing kiln, Shandong, Liaocheng city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eT\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDark blue, brown and transparent glazes (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVery fine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSome bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eWhite stoneware clay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eUnknown kiln, Yangzhou city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e1\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTransparent/yellowish base decorated with dark brown and green dots. (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSome bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite interphase or slip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLight grey stoneware clay\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Changsha city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e2\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eTransparent-light green glaze with decorations in brown and purple red (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eVery fine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eMany bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrey and pinkish stone ware clay with localized air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Yangzhou city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e3\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eBrown glaze (exterior) and transparent glaze (interior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eFine bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite interphase or slip (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eSalmon and dark grey stoneware clay with fine cracks\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Changsha city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e4\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDark and light green glaze with yellow depositions and black spots (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eSome bubbles\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite interphase or slip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrey stoneware clay with small and large air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Unknown site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e5\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eGreen glaze applied on creamy opaque glaze (exterior)\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eBursts in circular shape\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eWhite interphase or slip\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eLight brown stoneware clay with many large air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Unknown site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003ctr\u003e \u003ctd align=\"left\" colname=\"c1\"\u003e \u003cp\u003eC\u003csub\u003e6\u003c/sub\u003e\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c2\"\u003e \u003cp\u003eDark green opaque glossy and transparent glaze with black spots\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c3\"\u003e \u003cp\u003eFine crazing\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c4\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c5\"\u003e \u003cp\u003eNot visible\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c6\"\u003e \u003cp\u003eGrey stoneware clay with small air pockets\u003c/p\u003e \u003c/td\u003e \u003ctd align=\"left\" colname=\"c7\"\u003e \u003cp\u003eChangsha kiln, Changsha city site\u003c/p\u003e \u003c/td\u003e \u003c/tr\u003e \u003c/tbody\u003e \u003c/colgroup\u003e \u003c/table\u003e\u003c/div\u003e \u003c/p\u003e \u003cp\u003e \u003cb\u003eGlaze compositions.\u003c/b\u003e A survey of Tang Sancai and Changsha glazes is conducted with their chemical compositions summarized. The glaze compositions of the samples in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) and (d) are also analysed and presented in Supplementary Tables S2 and S3. In Supplementary Table S2, PbO, SiO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e are three major components in Sancai glazes, in which alkali PbO serves as the flux agent to reduce melting temperature of the glaze. Alternatively, CaO is the flux agent and forms the majority of Changsha glaze together with SiO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e in Supplementary Table S3. In both Sancai and Changsha samples, the top three components take about 90% of the overall weight of the glaze, which determine the glaze properties to a large extent. Other minor elements, like Mg, K, Na, Fe, Ti, are also detected in both Sancai and Changsha glazes. Cu is observed in some green coloured Sancai and Changsha glazes. Comparing with non-detectable phosphorus in Sancai glazes, Changsha glazes often contain a small amount of phosphorus. These minor elements also play important roles as colorants and/or flux agents.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003eThe varieties in glazing effects of Tang Sancai and Changsha samples presented above are of great interests in understanding the development of early polychromic ceramics. Modern analytical methods have been used as a powerful tool to study heritage materials.\u003csup\u003e\u003cspan citationid=\"CR24\" class=\"CitationRef\"\u003e24\u003c/span\u003e, \u003cspan citationid=\"CR25\" class=\"CitationRef\"\u003e25\u003c/span\u003e, \u003cspan citationid=\"CR26\" class=\"CitationRef\"\u003e26\u003c/span\u003e, \u003cspan citationid=\"CR27\" class=\"CitationRef\"\u003e27\u003c/span\u003e\u003c/sup\u003e For the case of Tang ceramics, F.K. Zhang et al. published compositional characterizations of several Sancai glazes from Gongxian kiln in 1980s.\u003csup\u003e\u003cspan citationid=\"CR28\" class=\"CitationRef\"\u003e28\u003c/span\u003e, \u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e\u003c/sup\u003e N. Wood compiled testing results of Tang Sancai samples from Henan, Shaanxi and ancient city sites in Egypt, Iraq and Sri Lanka.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e B.P. Li et al. analysed trace elements in Sancai wares from Gongxian and Yaozhou kilns.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e\u003c/sup\u003e Q.Q. Jiang did a survey of Sancai wares from several kiln sites.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e\u003c/sup\u003e J.F. Cui studied Sancai glazes from the Liquanfang site with a focus on the compositions of ceramic bodies.\u003csup\u003e\u003cspan citationid=\"CR19\" class=\"CitationRef\"\u003e19\u003c/span\u003e\u003c/sup\u003e J.Y. Shen conducted a comparative study of Sancai wares from Northern China and Mid-East through chemical analysis.\u003csup\u003e\u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e For Changsha wares, Z.G. Zhang et al. examined the compositions of several Changsha samples.\u003csup\u003e\u003cspan citationid=\"CR31\" class=\"CitationRef\"\u003e31\u003c/span\u003e\u003c/sup\u003e In 1986, F.K. Zhang provided more testing results and explanation of colouration in Changsha wares.\u003csup\u003e\u003cspan citationid=\"CR32\" class=\"CitationRef\"\u003e32\u003c/span\u003e\u003c/sup\u003e X.Q. Chen et al. reported the phenomenon of phase-separation in Changsha samples.\u003csup\u003e\u003cspan citationid=\"CR33\" class=\"CitationRef\"\u003e33\u003c/span\u003e\u003c/sup\u003e Y.Q. Li et al. studied the coloration of Changsha copper-red glaze.\u003csup\u003e\u003cspan citationid=\"CR34\" class=\"CitationRef\"\u003e34\u003c/span\u003e\u003c/sup\u003e B. Shen et al. also explored the micro-structures of several Changsha wares and discussed the roles of colorants.\u003csup\u003e\u003cspan citationid=\"CR35\" class=\"CitationRef\"\u003e35\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eFrom the previous studies, it is noted that Tang Sancai and Changsha glazes belong to two glaze systems, PbO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e and CaO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e, respectively. The different flux agents (Pb in Sancai and Ca in Changsha) result in distinctive glaze properties. The lead-glazed Sancai wares are relatively weaker in mechanical strength, so they were used as burial or worship objects.\u003csup\u003e\u003cspan citationid=\"CR12\" class=\"CitationRef\"\u003e12\u003c/span\u003e, \u003cspan citationid=\"CR36\" class=\"CitationRef\"\u003e36\u003c/span\u003e\u003c/sup\u003e In contrast, the more durable Changsha wares were mainly for daily use or trading purposes.\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e, \u003cspan citationid=\"CR37\" class=\"CitationRef\"\u003e37\u003c/span\u003e, \u003cspan citationid=\"CR38\" class=\"CitationRef\"\u003e38\u003c/span\u003e\u003c/sup\u003e Generally, Sancai colours are bright and alluring, and Changsha glazes often have soft and warm hues. Sancai and Changsha wares share a common feature of variegated glazes. In spite of these observations, a comprehensive study is necessary to deal with the varieties of Tang glazes and explore the coloration mechanisms. In addition to the individual factors, like glaze chemistry, corrosion effect, colorants, phase structure and even impurity, their synergistic effects also need to be taken into account to elaborate the complicated Tang glazes.\u003c/p\u003e \u003cp\u003e \u003cb\u003eGlaze chemistry and corrosion.\u003c/b\u003e The ternary phase diagrams of PbO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e and CaO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e are shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e (a) and (b) with isothermal contour curves, indicating solid-liquid transition temperatures with respect to compositional variations.\u003csup\u003e\u003cspan citationid=\"CR39\" class=\"CitationRef\"\u003e39\u003c/span\u003e, \u003cspan citationid=\"CR40\" class=\"CitationRef\"\u003e40\u003c/span\u003e\u003c/sup\u003e The Sancai and Changsha samples are mapped in the diagrams according to their compositions (see Supplementary Tables S2 and S3). It is found that Sancai glazes have a high PbO content of 50\u0026ndash;75%, a SiO\u003csub\u003e2\u003c/sub\u003e content around 25\u0026ndash;35% and an Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e content of 6\u0026ndash;8%. In contrast, the flux CaO content in Changsha glaze is around 12\u0026ndash;20%, and the SiO\u003csub\u003e2\u003c/sub\u003e and Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e contents are about 55\u0026ndash;65% and 8\u0026ndash;15%, respectively. It is interesting to find that the sample compositions are just around the regions with the lowest melting temperature for both Sancai (PbO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e) and Changsha (CaO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e) glaze systems. The results indicate ancient potters had engineered their glaze recipes quite well so only a minimized temperature was required. Such optimized firing conditions could benefit the ceramic industry by saving cost and improving yields.\u003c/p\u003e \u003cp\u003eIn Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(c), the Changsha glaze (C\u003csub\u003e4\u003c/sub\u003e) has a Raman shift profile similar with 0.2CaO-0.8SiO\u003csub\u003e2\u003c/sub\u003e glass, which has major peaks around 960 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1030 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e for Si-O-Si bond Q\u003csub\u003e2\u003c/sub\u003e and Q\u003csub\u003e3\u003c/sub\u003e vibrations.\u003csup\u003e\u003cspan citationid=\"CR41\" class=\"CitationRef\"\u003e41\u003c/span\u003e, \u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e\u003c/sup\u003e The peaks around 460 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are attributed to Si-O-Si D\u003csub\u003e1\u003c/sub\u003e and D\u003csub\u003e2\u003c/sub\u003e vibration modes.\u003csup\u003e\u003cspan citationid=\"CR42\" class=\"CitationRef\"\u003e42\u003c/span\u003e, \u003cspan citationid=\"CR43\" class=\"CitationRef\"\u003e43\u003c/span\u003e, \u003cspan citationid=\"CR44\" class=\"CitationRef\"\u003e44\u003c/span\u003e\u003c/sup\u003e The peak at 1385 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e is related to P-O bond vibration.\u003csup\u003e\u003cspan citationid=\"CR45\" class=\"CitationRef\"\u003e45\u003c/span\u003e\u003c/sup\u003e For the Sancai glaze (T\u003csub\u003e5\u003c/sub\u003e), the Raman peak around 460\u0026ndash;550 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 950 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e are assigned to various Si-O-Si bonds in Pb rich glasses.\u003csup\u003e\u003cspan citationid=\"CR46\" class=\"CitationRef\"\u003e46\u003c/span\u003e, \u003cspan citationid=\"CR47\" class=\"CitationRef\"\u003e47\u003c/span\u003e, \u003cspan citationid=\"CR48\" class=\"CitationRef\"\u003e48\u003c/span\u003e\u003c/sup\u003e The high frequency peaks at 1360 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e and 1600 cm\u003csup\u003e\u0026minus;\u0026thinsp;1\u003c/sup\u003e could be associated with vibrations of slip/body materials.\u003csup\u003e\u003cspan citationid=\"CR49\" class=\"CitationRef\"\u003e49\u003c/span\u003e\u003c/sup\u003e In addition, no characteristic diffraction peaks were observed in the XRD patterns of Sancai or Changsha glazes in Supplementary Fig. S1(a). From the XRD and Raman results, it can be concluded that both Sancai and Changsha glazes exhibit a long-range disordered but short-range ordered glass structure.\u003c/p\u003e \u003cp\u003eCorrosion is an inevitable process that affects the appearance of ancient ceramics.\u003csup\u003e\u003cspan citationid=\"CR50\" class=\"CitationRef\"\u003e50\u003c/span\u003e\u003c/sup\u003e The famous silvery iridescence of \u0026ldquo;Han green glaze\u0026rdquo; has been well studied with the decomposed structure and corrosion mechanisms established.\u003csup\u003e\u003cspan citationid=\"CR29\" class=\"CitationRef\"\u003e29\u003c/span\u003e, \u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e\u003c/sup\u003e Similar corrosion effects are detected on Tang Sancai wares as well.\u003csup\u003e\u003cspan citationid=\"CR18\" class=\"CitationRef\"\u003e18\u003c/span\u003e, \u003cspan citationid=\"CR20\" class=\"CitationRef\"\u003e20\u003c/span\u003e, \u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e, \u003cspan citationid=\"CR30\" class=\"CitationRef\"\u003e30\u003c/span\u003e\u003c/sup\u003e Among the Sancai samples examined in this work (Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003ec), the dual-coloured specimen C\u003csub\u003e3\u003c/sub\u003e has a much degraded glaze with pearly lustre, and the corrosion is more severe on the green part in contrast to the yellow part. Close SEM examination and comparison of this degraded piece (T\u003csub\u003e3\u003c/sub\u003e) and a high-fired Changsha counterpart (C\u003csub\u003e1\u003c/sub\u003e) are provided in Supplementary Fig. S1. In Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(d), distinctive crystal grains are found in the corroded area of T\u003csub\u003e3\u003c/sub\u003e. The XRD pattern in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(f) further confirmed the crystal structures of 3PbCO\u003csub\u003e3\u003c/sub\u003e\u0026middot;2Pb(OH)\u003csub\u003e2\u003c/sub\u003e\u0026middot;2H\u003csub\u003e2\u003c/sub\u003eO (PDF #09-0356), Al\u003csub\u003e2\u003c/sub\u003eCa(SiO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e2\u003c/sub\u003e (PDF #02-0537) and PbSiO\u003csub\u003e3\u003c/sub\u003e (PDF #29\u0026ndash;0782) in the area (ii) of T\u003csub\u003e3\u003c/sub\u003e. It indicates a separation of Pb and Si near the corroded surface, which is resulted from Pb leaching.\u003csup\u003e\u003cspan citationid=\"CR51\" class=\"CitationRef\"\u003e51\u003c/span\u003e, \u003cspan citationid=\"CR52\" class=\"CitationRef\"\u003e52\u003c/span\u003e\u003c/sup\u003e This also explains the compositional shift of T\u003csub\u003e3\u003c/sub\u003e to a relatively Si rich and Pb poor position in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(a). Comparatively, the Changsha sample C\u003csub\u003e1\u003c/sub\u003e is less corroded with a disintegrated pitting-like structure in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(e). Its XRD pattern in Fig.\u0026nbsp;\u003cspan refid=\"Fig2\" class=\"InternalRef\"\u003e2\u003c/span\u003e(f) suggests an amorphous nature of the weathered area (II) of C\u003csub\u003e1\u003c/sub\u003e. Overall, a drastic corrosion involving glaze disintegration and re-construction brings about a silvery lustre on the Sancai green glaze. The Changsha glaze has a frosted appearance due to its corroded structures.\u003c/p\u003e\u003cp\u003e \u003cb\u003eColorants and phase separation.\u003c/b\u003e The samples in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) and (d) are mapped on a standard colour wheel chart in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) according to their individual colours. These samples cover a wide spectrum from yellow to brown, red to purple and green to blue with various hues. The colorants and microstructures of the glazes need to be identified to access their colouring effects. First, a new colorant, cobalt (Co), should be pointed out, as it brought chemical blue in Tang glazes. It even turned to be a signature of Tang ceramics when several high-fired dishes with blue painted patterns were salvaged from the Belitung cargo. Actually, there are even more cases in low-fired Sancai wares that have blue glazes attributing to the colorant of Co. In Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(c), the sample T\u003csub\u003e6\u003c/sub\u003e has a painted blue glaze and its composition in Supplementary Table S2 confirms the existence of Co. The pursuit of blue and application of Co pigment are believed to be influenced by Islamic customs.\u003csup\u003e\u003cspan citationid=\"CR53\" class=\"CitationRef\"\u003e53\u003c/span\u003e, \u003cspan citationid=\"CR54\" class=\"CitationRef\"\u003e54\u003c/span\u003e\u003c/sup\u003e Nevertheless, Fe and Cu still remain as two dominant colouring elements in Tang ceramics, complying with earlier traditions of Chinese glazes.\u003csup\u003e\u003cspan citationid=\"CR23\" class=\"CitationRef\"\u003e23\u003c/span\u003e\u003c/sup\u003e The finely potted Yue kiln wares represented one of glorious periods of Fe coloured celadon glazes. Meanwhile, the application of copper in high-fired glazes became a new fashion. Changsha potters were masters of the technique and proficiently practised polychromic decorations on their products. Following the yellow arrow in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a), a colour changing from light yellow to dark brown with increasing Fe content is demonstrated in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(b). The mixing of Fe and Cu also generates different colouring effects. The relative ratios of Fe and Cu in the samples distributed across yellow to green spectrum are plotted in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(c). The various colours from yellow to olive green, bean green and light green along the green arrow in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a) indicate synergistic effects of the mixed Fe and Cu colorants.\u003csup\u003e\u003cspan citationid=\"CR11\" class=\"CitationRef\"\u003e11\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eMore importantly, the unique copper red glaze also appeared in this period. The effects of copper are further investigated here by a comparison of the Sancai sample T\u003csub\u003e5\u003c/sub\u003e and Changsha sample C\u003csub\u003e4\u003c/sub\u003e. In Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(d), optical cross-section image of T\u003csub\u003e5\u003c/sub\u003e shows a uniform green glaze (~\u0026thinsp;0.10 mm) on top of a white slip layer (~\u0026thinsp;0.15 mm). The glaze is also very smooth as revealed by its SEM image in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(e). In contrast, a thicker glaze (~\u0026thinsp;0.20 mm) is directly applied on the body of C\u003csub\u003e4\u003c/sub\u003e (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ef). The C\u003csub\u003e4\u003c/sub\u003e glaze manifests a layered structure with a milky greenish top layer and a red/purple bottom layer. Comparing with the amorphous nature of T\u003csub\u003e5\u003c/sub\u003e and C\u003csub\u003e4\u003c/sub\u003e green glaze (Supplementary Fig. S1; Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg and i), diffraction peaks of metallic Cu (PDF #02-9026) are revealed in the red area of C\u003csub\u003e4\u003c/sub\u003e glaze (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003eg). The results agree well with the reported coloration of copper red and green glazes.\u003csup\u003e\u003cspan citationid=\"CR10\" class=\"CitationRef\"\u003e10\u003c/span\u003e, \u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e, \u003cspan citationid=\"CR56\" class=\"CitationRef\"\u003e56\u003c/span\u003e, \u003cspan citationid=\"CR57\" class=\"CitationRef\"\u003e57\u003c/span\u003e\u003c/sup\u003e Synthetic studies also demonstrated a consistent correlation between the green/red colours and the oxidation states of copper.\u003csup\u003e\u003cspan citationid=\"CR58\" class=\"CitationRef\"\u003e58\u003c/span\u003e, \u003cspan citationid=\"CR59\" class=\"CitationRef\"\u003e59\u003c/span\u003e\u003c/sup\u003e Interestingly, the C\u003csub\u003e4\u003c/sub\u003e glaze contains many small particles as shown in the image of a thin FIB sample in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(h). The TEM image in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(j) revealed that the particle size is about 100 nm. This type of nanostructures is resulted from liquid-liquid (L-L) phase separation during glaze formation, which gives rise to a milky blueish colour due to light scattering.\u003csup\u003e\u003cspan citationid=\"CR60\" class=\"CitationRef\"\u003e60\u003c/span\u003e, \u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e, \u003cspan citationid=\"CR62\" class=\"CitationRef\"\u003e62\u003c/span\u003e\u003c/sup\u003e The compositional differences between two liquid phases are further analysed by EDX mapping and quantified in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(j) and (k) and Supplementary Fig. S2. It shows that the particle-like phase (Phase 1) is rich in Si, K and O, and the matrix-like phase (Phase 2) is rich in Ca and Mg. The contents of Al are similar in both phases. The colorants Fe and Cu are slightly more concentrated in Phase 2 (Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003ek and Fig. S2).\u003csup\u003e\u003cspan citationid=\"CR61\" class=\"CitationRef\"\u003e61\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eHerein, four colouring factors, i.e. yellow from oxidized Fe, green from oxidized Cu, red from reduced Cu and opaque white/blue from L-L separation, are figured out and labelled in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a). How these colouring factors cooperate and generate more effects can be described as follows. Different concentrations of oxidized Fe give rise to colours from light yellow to dark brown. The mixture of oxidized Fe and Cu brings about a wide range of yellow-green colours. Moreover, when the reduced copper red is mixed with L-L separation (C\u003csub\u003e4\u003c/sub\u003e), the colours ranging from red to purple are created as shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a). The thickness of glaze also matters, as more purplish tint is observed when the glaze goes thicker in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(f). The opaque blueish green colour on the painted surface can be attributed to a mixed effect of oxidized copper green with L-L separation in Fig.\u0026nbsp;\u003cspan refid=\"Fig3\" class=\"InternalRef\"\u003e3\u003c/span\u003e(a).\u003c/p\u003e \u003cp\u003e \u003cb\u003eImpurity.\u003c/b\u003e The Changsha sample C\u003csub\u003e4\u003c/sub\u003e has shown rich glaze effects with various colours and structures. Another interesting feature is discovered when having a close look at the glaze surface. Figure\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(a) presents a magnified image of the squared area of C\u003csub\u003e4\u003c/sub\u003e in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e(d). In addition to the opaque light blue/green glaze, deep green/blue paints and their purplish boundary, some black dots are scattered on the surface of painted area. Similar black dots can also be found along cracks on the sample C\u003csub\u003e6\u003c/sub\u003e (see Supplementary Table S1). In order to find out their origins, an EDX scan (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb) is performed on one black dot with the scanned area indicated in the inset SEM image. A cross-section sample near a black spot is also prepared and shown in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c). Further EDX elemental mappings (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ef) are carried out on the marked area in Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003e(c). The elemental analyses (Figs.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003eb and f) suggest different chemical compositions of the black material from the surrounding glaze. The black substance is rich in S, Fe and Cu, and the ratio of Cu: Fe: S is around 1.2: 1.0: 2.0. The XRD (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ed) and Raman (Fig.\u0026nbsp;\u003cspan refid=\"Fig4\" class=\"InternalRef\"\u003e4\u003c/span\u003ee) measurements indicate the existence of crystal phases of CuFeS\u003csub\u003e2\u003c/sub\u003e (PDF #35\u0026ndash;0752) and CuS\u003csub\u003e2\u003c/sub\u003e (PDF #19\u0026ndash;0381).\u003csup\u003e\u003cspan citationid=\"CR63\" class=\"CitationRef\"\u003e63\u003c/span\u003e, \u003cspan citationid=\"CR64\" class=\"CitationRef\"\u003e64\u003c/span\u003e, \u003cspan citationid=\"CR65\" class=\"CitationRef\"\u003e65\u003c/span\u003e\u003c/sup\u003e Regarding the source of the chemicals, the fuels of Changsha kilns were woods instead of coals used in northern kilns in Tang period,\u003csup\u003e\u003cspan citationid=\"CR13\" class=\"CitationRef\"\u003e13\u003c/span\u003e\u003c/sup\u003e so there should not be significant sulphur from the fuels for Changsha wares. Also considering the black dots only appear on the painted areas, it is highly possible that the material comes from the Cu and S contained mineral pigments for green/red decorations.\u003csup\u003e\u003cspan citationid=\"CR55\" class=\"CitationRef\"\u003e55\u003c/span\u003e\u003c/sup\u003e\u003c/p\u003e \u003cp\u003eIn summary, to unravel the mysteries of colourful Tang glazes, we carried out a comprehensive study on glaze chemistry, corrosion, colorants, microstructure of some Sancai and Changsha samples. Their optical effects and colouring mechanisms are discussed with fresh experimental observations. A collective exhibition of compositions in Sancai and Changsha glazes and their corresponding phase diagrams provide chemical insights on the distinctive features of base glazes in terms of firing temperature, crystal structure and corrosion resistance. As for colouring effects, in spite of the newly introduced colorant Co, Fe and Cu remain as the dominant colouring agents in Tang glazes. The concentration, oxidation state and relative ratio of Fe and Cu in glazes bring about a wide range of colours. More importantly, the structural colours resulted from L-L phase separations start to play important roles in Tang ceramics. The mixed effects of copper-red, copper-green and structural blue and milky white are of particular interests, which create more rich and pleasant hues. In addition, some black dots found on Changsha samples help reveal the raw pigment materials used in the copper glazes. The chemical insights and understanding of colouration mechanisms obtained in this work will shed new lights on the studies of historical ceramic glazes.\u003c/p\u003e"},{"header":"Methods","content":"\u003cp\u003e \u003cb\u003eSample preparation.\u003c/b\u003e Original samples without any treatment were observed for sample descriptions in Tables\u0026nbsp;\u003cspan refid=\"Tab1\" class=\"InternalRef\"\u003e1\u003c/span\u003e and Supplementary Table S1. Testing specimens with various colours were obtained from the shards in Fig.\u0026nbsp;\u003cspan refid=\"Fig1\" class=\"InternalRef\"\u003e1\u003c/span\u003e (c) and (d). A portable electric grinder was used to cut the samples and remove excess body clays. To remove residual accretions and small particles, the specimens were cleaned in DI-water and ethanol by an ultra-sonic bath for 15 min. Then, they were dried by using a nitrogen gas spray gun before any chemical or microstructural analyses. The deep green/blue specimen from Changsha sample C\u003csub\u003e4\u003c/sub\u003e is polished to remove the surface layer so that the red part underneath is uncovered for easy access. Dual beam focused ion beam (FIB) technique (FEI, DB Helios 600 Nanolab) was applied to prepare an ultra-thin sample (100 nm) for transmission electron microscopy (TEM) measurements.\u003c/p\u003e \u003cp\u003e \u003cb\u003eInstrumental analyses.\u003c/b\u003e Digital Microscope (Keyence VHX-6000) with VH-ZST dual objective zoom lens (20x to 200x) was used to observe morphological and optical features of the samples. The magnified microstructures were characterized by using a field-emission scanning electron microscopy (FESEM) (JEOL, JSM 7600F). An energy dispersive X-ray (EDX) analyser, which is equipped in the FESEM system, was applied to analyse the elemental compositions and areal distributions. The crystalline structures of the glazes were determined by X-ray diffraction (Bruker, 2D Micro XRD). Further chemical structure and bonding of the glaze samples were also studied by a Raman microscope (Renishaw inVia confocal Raman system). The high-magnification morphologies and phase separations were analysed by a TEM system (FEI, Tecnai G2 TF20) with EDX analyser and selected area electron diffraction (SAED).\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eData availability\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare that all data supporting the findings of this study are available within the paper and supplementary information.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAuthor contributions:\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eX.Y., C.P. and Q.L. conceived the concept and planed the study. B.M.A. conducted sample observation and description. X.Y., B.M.A., H.K.H, Y.Y.K.H., P.C.L, N.D. and N.N.T performed the experiments. X.Y. and Q.L. did data analysis. X.Y., B.M.A. C.P., Q.L., J.Z. Q.Z., H.L. and S.Y.C. contributed in paper writing. All authors reviewed the manuscript.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eAcknowledgement\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors thank Dr. Kevin Lam from Asian Civilizations Museum for reviewing the manuscript. X.Y. acknowledges support from MRCA project (RGOV221031aIMRCOL) and A*STAR career development fund (CDF) SC25/21-811812 (grant no. C210812038). Q.L. and H.L acknowledge support from National Science Foundation of China (No. 51732008).\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eBoaretto, E., et al\u003cem\u003e.\u003c/em\u003e Radiocarbon dating of charcoal and bone collagen associated with early pottery at Yuchanyan Cave, Hunan Province, China. \u003cem\u003eProc. Natl Acad. Sci. USA\u003c/em\u003e \u003cstrong\u003e106\u003c/strong\u003e, 9595-9600 (2009).\u003c/li\u003e\n\u003cli\u003eHendy, J., et al. Ancient proteins from ceramic vessels at Catalhoyuk West reveal the hidden cuisine of early farmers. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e9\u003c/strong\u003e, 4064 (2018).\u003c/li\u003e\n\u003cli\u003eLiu, L., et al. The origins of specialized pottery and diverse alcohol fermentation techniques in early neolithic China. \u003cem\u003eProc. Natl Acad. Sci. USA\u003c/em\u003e \u003cstrong\u003e116\u003c/strong\u003e, 12767-12774 (2019).\u003c/li\u003e\n\u003cli\u003eBenn, C.D. \u0026amp; Benn, C. \u003cem\u003eChina\u0026apos;s Golden Age: Everyday Life in the Tang Dynasty.\u003c/em\u003e (Oxford University Press, 2004).\u003c/li\u003e\n\u003cli\u003eYe, L., Fei, Z. \u0026amp; Wang, T. \u003cem\u003eChina: Five thousand years of history and civilization.\u003c/em\u003e (City University of HK Press, 2007).\u003c/li\u003e\n\u003cli\u003eGarver, J.W. \u003cem\u003eChina and Iran: Ancient Partners in a Post-imperial World.\u003c/em\u003e (University of Washington Press, 2011).\u003c/li\u003e\n\u003cli\u003eLei, Z., Tantcheva-Burdge, E. \u0026amp; Cheung, V. Investigation into the colours of the DunHuang murals from the Tang Dynasty: \u003cem\u003eProceedings of the 14th International Colour Association (AIC) Congress, 2021\u003c/em\u003e, 1059-1064 (International Colour Association, 2021).\u003c/li\u003e\n\u003cli\u003eMikami, T. 9th-10th Century Chinese Ceramics Found in Southeast Asia. (Ceramics and Kiln Technology, Centre of Asian Studies, University of Hong kong, 1990).\u003c/li\u003e\n\u003cli\u003eMikami, T. \u003cem\u003eRoad of Ceramics (Chinese translation). \u003c/em\u003e(Tianjin People\u0026apos;s Publishing House, 1983).\u003c/li\u003e\n\u003cli\u003eJiang, X., et al. Early globalized industrial chain revealed by residual submicron pigment particles in Chinese imperial blue-and-white porcelains. \u003cem\u003eProc. Natl Acad. Sci. USA\u003c/em\u003e \u003cstrong\u003e117\u003c/strong\u003e, 6446-6452 (2020).\u003c/li\u003e\n\u003cli\u003eWood, N. \u003cem\u003eChinese glazes: Their origins, chemistry, and recreation.\u003c/em\u003e (University of Pennsylvania Press, 1999).\u003c/li\u003e\n\u003cli\u003eJiang, Q. Tang Sancai. (PhD thesis, University of Oxford, 2009).\u003c/li\u003e\n\u003cli\u003eYang, L. Tang Dynasty Changsha Ceramics: \u003cem\u003eShipwrecked,\u003c/em\u003e 145-159\u003cem\u003e \u003c/em\u003e(Singapore: Arthur M Sackler Gallery, Smithsonian Institution, 2011).\u003c/li\u003e\n\u003cli\u003eGiang, D.T. Diplomacy, trade and networks: Champa in the Asian commercial context (7th-10th Centuries). \u003cem\u003eMoussons Recherche en sciences humaines sur l\u0026rsquo;Asie du Sud-Est\u003c/em\u003e \u003cstrong\u003e27, \u003c/strong\u003e59-82 (2016).\u003c/li\u003e\n\u003cli\u003eNishino, N., et al. Nishimura project: the oldest shipwreck found in Vietnam\u0026ndash;testimony to the maritime ceramic route:\u003cem\u003e The international symposium on underwater archaeology in Vietnam and Southeast Asia: Co-operation for the development of Quang Ngai Province, 2014\u003c/em\u003e, 14-15 (2014).\u003c/li\u003e\n\u003cli\u003eLi, Q. \u003cem\u003eMaritime Silk Road\u003c/em\u003e. (China Intercontinental Press, 2006).\u003c/li\u003e\n\u003cli\u003eMiksic, J. Chinese ceramic production and trade. In \u003cem\u003eOxford Research Encyclopedia of Asian History\u003c/em\u003e (2017).\u003c/li\u003e\n\u003cli\u003eLi, B.P., et al. Characterisation of Chinese Tang sancai from Gongxian and Yaozhou kilns using ICP-MS trace element and TIMS Sr\u0026ndash;Nd isotopic analysis. \u003cem\u003eJ. Archaeol. Sci.\u003c/em\u003e \u003cstrong\u003e33, \u003c/strong\u003e56-62 (2006).\u003c/li\u003e\n\u003cli\u003eCui, J.F., Lei, Y., Jin, Z.B., Huang, B.L. \u0026amp; Wu, X.H. Lead isotope analysis of Tang Sancai pottery glazes from Gongyi kiln, Henan Province and Huangbao kiln, Shaanxi Province. \u003cem\u003eArchaeometry \u003c/em\u003e\u003cstrong\u003e52,\u003c/strong\u003e 597-604 (2009).\u003c/li\u003e\n\u003cli\u003eCui, J., et al. Western technical traditions of pottery making in Tang Dynasty China: chemical evidence from the Liquanfang kiln site, Xi\u0026apos;an city. \u003cem\u003eJ. Archaeol. Sci.\u003c/em\u003e \u003cstrong\u003e37,\u003c/strong\u003e 1502-1509 (2010).\u003c/li\u003e\n\u003cli\u003eHuang, P.H. Excavation bulletin (1999) of Changsha kiln at Wangchen county of Hunan province (in Chinese). \u003cem\u003eArchaeology\u003c/em\u003e \u003cstrong\u003e5, \u003c/strong\u003e49-62 (2003).\u003c/li\u003e\n\u003cli\u003eRogers, A. \u003cem\u003eFull spectrum: how the science of color made us modern\u003c/em\u003e. (Houghton Mifflin, 2021).\u003c/li\u003e\n\u003cli\u003eHetherington, A.L. \u003cem\u003eChinese ceramic glazes\u003c/em\u003e. (PD and I. Perkins, 1948).\u003c/li\u003e\n\u003cli\u003ePollard, A.M., Batt, C.M., Stern, B., Young, S.M. \u0026amp; Young, S.\u003cem\u003e Analytical chemistry in archaeology\u003c/em\u003e. (Cambridge University Press, 2007).\u003c/li\u003e\n\u003cli\u003eBleasdale, M., et al. Ancient proteins provide evidence of dairy consumption in eastern Africa. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e12,\u003c/strong\u003e 632 (2021).\u003c/li\u003e\n\u003cli\u003eZavala, E.I., et al. Pleistocene sediment DNA reveals hominin and faunal turnovers at Denisova Cave. \u003cem\u003eNature\u003c/em\u003e \u003cstrong\u003e595\u003c/strong\u003e, 399-403 (2021).\u003c/li\u003e\n\u003cli\u003eDambrogio, J., et al. Unlocking history through automated virtual unfolding of sealed documents imaged by X-ray microtomography. \u003cem\u003eNat. Commun.\u003c/em\u003e \u003cstrong\u003e12,\u003c/strong\u003e 1-10 (2021).\u003c/li\u003e\n\u003cli\u003eZhang, F.K. \u0026amp; Zhang, Z.G. Low-temperature colored glazes of successive dynasties in ancient China. \u003cem\u003eJ. Chin. Ceram. Soc. \u003c/em\u003e\u003cstrong\u003e8,\u003c/strong\u003e 9-19 (1980).\u003c/li\u003e\n\u003cli\u003eZhang, F.K. \u003cem\u003eThe science of Chinese ancient ceramics.\u003c/em\u003e (Shanghai People\u0026apos;s Fine Arts Publishing House, Shanghai, 2000).\u003c/li\u003e\n\u003cli\u003eShen, J. Chemical and Isotopic Analysis in the Investigation of Glazes from Northern China and the Middle East, 7th-14th Centuries AD. (University of Nottingham, 2017).\u003c/li\u003e\n\u003cli\u003eZhang, Z.G. \u0026amp; Guo, Y.Y. Study of coloured glazes of Changsha Tongguan kiln (in Chinese). \u003cem\u003eJ. Jingdezhen Univ.\u003c/em\u003e \u003cstrong\u003e1,\u003c/strong\u003e 6 (1985).\u003c/li\u003e\n\u003cli\u003eZhang, F.K. Study of Changsha ware.\u003cem\u003e J. Chin. Ceram. Soc. \u003c/em\u003e\u003cstrong\u003e14, \u003c/strong\u003e339-346 (1986).\u003c/li\u003e\n\u003cli\u003eChen, X.Q., Zhang, Z.G. \u0026amp; Huang, R.F. Opaque glaze of the Changsha Tongguan ware-Another Tang Dynasty\u0026apos;s phase separated glaze.\u003cem\u003e J. Chin. Ceram. Soc. \u003c/em\u003e\u003cstrong\u003e19, \u003c/strong\u003e234-240 (1991).\u003c/li\u003e\n\u003cli\u003eLi, Y., et al. Colour-generating mechanism of copper-red porcelain from Changsha Kiln (A.D. 7th\u0026ndash;10th century), China. \u003cem\u003eCeram. Int.\u003c/em\u003e \u003cstrong\u003e42,\u003c/strong\u003e 8495-8500 (2016).\u003c/li\u003e\n\u003cli\u003eShen, B., et al. Micro-structural study of colored porcelains of Changsha kiln using imaging and spectroscopic techniques. \u003cem\u003eCeram. Int.\u003c/em\u003e \u003cstrong\u003e44,\u003c/strong\u003e 18528-18534 (2018).\u003c/li\u003e\n\u003cli\u003eRawson, J., Tite, M. \u0026amp; Hughes, M. The export of Tang sancai wares: some recent research. \u003cem\u003eTrans. Orient. Ceram. Soc.\u003c/em\u003e \u003cstrong\u003e52,\u003c/strong\u003e 39-61 (1989).\u003c/li\u003e\n\u003cli\u003eHo, C., Charoenwongsa, P. \u0026amp; Bronson, B. Newly identified Chinese ceramic wares from ninth century trading ports in southern Thailand. \u003cem\u003eSPAFA Digest (1980-1990)\u003c/em\u003e \u003cstrong\u003e11,\u003c/strong\u003e 12 (1990).\u003c/li\u003e\n\u003cli\u003eFlecker, M. A ninth-century AD Arab or Indian shipwreck in Indonesia: first evidence for direct trade with China. \u003cem\u003eWorld Archaeol.\u003c/em\u003e \u003cstrong\u003e32,\u003c/strong\u003e 335-354 (2001).\u003c/li\u003e\n\u003cli\u003eChen, S., Zhao, B., Hayes, P. \u0026amp; Jak, E. Experimental study of phase equilibria in the PbO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e system. \u003cem\u003eMetall. Mater. Trans. B\u003c/em\u003e \u003cstrong\u003e32, \u003c/strong\u003e997-1005 (2001).\u003c/li\u003e\n\u003cli\u003eHarada, Y., Saito, N. \u0026amp; Nakashima, K. Crystallinity of supercooled oxide melts quantified by electrical capacitance measurements. \u003cem\u003eISIJ Int.\u003c/em\u003e \u003cstrong\u003e57,\u003c/strong\u003e 23-30 (2017).\u003c/li\u003e\n\u003cli\u003eRetsinas, A., Kalampounias, A.G. \u0026amp; Papatheodorou, G.N. Glass formation and Raman spectra of CaO-SiO\u003csub\u003e2\u003c/sub\u003e glasses towards the orthosilicate limit. \u003cem\u003eJ. Phys. Chem. Solids\u003c/em\u003e \u003cstrong\u003e99,\u003c/strong\u003e 19-24 (2016).\u003c/li\u003e\n\u003cli\u003eKucharczyk, S., Sitarz, M., Zajac, M. \u0026amp; Deja, J. The effect of CaO/SiO\u003csub\u003e2\u003c/sub\u003e molar ratio of CaO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-SiO\u003csub\u003e2\u003c/sub\u003e glasses on their structure and reactivity in alkali activated system. \u003cem\u003eSpectrochim. Acta A Mol. Biomol. Spectrosc.\u003c/em\u003e \u003cstrong\u003e194,\u003c/strong\u003e 163-171 (2018).\u003c/li\u003e\n\u003cli\u003eKalampounias, A.G. IR and Raman spectroscopic studies of sol-gel derived alkaline-earth silicate glasses. \u003cem\u003eBull. Mater. Sci. \u003c/em\u003e\u003cstrong\u003e34,\u003c/strong\u003e 299-303 (2011).\u003c/li\u003e\n\u003cli\u003eRobinet, L., et al. Raman spectrometry, a non-destructive solution to the study of glass and its alteration. \u003cem\u003eICOM Committee for Conservation 15th triennial meeting, \u003c/em\u003e\u003cstrong\u003eI,\u003c/strong\u003e\u003cem\u003e \u003c/em\u003e190 (2008).\u003c/li\u003e\n\u003cli\u003eYadav, A.K. \u0026amp; Singh, P. A review of the structures of oxide glasses by Raman spectroscopy. \u003cem\u003eRSC Adv.\u003c/em\u003e \u003cstrong\u003e5,\u003c/strong\u003e 67583-67609 (2015).\u003c/li\u003e\n\u003cli\u003eColomban, P. \u0026amp; Prinsloo, L.C. Optical spectroscopy of silicates and glasses. In \u003cem\u003eSpectroscopic Properties of Inorganic and Organometallic Compounds, \u003c/em\u003e128-149\u003cem\u003e \u003c/em\u003e(2009).\u003c/li\u003e\n\u003cli\u003eColomban, P., Simsek Franci, G. \u0026amp; Koleini, F. On-site raman spectroscopic study of beads from the Necropolis of Vohemar, northern Madagascar (\u0026gt;13th C.). \u003cem\u003eHeritage\u003c/em\u003e \u003cstrong\u003e4,\u003c/strong\u003e 524-540 (2021).\u003c/li\u003e\n\u003cli\u003eSilva, D.C., et al. Synthesis of PbO\u0026middot;SiO\u003csub\u003e2\u003c/sub\u003e glass by CO\u003csub\u003e2\u003c/sub\u003e laser melting method. \u003cem\u003eJ. Non-Cryst. Solids \u003c/em\u003e\u003cstrong\u003e522,\u003c/strong\u003e 119572 (2019).\u003c/li\u003e\n\u003cli\u003eColomban, P., Sagon, G.R. \u0026amp; Faurel, X. Differentiation of antique ceramics from the Raman spectra of their coloured glazes and paintings. \u003cem\u003eJ. Raman Spectrosc.\u003c/em\u003e \u003cstrong\u003e32,\u003c/strong\u003e 351-360 (2001).\u003c/li\u003e\n\u003cli\u003eHe, Y., Li, W., Li, J., Xu, C. \u0026amp; Lu, X. Research on the degradation of ancient Longquan celadons in the Dalian Island shipwreck. \u003cem\u003enpj Mater. Degrad.\u003c/em\u003e \u003cstrong\u003e6,\u003c/strong\u003e 1-10 (2022).\u003c/li\u003e\n\u003cli\u003eYin, X., Huang, T.J. \u0026amp; Gong, H. Chemical evolution of lead in ancient artifacts-A case study of early Chinese lead-silicate glaze. \u003cem\u003eJ. Eur. Ceram. Soc.\u003c/em\u003e \u003cstrong\u003e40,\u003c/strong\u003e 2222-2228 (2020).\u003c/li\u003e\n\u003cli\u003eZhu, T.Q., Wang, C.S., Mao, Z.W., Li, L.X. \u0026amp; Huang, H. Identification of different corrosion covering the surface of Chinese ancient lead glazed potteries. \u003cem\u003eSpectrosc. Spect. Anal.\u003c/em\u003e \u003cstrong\u003e30,\u003c/strong\u003e 266-269 (2010).\u003c/li\u003e\n\u003cli\u003eWood, N. \u0026amp; Priestman, S. New light on Chinese Tang Dynasty and Iraqi Blue and White in the ninth century: the material from Siraf, Iran. \u003cem\u003eBull. Chin. Ceram. Art Archaeol.\u003c/em\u003e \u003cstrong\u003e7,\u003c/strong\u003e 47-60 (2016).\u003c/li\u003e\n\u003cli\u003eSpataro, M., Wood, N., Meeks, N., Meek, A., \u0026amp; Priestman, S. Pottery technology in the Tang dynasty (ninth century AD): archaeometric analyses of a Gongyi sherd found at Siraf, Iran. \u003cem\u003eArchaeometry\u003c/em\u003e \u003cstrong\u003e61,\u003c/strong\u003e 574-587 (2019).\u003c/li\u003e\n\u003cli\u003eJia, C., et al. A short but glorious porcelain glaze of Early Ming Dynasty: New finding of raw material and colorants in the copper red glaze. \u003cem\u003eJ. Eur. Ceram. Soc.\u003c/em\u003e \u003cstrong\u003e41,\u003c/strong\u003e 3809-3815 (2021).\u003c/li\u003e\n\u003cli\u003eBrown, S. \u0026amp; Norton, F. Constitution of copper-red glazes. \u003cem\u003eJ. Am. Ceram. Soc.\u003c/em\u003e\u003cstrong\u003e42, \u003c/strong\u003e499-503 (1959).\u003c/li\u003e\n\u003cli\u003eJackson, S.H. A monograph on the copper-red glazes. \u003cem\u003eTrans. Orient. Ceram. Soc.\u003c/em\u003e\u003cstrong\u003e2,\u003c/strong\u003e 22-32 (1922).\u003c/li\u003e\n\u003cli\u003eCuvelier, P.A., Andraud, C., Chaudanson, D., Lafait, J. \u0026amp; Nitsche, S. Copper red glazes: a coating with two families of particles. \u003cem\u003eAppl. Phys. A\u003c/em\u003e \u003cstrong\u003e106,\u003c/strong\u003e 915-929 (2012).\u003c/li\u003e\n\u003cli\u003eTurner, T. Chemically reduced copper reds in oxidation. \u003cem\u003eCeram. Technical\u003c/em\u003e \u003cstrong\u003e35,\u003c/strong\u003e 94-101 (2012).\u003c/li\u003e\n\u003cli\u003eKingery, W., Vandiver, P.B., Huang, I.W. \u0026amp; Chiang, Y.M. Liquid-liquid immiscibility and phase separation in the quaternary systems K\u003csub\u003e2\u003c/sub\u003eO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-CaO-SiO\u003csub\u003e2\u003c/sub\u003e and Na\u003csub\u003e2\u003c/sub\u003eO-Al\u003csub\u003e2\u003c/sub\u003eO\u003csub\u003e3\u003c/sub\u003e-CaO-SiO\u003csub\u003e2\u003c/sub\u003e. \u003cem\u003eJ. Non-Cryst. Solids \u003c/em\u003e\u003cstrong\u003e54,\u003c/strong\u003e 163-171 (1983).\u003c/li\u003e\n\u003cli\u003eLi, W., Li, J., Wu, J. \u0026amp; Guo, J. Study on the phase-separated opaque glaze in ancient China from Qionglai kiln. \u003cem\u003eCeram. Int.\u003c/em\u003e \u003cstrong\u003e29,\u003c/strong\u003e 933-937 (2003).\u003c/li\u003e\n\u003cli\u003eShi, P., et al. Amorphous photonic crystals and structural colors in the phase separation glaze. \u003cem\u003eJ. Eur. Ceram. Soc.\u003c/em\u003e \u003cstrong\u003e38,\u003c/strong\u003e 2228-2233 (2018).\u003c/li\u003e\n\u003cli\u003eAliyev, Y., et al. The structural and vibrational properties of Ni-doped chalcopyrite CuFeS\u003csub\u003e2\u003c/sub\u003e. \u003cem\u003eJ. Ovonic Res. \u003c/em\u003e\u003cstrong\u003e14,\u003c/strong\u003e 165-169 (2018).\u003c/li\u003e\n\u003cli\u003eMunce, C.G., Parker, G.K., Holt, S.A. \u0026amp; Hope, G.A. A Raman spectroelectrochemical investigation of chemical bath deposited Cu\u003csub\u003ex\u003c/sub\u003eS thin films and their modification. \u003cem\u003eColloids Surf. A: Physicochem. Eng. Asp. \u003c/em\u003e\u003cstrong\u003e295,\u003c/strong\u003e 152-158 (2007).\u003c/li\u003e\n\u003cli\u003eUrbano, G., et al. Electrochemical and spectroscopic study of interfacial interactions between chalcopyrite and typical flotation process reagents. \u003cem\u003eInternational Journal of Minerals, Metallurgy, and Materials\u003c/em\u003e \u003cstrong\u003e23,\u003c/strong\u003e 127-136 (2016).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":true,"highlight":"","institution":"","isAcceptedByJournal":false,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true},"keywords":"Ancient ceramics, coloration, Tang Sancai, Changsha kiln, polychromic, structural colour","lastPublishedDoi":"10.21203/rs.3.rs-2540579/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-2540579/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003eAncient ceramics have profound influences on the living habits of human beings. The emergence of high-fired polychromic glazes during Tang period (618\u0026ndash;907 AD) highlights a significant advancement in ceramic history that reflected inter-civilizational communications more than 1000 years ago. However, the understanding of colouration mechanisms in Tang glazes are still not satisfactory. In this work, we unravel the mysteries of colourful Tang glazes through a comparative study of Tang Sancai and Changsha kiln samples. Multiple chemical and structural factors, including colourants in varied concentrations and oxidation states as well as microstructures resulted from phase separation, impurity and corrosion, are found responsible for the glaze appearance. More importantly, the combination of different coloration ingredients brings about additional colours and optical effects that any individual factor can hardly generate. These fresh observations and comprehensive analyses provide an insightful assessment of the diversity of Tang glazes and promote the perception of ancient ceramics in a more scientific manner. The knowledge and methodology revealed here are expected to inspire more studies of heritage materials.\u003c/p\u003e","manuscriptTitle":"Synergistic chemical and structural colorations in early polychromic ceramic glazes over 1000 years ago","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2023-02-08 20:31:29","doi":"10.21203/rs.3.rs-2540579/v1","editorialEvents":[{"type":"communityComments","content":0}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"researchsquare","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":true,"externalIdentity":"","sideBox":"","snPcode":"","submissionUrl":"/submission","title":"Research Square","twitterHandle":"researchsquare","acdcEnabled":true,"dfaEnabled":false,"editorialSystem":"","reportingPortfolio":"","inReviewEnabled":false,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"813c3d40-5159-4389-b65e-d5a45f3d7f7b","owner":[],"postedDate":"February 8th, 2023","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"posted","subjectAreas":[{"id":19018574,"name":"Physical sciences/Chemistry"},{"id":19018575,"name":"Physical sciences/Materials science"}],"tags":[],"updatedAt":"2023-06-11T04:14:17+00:00","versionOfRecord":[],"versionCreatedAt":"2023-02-08 20:31:29","video":"","vorDoi":"","vorDoiUrl":"","workflowStages":[]},"version":"v1","identity":"rs-2540579","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-2540579","identity":"rs-2540579","version":["v1"]},"buildId":"7rjqhiLT3MXkJMwkYKINL","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}