Research on Traditional Craftsmanship of ‘Shengfanhong’

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Its coloration varied significantly across different historical periods in China, and even within the same era, a phenomenon intricately linked to the complexity of ‘Shengfanhong’ (calcined iron vitriol) production techniques. Historical texts such as TiangongKaiwu document the preparation of ‘Shengfanhong’, but these records remain largely descriptive, lacking technical specificity and scientific explanations of underlying principles. This study employs experimental archaeology combined with Differential Scanning Calorimetry-Thermogravimetry (DSC-TG), X-ray Diffraction (XRD), Colorimetric analysis, and particle size testing to scientifically decode the "tacit knowledge" embedded in the traditional craftsmanship of ‘Shengfanhong’ production. Figures Figure 1 Figure 2 Figure 3 Figure 4 Figure 5 Figure 6 Figure 7 Figure 8 Figure 9 Figure 10 Figure 11 Figure 12 Introduction 'Fanhong' is an overglaze pigment utilizing Fe₂O₃ as a chromophore, which can also be fired in an oxidizing atmosphere to produce monochromatic glaze. Its origins trace back to the Song Dynasty's red-and-green polychrome wares, serving as a precursor to later multi-colored overglaze techniques. The term 'Fanhong' first appeared in the DaMingHuiDian : "In the second year of Jiajing (1523), Jiangxi kilns were ordered to replace underglaze copper red with deep iron oxide red in porcelain production." In the mid-Ming Dynasty during the Chenghua period (1465–1487), the combination of underglaze blue and white with overglaze polychrome led to the production of uniquely styled 'doucai' porcelain, which, during this period, were known for their extremely thin body and rich colors, described as 'exquisite quality and vibrant colors' 1,2 . In the Jiajing period of the Ming Dynasty (1522–1566), the Imperial Porcelain Factory in Jingdezhen began to use iron red glaze in place of copper red glaze. By the Kangxi period of the Qing Dynasty (1662–1722), 'Fanhong' evolved into a brilliantly saturated pigment, predominantly used in 'wucai' (five-color) and 'doucai' decorative schemes. However, after the Jiaqing period of the Qing Dynasty (1796–1820), the quality of the iron red overglaze color significantly declined, with only a slight improvement during the Guangxu (1875–1908) Emperor’s reign. The production techniques of 'Shengfanhong' are documented in The Science of Ancient Chinese Ceramics 3 and Ceramic Decorative Materials 4 . The preparation of 'Shengfanhong' involves sequential steps: dehydration of iron vitriol (FeSO₄·7H₂O), crushing and sieving, calcination, acid-leaching, and drying. The resultant material is then ground with water, purified through sedimentation, mixed with lead powder and ox glue, and finally fired twice to produce 'Fanhong' porcelains (Fig 1). The traditional production process of 'Shengfanhong' involves three key steps: calcination, acid-leaching, and particle size classification of iron vitriol. During calcination, the crystal size and phase composition of iron vitriol undergo significant changes, directly influencing the chromatic properties of the final 'fanhong' pigment. Hiroshi Asaoka et al 5 . synthesized iron oxide powders by calcining FeSO₄·7H₂O, reporting Fe₂O₃ crystal sizes of 50 nm at 650°C and 100 nm at 770°C, with reduced calcination temperatures enhancing chromaticity. Hirofumi Inada et al 6 . characterized a traditional red pigment via X-ray diffraction (XRD), confirming the dominance of α-Fe₂O₃ phase at 700°C, while scanning electron microscopy (SEM) revealed α-Fe₂O₃ crystal sizes ranging from 30 to 100 nm. S. Kajihara et al 7 . observed abundant sulfur-containing microcrystals in FeSO₄·7H₂O at 550°C, which disappeared upon heating to 650°C, yielding pure Fe₂O₃. P.K. Gallagher et al 8 . identified Fe₂O(SO₄)₂ as an intermediate during thermal decomposition of FeSO₄·7H₂O. R. Zboril et al 9-11 . further demonstrated that FeSO₄·7H₂O transforms into various Fe₂O₃ polymorphs during heating, with α-Fe₂O₃ stabilized at 700°C. The classification process of 'Shengfanhong' essentially involves sorting powder materials into different categories based on particle size distribution. In the study of factors influencing pigment coloration, particle size has been identified as a critical determinant 12-13 . The coarse particle size of 'Shengfanhong' powder leads to a highly rough surface in the resulting glaze. After firing, pronounced crystal precipitation occurs, which significantly affects the coloration of 'fanhong' porcelain (Fig 2). Scholars have employed high-energy ball milling techniques 14 to analyze the refractive index, reflectance, and chromaticity of mineral pigments with varying particle sizes. The results demonstrate that mineral pigments exhibit distinct coloration at different particle sizes, and the influence of particle size on coloration varies significantly depending on the material composition 15-16 . The crystal size of powdered pigments primarily governs the interaction between light and mineral pigment particles, with this effect exhibiting nonlinear characteristics 17 . Chen 18 conducted a study on the grinding stability of iron oxide red (α-Fe₂O₃), revealing that mechanical force activation occurs during wet grinding. The relationship between ball milling time and particle size change is nonlinear—the particle diameter initially decreases but subsequently increases with prolonged grinding . This enlargement of particle size shifts the pigment's hue toward yellow-blue tones while reducing both redness and brightness 19-21 . The coloration mechanism of 'fanhong' porcelain constitutes a systematic issue, where the traditional craftsmanship of 'shengfanhong' critically influences its chromatic performance. Currently, academic research lacks a comprehensive scientific explanation for the traditional craftsmanship of 'shengfanhong'. The theory of tacit knowledge reveals the intangible dimensions of human expertise that are difficult to articulate—a phenomenon equally present in the traditional craftsmanship of 'shengfanhong'. Based on this, this study explains the scientific mechanism of the traditional craftsmanship of 'shengfanhong' through experimental archaeology and scientific testing methods, revealing the exquisite porcelain-making techniques of ancient people and scientifically quantifying this process. The traditional preparation craftsmanship of ‘shengfanhong’ Test Methods Differential Scanning Calorimetry-Thermogravimetric Analysis (DSC-TG) The raw material for the differential scanning calorimetric-thermogravimetric analysis was iron vitriol, and the thermal analyzer was supplied by Netzsch Instruments Manufacturing Co., Ltd. in Selb, Germany, model STA449C, with a resolution of 0.1 µg, and a temperature range from room temperature to 1650℃. The mass of the experimental sample was 9.91 mg, with a heating rate of 10℃/min in an Ar atmosphere. The testing temperature range was from room temperature to 900℃measuring the mass changes of iron vitriol and the temperature points of endothermic and exothermic reactions during heating. X-ray Diffraction (XRD) The samples for XRD testing were iron vitriol powders calcined at different temperatures. The XRD was from Bruker AXS GmbH in Karlsruhe, Germany, model D8 Advance, with a Cu target and a power of 6.5kW; the scanning step length was 0.01 ◦ and the scanning speed was 0.05 s per step, testing the mineral composition of iron vitriol during heating. Colorimetric analysis The samples for chromaticity analysis were 'Fanhong' pigment made from 'Shengfanhong'powder of different particle sizes, and the chromaticity meter used was a NF-333 portable spectrophotometric chroma meter with a wavelength range of 400–700 nm. All measurements were made under standard 10 ◦ observation conditions and D65 illuminant to test the relevant chromaticity parameters of different iron red. L* represents the brightness of the object: 0–100, indicating from black to white; a* represents the red green of the object: a positive value indicates red, and a negative value indicates green; b* represents the yellow blue of the object: a positive value indicates yellow, and a negative value indicates blue. Particle size testing The vertical planetary ball mill is used for ball milling 'Shengfanhong' powder, and comes from Changsha Deke Instrument Equipment Co., Ltd., with the model of DECO-PBM-V-0.4L. The experiment was configured with a mass ratio of powder: grinding balls: water = 1: 1: 1. Control groups were established with ball milling durations of: 20 minutes, 30 minutes, and 60 minutes, maintaining a constant rotational speed of 400 revolutions per minute. The laser particle size analyzer is used to test the particle size of 'Shengfanhong' powder, and from Malvern Instruments Limited in the UK, model Mastersizer2000, with a particle size range of 0.02-2000 microns and a scanning speed of 1000 times per second. Pretreatment process of iron vitriol In this experiment, industrial iron vitriol (FeSO 4 ·7H 2 O) was used as the raw material, and the supplier of industrial iron vitriol was WuHan Carnoss Co., Ltd. in Wuhan, China, this kind of industrial iron vitriol’s purity was 99%. The treatment process of iron vitriol involves three key steps. First, to address the difficulty in physical grinding caused by the strong hygroscopicity of the raw material, a gradient heating pretreatment method was adopted: dehydration was performed within the temperature range of room temperature to 120°C. Through thermal decomposition (FeSO 4 ·7H 2 O → FeSO 4 ·nH 2 O + (7-n)H 2 O↑ 22 ), crystal water was gradually released, accompanied by distinct phase transformation characteristics—the color of the crystals transitioned from the initial pale green (characteristic of Fe 2+ hydrated ions) to grayish-white. Second, to mitigate the agglomeration and caking of the dehydrated material, grinding was conducted using an agate mortar, and particle size control was achieved by sieving through a standard 250μm mesh. Finally, considering the susceptibility of FeSO 4 to oxidation and deterioration in air, the processed anhydrous ferrous sulfate powder was stored in a vacuum drying oven (Fig 3). Calcination process of iron vitriol According to the records in references 3-4 regarding the calcination process of iron vitriol, this step adopts dynamic calcination to prepare 'Shengfanhong'. The specific operational procedure is as follows: The pretreated dehydrated ferrous sulfate (FeSO₄) is placed in an iron pot and subjected to gradient pyrolysis using an open flame. During calcination, real-time visual colorimetric monitoring is required to observe the phase transition characteristics of the material, corresponding to the historical description that " Using an open flame to calcine iron vitriol until it turns slightly black, then transforms into orange-red upon cooling . " The color evolution exhibits distinct stages: the initial grayish-white material gradually turns yellowish-brown during heating, when the color becomes slightly blackened, heating is terminated, upon cooling, it transforms into a reddish-orange hue (Fig 4). This transformation marks the completion of standard 'Shengfanhong' production. Comparative studies with modern calcination processes indicate that this state of 'Shengfanhong' achieves equivalent results to those obtained through contemporary 700°C calcination techniques. Rinsing process of ‘Shengfanhong’ The prepared 'Shengfanhong' powder is transferred into a beaker, and room-temperature clean water is added while stirring rapidly and uniformly with a wooden stick. Under agitation, the mixture in the beaker gradually clarifies, at which point the undissolved particles in the supernatant are removed by decantation. The addition of cold water is then stopped, and hot water is used for eight or nine additional washings until all alum liquor is completely eliminated. In ancient practices, tea infusion was typically employed to test whether the alum liquor had been fully removed. As shown in Fig 5, if alum liquor remains, the liquid in the cup turns black; conversely, if the liquid's color remains unchanged, it indicates complete removal of alum liquor, marking the completion of the rinsing process and confirming that the 'Shengfanhong' has achieved the required purity. Before classifying the 'Shengfanhong', it must undergo thorough grinding. After grinding, an appropriate amount of clean water is added to the 'Shengfanhong' to form a thin slurry consistency. Classification process of ‘Shengfanhong’ The classification process applied to rinsed 'Shengfanhong' powder primarily aims to achieve standardized particle size control through physical classification methods, thereby meeting specific granularity requirements for ancient 'Fanhong' pigment preparation. In this classification process, two aluminum trays are first aligned linearly with the container (beaker) holding 'Shengfanhong', connected by an absorbent medium (such as straw paper) to create a fluid transfer channel. This setup allows the suspended slurry in the beaker to flow along the medium into the first aluminum tray. During this procedure, particle sedimentation occurs in the first aluminum tray while supernatant moisture continues migrating via capillary action through the straw paper into the second aluminum tray. After sufficient settling time, the slurry sedimented at the bottom of the first aluminum tray is selected as the raw material for ancient 'Fanhong' due to its optimal particle size distribution characteristics. This sediment undergoes secondary rinsing to eliminate residual soluble impurities, after sun drying treatment, the entire classification process is completed (Fig 6). Discussion 'Fanhong' constitutes a vital component of overglaze ceramic decoration, the manuscript roughly restores the traditional craftsmanship of producing 'Shengfanhong', interpreting the scientific principles of the preparation process of 'Shengfanhong' through scientific restoration and related testing. Heating process of iron vitriol The physicochemical reactions during iron vitriol calcination were characterized by DSC-TG analysis. As shown in Fig 7, four distinct weight loss stages (I-IV) were observed in the TG curve 23 , with respective mass losses of 17.66%, 20.74%, 8.88%, and 25.23%. The DSC curve revealed three endothermic peaks and one exothermic peak during thermal treatment: The temperatures at which the endothermic peaks (①, ②, ④) appear are 75.6℃, 122.7℃, 661.7℃, along with one exothermic peak (③) at 567.6°C. Based on these findings, the heating process of green vitriol can be interpreted as follows: 1. During the pretreatment process of iron vitriol, dehydration treatment is carried out within the temperature range of room temperature to approximately 120℃. FeSO₄·7H₂O itself appears green, which is due to the absorption of specific wavelengths of light by the d-d electron transition of ferrous ions (Fe 2+ ). The appearance of the endothermic peak ① and ② correspond precisely to the temperature node where FeSO₄·7H₂O undergoes two dehydration processes, while I and II correspond to two distinct dehydration stages of FeSO₄·7H₂O. Through the thermal decomposition reaction （FeSO4·7H2O → FeSO4·nH2O + (7-n)H2O↑ 22 ）facilitates gradual liberation of crystalline water molecules, accompanied by distinct phase transformation characteristics--the color of the crystal manifested by a progressive chromatic transition from initial pale green coloration (characteristic of hydrated Fe ²+ ions) to grayish-white appearance. 2. In the calcination process of iron vitriol, open-flame heating is initiated from room temperature. during which process III corresponds to the thermal conversion of FeSO₄ into Fe₂(SO₄)₃, with an exothermic peak ③ observed at a critical temperature node of 567°C where FeSO₄ reacts with O₂ forming intermediate product Fe₂O(SO₄)₂, and process IV represents subsequent decomposition into Fe₂(SO₄)₃, Fe₂O₃ and SO₃ 8 . The temperature node of the exothermic peak ④ is 661℃, at which both Fe₂(SO₄)₃ and Fe₂O(SO₄)₂ undergo desulfurization to upon α-Fe₂O₃. According to the principle of oxidation-reduction reaction, Fe 2+ is oxidized to trivalent iron ions (Fe 3+ ), According to redox principles, oxidation of Fe²⁺ to trivalent iron ions (Fe 3+ ) occurs concomitantly with sulfate ion decomposition (SO₄ 2- ). This valence transition alters electronic configurations and associated absorption spectra, resulting in characteristic orange-red coloration upon formation of α-Fe₂O₃ particles. When the calcination temperature exceeds 700°C, progressive chromatic shifts occur toward jujube-red and eventually black hues (Fig 8). This provides a reasonable physicochemical explanation for key processes in iron vitriol's thermal treatment: dehydration, oxidation of divalent iron ions to trivalent iron ions, and decomposition reactions of sulfate ions, thereby scientifically validating how heating transforms iron vitriol into red pigment. The empirical observation where craftsmen cease firing upon watching slight blackening, later cooling into orange-red, results from superimposed thermal radiation and reflection spectra effects during high-temperature processing. At precisely controlled calcination temperatures around 700°C where α-Fe₂O₃ has been completely formed (Fig 9), its hexagonal close-packed crystal structure demonstrates maximum reflectance in red spectral regions 25 . At this temperature, thermal radiation occurs according to blackbody radiation theory where high-temperature objects emit electromagnetic waves while simultaneously reflecting external light 26 . Under high temperatures, thermal radiation intensity may surpass reflected light intensity and superimpose onto reflection spectra, causing slight blackening in appearance. After cooling, the thermal radiation of the material disappears, and the reflection spectrum dominates the coloration. At this point, the strong reflection of red light by α-Fe₂O₃ appears, and the color returns to the original red color of the material 27 . To further verify the influence of surface thermal radiation of the powder on the coloration, samples were divided into two cooling methods: one portion was cooled in ambient air at 20°C, while another portion was cooled in water maintained at the same room temperature. As established principles dictate, water cooling achieves significantly faster heat dissipation than air cooling at identical temperatures—a phenomenon experimentally confirmed by observing more rapid chromatic transition from black to red in water-quenched powder compared to air-cooled powder. In addition, this process is reversible, and α-Fe₂O₃ does not undergo crystal transformation at 700°C 27 , these results conclusively demonstrate that high-temperature darkening originates from transient superposition effects between thermal radiation and reflection spectra Rinsing and classification process of ‘Shengfanhong’ (1) In the rinsing process for 'Shengfanhong' preparation, calcined iron vitriol undergoes sequential rinsing with cold and hot water respectively, the former removes undissolved particles from supernatant while the latter eliminates residual sulfate groups from powder particles. When treated with hot water, Fe 2 (SO 4 ) 3 reacts with water and hydrolyzes to form a reddish brown colloidal precipitate of Fe(OH) 3 and H₂SO₄. The chemical equation is: Fe 2 (SO 4 ) 3 + 6H 2 O → 2Fe(OH) 3 + 3H 2 SO 4 , and multiple rinses remove the colloidal precipitate of Fe(OH) 3 and H₂SO₄. Tea infusion was employed to verify complete removal of alum liquor residues, in the field of analytical chemistry, a colorimetric detection method can be established through the chromogenic reactions between tannic acid and metal ions. When using tea infusion as an indicator system to verify whether alum water remains residual iron species (mainly containing Fe 2+ ), if there are uncleaned ferrous salts in the system, they are easily dissolved and oxidized to Fe 3+ in the aqueous phase. At this stage, tannic acid (C 76 H 52 O 46 ) abundantly present in tea solution undergoes specific complexation with Fe 3+ , forming black-colored iron tannate (Fe(C 76 H 52 O 46 )) through coordination chemistry principles，it is a classic example of metal-organic ligand chromogenic reaction. Experimental observations demonstrate that solution coloration transitions from amber to deep ink-black within 30 seconds, with chromatic intensity positively correlating to Fe 3+ concentration as governed by Lambert-Beer's law fundamentals for colorimetric detection 24 . Therefore, the use of tea infusion is used for the inspection of trivalent iron salts, and the color change of tea infusion is used to characterize whether the impurities in alum water have been removed completely 24 . (2) In the classification process for 'Shengfanhong' preparation, its core mechanism involves hydrodynamic sorting of raw alum red powder particles. through a multi-stage gradient sieving system, the primary grading phase achieves separation of coarse particle fractions target particle-size-range powder forms a dominant enrichment zone within the first aluminum tray. The first aluminum tray not only collects sediment with optimal particle size distribution but also facilitates secondary impurity removal as supernatant liquid flows into the second aluminum tray during sedimentation. Accordingly, we conducted particle size analysis on straw paper-filtered 'Shengfanhong' powder samples and post-filtration fractions obtained through straw paper sieving (as quantitatively characterized in Table 1 and Fig10). Parallel experiments employed modern ball milling technology to systematically evaluate time-dependent particle size distributions across different processing durations, and conducted particle size tests on the powders (as shown in Table 2 and Fig 11). Comparative analysis revealed that the particle size distribution obtained through traditional classification processes corresponds approximately to that achieved after 20–30 minutes of modern ball milling treatment. To systematically investigate how particle size variations affect 'Fanhong' glaze coloration characteristics, simulation experiments were conducted using modern processing techniques with differently sized raw alum red fractions, chromaticity measurements (CIELAB values) were performed on resultant glazes using standardized spectrophotometry. As shown in Fig 12, the L * , a * , and b * values of the simulated 'Fanhong' glaze for 'Shengfanhong' powder at 20min, 30min, and 60min ball milling time are as follows: 35.318, 30.36, 42.234, and 35.388, 31.072, 43.908, and 37.448, 32.114, 39.78. Through particle size comparison, the granulation of traditionally classified 'Shengfanhong' powder is similar to that of modern ball-milled 'Shengfanhong' powder processed for 20-30 minutes. Chromaticity tests reveal that the coloration of ‘Fanhong’ glaze follows a normal distribution relative to particle size distribution. Under modern techniques, the optimal effect of 'Fanhong' glaze is achieved with 20-30 minutes of ball milling, as finer particle sizes result in darker hues. Therefore, ancient craftsmen selected 'Shengfanhong' powder from the first aluminum tray for making 'Fanhong' glaze. Table 1. Particle size table of 'Shengfanhong' powder on and through straw paper in the classification process (Unit: μm) Density of volume (%) 'Shengfanhong' powder on straw paper 'Shengfanhong' powder through straw paper Dv(10) 2.075 1.536 Dv(50) 7.413 5.906 Dv(90) 63.616 32.186 Table 2. Particle size of 'Shengfanhong' powder at the same calcination temperature under different ball milling times (Unit: μm) Density of volume (%) 20min 30min 60min Dv(10) 1.802 1.867 1.216 Dv(50) 7.647 6.788 5.032 Dv(90) 1210.173 714.537 939.056 Results From the perspective of "tacit knowledge" in the history of science and technology, this study investigates the traditional craftsmanship of 'Shengfanhong', integrating empirical practices from traditional ceramic techniques with scientific understanding. The experiments reveal that many critical steps in actual operations rely on the craftsmen's tacit knowledge. The control of calcination temperature exhibits distinct empirical characteristics. Ancient kiln workers had to repeatedly extract samples during the firing process and visually compare them with pre-selected 'Fanhong' glaze specimens, this rooted in perceptual skills and the intergenerational transmission of visual experience through master-apprentice traditions. In the heating process, iron vitriol undergoes dehydration at around 120°C, causing its color to shift from green to gray. As temperature further increases, the conversion of Fe²⁺ to Fe³⁺ and the decomposition of iron sulfates lead to a color transition in 'Shengfanhong' powder from gray to pale yellow, orange-red, and eventually deep red. The orange-red hue described in historical records corresponds to a calcination temperature of approximately 700°C under modern processes 22 . When craftsmen observed the powder turning slightly black during iron vitriol calcination and halted firing, the cooled product exhibited an orange-red color. This phenomenon results from the superposition effect of high-temperature thermal radiation and reflected spectra. In the rinsing process, the degree of soluble salt elimination is directly related to the color stability of 'Shengfanhong' powder. However, historical texts only vaguely mention "thorough washing" without specifying the rationale behind using cold water, hot water, or tea infusion, it means that craftsmen relied on observing changes in water turbidity to determine the endpoint. Based on physicochemical principles, cold water rinsing removes undissolved particles from the supernatant, hot water rinsing triggers the precipitation of Fe(OH)₃ as iron sulfate salts react with hot water, thereby eliminating sulfate residues from the powder, tea infusion rinsing leverages its high tannic acid (C 76 H 52 O 46 ) content to form a specific black iron-tannate complex (Fe(C 76 H 52 O 46 )) upon reacting with Fe 3+ . This visually manifests as the "black water" observed by craftsmen, serving as an indicator of incomplete impurity removal. In the classification process, the particle size of the powder directly affects the final coloration of 'Fanhong' glaze. Craftsmen traditionally relied solely on straw paper filtration and empirical judgment to select 'Shengfanhong' powder from the first aluminum tray. Experiments using a laser particle size analyzer characterized the particle size distribution of powders processed through traditional classification methods versus modern ball milling for varying durations. The results showed that the particle size of 'Shengfanhong' powder used by ancient craftsmen for glaze production closely matched that of modern ball-milled powder processed for 20-30 minutes, with an average particle size of approximately 7μm. Further modern process experiments revealed that the relationship between particle size and 'Fanhong' glaze coloration is not linear. The optimal glaze effect was achieved within the 20-30 minutes ball milling range, while prolonged milling resulted in darker hues. This validates the empirical selection of 'Shengfanhong' powder particle size by ancient craftsmen. Thus, the scientific foundation of 'Shengfanhong' production lies in the chemical nature of iron reactions and the quantification of particle size, while its practical efficacy relies on a tacit knowledge system. Together, these uncodifiable techniques form the deep knowledge structure of traditional technology—"knowing not only how but also why." Under modern processes, this study deciphers the tacit knowledge of 'Shengfanhong' by scientifically quantifying technical parameters across production stages. The synergy between scientific knowledge and empirical practice precise 'Shengfanhong' core mechanism by which ancient Chinese handicraft technologies achieved remarkable artistic excellence despite limited theoretical understanding. Declarations Acknowledgements This research work was partly supported by National Social Science Foundation of China (No. 19VJX143) and National Natural Science Foundation of China (No. 52462003). Author contributions Anjian Wu: Methodology, Conceptualization, Investigation, Experimentation, Data collection, Writing—original draft, Writing—review and editing. Degang Yi: Conceptualization, Methodology, Writing—review and editing, Funding acquisition, Software. Qijiang Li: Funding acquisition, Conceptualization, Methodology, Investigation, Supervision. Jinwei Li: Experimentation, Investigation, Data curation, Writing—review and editing. Jia Zhang: Investigation, Conceptualization, Validation, Visualization. Competing interests The authors declare no competing interests. Additional information Correspondence and requests for materials should be addressed to Degang Yi or Qijiang Li. References Li, J. History of Science in China (Volume on Ceramics) ; China Science Publishing & Media: Beijing, China, 1998. Qiu, g. Chinese handicrafts: Ceramic Firing Technology ; China Elephant Press: Zhengzhou, China, 2010. Zhang, F. The Science of Ancient Chinese Ceramics . 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Also discoverable on Platform About Our Team In Review Editorial Policies Advisory Board Help Center Resources Author Services Accessibility API Access RSS feed Manage Cookie Preferences © Research Square 2026 | ISSN 2693-5015 (online) Privacy Policy Terms of Service Do Not Sell My Personal Information {"props":{"pageProps":{"initialData":{"identity":"rs-6752421","acceptedTermsAndConditions":true,"allowDirectSubmit":false,"archivedVersions":[],"articleType":"Article","associatedPublications":[],"authors":[{"id":465793022,"identity":"a62c3b60-7c91-4d1a-b6a0-a72c7af49103","order_by":0,"name":"Anjian Wu","email":"","orcid":"","institution":"Donghua University","correspondingAuthor":false,"prefix":"","firstName":"Anjian","middleName":"","lastName":"Wu","suffix":""},{"id":465793023,"identity":"bfb18bef-384e-4c7a-a0d9-649e8579643e","order_by":1,"name":"Degang Yi","email":"data:image/png;base64,iVBORw0KGgoAAAANSUhEUgAAAZAAAAAyAQMAAABI0h/eAAAABlBMVEX///8AAABVwtN+AAAACXBIWXMAAA7EAAAOxAGVKw4bAAAA2UlEQVRIiWNgGAWjYDACZgYDMM3PwNxwgDQtkg2MxGphgGoxOMDYQKT648wbH36puWO3+fjBxsO8bXcY+Nu7E/BrOcxWbCxz7FnytjOJDUAtzxgkzpzdQEALj5m0BNvhZLMDYC2HGQwkcglqMf8t8e9wsnH/Q+K1mDF+bDtsZyBBrC2SQL9IM/YdTpC48bDh4Jxzh3kI+oXv/OGNH398O2zP3598+MObssNy/O29+LUoHADGJg8DQ2IDkMMEZPDgVQ4C8kCljD8YGOxBHBBjFIyCUTAKRgEGAABqMVJTAX/+8QAAAABJRU5ErkJggg==","orcid":"","institution":"Donghua University","correspondingAuthor":true,"prefix":"","firstName":"Degang","middleName":"","lastName":"Yi","suffix":""},{"id":465793024,"identity":"dc1bab89-1f37-460a-b290-28ab9a2a756b","order_by":2,"name":"Qijiang Li","email":"","orcid":"","institution":"Jingdezhen Ceramic University","correspondingAuthor":false,"prefix":"","firstName":"Qijiang","middleName":"","lastName":"Li","suffix":""},{"id":465793025,"identity":"1ceaec94-3747-4cb7-bfa1-2ee98c2ad201","order_by":3,"name":"Jia Zhang","email":"","orcid":"","institution":"Jingdezhen Ceramic University","correspondingAuthor":false,"prefix":"","firstName":"Jia","middleName":"","lastName":"Zhang","suffix":""},{"id":465793026,"identity":"92e4c223-0a58-4e30-930e-67d5df9207c1","order_by":4,"name":"Jinwei Li","email":"","orcid":"","institution":"Jingdezhen Ceramic University","correspondingAuthor":false,"prefix":"","firstName":"Jinwei","middleName":"","lastName":"Li","suffix":""}],"badges":[],"createdAt":"2025-05-26 15:53:28","currentVersionCode":1,"declarations":"","doi":"10.21203/rs.3.rs-6752421/v1","doiUrl":"https://doi.org/10.21203/rs.3.rs-6752421/v1","draftVersion":[],"editorialEvents":[{"content":"https://doi.org/10.1038/s40494-025-02226-4","type":"published","date":"2025-12-10T15:58:00+00:00"}],"editorialNote":"","failedWorkflow":false,"files":[{"id":83939090,"identity":"75923dde-c4a5-401b-bb7e-b4580cee260d","added_by":"auto","created_at":"2025-06-04 17:29:34","extension":"jpg","order_by":1,"title":"Figure 1","display":"","copyAsset":false,"role":"figure","size":4882870,"visible":true,"origin":"","legend":"\u003cp\u003ePhotos of ancient Chinese iron red from different periods. Samples\u003csup\u003e22\u003c/sup\u003e (\u003cstrong\u003ea\u003c/strong\u003e,\u003cstrong\u003eb\u003c/strong\u003e) are from the Yuan Dynasty period (1271–1368), samples (\u003cstrong\u003ec\u003c/strong\u003e–\u003cstrong\u003ee\u003c/strong\u003e) are from Ming Dynasty period (1368–1644), sample (\u003cstrong\u003ec\u003c/strong\u003e) is from the mid of Ming Dynasty period, samples (\u003cstrong\u003ed\u003c/strong\u003e,\u003cstrong\u003ee\u003c/strong\u003e) are from the terminal of Ming Dynasty period, samples (\u003cstrong\u003ef\u003c/strong\u003e–\u003cstrong\u003eh\u003c/strong\u003e) are from Qing Dynasty period (1644–1911), sample (\u003cstrong\u003ef\u003c/strong\u003e) is from the mid of Qing Dynasty period, and samples (\u003cstrong\u003eg\u003c/strong\u003e,\u003cstrong\u003eh\u003c/strong\u003e) are from the terminal of Qing Dynasty period.\u003c/p\u003e","description":"","filename":"Fig1..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/714e9550137aa99aac805b37.jpg"},{"id":83938619,"identity":"496e9cef-b8e4-4f2a-9c86-19e904c41d86","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"jpg","order_by":2,"title":"Figure 2","display":"","copyAsset":false,"role":"figure","size":315859,"visible":true,"origin":"","legend":"\u003cp\u003e'fanhong' glaze sample made from unground 'shengfanhong' powder\u003c/p\u003e","description":"","filename":"Fig2..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/35be6dfbda406e596bce5161.jpg"},{"id":83938621,"identity":"f6a7f6e7-6ab2-43ab-968b-031ce152c0cd","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"jpg","order_by":3,"title":"Figure 3","display":"","copyAsset":false,"role":"figure","size":59690,"visible":true,"origin":"","legend":"\u003cp\u003ePretreatment process of iron vitriol ((a). Raw material of iron vitriol (b). Grinding iron vitriol after heating at 120℃ (c). The ground Powder)\u003c/p\u003e","description":"","filename":"Fig3..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/e3f43def2bce8b8ec96f833b.jpg"},{"id":83938618,"identity":"caffee19-0b85-4c63-a6f1-c1c3f84488b7","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"jpg","order_by":4,"title":"Figure 4","display":"","copyAsset":false,"role":"figure","size":65540,"visible":true,"origin":"","legend":"\u003cp\u003eThe calcination process of 'Shengfanhong' (Color changes observed during the experimental process: (a) Iron vitriol at initial heating stage; (b) Iron vitriol heated to blackened state; (c) Transition to reddish-orange after cooling.)\u003c/p\u003e","description":"","filename":"Fig4..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/b0d8f40c475d5346bd6fe07c.jpg"},{"id":83939091,"identity":"d12ae029-0e69-4f08-8faf-c35ab9e25a96","added_by":"auto","created_at":"2025-06-04 17:29:34","extension":"jpg","order_by":5,"title":"Figure 5","display":"","copyAsset":false,"role":"figure","size":106606,"visible":true,"origin":"","legend":"\u003cp\u003eRinsing process of 'Shengfanhong' ((a). Rinsing 'Shengfanhong', (b). Mixing 'Shengfanhong' into a slurry, (c). Tea infusion, (d). The untreated alum water turns black after being added to the tea water)\u003c/p\u003e","description":"","filename":"Fig5..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/7a0326d61596be6f859c13bc.jpg"},{"id":83939097,"identity":"720b3cf7-a372-4dd2-80a6-ebd651142db7","added_by":"auto","created_at":"2025-06-04 17:29:34","extension":"jpg","order_by":6,"title":"Figure 6","display":"","copyAsset":false,"role":"figure","size":345256,"visible":true,"origin":"","legend":"\u003cp\u003eClassification process of 'Shengfanhong' ((a). Schematic diagram of the classification process of 'Shengfanhong'; (b) The actual operation diagram of the classification process for 'Shengfanhong'.)\u003c/p\u003e","description":"","filename":"Fig6..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/873eb01308edeaa8963e8651.jpg"},{"id":83938624,"identity":"5fed66e0-0575-4260-9872-1b6585495607","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"jpg","order_by":7,"title":"Figure 7","display":"","copyAsset":false,"role":"figure","size":30443,"visible":true,"origin":"","legend":"\u003cp\u003eDSC-TG of iron vitriol powder\u003csup\u003e22\u003c/sup\u003e\u003c/p\u003e","description":"","filename":"Fig7..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/79c7d4fd3a2420ceb241dbe7.jpg"},{"id":83939093,"identity":"580d7225-bb88-4afd-a624-e8a4639b0d2b","added_by":"auto","created_at":"2025-06-04 17:29:34","extension":"jpg","order_by":8,"title":"Figure 8","display":"","copyAsset":false,"role":"figure","size":66663,"visible":true,"origin":"","legend":"\u003cp\u003eImages of calcined 'Shengfanhong' powder at different temperatures\u003csup\u003e22\u003c/sup\u003e ((a). 550°C); (b).600°C; (c).650°C; (d).700°C; (e).750°C; (f).800°C; (g).850°C; (h).900°C）\u003c/p\u003e","description":"","filename":"Fig8..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/a95d0a1ef2cd07706bc1fa57.jpg"},{"id":83939337,"identity":"219d35f9-9980-45da-8334-a59655382d56","added_by":"auto","created_at":"2025-06-04 17:37:34","extension":"png","order_by":9,"title":"Figure 9","display":"","copyAsset":false,"role":"figure","size":219390,"visible":true,"origin":"","legend":"\u003cp\u003eSee image above for figure legend\u003c/p\u003e","description":"","filename":"9.png","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/13ae4a59f6e54c418aad34ab.png"},{"id":83939340,"identity":"41c438c7-661e-4954-bc41-a834e3b86f90","added_by":"auto","created_at":"2025-06-04 17:37:34","extension":"jpg","order_by":10,"title":"Figure 10","display":"","copyAsset":false,"role":"figure","size":168076,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution of 'Shengfanhong' powder on and through the straw paper in the classification process ((a). 'Shengfanhong' powder on the straw paper; (b) 'Shengfanhong' powder through the straw paper)\u003c/p\u003e","description":"","filename":"Fig10..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/6b3971bcc532c64d218f50c2.jpg"},{"id":83938633,"identity":"513bd429-44d0-40ce-9f48-085d692bfbeb","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"jpg","order_by":11,"title":"Figure 11","display":"","copyAsset":false,"role":"figure","size":232512,"visible":true,"origin":"","legend":"\u003cp\u003eParticle size distribution of 'Shengfanhong' powder at the same calcination temperature under different ball milling times ((a). 20min; (b).30min; (c).60min）\u003c/p\u003e","description":"","filename":"Fig11..jpg","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/890affa5627851deec6bd544.jpg"},{"id":83938631,"identity":"4f66b19d-137c-4513-a65d-ef0f73591aec","added_by":"auto","created_at":"2025-06-04 17:21:34","extension":"png","order_by":12,"title":"Figure 12","display":"","copyAsset":false,"role":"figure","size":259778,"visible":true,"origin":"","legend":"\u003cp\u003eThe chromaticity of ‘Fanhong’ pigment at different ball milling times for the same calcination temperature of 'Shengfanhong' ((a). Ball milling for 20 minutes; (b) Ball milling for 30 minutes; (c) Ball milling for 60 minutes)\u003c/p\u003e","description":"","filename":"12.png","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/0cee2e46d49e05331a9c377a.png"},{"id":98244913,"identity":"14763b5a-58f7-4d06-a3ee-6f1502e2e995","added_by":"auto","created_at":"2025-12-15 16:16:00","extension":"pdf","order_by":0,"title":"","display":"","copyAsset":false,"role":"manuscript-pdf","size":9882930,"visible":true,"origin":"","legend":"","description":"","filename":"manuscript.pdf","url":"https://assets-eu.researchsquare.com/files/rs-6752421/v1/f9f2f32d-414c-4a31-9e6b-ac554e29aed8.pdf"}],"financialInterests":"No competing interests reported.","formattedTitle":"Research on Traditional Craftsmanship of ‘Shengfanhong’","fulltext":[{"header":"Introduction","content":"\u003cp\u003e\u0026apos;Fanhong\u0026apos; is an overglaze pigment utilizing Fe₂O₃ as a chromophore, which can also be fired in an oxidizing atmosphere to produce monochromatic glaze. Its origins trace back to the Song Dynasty\u0026apos;s red-and-green polychrome wares, serving as a precursor to later multi-colored overglaze techniques. The term \u0026apos;Fanhong\u0026apos; first appeared in the \u003cem\u003eDaMingHuiDian\u003c/em\u003e: \u0026quot;In the second year of Jiajing (1523), Jiangxi kilns were ordered to replace underglaze copper red with deep iron oxide red in porcelain production.\u0026quot; In the mid-Ming Dynasty during the Chenghua period (1465\u0026ndash;1487), the combination of underglaze blue and white with overglaze polychrome led to the production of uniquely styled \u0026apos;doucai\u0026apos; porcelain, which, during this period, were known for their extremely thin body and rich colors, described as \u0026apos;exquisite quality and vibrant colors\u0026apos;\u003csup\u003e1,2\u003c/sup\u003e. In the Jiajing period of the Ming Dynasty (1522\u0026ndash;1566), the Imperial Porcelain Factory in Jingdezhen began to use iron red glaze in place of copper red glaze. By the Kangxi period of the Qing Dynasty (1662\u0026ndash;1722), \u0026apos;Fanhong\u0026apos; evolved into a brilliantly saturated pigment, predominantly used in \u0026apos;wucai\u0026apos; (five-color) and \u0026apos;doucai\u0026apos; decorative schemes. However, after the Jiaqing period of the Qing Dynasty (1796\u0026ndash;1820), the quality of the iron red overglaze color significantly declined, with only a slight improvement during the Guangxu (1875\u0026ndash;1908) Emperor\u0026rsquo;s reign. The production techniques of \u0026apos;Shengfanhong\u0026apos; are documented in \u003cem\u003eThe Science of Ancient Chinese Ceramics\u003c/em\u003e\u003csup\u003e3\u003c/sup\u003e and \u003cem\u003eCeramic Decorative Materials\u003c/em\u003e\u003csup\u003e4\u003c/sup\u003e. The preparation of \u0026apos;Shengfanhong\u0026apos; involves sequential steps: dehydration of iron vitriol (FeSO₄\u0026middot;7H₂O), crushing and sieving, calcination, acid-leaching, and drying. The resultant material is then ground with water, purified through sedimentation, mixed with lead powder and ox glue, and finally fired twice to produce \u0026apos;Fanhong\u0026apos; porcelains (Fig 1).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;The traditional production process of \u0026apos;Shengfanhong\u0026apos; involves three key steps: calcination, acid-leaching, and particle size classification of iron vitriol. During calcination, the crystal size and phase composition of iron vitriol undergo significant changes, directly influencing the chromatic properties of the final \u0026apos;fanhong\u0026apos; pigment. Hiroshi Asaoka et al\u003csup\u003e5\u003c/sup\u003e. synthesized iron oxide powders by calcining FeSO₄\u0026middot;7H₂O, reporting Fe₂O₃ crystal sizes of 50 nm at 650\u0026deg;C and 100 nm at 770\u0026deg;C, with reduced calcination temperatures enhancing chromaticity. Hirofumi Inada et al\u003csup\u003e6\u003c/sup\u003e. characterized a traditional red pigment via X-ray diffraction (XRD), confirming the dominance of \u0026alpha;-Fe₂O₃ phase at 700\u0026deg;C, while scanning electron microscopy (SEM) revealed \u0026alpha;-Fe₂O₃ crystal sizes ranging from 30 to 100 nm. S. Kajihara et al\u003csup\u003e7\u003c/sup\u003e. observed abundant sulfur-containing microcrystals in FeSO₄\u0026middot;7H₂O at 550\u0026deg;C, which disappeared upon heating to 650\u0026deg;C, yielding pure Fe₂O₃. P.K. Gallagher et al\u003csup\u003e8\u003c/sup\u003e. identified Fe₂O(SO₄)₂ as an intermediate during thermal decomposition of FeSO₄\u0026middot;7H₂O. R. Zboril et al\u003csup\u003e9-11\u003c/sup\u003e. further demonstrated that FeSO₄\u0026middot;7H₂O transforms into various Fe₂O₃ polymorphs during heating, with \u0026alpha;-Fe₂O₃ stabilized at 700\u0026deg;C. The classification process of \u0026apos;Shengfanhong\u0026apos; essentially involves sorting powder materials into different categories based on particle size distribution. In the study of factors influencing pigment coloration, particle size has been identified as a critical determinant\u003csup\u003e12-13\u003c/sup\u003e. The coarse particle size of \u0026apos;Shengfanhong\u0026apos; powder leads to a highly rough surface in the resulting glaze. After firing, pronounced crystal precipitation occurs, which significantly affects the coloration of \u0026apos;fanhong\u0026apos; porcelain (Fig 2). Scholars have employed high-energy ball milling techniques\u003csup\u003e14\u003c/sup\u003e to analyze the refractive index, reflectance, and chromaticity of mineral pigments with varying particle sizes. The results demonstrate that mineral pigments exhibit distinct coloration at different particle sizes, and the influence of particle size on coloration varies significantly depending on the material composition\u003csup\u003e15-16\u003c/sup\u003e. The crystal size of powdered pigments primarily governs the interaction between light and mineral pigment particles, with this effect exhibiting nonlinear characteristics\u003csup\u003e17\u003c/sup\u003e. Chen\u003csup\u003e18\u003c/sup\u003e conducted a study on the grinding stability of iron oxide red (\u0026alpha;-Fe₂O₃), revealing that mechanical force activation occurs during wet grinding. The relationship between ball milling time and particle size change is nonlinear\u0026mdash;the particle diameter initially decreases but subsequently increases with prolonged grinding . This enlargement of particle size shifts the pigment\u0026apos;s hue toward yellow-blue tones while reducing both redness and brightness\u003csup\u003e19-21\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003eThe coloration mechanism of \u0026apos;fanhong\u0026apos; porcelain constitutes a systematic issue, where the traditional craftsmanship of \u0026apos;shengfanhong\u0026apos; critically influences its chromatic performance. Currently, academic research lacks a comprehensive scientific explanation for the traditional craftsmanship of \u0026apos;shengfanhong\u0026apos;. The theory of tacit knowledge reveals the intangible dimensions of human expertise that are difficult to articulate\u0026mdash;a phenomenon equally present in the traditional craftsmanship of \u0026apos;shengfanhong\u0026apos;. Based on this, this study explains the scientific mechanism of the traditional craftsmanship of \u0026apos;shengfanhong\u0026apos; through experimental archaeology and scientific testing methods, revealing the exquisite porcelain-making techniques of ancient people and scientifically quantifying this process.\u003c/p\u003e"},{"header":"The traditional preparation craftsmanship of ‘shengfanhong’ ","content":"\u003cp\u003e\u003cstrong\u003eTest Methods\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eDifferential Scanning Calorimetry-Thermogravimetric Analysis (DSC-TG)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe raw material for the differential scanning calorimetric-thermogravimetric analysis was iron vitriol, and the thermal analyzer was supplied by Netzsch Instruments Manufacturing Co., Ltd. in Selb, Germany, model STA449C, with a resolution of 0.1 µg, and a temperature range from room temperature to 1650℃. The mass of the experimental sample was 9.91 mg, with a heating rate of 10℃/min in an Ar atmosphere. The testing temperature range was from room temperature to 900℃measuring the mass changes of iron vitriol and the temperature points of endothermic and exothermic reactions during heating.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eX-ray Diffraction (XRD)\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe samples for XRD testing were iron vitriol powders calcined at different temperatures. The XRD was from Bruker AXS GmbH in Karlsruhe, Germany, model D8 Advance, with a Cu target and a power of 6.5kW; the scanning step length was 0.01\u003cem\u003e◦\u0026nbsp;\u003c/em\u003eand the scanning speed was 0.05 s per step, testing the mineral composition of iron vitriol during heating.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eColorimetric analysis\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe samples for chromaticity analysis were 'Fanhong' pigment made from 'Shengfanhong'powder of different particle sizes, and the chromaticity meter used was a NF-333 portable spectrophotometric chroma meter with a wavelength range of 400–700 nm. All measurements were made under standard 10\u003cem\u003e◦\u0026nbsp;\u003c/em\u003eobservation conditions and D65 illuminant to test the relevant chromaticity parameters of different iron red. L* represents the brightness of the object: 0–100, indicating from black to white; a* represents the red green of the object: a positive value indicates red, and a negative value indicates green; b* represents the yellow blue of the object: a positive value indicates yellow, and a negative value indicates blue.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eParticle size testing\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe vertical planetary ball mill is used for ball milling 'Shengfanhong' powder, and comes from Changsha Deke Instrument Equipment Co., Ltd., with the model of DECO-PBM-V-0.4L. The experiment was configured with a mass ratio of powder: grinding balls: water = 1: 1: 1. Control groups were established with ball milling durations of: 20 minutes, 30 minutes, and 60 minutes, maintaining a constant rotational speed of 400 revolutions per minute. The laser particle size analyzer is used to test the particle size of 'Shengfanhong' powder, and from Malvern Instruments Limited in the UK, model Mastersizer2000, with a particle size range of 0.02-2000 microns and a scanning speed of 1000 times per second.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003ePretreatment process of iron vitriol\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eIn this experiment, industrial iron vitriol (FeSO\u003csub\u003e4\u003c/sub\u003e·7H\u003csub\u003e2\u003c/sub\u003eO) was used as the raw material, and the supplier of industrial iron vitriol was WuHan Carnoss Co., Ltd. in Wuhan, China, this kind of industrial iron vitriol’s purity was 99%. The treatment process of iron vitriol involves three key steps.\u0026nbsp;First, to address the difficulty in physical grinding caused by the strong hygroscopicity of the raw material, a gradient heating pretreatment method was adopted: dehydration was performed within the temperature range of room temperature to 120°C. Through thermal decomposition (FeSO\u003csub\u003e4\u003c/sub\u003e·7H\u003csub\u003e2\u003c/sub\u003eO → FeSO\u003csub\u003e4\u003c/sub\u003e·nH\u003csub\u003e2\u003c/sub\u003eO + (7-n)H\u003csub\u003e2\u003c/sub\u003eO↑\u003csup\u003e22\u003c/sup\u003e), crystal water was gradually released, accompanied by distinct phase transformation characteristics—the color of the crystals transitioned from the initial pale green (characteristic of Fe\u003csup\u003e2+\u003c/sup\u003e hydrated ions) to grayish-white. Second, to mitigate the agglomeration and caking of the dehydrated material, grinding was conducted using an agate mortar, and particle size control was achieved by sieving through a standard 250μm mesh. Finally, considering the susceptibility of FeSO\u003csub\u003e4\u003c/sub\u003e to oxidation and deterioration in air, the processed anhydrous ferrous sulfate powder was stored in a vacuum drying oven (Fig 3).\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eCalcination process of iron vitriol\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAccording to the records in references\u003csup\u003e3-4\u0026nbsp;\u003c/sup\u003eregarding the calcination process of iron vitriol, this step adopts dynamic calcination to prepare 'Shengfanhong'. The specific operational procedure is as follows: The pretreated dehydrated ferrous sulfate (FeSO₄) is placed in an iron pot and subjected to gradient pyrolysis using an open flame. During calcination, real-time visual colorimetric monitoring is required to observe the phase transition characteristics of the material, corresponding to the historical description that \" Using an open flame to calcine iron vitriol until it turns slightly black, then transforms into orange-red upon cooling\u003cstrong\u003e.\u0026nbsp;\u003c/strong\u003e\" The color evolution exhibits distinct stages: the initial grayish-white material gradually turns yellowish-brown during heating, when the color becomes slightly blackened, heating is terminated, upon cooling, it transforms into a reddish-orange hue (Fig 4). This transformation marks the completion of standard 'Shengfanhong' production. Comparative studies with modern calcination processes indicate that this state of 'Shengfanhong' achieves equivalent results to those obtained through contemporary 700°C calcination techniques.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRinsing process of ‘Shengfanhong’\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe prepared 'Shengfanhong' powder is transferred into a beaker, and room-temperature clean water is added while stirring rapidly and uniformly with a wooden stick. Under agitation, the mixture in the beaker gradually clarifies, at which point the undissolved particles in the supernatant are removed by decantation. The addition of cold water is then stopped, and hot water is used for eight or nine additional washings until all alum liquor is completely eliminated. In ancient practices, tea infusion was typically employed to test whether the alum liquor had been fully removed. As shown in Fig 5, if alum liquor remains, the liquid in the cup turns black; conversely, if the liquid's color remains unchanged, it indicates complete removal of alum liquor, marking the completion of the rinsing process and confirming that the 'Shengfanhong' has achieved the required purity. Before classifying the 'Shengfanhong', it must undergo thorough grinding. After grinding, an appropriate amount of clean water is added to the 'Shengfanhong' to form a thin slurry consistency.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eClassification process of ‘Shengfanhong’\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe classification process applied to rinsed 'Shengfanhong' powder primarily aims to achieve standardized particle size control through physical classification methods, thereby meeting specific granularity requirements for ancient 'Fanhong' pigment preparation. In this classification process, two aluminum trays are first aligned linearly with the container (beaker) holding 'Shengfanhong', connected by an absorbent medium (such as straw paper) to create a fluid transfer channel. This setup allows the suspended slurry in the beaker to flow along the medium into the first aluminum tray. During this procedure, particle sedimentation occurs in the first aluminum tray while supernatant moisture continues migrating via capillary action through the straw paper into the second aluminum tray. After sufficient settling time, the slurry sedimented at the bottom of the first aluminum tray is selected as the raw material for ancient 'Fanhong' due to its optimal particle size distribution characteristics. This sediment undergoes secondary rinsing to eliminate residual soluble impurities, after sun drying treatment, the entire classification process is completed (Fig 6).\u003c/p\u003e"},{"header":"Discussion","content":"\u003cp\u003e\u0026apos;Fanhong\u0026apos; constitutes a vital component of overglaze ceramic decoration, the manuscript roughly restores the traditional craftsmanship of producing \u0026apos;Shengfanhong\u0026apos;, interpreting the scientific principles of the preparation process of \u0026apos;Shengfanhong\u0026apos; through scientific restoration and related testing.\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eHeating process of iron vitriol\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe physicochemical reactions during iron vitriol calcination were characterized by DSC-TG analysis. As shown in Fig 7, four distinct weight loss stages (I-IV) were observed in the TG curve\u003csup\u003e23\u003c/sup\u003e, with respective mass losses of 17.66%, 20.74%, 8.88%, and 25.23%. The DSC curve revealed three endothermic peaks and one exothermic peak during thermal treatment: The temperatures at which the endothermic peaks (①,\u0026nbsp;②,\u0026nbsp;④) appear are 75.6℃, 122.7℃, 661.7℃, along with one exothermic peak (③) at 567.6\u0026deg;C. Based on these findings, the heating process of green vitriol can be interpreted as follows:\u003c/p\u003e\n\u003cp\u003e1. During the pretreatment process of iron vitriol, dehydration treatment is carried out within the temperature range of room temperature to approximately 120℃. FeSO₄\u0026middot;7H₂O itself appears green, which is due to the absorption of specific wavelengths of light by the d-d electron transition of ferrous ions (Fe\u003csup\u003e2+\u003c/sup\u003e). The appearance of the endothermic peak\u0026nbsp;①\u0026nbsp;and\u0026nbsp;②\u0026nbsp;correspond precisely to the temperature node where FeSO₄\u0026middot;7H₂O undergoes two dehydration processes, while I and II correspond to two distinct dehydration stages of FeSO₄\u0026middot;7H₂O. Through the thermal decomposition reaction\u0026nbsp;（FeSO4\u0026middot;7H2O \u0026rarr; FeSO4\u0026middot;nH2O + (7-n)H2O\u0026uarr;\u003csup\u003e22\u003c/sup\u003e）facilitates gradual liberation of crystalline water molecules, accompanied by distinct phase transformation characteristics--the color of the crystal manifested by a progressive chromatic transition from initial pale green coloration (characteristic of hydrated Fe\u003csup\u003e\u0026sup2;+\u003c/sup\u003e ions) to grayish-white appearance.\u003c/p\u003e\n\u003cp\u003e2. In the calcination process of iron vitriol, open-flame heating is initiated from room temperature. during which process III corresponds to the thermal conversion of FeSO₄ into Fe₂(SO₄)₃, with an exothermic peak ③ observed at a critical temperature node of 567\u0026deg;C where FeSO₄ reacts with O₂ forming intermediate product Fe₂O(SO₄)₂, and process IV represents subsequent decomposition into Fe₂(SO₄)₃, Fe₂O₃ and SO₃\u003csup\u003e8\u003c/sup\u003e. The temperature node of the exothermic peak\u0026nbsp;④\u0026nbsp;is 661℃, at which both Fe₂(SO₄)₃ and Fe₂O(SO₄)₂ undergo desulfurization to upon\u0026nbsp;\u0026alpha;-Fe₂O₃. According to the principle of oxidation-reduction reaction, Fe\u003csup\u003e2+\u003c/sup\u003e is oxidized to trivalent iron ions (Fe\u003csup\u003e3+\u003c/sup\u003e), According to redox principles, oxidation of Fe\u0026sup2;⁺ to trivalent iron ions (Fe\u003csup\u003e3+\u003c/sup\u003e) occurs concomitantly with sulfate ion decomposition (SO₄\u003csup\u003e2-\u003c/sup\u003e). This valence transition alters electronic configurations and associated absorption spectra, resulting in characteristic orange-red coloration upon formation of \u0026alpha;-Fe₂O₃ particles. When the calcination temperature exceeds 700\u0026deg;C, progressive chromatic shifts occur toward jujube-red and eventually black hues (Fig 8).\u003c/p\u003e\n\u003cp\u003eThis provides a reasonable physicochemical explanation for key processes in iron vitriol\u0026apos;s thermal treatment: dehydration, oxidation of divalent iron ions to trivalent iron ions, and decomposition reactions of sulfate ions, thereby scientifically validating how heating transforms iron vitriol into red pigment. The empirical observation where craftsmen cease firing upon watching slight blackening, later cooling into orange-red, results from superimposed thermal radiation and reflection spectra effects during high-temperature processing. At precisely controlled calcination temperatures around 700\u0026deg;C where \u0026alpha;-Fe₂O₃ has been completely formed (Fig 9), its hexagonal close-packed crystal structure demonstrates maximum reflectance in red spectral regions\u003csup\u003e25\u003c/sup\u003e. At this temperature, thermal radiation occurs according to blackbody radiation theory where high-temperature objects emit electromagnetic waves while simultaneously reflecting external light\u003csup\u003e26\u003c/sup\u003e. Under high temperatures, thermal radiation intensity may surpass reflected light intensity and superimpose onto reflection spectra, causing slight blackening in appearance. After cooling, the thermal radiation of the material disappears, and the reflection spectrum dominates the coloration. At this point, the strong reflection of red light by \u0026alpha;-Fe₂O₃ appears, and the color returns to the original red color of the material\u003csup\u003e27\u003c/sup\u003e. To further verify the influence of surface thermal radiation of the powder on the coloration, samples were divided into two cooling methods: one portion was cooled in ambient air at 20\u0026deg;C, while another portion was cooled in water maintained at the same room temperature. As established principles dictate, water cooling achieves significantly faster heat dissipation than air cooling at identical temperatures\u0026mdash;a phenomenon experimentally confirmed by observing more rapid chromatic transition from black to red in water-quenched powder compared to air-cooled powder. In addition, this process is reversible, and \u0026alpha;-Fe₂O₃ does not undergo crystal transformation at 700\u0026deg;C\u003csup\u003e27\u003c/sup\u003e, these results conclusively demonstrate that high-temperature darkening originates from transient superposition effects between thermal radiation and reflection spectra\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eRinsing and classification process of \u0026lsquo;Shengfanhong\u0026rsquo;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003e\u0026nbsp; (1) In the rinsing process for \u0026apos;Shengfanhong\u0026apos; preparation, calcined iron vitriol undergoes sequential rinsing with cold and hot water respectively, the former removes undissolved particles from supernatant while the latter eliminates residual sulfate groups from powder particles. When treated with hot water, Fe\u003csub\u003e2\u0026nbsp;\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u003c/sub\u003e reacts with water and hydrolyzes to form a reddish brown colloidal precipitate of Fe(OH)\u003csub\u003e3\u003c/sub\u003e and H₂SO₄. The chemical equation is: Fe\u003csub\u003e2\u003c/sub\u003e(SO\u003csub\u003e4\u003c/sub\u003e)\u003csub\u003e3\u0026nbsp;\u003c/sub\u003e+ 6H\u003csub\u003e2\u003c/sub\u003eO \u0026rarr; 2Fe(OH)\u003csub\u003e3\u003c/sub\u003e + 3H\u003csub\u003e2\u003c/sub\u003eSO\u003csub\u003e4\u003c/sub\u003e, and multiple rinses remove the colloidal precipitate of Fe(OH)\u003csub\u003e3\u003c/sub\u003e and H₂SO₄. Tea infusion was employed to verify complete removal of alum liquor residues, in the field of analytical chemistry, a colorimetric detection method can be established through the chromogenic reactions between tannic acid and metal ions. When using tea infusion as an indicator system to verify whether alum water remains residual iron species (mainly containing Fe\u003csup\u003e2+\u003c/sup\u003e), if there are uncleaned ferrous salts in the system, they are easily dissolved and oxidized to Fe\u003csup\u003e3+\u003c/sup\u003e in the aqueous phase. At this stage, tannic acid (C\u003csub\u003e76\u003c/sub\u003eH\u003csub\u003e52\u003c/sub\u003eO\u003csub\u003e46\u003c/sub\u003e) abundantly present in tea solution undergoes specific complexation with Fe\u003csup\u003e3+\u003c/sup\u003e, forming black-colored iron tannate (Fe(C\u003csub\u003e76\u003c/sub\u003eH\u003csub\u003e52\u003c/sub\u003eO\u003csub\u003e46\u003c/sub\u003e)) through coordination chemistry principles，it is a classic example of metal-organic ligand chromogenic reaction. Experimental observations demonstrate that solution coloration transitions from amber to deep ink-black within 30 seconds, with chromatic intensity positively correlating to Fe\u003csup\u003e3+\u003c/sup\u003e concentration as governed by Lambert-Beer\u0026apos;s law fundamentals for colorimetric detection\u003csup\u003e24\u003c/sup\u003e. Therefore, the use of tea infusion is used for the inspection of trivalent iron salts, and the color change of tea infusion is used to characterize whether the impurities in alum water have been removed completely\u003csup\u003e24\u003c/sup\u003e.\u003c/p\u003e\n\u003cp\u003e(2) In the classification process for \u0026apos;Shengfanhong\u0026apos; preparation, its core mechanism involves hydrodynamic sorting of raw alum red powder particles. through a multi-stage gradient sieving system, the primary grading phase achieves separation of coarse particle fractions target particle-size-range powder forms a dominant enrichment zone within the first aluminum tray. The first aluminum tray not only collects sediment with optimal particle size distribution but also facilitates secondary impurity removal as supernatant liquid flows into the second aluminum tray during sedimentation. Accordingly, we conducted particle size analysis on straw paper-filtered \u0026nbsp;\u0026apos;Shengfanhong\u0026apos; powder samples and post-filtration fractions obtained through straw paper sieving (as quantitatively characterized in Table 1 and Fig10). Parallel experiments employed modern ball milling technology to systematically evaluate time-dependent particle size distributions across different processing durations, and conducted particle size tests on the powders (as shown in Table 2 and Fig 11). Comparative analysis revealed that the particle size distribution obtained through traditional classification processes corresponds approximately to that achieved after 20\u0026ndash;30 minutes of modern ball milling treatment. To systematically investigate how particle size variations affect \u0026apos;Fanhong\u0026apos; glaze coloration characteristics, simulation experiments were conducted using modern processing techniques with differently sized raw alum red fractions, chromaticity measurements (CIELAB values) were performed on resultant glazes using standardized spectrophotometry. As shown in Fig 12, the L\u003csup\u003e*\u003c/sup\u003e, a\u003csup\u003e*\u003c/sup\u003e, and b\u003csup\u003e*\u003c/sup\u003e values of the simulated \u0026apos;Fanhong\u0026apos; glaze for \u0026apos;Shengfanhong\u0026apos; powder at 20min, 30min, and 60min ball milling time are as follows: 35.318, 30.36, 42.234, and 35.388, 31.072, 43.908, and 37.448, 32.114, 39.78. Through particle size comparison, the granulation of traditionally classified \u0026apos;Shengfanhong\u0026apos; powder is similar to that of modern ball-milled \u0026nbsp;\u0026apos;Shengfanhong\u0026apos; powder processed for 20-30 minutes. Chromaticity tests reveal that the coloration of \u0026lsquo;Fanhong\u0026rsquo; glaze follows a normal distribution relative to particle size distribution. Under modern techniques, the optimal effect of \u0026apos;Fanhong\u0026apos; glaze is achieved with 20-30 minutes of ball milling, as finer particle sizes result in darker hues. Therefore, ancient craftsmen selected \u0026apos;Shengfanhong\u0026apos; powder from the first aluminum tray for making \u0026apos;Fanhong\u0026apos; glaze. \u0026nbsp;\u003c/p\u003e\n\u003cp\u003e\u003cstrong\u003eTable 1. Particle size table of \u0026apos;Shengfanhong\u0026apos; powder on and through straw paper in the classification process (Unit: \u0026mu;m)\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003eDensity of volume (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003e\u0026apos;Shengfanhong\u0026apos;\u0026nbsp;powder on straw paper\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 214px;\"\u003e\n \u003cp\u003e\u0026apos;Shengfanhong\u0026apos;\u0026nbsp;powder through straw paper\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003eDv(10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003e2.075\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 214px;\"\u003e\n \u003cp\u003e1.536\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003eDv(50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003e7.413\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 214px;\"\u003e\n \u003cp\u003e5.906\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 151px;\"\u003e\n \u003cp\u003eDv(90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003e63.616\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 214px;\"\u003e\n \u003cp\u003e32.186\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e\n\u003cp\u003e\u003cstrong\u003e\u0026nbsp;\u003c/strong\u003e\u003cstrong\u003eTable 2. Particle size of \u0026apos;Shengfanhong\u0026apos; powder at the same calcination temperature under different ball milling times (Unit: \u0026mu;m)\u003c/strong\u003e\u003c/p\u003e\n\u003ctable border=\"1\" cellspacing=\"0\" cellpadding=\"0\"\u003e\n \u003ctbody\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003eDensity of volume (%)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e20min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e30min\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e60min\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003eDv(10)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e1.802\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e1.867\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e1.216\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003eDv(50)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e7.647\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e6.788\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e5.032\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003ctr\u003e\n \u003ctd valign=\"top\" style=\"width: 189px;\"\u003e\n \u003cp\u003eDv(90)\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 88px;\"\u003e\n \u003cp\u003e1210.173\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e714.537\u003c/p\u003e\n \u003c/td\u003e\n \u003ctd valign=\"top\" style=\"width: 138px;\"\u003e\n \u003cp\u003e939.056\u003c/p\u003e\n \u003c/td\u003e\n \u003c/tr\u003e\n \u003c/tbody\u003e\n\u003c/table\u003e"},{"header":"Results","content":"\u003cp\u003eFrom the perspective of \u0026quot;tacit knowledge\u0026quot; in the history of science and technology, this study investigates the traditional craftsmanship of \u0026apos;Shengfanhong\u0026apos;, integrating empirical practices from traditional ceramic techniques with scientific understanding. The experiments reveal that many critical steps in actual operations rely on the craftsmen\u0026apos;s tacit knowledge.\u003c/p\u003e\n\u003col\u003e\n \u003cli\u003eThe control of calcination temperature exhibits distinct empirical characteristics. Ancient kiln workers had to repeatedly extract samples during the firing process and visually compare them with pre-selected \u0026apos;Fanhong\u0026apos; glaze specimens, this rooted in perceptual skills and the intergenerational transmission of visual experience through master-apprentice traditions. In the heating process, iron vitriol undergoes dehydration at around 120\u0026deg;C, causing its color to shift from green to gray. As temperature further increases, the conversion of Fe\u0026sup2;⁺ to Fe\u0026sup3;⁺ and the decomposition of iron sulfates lead to a color transition in \u0026apos;Shengfanhong\u0026apos; powder from gray to pale yellow, orange-red, and eventually deep red. The orange-red hue described in historical records corresponds to a calcination temperature of approximately 700\u0026deg;C under modern processes\u003csup\u003e22\u003c/sup\u003e. When craftsmen observed the powder turning slightly black during iron vitriol calcination and halted firing, the cooled product exhibited an orange-red color. This phenomenon results from the superposition effect of high-temperature thermal radiation and reflected spectra.\u003c/li\u003e\n \u003cli\u003eIn the rinsing process, the degree of soluble salt elimination is directly related to the color stability of \u0026apos;Shengfanhong\u0026apos; powder. However, historical texts only vaguely mention \u0026quot;thorough washing\u0026quot; without specifying the rationale behind using cold water, hot water, or tea infusion, it means that craftsmen relied on observing changes in water turbidity to determine the endpoint. Based on physicochemical principles, cold water rinsing removes undissolved particles from the supernatant, hot water rinsing triggers the precipitation of Fe(OH)₃ as iron sulfate salts react with hot water, thereby eliminating sulfate residues from the powder, tea infusion rinsing leverages its high tannic acid (C\u003csub\u003e76\u003c/sub\u003eH\u003csub\u003e52\u003c/sub\u003eO\u003csub\u003e46\u003c/sub\u003e) content to form a specific black iron-tannate complex (Fe(C\u003csub\u003e76\u003c/sub\u003eH\u003csub\u003e52\u003c/sub\u003eO\u003csub\u003e46\u003c/sub\u003e)) upon reacting with Fe\u003csup\u003e3+\u003c/sup\u003e. This visually manifests as the \u0026quot;black water\u0026quot; observed by craftsmen, serving as an indicator of incomplete impurity removal.\u003c/li\u003e\n \u003cli\u003eIn the classification process, the particle size of the powder directly affects the final coloration of \u0026apos;Fanhong\u0026apos; glaze. Craftsmen traditionally relied solely on straw paper filtration and empirical judgment to select \u0026apos;Shengfanhong\u0026apos; powder from the first aluminum tray. Experiments using a laser particle size analyzer characterized the particle size distribution of powders processed through traditional classification methods versus modern ball milling for varying durations. The results showed that the particle size of \u0026apos;Shengfanhong\u0026apos; powder used by ancient craftsmen for glaze production closely matched that of modern ball-milled powder processed for 20-30 minutes, with an average particle size of approximately 7\u0026mu;m. Further modern process experiments revealed that the relationship between particle size and \u0026apos;Fanhong\u0026apos; glaze coloration is not linear. The optimal glaze effect was achieved within the 20-30 minutes ball milling range, while prolonged milling resulted in darker hues. This validates the empirical selection of \u0026apos;Shengfanhong\u0026apos; powder particle size by ancient craftsmen.\u003c/li\u003e\n\u003c/ol\u003e\n\u003cp\u003eThus, the scientific foundation of \u0026apos;Shengfanhong\u0026apos; production lies in the chemical nature of iron reactions and the quantification of particle size, while its practical efficacy relies on a tacit knowledge system. Together, these uncodifiable techniques form the deep knowledge structure of traditional technology\u0026mdash;\u0026quot;knowing not only how but also why.\u0026quot; Under modern processes, this study deciphers the tacit knowledge of \u0026apos;Shengfanhong\u0026apos; by scientifically quantifying technical parameters across production stages. The synergy between scientific knowledge and empirical practice precise \u0026apos;Shengfanhong\u0026apos; core mechanism by which ancient Chinese handicraft technologies achieved remarkable artistic excellence despite limited theoretical understanding.\u003c/p\u003e"},{"header":"Declarations","content":"\u003cp\u003e\u003cstrong\u003eAcknowledgements\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThis research work was partly supported by National Social Science Foundation of China (No. 19VJX143) and National Natural Science Foundation of China (No. 52462003).\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAuthor contributions\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eAnjian Wu: Methodology, Conceptualization, Investigation, Experimentation, Data collection, Writing\u0026mdash;original draft, Writing\u0026mdash;review and editing. Degang Yi: Conceptualization, Methodology, Writing\u0026mdash;review and editing, Funding acquisition, Software. Qijiang Li: Funding acquisition, Conceptualization, Methodology, Investigation, Supervision. Jinwei Li: Experimentation, Investigation, Data curation, Writing\u0026mdash;review and editing. Jia Zhang: Investigation, Conceptualization, Validation, Visualization.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eCompeting interests\u0026nbsp;\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eThe authors declare no competing interests.\u003c/p\u003e\n\u003cp\u003e\u0026nbsp;\u003cstrong\u003eAdditional information\u003c/strong\u003e\u003c/p\u003e\n\u003cp\u003eCorrespondence and requests for materials should be addressed to Degang Yi or Qijiang Li.\u003c/p\u003e"},{"header":"References","content":"\u003col\u003e\n\u003cli\u003eLi, J. \u003cem\u003eHistory of Science in China (Volume on Ceramics)\u003c/em\u003e; China Science Publishing \u0026amp; Media: Beijing, China, 1998.\u003c/li\u003e\n\u003cli\u003eQiu, g. \u003cem\u003eChinese handicrafts: Ceramic Firing Technology\u003c/em\u003e; China Elephant Press: Zhengzhou, China, 2010.\u003c/li\u003e\n\u003cli\u003eZhang, F. \u003cem\u003eThe Science of Ancient Chinese Ceramics\u003c/em\u003e. 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Effect of calcinate temperature on properties of ferric oxide dye from iron mud through dry process. \u003cem\u003eChemical Industry and Engineering\u003c/em\u003e, \u003cstrong\u003e01\u003c/strong\u003e, 14-16 (2005).\u003c/li\u003e\n\u003c/ol\u003e"}],"fulltextSource":"","fullText":"","funders":[],"hasAdminPriorityOnWorkflow":false,"hasManuscriptDocX":true,"hasOptedInToPreprint":true,"hasPassedJournalQc":"","hasAnyPriority":false,"hideJournal":false,"highlight":"","institution":"","isAcceptedByJournal":true,"isAuthorSuppliedPdf":false,"isDeskRejected":"","isHiddenFromSearch":false,"isInQc":false,"isInWorkflow":false,"isPdf":false,"isPdfUpToDate":true,"isWithdrawnOrRetracted":false,"journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true},"keywords":"","lastPublishedDoi":"10.21203/rs.3.rs-6752421/v1","lastPublishedDoiUrl":"https://doi.org/10.21203/rs.3.rs-6752421/v1","license":{"name":"CC BY 4.0","url":"https://creativecommons.org/licenses/by/4.0/"},"manuscriptAbstract":"\u003cp\u003e‘Fanhong’ (Iron Oxide Red) pigment is an overglaze colorant fired at approximately 800°C, primarily using PbO as a flux and Fe₂O₃ crystalline phases as the chromophore. Its coloration varied significantly across different historical periods in China, and even within the same era, a phenomenon intricately linked to the complexity of ‘Shengfanhong’ (calcined iron vitriol) production techniques. Historical texts such as \u003cem\u003eTiangongKaiwu\u003c/em\u003e document the preparation of ‘Shengfanhong’, but these records remain largely descriptive, lacking technical specificity and scientific explanations of underlying principles. This study employs experimental archaeology combined with Differential Scanning Calorimetry-Thermogravimetry (DSC-TG), X-ray Diffraction (XRD), Colorimetric analysis, and particle size testing to scientifically decode the \"tacit knowledge\" embedded in the traditional craftsmanship of ‘Shengfanhong’ production.\u003c/p\u003e","manuscriptTitle":"Research on Traditional Craftsmanship of ‘Shengfanhong’","msid":"","msnumber":"","nonDraftVersions":[{"code":1,"date":"2025-06-04 17:21:30","doi":"10.21203/rs.3.rs-6752421/v1","editorialEvents":[{"type":"communityComments","content":0},{"type":"decision","content":"Revision requested","date":"2025-07-10T20:30:22+00:00","index":"","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-07-04T18:10:25+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-17T07:37:10+00:00","index":"hide","fulltext":""},{"type":"editorInvitedReview","content":"","date":"2025-06-15T12:05:07+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"91042900872061376834777472519704938968","date":"2025-06-11T17:00:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"159662274772748952190183213290441915467","date":"2025-06-07T17:37:32+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"292409571023150205944541508018520945379","date":"2025-06-07T11:35:51+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"68871501962710563723069026164870612116","date":"2025-06-05T08:50:54+00:00","index":"hide","fulltext":""},{"type":"reviewerAgreed","content":"130509395420042438170794251168864716119","date":"2025-06-05T06:04:19+00:00","index":"hide","fulltext":""},{"type":"reviewersInvited","content":"","date":"2025-06-02T16:30:13+00:00","index":"","fulltext":""},{"type":"editorAssigned","content":"","date":"2025-05-27T05:03:09+00:00","index":"","fulltext":""},{"type":"checksComplete","content":"","date":"2025-05-27T05:02:55+00:00","index":"","fulltext":""},{"type":"submitted","content":"npj heritage science","date":"2025-05-26T15:49:49+00:00","index":"","fulltext":""}],"status":"published","journal":{"display":true,"email":"[email protected]","identity":"npj-heritage-science","isNatureJournal":false,"hasQc":true,"allowDirectSubmit":false,"externalIdentity":"hsci","sideBox":"Learn more about [Heritage Science](http://heritagesciencejournal.springeropen.com)","snPcode":"40494","submissionUrl":"https://submission.nature.com/new-submission/40494/3","title":"npj Heritage Science","twitterHandle":"@SpringerOpen","acdcEnabled":true,"dfaEnabled":true,"editorialSystem":"em","reportingPortfolio":"BMC/SO AJ","inReviewEnabled":true,"inReviewRevisionsEnabled":true}}],"origin":"","ownerIdentity":"d77f976e-fc52-4852-a100-bd29c220d2e4","owner":[],"postedDate":"June 4th, 2025","published":true,"recentEditorialEvents":[],"rejectedJournal":[],"revision":"","amendment":"","status":"published-in-journal","subjectAreas":[],"tags":[],"updatedAt":"2025-12-15T16:10:40+00:00","versionOfRecord":{"articleIdentity":"rs-6752421","link":"https://doi.org/10.1038/s40494-025-02226-4","journal":{"identity":"npj-heritage-science","isVorOnly":false,"title":"npj Heritage Science"},"publishedOn":"2025-12-10 15:58:00","publishedOnDateReadable":"December 10th, 2025"},"versionCreatedAt":"2025-06-04 17:21:30","video":"","vorDoi":"10.1038/s40494-025-02226-4","vorDoiUrl":"https://doi.org/10.1038/s40494-025-02226-4","workflowStages":[]},"version":"v1","identity":"rs-6752421","journalConfig":"researchsquare"},"__N_SSP":true},"page":"/article/[identity]/[[...version]]","query":{"redirect":"/article/rs-6752421","identity":"rs-6752421","version":["v1"]},"buildId":"8U1c8b4HqxoKbykW_rLl7","isFallback":false,"isExperimentalCompile":false,"dynamicIds":[84888],"gssp":true,"scriptLoader":[]}