Technological Analysis of a Qianlong Doucai Vase with Dragon Motifs: Manufacturing Stages and Diagnostic Micro-Traces

Abstract This paper reconstructs the manufacturing sequence of a porcelain vase decorated in the doucai technique and attributed to the Qianlong reign (1736–1795) of the Qing dynasty. The study details each technological stage—from body formation through the two-fire decoration workflow—and enumerates the corresponding diagnostic traces observable at macro and micro scales. Special emphasis is placed on (i) the simultaneous application of the underglaze cobalt outline and the underglaze reign mark, (ii) the high-fired feldspathic glaze covering the underglaze painting, and (iii) low-temperature lead-rich overglaze enamels (including lead-arsenate opacified whites, Naples yellow lead-antimonate pyrochlore, copper greens, hematite reds, and Cassius purple/colloidal Au pinks). Non-invasive micro-Raman and micro-XRF are outlined as the core analytical tools for attribution and authentication, with references to recent comparative datasets on Qing enamels and marks. britishmuseum.orgWikipedia Keywords: Qianlong; Qing dynasty; doucai; underglaze cobalt; overglaze enamels; lead-arsenate opacifier; Naples yellow; Cassius purple; Raman microscopy; micro-XRF; authentication 1. Introduction Doucai (“fitted/contrasting colors”) combines an underglaze cobalt outline painted on the biscuit, covered by a transparent high-fired glaze, and then overglaze enamels applied and re-fired at ≈850–900 °C. The technique was perfected in Ming Chenghua and revived under the Qing, including Qianlong; it is distinct from wucai though related in workflow. britishmuseum.orgWikipedia+1 2. Materials and Methods (non-invasive) Optical microscopy (macro/micro): contour diffusion, enamel micro-cracking, bubble morphology. Micro-Raman spectroscopy: pigment and glass matrix identification, e.g., Pb-arsenate (white/opacifier), Naples yellow pyrochlores (Sb- and/or Sn-rich), hematite (α-Fe₂O₃) reds, Cu²⁺ greens, and Cassius purple (Au⁰ nanoparticles). PMCMDPI+1 Portable micro-XRF: elemental mapping (Co, As, Pb, Sb, Sn, Au, Cu, Fe), discrimination of underglaze vs. overglaze features, and provenance/technology signals (e.g., As with Co in some blues). PMCScienceDirectpdfs.semanticscholar.org 3. Manufacturing Technology and Stage-by-Stage Diagnostic Traces Stage 1 — Body forming and biscuit firing Process: Throwing or molding a fine, dense Jingdezhen porcelain body; biscuit firing.Diagnostic traces: Fine, white, compact paste; sparse quartz/iron specks under magnification. Pores in biscuit facilitating later cobalt penetration.Recommended tools: optical microscopy (OM). Stage 2 — Underglaze cobalt painting and underglaze reign mark (applied simultaneously) Process (corrected): On the biscuit, artisans paint both the cobalt outline (e.g., dragon, lotus scrolls) and the reign mark; then the piece is glazed and high-fired.Diagnostic traces: Identical diffusion/“softening” of cobalt linework in both design outlines and the mark; both lie under the glaze. Cobalt bleed into body pores; haloing at edges visible microscopically. Contrast with later overglaze additions: crisp edges with little/no diffusion, sitting on top of glaze.Recommended tools: OM; micro-XRF mapping of Co; Raman (silicate matrix vs. enamel). pdfs.semanticscholar.org Stage 3 — Application of transparent high-fired glaze (feldspathic) Process: Dipping/spraying a feldspathic transparent glaze; high firing (porcelain maturing range).Diagnostic traces: Clear feldspathic glaze with entrapped bubbles; underglaze cobalt appears “submerged”. (Important distinction) The high-fire glaze is feldspathic, whereas lead is characteristic of the later overglaze enamels. repository.si.eduPMCRecommended tools: OM; Raman glass network parameters. Stage 4 — Overglaze enamels application Process: After cooling, polychrome enamels are painted over the glaze.Diagnostic traces (composition & structure): White (opaque): lead-arsenate opacifier signatures (Raman; As Kα in XRF). PMC Yellow: Naples yellow (lead-antimonate pyrochlore), sometimes Sn-bearing; variable Sb/Sn/Zn/Fe solid solutions. MDPI+1 Green/turquoise: Cu²⁺ in lead-rich glass; hue modulated by glass composition and firing. MDPI Red: hematite in lead glass for iron red enamels. MDPI Pink/rose to ruby: Cassius purple (Au⁰ nanoparticles) as a hallmark of Qing famille-rose palette that often co-exists on Qianlong doucai/falangcai wares; Au detected by XRF, characteristic Raman background. (Note: manganese purple can occur but is analytically distinct.) ScienceDirectMDPI Micro-features: phase separation in the lead glass (droplets/veins), micro-crazing, slight iridescence from low-fire enamel vitrification. MDPIRecommended tools: micro-Raman; micro-XRF elemental mapping. Stage 5 — Low-temperature re-firing (≈850–900 °C) Process: Second firing fixes the enamels.Diagnostic traces: Enamel menisci slightly “sink” into the glaze surface; micro-crazing networks; localized iridescence; no change to underglaze cobalt. Wikipedia 4. Qianlong Doucai: Glaze & Enamel Diagnostics in Context Technical studies document a decisive 18th-century technology transfer and hybridization: lead-rich overglaze glasses with European-derived pigments/opacifiers (notably lead-arsenate and Naples yellow) appear on Qing wares, while the porcelain glaze itself remains feldspathic and high-fired. The rose palette is explained by colloidal gold (“Purple of Cassius”); Au can be confirmed non-invasively. These signatures—paired with the underglaze cobalt behavior—are central to authenticating Qianlong doucai. PMC+1MDPI+1 Further, micro-XRF/Raman datasets show: Consistent Pb-As signals in white/blue enamels (opacification; sometimes As associated with Co sources), Multiple pyrochlore chemistries in yellows (Sb-rich, Sn-rich, mixed), and Clear Raman backgrounds indicative of Au nanoparticles in pink to ruby enamels. ScienceDirectMDPI 5. Practical Authentication Criteria (summary) Underglaze cobalt outline and underglaze reign mark applied together (identical diffusion under the glaze). pdfs.semanticscholar.org High-fired feldspathic glaze over the cobalt outline (bubble morphology; “submerged” outline). repository.si.edu Lead-rich overglaze enamels with: Lead-arsenate opacifier (white/blue), Naples yellow in yellows, Cu²⁺ greens, hematite reds, and Cassius purple (Au) pinks. MDPIPMC Phase separation within enamels; micro-crazing; mild iridescence from low-temperature firing. MDPI 6. Table — Stage → Diagnostic traces → Preferred methods Stage Key diagnostic micro-traces Preferred methods Body & biscuit Fine white paste; pores; sparse quartz/Fe specks OM Cobalt outline + reign mark (together) Identical underglaze diffusion/halos in outline & mark OM; micro-XRF (Co); Raman High-fired glaze Feldspathic glass; bubbles; outline “under” glaze OM; Raman (glass network) Overglaze enamels Lead-rich glass; Pb-As (white); Naples yellow (Sb/Sn); Cu greens; hematite reds; Cassius Au pinks; phase separation micro-Raman; micro-XRF (Pb, As, Sb, Sn, Cu, Fe, Au) Low-temp re-firing Enamel menisci; micro-crazing; iridescence OM (Citations applicable across the table.) MDPIPMCpdfs.semanticscholar.org 7. Discussion The convergence of structural (underglaze cobalt diffusion; mark behavior; glaze morphology) and compositional markers (Pb-As opacifiers; pyrochlore yellows; Au-bearing pinks) is typical for imperial Qianlong practices in doucai/falangcai contexts and allows discrimination from later reproductions or export wares decorated with different recipes. The simultaneity of mark and outline application is particularly decisive when confronted with suspected later overglaze reign-mark additions. pdfs.semanticscholar.org 8. Conclusions The vase’s technology follows the canonical two-fire doucai workflow: underglaze cobalt (outline and mark) → feldspathic glaze high-fire → lead-rich overglaze enamels and low-fire fixing. Wikipedia Authentication hinges on paired underglaze cobalt diffusion (outline & mark), feldspathic glaze evidence, and enamel Pb-As/pyrochlore/Au signatures documented in Qing datasets. MDPIPMC Acknowledgements The author thanks colleagues in ceramic materials science and conservation science communities for comparative datasets and methodological advances in non-invasive analysis. Data Availability Representative microphotographs and observational notes can be deposited under the author’s Zenodo collections and cited alongside this article (e.g., related DOIs in References). Conflicts of Interest None declared. References British Museum collection note — Porcelain ovoid jar with decoration in underglaze blue and overglaze enamel in ‘doucai’ style (description page). Confirms doucai workflow on Qing examples. britishmuseum.org Doucai technique (overview). General description of underglaze outline, glaze, and low-fire enamels (contextual). Wikipedia Colomban, P. Distinguishing Genuine Imperial Qing Dynasty Porcelain… Heritage 2022. Notes lead-arsenate opacifier identification by Raman; cautions on overglaze matrix contributions in XRF. PMC Colomban, P. Investigation of the Pigments and Glassy Matrix of Painted Enamelled Qing Dynasty Chinese Porcelains by Non-invasive On-Site Raman Microspectrometry. Heritage 2020. Identifies Naples yellow pyrochlore, hematite, manganese oxide, carbon pigments, and lead-arsenate opacifiers; shows colloidal Au signatures. MDPI Colomban, P. Non-invasive Raman analyses of Chinese huafalang and painted enamels on metal objects and porcelains (17th–18th c.). J. Eur. Ceram. Soc. 2017. Links Cassius purple (Au nanoparticles) to rose enamels in Qing contexts. ScienceDirect Colomban, P. Non-Invasive On-Site Raman Study of Pigments and Glassy Matrix of 17th–18th Century Painted Enamelled Chinese Metal Wares… Coatings 2020; and relate