WU Chenyu ^{1, 2}, WU Qingwen ³,WU Weihua ⁴, WU Qiang ^{1, 2}, LI Jinwei ^{1, 2}, LI Qijiang ^{1, 2}
(1. Research Center of Ancient Ceramics, Jingdezhen Ceramic University, Jingdezhen 333001, Jiangxi, China; 2. Jiangxi Ceramic and Cultural Relics Protection and Royal Kiln Research Collaborative
Innovation Center, Jingdezhen 333001 Jiangxi, China; 3. Jiangxi Arts & Ceramics Technology Institute, Jingdezhen 333000, Jiangxi, China; 4. Pucheng Museum, Nanping 353400, Fujian, China)

Extended Abstract: [Background and purpose] The Dakou Kiln, first discovered in 1958, is located on the eastern slope of a rectangular basin in Dakou Village, Pucheng County, which dates back to the Song and Yuan Dynasties. It is one of the kilns associated with the Fujian bluish white porcelain tradition. The Dakou Kiln possesses significant geographical, historical and mineral resources, which have played a crucial role in the production and development of bluish and white porcelain. Products from the Dakou Kiln were exported worldwide via the Maritime Silk Road, serving as an important testament to the Minyue culture. However, previous studies on the Dakou Kiln's bluish white porcelain primarily focused on archaeological, historical and cultural dissemination perspectives, with limited exploration on the scientific connotations and production techniques of the porcelain. In this study, 25 pieces of bluish white porcelain from the mid-Southern Song to the late Song and early Yuan periods were analyzed, along with 5 supporting ring samples, excavated by an official archaeological in 2018. Scientific analysis methods were employed, including statistical analysis and factor analysis, to study the chemical composition characteristics, microstructural features, and pottery-making techniques of Dakou Kiln's bluish white porcelain, aiming to elucidate the primary technological principles behind its production process.[Methods] Chemical composition of the samples was quantitatively analyzed using the Eagle Ⅲ XXL micro-focused energy dispersive X-ray fluorescence spectrometer (EDAX, USA). The instrument was configured with a beam spot diameter of 300 μm, operating at 25 kV and 600 μA for a testing duration of 300 s. Rock structure of the samples was observed using Zeiss Axio Scope. A1 polarized light microscope. The firing temperature analysis was conducted using the DIL402C thermal expansion instrument (Netzsch, Germany), with a heating rate of 15 ℃·min−1. X-ray photoelectron spectroscopy (XPS) for Fe ions was recorded using a Thermo Scientific Nexsa instrument, with a monochromatic Al target (E=1486.68 eV), operating at 12 kV and 72 W. Colorimetric testing of the glaze surface was carried out using an NF333 colorimeter (Japan).[Results] The Dakou Kiln's bluish white porcelain body consisted of 17.53–25.41 wt.% Al₂O₃, 65.97–76.55 wt.% SiO₂ and 0.52–1.52 wt.% TiO₂. The glaze had 12.69–18.74 wt.% Al₂O₃, 63.93–73.66 wt.% SiO₂, 0.03–0.15 wt.% MnO, 0.01–0.24 wt.% P₂O₅ and 0.55–1.61 wt.% Fe₂O₃. The fired samples primarily consisted of cryptocrystalline clay materials, with minor fine quartz particles and occasional remnants of fine-grained biotite. Some raw materials exhibited signs of vitrification. The glaze was predominantly a transparent glassy glaze, with a clear reaction layer visible at the body-glaze interface, characterized by a thin layer of calcite growing towards the glaze layer. XPS results indicated Fe²⁺/Fe³⁺ ratios of 53.76/46.24, 80.22/19.78, 60.25/39.75 and 70.34/29.66. In the L*a*b* color model, the a* values ranged from −4.62 to 2.09, while the b* values ranged from −2.00 to 14.66. The water absorption rate of the body was between 0.1% and 0.5%, with a firing temperature of about 1200 ℃.[Conclusions] (1) The chemical composition of the Dakou Kiln's bluish white porcelain body and supporting kiln tools exhibits a "high silica, low alumina" characteristic, utilizing a "single raw material" formulation for body production, with locally sourced high-alumina porcelain stone as the primary raw material. By the mid to late Southern Song period, multiple sources of porcelain stone were employed. (2) The glazes of Dakou Kiln's bluish white porcelain can be categorized into calcium glaze and calcium-alkali glaze. The glaze materials included porcelain stone and calcined limestone (glaze ash from the primary processing stage). The calcined limestone process was unstable, resulting in significant fluctuations in the CaO content of the glaze. (3) The coloring oxide in the glaze of Dakou Kiln's bluish white porcelain was Fe₂O₃, produced in reducing atmosphere. The glaze layer thickness ranged from 100 μm to 200 μm, with few bubbles and residual crystals. The glaze predominantly appeared in a celadon color, with a primary hue of light greenish celadon. Some specimens exhibited color variations influenced by the body color. (4) The firing temperature for Dakou Kiln's bluish white porcelain was about 1200 ℃, with a water absorption rate of less than 0.5%, indicating good body densification. The body-glaze adhesion was strong, with a clearly visible reaction layer at the interface, characterized by a thin layer of calcite growing towards the glaze layer.
Key words: Dakou kiln; bluish white porcelain; scientific and technological archaeology; process preparation