XRF CHARACTERIZATION OF A PALE GREY-BLUISH BRUSH WASHER: GLAZE CHEMISTRY IN THE CONTEXT OF SOUTHERN SONG GUAN WARE TECHNOLOGY

This study presents the results of portable X-ray fluorescence (pXRF) analysis of a pale grey-bluish ceramic brush washer. Two measurements were obtained from the vessel: one from the side wall and one from the glazed base. The analytical results demonstrate an exceptionally high degree of compositional consistency between both measurement locations. Major and trace element concentrations are virtually identical, indicating that the vessel is covered by a single homogeneous glaze and shows no evidence of secondary glazing, restoration, or later surface modification. The glaze is characterized by elevated silica and calcium concentrations, a strong predominance of lime over alkali fluxes, extremely low titanium content, negligible lead concentrations, and the complete absence of artificial coloring agents. Comparison with published analytical studies of Southern Song Guan kilns from Jiaotanxiao, Laohudong, and Wansongling demonstrates close correspondence in major technological parameters, including high-calcium glaze chemistry, iron-based coloration, low titanium values, and lead-free high-temperature firing technology. The analytical data define a coherent high-fired lime glaze system colored exclusively by iron and closely aligned with the archaeometric characteristics of Southern Song Guan ware. Keywords: Guan ware, Southern Song Dynasty, brush washer, celadon, XRF analysis, archaeometry, lime glaze, Chinese ceramics, high-fired glaze technology. 1. Introduction Guan ware (官窑) occupies a distinguished position among the imperial ceramic productions of the Southern Song Dynasty. One of the defining technological characteristics of Southern Song Guan ceramics is the use of high-fired lime-rich glazes producing subtle grey-blue, grey-green, and jade-like surface tones. These visual effects were achieved through carefully controlled glaze compositions and reducing firing atmospheres rather than through the addition of artificial pigments. Archaeometric investigations conducted on kiln materials from Jiaotanxiao, Laohudong, and Wansongling have established a characteristic technological profile for Guan glazes, including elevated calcium concentrations, low titanium content, iron-controlled coloration, and the absence of lead-based flux systems. The present study examines the glaze chemistry of a pale grey-bluish brush washer and compares the analytical results with published archaeometric data from Southern Song Guan kiln sites. 2. Description of the Object The investigated object is a glazed ceramic brush washer. Visual examination reveals: a uniform monochrome glaze; pale grey-bluish coloration; absence of painted decoration; absence of localized artificial color effects; soft vitreous surface luster; visually homogeneous glaze coverage across the entire vessel. The glaze extends continuously over both the body and the base of the vessel. The analytical target images demonstrate excellent contact between the instrument window and the glaze surface, resulting in high-quality measurements. 3. Materials and Methods The analysis was conducted using a Geochem (3-Beam) Extra portable X-ray fluorescence spectrometer. Measurement conditions: acquisition time: 30 seconds; non-destructive in situ analysis; Geochem analytical mode. Two analytical locations were examined: ID 1 – Side Wall Glazed side surface of the vessel. ID 2 – Base Glazed lower surface of the vessel. The lightweight-element index (LE) ranged between approximately 45% and 46%, indicating excellent analytical conditions and high confidence in the elemental results. 4. XRF Results Table 1. Principal Elemental Composition Element Side Wall Base Si 38.21% 38.74% Ca 6.280% 5.951% Al 5.75% 5.60% K 2.336% 2.378% Fe 6020 ppm 6160 ppm Mn 255 ppm 340 ppm Ba 289 ppm 259 ppm Rb 199 ppm 211 ppm Sr 101 ppm 96 ppm Zr 38 ppm 37 ppm Y 20 ppm 23 ppm Nb 14 ppm 17 ppm Pb 13 ppm 20 ppm The two measurements display almost complete chemical agreement. The correspondence extends not only to major elements but also to the entire suite of detected trace elements. 5. Homogeneity of the Glaze One of the most significant results of this investigation is the remarkable compositional consistency between the two analyzed locations. Silicon, calcium, aluminum, potassium, iron, rubidium, strontium, zirconium, yttrium, and niobium all occur at nearly identical concentrations. The glaze on the body and the glaze on the base therefore represent a single technological batch and a single firing system. No evidence of reglazing, restoration, or later surface modification was detected. The analytical data define a fully homogeneous glaze system. 6. Oxide Composition Table 2. Calculated Oxide Equivalents Oxide Side Wall Base SiO₂ 77.7% 77.2% Al₂O₃ 10.3% 9.9% CaO 8.4% 7.8% K₂O 2.7% 2.7% Fe₂O₃ 0.8% 0.8% TiO₂ <0.1% <0.1% The calculated CaO/K₂O ratios are: 3.1 for the side wall; 2.9 for the base. These values indicate a glaze system dominated by lime fluxes rather than alkali fluxes. 7. Iron as the Sole Coloring Agent Iron is present at a calculated concentration of approximately: Fe₂O₃ ≈ 0.8 wt.% No evidence was found for the presence of: cobalt; chromium; vanadium; cadmium; selenium. The glaze therefore contains no artificial colorants. Its pale grey-bluish appearance is produced entirely through iron dissolved within the glaze matrix under reducing firing conditions. This coloring mechanism is characteristic of traditional celadon and Guan glaze technologies. 8. Comparison with Published Southern Song Guan Ware Studies Comparison with published analytical datasets from the Southern Song kiln sites of Jiaotanxiao, Laohudong, and Wansongling demonstrates strong agreement across several key technological indicators. Lime-Dominated Glaze System The calculated CaO content of 7.8-8.4 wt.% falls within the documented range of Southern Song Guan glazes. The CaO/K₂O ratio of approximately 3 corresponds closely to high-lime imperial glaze formulations. Iron-Based Coloration The calculated Fe₂O₃ value of approximately 0.8 wt.% falls within the range reported for Southern Song Guan glazes. This concentration is sufficient to produce the characteristic jade-like grey-blue coloration associated with Guan ceramics. Extremely Low Titanium The calculated TiO₂ value remains below 0.1 wt.%. This closely matches published values for Guan kiln glazes from Laohudong and Wansongling. Such low titanium concentrations are generally associated with exceptionally pure siliceous glaze raw materials. Lead-Free Technology Lead concentrations of only 13-20 ppm confirm a completely lead-free high-temperature glaze system. Absence of Modern Technological Markers No chromium, cobalt, vanadium, cadmium, selenium, elevated zirconium, or elevated barium concentrations were detected. The glaze chemistry is therefore entirely consistent with a traditional high-fired ceramic technology. 9. Archaeometric Interpretation The glaze exhibits an exceptionally clean and internally consistent chemical profile. Its defining characteristics include: high silica content; calcium-dominated flux system; iron-controlled coloration; extremely low titanium concentration; lead-free technology; absence of artificial pigments; full compositional homogeneity across the vessel. The combined presence of high calcium, iron coloration, and exceptionally low titanium is particularly significant, as this combination represents one of the principal technological signatures repeatedly documented in Southern Song Guan glazes. 10. Conclusion Portable X-ray fluorescence analysis of Brush Washer No. 1 established the following characteristics: The side wall and base are covered by a chemically identical glaze derived from a single glaze formulation. The glaze belongs to a high-fired lime-alkali system with a CaO/K₂O ratio close to 3. The glaze coloration is produced exclusively by iron in the absence of artificial coloring agents. The calculated Fe₂O₃ concentration of approximately 0.8 wt.% corresponds closely with the color-forming mechanism documented in Southern Song Guan glazes. Titanium concentrations remain exceptionally low (<0.1 wt.% TiO₂). Lead occurs only at trace levels and plays no technological role in the glaze. Modern pigment markers and modern glaze modifiers are completely absent. General Conclusion The glaze chemistry of Brush Washer No. 1 exhibits a high degree of correspondence with published archaeometric data from the Southern Song Guan kilns of Jiaotanxiao, Laohudong, and Wansongling. High calcium content, a CaO/K₂O ratio near 3, iron-based coloration, extremely low titanium levels, lead-free technology, and the complete absence of modern pigment markers together define a coherent technological system characteristic of Southern Song Guan ware. The XRF results strongly support attribution of the glaze to the high-fired imperial lime-glaze tradition of Southern Song Guan ceramics. 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