XRF CHARACTERIZATION OF A LARGE CRACKLE-GLAZED GUAN-TYPE VASE: GLAZE AND BLACK-BODIED CERAMIC COMPOSITION IN THE CONTEXT OF SOUTHERN SONG TECHNOLOGY

Abstract This study presents the results of portable X-ray fluorescence (pXRF) analysis of a large crackle-glazed ceramic vase attributed to the Guan ware (官窑) tradition of the Southern Song Dynasty (1127-1279 CE). The investigation was performed on two areas of the vessel: the glazed exterior surface and an unglazed section of the foot ring representing the ceramic body. The analytical results reveal pronounced chemical differentiation between glaze and body. The glazed surface is enriched in silicon (40.81 wt.%), potassium (3.785 wt.%), and calcium (3.616 wt.%), whereas the ceramic body exhibits substantially higher concentrations of aluminum (19.14 wt.%), iron (1.439 wt.%), and titanium (1700 ppm). Only trace amounts of lead were detected in both areas, confirming the use of a lead-free high-fired ceramic technology. The compositional data demonstrate a technological system consisting of a silica-rich glaze applied over a dark iron-bearing ceramic body. This combination corresponds to the principal technological characteristics associated with crackled Guan-type ceramics of the Southern Song tradition. Keywords: Guan ware, Southern Song Dynasty, celadon, crackle glaze, black-bodied ceramics, XRF, archaeometry, Chinese ceramics, high-fired glaze technology. 1. Introduction Guan ware (官窑) represents one of the most celebrated achievements of imperial ceramic production during the Southern Song Dynasty. Ceramics of this tradition are renowned for: thick bluish-grey glazes; extensive crackle networks; jade-like surface appearance; dark iron-bearing ceramic bodies; strong visual contrast between pale glaze and dark foot. Archaeometric investigations of kiln sites traditionally associated with Guan ware have demonstrated the technological importance of high-fired silica-rich glazes combined with iron-bearing ceramic bodies. The present study examines a large crackle-glazed vase through portable X-ray fluorescence spectroscopy in order to characterize the chemical composition of both glaze and ceramic body and to document the technological structure of the vessel. 2. Description of the Object The investigated object is a large monumental vase approximately 40 cm in height with an elongated body and tall neck. The vessel exhibits the following characteristics: bluish-grey glaze; extensive crackle decoration of two distinct scales; thick vitreous glaze layer; glazed base with firing-contact marks; unglazed dark foot ring; nearly black exposed ceramic body. Five circular firing-contact marks are visible on the base and are arranged around the center of the vessel. The central area of the base remains fully glazed and is covered by a dense network of fine crackles. The exposed ceramic body displays a dark grey to nearly black coloration with localized brownish tones characteristic of iron-bearing high-fired ceramic fabrics. 3. Materials and Methods The analysis was carried out using a Geochem (3-Beam) Extra portable X-ray fluorescence spectrometer. Analytical parameters: Geochem (3-Beam) Extra mode; acquisition time: 30 seconds; non-destructive in situ analysis. Two measurement points were selected: Measurement No. 11 Glazed exterior surface of the vessel. Measurement No. 12 Unglazed ceramic body exposed on the foot ring. Results are reported as elemental concentrations in weight percent and parts per million (ppm). 4. XRF Results Table 1. Principal Elemental Composition Element Glaze Ceramic Body Si 40.81% 20.84% Al 4.35% 19.14% K 3.785% 2.026% Ca 3.616% 1.116% Fe 3260 ppm 14,390 ppm Ti <280 ppm 1700 ppm Mn 299 ppm 567 ppm Rb 284 ppm 267 ppm Sr 96 ppm 41 ppm Y 7 ppm 29 ppm Zr 19 ppm 50 ppm Nb 9 ppm 31 ppm Ba 185 ppm 198 ppm Pb 8 ppm 23 ppm The chemical contrast between glaze and ceramic body is pronounced. The most significant differences are observed in aluminum, iron, and titanium concentrations. 5. Glaze Composition The glaze is characterized by a high concentration of silicon: Si = 40.81 wt.% together with significant amounts of: potassium; calcium; strontium. The elevated silicon content indicates the presence of a well-developed vitreous phase. Potassium and calcium function as principal fluxing agents within the glaze system. Iron concentration in the glaze is limited to 3260 ppm, substantially lower than in the ceramic body. This elemental distribution is characteristic of high-fired silicate glazes associated with celadon technologies. 6. Ceramic Body Composition The ceramic body displays a fundamentally different compositional profile. The principal components are: Al = 19.14 wt.%; Fe = 14,390 ppm; Ti = 1700 ppm. Iron concentration within the body exceeds that of the glaze by more than four times. This result corresponds closely to the dark coloration observed in the exposed ceramic fabric. Elevated aluminum indicates the use of highly refractory aluminosilicate raw materials appropriate for high-temperature firing. 7. Formation of the Black Ceramic Body The analytical results reveal a characteristic concentration of iron-bearing and titanium-bearing components within the ceramic fabric. The body is enriched in: iron; titanium; manganese; aluminum. This elemental association corresponds to the technological characteristics of dark-bodied high-fired ceramics traditionally associated with crackled Southern Song wares. Iron concentration corresponds to approximately 2.06 wt.% Fe₂O₃ equivalent. Titanium concentration corresponds to approximately 0.284 wt.% TiO₂ equivalent. The combined presence of iron and titanium contributes significantly to the formation of the dark ceramic body observed in the vase. 8. Trace Element Distribution Particular archaeometric significance is attached to rubidium, zirconium, yttrium, niobium, and strontium. Measured concentrations are presented below: Element Glaze Ceramic Body Rb 284 ppm 267 ppm Sr 96 ppm 41 ppm Zr 19 ppm 50 ppm Y 7 ppm 29 ppm Nb 9 ppm 31 ppm The ceramic body displays notable enrichment in yttrium, zirconium, and niobium. These elements are widely recognized as useful geochemical indicators in archaeometric provenance studies of Chinese ceramics. 9. Crackle Formation and Firing Technology The vase exhibits a complex crackle structure composed of both coarse and fine crackle networks. Large crackles dominate the exterior surface, while a much finer crackle network is present on the base. This distribution reflects differences in glaze thickness and thermal stresses generated during cooling after firing. The combination of: a thick glaze layer; a silica-rich vitreous phase; an iron-bearing ceramic body; extremely low lead concentrations constitutes a characteristic high-fired crackle-glaze ceramic technology. 10. Archaeometric Interpretation The analytical results document the presence of two technologically distinct materials: A silica-rich potassium-calcium glaze. A dark iron-bearing aluminosilicate ceramic body. This combination represents one of the defining technological characteristics of crackled Guan-type ceramics. Particularly significant features include: fourfold enrichment of iron within the ceramic body; pronounced titanium differentiation between glaze and body; elevated aluminum concentration in the ceramic fabric; lead-free glaze technology; extensive crackle development; dark exposed foot ring. Together these characteristics define a coherent technological system associated with high-fired crackled ceramics of the Southern Song tradition. 11. Conclusion Portable X-ray fluorescence analysis of the large crackle-glazed vase established the following technological characteristics: The glaze is enriched in silicon (40.81 wt.%), potassium (3.785 wt.%), and calcium (3.616 wt.%). The ceramic body contains elevated concentrations of aluminum (19.14 wt.%), iron (1.439 wt.%), and titanium (1700 ppm). Iron concentration in the ceramic body exceeds that of the glaze by more than four times. Lead is present only at trace levels (8-23 ppm), confirming a lead-free high-fired ceramic technology. The overall distribution of major and trace elements demonstrates the deliberate combination of a silica-rich crackle glaze and a dark iron-bearing ceramic body.