Microscopic and X-Ray Fluorescence Investigation of a Large Grey-Blue Ru-Type Vase: Chemical Comparisons with Northern Song Ceramics from Qingliangsi and Related Kiln Sites

Professor Nona Dronova Research article prepared for publication in Zenodo Date of XRF examination: 28 October 2026Research field: Archaeometry, Ceramic Technology, Chinese Art History, Materials Science Abstract This paper presents a non-destructive examination of a large grey-blue glazed ceramic vase investigated within the technological and artistic tradition of Ru ware (汝窑), historically associated with the Northern Song dynasty (960–1127 CE). The investigation combines microscopic and visual examination of the glaze surface, crackle network, optical characteristics, foot-ring construction, and apparent firing-related features with portable X-ray fluorescence (pXRF) analysis performed on 28 October 2026 using an Olympus analyser. Three locations were examined: the glazed surface at the widest part of the body, the glazed underside, and an exposed ceramic-body area on the foot ring. The resulting elemental dataset provides information on major constituents and trace elements, including Si, Al, K, Ca, Fe, Ti, Mn, Zn, Rb, Sr, Y, Zr, Nb, Ba, Ce, La, Th, and Cr. The glaze exhibits a calcium-bearing silicate composition, with measured Ca concentrations of 6.503–7.599 wt.% and Fe concentrations of 0.856–0.866 wt.%. The ceramic body contains 13.270 wt.% Al, 1.356 wt.% Fe, and 5,740 ppm Ti. Comparisons are made with published archaeological and museum investigations of Ru ware from Qingliangsi (清凉寺), celadon from Zhanggongxiang (张公巷), and related Song-period ceramic traditions. Particular attention is given to the research of Li Weidong and colleagues, Zhao Weijuan and colleagues, Wu Zhanjun and colleagues, and researchers associated with the Palace Museum and the British Museum. The investigated vase exhibits several chemical and technological characteristics comparable to Northern Chinese celadon traditions, including archaeological Northern Song Ru ware. However, differences in potassium, strontium, and certain trace-element relationships distinguish the object from some published reference groups. The paper also addresses an important methodological issue: archaeological kiln-site assemblages may contain manufacturing rejects, experimental pieces, firing failures, and fragments of originally successful vessels, whereas a complete, carefully finished vase provides access to a different range of technological evidence. The results support continued investigation of the vase within the context of Northern Song Ru-type ceramic technology while identifying specific questions requiring further analytical verification. Keywords: Ru ware; Ru yao; Northern Song dynasty; Qingliangsi kiln; Zhanggongxiang kiln; grey-blue glaze; crackle; portable XRF; ceramic body; trace elements; provenance; archaeometry; anorthite; phase separation. 1. Introduction Ru ware occupies a distinctive position in the history of Chinese ceramics. Its reputation rests upon the exceptional refinement of its glaze, the subtlety of its blue-green and grey-blue colouration, and its association with the courtly ceramic culture of the late Northern Song dynasty. Archaeological investigations at Qingliangsi, Baofeng County, Henan Province, have substantially expanded knowledge of Ru ceramic production. Excavations have revealed kiln structures, production debris, ceramic fragments, and technological evidence relevant to the manufacture of high-quality celadons. Scientific investigation has further demonstrated that the characteristic appearance of Ru glazes cannot be explained by chemical composition alone. Colour and translucency are influenced by iron chemistry, firing conditions, microcrystalline phases, gas inclusions, and structural heterogeneity within the glaze. The study by Li Weidong and colleagues (2005) was particularly important in establishing the relevance of crystalline phases and phase separation to the appearance of Northern Song Ru glaze. Subsequent investigations using particle-induced X-ray emission (PIXE), neutron activation analysis (NAA), energy-dispersive X-ray fluorescence (EDXRF), electron microscopy, and other analytical methods have examined the relationships among Qingliangsi, Zhanggongxiang, and other Chinese ceramic production centres. These investigations provide a substantial scientific framework for examining individual objects. Nevertheless, comparison is complicated by differences in analytical methodology, sample preparation, instrument calibration, the archaeological contexts of reference materials, and the distinction between complete vessels and excavated fragments. The present study examines a large grey-blue vase exhibiting a visually complex glaze, a developed crackle network, and a carefully formed foot ring. The principal objective is to document its elemental characteristics and compare them with published data relating to Northern Chinese celadon manufacture, especially the Ru ware tradition of the Northern Song dynasty. A further objective is to consider whether archaeological production assemblages adequately represent the technological range of carefully finished, successfully fired vessels. 2. Description of the Investigated Vase 2.1. General characteristics The object is a large ceramic vase with a rounded body, a developed neck, an outward-flaring mouth, and a circular supporting foot. The exterior is covered with a soft grey-blue glaze possessing considerable visual depth. The glaze extends across the principal body surfaces and is also present on the recessed central area of the underside. The foot ring includes exposed ceramic-body surfaces. The surface displays a network of fine intersecting glaze cracks, commonly described as crackle. The grey-blue colour varies subtly with viewing conditions and surface curvature. In certain areas, the glaze appears relatively translucent, whereas elsewhere it exhibits a more diffuse, jade-like optical character. The underside includes localised darker reddish marks, including apparently paired features. These are relevant to the technological examination of the object but cannot be assigned to a specific firing-support system without further documentation. 2.2. Significance of the complete form Unlike isolated archaeological sherds, the vase survives as a complete vessel. This permits examination of the relationship between its overall shape, glaze distribution, crackle development, supporting structure, and exposed ceramic body. The complete form also allows analytical measurements to be made at several positions belonging to the same object. Such information is valuable for investigating technological consistency and possible variation between different areas of the glaze. The survival of a complete vessel does not, by itself, establish its date or kiln of manufacture. Its significance lies in the broader range of technological information available for examination. 3. Microscopic and Visual Examination 3.1. Research approach The microscopic examination conducted by Professor Nona Dronova forms the initial stage of the investigation. The principal subjects of observation are the glaze surface, its optical character, the crackle network, localised surface features, and the relationship between the glazed and unglazed areas of the vessel. The present manuscript records the principal morphological observations associated with the examination. Instrument model, magnification, illumination conditions, image scales, and the precise dimensions of microscopic features should be supplied from the original examination records before final publication. 3.2. Optical properties of the glaze The glaze possesses a soft grey-blue colour and an apparent optical depth that differs from a simple opaque surface coating. Its appearance is consistent with the broad category of complex silicate glazes in which light transmission and scattering may be influenced by several interacting factors. These include the chemical state of iron, microscopic bubbles, crystalline inclusions, and heterogeneity within the glassy matrix. Previous research on excavated Ru ware has demonstrated the importance of anorthite crystallisation and phase-separated structures in the optical behaviour of certain historical glazes. The appearance of the investigated vase is compatible with the possibility of comparable structural mechanisms. However, the presence of anorthite or any particular phase-separated microstructure in this specific object has not been independently established by the available XRF measurements. Such identification would require appropriate structural or spectroscopic examination. 3.3. Crackle morphology The glaze displays a developed network of intersecting cracks. The lines vary in orientation and form irregular polygonal and curvilinear patterns. Crackle formation in ceramic glazes is commonly associated with stress generated by differences in thermal expansion between the glaze and ceramic body. Additional factors may include glaze thickness, cooling history, mechanical relaxation, and subsequent environmental exposure. The crackle network is therefore a technologically relevant feature. Nevertheless, crackle alone is not diagnostic of a particular historical period, since comparable structures can occur in ceramics of different dates and manufacturing traditions. Further microscopic documentation should establish the widths, intersections, distribution, and possible secondary deposits associated with the cracks. 3.4. Foot ring and underside The circular foot ring provides an opportunity to examine exposed ceramic material without sampling the glazed surface. The relationship between the foot, the recessed glazed underside, and localised contact marks is relevant to reconstructing the manufacturing and firing processes. The relatively large dimensions of the vase are also important. A large ceramic vessel imposes different mechanical and thermal demands from those of small dishes or bowls. Consequently, com