Composite Structure and Manufacturing Technique of a Black-Coated Inkstone from Wolji, Unified Silla, Korea

The black-coated inkstone (traditionally classified as a lacquered inkstone) excavated from Wolji (Unified Silla, 7th–8th century CE) is a composite artefact consisting of a low-fired ceramic core, wooden structural components, textile reinforcement, and multilayered presumed lacquer (organic dark) coatings. This study employed integrated archaeometric methods, including X-ray diffraction (XRD), radiography, wood identification, optical microscopy, and SEM–EDS, to investigate its material composition and manufacturing structure. The ceramic core was fired at approximately 550–900 °C, resulting in a porous microstructure suitable for grinding use. Wood analysis indicates selective material use, with Abies holophylla identified in the curved lateral frame, while a denser hardwood likely functioned as a supporting component. Radiographic analysis demonstrated that the ceramic body was manufactured as a primary unit and subsequently combined with wooden elements. Stratigraphic analysis revealed repeated lacquer-like composite layers incorporating Ca- and P-rich fillers, clay, and textile materials, which functioned as adhesive and reinforcing media between heterogeneous components. The textile interlayer is interpreted as a reinforcing component within the composite structure. Comparative analysis indicates technological similarities with multilayer lacquer systems reported in earlier East Asian lacquerware traditions. The Wolji inkstone provides rare evidence for the application of such composite manufacturing techniques to a writing implement during the Unified Silla period. These findings contribute to a broader understanding of composite coating technologies and material adaptation in East Asian archaeological lacquerware.