Northern Wei blue — Localized production of sodium calcium glass in Northern China from the 4th to the 6th century AD

The Pingcheng period of the Northern Wei Dynasty (398–494 CE) saw a significant revival of the Silk Road, bolstering trade between the East and West. As the capital, Pingcheng (today’s Datong City, Shanxi Province) played a pivotal role in the introduction of Western glass products and their fabrication techniques to Eastern regions. While the Book of Wei: Western Regions provides textual evidence of the introduction of glassmaking technology, modern instrumental analysis is required to understand the components and craftsmanship of Pingcheng-period glassware. In this study, three typical glassware from the Northern Wei period in Datong area were analyzed using a 3D digital microscope with an extended depth of field and a scanning electron microscope-energy dispersive spectrometer (SEM-EDS). This non-destructive, micro-level analysis focused on the glass’ chemical composition and microscopic morphology. Preliminary investigations were conducted into production techniques, raw materials, and their sources. Compared with the same type of glassware and pottery unearthed in neighboring areas of the same period, the research shows that the foreign blowing technology and aesthetic exchange and fusion of Xianbei nationality produced a unique style of ware. The findings indicate that these glassware belonged to a high Mg, plant ash-based Na₂O-CaO-SiO₂ glass system, the average content of MgO is 7.2%, and high magnesium sodium calcium glass is relatively rare in the world’s ancient glass lineage. The glassware’ shape, micro shape, and high Mg concentration suggest local production using indigenous materials, likely influenced by Roman glassblowing techniques. This study provides important scientific information regarding the trade and technical exchange of glass between China and foreign countries in Pingcheng period of the Northern Wei Dynasty.