<p>This study presents the results of a comprehensive archaeometric investigation of a glass assemblage from the early medieval levels of San Pietro in Castello (Olivolo, Venice), a site of strategic importance during the formative stages of the city. A total of 45 samples, including finished vessels, architectural glass, production waste and a crucible, were analysed using SEM-EDS, EMPA, and LA-ICP-MS. As for glassmaking technology, the results reveal various colouring and opacification strategies, including the use of metallurgical by-products such as cobalt-bearing slag and the co-occurrence of calcium antimonates and lead stannates for the realization of decorative threads. Furthermore, the analysis of the steatite crucible and adhering glass provides insight into contamination processes and their implications for provenance studies. As for glass provenance, the chemical composition shows a near-equal distribution of Levantine and Egyptian natron glass, though differently distributed from a chronological standpoint (Levantine only in later phases). Of particular interest is also the finding of two plant-ash based glass samples, with the earliest one dating to the 8^th century and attributed to Syro-Levantine production. Overall, the findings highlight Venice’s early involvement in the technological transition from natron- to plant ash-based glass and suggest that the San Pietro in Castello site may have played a pivotal role in the distribution and reworking of imported raw materials.</p>