Venice’s reputation for glass is usually centred on the Renaissance, but new scientific work suggests the lagoon’s glass story was already developing centuries earlier. An archaeometric study of material from San Pietro di Castello (the ancient island of Olivolo), positioned near the lagoon’s port entrance, indicates that early medieval Venice was already plugged into long-distance supply chains—and experimenting with techniques that look strikingly sophisticated for the period.
The study, published in Archaeological and Anthropological Sciences, analyses 45 samples dated from the 6th to the 9th centuries, including finished vessels, architectural glass, production waste, and a crucible. The team used a suite of microscopic and chemical techniques (including SEM-EDS, EMPA, and LA-ICP-MS) to examine how these objects were made, coloured, and circulated.
A busy early medieval waterfront, then an 8th-century building with elite signals San Pietro di Castello/Olivolo has a long and changing occupation. The article outlines three broad phases: a first period from the 4th to mid-6th century with waterfront structures; a second from the late 6th to late 7th involving roads and connections along the lagoon; and a third from the early 8th to early 9th, when a new substantial building was constructed.
That Period 3 building is described as a sizeable structure with a wooden superstructure, clay-packed floors, and foundations incorporating bricks, roof tiles, and reused stone, with at least two rooms identified.
What makes this context especially intriguing is the company it keeps: the same phase is associated with a gold tremissis of Emperor Heraclius (r. 610–641) and three Byzantine seals dated to the 7th century. The authors suggest the building may have been linked to Byzantine administration—possibly even tied to a magister militum—or to the storage of public documents.
From natron to plant ash: Venice and a major technological transition
San Pietro di Castello/Olivolo depicted by Jacopo de’ Barbari as part of his woodcut of Venice from 1500
One of the most important transitions in the history of glassmaking was the move away from natron-based glass (the Roman recipe) toward plant-ash glass, a shift tied in the article’s overview to changing Mediterranean supply conditions from the late 7th/early 8th century onward.
What stands out at San Pietro di Castello is the early appearance of plant-ash glass. The study reports two plant-ash samples, with the earliest dated to the 8th century and attributed to Syro-Levantine production—evidence that early medieval Venice had access to “cutting-edge” materials being produced far to the east.
“The answer emerging from the excavations at San Pietro di Castello is surprising,” explains Margherita Ferri, a researcher at Ca’ Foscari University of Venice and one of the study’s authors. “Here we have fragments of plant-ash glass dating back as early as to the eighth century. But the real twist is another: chemical analysis attributes these ancient fragments to Syro-Levantine production. This means that Venice 1,300 years ago not only was aware of this new technology, but its trade networks were so efficient that it imported cutting-edge materials produced hundreds of kilometres away. This places Venice among the very first centres in Italy to embrace and master this technology, revealing a remarkably receptive and well-connected city.”
The authors go a step further in interpreting what this might mean on the ground: San Pietro in Castello may have played a pivotal role in the distribution and reworking of imported raw materials in early medieval Venice.
Recycling, mixed techniques, and blue made from industrial leftovers
Laser Ablation used to examine medieval glass – photo courtesy Ca’ Foscari University of Venice
Several observations in the paper point to reuse and recycling—processes that can be hard to spot without laboratory work. In the study’s summary, the authors highlight evidence for the use of cobalt-bearing metallurgical by-products (rather than neatly refined pigments) and the co-occurrence of calcium antimonates and lead stannates in decorative elements—signals of technological mixing and reworked materials.
A more detailed discussion of the blue colourant argues that it was likely not a purified cobalt pigment at all, but a metallurgical by-product linked to copper extraction; the paper also notes a cobalt-coloured sample whose trace-element pattern is consistent with recycled glass.
The provenance results reinforce Venice’s position within wider Mediterranean exchange networks. The assemblage includes substantial representation from the two major production zones of the era—Egypt and the Levant—and the authors note an important chronological pattern: Levantine material appears only in later phases, while the plant-ash glasses are associated with the 7th–8th century horizon.
Taken together, the San Pietro di Castello evidence pushes against the idea that Venice’s glass story begins late. Instead, it presents an early medieval community that could obtain eastern materials, adapt them to local needs, and participate actively in the technological and commercial currents of the early medieval Mediterranean.
The article, “The glass assemblage from San Pietro in Castello: tracing glass technology and innovations in the Venetian lagoon,” by Elisabetta Gliozzo, Margherita Ferri and Eleonora Braschi, appears in Archaeological and Anthropological Sciences. Click here to read it.
Top Image: Early medieval chalice from San Pietro di Castello, similar to those analyzed, currently being restored. Photo courtesy Ca’ Foscari University of Venice
Venice’s reputation for glass is usually centred on the Renaissance, but new scientific work suggests the lagoon’s glass story was already developing centuries earlier. An archaeometric study of material from San Pietro di Castello (the ancient island of Olivolo), positioned near the lagoon’s port entrance, indicates that early medieval Venice was already plugged into long-distance supply chains—and experimenting with techniques that look strikingly sophisticated for the period.
The study, published in Archaeological and Anthropological Sciences, analyses 45 samples dated from the 6th to the 9th centuries, including finished vessels, architectural glass, production waste, and a crucible. The team used a suite of microscopic and chemical techniques (including SEM-EDS, EMPA, and LA-ICP-MS) to examine how these objects were made, coloured, and circulated.
A busy early medieval waterfront, then an 8th-century building with elite signals San Pietro di Castello/Olivolo has a long and changing occupation. The article outlines three broad phases: a first period from the 4th to mid-6th century with waterfront structures; a second from the late 6th to late 7th involving roads and connections along the lagoon; and a third from the early 8th to early 9th, when a new substantial building was constructed.
That Period 3 building is described as a sizeable structure with a wooden superstructure, clay-packed floors, and foundations incorporating bricks, roof tiles, and reused stone, with at least two rooms identified.
What makes this context especially intriguing is the company it keeps: the same phase is associated with a gold tremissis of Emperor Heraclius (r. 610–641) and three Byzantine seals dated to the 7th century. The authors suggest the building may have been linked to Byzantine administration—possibly even tied to a magister militum—or to the storage of public documents.
From natron to plant ash: Venice and a major technological transition
One of the most important transitions in the history of glassmaking was the move away from natron-based glass (the Roman recipe) toward plant-ash glass, a shift tied in the article’s overview to changing Mediterranean supply conditions from the late 7th/early 8th century onward.
What stands out at San Pietro di Castello is the early appearance of plant-ash glass. The study reports two plant-ash samples, with the earliest dated to the 8th century and attributed to Syro-Levantine production—evidence that early medieval Venice had access to “cutting-edge” materials being produced far to the east.
“The answer emerging from the excavations at San Pietro di Castello is surprising,” explains Margherita Ferri, a researcher at Ca’ Foscari University of Venice and one of the study’s authors. “Here we have fragments of plant-ash glass dating back as early as to the eighth century. But the real twist is another: chemical analysis attributes these ancient fragments to Syro-Levantine production. This means that Venice 1,300 years ago not only was aware of this new technology, but its trade networks were so efficient that it imported cutting-edge materials produced hundreds of kilometres away. This places Venice among the very first centres in Italy to embrace and master this technology, revealing a remarkably receptive and well-connected city.”
The authors go a step further in interpreting what this might mean on the ground: San Pietro in Castello may have played a pivotal role in the distribution and reworking of imported raw materials in early medieval Venice.
Recycling, mixed techniques, and blue made from industrial leftovers
Several observations in the paper point to reuse and recycling—processes that can be hard to spot without laboratory work. In the study’s summary, the authors highlight evidence for the use of cobalt-bearing metallurgical by-products (rather than neatly refined pigments) and the co-occurrence of calcium antimonates and lead stannates in decorative elements—signals of technological mixing and reworked materials.
A more detailed discussion of the blue colourant argues that it was likely not a purified cobalt pigment at all, but a metallurgical by-product linked to copper extraction; the paper also notes a cobalt-coloured sample whose trace-element pattern is consistent with recycled glass.
The provenance results reinforce Venice’s position within wider Mediterranean exchange networks. The assemblage includes substantial representation from the two major production zones of the era—Egypt and the Levant—and the authors note an important chronological pattern: Levantine material appears only in later phases, while the plant-ash glasses are associated with the 7th–8th century horizon.
Taken together, the San Pietro di Castello evidence pushes against the idea that Venice’s glass story begins late. Instead, it presents an early medieval community that could obtain eastern materials, adapt them to local needs, and participate actively in the technological and commercial currents of the early medieval Mediterranean.
The article, “The glass assemblage from San Pietro in Castello: tracing glass technology and innovations in the Venetian lagoon,” by Elisabetta Gliozzo, Margherita Ferri and Eleonora Braschi, appears in Archaeological and Anthropological Sciences. Click here to read it.
Top Image: Early medieval chalice from San Pietro di Castello, similar to those analyzed, currently being restored. Photo courtesy Ca’ Foscari University of Venice
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