They discover the secret of Viking beads that reused tiles from Roman and Byzantine mosaics

Danish Ribe was an important trading city in the Viking Age. In the early 8th century, a trading emporium was established on the north bank of the River Ribe, bringing merchants and artisans from far and wide to make and sell goods such as brooches, suit buckles, combs, and colored glass beads.

When glass became a rare commodity in the early Middle Ages, cubes of colored glass – called tesserae – were torn from the mosaics of abandoned Roman and Byzantine temples, palaces and baths, transported north and traded in emporium cities such as Ribe, where bead makers melted them into large vessels and shaped them into beads.

Until now, archaeologists assumed that pearl makers used opaque white tesserae as raw material for the production of opaque white beads.

Glass analyzed in this study; Colorless and faintly greenish-yellowish glass “cubes” gilded with a fine gold plate on one of their outer surfaces (still attached to the cube at the top right of the basin) and white Viking beads analyzed in this study | photo Museum of Southwest Jutland

A smart and sustainable production

And it is here that a geochemist and an archaeologist from Aarhus University, together with a curator from the Ribe museum, have made a startling discovery, which they have just published in the scientific journal Archaeological and Anthropological Sciences.

The chemical composition of the Viking white beads from one of the first workshops showed that glassmakers had found a more sustainable way to save time and wood for their kilns: crush cubes of clear and gold glass, remelt them at a low temperature, stir them to trap the air into bubbles and finally wrap the glass around an iron mandrel to form beads and voila! – opaque white accounts created in a short time and with a minimum of resources.

The precious ultra-thin sheets of gold adhered to the surface of the tesserae were, of course, salvaged by the glazier before remelting the glass, but the new finds show that some of the gold had inevitably ended up in the crucible. The tiny drops of gold in the white beads, the numerous air holes (which is why the beads are opaque), as well as the fact that no colored chemical traces are present, all prove that they were, in fact, the stones of golden mosaic the raw material of the beads.

Fused Roman glass cubes with traces of gold | photo Museum of South West Jutland

These traces of gold were found not only in the white beads but also in the blue ones from the same workshop. Here chemistry shows that the glazier’s recipe consisted of a mixture of blue and gold tiles. The mixing was necessary because Roman blue tiles contained high concentrations of chemicals that made them opaque, and therefore ideal for mosaics, but not for blue beads. By diluting the chemicals in this way, the result was the deep blue, transparent glass we know from Viking Age beads.

The Ribe beadmaker might have chosen to dilute the glass mixture with old glass fragments, which were also found in the workshop. But these turned out to be old, contaminated Roman glass that had been remelted over and over again.

And Ribe’s glassmakers were clearly experts who preferred the clearest glass they could get their hands on.says Gry Hoffmann Barfod, from the Department of Geosciences at Aarhus University. And he adds: For a geochemist, it has been a privilege to work with this fantastic material and discover the relevance of the knowledge stored here for our current society..

Viking beads and trinkets at an exhibition in Oslo | photo Wolfmann on Wikimedia Commons

The interdisciplinary study was a collaboration between Gry Barfod, Søren Sindbæk, professor of archeology at the Danish National Research Foundation’s Center for the Development of Urban Networks (UrbNet) at Aarhus University, and museum curator Claus Feveile of the Museum of South West Jutland, specializing in the Viking Age and the oldest history of Ribe. The most outstanding achievements of the Ribe emporium were not only the products, but also the circular economy and its conscience to preserve limited resources.says Professor Søren Sindbæk.

Museum curator Claus Feveile comments: These exciting results clearly show the potential to unravel new facts about the Vikings. Combining our high resolution excavations with these chemical analyses, I foresee many more revelations in the near future..

Søren Sindbæk and Claus Feveile led the archaeological excavations of the Northern Emporium Project between 2016 and 2018, where new high-definition approaches allowed for the first time a resolution of up to a few decades within the extremely well-preserved Ribe stratigraphy. Findings from the excavations are currently displayed inside reconstructed replicas of the bead makers’ workshops in the Ribe Viking Museum’s new special exhibition.


Sources

Aarhus University | Barfod, GH, Feveile, C. & Sindbæk, SM Splinters to splendours: from upcycled glass to Viking beads at Ribe, Denmark. Archaeol Anthropol Sci 14, 180 (2022). doi.org/10.1007/s12520-022-01646-8