Kaare Lund Rasmussen from University of Southern Denmark with Thomas Delbey from Cranfield University in the UK and the classical archaeologists Birte Poulsen and Poul Pedersen from Aarhus University and University of Southern Denmark have performed archaeometric analysis using inductively coupled plasma mass spectrometry (ICP-MS) of 19, approximately, 1600-year old mosaic tesserae.
The tesserae originate from an excavation of a villa from late antiquity, located in Halikarnassos (today Bodrum in Anatolia, Turkey). Halikarnassos was famous for King Mausolus’ giant and lavish tomb, which was considered one of the seven wonders of the world.
The villa was laid out around two courtyards and the many rooms were adorned with mosaic floors. In addition to geometric patterns, there were also motifs of various mythological figures and scenes taken from Greek mythology; e.g. Princess Europa being abducted by the god Zeus in the form of a bull and Aphrodite at sea in her seashell. Motifs from the stories of the much younger Roman author Virgil are also represented.
Inscriptions in the floor have revealed that the owner was named Charidemos and that the villa was built in the mid-fifth century.
Mosaic flooring was a costly luxury: expensive raw materials like white, green, black and other colours of marble had to be transported from distant quarries. Other stone materials, ceramics and glasses also had to be imported.
“I received 19 mosaic tesserae for analysis in my lab in Denmark. Of these, seven were of glass in different colours; purple, yellow, red and deep red. My conclusion is that six of them are probably made of recycled glass”, says Kaare Lund Rasmussen.
This conclusion is based on chemical analysis with ICP-MS. With it, the research team has determined the concentrations of no less than 27 elements, some of them at a concentration of billionths of a gram.
“We were able to distinguish between base glass from Egypt and base glass from the Middle East and also, we could determine which elements were added by the ancient craftsmen to colour the glasses and to make them opaque, which was preferred at the time”, he says.
It is, of course, difficult to extrapolate from only seven glass mosaic tesserae, but the new results fit very well with the picture of Anatolia in late antiquity. As the power of the Roman Empire waned, trade routes were closed or rerouted, which probably led to a shortage of goods in many places—including raw materials for glass production in Anatolia.
This, together with the stories depicted on the floors, allows the classical archaeologists to put together a more detailed picture of what was fashionable in late antiquity and what the possibilities were for the artistic unfolding.