The carolingian site of Germigny-des-Prés (Loiret, France), micro and macro-scales methods for the identification of a mosaic production.

The church of Germigny-des-Prés is one of the oldest in France. It holds the only early medieval mosaics preserved north of the Alps, ordered by Theodulph, close counselor of Charlemagne, at the beginning of the 9th century AD to decorate the oratory of his villa 1. Restored in the 19th century, it still conserved a part of the original material. These tesserae are a great opportunity to reach the glass from the early Middle Ages, period of change for glass production. Moreover, this site could have hold a mosaic workshop and it could be the first settlement of this type ever discovered 2.

In situ, a macroscopic exam and pXRF analyses done on the tesserae from the vault and arches allow to distinguish original material and restored area. 15 glass samples were analysed using EMP-WDS and LA-ICP-MS in order to identify their materials and techniques as well as their origins. A 3D scan of the building makes possible to quantify accurately the materials, to manage the information and to view the results. Finally, ground penetrating radar prospections were done on the site in order to locate a potential workshop.

The concentrations of lead, potassium and iron allow us to distinguish the early medieval tesserae from the new ones. Thanks to this, the original part of the mosaic can be precisely differentiated from the restoration of the 19th century that is vaster than previously thought. Still, the figures of the vault appear to be original. The analysed cubes show that some were re-used roman tesserae but the ones with gold and silver, the most numerous in the mosaic of the vault, come from an original production, specific to this site. Structures were found by prospections in different locations around the church and excavations will now take place in order to identify this remains and a potential workshop.

Acknowledgements: to the council of Germigny-des-Prés and the DRAC Centre Val-de-Loire for the research authorizations. The missions were financed by the FRS-FNRS, The Comhaire prize of the foundation Roi Baudouin and by ARCHEA.

1 A. Freeman, P. Meyvaert, Gesta (2001), 125- 139.
2 L. James, E. Soproni, B. Bjornholt, in «Mosaics by numbers, (2013), 310-328.