Five centuries of mosaic glass at Saint Severus (Classe, Ravenna)

The Basilica and Monastery of Saint Severus are archaeological contexts of paramount importance for the study of expansion of monumental buildings in Classe (Ravenna) from the 5th century AD. The archaeological campaign of 2011 in the area of the monastery - dated to the end of the 9th century - has enabled the collection of several mosaic tesserae. Besides, recent restoration works on mosaic discovered in the 1960s allowed the collection of few glass tesserae, sampled from two different mosaic floors removed from the Saint Severus area: two floor fragments detached from the area of the so-called St Rufillo’s sacellum (4th century) and from the northern aisle of the basilica (6th century), this latter is now located as a pastiche on the floor of an 18th century building in Ravenna (the so called Cripta Rasponi). Forty-one glass tesserae of different colours were analysed by means of EMPA-WDS, XRPD and SEM-EDS. The aim is to identify the raw materials employed in the mosaic glass production from the Saint Severus area, to compare the three sample sets and verify their different chronolog y. The analysed tesserae were all of the natron type, nonetheless, on the basis of colorants and accessory components a discrimination among the different sample sets was clearly established.