Analisi Multitecnica dei Materiali Decorativi della Villa di Teoderico a Galeata

Several glass mosaic tesserae were recovered during the archaeological excavations at Villa di Teoderico in Galeata (FC), dated to early sixth century A.D. This work reports the results of an archaeometrical investigation realized through a multitechnique approach on 12 tesserae. The aims of the study were the structure of glass, the characterization of coloring and opacifying agents and the definition of the technological processes involved. The glass matrix and the dispersed crystallites were characterized in detail through micro-Raman spectroscopy, field emission scanning electron microscopy with energy dispersive X-ray spectroscopy and X-ray powder diffraction analyses, while UV-visible-NIR diffuse reflectance spectrophotometry with optic fibres was essential to identify all chromophores. Every glass shows the typical soda-lime-silicate composition. Calcium antimoniates were employed to obtain white color and in cobalt-colored blue glass, lead-tin yellow type II and cassiterite or calcium phosphate and cassiterite were used with copper and iron ions in green color. Cassiterite was also used in copper-colored red and orange glass, while calcium phosphate was employed in copper and iron-colored light blue glass. Antimony-based opacifiers were common during imperial age, but lead-tin yellow type II, cassiterite and calcium phosphate were attested from lateantiquity. These results prove the high technological level reached by glassmakers in a transition period between traditional and new techniques.