Raman characterization of painted mortar in Republican Roman mosaics



In several Italian archaeological sites, the presence of the so-called emblemata has been attested to the Republican Roman Age (2nd to 1st century B.C.). They are small mosaics made on a stone or terracotta tray using the opus vermiculatum. This particular technique, which originated in Egypt and/or in Greece during the Hellenistic period (3rd century B.C.), uses very small tesserae (of size less than 0.5 cm) producing a pictorial effect. In the literature, this type of mosaic has been studied from a technical approach only for a small group of mosaics from Greece (Delos, Samos and Rhodes island), while for the Italian area, a project on their archaeometrical and archaeological study is in progress. In a few cases, by observing the surface of the mosaics, it was possible to detect the presence of a painting layer on the mortar. This feature was never reported in the literature, probably because the painted details have survived only in traces, and they are visible only by direct observation. A mosaic from Rome (preserved in site, under the church of St. Susanna), was sampled and analyzed by Raman spectrometry, while two vermiculata mosaics from Privernum (LT) were observed in situ by a portable instrument. Thanks to the characterization, it was possible to observe the use of a luxurious palette of pigments, including cinnabar and Egyptian Blue. Copyright © 2008 John Wiley & Sons, Ltd.