Chapter 40 The Provenance of Paste and Temper in Roman Amphorae from the Istrian Peninsula, Croatia

Abstract

Abstract Roman amphorae, manufactured in the Laecanius workshop in Istria, Croatia, between 10-5 B.C. and 78 A.D, were analysed by integrating archaeological and geological laboratory methods, including thin section petrography, X-ray diffractometry (XRD) and, for the first time, heavy mineral analysis. Characteristics of the fabric allow categorisation of the amphora sherds into fabric groups. Petrography shows that quartz is the dominant clastic component in the sherds while carbonate is common as temper; XRD provided information on firing temperatures that ranged between 750 and 900°C. The amphora sherds contain diverse detrital heavy minerals with generally high epidote and garnet quantities. Occasionally zircon is also important. Garnet/epidote ratios and the presence of diagnostic species (pyroxene, hornblende) show systematic variations that coincide with similar variations in fabric characteristics. Heavy mineral signatures in amphorae produced in other workshops facilitated their distinction from the Laecanius sherds. Comparative heavy mineral analysis of terra rossa found close to the workshop indicate that terra rossa was the major source of the paste. Differences observed in the heavy mineral composition of the amphora sherds and terra rossa are interpreted by the polygenetic nature and spatial heterogeneity of the latter and the mixing of the paste with sandy temper. Modern Adriatic sponge spicules present in the majority of Laecanius amphora sherds and the temper-derived, generally immature, heavy mineral assemblages suggest that the sandy material for the temper was obtained from Adriatic deposits. The heavy mineral technique, as a powerful archaeometric tool, is demonstrated by revealing the provenance of raw materials, and by recognising the compositional difference between the Laecanius amphorae and the sherds from other workshops and the spica sample.