The colourless glass of Iulia Felix

The present paper focuses on 85 colourless glass samples selected among the recycling cullet found in the Roman ship Iulia Felix, wrecked off the town of Grado (province of Udine, North Italy) in the first half of the 3rd century AD, with the aim of examining their chemical composition, investigating similarities within and between the three established group types (cups, plates, bottles), and comparing the chemical compositions of the Iulia Felix glass samples with groups reported in the literature for colourless glasses. Chemical analyses, performed by X-ray fluorescence and electron microprobe, indicate that the samples were all soda-lime–silica in composition, with natron as flux, according to typical Roman production technologies. Chemical data are treated by multivariate statistical tools, such as cluster analysis and the NPC test. Statistical analyses allow us to conclude that the Iulia Felix colourless glasses were produced by at least two different production technologies related to group type, confirming the trend recently identified in the literature. In addition, the trace element patterns (particularly those of Sr, Zr and Ba) suggest that beach sand with differing amounts of alkali feldspars was predominantly used as raw material, like those specifically mentioned by Pliny for glass production.