Weathering and deterioration of archeological glasses from late Roman Sicily

Abstract

Glass is found at archeological excavations in a variety of conditions ranging from pristine—where no deterioration is visible—to very heavily degraded. Although the chemical processes of glass deterioration have been extensively studied, they are not yet entirely understood, due in part to the numerous factors that must be considered, from the composition of the glass paste and its manufacture to the type of soil in which the glass is buried. In this study, we analyze an assemblage of Late Roman glass from the catacombs of Saint Lucy in eastern Sicily, in order to study the effects of this particular hypogeal environment on glass. The study regards the correlation between the weathered glass surfaces and the compositional changes occurred in the samples. Close attention is paid to optical observations of the outer layers of the glasses as manifestations of chemical deterioration of the bulk. The chemical analysis of the fragments of glass was carried out nondestructively using PIXE‐PIGE analyses without any sample preparation. Weathering was observed with an optical microscope.

Non-Invasive Approach to Investigate the Mineralogy and Production Technology of the Mosaic Tesserae from the Roman Domus of Villa San Pancrazio (Taormina, Italy)

“…15-17%. Conversely, the data here collected, evidencing much lower levels of sodium and slightly higher concentrations of Si and Al, can be explained in terms of the typical degradation of archaeological glasses, i.e., the leaching of alkali due to the prolonged contact with soil which produces a surface hydrated, alkalidepleted layer, together with the dissolution of the glass matrix [78,79]. In order to further confirm this hypothesis, the sample 2118V was gently brushed to eliminate the iridescent patina, then analyzed again by EDXRF.…”

“…However, Pb and Mn were found in higher concentrations, reaching values higher than 1 wt.% in 18117BV. Sample 17117BV showed the lowest Na values and a slight increase in Si and Al, being also the only blue tessera in which sulfur was detected, suggesting the occurrence of a heavy alkali leaching phenomenon [78,79]. The whole set of elemental data collected on the blue tesserae seems to match the typical silica-soda-lime Roman glasses, although for these tesserae, the level of Pb was even higher than the one found for the semi-opaque tesserae and thus the use of cullet or the recycling of glass resulting in the decrease of sodium levels cannot be ruled out [83,84].…”

Archaeometric Studies on the Characterization and Deteriorations of Glass Artifacts of Su Terazisi and Kral Kızı Regions in Enez (Ainos) Excavation

“…37 According to another opinion, black discoloration formation may be caused by oxidation of iron and manganese ions present in the glass. 38 Fe 2 O 3 content of less than 0.5% enters the glass from the sand used in glass production. Similarly, MnO content lower than 1% can be found as an impurity in the glass composition.…”

On the Surface and Beyond. Degradation Morphologies Affecting Plant Ash-Based Archaeological Glass from Kafir Kala (Samarkand, Uzbekistan)

“…According to current knowledge, it is still unclear to what concomitance of factors the onset and development of different forms of degradation affecting archaeological glass are attributable, nor to what extent they can compromise the durability of glass. To date, much of the investigation into glass deterioration and related mechanisms have been centred around European medieval window glass, while very little attention has been paid to the degradation morphologies affecting archaeological artefacts [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15]. Moreover, the use of a tailored vocabulary to describe the visible symptoms of deterioration in the conservation and scientific literature is inconsistent and confusing [10], thus resulting in the lack of a shared vocabulary among scholars and experts from different fields working on archaeological glass studies and conservation.…”