Characterization of Roman glass tesserae from the Coriglia excavation site (Italy) via energy-dispersive X-ray fluorescence spectrometry and Raman spectroscopy

Abstract

The combined use of handheld energy-dispersive X-ray fluorescence spectrometry, Raman spectroscopy, and micro-energy-dispersive X-ray fluorescence spectrometry permitted the characterization of Roman glass tesserae excavation from the Coriglia (Italy) archeological site. Analyses of ten different glass colors were conducted as spot analyses on intact samples and as both spot analyses and line scans on select cross-sectioned samples. The elemental and molecular information gained from these spectral measurements allowed for the qualitative chemical characterization of the bulk glass, decolorants, opacifiers, and coloring agents. The use of an antimony opacifier in many of the samples supports the late Imperial phasing as determined through numismatic, fresco, ceramics, and architectural evidence. And dealinization of the exterior glass layers caused by the burial environment was confirmed.

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

“…The only red opaque glass sample investigated, 15117RV (Figure 5, Table 2), was featured by a surface golden layer, as well as small spherical holes and craters, indicating the occurrence of a macroscopic alteration quite common in archaeological glass [99]. The core piece displayed as its main elements, found by EDXRF, Si, Pb and Na (with amounts of Furthermore, rutile (TiO 2 , signals at 143, 241, 445 and 610 cm −1 ), and different Si-O bonds of the glassy phase (at 550 and 1093 cm −1 , and also at 480 and 1065 cm −1 ) were identified, together with some calcium and/or aluminum-silicate, incorporating cobalt ions or some alkali sulfate [80,101] as indicated by the signals collected at 459, 616, 637, 996, 1076, 1130 and 1198 cm −1 . Since it is known that cobalt is able to impart a dark blue color in the glass matrix even if present at levels of few µg/g, it can be concluded that the samples' deep blue color is due very likely to its occurrence, as the Co amount was found to range from 0.24 to 0.10 wt.%.…”

“…In addition, since it is known that the combination of PbO and SnO2 at temperatures above 600 °C, with a Pb/Sn ratio around 3.5%, forms Pb2SnO4 [106], and considering that the 15117RV sample displayed a much higher Pb/Sn ratio without any compositional difference between the surface and inner parts, the surface golden leaf could have been the result of Pb2SnO4 formation, which is yellow and also featured by Raman signatures close to anatase [107,108]. The analyses reported mainly two typologies on the red archaeological glasses document, both copper-based, the first where cuprite (Cu2O) was the compound imparting the color, and the other characterized by the presence of micro-sized copper particles into the matrix [101]. Although the detection of copper by the EDXRF could be indicative of both technologies, the Raman analysis could not clarify this point since the copper compound responsible for the red color could not be identified.…”

“…The cited glass technology required the capability to strictly control the redox conditions during firing, since the formation of monovalent copper inside the glass matrix could be obtained either by adding proper reducing agents (such as iron) and/or tuning the furnace atmosphere using a limited range of oxygen partial pressures [106]. Furthermore, the addition of PbO to the recipe of copper-red glass was often used since PbO increases the density of the flux thus providing a better distribution of copper into the glass matrix, resulting in an intense and The analyses reported mainly two typologies on the red archaeological glasses document, both copper-based, the first where cuprite (Cu 2 O) was the compound imparting the color, and the other characterized by the presence of micro-sized copper particles into the matrix [101]. Although the detection of copper by the EDXRF could be indicative of both technologies, the Raman analysis could not clarify this point since the copper compound responsible for the red color could not be identified.…”

A non-destructive analytical study of cultural heritage object from Late Antiquity: gold framework and gemstone inlays

“…Raman spectra yielded in glass inlays correlate with the possible band positions for soda-lime glasses of that age [38]. A roughly 5000 cm −1 strong luminescence was recorded, which most likely belongs to a type of chromophore or decolouring compound present in the glass structure [39].…”

A comparative mobile Raman study for the on field analysis of the Mosaico de los Amores of the Cástulo Archaeological Site (Linares, Spain)

“…Galli et al [22] gave an overview of common colourants and opacifiers that are encountered in Roman tesserae. Previous studies were performed on samples [23] or by direct methods, using Raman spectroscopy as single technique [24] or in combination with other analytical methods. [25] The measuring campaign of the Cástulo archaeological site was conducted during the day, whereas measuring the fibre optics probes or the optical head of the mobile Raman instruments were in complete contact with the tesserae of the mosaic (with or without light blockers) on fixed working distances.…”