Influence of degradation in the production of quantitative data by using portable-XRF on glassy matrices of Limousin composition

Commercial portable X-ray fluorescence (p-XRF) instrumentation offers the advantages of performing nondestructive, in situ analyses but, when sampling or sample preparation on cultural heritage materials is precluded, reliability of its quantitative results can be compromised due to the presence of deterioration processes. For this reason, a validation of quantitative p-XRF analyses is essential: the present work aims to validate the quantitative p-XRF analyses performed on artificially altered medieval-like Limoges enamels. In particular, our research focuses on cobalt blue enamels opacified with tin oxide, one of the most employed in medieval Limousin ateliers (Biron et al., 1996). Glass degradation processes are strongly affected by environmental conditions, especially pH. Leaching phenomena of network modifiers prevail for pH<9, whereas at pH>9 the corrosion of the network predominates. Accelerated weathering treatments (i.e. immersion tests in acidic and basic solutions) were thus performed on a set of laboratory-synthesized samples for variable times of exposure, simulating natural deterioration processes (Greiner-Wronowa et al., 1999; De Bardi et al., 2013). Samples were analyzed with p-XRF before and after accelerated Fig. 1: SEM SE image of sample exposed for 48 hours to NaOH solution at 70 °C (100x). weathering treatments, in order to evaluate possible compositional variations linked to the presence of deterioration. Since temperature plays a fundamental role in the reaction kinetic, tests were also performed at high temperature. Morphological and compositional surface changes were monitored by Scanning Electron Microscopy coupled with Energy Dispersive X-ray analyses (SEM-EDX). Finally, possible structural variations of glassy matrices were preliminarily undertaken by performing in-depth analyses with confocal micro-Raman instrumentation.