Laser Ablation ICP-MS elemental imaging to investigate corroded surfaces of ancient glass

The partial or total physicochemical transformation of historical glass constituents into corroded products can induce different indicators of alteration that are detectable on its surface, such as iridescence, opalescence, pitting, and crizzling [1]. Notwithstanding the large body of research on historical objects, much remains unclear about the complex mechanism of glass degradation. In this work, we employed laser ablation-ICP-mass spectrometry as a means to obtain in-depth elemental imaging of altered layers and investigate glass weathering mechanism. The concentration gradient of multiple elements, from the surface to the bulk pristine glass, was captured by multiple ablations on degraded regions of interest in order to highlight the dissolution of the glass network due to the hydration and leaching processes. Silica-soda-lime glass fragments, affected by several corrosion indicators, were studied using multiple raster-scanning ablation with high depth and lateral resolution. Using this procedure, we collected images of each ablated layer, and monitored the chemical distribution of elements that indicates an enrichment of silicon and a depletion of alkaline/earth alkaline ion concentration in the first few microns of depth under the surface area. The maps clearly showed the presence of sharp concentration gradients of leached-out ions between the pristine glass and the altered surface layers, and the preferential distribution of Co and Mn within certain areas (Figure 1), suggesting the possible occurrence of cyclic dissolutionreprecipitation processes [2]. Multi-elemental LA-ICP-MS imaging of altered glass turned out to be a useful method to investigate the corrosion process of ancient glass. The layer-by-layer elemental distribution shows how the composition changes from the bulk to the surface of the samples, thus providing information about the kinetic of the corrosion mechanism. The results obtained for weathered ancient glass support dealkalinisation as the main phenomenon occurring at the glass surface in burial conditions.