Characterization of medieval-like glass alteration layers by laser spectroscopy and nonlinear optical microscopy

Mohamed Oujja,Marina Martínez-Weinbaum,Teresa Palomar,Marta Castillejo,Sagrario Martínez-Ramírez

doi:10.1140/epjp/s13360-021-01834-w

Abstract

Historical glass-based objects undergo, since the time of their manufacture, different degradation phenomena that are related to their composition and to the environment to which they were exposed. Three-dimensional (3D) structural and chemical characterization of the degradation layers is important to select the most adequate conservation strategies for glass objects. Optical microscopy (OM) is the most frequently used non-destructive method to examine the surface of historical glasses; however, the 3D structural assessment of alteration layers requires applying the destructive modality of this technique to conduct a cross-sectional study. In this work, a different approach for structural and compositional characterization of alteration layers on model medieval-like glasses is presented, based on the combination of the laser spectroscopies of laser-induced breakdown spectroscopy (LIBS), laser-induced fluorescence (LIF) and FT-Raman, and the emerging, cutting edge technique of nonlinear optical microscopy (NLOM) in the modality of multiphoton excitation fluorescence (MPEF). The results obtained through this multi-analytical photonic approach were compared with those retrieved by examination of the surface and cross sections of the samples by OM and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS). While the combination of LIBS, LIF and FT-Raman served to assess the composition of the various alteration layers, the use of MPEF microscopy allowed the non-destructive determination of the thicknesses of these layers, showing for both thickness and composition a good agreement with the OM and SEM–EDS results. Thus, the proposed approach, which avoids sample preparation, illustrates the capability of non-destructive, or micro-destructive in the case of LIBS, laser spectroscopies and microscopies for the in situ study of glass objects of historic or/and artistic value.Graphic

Highlights

Historical glasses are exposed to different alteration phenomena as a result of their interaction with the environment
While the combination of laser-induced breakdown spectroscopy (LIBS), laser-induced fluorescence (LIF) and FT-Raman served to assess the composition of the various alteration layers, the use of multiphoton excitation fluorescence (MPEF) microscopy allowed the non-destructive determination of the thicknesses of these layers, showing for both thickness and composition a good agreement with the Optical microscopy (OM) and scanning electron microscopy–energy-dispersive X-ray spectroscopy (SEM–EDS) results
The surface and stratigraphy of the glass samples was studied by OM (Fig. 2) and their chemical composition determined by SEM–EDS (Table 1)

Summary

Introduction

Historical glasses are exposed to different alteration phenomena as a result of their interaction with the environment. The alteration mechanisms of glasses exposed to outdoor and indoor environments are controlled by rainwater and environmental humidity. These alteration agents induce the hydrolytic attack on the glass surface producing the lixiviation of alkaline and alkaline earth elements. A continuous alteration layer is usually formed on the glass surface [7,8,9,10] In dry atmospheres, this layer can appear fissured and even detached, leaving the inner glass core exposed to new alteration processes

Methods

Results

Conclusion