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

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 Abstract

Spectroscopic and Microscopic Characterization of Flashed Glasses from Stained Glass Windows

“…The emission in the 300-500 nm range encompasses the contribution of oxygen deficiency centers (ODC) from the glass network [42,44,48]. Besides, an additional shoulder with different relative intensities in each sample is noticed around 520 nm and assigned to Ca 2+ of the glass lattice [39,49]. The LIF spectra of colored layers (red lines in Figure 6) display some specific features in addition to those observed in the base glass.…”

“…LIBS is a micro-invasive technique based on the spectral analysis of the luminous plume generated by the pulsed laser ablation of a small amount of material from the surface of the sample and has the capacity for quantitative determination. LIBS has been shown to be an effective technique for the characterization of glasses from a wide variety of perspectives [30,[33][34][35][36][37][38][39]. Previous works, using LIBS, have focused on finding the optimal parameters for the analysis of model soda-lime silicate [33] and historical lead silicate glasses [34], on the characterization of chromophores and opacifiers of ancient glasses, and on characterizing degradation pathologies [35,37,39,40].…”

“…LIBS has been shown to be an effective technique for the characterization of glasses from a wide variety of perspectives [30,[33][34][35][36][37][38][39]. Previous works, using LIBS, have focused on finding the optimal parameters for the analysis of model soda-lime silicate [33] and historical lead silicate glasses [34], on the characterization of chromophores and opacifiers of ancient glasses, and on characterizing degradation pathologies [35,37,39,40]. From a complementary perspective, LIF spectroscopy provides valuable molecular information and facilitates the detection of trace elements and/or chromophores responsible for the glass coloration in a totally non-invasive way [30,[41][42][43][44].…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…This was highlighted in two papers by Oujja et al who used a variety of techniques including LIBS, LIF, non-linear optical microscopy and multi-photon excitation fluorescence to analyse historical glass Grisailles 406 and medieval-like glass alteration layers. 407 Both papers managed to analyse layers and the depth of these layers causing no damage in most cases and minimal damage in the case of LIBS. In the latter case, the thickness of the layers determined using multi-phase excitation fluorescence microscopy were compared and were in agreement with thickness determined using SEM-EDS and optical microscopy.…”

Emerging photonic technologies for cultural heritage studies: the examples of non-linear optical microscopy and photoacoustic imaging

“…MPEF has been applied to the evaluation of phthalocyanine acrylic paint layer thickness [41], to probe the stratigraphy of egg-tempera mock-up paintings [42] and to characterize grisaille paint layers on historical stained glasses [43]. Recently, the same non-linear modality has been employed for the thickness determination of model medieval-like glass layers in a nondestructive manner [44]. Furthermore, non-linear imaging techniques have been applied to extract information from historical coatings samples [45].…”