Comparison of Hyperspectral Imaging and Fiber-Optic Reflectance Spectroscopy for Reflectance and Transmittance Measurements of Colored Glass

Abstract

The work presented in this paper is part of a wider research project, which aims at documenting and analyzing stained glass windows by means of hyperspectral imaging. This technique shares some similarities with UV-VIS-IR spectroscopy, as they both provide spectral information; however, spectral imaging has the additional advantage of providing spatial information, since a spectrum can be collected in each pixel of the image. Compared to UV-VIS-IR spectroscopy, spectral imaging has rarely been used for the investigation of stained glass windows. One of the objectives of this paper is, thus, to compare the performance of these two instruments to validate the results of hyperspectral imaging. The second objective is to evaluate the potential of analyzing colored-glass pieces in reflectance modality and compare the results with those obtained in transmittance, in order to highlight the differences and similarities between the two approaches. The geometry of the systems and the backing material for the glass, as well as the characteristics of the glass pieces, are discussed. L*a*b* values obtained from the spectra, as well as the calculated color difference ΔE00, are provided, to show the degree of agreement between the instruments and the two measurement modalities.

The Non-Invasive Characterization of Iron Age Glass Finds from the “Gaetano Chierici” Collection in Reggio Emilia (Italy)

“…RE11, like in all the beads of Group 7 (disk-shaped beads), shows absorption bands of an unclear chromophore at 590 and 650 nm. Similar spectra have been reported in [35] without any clear interpretation. Most of the spectra of the Fe-Co type show variously pronounced Fe 2+ absorption bands in the NIR region, with intensities between those of RE25 (no absorption) and RE8 (pronounced absorption).…”

“…Manganese may also have a decolorizing function in these glasses, although its low concentration (which is consistently higher than that of iron) would indicate a natural abundance of Mn-and Fe-containing minerals in the silica source. The absorption at 600 and 650 nm observed in other glasses [35] remains unexplained. These beads are more recent than the rest of the set [21] and are an example of the glass industry's simultaneous progress in glass decolorization processes [34].…”

Chemical and Mechanical Characterization of the Alternative Kriab-Mirror Tesserae for Restoration of 18th to 19th-Century Mosaics (Thailand)

“…For the blue Kriab mirror samples, both ancient and alternative samples display three well-defined cobalt (Co 2+ ) bands at approximately 530-540, 590-600, and 650-670 nm [39][40][41][42], but the alternative Kriab sample has higher %reflectance than that of ancient one. The red Kriab mirrors of both ancient and alternative ones exhibit distinct absorbance bands that correspond to the surface plasmonic resonance (SPR) of the copper nanoparticles, at around 565 nm, and to isolated Cu 0 atoms, at approximately 430 nm [41,[43][44][45].…”