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Authenticity screening of stained glass windows using optical spectroscopy

View Article: PubMed Central - PubMed

ABSTRACT

Civilized societies should safeguard their heritage as it plays an important role in community building. Moreover, past technologies often inspire new technology. Authenticity is besides conservation and restoration a key aspect in preserving our past, for example in museums when exposing showpieces. The classification of being authentic relies on an interdisciplinary approach integrating art historical and archaeological research complemented with applied research. In recent decades analytical dating tools are based on determining the raw materials used. However, the traditional applied non-portable, chemical techniques are destructive and time-consuming. Since museums oftentimes only consent to research actions which are completely non-destructive, optical spectroscopy might offer a solution. As a case-study we apply this technique on two stained glass panels for which the 14th century dating is nowadays questioned. With this research we were able to identify how simultaneous mapping of spectral signatures measured with a low cost optical spectrum analyser unveils information regarding the production period. The significance of this research extends beyond the re-dating of these panels to the 19th century as it provides an instant tool enabling immediate answering authenticity questions during the conservation process of stained glass, thereby providing the necessary data for solving deontological questions about heritage preservation.

No MeSH data available.


Spectral signature differences classify all stained fragments in four groups SY1–SY4 (the sample numbers of each group population are given in Supplementary Table 1).SY1–3 have an almost coincident absorption maximum close to 419 nm and differ in FWHM value. Panes of SY4 have red-shifted spectra with broad FWHM values tailing towards 450–550 nm.
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f8: Spectral signature differences classify all stained fragments in four groups SY1–SY4 (the sample numbers of each group population are given in Supplementary Table 1).SY1–3 have an almost coincident absorption maximum close to 419 nm and differ in FWHM value. Panes of SY4 have red-shifted spectra with broad FWHM values tailing towards 450–550 nm.

Mentions: Both panels contain several silver stained fragments. Study of the spectral signatures reveals four separate groups: SY1–4 (Fig. 8). All spectra of SY1–3 are characterized by an almost coincident spectral position of the absorption maximum close to 419.4 (±2.9) nm. The classification is based on a difference in spectral bandwidth ranging between 22.5–75 nm. In the case that the silver stain pieces were fabricated under equal firing temperatures, the appearing coincident absorption peak maxima values might indicate a similar firing temperature with the difference in FWHM pointing out a change in particle dimensions. Using Doyle’s formula35 the calculated corresponding average cluster radii R span 1.8–5.7 nm. Since almost the entire central motif is decorated with silver stain belonging to SY1–2, hypothetically it is plausible that both groups contain an equal glass type and reflect the genuine manufacturing of the panel. SY3 spectra demonstrate a clear second (weaker) blue shifted band between 380–450 nm. This band is already visible in the second group of panes; though at a much lower intensity. Mock et al.36 describes the development of a single band due to a formation of spherical particles while the appearance of two bands may originate from either a bi-modal distribution of nearly spherical particles or a distribution of particles with non-spherical symmetry. Currently the cause of the appearance of this second band remains an open question. Referring to the spectral similarities of the SY1–3 stained fragments a possible explanation might be that the double shifted peaks are caused by a higher density of particles6 and the groups simply correspond to the use of different concentrations of precursor mixture. The SY4 stained fragments have a deviant spectral shape. The peak maxima are red shifted near 428.2 (±2.6) nm and the broad band with FWHM value close to 67 nm has a tail towards the 450–550 nm region. This shape leads to an orange hue which might indicate the use of clays35 or the presence of a mixture of Ag and Cu in the paste composition37. The strong correlation in spectral shape of these spectra with the laboratory-made glass fragments reported in Delgado’s paper37, favours the second option.


Authenticity screening of stained glass windows using optical spectroscopy
Spectral signature differences classify all stained fragments in four groups SY1–SY4 (the sample numbers of each group population are given in Supplementary Table 1).SY1–3 have an almost coincident absorption maximum close to 419 nm and differ in FWHM value. Panes of SY4 have red-shifted spectra with broad FWHM values tailing towards 450–550 nm.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC5121600&req=5

f8: Spectral signature differences classify all stained fragments in four groups SY1–SY4 (the sample numbers of each group population are given in Supplementary Table 1).SY1–3 have an almost coincident absorption maximum close to 419 nm and differ in FWHM value. Panes of SY4 have red-shifted spectra with broad FWHM values tailing towards 450–550 nm.
Mentions: Both panels contain several silver stained fragments. Study of the spectral signatures reveals four separate groups: SY1–4 (Fig. 8). All spectra of SY1–3 are characterized by an almost coincident spectral position of the absorption maximum close to 419.4 (±2.9) nm. The classification is based on a difference in spectral bandwidth ranging between 22.5–75 nm. In the case that the silver stain pieces were fabricated under equal firing temperatures, the appearing coincident absorption peak maxima values might indicate a similar firing temperature with the difference in FWHM pointing out a change in particle dimensions. Using Doyle’s formula35 the calculated corresponding average cluster radii R span 1.8–5.7 nm. Since almost the entire central motif is decorated with silver stain belonging to SY1–2, hypothetically it is plausible that both groups contain an equal glass type and reflect the genuine manufacturing of the panel. SY3 spectra demonstrate a clear second (weaker) blue shifted band between 380–450 nm. This band is already visible in the second group of panes; though at a much lower intensity. Mock et al.36 describes the development of a single band due to a formation of spherical particles while the appearance of two bands may originate from either a bi-modal distribution of nearly spherical particles or a distribution of particles with non-spherical symmetry. Currently the cause of the appearance of this second band remains an open question. Referring to the spectral similarities of the SY1–3 stained fragments a possible explanation might be that the double shifted peaks are caused by a higher density of particles6 and the groups simply correspond to the use of different concentrations of precursor mixture. The SY4 stained fragments have a deviant spectral shape. The peak maxima are red shifted near 428.2 (±2.6) nm and the broad band with FWHM value close to 67 nm has a tail towards the 450–550 nm region. This shape leads to an orange hue which might indicate the use of clays35 or the presence of a mixture of Ag and Cu in the paste composition37. The strong correlation in spectral shape of these spectra with the laboratory-made glass fragments reported in Delgado’s paper37, favours the second option.

View Article: PubMed Central - PubMed

ABSTRACT

Civilized societies should safeguard their heritage as it plays an important role in community building. Moreover, past technologies often inspire new technology. Authenticity is besides conservation and restoration a key aspect in preserving our past, for example in museums when exposing showpieces. The classification of being authentic relies on an interdisciplinary approach integrating art historical and archaeological research complemented with applied research. In recent decades analytical dating tools are based on determining the raw materials used. However, the traditional applied non-portable, chemical techniques are destructive and time-consuming. Since museums oftentimes only consent to research actions which are completely non-destructive, optical spectroscopy might offer a solution. As a case-study we apply this technique on two stained glass panels for which the 14th century dating is nowadays questioned. With this research we were able to identify how simultaneous mapping of spectral signatures measured with a low cost optical spectrum analyser unveils information regarding the production period. The significance of this research extends beyond the re-dating of these panels to the 19th century as it provides an instant tool enabling immediate answering authenticity questions during the conservation process of stained glass, thereby providing the necessary data for solving deontological questions about heritage preservation.

No MeSH data available.