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Study of Raman scattering and luminescence properties of orchil dye for its nondestructive identification on artworks

Authors

  • F. Rosi,

    Corresponding author
    1. CNR-ISTM Istituto di Scienze e Tecnologie Molecolari, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    2. Centro di Eccellenza SMAArt, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    • Correspondence to: Francesca Rosi, CNR-ISTM Istituto di Scienze e Tecnologie Molecolari c/o Dipartimento di Chimica Università degli Studi di Perugia, Italy

      E-mail: francesca.rosi@cnr.it

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  • C. Clementi,

    1. Centro di Eccellenza SMAArt, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    2. Università degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
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  • M. Paolantoni,

    1. Università degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
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  • A. Romani,

    1. Centro di Eccellenza SMAArt, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    2. Università degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
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  • R. Pellegrino,

    1. Università degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
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  • B. G. Brunetti,

    1. Centro di Eccellenza SMAArt, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    2. Università degli Studi di Perugia, Dipartimento di Chimica, Perugia, Italy
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  • W. Nowik,

    1. Analytical Department, Laboratoire de Recherche des Monuments Historiques, Champs-sur-Marne, France
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  • C. Miliani

    1. CNR-ISTM Istituto di Scienze e Tecnologie Molecolari, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
    2. Centro di Eccellenza SMAArt, Dipartimento di Chimica Università degli Studi di Perugia, Perugia, Italy
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  • This article is from the GISR part of the joint special issue on the European Conference on Nonlinear Optical Spectroscopy (ECONOS 2012) with Guest Editors Johannes Kiefer and Peter Radi and the II Italian Conference of the National Group of Raman Spectroscopy and Non-Linear Effects (GISR 2012) with Guest Editor Maria Grazia Giorgini.

Abstract

Ultraviolet and visible (UV-vis) fluorescence and subtracted shifted Raman spectroscopy have exploited to identify orchil in a fragment from the ninth century Bible de Théodulphe and a parchment fragment sampled from a 16th century map of Auvergne.

Orchil is a purple lichen dye widely used since ancient times in place of the more expensive Tyrian purple and therefore known as the ‘poor person's purple’. Unlike the latter, orchil has a low lightfastness, and in ancient works, it is often faded. Orchil is a complex mixture of different coloured compounds, and they all share a common structure resulting from phenoxazone with a number of different substituents. In this work, UV-vis fluorescence combined with resonance Raman spectroscopy allowed for the identification of orchil in a fragment from the ninth century Bible de Théodulphe. Raman spectroscopy has been applied also for studying a parchment fragment sampled from a 16th century map of Auvergne. In both cases, subtracted shifted Raman spectroscopy (SSRS) has been exploited for removing the strong fluorescence background. Overall results have been confirmed by liquid chromatography with quadrupole time-of-flight mass spectrometry (LC/ QTOF-MS).

Both the electronic and vibrational spectral features of ancient orchil showed some interesting differences with respect to those of the standard sample. Taking into account the poor lightfastness of the purple dye, the same investigation has been carried out on photochemically aged orchil reproducing the spectral modification observed on the ancient fragments. Copyright © 2013 John Wiley & Sons, Ltd.

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