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Raman study of different crystalline forms of PbCrO4 and PbCr1−xSxO4 solid solutions for the noninvasive identification of chrome yellows in paintings: a focus on works by Vincent van Gogh

Authors

  • Letizia Monico,

    1. Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Perugia, Italy
    2. University of Antwerp, Department of Chemistry, Antwerp, Belgium
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  • Koen Janssens,

    1. University of Antwerp, Department of Chemistry, Antwerp, Belgium
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  • Ella Hendriks,

    1. Van Gogh Museum, Amsterdam, The Netherlands
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  • Brunetto G. Brunetti,

    1. Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Perugia, Italy
    2. Centre SMAArt and Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Perugia, Italy
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  • Costanza Miliani

    Corresponding author
    1. Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), c/o Dipartimento di Chimica, Università degli Studi di Perugia, Perugia, Italy
    2. Centre SMAArt and Dipartimento di Chimica, Biologia e Biotecnologie, Università degli Studi di Perugia, Perugia, Italy
    • Correspondence to: Costanza Miliani, Istituto CNR di Scienze e Tecnologie Molecolari (CNR-ISTM), c/o Dipartimento di Chimica, Università degli Studi di Perugia, via Elce di Sotto 8, I-06123 Perugia, Italy.

      E-mail: costanza.miliani@cnr.it

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  • This article is part of the special issue of the Journal of Raman Spectroscopy entitled “Raman in Art and Archaeology 2013” edited by Polonca Ropret and Juan Manuel Madariaga.

Abstract

Chrome yellows, a class of pigments frequently used by painters of the Impressionism and Post-impressionism period, are known for their different chemical stability; the latter depends on the chemical composition (PbCrO4, PbCr1−xSxO4) and crystalline structure (monoclinic or orthorhombic) of the material. The possibility to distinguish among different forms of this pigment is therefore relevant in order to extend knowledge on the corresponding degradation process that is observed on several original paintings. For this purpose, three paintings conserved at the Van Gogh Museum (Amsterdam) were analyzed using noninvasive Raman spectroscopy, while equivalent investigations employing bench-top instrumentation were performed to obtain information from micro-samples originating from these works of art. In each painting, the chrome yellow was identified either as monoclinic PbCrO4 or in the form of monoclinic PbCr1−xSxO4 (x < 0.25) or S-rich orthorhombic PbCr1−xSxO4 (x ~ 0.5). Our ability to make this fairly subtle distinction is based on a Raman study of several oil paint model samples made up of monoclinic and/or orthorhombic crystalline forms of PbCrO4 and PbCr1−xSxO4 (0.1 ≤ × ≤ 0.8). These paints were studied using several excitation wavelengths (namely 785.0, 532.0, 514.5, and 488 nm). Because of the absence of the resonance Raman effect, which strongly enhances the chromate symmetric stretching band, and the absence of any laser-induced photodecomposition, it is advantageous to acquire data at 785.0 nm. The band-shape and the position of the chromate bending modes proved to be more sensitive to the solid solution composition and crystalline structure than the stretching modes and can be used as distinctive spectral markers to discriminate among the different chrome yellow forms that are present. Copyright © 2014 John Wiley & Sons, Ltd.

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