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Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X-ray diffraction study

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    0441814 - ÚACH 2016 RIV GB eng J - Journal Article
    Čermáková, Zdeňka - Bezdička, Petr - Němec, I. - Hradilová, J. - Šrein, V. - Blažek, Jan - Hradil, David
    Naturally irradiated fluorite as a historic violet pigment: Raman spectroscopic and X-ray diffraction study.
    Journal of Raman Spectroscopy. Roč. 46, č. 2 (2015), s. 236-243. ISSN 0377-0486
    R&D Projects: GA ČR GAP103/12/2211
    Institutional support: RVO:61388980 ; RVO:67985556
    Keywords : fluorite * pigment * fluorescence bands * diffraction lines broadening * irradiation
    Subject RIV: CA - Inorganic Chemistry
    Impact factor: 2.395, year: 2015

    Naturally irradiated violet fluorite, a cubic CaF2mineral, is a rare historic pigment. Its documented usage in Europe stretches from ca. 1450 to ca. 1550. The intensely coloured violetish black naturally irradiated fluorite is commonly called antozonite, which is only vaguely defined based on its dark colour and specific odour emanated during grinding. In the published literature, there have been some discrepancies about its Raman spectrum. Therefore, sixteen samples of antozonite were analysed by Raman (micro-)spectroscopy using five different excitation laser wavelengths (445, 532, 633, 780 and 1064 nm), which revealed specific bands located below500 cm 1 probably related to radiation-caused defects. Their intensity increasedwith increasing violet colour saturation, thus providing a specification for antozonite’s definition. Spectra excited at 445 and 780nmcontained also numerous broad bands above 500 cm 1, which seem to be caused by the presence of rare earth elements. The structural damage of antozonite samples has been assessed by X-ray diffraction and related to their lightness using analysis of image histograms. The obtained results have been applied in the analysis of micro-samples of a Late Gothic altarpiece located in an Italian Court in UNESCO city Kutná Hora, Czech Republic, which contained exceptionally large grains of deep violet fluorite identified as antozonite.
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