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Temperature-related degradation and colour changes of historic paintings containing vivianite

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    0442179 - ÚACH 2016 RIV NL eng J - Journal Article
    Čermáková, Zdeňka - Švarcová, Silvie - Hradilová, J. - Bezdička, Petr - Lančok, Adriana - Vašutová, V. - Blažek, Jan - Hradil, David
    Temperature-related degradation and colour changes of historic paintings containing vivianite.
    Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy. Roč. 140, APR (2015), s. 101-110. ISSN 1386-1425
    R&D Projects: GA ČR GAP103/12/2211
    Institutional support: RVO:61388980 ; RVO:67985556
    Keywords : Degradation * High-temperature X-ray diffraction * Model experiments * Mossbauer spectroscopy * Vivianite
    Subject RIV: CA - Inorganic Chemistry
    OBOR OECD: Inorganic and nuclear chemistry
    Impact factor: 2.653, year: 2015

    Temperature-related degradation of pure synthetic as well as partly oxidised natural vivianite has been studied by high-temperature X-ray diffraction (HT-XRD) covering the whole extent of the temperature-related stability of its structure. While temperatures around 70°C are already damaging to vivianite, exposition to 160°C results in complete amorphisation of both the vivianite and its oxidation products. As indicated by Mossbauer spectroscopy, temperature-induced oxidation of vivianite starts at 90°C. To study the occurring structural as well as accompanying colour changes in more detail, model vivianite paint layer samples with different historic binders were prepared and subjected to increased temperatures. Exposition to 80°C caused pronounced colour changes of all the samples: ground natural blue vivianite became grey - a colour change which has been described in actual works of art. Regarding the binders, the oil seemed to facilitate the transfer of heat to vivianite's grains. To simulate conditions of conservation treatment under which the painting is exposed to increased temperatures, oil-on-canvas mock-ups with vivianite were prepared and relined in a traditional way using iron. The treatment affected preferentially larger grains of vivianite; the micro-samples documented their change to grey, and their Raman spectra showed the change from vivianite to metavivianite.
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