title: Temperature-related degradation and colour changes of historic paintings containing vivianite.
abstract: 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 Mössbauer 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.
authors.affiliation: Institute of Inorganic Chemistry of the AS CR, v.v.i., ALMA Laboratory & Laboratory of Low Temperatures, Husinec-Řež 1001, 250 68 Řež, Czech Republic; Academy of Fine Arts in Prague, ALMA Laboratory, U Akademie 4, 170 22 Prague 7, Czech Republic; Institute of Geochemistry, Mineralogy and Mineral Resources, Faculty of Science of Charles University in Prague, Albertov 6, 128 43 Prague 2, Czech Republic. Electronic address: cermakova@iic.cas.cz.
authors.forename: Zdeňka
authors.initials: Z
authors.lastname: Čermáková
authors.affiliation: Institute of Inorganic Chemistry of the AS CR, v.v.i., ALMA Laboratory & Laboratory of Low Temperatures, Husinec-Řež 1001, 250 68 Řež, Czech Republic.
authors.forename: Silvie
authors.initials: S
authors.lastname: Švarcová
authors.affiliation: Academy of Fine Arts in Prague, ALMA Laboratory, U Akademie 4, 170 22 Prague 7, Czech Republic.
authors.forename: Janka
authors.initials: J
authors.lastname: Hradilová
authors.affiliation: Institute of Inorganic Chemistry of the AS CR, v.v.i., ALMA Laboratory & Laboratory of Low Temperatures, Husinec-Řež 1001, 250 68 Řež, Czech Republic; Academy of Fine Arts in Prague, ALMA Laboratory, U Akademie 4, 170 22 Prague 7, Czech Republic.
authors.forename: Petr
authors.initials: P
authors.lastname: Bezdička
authors.affiliation: Institute of Inorganic Chemistry of the AS CR, v.v.i., ALMA Laboratory & Laboratory of Low Temperatures, Husinec-Řež 1001, 250 68 Řež, Czech Republic.
authors.forename: Adriana
authors.initials: A
authors.lastname: Lančok
authors.affiliation: Academy of Fine Arts in Prague, ALMA Laboratory, U Akademie 4, 170 22 Prague 7, Czech Republic.
authors.forename: Vlasta
authors.initials: V
authors.lastname: Vašutová
authors.affiliation: Institute of Information Theory and Automation of the AS CR, v.v.i., Pod Vodárenskou věží 4, 182 08 Prague 8, Czech Republic.
authors.forename: Jan
authors.initials: J
authors.lastname: Blažek
authors.affiliation: Institute of Inorganic Chemistry of the AS CR, v.v.i., ALMA Laboratory & Laboratory of Low Temperatures, Husinec-Řež 1001, 250 68 Řež, Czech Republic; Academy of Fine Arts in Prague, ALMA Laboratory, U Akademie 4, 170 22 Prague 7, Czech Republic.
authors.forename: David
authors.initials: D
authors.lastname: Hradil
mesh_terms: D004396:Coloring Agents / Q000032:analysis*; D005296:Ferrous Compounds / Q000032:analysis*; D049669:History, 16th Century; D049670:History, 17th Century; D006358:Hot Temperature; D010084:Oxidation-Reduction; D010150:Paint / Q000032:analysis* / Q000266:history; D010151:Paintings / Q000266:history; D010710:Phosphates / Q000032:analysis*; D015204:Spectroscopy, Mossbauer; D013059:Spectrum Analysis, Raman; D014961:X-Ray Diffraction
chemical_list: D004396:Coloring Agents; D005296:Ferrous Compounds; D010710:Phosphates; C518753:ferrous phosphate
keywords: Degradation; High-temperature X-ray diffraction; Model experiments; Mössbauer spectroscopy; Vivianite