Browsing by Author "Ranguelov B."

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    Characterization of art materials and degradation processes in the exterior wall paintings of the main church of Rila Monastery, Bulgaria
    (2023-09-01) Stamboliyska B.; Tapanov S.; Kovacheva D.; Atanasova-Vladimirova S.; Ranguelov B.; Yancheva D.; Velcheva E.; Stoyanov S.; Guncheva M.; Fischer D.; Lederer A.
    The present study focused on the characterization of the art materials and the degradation processes in the exterior (exonarthex) mural paintings of the main church of the Nativity of the Virgin in Rila monastery, Bulgaria, which is believed to be the last large-scale example of Eastern Orthodox wall painting. For the first time the art materials used to create a unique and colourful polychrome decoration of the outer gallery and the possible degradation products, caused by atmospheric influence - permanent exposure to open air and moisture - were revealed by a multi-technique approach. The mineral pigments were identified by means of attenuated total reflectance Fourier transform infrared (ATR-FTIR), micro-Raman spectroscopy, scanning electron microscopy energy dispersive X-ray spectroscopy (SEM-EDS) and X-ray diffraction (XRD). The natural yellow, red ochre, and green earth pigments, as well as some synthetic ones such as ultramarine and vermillion, were found in stable condition. Minium and emerald green pigments showed chemical transformations due to adverse environmental conditions which lead to chromatic changes of wall paintings. Black discolouration occurred due to the conversion of orange minium to black plattnerite (PbO2) and white discolouration – due to its transformation to white lead carbon oxide (PbCO3). The copper acetoarsenite (Cu(CH3COO)2.3Cu(AsO2)2) in the emerald green pigment showed partial transformation to arsen-containing mineral phases clinoclase and lindackerite, which fortunately did not affect much the colour appearance. Gypsum and calcium oxalate were found in the majority of the microsamples as decay products. Analysis of the binders by enzyme-linked immunosorbent assay (ELISA) implied the use of the Orthodox Church post-Byzantine egg-tempera technique. The registered Ca metal oxalates in accordance with ELISA results suggested binder chemical degradation induced by external factors. Most of the used painting materials are close to the those found in other Eastern Orthodox Byzantine and post-Byzantine monuments which indicates that the wall painting decoration of the main church of Rila monastery continues the post-Byzantine traditions. On the other hand, the study showed that the exonarthex wall paintings of the main charge of Rila monastery bear some new features as the religious artists supplemented the colourful scheme by emerald green as a new pigment and replaced smalt by the brighter synthetic ultramarine.
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    Synthesis Of Znteo3 by crystallization of glasses in TeO2-Bi2O3-ZnO-Nb2O5 system
    (2018-01-01) Ganev S.; Bachvarova-Nedelcheva A.; Iordanova R.; Ranguelov B.; Parvanov S.
    The aim of the present work is to verify the synthesis of zinc tellurite by crystallization of glasses in TeO2 - Bi2O3 - ZnO - Nb2O5 system. The investigation refers to TeO2 - based glasses containing up to 10 mol % of Nb2O5 and Bi2O3 and ZnO content raging from 5 mol % to 10 mol %. Several glasses are selected and heat treated for 6h at 500°C. The XRD analysis detects formation of several ZnTeO3, TeO2 and ZnO crystalline phases. Additional information for the formation of ZnTeO3 crystalline phase is obtained by infrared spectroscopy (IR). There is a difference in the IR spectra of the crystalline sample of 50TeO2.50ZnO (ZnTeO3) and those of the multicomponent glasses. The spectra analysis shows that the glass network consists mainly of TeO4 (tbp) units, while TeO3 (tp) are the main structural units in the crystalline ZnTeO3 phase. The microstructure of the selected crystallized samples is examined by SEM analysis.