Caracterização da colonização microbiana da pintura mural de três igrejas
: estudo preliminar do crescimento microbiano, avaliação da actividade de biocidas e proposta de intervenção futura

  • Alexandra Marco (Student)

Student thesis: Master's Thesis

Abstract

The present study relates to an investigation around three sets of fresco mural paintings showing surface alteration due to microbial colonization. The aim was both to document the procedures for collecting and processing samples in order to gather a wide range of knowledge of the original mural painting technique, and to characterize the current state of heritage conservation so as to plan conservation and restoration measures. The research comes to a focus on three case studies: Santa Eulália Church of the Monastery of Arnoso/São Salvador Church, in Vila Nova de Famalicão; São Tiago Church/Parish Church of Valadares, in Baião; and Santa Cristina of Serzedelo Church, in Guimarães. The three Romanic churches, made of porphyritic granite (biotitic) with coarse grain, fall within rural environments as perceived by the consultation of geological maps. Santa Eulália is from the XIIth century, Santa Cristina of the middle of the XIIIth century, and São Tiago probably of the end of the XIIIth century. The interior walls are partially covered with mural paintings: Sta. Eulalia presents a first campaign possibly from the XVth century and overlaying it, one from the XVIth century. Sta. Cristina has several campaigns on different walls, being the latest from the XVIth century. S. Tiago has only one campaign from the XVth century. Twenty seven samples were collected during the investigation and underwent analysis to identify the constitution of the mural paintings by using μS-FTIR combined with stratigraphic. The analysis revealed they feature as frescos, showing mostly just one layer of mortar and extremely thin layers of plaster and polycromy. The study of the surface changes unveiled a degradation, common to the three monuments, shown by the presence of black biofilms of microbiological origin. Different methods of exam were undertaken for their study and characterization assessment: optical microscopy; classical microbiology methods and isolate identification by molecular biology; spectrometry of UV-Visible; CIE L*a*b*; and scanning electron microscopy (SEM). Based on thirty six samples taken from the location where the chromatic changes were visible, twenty six filamentous fungi and forty three bacteria/yeasts were isolated. Seven filamentous fungi were identified to the species and belonged to three different genera – Aspergillus, Penicillium and Alternaria. Four fungi isolates were selected among those with the capability of producing black pigmentation for treatments with four commercial biocides and five essential oils, and the minimum inhibitory concentrations determination. Assays were implemented for the pigment chemical isolation and characterization produced by these fungi and for the removal of the patina through pigment extraction protocols and fungal peroxidase enzymatic degradation. A diminished coloration was obtained in test specimens’, forecasting future use. Water is the main deterioration agent of frescos in the three case studies, with particular emphasis in Sta. Eulália and Sta. Cristina due to capillarity migration towards the granite interior. Values of Relative Humidity and Temperature were collected both inside and outside of the monuments. In the case of Santa Eulalia, direct sunlight is another important risk factor. The combination of these three factors is responsible for significant loss of chromatic surfaces and unaesthetic black stains by fungal biocolonization, since the removal of the altars (1941 and 1945). Thus, it has been considerd appropriate to evaluate the factors and magnitude of risk, aiming the development of an interpretative framework for decisionmaking on priority measures to be executed on a future preventive conservation plan. This paper aims to fill a gap in the conservation and restoration of mural paintings in relation to the frequent absence of analysis regarding the characterization and identification of black biofilms of microbiological origin, or how to remove them.
Date of Award12 Jul 2016
Original languagePortuguese
Awarding Institution
  • Universidade Católica Portuguesa
SupervisorEduarda Vieira (Supervisor), Patrícia Moreira (Co-Supervisor) & Joaquim Caetano (Co-Supervisor)

Keywords

  • Black biofilms
  • Fungi
  • Relative humidity/temperature
  • Risk assessment

Designation

  • Mestrado em Conservação e Restauro de Bens Culturais

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