Bobos, Iuliu

Campos, Bruno

Marco, Alexandra

Moreira, Patricia

Pintado, Manuela

Valadas, Sara

Vieira, Eduarda

English

Repositório Institucional da Universidade Católica Portuguesa

Chemical characterization of black stains on mural paintings with granite support from churches of Northern Portugal Bruno Campos1, Alexandra Marco2, Sara Valadas3, Iuliu Bobos4, Eduarda Vieira2, Manuela Pintado1, Patrícia Moreira1,21  CBQF Centre for Biotecnology and Fine Chemistry, Universidade Católica Portuguesa2  CITAR Research Centre for Science and Technology of the Arts, Universidade Católica Portuguesa3  Laboratory HERCULES, School of Sciences and Technology, University of Évora4  Institute of Earth Sciences (ICT) – Geology Centre of the University of Porto (CGUP)Introduction Goals & MethodsResults & DiscussionConclusionsMural paintings are art elements inseparable from the architectural monument which aids to definethe cultural identity of a country and contribute to the economic development of their implantationregions1,2.The main problems associated to mural paintings, inside churches, are intrinsically inherent to thedeterioration phenomena, namely, biocolonisation and physical-chemical weathering leading toaesthetical alterations and weakening the mechanical properties of materials3.During recent surveys, black stains were detected in 15th-16th centuries mural paintings andrespective granite support in several Romanic churches in the north of Portugal.The present poster intends to elucidate the chemical composition of black stains on the granitesupport in order to establish the hypothetical relation between the black stains on mural paintingand their support.This research work is part of Bio4mural, a project aiming at the development of innovative solutionsfor cleanings and preventive conservation of mural paintings. In order to develop cleaning andpreventive solutions, chemical characterization of pigmentation on the granite support and itsrelationship with the mural painting is a crucial task. The fulfillment of this task has required theselection of cases studies, sample collecting protocols and application of characterizationtechniques in situ and in laboratory. The used methods are briefly described below:• Cases studies: Church of Vila Marim and Church of Folhadela (district of Vila Real);• Samples collecting: scrapping with scalpel;• In situ: Digital Microscopy (Dino-lite Pro-X); Colorimetry (Visible spectrometer DatacolorMercury 3000) and EDXRF (Bruker Tracer III/IV SD);• Laboratory: FT-IR (Bruker Tensor 27 spectrometer).The blackening of mural paintings and the respective granite support is a peculiar deterioration of the constituent materials.The Church of Vila Marim and the Church of Folhadela are two examples of this phenomenon and have in common theproximity (district of Vila Real) and the building blocks are essentially made of granite. The most abundant type of blackeningare stains, pigmentated dots were mostly found in wall C (Folhadela). Moreover, mostly of hyphae images were also found inwall C, suggesting the possible formation of pigmentated dots by microbial influence. The CIELAB colour coordinates showsome similarity between brown and black-purple pigmentation of both churches and XRF showed that Fe and Mn are themost abundant elements in brown and black-purple pigmentation, respectively, possibly by efflorescence of their soluble saltsand the formation of Fe and Mn oxides at the surface. The FT-IR analysis may support this hypothesis showing a possiblepresence of Fe and Mn oxides (at 582 and 532 cm-1) and a probable blackening attributed to a microbial community due tothe carbonaceous assignments (at 2924 and 2851 cm-1).FrameworkThe two cases studies selected were the Church of Vila Marim or Sta. Marinha (Fig. 1a) and the Church of Folhadela or St.Tiago (Fig 1b). The criteria was based on the blackening of chromatic layer and granite and the geographical proximity(district of Vila Real). The two Romanic churches are made of coarse-grained granite, probably built between 13th-14thcentury. The interior walls are partially covered with mural paintings with several campaigns and dated from the 15th century,being attributed to the painter Arnão.a                                                                                     bFig. 1 Pictures of the selected case studies. (a.) On the left the church of Vila Marim and (b.) on the right the church ofFolhadela. The expanded pictures represent the areas of sampling and analysis on granite. Wall A = left wall; Wall C = rightwall.Digital Microscopy & ColorimetryThe typology of pigmentation found in the expanded pictures of Fig. 1 can bedesignated by stains (Vila Marim and wall A of Folhadela) and by dots (wall C ofFolhadela). The colour observed varies from brown (Fig. 2a) to a bright black-purple (Fig. 2b) and images taken by a digital microscope showed the presence ofhyphae (Fig. 2c) in some samples, revealing the possible influence of fungi in theformation of the pigmentation4.a                              b                              cFig. 2 Digital microscopy images (435x magnification) of a brown (a) and a black-purple stain (b) of wall A and a brown dot with hyphae found in wall C (c).The CIELAB parameters (Table 1), obtained by colorimetry, and the calculated ΔE*ab(∆E*ab = [(∆L2 ) + (∆a2 ) + (∆b2 )]1/2) for black-purple (9,05) and brown (15,23)pigmentation shows some similarity between the pigmentation of Vila Marim (VM)and Folhadela (F).Table 1. CIELAB colour coordinates for Vila Marim and Folhadela samples. L = lightness; a = red/green value and b = yellow/blue value.EDXRFThe EDXRF analysis made in situ on brown and black-purple pigmentation and granite revealed the presence of sometypical inorganic elements, such as Al, Ca, Fe, K and Si (Table 2). For brown pigmentation the higher percentage canbe attributed to Fe (28%-77%) and for black-purple to Mn (8%-51%). The possible formation of pigmentation can beassigned to the efflorescence of Fe (probably from biotite) and Mn soluble ions through the granite, forming at thesurface Fe and Mn oxides. Some authors ascribed the oxidation of Mn (II into III/IV) to the presence of a microbialcommunity5 and Mn and Fe are also found in Fungal peroxidases (heme plus cofactor). The element K (2%-14%) andCa (1%-23%) are also elements with representativity, mainly for granite, probably, due to the presence of thepotassic- and calcic-feldspars minerals and the calcium carbonate of the lime mortar.Table 2. Relative abundance (%) of atomic elements present in brown and black-purple pigmentation and granite.ReferencesPigmentation L a b ΔL Δa Δb ΔE*abBlack-Purple (VM) 17,10 0,52 1,918,57 1,90 2,18 9,05Black-Purple (F) 25,67 2,42 4,09Brown (VM) 22,20 0,68 3,088,23 6,09 11,29 15,23Brown (F) 30,43 6,77 14,37Wall A Wall C1. Rosewell, R. (2014). Medieval wall paintings. Oxford: Shire Publ.2. Palmeirão, J. et al (2018). The shift of paradigm when religious art works become heritage: The dilemma of material vs.immaterial significance. An overview of Portuguese Reliquaries and Mural Paintings. In: U. Schädler-Saub and B. Szmygin,ed., CONSERVATION ETHICS TODAY: ARE OUR CONSERVATION-RESTORATION THEORIES AND PRACTICE READY FOR THE 21STCENTURY?. Lublin: International Scientific Committee for Theory and Philosophy of Conservation and Restoration ICOMOS,pp.375-379.3. Costantini, I., Castro, K. and Madariaga, J. (2018). Portable and laboratory analytical instruments for the study of materials,techniques and environmental impacts in mediaeval mural paintings. Analytical Methods, 10(40), pp.4854-4870.4. De la Rosa, J., Martin-Sanchez, P., Sanchez-Cortes, S., Hermosin, B., Knicker, H. and Saiz-Jimenez, C. (2017). Structure ofmelanins from the fungi Ochroconis lascauxensis and Ochroconis anomala contaminating rock art in the LascauxCave. Scientific Reports, 7(1).5. Saiz-Jimenez, C., Miller, A., Martin-Sanchez, P. and Hernandez-Marine, M. (2012). Uncovering the origin of the black stains inLascaux Cave in France. Environmental Microbiology, 14(12), pp.3220-3231.6. Casanova Municchia, A., Bartoli, F., Bernardini, S., Caneva, G., Della Ventura, G., Ricci, M., Boun Suy, T. and Sodo, A. (2016).Characterization of an unusual black patina on the Neang Khmau temple (archaeological Khmer area, Cambodia): amultidisciplinary approach. Journal of Raman Spectroscopy, 47(12), pp.1467-1472.FT-IRThe pigmentation analysed by FT-IR (Fig. 3) was collected by scrapping and thoroughlyselected by optical microscope. The presence of carbonaceous compounds is indicated at2924 and 2851 cm-1 (νCH3/νCH2) and the νOH at 3433 cm-1. A sharp stronger band at1385 cm-1 is related to the ν3 stretching mode of NO3-. The weak bands at 1150 and 1100cm-1 are typical of gypsum bands. The range of bands between 1034 and 690 cm-1 may beascribed to the νSi-O of different minerals, probably Kaolinite (1034 cm-1), Quartz (783, 721and 690 cm-1) and Orthoclase (640 cm-1). The bands at 582 and 532 cm-1 suggest thepresence of νFe-O, probably Magnetite and Hematite, respectively. In the literature6 wasalso found a reference to a Mn oxide mineral at 532 cm-1.Fig. 3 FT-IR spectrum of brown and black-purple pigmentation. AcknowledgementsRelative Abundance (%)Church Pigmentation Al Ar Ca Cl Cu Fe K Mn Ni P Pb Pd Rh S Si Sr Ti ZnVila MarimBrown 0,20 5,15 7,83 0,48 2,33 28,97 6,16 21,14 6,00 0,05 0,71 4,23 10,03 0,12 2,41 1,21 2,33 0,66Black-Purple 0,14 3,75 9,41 0,33 1,15 22,88 2,82 39,90 4,52 0,04 0,33 3,18 7,17 0,10 1,39 0,92 1,43 0,54Granite 0,21 7,14 21,10 0,39 2,26 30,46 5,84 0,76 7,28 0,00 1,90 4,71 13,03 0,01 1,54 0,83 2,37 0,17FolhadelaBrown (wall A) 0,18 3,59 21,05 1,12 1,14 28,56 9,71 11,06 6,43 0,05 0,41 3,74 3,66 4,78 0,05 2,65 0,36 1,47Black-Purple (wall A) 0,07 2,52 5,25 0,52 0,90 21,86 3,70 50,65 3,43 0,03 0,42 2,50 2,12 3,24 0,04 1,03 0,38 1,32Brown (wall C) 0,04 2,61 1,41 0,30 1,12 76,69 6,59 0,92 1,96 0,02 1,05 1,45 1,21 3,08 0,06 0,28 0,44 0,76Black-Purple (wall C) 0,33 5,13 5,98 1,57 2,12 28,83 13,19 8,93 7,83 0,06 0,77 5,79 5,39 6,53 0,08 5,29 0,55 1,62Granite 0,41 3,87 22,82 1,17 1,53 29,01 11,82 1,73 6,85 0,02 0,33 4,48 4,70 5,45 0,11 4,02 0,33 1,36

Chemical characterization of black stains on mural paintings with granite support from churches of Northern Portugal

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Chemical characterization of black stains on mural paintings with granite support from churches of Northern Portugal

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