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Fig. 3 Stereomicroscope images of the plaquette samples collected on the South fagade of the Church of the Third Order of St. Francis (Porto): a black film, b green layer and ¢ ochre patina During desorption, the sample capsule was introduced in he furnace preheated at 100°C and the temperature was The black films, covering approximately 70% of the granite surface of the Terceiros Church South facade, varied either in morphology and dark tone. The experi- mental measurements on black areas (Table 1) show there

Figure 3 Stereomicroscope images of the plaquette samples collected on the South fagade of the Church of the Third Order of St. Francis (Porto): a black film, b green layer and ¢ ochre patina During desorption, the sample capsule was introduced in he furnace preheated at 100°C and the temperature was The black films, covering approximately 70% of the granite surface of the Terceiros Church South facade, varied either in morphology and dark tone. The experi- mental measurements on black areas (Table 1) show there

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Fig. 1 South fagade of the Church of the Third Order of St. Francis (Porto) before the conservation and restoration works
Fig. 1 South fagade of the Church of the Third Order of St. Francis (Porto) before the conservation and restoration works
Fig. 2 Photogrammetric framework of the South facade of the Church of the Third Order of St. Francis (Porto) depicting the mapping of black films (grey colour) and the sampling sites [2007 campaign (orange filled circle) and 2008 campaign (blue filled circle)|
Fig. 2 Photogrammetric framework of the South facade of the Church of the Third Order of St. Francis (Porto) depicting the mapping of black films (grey colour) and the sampling sites [2007 campaign (orange filled circle) and 2008 campaign (blue filled circle)|
Table 1 Comparison of chromatic parameters of stone affected and not affected by black films at the Church of the Third Order of St. Franci (Porto)
Table 1 Comparison of chromatic parameters of stone affected and not affected by black films at the Church of the Third Order of St. Franci (Porto)
Fig. 4 SEM images depicting: a black film deposited on the cleavage planes of exfoliated biotite and a fly ash rich in carbon, b small particles filling the spaces between the cleavage planes of muscovite, ¢e black film associated with abundant filamentous biological struc- tures (hyphae), d porous round particle rich in carbon
Fig. 4 SEM images depicting: a black film deposited on the cleavage planes of exfoliated biotite and a fly ash rich in carbon, b small particles filling the spaces between the cleavage planes of muscovite, ¢e black film associated with abundant filamentous biological struc- tures (hyphae), d porous round particle rich in carbon
Fig. 5 Stereomicroscopy image of mineral grains delimited by a black rim attributed to dematiaceous fungi
Fig. 5 Stereomicroscopy image of mineral grains delimited by a black rim attributed to dematiaceous fungi
The stone used in this monument is an inherited slightly weathered granite; in quarry stone samples, analysed by Sequeira Braga et al. (2002), dissolution features
The stone used in this monument is an inherited slightly weathered granite; in quarry stone samples, analysed by Sequeira Braga et al. (2002), dissolution features
Fig. 7 Apothecium of the lichen Sarcogyne privigna identified in samples from the South fagade of the Church of the Third Order of St. Francis
Fig. 7 Apothecium of the lichen Sarcogyne privigna identified in samples from the South fagade of the Church of the Third Order of St. Francis
Fig. 8 SEM images of the green layers revealing: a albite (Ab) crystal with dissolution features embedded in the algal layer, b kaolinize feldspar extensively etched, ¢ quartz grain clearly defined triangular etch pits
Fig. 8 SEM images of the green layers revealing: a albite (Ab) crystal with dissolution features embedded in the algal layer, b kaolinize feldspar extensively etched, ¢ quartz grain clearly defined triangular etch pits
Fig. 9 SEM images showing: a flattened-shaped material occurring beneath the green layer, b EDS spectrum of the carbon-rich material, c calcium oxalate, whewellite (Whe)
Fig. 9 SEM images showing: a flattened-shaped material occurring beneath the green layer, b EDS spectrum of the carbon-rich material, c calcium oxalate, whewellite (Whe)
the fractures of minerals and have a very slow growth. However, it is hard to confirm if there is a significant contribution of the fungi listed in the Table 2 to the blackening of granite, because they are commonly identi- fied in the air, grow fast in cultures and could represent airborne spores deposited on the granite surface.
the fractures of minerals and have a very slow growth. However, it is hard to confirm if there is a significant contribution of the fungi listed in the Table 2 to the blackening of granite, because they are commonly identi- fied in the air, grow fast in cultures and could represent airborne spores deposited on the granite surface.
Fig. 11 SEM-EDS images depicting: a oxalate patina entrapped in endolithic structures, b aggregates of oxalate patina, ec EDS spectrum confirming the presence of whewellite (Whe)
Fig. 11 SEM-EDS images depicting: a oxalate patina entrapped in endolithic structures, b aggregates of oxalate patina, ec EDS spectrum confirming the presence of whewellite (Whe)
represented by the phytadiene peaks (br17), etc. The detection of benzonitriles (A8, A1l2 and A14), along with the detection of compounds directly derived from peptidic material confirms the significant presence of proteins in the studied films (Saiz-Jimenez et al. 1990, 1995). typically synthesised by living organisms (Saiz-Jimenez 1995). Lipids are represented in the desorption products by aliphatic hydrocarbons, fatty acids, carotenoids and ste- roids. N-alkanes and n-alkenes in the range Cio—-C19 were minor compounds in the evaporate and showed an increasing in the pyrolysis at 500°C. Phytadienes are thermal degradation products from chlorophylls (Saiz- Jimenez et al. 1990) and their presence cou contribution of algae, which is in fair agree d indicate the ment with the relatively important presence of heptadecane, a predomi- nant constituent of most cyanobacteria and 1969; Gelpi et al. 1970). algae (Jones In this type of pyrolysis, there is an abundance of aromatic hydrocarbons and phenols (see peaks A4—A15 in Fig. 12b). Benzene derivatives (A4—-A6) and phenols (A7, A9, A10) were related to pyrolysis of amino acids (Saiz-Jimenez et al. 1990; Moldoveanu 2010). Polycyclic aromatic hydrocarbons (PAH) were also identified (A1: dimethylnaphthalene; A2: dibenzo[a,cJanthracene; A3: triphenylene-2-carbonitrile; All: naphthalene; A15: flu- orene). They could be anthropogenic compounds derived from incomplete combustion of organic matter (Schiavon et al. 1995) and have been identified, amongst other sources, in smoke particles from plant burning (Standley and Simoneit 1987) and diesel or gasoline engine soot (Yu and Hites 1981). However, some aromatic structures (i.e. benzene, toluene, phenol, benzonitrile, naphthalene and fluorene) were produced in the pyrolysis of 5-amino- isophthalic acid, the two latter compounds denoting condensation reactions from single rings (Moldoveanu 2010), a reaction that cannot be ruled out in our case. To summarise, the data obtained from analytical pyrolysis indicate that the main sources of organic matter in the black films are biogenic, particularly reflecting a cyanobacterial and algae origin, and is compatible with the pyrolysis of lichen thalli, as described by Saiz- Timenez7 et al. (1991).
represented by the phytadiene peaks (br17), etc. The detection of benzonitriles (A8, A1l2 and A14), along with the detection of compounds directly derived from peptidic material confirms the significant presence of proteins in the studied films (Saiz-Jimenez et al. 1990, 1995). typically synthesised by living organisms (Saiz-Jimenez 1995). Lipids are represented in the desorption products by aliphatic hydrocarbons, fatty acids, carotenoids and ste- roids. N-alkanes and n-alkenes in the range Cio—-C19 were minor compounds in the evaporate and showed an increasing in the pyrolysis at 500°C. Phytadienes are thermal degradation products from chlorophylls (Saiz- Jimenez et al. 1990) and their presence cou contribution of algae, which is in fair agree d indicate the ment with the relatively important presence of heptadecane, a predomi- nant constituent of most cyanobacteria and 1969; Gelpi et al. 1970). algae (Jones In this type of pyrolysis, there is an abundance of aromatic hydrocarbons and phenols (see peaks A4—A15 in Fig. 12b). Benzene derivatives (A4—-A6) and phenols (A7, A9, A10) were related to pyrolysis of amino acids (Saiz-Jimenez et al. 1990; Moldoveanu 2010). Polycyclic aromatic hydrocarbons (PAH) were also identified (A1: dimethylnaphthalene; A2: dibenzo[a,cJanthracene; A3: triphenylene-2-carbonitrile; All: naphthalene; A15: flu- orene). They could be anthropogenic compounds derived from incomplete combustion of organic matter (Schiavon et al. 1995) and have been identified, amongst other sources, in smoke particles from plant burning (Standley and Simoneit 1987) and diesel or gasoline engine soot (Yu and Hites 1981). However, some aromatic structures (i.e. benzene, toluene, phenol, benzonitrile, naphthalene and fluorene) were produced in the pyrolysis of 5-amino- isophthalic acid, the two latter compounds denoting condensation reactions from single rings (Moldoveanu 2010), a reaction that cannot be ruled out in our case. To summarise, the data obtained from analytical pyrolysis indicate that the main sources of organic matter in the black films are biogenic, particularly reflecting a cyanobacterial and algae origin, and is compatible with the pyrolysis of lichen thalli, as described by Saiz- Timenez7 et al. (1991).
Table 3 Peak identification of pyrolysis gas chromatography—mass spectrometry products by classes component Carbohydrates (polysaccharidic-derived structures)
Table 3 Peak identification of pyrolysis gas chromatography—mass spectrometry products by classes component Carbohydrates (polysaccharidic-derived structures)
Peak labels P, C, FA and A refers to molecules derived from peptides, carbohydrates, fatty acids and aromatic structures, respectively Conclusions also detected in this study, colonising the blackish granite outer surfaces of the Terceiros Church. Chemical analysis confirms the microscopic results obtained in this study and pointed out to the presence of organic matter synthesised by phototrophic organisms. Numerous biological marker compounds indicate a signifi- cant presence of biogenically derived material, indicating that biological activity is playing a major role in the bio- geochemical processes occurring in this historic building, evidenced by the blackening of the South facade. In addi- tion, the industrialised twentieth century and subsequent air pollution, as in most European cities, also contributed to the blackening of the granite surface. Analytical pyrolysis in combination to SEM-EDS and XRD provided valuable information concerning the composition of the coloured The scientific approach carried out to study the granite surfaces of the Third Order of St. Francis (Porto) revealed that the detachment process have been caused essentially by the activity of phototrophic microorganisms. In fact, the growth of endolithic lichens, as Sarcogyne privigna, and cyanobacteria is compatible with the detachment process because their growth produces dissolution of minerals and generates a weak interface in the granite, prone to its detachment as plaquettes. Numerous biological marker compounds indicate a signifi- because their growth produces dissolution of minerals and
Peak labels P, C, FA and A refers to molecules derived from peptides, carbohydrates, fatty acids and aromatic structures, respectively Conclusions also detected in this study, colonising the blackish granite outer surfaces of the Terceiros Church. Chemical analysis confirms the microscopic results obtained in this study and pointed out to the presence of organic matter synthesised by phototrophic organisms. Numerous biological marker compounds indicate a signifi- cant presence of biogenically derived material, indicating that biological activity is playing a major role in the bio- geochemical processes occurring in this historic building, evidenced by the blackening of the South facade. In addi- tion, the industrialised twentieth century and subsequent air pollution, as in most European cities, also contributed to the blackening of the granite surface. Analytical pyrolysis in combination to SEM-EDS and XRD provided valuable information concerning the composition of the coloured The scientific approach carried out to study the granite surfaces of the Third Order of St. Francis (Porto) revealed that the detachment process have been caused essentially by the activity of phototrophic microorganisms. In fact, the growth of endolithic lichens, as Sarcogyne privigna, and cyanobacteria is compatible with the detachment process because their growth produces dissolution of minerals and generates a weak interface in the granite, prone to its detachment as plaquettes. Numerous biological marker compounds indicate a signifi- because their growth produces dissolution of minerals and
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