Colonisation of wall paintings by microorganisms and other organisms is a well-known problematic phenomenon. Besides taxonomic identification of the biodeteriogen, it is essential to evaluate the consequences of the colonisation, e.g., unsightly coloured patinas. This work proposes new methodology for characterisation of the nature of the main carotenoids and their distribution in brown stains or patinas of a deteriorated wall painting on the north wall of the atrium of Marcus Lucretius House (Pompeii, Italy). Characterisation of the brown patinas and surrounding areas (plaster and polychromy) from the wall painting started with in situ screening using, mainly, a portable Raman instrument with a handheld FTIR (DRIFTS sampling interface) in order to select the sampling areas suitable for further analysis in the laboratory. Two wall painting fragments were then analysed in the laboratory in two steps. First, microscopic observations (SEM and phase-contrast microscopy) were used to determine whether biodeteriogens were present in the samples. In a second step, confocal Raman microscopy (785 and 514 nm excitation lasers) was used to characterise the main biogenic compounds of the brown stains. Because of the resonance Raman effect (514 nm excitation laser), it was possible to obtain reliable Raman features to assign not only the nature of the main biogenic pigments (carotenoids) present in the stains, but also their spatial conformation. Moreover, Raman confocal applications, for example, Raman imaging and depth profiling were also used in a first attempt to determine the distribution of biosynthesised carotenoids in the stains, and to determine the thickness of the brown patinas.
Non-invasive Raman spectroscopy for molecular analysis, assisted with other analytical techniques such as X-ray fluorescence for elemental analysis were applied to characterise possible pathologies on cement mortar and concrete (cementitious materials) from a historical 19 th century lighthouse exposed to the open air, in Igueldo (San Sebastian, Basque Country, North of Spain). The spectroscopic observations were compared with quantitative concentration values of cations and anions extracted as soluble salts, treated by chemometric tools. The integrated analytical techniques were used to diagnose the influence of (1) marine aerosol, (2) seagull droppings and (3) original addition of sulphates to the cementitious materials, on the formation of decaying products such as chlorides, sulphates, nitrates, etc., that affect the integrity of the lighthouse outdoor area.
In this work, a multianalytical methodology based on a combination of spectroscopic techniques such as Raman spectroscopy and micro energy dispersive X-ray fluorescence spectroscopy, and soluble salt analysis by means of ion chromatography followed by a correlation analysis of these data was applied, in order to identify the nature of the deterioration compounds present in different building materials located on inner rooms from the ground floor of the Igueldo lighthouse (San Sebastian, Basque Country, North of Spain), and in order to prove if marine aerosol could contribute to cause deterioration processes in this kind of materials. The main deterioration compounds identified were sulfate and nitrate salts. Taking into consideration the positioning of some materials, a gypsum plaster covering them could be the sulfate source responsible of the crystallisation process of a wide variety of sulfate salts. Nevertheless, in some areas were no gypsum plaster remains are present, ammonium sulfate crystallisations were identified. The presence of this kind of sulfate could suggest a possible sulfate input coming from the migration of ammonium sulfate (among other sulfate salts) carried on marine aerosol, which can be deposited on the facade of the lighthouse and migrate to its inner areas. The possible source of nitrates that could cause the crystallisation of a wide variety of nitrate salts identified in this work could be the infiltration of ammonium nitrates coming from seagull droppings from outdoor to indoor areas.
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