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Supplementary Materials: The following supporting information can be downloaded at: https: //www.mdpi.com/article/10.3390/min13020289/s1, Figure S1: Diffractograms of hematite paintmock- ups before and after SO2-exposure test. Figure S2: Diffractograms of CIN-ST paint-mock-ups before and after SO2-exposure test. Figure S3: Diffractograms of CIN-EF paint-mock-ups before and after SO2-exposure test. Figure S4: Diffractograms of CIN-M paint-mock-ups before and after SO2- exposure test. Figure S5: Diffractograms of CIN-C paint-mock-ups before and after SO2-exposure test., Hematite- and cinnabar-based paint mock-ups prepared with either rabbit glue or egg yolk binder were artificially aged in an SO2-rich atmosphere, as a model system for investigating the deterioration of tempera paints exposed to an industrial atmosphere. The overall research aim was to identify the type of degradation occurring in tempera paints and the different alteration mechanisms related to the physical, mineralogical and chemical characteristics of the paint. Tempera mock-ups were prepared by mixing binder (egg yolk or rabbit glue) and pigment (cinnabar of different particle sizes or hematite) and were then exposed to SO2 for 2 months in accelerated aging tests. The colour, gloss, reflectance, roughness and micro-texture of the surfaces of the mock-ups were determined before and after the tests. In addition, chemical and mineralogical changes were determined by X-ray Powder Diffraction (XRPD), Attenuated Total Reflection-Fourier Transform Infrared spectroscopy (ATR-FTIR) and Scanning Electron Microscopy with Energy-Dispersive X-ray Spectroscopy (SEMEDS) analysis. Colorimetric changes were confirmed, mainly in the cinnabar-based paints containing egg yolk, and in the hematite-based paints containing rabbit glue. Neoformed mineral phases have not been detected by XRPD, but precipitation of gypsum on the exposed surfaces has been confirmed by SEM. For cinnabar-based paints, the amount of sulfate-rich deposits was higher on egg yolk mock-ups than on rabbit glue samples, though the opposite was observed for the hematite-based paints. This confirmed the influence of the binder composition and pigment-binder tandem in the susceptibility to SO2 deposition. Pigment particle size did not have a clear influence on the physical and chemical changes in the tempera mock-ups during the ageing tests., Galician Research Project LASERING-PH (ED431F 2022/07), Spanish Research Projects LASERING-PH (PID2021-123395OA-I00), AERIMPACT (CGL2012-30729), EXPOAIR (P12-FQM-1889), European Regional Development Fund (ERDF), Andalusian Research Group RNM-179, Ministry of Science and Innovation, Government of Spain through the project RYC2020-028902-I

This study describes the different alteration forms in 25 street art murals created between 2007 and 2018 on different substrates and located in different cities in NW Spain. The deterioration forms described affect the entire layer of the paintings as well as the substrates, with the most common being loss of colour (fading), loss of the pictorial layer -with or without loss of part of the substrate and biodeterioration. Physical, chemical, mineralogical and micromorphological analyses of samples from 10 murals revealed that (1) the deterioration mechanisms are related to environmental conditions and also to the inherent properties of the painting materials and to paint-substrate interaction, (2) the deterioration is closely associated with inherent aspects of urban art and (3) the loss of the pictorial record sometimes occurs in a very short period of time. The study findings highlight the need for preventive conservation measures in artworks (generally commissioned) that are intended to last. Graphical Abstract

Roughness, pigment impurities, and neoformed minerals are important factors affecting the reflectance of painted surfaces. However, other factors that have not yet been studied in detail, such as the total thickness of the paint layer and the amount of binder, should also be considered. In this research, oil painting mock-ups, each made with a different number of layers of paint containing a single pigment (lead white, orpiment, cinnabar, azurite or malachite) mixed with different proportions of oil binder, were examined using a hyperspectral imaging system. The results indicate that these characteristics do not directly influence the reflectance of the painted surface. Interestingly, we found that the distribution of the pigments and the oil binder in the paint system (and pigment-binder interaction) are also key to understanding the reflectance values. Thus, accumulation of oil on top of the uppermost paint layer in the multilayer painting mock-ups caused a reduction in reflectance. The increased translucency of the oil paint containing lead white pigment also modified the reflectance, possibly due to the formation of metal soap. Other factors found to affect the reflectance of the painting mock-ups are discussed. Universidade de Vigo | Ref. CINTECX Universidad de Granada | Ref. RMN-179 Ministerio de Ciencia e Innovación | Ref. RYC2020-028902-I

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG This paper provides preliminary data on the use of three different mechanical procedures to remove the lichen Diploschistes scruposus and a gypsum black crust from an ornamental granite. The methods used were wet sandblasting (Hydrogommage®), dry sandblasting (IBIX®) and dry-ice blasting. In addition, lichens were also removed by scraping with a scalpel. The cleaning efficacy and undesirable effects to granite were evaluated by stereomicroscopy, colour spectrophotometry, Fourier-transform infrared spectroscopy and scanning electron microscopy. The cleaning efficacy of the mechanical methods depended on the deposit being removed: i) for lichen, dry sandblasting and dry ice blasting produced the best results, while for the black gypsum crust, although both dry and wet sandblasting removed the black particulate matter from the crust, gypsum crystals remained on the surface; ii) the dry sandblasting method induced extraction of granite grains with the subsequent appearance of fissures; iii) for the lichen, the wet sandblasting method was totally unsatisfactory and iv) for the gypsum black crust, dry ice blasting failed to remove the black particulate matter from the crust. Ministerio de Economía, Industria y Competitividad | Ref. IJCI-2017-32771

Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG Lichen mosaics on different-textured schists located in the Coa Valley (Portugal) and Siega Verde (Spain) archaeological sites were cleaned using different chemicals, namely ethanol (50% v/v in distilled water), benzalkonium chloride (3% v/v) or Biotin T® (3% v/v), and different Nd:YAG laser wavelengths (1064 nm or 266 nm). The surfaces were evaluated 24 h and 4 years after cleaning to determine its durability using colour spectrophotometry and Raman spectroscopy. Unlike lasers, chemicals achieved overall satisfactory results. Cleaning effectiveness, harmfulness and durability of chemicals were highly influenced by the orientation of the schistosity planes of the stone; in Siega Verde samples, the schistosity planes parallel to the surface contributed to a low impact of the methods on the surface colour and absence of lichen recolonization. Cleaning carried out upon the devitalization of lichens with benzalkonium chloride and Biotin T were maintained longer in both sites. Ministerio de Economía y Competitividad | Ref. IJCI-2017-32771 Ministerio de Ciencia e Innovación | Ref. CGL2011-22789

Gypsum black crust is one of the most severe deterioration forms affecting the built Cultural Heritage (CH) worldwide. Its removal from granitic substrates is necessary since gypsum layer favours the deterioration of the rock. This study investigates the laser assisted removal of gypsum black crust, from a Hercynian granite from the North-West (NW) Iberian Peninsula. The suggested laser cleaning methodology involves the combination of two wavelengths (1064 nm and 355 nm) from a QS Nd:YAG laser system and is based on their simultaneous interaction with the involved materials at various fluence values and FIR/FUV ratios (1/1, 1/3 and 3/1). This ablative scheme was initially introduced in order to overcome undesirable discoloration issues recorded upon single wavelength laser cleaning of black crusts but its role to effectively remove different undesired over-layers was also acknowledged. The results of this study were comparatively evaluated with surfaces irradiated using one of the two specific wavelengths, while the presence of water as an enhancing cleaning agent was also considered. A multi-analytical evaluation methodology based on stereomicroscopy, Raman spectroscopy, Fourier Transform Infrared spectroscopy (FTIR) and Scanning Electron Microscopy with Energy Dispersive X-ray Spectroscopy (SEM-EDS), was carried out to determine the optimum cleaning strategy in terms of crust removal effectiveness and minimisation of damages to the substrate. The optimum irradiation condition determined in this study is the simultaneous application of the two wavelengths in FIR/FUV = 1/1 ratio (with FIR = FUV = 0.3 J·cm−2) on a pre-wetted surface. Under this irradiation condition a high removal level of carbonaceous pollution particles and gypsum was achieved, without any damage to the granitic minerals in the form of melting and spallation and/or exfoliation of planes of biotite and K-feldspar and cleavage fracture of quartz.

The use of adhesives to repair stone is a common conservation and restoration practice. Thermoplastic (acrylic) and thermostable (epoxy, polyester, etc) adhesives are often combined to take advantage of the benefits of both types. An intervention layer in the form of an acrylic adhesive is typically previously applied to enhance the reversibility of the structural adhesive used. However, research into the mechanical strength of the bonded stone and into the harmful effects of different adhesives on stone is scarce and is even non-existent for granites. We evaluate the effectiveness, harmful effects and reversibility of the structural adhesives Araldite AY 103-1 (epoxy resin) and Fluoline A (acrylic resin) applied with and without a previous intervention layer of Paraloid B-72, and with and without the addition of micronized silica to the structural adhesives (a common practice among restorers to change the mechanical properties of the adhesives and enhance the reversibility). We used a multi-analytical approach based on assessing shear strength of adhesive bond, water absorption by capillarity, water vapour permeability, colour, stereomicroscopy and scanning electron microscopy. Araldite with a Paraloid intervention layer, both with and without silica, proved to have the best adhesive capacity. However, failure tended to occur in the rock rather that at the join. The Paraloid B-72 intervention layer, while it enhanced reversibility, also acted as a barrier to water transport. The micronized silica enhanced both the hydric properties of the stone and the reversibility of adhesive application. Fluoline had the best reversibility profile. These findings should prove useful in informing granite-built cultural heritage interventions.

Correctly describing the deterioration patterns is of great importance for the conservation of built cultural heritage. Also, their rapid in situ quantification is an essential requisite when studying exposed stone objects, to define satisfactory restoration actions and to avoid greater damage due to the application of incorrect treatments. The research described in this paper targets developing a methodology to compute the extent of different deterioration patterns on a granitic cultural heritage object using as a case study an overpass bridge called Puente Nuevo in Ourense (NW Spain). The applied methodology consisted of the combination of the geometric and radiometric information collected from a non-invasive and in situ mobile LiDAR system (MLS) and micro destructive analytical techniques. Laser scanning points were used as a base to create orthophotos, being their intensity values the input for an unsupervised classification method to determine the areas occupied for those different deterioration patterns. In parallel, as part of this multi-analytical approach different conventional analytical techniques (X ray diffraction, Fourier transform infrared spectroscopy and optical microscopy) were applied to chemically and mineralogically characterize those deterioration patterns, namely, gypsum black crust, calcite encrustations and biological colonization (mosses). LiDAR technology allowed to determine three different clusters considering the reflectance of those surfaces: uncoated granite, calcite encrustations and black crusts and biological colonization patinas in a combined cluster due to their close reflectance spectra. The computed extent and the location of those deterioration patterns will allow to identify the most suitable cleaning treatment saving money and time.

This paper shows a study on the consolidation effectiveness of nano-silica and nano-lime-based consolidants (i.e. Nano Estel®and Nanorestore®, respectively), both available on the market, on two stones with different mineralogy and texture (i.e. two micas granite and Lioz limestone) previously subjected to 500 °C during 24 h with a rapid cooling by water jet simulating the real practice in a fire. The consolidation effectiveness was determined through the evaluation of hydro-physical properties (i.e. open porosity, apparent density, water absorption by capillarity and water absorption at atmospheric pressure), the determination of P-wave velocity (compressional wave velocity) and the study of their side-effects by using stereomicroscopy, colour spectrophotometry, Fourier transform infrared spectroscopy and scanning electron microscopy. Durability of the consolidants was determined by measuring their resistance to salt crystallization cycles and the subsequent surfaces were evaluated by open porosity measurements, stereomicroscopy, Fourier transform infrared spectroscopy and scanning electron microscopy. Results showed, as expected, that both granite and limestone samples increased their porosity after the heating process. In the case of granite stone, both products yielded similar reduction of the porosity and similar resistance to salt crystallization cycles. In case of limestone, nanolime samples yielded lower effectiveness in terms of dry matter, porosity and water absorption by capillary coefficient, which is attributed to the low penetration of Nanorestore® particles in the fine pore structure of this stone. Ethyl silicate treated samples presented higher levels of decay after crystallization cycles in the limestone samples, which could be attributed to the difficulty to bond silicate materials to fine porous calcite-based substrates.

This paper draws on the study of the prehistoric art site of Penedo Gordo (NW Spain) resulting from a collaborative interdisciplinary research. One of its primary goals was to design and put into practice a multi-analytical protocol for characterising prehistoric rock paintings, combining in situ and laboratory analytical techniques. Thus, following the archaeological assessment of the site, the panels exhibiting red paintings were analysed by colour spectrophotometry and portable Raman spectroscopy. Analytical techniques were applied to a collection of samples exhumed from the excavation that simultaneously took place on site. These included three red accretions on different substrates (compact soil, white quartzite and grey quartzite) and stone fragments representative of the outcrop’s petrographic variability, aiming to determine their mineralogical composition, texture and study the stone-paint boundaries. Moreover, colouring materials exhumed from the excavation and collected in the immediate surroundings of the rock outcrop were analysed in order to scrutinise the provenience rock art’s raw materials. Laboratory analysis consisted of stereomicroscopy, X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy. One of the major outcomes was the discovery of a drop of red pigment preserved in an archaeological layer associated with Late Neolithic/Copper Age material remains. Ministerio de Economía, Industria y Competitividad | Ref. IJCI-2017-3277

The Spanish Ministry of Economy and Competitiveness (MINECO) provided J. Santiago Pozo-Antonio award of a postdoctoral contract: Juan de la Cierva-incorporacion (IJCI-2017-3277). C. Cardell thanks the financial support provided by Spanish Research Projects AERIMPACT (CGL2012-30729) and EXPOAIR (P12-FQM-1889), the European Regional Development Fund (ERDF), and the Andalusian Research Group RNM-179. Funding for open access charge was provided by Universidade de Vigo/CISUG., Black crusts (BCs) are one of the most critical alteration forms found on stones belonging to architectural heritage. Since they could be considered as passive samplers of atmospheric pollution, it would be plausible to establish relations between the air contamination and the BCs. With this aim, we have characterized BCs collected on historic buildings from two Spanish cities (Granada and Vigo) with different polluted atmospheres, as well as formed on stone substrates of varied mineralogy and texture. Likewise, in order to assess the impact of the atmospheric pollutants on the growth of BCs, quartz fiber filters were used as surrogate substrates and placed nearby the studied buildings to collect and analyze the aerosol particulate matter (PM). To this end, an array of complementary analytical techniques was used to evaluate the mineralogy, chemical composition, and texture of the BCs and to establish the correlation with the ions, OC (organic carbon), and EC (elemental carbon) detected in the PMon the quartz fiber filters. As result, BCs developed on carbonate substrates fromGranada show more complex structure than those from Vigo, which are thinner because of frequent rain episodes. In both cities, NaCl, Pb-Cl, and Ca-Cl-rich particles, Ca-phosphate particles and clusters of Ba-sulfate-rich particles were detected. However, metal-rich rounded particles were more abundant in Granada’s BCs, including soot particles. BCs from Granada were richer in carbonaceous components (OC and EC) than the Vigo’s BCs. Although in the filters PM did not show EC—mainly due to traffic—, in the BCs from both locations OC and EC were detected. Therefore, this different composition was related to the mineralogy of the stones and the higher pollution of Granada in contrast to the industrial and sea-exposed city of Vigo., The Spanish Ministry of Economy and Competitiveness (MINECO) IJCI-2017-3277, Spanish Research Projects AERIMPACT CGL2012-30729, EXPOAIR P12-FQM-1889, European Commission, Andalusian Research Group RNM-179, Universidade de Vigo/CISUG

The physical–chemical characterization of natural and synthetic historical inorganic and mineral pigments, which may be found embedded in paintings (real or mock-ups), glass, enamel, ceramics, beads, tesserae, etc., as well as their alteration under different decay scenarios, is a demanding line of investigation. This field of research is now both well established and dynamic, as revealed by the numerous publications in high-quality journals of varied scientific disciplines. [...]

Over the last two decades, nanolime has been recognized as a promising consolidation approach to consolidate historic calcareous substrates due to its compatibility, durability and fast carbonation. The effectiveness of nanolime products has been widely proven for superficial consolidation treatments, especially in historic wall-paintings. However, its consolidation mechanism in highly porous substrates, such as in the case of limestones or lime mortars, still needs to be fully understood. This paper aims to study the influence of application method and number of applications on the effectiveness of nanolime treatments, which has never been targeted until now. In this experimental work, the Ca(OH)2 nanoparticles were freshly synthetized by anion exchange resins and applied in historic Doulting limestone samples, extracted from a capital from the Cathedral of Wells (Somerset, UK). In order to study the influence of application method on the effectiveness of treatments, samples were treated by: (1) brush; (2) spray; and (3) capillary absorption. Additionally, to study the influence of the number of applications on the consolidation effectiveness, these three application methods were applied by: (1) 1 application; (2) 5 applications; (3) 10 applications. The consolidation effectiveness of the resulting nanolime treatments was studied by assessing changes in porosity, superficial and internal stone’s density, superficial cohesion, water absorption by capillarity and aesthetic properties. Results showed that repeated applications (i.e. 10 applications) of a low concentrated nanolime (i.e. 5 g/L) by spray and brush can increase the superficial cohesion, mechanical properties and density of the stone at the surface. Additionally, results suggest that the application method does not significantly affect the consolidation effectiveness of nanolime treatment, contrary to what was commonly believed. Results also show that a single application treatment of low concentrated nanolime (i.e. 5 g/L) does not significantly provide noticeable consolidation effectiveness regardless of the application method, also contrary to what was commonly believed. These results suggest that for a noticeable consolidation treatment with low concentrated nanolime the application must consist of several applications (> 10). This could have a high impact on the Built Heritage conservation community that commonly use nanolime in conservation activities.

[EN] Microorganisms that can act as biocleaning agents can potentially be isolated from existing graffiti. In this study, a total of 30 different isolates of bacteria, fungi and yeasts were obtained from black, blue, red and silver graffiti coatings exposed outdoors conditions for 10 years. An additional strain was obtained from samples of black powdered graffiti exposed under laboratory conditions for 5 years. Each of the isolates from the most prolific sources (i.e. red and silver graffiti coatings and black powdered graffiti) was evaluated alone and in combination with Tween? 20, to determine their potential as biocleaning agents, in test tube assays. Two strains isolated from the red graffiti coating (identified as Candida parapsilosis) and one strain isolated from the black powered graffiti (identified as Rhodococcus erythropolis) performed best alone. The quantity of live cells throughout the trials and biofilm formation indicated that both strains were able to utilize the paint as a substrate. When the microorganisms isolated were combined with Tween? 20, the quantity of live cells increased notably throughout the incubation time, and turbidity and graffiti discoloration were observed. Infrared spectroscopic examination revealed that R. erythropolis performed the best alone, while the addition of Tween? 20 to C. parapsilosis enhanced the oxidative degradation of the graffiti., J.S. Pozo-Antonio is grateful to the Spanish Ministry of Economy and Competitiveness (MINECO) for a post-doctoral contract (Juan de la Cierva-Incorporacion, IJCI-2017-3277). P. Sanmartin is grateful for financial support from the Xunta de Galicia (grant ED431C 2018/32).

Two carbonate stones (a limestone and a marble), commonly used for flooring, wall cladding and countertops, were exposed to different staining agents. After each cycle (staining and cleaning with a non-ionic detergent solution), the surface degradation was assessed on a scale ranging from unchanged to severe change (based on the qualitative characterization presented on the standard UNE-EN 16301:2014), stereomicroscopy and colour spectrophotometry. After the 3 cycles, surfaces were additionally evaluated by measuring specular gloss, roughness and static contact angle and also by an optical and a scanning electron microscopes. Stones with similar chemical composition and similar physical properties, but with different microstructure and grain size, exhibited distinct sensitivity levels to the same stains. Despite chromatic changes were different depending on the stain applied, higher ΔE*ab were detected on the marble surfaces. Gloss only increased on the olive oil stained limestone, while it decreased for the rest of the surfaces; higher gloss changes were detected on the surfaces stained with red wine, blueberry juice, ketchup, citric acid and lime, being these last three surfaces those with the highest roughness increases. Hydrophilicity increased in both stones, regardless of the stain, being more marked on the surfaces with greater roughness increases. These different trends were related to the different dissolution levels of calcite grains considering the stain applied. Financiado para publicación en acceso aberto: Universidade de Vigo/CISUG Ministerio de Economía y Competitividad | Ref. IJCI-2017-32771 Fundação para a Ciência e a Tecnologia | Ref. UIDB/04028/2020

The recently proposed concept of quaternary bioreceptivity applies to substrates treated with coating materials and it is considered in the present study with the alga Bracteacoccus minor and the cyanobacterium Nostoc sp. onto granite specimens treated with ethyl silicate and nano-sized silica doped with different amounts of TiO2 (0, 0.5, 1 and 3 wt%). The findings showed a lack of correlation between the amount of TiO2 and the level of colonization (main bioreceptivity estimator) to the presence of cracks on the surface, which annul the biocidal power of TiO2. Crack formation, which depends on the mechanical properties, greatly influences the bioreceptivity of the material. Thus, the cracks provided anchor points where water is retained, in turn strongly influencing the early stages of colonization kinetics, to a greater extent than the biocidal power of TiO2, which will probably increase as the biofilm develops over the entire surface. In addition, although the cracks were more abundant and wider in the ethyl silicate-based consolidant, the nano-sized silica provided better anchoring points, making the material treated with the corresponding consolidant more bioreceptive SI

This study evaluated the self-cleaning ability and durability of Si-based consolidants (an ethyl silicate consolidant and a consolidant based on nanosized silica) spiked with nanocrystalline TiO2 activated by either UV-A radiation (spectral region between 340 and 400 nm, and main peak at 365 nm) or UV-B radiation (spectral region between 270 and 420 nm, and main peak at 310 nm). Granite samples were coated with consolidant, to which nanocrystalline TiO2 was added at different concentrations (0.5, 1, and 3%, by wt.). Diesel soot was then applied to the coated surfaces, and the samples were exposed to UV-A or UV-B radiation for 1650 h. The surface color changes, relative to the color of untreated granite, were determined every 330 h by color spectrophotometry. Slight color changes indicated a recovery of the reference color due to the degradation of the soot. The final surfaces of both the untreated and treated surfaces were compared by stereomicroscopy and scanning electron microscopy. The main findings were that: (1) In general, the consolidant containing nanosized silica induced the most intense photocatalytic activity. In the more compact xerogel coating formed by the nanosized silica, more TiO2 nanoparticles were available to interact with the radiation. (2) For all consolidant mixtures, soot degradation remained constant or decreased over time, except with ethyl silicate with 0.5 wt % TiO2 (no self-cleaning capacity). (3) Soot degradation increased with the concentration of TiO2. (4) The UV-B radiation was the most effective in terms of soot degradation, except for the surface coated with the ethyl silicate and 3% wt. TiO2 J.S. Pozo-Antonio was supported by the Ministry of Economy and Competitiveness, Government of Spain (grant IJCI-2017-32771). P. Sanmartín is grateful for the financial support from the Xunta de Galicia (grant ED431C 2018/32). This research was performed within the framework of the teaching innovation group ODS Cities and Citizenship from University of Vigo (Spain) SI

The authors would like to acknowledge the contributions made by Ana Mato and Lara de Villalobos in the acquisition and curation of the data. They also acknowledge the support of the CERENA (strategic project FCT-UID/ECI/04028/2019). Analyses were performed in the CACTI (Centro de Apoyo a la Investigación) Research Support Centre at the University of Vigo. Accelerating SO2 aging test were performed in Instituto Superior Tecnico (University of Lisbon, Portugal)., The behavior of historic tempera paints exposed to pollutant gases is an important issue when developing conservation strategies. In this work, binary tempera paint mock-ups that were made with either smalt or lapis lazuli pigments mixed with either rabbit glue or egg yolk binders were exposed to an SO2 accelerated aging test in order to find out more about the forms and mechanisms of alteration resulting from pigment-binder interaction. To this end, spectrophotometry, hyperspectral image analysis, and profilometry were used to study macro-scale, physical changes taking place on the surface of the paints, affecting color, gloss, reflectance, and roughness. Likewise, chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (ATR-FTIR), polarized light microscopy (PLM), and scanning electron microscopy with micro-analysis (SEM-EDS), which was also used to visualize micro-texture changes in the paints. The smalt-based tempera showed a higher degree of deterioration than the lapis lazuli-based tempera, in particular a notable whitening related to the precipitation of sulfate-rich salts and to binder and pigment chemical alterations. Moreover, whereas aged egg yolk-based paints showed visible color change due to damage to the oily binder and the pigments, the most evident change in rabbit glue-based paints was binder loss. The alteration suffered by the pigments varied in line with their composition; thus, smalt (blue cobalt-containing glass) grains were more sensitive to SO2 exposure than lapis lazuli-(Na,Ca)8[(S,Cl,SO4,OH)2|(Al6Si6O24)]-crystals. In the smalt grains, the SO2 test caused K+ leaching from the glass matrix, which was detected by means of K/Co ratios, but the lazurite crystals (main component of lapis lazuli) were unaffected (regardless of the binder used in the tempera). The most likely source of the crystallized sulfate rich salts were the impurities that were detected in association with the natural lapis lazuli pigment, i.e., calcite and diopside. Indeed, the precipitation of efflorescences is the main cause of the optical changes found in the smalt- and lapis lazuli-based tempera, in addition to the physical-chemical damage to the binders. The information reported here would be useful for preventive conservation, as well as for art restorers, who are planning work on paintings in which paints of this kind were used., Spanish Research Project AERIMPACT CGL2012-30729, Spanish Research Project EXPOAIR P12-FQM-1889, European Union (EU), Andalusian Research Group RNM-179, Spanish Ministry of Economy and Competitiveness (MINECO) IJCI-2017-3277

In order to improve our knowledge of the weathering response of tempera paints exposed to an industrial atmosphere, azurite- and malachite-based paint mock-ups prepared with either rabbit glue or egg yolk binders were artificially aged in an SO2 rich atmosphere. The aim was to identify the different alteration mechanisms and forms of degradation in the paints by observing their physical (color, gloss, reflectance, and roughness), mineralogical, chemical, and micro-textural characteristics. Superficial physical changes were evaluated by stereomicroscopy, spectrophotometry, gloss measurement, hyperspectral imaging, and roughness measurements. Chemical and mineralogical changes were evaluated by X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FTIR), and scanning electron microscopy with microanalysis (SEM-EDS), which was also used to evaluate the micro-texture of the paints. The differences between the fresh temperas were due mainly to the binder (egg yolk or rabbit glue) used in the paint mixture, which also played a crucial role in the different deterioration patterns in the artificially aged paint mock-ups. Thus, the egg yolk-based paints remained physically quite intact after SO2 exposure, although they suffered more significant chemical degradation, above all in the form of copious precipitation of Cu and Ca-rich sulfate salts and the subsequent yellowing of the egg yolk binder. The SO2 aged rabbit glue-based mock-ups showed microscopically important crack formation and binder loss and fewer sulfated salts precipitated on the surface of the paints., Spanish Research Project AERIMPACT CGL2012-30729, Spanish Research Project EXPOAIR P12-FQM-1889, European Union (EU), Andalusian Research Group RNM-179, Spanish Ministry of Economy and Competitiveness (MINECO) IJCI-2017-3277

One of the aims of Goal 11 of the UN’s 2030 Agenda for Sustainable Development is to make human settlements sustainable. Some effort should therefore focus on developing maintenance strategies for buildings. Polished granite cladding tiles are very popular for use as flooring material in private and public buildings. These tiles are often treated by mechanical cleaning with detergents and scrubbers, and anionic detergents without chelating agents are usually used to prevent damaging the material. In this study, the anionic detergent Teepol® was applied to granite tiles in order to determine the effect of the treatment on the surface properties of this stone, i.e. appearance, colour, gloss, roughness and hydrophobicity. The results obtained were explained by scanning electron microscopy observations, which enabled characterisation of the microtexture of the surfaces, chemical contamination and any damage to the different granite-forming minerals. The results were compared with those obtained for tiles cleaned by the same mechanical procedure but with tap water in place of detergent and for tiles treated by immersion in water without any mechanical action. In summary, the properties evaluated were affected by the extraction of the typical oxyhydroxylated iron forms that fill cracks in the granite and by the formation of new cracks due to the mechanical action. Moreover, colour changes and the chemical contamination (C-rich deposits with Na, S, Cl, Ca and Mg) hindered the effectiveness of the cleaning procedure.

The colonization of stone-built monuments by different organisms (algae, fungi, lichens, bacteria, and cyanobacteria) can lead to biodeterioration of the stone, negatively affecting the artistic value of the heritage. To address this issue, laser cleaning has been widely investigated in recent years, due to the advantages it offers over traditional mechanical and chemical methods: it is gradual, selective, contactless, and environmentally friendly. That said, the laser parameters should be optimized in order to avoid any by-effects on the surface as a result of overcleaning. However, as the adjustment of each parameter to clean polymineralic stones is a difficult task, it would be useful to know the effect of overcleaning on the different forming minerals depending on the wavelength used. In this paper, three different wavelengths (355 nm, 532 nm, and 1064 nm) of a Q-Switch neodymium-doped yttrium aluminum garnet (Nd:Y3Al5O12) laser, commonly known as QS Nd:YAG laser were applied to extract a naturally developed sub-aerial biofilm from Vilach&aacute, n granite, commonly used in monuments in the Northwest (NW)Iberian Peninsula. In addition to the removal rate of the biofilm, the by-effects induced for fluences higher than the damage threshold of the stone were evaluated using stereomicroscopy, color spectrophotometry, and scanning electron microscopy with energy-dispersive x-ray spectroscopy. The results showed that different removal rates were obtained depending on the wavelength used and 532 nm obtained the highest removal level. In terms of by-effects, biotite melting was registered on all surfaces regardless of the wavelength. In addition, 532 nm seemed to be the most aggressive laser system, inducing the greatest change in appearance as a result of extracting the kaolinite crackled coating and the segregations rich in Fe, which are a result of natural weathering. These changes were translated into colorimetric changes visible to the human eye. The surfaces treated with 355 nm and 1064 nm showed lower surface changes.

The effects of the four common commercial finishes (polished, honed, disc cutting and bush hammering) on several properties of ornamental granites were evaluated. Two granites of different texture, widely used as ornamental stones in NW Iberian Peninsula, were selected. Roughness, colour and reflectance (properties used as cleaning indicators of cultural heritage objects) of the surfaces subjected to each finish were characterized and the correlations among these parameters were obtained. The results show that the roughness generated by disk cutting and polishing is higher in Vilachan than in Rosa Porrino, showing that the finer the grain size, the higher the roughness generated. The lightness parameter (L∗) in CIELAB space is dependent on the roughness of the surface. The rest of the colour parameters (a∗, b∗, C∗ab and hab) does not depend on roughness and they are related mostly with the colour of the surface by itself. Reflectance features are not affected by the different content of forming minerals and superficial colour which condition the reflectance intensity of each commercial finish. Reflectance is directly related with the roughness of the granite; the rougher the surface the higher the reflectance intensity. In addition, the lightness L∗ and the reflectance are directly related while the other colour parameters do not show any relation with the reflectance. These results can be used as an aesthetical criteria in order to standardize an objective methodology to evaluate the cleaning effectiveness in the conservation of cultural heritage objects.

This paper addresses the evaluation of the cleaning of crustose lichens developing on granite. The evaluation was performed considering the effectiveness of the cleanings and harmfulness exerted on the granite. The laser cleaning of lichen was compared with the most conventional procedure, scalpel. The combination of both procedures was also tested. The study, which was carried out with two different species of crustose lichen, was also focused on the influence of the intrinsic characteristics of the lichen on the effectiveness. The cleanings were evaluated by optic and electronic microscopies, FTIR and colour spectrophotometry. A previous characterization of the lichen and its interaction with the granite using those analytical techniques were also performed. The laser cleaning effectiveness depends on the coverage and the colour of the lichen; also, the prior mechanical weakening of the lichen by scalpel seemed to improve the laser cleaning. The darkest lichen was satisfactorily removed by laser and with the combined cleaning. Conversely, the lightest lichen was more difficult to extract with laser than the darkest lichen, being necessary to apply both methods sequentially. Despite laser and the combination of methods cleaned satisfactorily the surface, they were unable to eliminate the thalli into fissures.

Interferometric profilometry and hyperspectral imaging techniques combined with traditional analytical techniques such as spectrophotometry, stereomicroscopy, X-ray diffraction, scanning electron microscopy, particle size analysis, and thermogravimetry were used to characterize tempera paint mock-ups. These paint mock-ups were prepared as binary mixtures made by mixing either egg yolk or rabbit glue binders with one of ten pigments traditionally used by mediaeval artists, namely lime, calcium sulfate, white lead, minium, hematite, cinnabar, azurite, lapis lazuli, blue smalt and malachite. We evaluated the effects of mineralogical composition, pigment particle size and morphology, as well as the type and concentration of the binder on the physical properties of the paintś surface. Results showed that all the above compositional aspects had a direct influence on the paintś color, reflectance, and roughness. Moreover, mineral impurities and neoformed minerals due to pigment-binder interaction during paint preparation had a crucial effect on the superficial physical properties of paints. The analytical results proved the usefulness of interferometric profilometry and hyperspectral imaging techniques for the characterization of paint surfaces. The gained information will help conservation specialists in the evaluation of the impact of conservation treatments on the paint surface and the assessment of surface damage caused by weathering processes.

Marking petroglyphs with chalk is a common practice to enhance them for documentation and reproduction. Although this procedure has started to be less frequently used, there is no knowledge about the interaction between the rock engravings nor about the effectiveness achieved by the common cleaning procedures of such markers considering the chalk extraction and the induced damage to the rock. This study evaluates the interaction between two chalks of different composition (calcite and gypsum) and a granite on which the majority of NW Iberian Peninsula-petroglyphs are carved. Granitic samples marked with these chalks were subjected to artificial rain events and high temperatures (700 °C) related to fires. After each aging test, chemical and physical modifications on the rock were analysed by means of stereomicroscopy, x-ray diffraction, Fourier transform infrared spectroscopy, scanning electron microscopy and colour spectrophotometry. Moreover, the evaluation of the effectiveness and harmfulness of several mechanical and chemical cleaning procedures commonly used in the field of cultural heritage conservation was carried out. Both chalks remained at different extent on the surface after the artificial rain events. Water would promote a different penetration-depth of the chalks into the stone, depending on their solubility. High temperatures led to mineral phase transformations of the chalks influencing the interaction with the rock. Regarding cleaning effectiveness, despite a few chalk remains were found in all the cleanings, chemical methods showed higher effectiveness than mechanical procedures even though some of them leave chemical contamination. Benzalkonium chloride can be considered as the cleaner with the best results to extract both types of chalk on granite.

Lime-, cement- and lime & cement-based mortars, containing different proportions of nanocrystalline TiO2 (1, 2.5 and 5 wt%) and fine aggregates of silicate nature have been investigated with the aim to improve the knowledge in terms of their chemical, physical and mechanical properties. The influence on the physical-mechanical properties induced by the addition of TiO2 were evaluated through measurement of chromatic parameters, open porosity, water absorption coefficient at atmospheric pressure, P-wave velocity, material loss by peeling test and microdrilling resistance and compared to the reference mortars ones, i.e., without the TiO2 nanoparticles addition. Moreover, stereo and electronic microscopy were used to study the morphology, the mineralogical and chemical composition of each mortar formulation. Fourier transform infrared spectroscopy was also applied to gather qualitative information on the chemistry of some of the characteristic components of the mortar. The results suggest that the physical-mechanical properties of the studied mortars were influenced by the TiO2 nanoparticles addition. Furthermore the influence of the TiO2 on the properties of the studied mortars is also dependent on the nature of the binder used. Nevertheless, in general terms, the global colour change showed a direct relationship with the TiO2 content. Regarding the hygric properties, mortars with higher addition of TiO2 content showed higher open porosity and water absorption coefficients, but an exception for the cement-based mortar with 2.5 wt% was detected. The values obtained in the mechanical properties evaluated were inversely related with the hygric parameters.

The polymineralic characteristic of granite implies an additional challenge during the laser cleaning of cultural heritage built of this rock, because the forming-minerals experience different behaviours under the laser radiation, leading to damages of variable nature and intensity. The aim of this work was to identify the ranges of fluence to satisfactorily and safely clean the four main constituent minerals of granite (quartz, K-feldspar, plagioclase and biotite) painted with three different graffiti colours. The cleaning was performed using a nanosecond Nd:YVO 4 laser which works at high pulse rate (kilohertz). The evaluation of cleaning effectiveness was performed in terms of graffiti extraction and mineral damage evaluated by optical, electronic and confocal microscopies and hyperspectral imaging technique. The results showed that, regardless of the graffiti colour to be cleaned, quartz and K-feldspar grains were satisfactorily cleaned at the same fluence range. However, in case of plagioclase, it depends on the colour of graffiti to be removed. In case of biotite the analytical techniques allowed to confirm that it was already cleaned with the lowest fluence tested and it was the mineral with the highest sensitivity to laser radiation. Therefore, in order to obtain a satisfactory and safe laser cleaning it would be required the prior identification of the granitic forming minerals to adjust the laser fluence.

This paper is focused on the reliability of the colour spectrophotometry as a non-destructive in situ technique to evaluate the cleaning effectiveness. A biofilm composed by filamentous green algae and cyanobacteria developed on a granitic building located in NW Iberian Peninsula was removed using different cleaners commonly used by professionals in stone conservation (distilled water, ethanol, benzalkonium chloride, Hyvar X , ethanol, sodium hypochlorite and the commercial products LimpiaFachadas1 and Biocida ). Also, the durability of some water repellents applied after the cleanings was evaluate. The colour measurements expressed in the CIEL*a*b* colour space were performed before and after the cleanings and after the water repelling products application, at eight moments during two years (since June 2011 until June 2013) of exposition under a temperate humid climate. As general results, the colour spectrophotometry resulted in a reliable method to monitor the cleaning effectiveness, allowing to identify the most effective methods, but also the rate of the recolonization of the granitic surface during time. However, this technique was not recommended as re-growth indicator when water repellents were applied after the cleanings, due to the impact produced by the products on the colour of the stone.

Black crusts on different substrates (carbonate and silicate stones, cement-based mortar and carbonate detrital deposits) in urban environments were characterized microscopically by analysing their morphologies and compositions. The objective of this article is to study the interaction between the substrate and the crust and the influence of the environmental conditions on the crust development. On the one hand, the internal structure and morphology of each sample were evaluated with stereo and scanning electron microscopies. On the other hand, the black crust composition was accessed by X-ray diffraction, Fourier transform infrared spectroscopy and scanning electron microscopy in backscattered electron mode combined with energy dispersive x-ray spectroscopy. The results of these analytical techniques provided interesting information about the composition and the mineralogical phases present in the collected black crusts. In most of the cases, gypsum was detected as the main component exhibiting different habits. Calcite was also detected in all the evaluated gypsum black crusts; its presence was attributed to different origins. The substrate-crust interaction was also evaluated, contributing to distinguish different crust development processes in relation to the substrate. In carbonate substrates (limestones, mortar and carbonate detrital deposits), it was detected a continuous diffuse boundary related to the replacement of Ca-carbonate by Ca-sulphate, while this boundary was significantly more defined for the granitic stone. This study shows that the substrate, the presence of different construction materials, (e.g. mortars), the motor exhaust particulate substances and the concentrations of atmospheric pollutants, the marine influence as well as biological or other anthropogenic compounds are decisive factors in the development of the black crust. Some ideas about the establishment of conservation strategies are also shown.

The application of anti-graffiti products to stones belonging to architectural heritage is a common procedure that is currently complementary to traditional graffiti removal treatments, such as chemical and mechanical cleaning. In this study, two anti-graffiti coatings (a sacrificial product and a permanent one) were tested on four stones (with a different texture, mineralogy, and surface finish) commonly found in the historical city center of Turin (Italy). In order to evaluate the effectiveness of the anti-graffiti products, the removal of two graffiti paints with different compositions was tested. The results of the cleaning procedures performed on the surfaces coated with anti-graffiti products were evaluated, considering both the graffiti remains and the alterations induced on the surface. Chemical cleaning based on the use of a low-toxic ternary solvent mixture was applied on the unprotected stones for a comparison with the results obtained on the surfaces coated with anti-graffiti products. The samples were observed under stereomicroscopy and ultraviolet fluorescence photography and all of the treated surfaces were evaluated by roughness measurements, the contact sponge method, static contact angle measurements, and scanning electron microscopy. The composition of the anti-graffiti product, the graffiti paint to be cleaned, and the remover recommended by the manufacturer proved to be key factors for the cleaning effectiveness achieved on coated surfaces. Moreover, to a lesser extent, the mineralogy, texture, and surface finish of the stone also influenced the results of the cleaning procedures. The sacrificial anti-graffiti product enhanced the cleaning effectiveness on all stones if compared to uncoated surfaces, however, the permanence of coating remains on the surface after cleaning proved to be critical. Regarding the use of the permanent anti-graffiti products, intense disparate results were achieved, depending on the graffiti paint composition.

Laser ablation is an accepted cleaning technology for cultural heritage stonework. Optimized laser ablation may, however, have different side effects depending on the mineralogical composition of the stone. In the case of granitic rocks, observed side effects – colour changes, fracturing or/and mineral melting – have been attributed to laser parameter interactions with the patina to be cleaned from this complex rock with a grained texture and polymineral composition. We describe the influence of the weathering degree of a granite on its response to laser irradiation, confirming that the existence of secondary minerals in the rock influences the intensity and typology of side effects. Knowledge of this influence is of special relevance to the conservation of heritage built with Western European Variscan granites, which are already slightly weathered in quarry. Two specimens of the same Variscan granite taken from the same quarry but with different colours (suggesting different weathering rates) were subjected to nanosecond (ns) Nd:YVO4 laser irradiation, working at 355 nm (UV irradiation) under different fluences. The specimens responded very differently to laser irradiation in terms of colour changes and resistance of the main minerals to laser radiation. The existence on one of the specimens of kaolinite deposits covering feldspar grains and Fe oxyhydroxides filling fissures seemed to be the reason for the different response to laser radiation. Our findings would suggest the need, during laser interventions, to take into account – in addition to texture and porosity – the degree of weathering of this particular kind of granite, widely used in the architectural and archaeological heritage of Western Europe.

Conservation strategies to reduce the degradation of stone caused by the action of water are focusing on increasing the hydrophobicity of the surface by imitating existing solutions in nature (lotus leafs and others). These are mainly based on the existence of hierarchical roughness with micro- and nanoscale structures. In the case of marble, research has focused on protective coatings that sometimes are dangerous for the health and the environment, and with undesirable effects such as color changes or reduction of water vapor permeability of the stone. Laser texturing, however, is an environmentally friendly technique, because no chemicals or toxic waste are added and, moreover, it can process nearly all types of materials. It has been used to change the surface texture of metals and other materials on a micro or even nanometric scale, to meet a specific functional requirement, such as hydrophobicity. The objective of this work was to analyze the feasibility of this technique to provide hydrophobic properties to a marble surface without appreciable changes in its appearance. Therefore, an analysis of the irradiation parameters with ultra-short-pulse laser was performed. Preliminary results demonstrate the ability of this technique to provide hydrophobic character the marble (contact angles well above 90 ∘ ). Besides, the analysis of the treated surfaces in terms of roughness, color and gloss indicates that changes in the appearance of the surface are minimal when properly selecting the process parameters.

A sub-aerial biofilm (SAB) developed on a granite commonly found in the built cultural heritage of the NW Iberian Peninsula was extracted with 2 different IR irradiations using an Nd:YAG laser at 1064 nm and an Er:YAG laser at 2940 nm. The methodology was based on the application of only one scan in order to evaluate the effect of the laser cleaning operated by applying different consecutive laser scanning and the suitability of these lasers as quick tools. The aim of this comparative study was twofold. The first goal was to find the most satisfactory level of extraction by comparing the results obtained by the different laser sources (IR wavelengths). The other aim was to investigate the by-effects induced by both lasers on each granite-forming mineral. Evaluations were made using stereomicroscopy, Fourier transform infrared spectroscopy, Raman spectroscopy and scanning electron microscopy with energy-dispersive x-ray spectroscopy. The results were interpreted in terms of SAB extraction and damage induced on the granite. The results showed that the Nd:YAG laser achieved the most successful level of cleaning, because it extracted the most SAB, while causing the least amount of damage to the surfaces. Regardless of the fluence applied, the Er:YAG laser did not completely extract the SAB in only one scan; in addition, a more intense melting of biotite grains was found, producing amorphous fusion crusts and losing the distinction of the cleavage planes.

Solar radiation is one of the deterioration factors par excellence of modern urban artworks, as among other manifestations, it causes loss of colour. This deterioration can compromise the durability of the works, although it is not known to what extent this durability can vary depending on the substrate supporting the paint. We evaluated the susceptibility to sunlight of 10 paints of differing compositions as typically used by urban artists, by exposing them, applied to concrete and brick, to artificial sunlight ageing test in laboratory conditions. Colour changes over time were studied, along with mineralogical (x-ray diffraction), chemical (scanning electron microscopy-energy dispersive x-ray spectroscopy) and physical (contact angle and peeling tests) changes. The durability of the paints on these substrates depends mainly on the paint composition (base, pigment and filler) but also on the type of substrate, as this influences paint adhesion capacity. The greatest colour modification was detected in fluorescent paints, which lose colour due to degradation of the organic phase, and with aggravation of defects during drying, eventually detach from the substrate.

Different decay factors influence the minero-chemical characteristics and the physico- mechanical properties of building stones. Weathering and exposure to high temperatures (such as those achieved during a fire) can contribute to their deterioration. The aim of this work was to identify and describe changes induced by weathering and fire exposure of a granite applied in a traditional Galician country property. In this real-case it was possible to collect granite blocks from fire affected and non-affected areas. Surface properties (color and gloss) and petrographic, mineralogical, physical (open porosity and capillary water absorption) and ultrasonic (VP, VS, VP/VS, E, K, µ and σ) parameters have been evaluated in both sets. The results shows that the granite used in this property has inherited alteration features (presence of kaolinite, chlorite and goethite associated to high values of porosity, capillary water uptake and moderate values of ultrasound velocities and elastic parameters). Identification of clay minerals and iron oxides in fire affected samples allowed to estimate that the temperature reached by this inherited altered granite was lower than 490 °C. Those intrinsic characteristics associated to a relatively low fire temperature justify the physical–mechanical modifications observed.

During the 20th century, the need for raw material promoted a commercial transportation trade of iron ores from the deposits in north-western Spain, where Vigo city was considered one of the most important ports. The global energy crisis in the 1970s, as well as the strong competition from other exporting countries, dented the prolific activity of companies dedicated to the extraction and trading of iron ore. The main goal of this article is the evaluation of one particular element of the mining and industrial heritage — two old mineral loading docks in Ria de Vigo in the Rande Strait, linking the municipalities of Redondela and Moana. Their development as a tourist resource would add to the cultural and economic activities already developed in the area.

Stone coatings, biological colonization, efflorescence and detachments are frequent on granitic surfaces of our cultural heritage infrastructure. In order to find the different origins for each deterioration form, this paper studies and compares several coatings, efflorescence and flakes found on granitic surfaces of bridges from different ages built in the same area (Ourense in NW Iberian Peninsula at 90 km from the sea) under the same environmental and traffic conditions. The most recent bridge was the New Bridge built in the beginning of 20th century and the oldest one was the Roman Bridge with the 1st century AD foundations but its current structure was built in 17th century. The New Bridge has exhibited a greater variety of deterioration forms such as black crusts, carbonate crusts, efflorescence and biological colonization. On the Roman Bridge, black crusts, efflorescence to a greater extent, and flakes associated with salt crystallization processes have been identified. Scanning electron microscopy with energy dispersive X-ray spectroscopy, X-ray diffraction and Fourier transform infrared (FTIR) spectroscopy studies were carried out in order to establish their composition, and optical and electronic microscopies and X-ray microtomography were used to study their morphologies. As a result, anthropogenic factors (industrial activities, traffic pollution and fertilizers) are considered to be the main contributors to crusts, efflorescence and flake formation on both studied substrates (granite ashlars and mortars). To a lesser extent, natural factors (marine influence and bird droppings) should be taken into account.

A study of the cleaning effectiveness of sulphated black crust developed on granite is presented. The sulphated black crust, previously characterized, was subjected to a cleaning by 1) a mechanical procedure –Hydrogommage– based on micro-sandblasting, 2) chemical procedures based on the application of poultices made on different mixes of thickening agents and cleaners and 3) laser cleaning using a 355 nm Nd:YVO4 nanosecond laser. Chemical, mineralogical and physical characterization of the cleaned surfaces were performed; the global effectiveness as well as the harmfulness were evaluated according to the level of black crust removal and the substrate damages. As result, none of the methods has been completely effective in removing the sulphated black crust and, also, all the methods produced undesirable effects on the stone. The crust nature, its degree of interaction with the stone and other factors related to the principle of the cleaning procedures were found as the main variables influencing the effectiveness of the cleaning procedures.

This paper reports the results from the comparative evaluation of the global cleaning effectiveness of four graffiti colours (red, blue, black and silver) applied on two granites with different textures and compositions. A conventional mechanical method and several chemical products were evaluated. Additionally, it was evaluated the cleaning based on laser ablation by means of a nanosecond pulsed Nd:YVO 4 at a wavelength of 355 nm. Optical and electronic microscopy, Fourier transformed infrared spectroscopy and spectrophotometry were applied in order to assess the cleaning effectiveness and also the harmful effects on the stones. Taking into account the graffiti extraction degree, it was found that blue, red and black colours were successfully extracted by all the evaluated methods. However, the extraction of silver colour, whose chemical composition differs from that of the other three colours, was more difficult and it was only achieved by the mechanical procedure and by several chemical products; Nd:YVO 4 laser at 355 nm was an ineffective procedure in removing this paint. All the cleaning methods produced damage on the granites: a roughness increase after the mechanical cleaning, chemical contamination related to some chemical procedures and melting of biotite crystals after laser cleaning. Moreover, the ability of different paints to penetrate into the rock affected the global cleaning effectiveness evaluation.

This study focuses on the characterization of black crusts collected from the Monza cathedral located in the homonymous city (N Italy), a hot spot from the point of view of the atmospheric pollution. Black crusts and substrate marble specimens were analyzed by a multi-analytical approach including X-ray Diffraction (XRD), Fourier Transform-Infrared spectroscopy (FT-IR), Stereomicroscopy (SM), Polarized Light Microscopy (PLM), High Resolution Scanning Electron Microscopy coupled with Energy Dispersive X-ray spectroscopy (HRSEM-EDX) and Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP/MS). The characterization of the carbon fraction (organic carbon, OC, and elemental carbon, EC) was performed using a new approach based on the use of Carbon Hydrogen Nitrogen (CHN) analysis and Thermogravimetric Analysis (TGA). The integrated approach allowed the identification of the pollution sources responsible for black crusts forming process. The precise identification of the main substances responsible for the surface degradation phenomena, in particular those leading to the blackening and disintegration of the carbonate substrates, is essential for the definition of conservative intervention and maintenance strategies, as well as for the development of emission reduction policies on a local scale.

As the UN Agenda 2030 recognizes heritage protection in several goals, this research was focused on the improvement of the graffiti removal from stones. The cleaning of two graffiti paints with different composition (an alkyd- and an acrylic&ndash, based paints) from two stones (gneiss and travertine) was performed considering a synergistic approach based on the combination of a low-toxic solvent ternary mixture, followed by an Nd:YAG laser. The different concentrations of the low-toxic solvents were based on the triangular Teas graph, keeping similar Hansen solubility of the products commonly used in conservation of cultural heritage: methyl ethyl ketone (MEK) and n-butyl acetate. The n-butyl acetate was replaced by mixture A (51% ethyl alcohol/11% acetone/38% isooctane) and MEK by mixture B (7%/13%/80%). Regardless of the graffiti composition, the gneiss was satisfactorily cleaned with the mixture A, while for the travertine, the best results were achieved by the mixture B. Then, surfaces treated with the mixtures were irradiated with a QS Nd:YAG laser working at 532 nm. The cleaning evaluation was performed by stereomicroscopy, color spectrophotometry, roughness measurements, reflectance measurements, and scanning electron microscopy. As result, regardless on the stone and the graffiti paints, it was confirmed the enhancement of cleaning of the mixtures followed by the Nd:YAG laser. However, it is crucial to identify previously the concentrations of the chemical products that allow the best performance considering the graffiti-stone interaction, on the one hand, and the optimal laser&rsquo, s parameters, on the other hand.

The weathering capacity of UV-A, UV-B and UV-C radiation (i.e. long, medium and short wave) was tested on granite, rhyolite and biocalcarenite samples and glass slide supports coated with silver, black, blue and red graffiti paint. Physical and chemical changes occurred in the red, blue and silver paints, but not the black paint. Red and blue paints appeared be sensitive to UV-B and UV-C radiation, and they were not altered by artificial daylight or UV-A radiation. By contrast, all three types of UV radiation caused chemical changes in silver paint. Unexpectedly, physical changes in the paint and photodegradation were not correlated.

Nowadays, graffiti paints are one of the most common human interventions on monuments and historic facades with damaging results. It is an aesthetic problem but also a serious threat to the conservation of built heritage. The aim of this article is to evaluate the suitability of a hyperspectral imaging technique as a non-destructive tool to determine the most adequate method of removing graffiti paints applied on granite rocks. Different cleaning procedures were analyzed; i.e., chemical, mechanical, and laser ablation. The cleaning effectiveness was evaluated based on the degree of paint extraction and the final appearance of the stone surface. The results obtained by hyperspectral technique were compared with those obtained by optical and electronic microscopies and color spectrophotometry. These results indicate the ability of hyperspectral imaging technique to assess the paint removal and thus to evaluate the suitability of the different graffiti cleaning procedures. © 2016 Wiley Periodicals, Inc. Col Res Appl, 2016

Soluble salts are considered a main cause of damage of porous building materials such as rocks, bricks or granites, which were commonly used in the building constructions of the architectural and archaeological heritage. Soluble salts are also responsible for various forms of deterioration such as sand disaggregation and superficial detachments. These problems can be solved by conservation technologies, which are aimed to decrease the salt concentration in rocks (desalination). The present study aimed to investigate the efficiency of electrokinetic techniques for desalination of two different kinds of rocks: granite and sandstone. These rocks were contaminated with NaCl solution, and samples with a thickness of 6 cm were used in the tests. This study compared the percentage of salt removal at different depths (efficacy) and the time needed to get the same percentage removal (effectiveness) achieved in both stones. From the results obtained, it was possible to find those inherent factors to each stone which could have an influence on the efficacy of the treatment. With this technique it was possible to reduce the salt concentration in the granite almost to 100%. However, in the sandstone samples the decreases were not equally high, mainly at the intermediate levels where slight enrichments were observed. The results indicate that although the used technique is efficient for salt removal regardless of the porosimetric distribution of the rock, the better interconnection between the pores in the granite samples (favored a faster desalination process).

In this paper, we present a study of the application of the hyperspectral imaging technique in order to non-destructively evaluate the laser cleaning of the biogenic patina and the sulphated black crust developed on a fine-grained granite used in the construction of Cultural Heritage in NW Spain. The grained polymineral texture of the granite hinders the adjustment of laser irradiation parameters during the cleaning, and therefore the in situ process control. The cleaning was performed with a nanosecond pulsed Nd:YVO4 laser at 355 nm. A hyperspectral camera was used to in situ assess the effectiveness of cleaning by recording images of the rock surfaces before and during the laser treatment. Different analytical techniques were used to test the ability of the hyperspectral imaging technique to evaluate the cleaning process of the granite samples: optical microscopy, scanning electron microscopy with energy dispersive X-ray spectrometry (SEM - EDX), Fourier transform infrared spectroscopy (FTIR) and spectrophotometer colour measurements. The results indicated that hyperspectral imaging technique is a reliable and more affordable technique to in situ evaluate the process of laser cleaning of the biogenic patina and the sulphated black crust in fine-grained granites.

In order to understand the behavior of the natural hydraulic lime, pure lime and lime cement-based mortars as a repair mortar it is necessary to investigate their mechanical-properties. In this paper, the specimens were made with limestone aggregate as the restorers prepared the restoration works. The mechanical-strength as well as the evolution of Young’s modulus and the drying shrinkage were monitored. The study was performed under curing conditions which lead to the development of a suitable mortar strength within the first 28 days without having to wait for longer curing periods. The study revealed that NHL5 (1:1.75) mortar exhibits, for 28 days in a 70 ± 5% RH chamber, better results from the point of view of strength and shrinkage. A NHL5 (1:1.75) mortar could be a good candidate to be used like a repair mortar due to its good response to the movements of the stones in the buildings and its higher strengths. However the shrinkage in a lime cement-based mortar as well as a pure lime-based mortar is high enough as to cause a decrease in their strength. This information is very useful for the design of repair mortars.