Identifying the Original Colour of the Paintwork on the Artistic and Industrial Recreation Pavilion Designed by Antonio Palacios for the Galician Regional Exhibition Held in 1909

The former Artistic and Industrial Recreation Pavilion, which was designed by Antonio Palacios (1874–1945) and built for the Galician Regional Exhibition held in 1909 in Santiago de Compostela (Galicia, north-western Spain), and which currently houses a nursery school, was completely restored in 2018. The main purpose of the restoration was to recover the original exterior colour of the building. For this purpose, a study was undertaken to identify the original colour of the paintwork by first consulting historical archives and then conducting a micromorphological analysis of stratigraphic paint samples by stereomicroscopic examination and scanning electron microscopy (SEM) coupled with electron dispersive spectroscopy (EDS). Three reformations of the building are documented: one carried out in 1926, when the metal roof was replaced with a tile roof; another conducted between 1967 (when the old pavilion was described as a "destroyed building") and the mid-1970s (when it began to be used as a nursery); and finally, another in 1981, when the building was repainted. The analytical results revealed layers of white or yellow ochre (vanilla) paint corresponding to different periods. The presence of titanium (Ti) in the paint was used as a marker of its age, as titanium white was first formulated in 1921. The original layers include Zn in their composition, indicating that zinc oxide (ZnO) was the pigment used in the “snow” white paint probably used on the building in its first years of existence. In all cases, the pigment base is lime mixed with silicates, kaolin and other claysThe Xunta de Galicia, Consellería de Servizos Sociais financially supported this work under a contract for the ’Rehabilitación Escuela infantil de Sta Susana (Santiago de Compostela)’ with Tragsa and Arrokabe architects, who commissioned the painting characterisation project to the GEMAP-USC research group, to which both authors of the manuscript belong. The authors are also grateful for funding awarded by the Xunta de Galicia within the project “Consolidación y estructuración de unidades de investigación competitivas—Grupos de referencia competitiva (GRC)” (Ref. ED431C 2018/32)S

A laboratory approach on the combined effects of granite bioreceptivity and parameters modified by climate change on the development of subaerial biofilms on cultural heritage

Conservation of cultural heritage buildings and monuments may be negatively affected by the impact of climate change on substrates and colonizing microorganisms. In this study, four types of commercial granite, in which the bioreceptivity ranged from very low to very high, were inoculated with a multispecies microbial culture and exposed to different temperatures (18 and 24 °C) and levels of water availability (1 day, 3 days and 7 days of water availability/week) to simulate different climatic conditions. The effects on biofilm formation of the interactions between the substrate bioreceptivity and the environmental parameters were investigated. Biofilm growth and photosynthetic efficiency were monitored over 42 days by pulse-amplitude modulated (PAM) fluorometry and spectrophotometric colour measurement. The primary bioreceptivity of the granite was a determining factor in the organisms' capacity to attach to the substrate and interacted through the experiment with the climatic conditions by modifying the development of the microorganisms. Water availability was a limiting factor for the colonizing microorganisms, in terms of both growth and photosynthetic efficiency. At the higher temperature, metabolic reactions were enhanced under water restriction (but not under maximum water availability) and the microbial ecology was altered, leading to a higher proportion of cyanobacteria relative to algaeThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN-FPI (BES-2017-079927)S

Assesing the risk of salt decay for wall paintings in historic building. Thermo-dynamic modeling and transition cycles count

Salt crystallisation is a major cause of deterioration of porous building materials, strongly related to the fluctuation of the environmental parameters. This paper explores the application of different methodologies to assess the potential damage caused by soluble salts to a series of sixteenth century frescoes with the thermo-hygrometric variations. The method of counting the transition cycles for six crystalline systems, the thermodynamic model ECOS for mixed salt solutions and a combination of both methodologies were used, in order to evaluate and compare these different approaches and to determine the risk of salt decay for this particularly sensitive case study. To this end, the temperature and relative humidity in the churches housing the wall paintings were monitored during a year and the salt content of the frescoes analysed. The seasonality of the salt crystallisation was studied and the range of relative humidity at which the transitions occurred determined. All methods identified a significant risk of salt decay, mainly related to the crystallisation of chlorides and nitrates, which corresponds well with the observations in situ. Finally, the advantages and inconveniences of each method were discussed, along with the results obtained in other published works, and the combined method was suggested as the most efficientThis work was supported by the Xunta de Galicia-Consellería de Educación e Ordenación Universitaria [INCITE program 2009] with the research project “Analysis of the risk factors of the wall paintings of A Ribeira Sacra”, by the Spanish Ministry of Education with L. Pereira-Pardo´s doctoral grant [FPU AP2009-4421] and the Barrié Foundation [Bolsas de Posgrao no estranxeiro 2013]S

Laboratory development of subaerial biofilms commonly found on buildings. A methodological review

Study of the biodeterioration of building materials is often hampered by the inaccessibility of the colonization and impossibility of sampling in protected buildings considered part of the cultural heritage. There is therefore a recognised need to develop a laboratory mesocosm that realistically represents nature and enables the study and analysis of both the substrate and the organisms involved. Although many studies have investigated the formation of biofilms on various building materials, there is a lack of homogeneity and consensus in the methods and protocols used, which hampers comparison of the results obtained. This review aims to identify the different methods reported in the scientific literature, to organise these according to different factors (water access and types of organism and substrata used) and thus provide the research community with a guide for selecting the most appropriate methods according to the different objectivesThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN (BES-2017-079927)S

Effects of changes in UV-B radiation levels on biofilm-forming organisms commonly found in cultural heritage surfaces

Accurate measuring and monitoring methods available since the 1980s have shown that the amount of Ultraviolet B (UV–B) radiation reaching the Earth's surface has increased as a result of degradation of the ozone layer. Since the adoption of the Montreal Protocol in 1987, ozone levels have been recovering successfully. However, in the context of the current climate change, other factors such as changes in cloud patterns and an increased incidence of natural disasters (e.g. fires) may be disrupting this recovery. The present study aimed to investigate the effects of different UV-B radiation levels on biofilms colonising heritage monuments. For this purpose, the effects of current UV-B levels on a biofilm composed of Synechocystis sp. (a cyanobacterium), Bracteacoccus minor (a green alga) and Fusarium sp. (a fungus) were compared at three points along a South-North transect: Portugal, Galicia (NW Spain) and Ireland (from highest to lowest UV-B radiation, respectively). Increased levels of UV-B radiation caused changes in the growth, physiological state and composition of subaerial biofilms, with cyanobacteria being more resistant than green algae to high levels of UV-B. A reduction of fungal growth and extracellular polymer substances (EPS) production was also observed, related to the reduction of biofilm aggregation at high UV-B levelsThis study was partly financed through EU funding (project CGL 2016-79778-R: AEI/FEDER, EU) and the Xunta de Galicia (ED431 2018/32). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN-FPI (BES-2017-079927). D. Pérez-Velón acknowledges receipt of a grant in the Programa de Doutoramento Industrial (16_IN606D_2021_2608973) financed by the Xunta de GaliciaS

Effect of Inorganic Carbon Concentration on the Development of Subaerial Phototrophic Biofilms on Granite

Organisms living at the stone–air interface are expected to be affected by changes in the atmospheric composition due to greenhouse gases emissions. Increased CO2 concentrations may particularly affect phototrophic microorganisms that colonize stone cultural heritage and form subaerial biofilms. However, little is known about the effects of the environmental changes on microorganisms that colonize stone and the consequences for cultural heritage conservation. In the present study, we investigated how an increase in inorganic carbon concentration affected the development of a subaerial biofilm composed by the cyanobacterium Synechocystis sp. PCC 6803 grown on granite. For this purpose, we established two experiments on biofilm formation, with and without addition of inorganic carbon to the growth medium. Higher concentrations of carbon promoted biofilm growth and increased the concentrations of the photosynthetic pigments chlorophyll a and carotenoids on granite surface, potentially exacerbating the aesthetic impact of these biofilms on stone-made cultural heritage. However, the extracellular polysaccharides produced were not significantly affected by carbon availability, so that physical stone biodeterioration might not be increased by the cyanobacterial matrix. The findings provide valuable data on how the existing global change scenario might affect organisms inhabiting stone cultural heritage and encourage to develop new sustainable treatments and methodologies to prevent biodeterioration and thus preserve stone cultural heritageThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). D. Vázquez-Nion was financially supported by Postdoctoral Fellowship-Contract from Xunta de Galicia (ED481B/2017/016). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN-FPI (BES-2017-079927)S

Role of Exposure on the Microbial Consortiums on Historical Rural Granite Buildings

Local granite has been used throughout history in Galicia (NW Spain), forming the basis of much of the region’s architecture. Like any other rock, granite provides an ecological niche for a multitude of organisms that form biofilms that can affect the physical integrity of the stone. In this study, for the first time, characterization of the microbial consortium forming biofilms that developed on historical rural granite buildings is carried out using a combination of culture-dependent and next generation sequencing (NGS) techniques. Results pointed to differences in biofilm composition on the studied rural granite buildings and that of previously analyzed urban granite buildings, especially in terms of abundance of cyanobacteria and lichenized fungi. Exposure was corroborated as an important factor, controlling both the diversity and abundance of microorganisms on walls, with environmental factors associated with a northern orientation favoring a higher diversity of fungi and green algae, and environmental factors associated with the west orientation determining the abundance of lichenized fungi. The orientation also affected the distribution of green algae, with one of the two most abundant species, Trentepohlia cf. umbrina, colonizing north-facing walls, while the other, Desmococcus olivaceus, predominated on west-facing wallsThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). E. Fuentes was financially supported by a PhD fellowship contract, MICINN-FPI (BES-2017-079927)S

Artificial weathering of granite

En este trabajo se hace una síntesis de varios ensayos de alteración artificial realizados con rocas graníticas. Estos ensayos tenían distintos objetivos: reproducir las formas de alteración encontradas en los edificios para llegar a conocer los mecanismos que las generan, determinar la resistencia de las diferentes rocas a la acción de las sales, evaluar la durabilidad de tratamientos de consolidación e hidrofugación y contrastar hipótesis acerca del origen de algunas sales, como el yeso, que aparecen frecuentemente en edificios graníticos. En los ensayos de cristalización de sales se utilizaron disoluciones de cloruro de sodio, sulfato de sodio, sulfato de calcio y agua de mar. Uno de estos ensayos se llevó a cabo en una cámara especialmente diseñada para reproducir la alteración por aerosol marino y otro se realizó en una cámara de SO2, con el objeto de comprobar sí en rocas graníticas se puede producir sulfatación. Se analizan los resultados obtenidos en cada ensayo y se discuten las limitaciones de los mismos para reproducir las patologías desarrolladas en los monumentos así como la influencia que pueden tener en dichas patologías aspectos como las condiciones de humectación y secado, el tipo de disolución salina y la influencia de los planos de debilidad de las rocas en el desarrollo de unas u otras ofmras de alteración.This article summarizes a series of artificial weathering tests run on granite designed to: simulate the action of weathering agents on buildings and identify the underlying mechanisms, determine the salt resistance of different types of rock; evaluate consolidation and water-repellent treatment durability; and confirm hypotheses about the origin of salts such as gypsum that are often found in granite buildings. Salt crystallization tests were conducted, using sodium chloride, sodium sulphate, calcium sulphate solutions and seawater. One of these tests was conducted in a chamber specifically designed to simulate salt spray weathering and another in an SO2 chamber to ascertain whether granite is subject to sulphation. The test results are analyzed and discussed, along with the shortcomings of each type of trial as a method for simulating the decay observed in monuments. The effect of factors such as wet-dry conditions, type of saline solution and the position of the planes of weakness on the type of decay is also addressed.S

Role of masonry fabric subsurface moisture on biocolonisation. A case study

High moisture is one of the main factors favouring the growth of algae and other organisms on stone surfaces. However, little is known about the specific effects of subsurface moisture on this process. Some regions will be exposed to longer periods of humidity and rainfall as a result of climate change. Understanding the role and internal dynamics of moisture in stone is therefore essential to enable development of mechanisms for controlling biological colonisation and thus preventing biodeterioration. The present case study is a preliminary investigation of the role of subsurface moisture in the biocolonisation process and was conducted on the walls of the Guard House of Stirling Castle. Moisture was measured at depth (up to 3, 11 and 30 cm) in both interior and exterior walls of the building with a portable device based on non-destructive microwave technology. Data were analysed in relation to the orientation of the walls, type of stone and biocolonisation. The subsurface moisture between 3 and 11 cm was found to play an important role in supporting colonising organisms on the building by modulating bioreceptivityThis study was partly financed through project CGL2016-79778-R (AEI/FEDER, UE) and Xunta de Galicia (ED431 2018/32). E. Fuentes was financially supported by a PhD Fellowship-Contract MICINN-FPI (BES-2017-079927)S

Shaping colour changes in a biofilm-forming cyanobacterium by modifying the culture conditions

This is the accepted manuscript of the following article: Prieto, B., Vázquez-Nion, D., Silva, B., & Sanmartín, P. (2018). Shaping colour changes in a biofilm-forming cyanobacterium by modifying the culture conditions. Algal Research, 33, 173-181. doi: 10.1016/j.algal.2018.05.010Cyanobacteria, pioneering microorganisms that create a conditioning layer on substrates and act as a source of nutrients for successive colonization by heterotrophic microbes, are commonly studied in relation to the microbial ecology of stones in indoor and outdoor habitats. They are well known for producing greenish-yellow, bluish-green or occasionally pink or pinkish-orange discolouration of surfaces. Such discolouration may be desirable for integrating new elements in landscapes and could be achieved by inoculating surfaces with cyanobacteria of a specific colour. In the present study, with the aim of producing cultures of perceptibly different hues, we modelled the colourimetric response of the biofilm-forming cyanobacterium Nostoc sp. PCC 9104 to variations in light intensity (L) and the concentrations of phosphorus (P) and nitrogen (N). The model obtained, which was validated from both mathematical and perceptual perspectives, enables production of cultures of a particular hue, within a range of 18° and with an efficacy of 92%. Coloured cultures of hue between 129° and 147°, corresponding to yellowish-green to bluish-green tones, were obtained by modifying nutrients inputs and the amount of light, without the need to resort to genetic manipulationThis study was partly financed through grant GRC2014/028 (Xunta de Galicia) and project CGL2016-79778-R (Ministerio de Economía, Industria y Competitividad). D. Vázquez-Nion is financially supported by a postdoctoral contract ED481B/2017/016 (Xunta de Galicia). P. Sanmartín is financially supported by a postdoctoral contract POS-B/ 2016/030 (Xunta de Galicia). The authors thank all the observers who generously agreed to collaborate in the psychophysical studyS