Natural corrosion-induced gold nanoparticles yield purple color of Alhambra palaces decoration

Despite its fame as a chemically inert noble metal, gold (alloys) may suffer degradation under specific scenarios. Here, we show evidence of electrochemically corroded gilded tin plasterwork in the Alhambra (Granada, Spain) driving spontaneously made gold nanospheres with the optimal size (ca. 70 nm) to impart purple color at the surface. Purple gold on damaged artworks is found sparsely, and its formation is not fully explained yet. We prove that our decayed gold/silver-tin ornament is due to sequential/coexisting galvanic corrosion, differential aeration corrosion, and dealloying of nonperfectly bonded and defect-based metals. Damage is enhanced by exposure to a chloride-rich atmosphere. A white gypsum coat applied during the 19th century to overlap the unaesthetic gilding assists observation of the gold-based purple color. Our work demonstrates gold dissolution, millimetric migration, physical translocation, and deposition as secondary pure gold nanospheres over a centurial time scale under natural environmental conditions.Junta de Andalucia RNM-179 P18-FR-4173Research Excellence Unit Science in the Alhambra from the University of Granada (Spain) UCE-PP2018-0

Effect of a SO2 Rich Atmosphere on Tempera Paint Mock-Ups. Part 2: Accelerated Aging of Azurite- and Malachite-Based Paints

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 CGL2012-30729Spanish Research Project EXPOAIR P12-FQM-1889European Union (EU)Andalusian Research Group RNM-179Spanish Ministry of Economy and Competitiveness (MINECO) IJCI-2017-327

A case study of renaissance wall paintings in Granada (Spain): historical–artistic analysis, materials characterization, and state of conservation

The research carried out on the wall paintings of Hernán Pérez del Pulgar’s Palace chapel in Granada (Spain) was aimed at determining its historical–artistic, stylistic, technical, and compositional aspects. For this, a 16th century frieze and an 18th century pendentive were studied. The mineralogical, chemical, and textural characterization of the constituent materials and the study of the state of conservation of the paintings have helped to determine the pictorial technique used, identify the nature of the salts present in the paintings, and other pathologies including a dormant fungal attack. To this end, optical microscopy (OM), X-ray diffraction (XRD), Field emission scanning electron microscopy with microanalysis (FESEM-EDS), and micro-Raman spectroscopy (MRS) were used. The information obtained helps clarify important aspects of the painting technique used, laying a basis to ensure effective and suitable conservation and restoration measures on the paintings that will ensure their durability over time.AERIMPACT | Ref. CGL2012-30729EXPOAIR | Ref. P12-FQM-1889Ministerio de Ciencia e Innovación | Ref. PID2020-119838RA-I00Grupo de Investigación de Andalucía | Ref. RNM-17

Effect of a SO2 Rich Atmosphere on Tempera Paint Mock-Ups. Part 1: Accelerated Aging of Smalt and Lapis Lazuli-Based Paints

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 CGL2012-30729Spanish Research Project EXPOAIR P12-FQM-1889European Union (EU)Andalusian Research Group RNM-179Spanish Ministry of Economy and Competitiveness (MINECO) IJCI-2017-327

Evaluación de las propiedades físicas de dos rocas carbonáticas usadas como material de construcción actual e histórico en Andalucía Oriental, España

We present a detailed characterization of two calcareous stones from Andalusia (Southern Spain), namely Escúzar calcarenite and Olivillo travertine. Both materials can replace two stones extensively used in the architectural heritage of Andalusia, i.e. La Escribana calcarenite and Alfacar travertine. To establish the suitability of the replacement of ancient materials, detailed examination was performed. X-ray diffraction, X-ray fluorescence, optical and scanning electron microscopy, hydric tests, mercury intrusion porosimetry, gas adsorption, ultrasounds and colorimetry were applied. The Escúzar calcarenite has large pore cavities and higher open porosity than La Escribana calcarenite. From a chromatic point of view both calcarenites are rather similar. The Olivillo travertine is a massive well cemented and heterogeneously colored rock. The ultrasounds velocities for this material are very homogeneous and elevated, indicating excellent mechanical properties. However the hydric and chromatic differences between both travertines point to reduced adequacy of Olivillo travertine as substitutive material for Alfacar.Se han caracterizado dos rocas carbonáticas de Andalucía Oriental; la calcarenita de Escúzar de Granada y el travertino Olivillo de Alhama de Almería. Ambas podrían reemplazar a dos materiales del patrimonio arquitectónico de Andalucía, la calcarenita La Escribana y el travertino Alfacar ambos de Granada. Los materiales mencionados se estudiaron mediante difracción y fluorescencia de rayos X, microscopías óptica y electrónica de barrido, ensayos hídricos, porosimetría de mercurio, adsorción de gases, pulsos ultrasónicos y parámetros cromáticos. La calcarenita Escúzar presenta grandes poros y una porosidad abierta y área superficial superior a la calcarenita La Escribana; el cromatismo de ambas es similar. El travertino Olivillo es una roca masiva poco porosa. Las propagaciones de ultrasonidos son homogéneas y elevadas, traduciéndose en excelentes propiedades mecánicas. Sin embargo, sus marcadas diferencias hídricas y cromáticas respecto al travertino Alfacar reducen su idoneidad como material sustitutivo de éste en el patrimonio arquitectónico

Environmental impact assessment on the Monza cathedral (Italy): a multi-analytical approach

This research deals with the characterization of black crusts collected from the Dome of Monza (Milan, Italy). Air pollution is responsible for the degradation of historical buildings surfaces. In urban and industrial areas, the degradation process is accelerated, due to carbonaceous particles and heavy metals emitted by combustion processes which contribute to the formation of black crust (BCs). In this study the characterization of BC was performed using different analytical techniques such as: HRSEM-EDX, IC, LA-ICP/MS and digital image analysis. In particular, the research focused on the study of "heavy metals" which contribute to the identify the main sources of pollution responsible for the surface’s deterioration over time. BCs variability in composition also depends on the exposure of the analyzed surfaces.J. Santiago Pozo-Antonio thanks the Spanish Ministry of Economy and Competitiveness (MINECO) for his “Juan de la Cierva-incorporación” (IJCI-2017-3277) contract. 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. SEM-EDX analyses were performed in the Scientific Instrumentation Centre (CIC) of the University of Granada (Spain)

Atmospheric turbulence triggers pronounced diel pattern in karst carbonate geochemistry

CO2 exchange between terrestrial ecosystems and the atmosphere is key to understanding the feedbacks between climate change and the land surface. In regions with carbonaceous parent material, CO2 exchange patterns occur that cannot be explained by biological processes, such as disproportionate outgassing during the daytime or nighttime CO2 uptake during periods when all vegetation is senescent. Neither of these phenomena can be attributed to carbonate weathering reactions, since their CO2 exchange rates are too small. Soil ventilation induced by high atmospheric turbulence is found to explain atypical CO2 exchange between carbonaceous systems and the atmosphere. However, by strongly altering subsurface CO2 concentrations, ventilation can be expected to influence carbonate weathering rates. By imposing ventilation-driven CO2 outgassing in a carbonate weathering model, we show here that carbonate geochemistry is accelerated and does play a surprisingly large role in the observed CO2 exchange pattern of a semi-arid ecosystem. We found that by rapidly depleting soil CO2 during the daytime, ventilation disturbs soil carbonate equilibria and therefore strongly magnifies daytime carbonate precipitation and associated CO2 production. At night, ventilation ceases and the depleted CO2 concentrations increase steadily. Dissolution of carbonate is now enhanced, which consumes CO2 and largely compensates for the enhanced daytime carbonate precipitation. This is why only a relatively small effect on global carbonate weathering rates is to be expected. On the short term, however, ventilation has a drastic effect on synoptic carbonate weathering rates, resulting in a pronounced diel pattern that exacerbates the non-biological behavior of soil–atmosphere CO2 exchanges in dry regions \mbox{with carbonate soils}.M. Roland was granted by the Institute for Promotion of Innovation through Science and Technology in Flanders (IWT-Vlaanderen). I. A. Janssens and R. Van Grieken acknowledge the Research Foundation – Flanders (FWO). P. Serrano-Ortiz is funded by a postdoctoral fellowship from the Spanish Ministry of Science and Innovation. S. Cuezva was funded by a postdoctoral fellowship from the Spanish Ministry of Science and Innovation, research programme Juan de la Cierva

Procesos de precipitación mineral bioinducidos en sistemas kársticos subterráneos: breve revisión y nuevas tendencias

Los microorganismos, en particular las bacterias, habitan en todos los ambientes posibles de la biosfera incluidos los ambientes subterráneos. Desempeñan un papel importante en procesos geológicos tales como la precipitación y disolución mineral, e influyen notablemente sobre los ciclos biogeoquímicos de diferentes elementos. Hasta este momento, son relativamente pocos los estudios orientados a conocer el papel activo de los microorganismos, especialmente las bacterias, en la formación de espeleotemas, de manera que la implicación de la actividad microbiana en la precipitación y disolución mineral en ambientes kársticos es un tema aún sin resolver en geomicrobiología. Actualmente, no está del todo aclarada cuál es la interrelación entre los microorganismos y las fábricas minerales, ni el papel que juegan los microorganismos en la precipitación de carbonatos. Las cuevas son ambientes protegidos donde las fábricas microbianas pueden preservarse sin sufrir modificaciones diagenéticas importantes o destrucción, ofreciendo, por ello, un excelente entorno para estudiar los procesos de biomineralización (desde los propios microorganismos activos a sus depósitos minerales). Las nuevas tendencias en geomicrobiología se basan en la conjunción de diferentes metodologías (microclima, petrología, geoquímica, hidroquímica, microbiología, biología molecular) con un objetivo común: 1) determinar el papel de las diferentes comunidades microbianas que habitan los ambientes subterráneos en los procesos de transformación mineral; 2) identificar las propiedades físicas y químicas de las fases cristalinas bioinducidas, y 3) determinar las condiciones ambientales y las propiedades composicionales y texturales de los soportes rocosos naturales (biorreceptividad) que favorecen o inhiben el desarrollo de las comunidades microbianas.Microorganisms, particularly bacteria, inhabit all possible environments in the biosphere including subterranean ones. They play an important role in geological processes such as mineral precipitation and dissolution, and significantly influence biogeochemical cycles. At present, relatively few studies have focused on the active role of microorganisms, especially bacteria, in the formation of speleothems. Thus, the involvement of microbial activity in the formation of speleothems in caves is a geomicrobiological issue still to be solved. Today, the relationship between microorganisms and mineral fabrics and the role played by microorganisms in carbonate precipitation is unclear. The processes of carbonate deposit formation in caves offers an excellent scenario for research on biomineralization processes (from active microorganisms to their mineral deposits), because caves are protected environments where microbial fabrics can be preserved without extensive diagenetic modification or destruction. The new tendencies on geomicrobiological studies consist on applying different and multidisciplinary methodological approaches (petrology, geochemistry, microbiology, molecular biology) to (1) determine the role of the different microbial communities inhabiting the hypogean environments in the processes of mineral transformation, (2) identifying the physical and chemical properties of bioinduced crystalline phases, and (3) determine the environmental conditions, composition and texture of natural substrates (bioreceptivity) favouring or inhibiting the development of microbial communities.Este trabajo es parte de los proyectos CGL2006-11561/BTE y CGL2006-07424/BOS

Cristalización de sales en calcarenitas : aplicación al monasterio de San Jeronimo : Granada

El objetivo de esta Tesis Doctoral ha sido el estudio del fenómeno de infiltración de soluciones salinas y cristalización de sales que afecta a los materiales constructivos y ornamentales (calcarenitas bioclásticas, morteros de unión y revestimiento, pinturas murales) de la Iglesia de San Jerónimo (s. XVI, Granada). Para ello, se han analizado tanto los materiales mencionados como los productos de la cristalización (eflorescencias y subeflorescencias salinas), lo cual ha permitido establecer un modelo para este complejo fenómeno que contempla un fuerte control de la cristalización por las condiciones termohigrométricas del interior del edificio. Adicionalmente, y con el fin de profundizar en los mecanismos de transferencia de materia en medios porosos, se han llevado a cabo simulaciones experimentales en el laboratorio. Esto ha permitido precisar el mecanismo de transporte (infiltración capilar más difusión iónica), de evolución química de las soluciones (concentración constante) y de cristalización de sales (nucleación y crecimiento contradictorios con predicciones termodinámicas basadas en modelos simples). Los resultados obtenidos se han integrado en un modelo general que ha sido, a su vez, contrastado con las observaciones realizadas en el monumento, apreciándose las dificultades de extrapolar este modelo general a un caso natural complejo. Los resultados de los estudios obtenidos en esta Memoria son extrapolables a otros edificios histórico-artísticos construidos con calcarenitas y otros tipos de areniscas y rocas sedimentarias porosas afectados por aguas de infiltración con la subsecuente cristalización de sales. No obstante, estos estudios permiten establecer directrices para posibles intervenciones de restauración y conservación del Patrimonio monumental afectado por estos procesos de cristalización de sales.Tesis Univ. Granada. Departamento de Mineralogía y PetrologíaEsta tesis se ha realizado gracias a la financiación del Grupo de Investigación 4065 de la Junta de Andalucí