Descripción de las fases de carbonato cálcico en la superficie de enlucidos de cal en pasta pintados al fresco

La técnica al fresco, ejecutada con cal en pasta como material conglomerante, ha sido utilizada desde hace miles de años. No obstante, los procesos físico-químicos y cristalográficos que hacen posible la pintura al fresco han sido descritos de manera generalista como parte del proceso de carbonatación del propio enlucido. Al aproximarse a la técnica desde el punto de vista del pintor-estucador, se observa que la evolución del film superficial del fresco durante las horas del periodo de ejecución -periodo de entre 0-20 horas, aproximadamente- no es correlacionable con la evolución de los estratos que conforman el enlucido: su textura, rigidez y compacidad son particulares. El motivo de esta tesis es investigar la formación y desarrollo de este film superficial. Para ello se ha recurrido a la caracterización de pinturas al fresco antiguas del periodo romano y románico y se han comparado con probetas experimentales de fresco. Mediante este proceso se ha observado la presencia de un film de aspecto geliforme en el conjunto de pinturas caracterizadas, tanto en las antiguas como en las probetas experimentales. Para la caracterización, estudio de la formación y evolución de este film geliforme se ha realizado un conjunto de probetas experimentales de fresco que han sido estudiadas pormenorizadamente durante un intervalo temporal de 0-24 horas. Además, se han incluido muestras de días, meses y años con el objetivo de evaluar la evolución de este film en el tiempo. La caracterización y observación de este film ha sido llevado a cabo mediante diversas técnicas analíticas: POM (microscopio óptico petrográfico), contaje y medición de partículas mediante tratamiento de imagen mediante el programa IMAGEJ, SEM-EDS(microscopio electrónico de barrido con análisis de rayos X) y FT-IR (espectroscopia infrarroja por transformada de Fourrier). Cabe destacar que para el desarrollo de esta investigación se ha optimizado en sistema de extracción y embutición de muestras. Esta optimización se ha considerado novedosa y ha conllevado la obtención de una patente de procedimiento. Las conclusiones indican que sobre la superficie de un enlucido/reenlucido pintado al fresco se desarrolla un gel amorfo compuesto por carbonato cálcico. Bajo este gel se sitúa una interfase en la que se desarrollan crecimientos cristalinos específicos, generados por una velocidad de crecimiento acelerada debido a una fuerte saturación, con fenómenos split growth. Esto es debido a la rápida evaporación del film acuoso creado durante la ejecución del fresco. Por debajo de esta interfase se encuentra la superficie del enlucido/reenlucido que aporta substancias y partículas que transforman rápidamente la composición y evolución del film, que adquiere en poco tiempo la naturaleza de una dispersión coloidal. La descripción y evolución de este film-gel tiene implicaciones en el campo de la investigación de la pintura al fresco, la investigación de la cal en pasta como material conglomerante y las metodologías de conservación y restauración de pinturas al fresco y pinturas murales en base a cal.The fresco technique, executed with lime putty as conglomerating material, has been used since thousands of years ago. However, the crystallographic and physico-chemical processes which make the fresco painting possible have been described in a general way, as part of the carbonation process of the intonaco itself. When approaching the technique from the point of view of the painter-stucco plasterer, it has been observed that the evolution of the superficial film of the fresco painting during the hours of the execution period (period of 0-20 hours, approximately) does not correspond to the evolution of the stratums which form the intonaco: its texture, stiffness and compactness are specific. The reason for this thesis is to investigate the formation and development of this superficial film. For this purpose, I have turned to the characterization of antique fresco paintings from the roman and romanesque periods, and I have compared them with experimental test tubes of fresco. Thanks to this process, it has been observed the presence of a film of geliform appearance in the whole of the characterized paintings, both in the antique paintings and in the experimental test tubes. For the characterization and the formation study, as well as the evolution of this geliform film, a set of fresco experimental test tubes have been realized, and have been thoroughly studied during a time range of 0-24 hours. Moreover, samples of days, months and years have been included, with the aim of assessing the evolution of this film through time. The characterization and the observation of this film have been carried out by means of different analytical techniques: POM (Petrographic Optic Microscope), count and measurement of particles through the treatment of images by means of the program IMAGEJ, SEM-EDS (Scanning Electron Microscope-Energy with atomical X-ray Spectroscopy) and FT-IR (Fourier Transform Infrared Spectroscopy). Please note that, for the development of this investigation, the system of detachment and vacuum forming of samples has been optimized. This optimization has been considered a novelty and has led to the securing of a process patent. This optimization has enabled the observation in detail of the morphological and crystallographical evolution of the pictorical film. The conclusions show that, over the surface of an intonaco/intonachino painted as a fresco, it can be seen the development of an amorphous gel composed by calcium carbonate. Below this gel, there is an interface on which specific crystalline growths are developed and evolved. These are generated in supersaturated conditions, conditions that accelerate de speed of growing promoting split growth phenomena. Thanks to the fast evaporation of the aqueous film –water and pigment-.Below this interface, the intonaco/intonachino surface can be found, that contribute with particles that convert quickly the composition and evolution of the film as to be gradually transformed in a colloidal dispersion. The description and evolution of this gel-film has consequences on the field of investigation of fresco painting, the investigation of lime putty as a conglomerating material, as well as the the preservation and restauration methodologies of fresco paintings and lime-based wall paintings

Descripción de las fases de carbonato cálcico en la superficie de enlucidos de cal en pasta pintados al fresco

La técnica al fresco, ejecutada con cal en pasta como material conglomerante, ha sido utilizada desde hace miles de años. No obstante, los procesos físico-químicos y cristalográficos que hacen posible la pintura al fresco han sido descritos de manera generalista como parte del proceso de carbonatación del propio enlucido. Al aproximarse a la técnica desde el punto de vista del pintor-estucador, se observa que la evolución del film superficial del fresco durante las horas del periodo de ejecución -periodo de entre 0-20 horas, aproximadamente- no es correlacionable con la evolución de los estratos que conforman el enlucido: su textura, rigidez y compacidad son particulares. El motivo de esta tesis es investigar la formación y desarrollo de este film superficial. Para ello se ha recurrido a la caracterización de pinturas al fresco antiguas del periodo romano y románico y se han comparado con probetas experimentales de fresco. Mediante este proceso se ha observado la presencia de un film de aspecto geliforme en el conjunto de pinturas caracterizadas, tanto en las antiguas como en las probetas experimentales. Para la caracterización, estudio de la formación y evolución de este film geliforme se ha realizado un conjunto de probetas experimentales de fresco que han sido estudiadas pormenorizadamente durante un intervalo temporal de 0-24 horas. Además, se han incluido muestras de días, meses y años con el objetivo de evaluar la evolución de este film en el tiempo. La caracterización y observación de este film ha sido llevado a cabo mediante diversas técnicas analíticas: POM (microscopio óptico petrográfico), contaje y medición de partículas mediante tratamiento de imagen mediante el programa IMAGEJ, SEM-EDS(microscopio electrónico de barrido con análisis de rayos X) y FT-IR (espectroscopia infrarroja por transformada de Fourrier). Cabe destacar que para el desarrollo de esta investigación se ha optimizado en sistema de extracción y embutición de muestras. Esta optimización se ha considerado novedosa y ha conllevado la obtención de una patente de procedimiento. Las conclusiones indican que sobre la superficie de un enlucido/reenlucido pintado al fresco se desarrolla un gel amorfo compuesto por carbonato cálcico. Bajo este gel se sitúa una interfase en la que se desarrollan crecimientos cristalinos específicos, generados por una velocidad de crecimiento acelerada debido a una fuerte saturación, con fenómenos split growth. Esto es debido a la rápida evaporación del film acuoso creado durante la ejecución del fresco. Por debajo de esta interfase se encuentra la superficie del enlucido/reenlucido que aporta substancias y partículas que transforman rápidamente la composición y evolución del film, que adquiere en poco tiempo la naturaleza de una dispersión coloidal. La descripción y evolución de este film-gel tiene implicaciones en el campo de la investigación de la pintura al fresco, la investigación de la cal en pasta como material conglomerante y las metodologías de conservación y restauración de pinturas al fresco y pinturas murales en base a cal.The fresco technique, executed with lime putty as conglomerating material, has been used since thousands of years ago. However, the crystallographic and physico-chemical processes which make the fresco painting possible have been described in a general way, as part of the carbonation process of the intonaco itself. When approaching the technique from the point of view of the painter-stucco plasterer, it has been observed that the evolution of the superficial film of the fresco painting during the hours of the execution period (period of 0-20 hours, approximately) does not correspond to the evolution of the stratums which form the intonaco: its texture, stiffness and compactness are specific. The reason for this thesis is to investigate the formation and development of this superficial film. For this purpose, I have turned to the characterization of antique fresco paintings from the roman and romanesque periods, and I have compared them with experimental test tubes of fresco. Thanks to this process, it has been observed the presence of a film of geliform appearance in the whole of the characterized paintings, both in the antique paintings and in the experimental test tubes. For the characterization and the formation study, as well as the evolution of this geliform film, a set of fresco experimental test tubes have been realized, and have been thoroughly studied during a time range of 0-24 hours. Moreover, samples of days, months and years have been included, with the aim of assessing the evolution of this film through time. The characterization and the observation of this film have been carried out by means of different analytical techniques: POM (Petrographic Optic Microscope), count and measurement of particles through the treatment of images by means of the program IMAGEJ, SEM-EDS (Scanning Electron Microscope-Energy with atomical X-ray Spectroscopy) and FT-IR (Fourier Transform Infrared Spectroscopy). Please note that, for the development of this investigation, the system of detachment and vacuum forming of samples has been optimized. This optimization has been considered a novelty and has led to the securing of a process patent. This optimization has enabled the observation in detail of the morphological and crystallographical evolution of the pictorical film. The conclusions show that, over the surface of an intonaco/intonachino painted as a fresco, it can be seen the development of an amorphous gel composed by calcium carbonate. Below this gel, there is an interface on which specific crystalline growths are developed and evolved. These are generated in supersaturated conditions, conditions that accelerate de speed of growing promoting split growth phenomena. Thanks to the fast evaporation of the aqueous film –water and pigment-.Below this interface, the intonaco/intonachino surface can be found, that contribute with particles that convert quickly the composition and evolution of the film as to be gradually transformed in a colloidal dispersion. The description and evolution of this gel-film has consequences on the field of investigation of fresco painting, the investigation of lime putty as a conglomerating material, as well as the the preservation and restauration methodologies of fresco paintings and lime-based wall paintings

New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty

The fresco technique performed with slaked lime putty as binding material has been well known since Antiquity. However, the geochemical processes that occur on the surface have been generally described as part of the carbonation process of the intonaco itself. When approaching this technique from experimental archaeology, it has been observed for the first time that during the execution period (from 0 to 20 h, approximately) the processes occurring on the surface of the stucco are different from those occurring inside. Furthermore, these processes lead to the formation of an epigenetic film of specific texture, stiffness and compactness. This study investigates the formation and evolution of this surface film using a series of slaked lime putty stucco test tubes. Samples were extracted at different intervals and subsequently analyzed by polarized optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Results indicate that the development of the film, composed of an amorphous gel-like stratum and a micro-crystalline stratum, occurs in parallel to the carbonation occurring inside the stucco. Moreover, this process does not respond to the classical geological processes of calcium carbonate formation. It was also observed that its presence slows down the carbonation in the underlying strata (intonaco, intonachino, arriccio, etc.) and that the surface becomes more crystalline over time. The identification of this film has implications for the field of the conservation–restoration of fresco paintings and lime-based wall paintings

Descripción y evolución de las fases de carbonato cálcico presentes en los enlucidos de cal en pasta pintados al fresco

La técnica al fresco, ejecutada con cal en pasta como material conglomerante, ha sido utilizada desde hace miles de años. No obstante, los procesos físico-químicos y cristalográficos que hacen posible la pintura al fresco han sido descritos de manera generalista como parte del proceso de carbonatación del propio enlucido. Al aproximarse a la técnica desde el punto de vista del pintor-estucador, se observa que la evolución del film superficial del fresco durante las horas del periodo de ejecución -periodo de entre 0-20 horas, aproximadamente- no es correlacionable con la evolución de los estratos que conforman el enlucido: su textura, rigidez y compacidad son particulares. El motivo de esta tesis es investigar la formación y desarrollo de este film superficial. Para ello se ha recurrido a la caracterización de pinturas al fresco antiguas del periodo romano y románico y se han comparado con probetas experimentales de fresco. Mediante este proceso se ha observado la presencia de un film de aspecto geliforme en el conjunto de pinturas caracterizadas, tanto en las antiguas como en las probetas experimentales. Para la caracterización, estudio de la formación y evolución de este film geliforme se ha realizado un conjunto de probetas experimentales de fresco que han sido estudiadas pormenorizadamente durante un intervalo temporal de 0-24 horas. Además, se han incluido muestras de días, meses y años con el objetivo de evaluar la evolución de este film en el tiempo. La caracterización y observación de este film ha sido llevado a cabo mediante diversas técnicas analíticas: POM (microscopio óptico petrográfico), contaje y medición de partículas mediante tratamiento de imagen mediante el programa IMAGEJ, SEM-EDS(microscopio electrónico de barrido con análisis de rayos X) y FT-IR (espectroscopia infrarroja por transformada de Fourrier). Cabe destacar que para el desarrollo de esta investigación se ha optimizado en sistema de extracción y embutición de muestras. Esta optimización se ha considerado novedosa y ha conllevado la obtención de una patente de procedimiento. Las conclusiones indican que sobre la superficie de un enlucido/reenlucido pintado al fresco se desarrolla un gel amorfo compuesto por carbonato cálcico. Bajo este gel se sitúa una interfase en la que se desarrollan crecimientos cristalinos específicos, generados por una velocidad de crecimiento acelerada debido a una fuerte saturación, con fenómenos split growth. Esto es debido a la rápida evaporación del film acuoso creado durante la ejecución del fresco. Por debajo de esta interfase se encuentra la superficie del enlucido/reenlucido que aporta substancias y partículas que transforman rápidamente la composición y evolución del film, que adquiere en poco tiempo la naturaleza de una dispersión coloidal. La descripción y evolución de este film-gel tiene implicaciones en el campo de la investigación de la pintura al fresco, la investigación de la cal en pasta como material conglomerante y las metodologías de conservación y restauración de pinturas al fresco y pinturas murales en base a cal.The fresco technique, executed with lime putty as conglomerating material, has been used since thousands of years ago. However, the crystallographic and physico-chemical processes which make the fresco painting possible have been described in a general way, as part of the carbonation process of the intonaco itself. When approaching the technique from the point of view of the painter-stucco plasterer, it has been observed that the evolution of the superficial film of the fresco painting during the hours of the execution period (period of 0-20 hours, approximately) does not correspond to the evolution of the stratums which form the intonaco: its texture, stiffness and compactness are specific. The reason for this thesis is to investigate the formation and development of this superficial film. For this purpose, I have turned to the characterization of antique fresco paintings from the roman and romanesque periods, and I have compared them with experimental test tubes of fresco. Thanks to this process, it has been observed the presence of a film of geliform appearance in the whole of the characterized paintings, both in the antique paintings and in the experimental test tubes. For the characterization and the formation study, as well as the evolution of this geliform film, a set of fresco experimental test tubes have been realized, and have been thoroughly studied during a time range of 0-24 hours. Moreover, samples of days, months and years have been included, with the aim of assessing the evolution of this film through time. The characterization and the observation of this film have been carried out by means of different analytical techniques: POM (Petrographic Optic Microscope), count and measurement of particles through the treatment of images by means of the program IMAGEJ, SEM-EDS (Scanning Electron Microscope-Energy with atomical X-ray Spectroscopy) and FT-IR (Fourier Transform Infrared Spectroscopy). Please note that, for the development of this investigation, the system of detachment and vacuum forming of samples has been optimized. This optimization has been considered a novelty and has led to the securing of a process patent. This optimization has enabled the observation in detail of the morphological and crystallographical evolution of the pictorical film. The conclusions show that, over the surface of an intonaco/intonachino painted as a fresco, it can be seen the development of an amorphous gel composed by calcium carbonate. Below this gel, there is an interface on which specific crystalline growths are developed and evolved. These are generated in supersaturated conditions, conditions that accelerate de speed of growing promoting split growth phenomena. Thanks to the fast evaporation of the aqueous film -water and pigment-.Below this interface, the intonaco/intonachino surface can be found, that contribute with particles that convert quickly the composition and evolution of the film as to be gradually transformed in a colloidal dispersion. The description and evolution of this gel-film has consequences on the field of investigation of fresco painting, the investigation of lime putty as a conglomerating material, as well as the the preservation and restauration methodologies of fresco paintings and lime-based wall paintings

New Insights into the Geochemical Processes Occurring on the Surface of Stuccoes Made of Slaked Lime Putty

The fresco technique performed with slaked lime putty as binding material has been well known since Antiquity. However, the geochemical processes that occur on the surface have been generally described as part of the carbonation process of the intonaco itself. When approaching this technique from experimental archaeology, it has been observed for the first time that during the execution period (from 0 to 20 h, approximately) the processes occurring on the surface of the stucco are different from those occurring inside. Furthermore, these processes lead to the formation of an epigenetic film of specific texture, stiffness and compactness. This study investigates the formation and evolution of this surface film using a series of slaked lime putty stucco test tubes. Samples were extracted at different intervals and subsequently analyzed by polarized optical microscopy, scanning electron microscopy, and Fourier transform infrared spectroscopy. Results indicate that the development of the film, composed of an amorphous gel-like stratum and a micro-crystalline stratum, occurs in parallel to the carbonation occurring inside the stucco. Moreover, this process does not respond to the classical geological processes of calcium carbonate formation. It was also observed that its presence slows down the carbonation in the underlying strata (intonaco, intonachino, arriccio, etc.) and that the surface becomes more crystalline over time. The identification of this film has implications for the field of the conservation–restoration of fresco paintings and lime-based wall paintings