Pictorial Layers Research Articles

Advanced methods for the analysis of Roman wall paintings: elemental and molecular detection by means of synchrotron FT-IR and SEM micro-imaging spectroscopy

The reconstruction of Roman decorative apparatus from delocalized fragments is an arduous challenge for the archaeologists. An archaeometric approach may integrate the archaeological analyses, based on the stylistic observations, improving the ability to merge adjacent fragments, especially in the absence of distinctive ornamental elements. In this work, the capacity of reflection FT-IR spectroscopy combined with chemometric tools to identify groups of fragments that have similar chemical composition of the pictorial layers is tested. Synchrotron radiation-based Fourier transform infrared (SR-FTIR) microspectroscopy coupled with scanning electron microscopy (SEM) and energy-dispersive X-ray micro-analysis (EDX) performed on cross section were used to enhance the performance of conventional FT-IR technique and to localize micrometric-size compounds. The chemometric approach proposed in this work turns out to be a powerful way to discriminate pictorial layers with similar chemical composition, by the identification of different compounds. The use of SR source has permitted to improve the lateral resolution and to discriminate neighboring micro-compounds, such as quartz and cuprorivaite in Egyptian blue pigments.

An easily transferable protocol for in-situ quasi-non-invasive analysis of protein binders in works of art

Proteomic approaches based on mass spectrometry have become increasingly popular for protein binder's identification in works of art. The identification of the binder employed may offer key information on paintings and other polychrome objects and contribute to assess their historical and technical context, also providing useful hints for a proper restoration and/or conservation treatment. Usually, the protocols employed to this purpose are invasive and at least micro sampling is required. Here, we present a simple transferable method for a quasi-non-invasive analysis of binders in artworks based on the use of a very small poly (2-hydroxyethyl methacrylate)/poly (vinylpyrrolidone) hydrogel (3 mm × 3 mm) previously loaded with trypsin for the in-situ digestion of proteins and applied onto the objects' surface. Upon extraction of digested peptides from the hydrogel, they were examined by MALDI-TOF-MS and/or LC-ESI-MS/MS. The method was validated on fresh and aged model pictorial layers; optical microscope images, and spectrophotocolorimetry confirmed that neither damage nor color alteration of the painting layer occurred, and no hydrogel residue was left. X-ray photoelectron spectroscopy carried out on paint models confirmed that the treatment with trypsin-loaded gels did not modify the pigment composition, even on aged samples. The protocol was successfully applied to a painting on wood mockup aged thirty years, a statue dated XV century exposed in San Lorenzo church (Bisceglie, Bari, Apulia), and a liturgical scroll Benedictio ignis et fontis (Benedizionale) of the Museo Diocesano of Bari dated eleventh century; in all these objects the proteinaceous binder was readily and successfully identified.

Fracture saturation in paintings makes them less vulnerable to environmental variations in museums

Understanding paintings as physical systems is fundamental for advancing environmental specifications that would allow for effective management of museum environments in terms of reducing energy use and carbon emissions while maintaining high standards of collection care. The current environmental specifications were derived using the criterion of the crack initiation in undamaged, usually new, material. In reality, historical paintings exhibit complex crack patterns called craquelures. The present paper analyses painted wood which is among the category of cultural objects most vulnerable to relative humidity and temperature fluctuations and frequently found in museum collections of various kinds. Fracture toughness determined experimentally for the most brittle component of pictorial layer—the ground layer (gesso) is used as a ‘failure criterion’. Comparison of energy release rate—calculated for the model of the gesso laid on a wooden substrate using finite element analysis—with the structure toughness, allowed the fracture saturation expressed as the ratio of spacing between cracks S to gesso layer thickness t to be determined for various combinations of the gesso stiffness and geometries of structural flaws at which cracks initiate. For flat geometry of a panel painting and panel thickness of 40 mm, representing the worst-case, largest stresses in the gesso layer, the fracture saturation occurs when S/t is larger than 5, even if flaws in the gesso layer are present. The paper shows that the fracture saturation significantly changes vulnerability of paintings to climate variations—a panel painting with developed craquelure network is significantly less vulnerable to climate variations than an undamaged one.

Macroscopic XRF imaging in unravelling polychromy on Mycenaean wall-paintings from the Palace of Nestor at Pylos

The wall painting fragments from the Mycenaean “Palace of Nestor” at Pylos, are characterized by their high artistic quality, their unusual iconographic variety and the use of tempera and secco painting techniques. Systematic in-situ XRF analyses combined with the results of other portable and laboratory analytical techniques have already revealed a rich gamut of inorganic pigments with respect to the common Aegean “palette”, including different white and black pigments, iron based ochres ranging from dark brown to orange and pinkish hues, manganese based umbers, natural copper based greens, goethite, Egyptian blue and organic purple dyes. Macroscopic X-ray Fluorescence (MA-XRF) imaging, although well-established for non-invasive analysis of historical or contemporary painted artworks has hitherto been applied in a few cases only regarding the study of ancient polychromy. The purpose of applying in-situ MA-XRF imaging on selected wall painting fragments from the Palace of Pylos was to evaluate the capabilities of this technique in identifying the composition of pigments and their spatial distribution within heavily deteriorated pictorial layers, and in revealing iconographic information invisible to the naked eye. The results of MA-XRF imaging allowed us to critically re-consider previous artistic reconstructions, providing significant evidence on the painting techniques and materials used by Late Bronze Age painters.

The archaeological site of St. Maria Veterana (Triggiano, Southern Italy): Archaeometric study of the wall paintings for the historical reconstruction

This paper focusses on the archaeometric investigation of wall paintings of the St. Maria Veterana archaeological site in Triggiano (Bari, Southern Italy) finalised to support the hypothesis on the historical reconstruction of the site based on iconographic interpretations. The site is an original and relevant example of medieval art in Apulia and in Southern Italy and includes a medieval church surrounded by several additionally architectural elements (chapels, crypts, tombs), nowadays buried below by a Renaissance church. Here, the presence of different pictorial cycles, only partially dated, and the evidence of re-use of painted blocks in Renaissance structures pertaining to medieval structures, suggested a complex scenario in which different artisans and clients were possibly succeeded. The site is also framed in a wider regional context, the Apulian region, currently object of an intense archaeological and scientific debate due to widespread action of valorisation of the cultural patrimony as an essential link between the territory and the cultural identity of the citizens.The study of the site involved the sampling and the analysis of 48 samples of painting fragments, investigated by optical microscopy, scanning electron microscopy with EDS microanalysis (SEM-EDS) and micro-Raman spectroscopy. The obtained results allowed a complete material characterization of mortars and pictorial layers, highlighting the use of precious and rare pigments as cinnabar and verdigris, along with more common recipes based on natural ochres and earths more commonly used in other similar sites through the Apulia region. The combined data obtained from the analysis of mortars and pigments allowed to finally propose a reliable hypothesis on the construction and decorative phases of the site, in agreement with the dating based on iconographic interpretations.Up to now, St. Maria Veterana Church was considered a minor site, mainly due to the scarcity of the written sources. However, the new stylistic interpretation of the pictorial cycles, the preciousness of the used materials, the quality of the manufacture technique and the numerous artistic executive phases identified through five centuries (11th–16th) suggest a continuous attendance of the site by artisans and client carriers of high cultural and artistic values.

Carotenoids produced by halophilic bacterial strains on mural paintings and laboratory conditions.

Due to the presence of efflorescences and improper microclimate conditions for conservation, pink-pigmented areas were reported in two historic monuments in Northern and Central part of Romania. The aims of the present study were to find the nature of pink pigments observed on the pictorial layer, original and infilling mortar, to investigate the presence of carotenoids both on mural paintings and in the isolated halophilic bacterial strains and to preliminary characterize and identify the producing strains. Their role in the aesthetical biodeterioration of historic monuments was also pointed out. Obtained Raman spectra of the pink pigments extracted both from the isolated bacterial cultures (molecularly identified as mostly related to Halobacillus hunanensis and Halobacillus naozhouensis) and from the mural painting samples contain diagnostic bands of carotenoids. These results were confirmed by FTIR spectroscopy. The strong Raman signal of bacterial carotenoids detected on mural painting indicated their potential use as biomarker molecules in the evaluation of contamination and state of conservation of mural paintings and lithic monuments. Our results contribute to opening a new direction in cultural heritage restoration to assess the conservation status on the basis of interdisciplinary research, starting with spectroscopic methods (Raman, FTIR) and confirmed by microbiological analysis.

Improvement of the Non-Destructive Testing of Heritage Mural Paintings Using Stimulated Infrared Thermography and Frequency Image Processing.

Within the framework of conservation and assistance for the restoration of cultural property, a method of analysis assistance has been developed to help in the restoration of cultural heritage. Several collaborations have already demonstrated the possibility of defects detection (delamination, salts) in murals paintings using stimulated infrared thermography. One of the difficulties encountered with infrared thermography applied to the analysis of works of art is the remanence of the pictorial layer. This difficulty can sometimes induce detection artifacts and false positives. A method of thermograms post-processing called PPT (pulse phase thermography) is described. The possibilities offered by the PPT in terms of reducing the optical effects associated with the pictorial layer are highlighted first with a simulation, and then through experiments. This approach can significantly improve the study of painted works of art such as wall paintings.

Pigments and plasters from the Roman temple of Deir El-Hagar, Dakhla Oasis, Egypt: vibrational spectroscopic characterization

Deir El-Hagar temple at the Dakhla Oasis of the Western desert is a rare example of the surviving complete Roman structures in Egypt. The temple was discovered in 1819, and since that date, several restoration attempts have been carried out for its preservation. In the present case study, pigment and plaster samples from Deir El-Hagar temple were analyzed, for the first time, using different analytical methods. Initially, the microscopic observations were applied to collect stratigraphic data on the pictorial layers and the appropriate areas for analysis. The vibrational characteristics of the contained mineral phases were determined using Raman microspectroscopy. The surface morphology and microfeatures of the samples were accomplished by an environmental scanning electron microscopy and the energy-dispersive X-ray micro-analyzer (SEM–EDAX). Additionally, the visible reflectance spectroscopy (vis-RS) was used as a complementary method to record the reflectance spectra of some pigment samples. As such, the analytical techniques used in this study allowed the identification of the vibrational spectroscopic characteristics and the mineralogical–chemical composition of the studied samples. The results showed that the temple walls were plastered with two layers, coarse plaster and thin whitewash render. The blue pigment sample was identified as Egyptian blue and the occurrence of arsenic-based compounds in the sample was also reported and discussed. It was confirmed that a heated goethite, rather than natural red ochre, was used to produce the red colour. Additionally, mixed pigments were used to produce different hues and tonalities. A charcoal black, most likely of a charred wood, was used as a black pigment. Moreover, several proportions of haematite and magnetite were detected along the scanned surface of the black pigment. The findings of the current research allowed delivering an analytical report on the painting materials used in an important example of the Roman monuments in the Western desert of Egypt.

Post-Processing of VIS, NIR, and SWIR Multispectral Images of Paintings. New Discovery on the The Drunkenness of Noah, Painted by Andrea Sacchi, Stored at Palazzo Chigi (Ariccia, Rome)

IR Reflectography applied to the identification of hidden details of paintings is extremely useful for authentication purposes and for revealing technical hidden features. Recently, multispectral imaging has replaced traditional imaging techniques thanks to the possibility to select specific spectral ranges bringing out interesting details of the paintings. VIS–NIR–SWIR images of one of the The Drunkenness of Noah versions painted by Andrea Sacchi, acquired with a modified reflex and InGaAs cameras, are presented in this research. Starting from multispectral images we performed post-processing analysis, using visible and infrared false-color images and principal component analysis (PCA) in order to highlight pentimenti and underdrawings. Radiography was performed in some areas to better investigate the inner pictorial layers. This study represents the first published scientific investigation of The Drunkenness of Noah’s artistic production, painted by Andrea Sacchi.

From the Pyrenees to the Alps: Evidence of the use of aerinite on XII century fresco paintings at Novalesa abbey (Piemonte)

The chemical analysis of paintings is a powerful source of information when aiming to find relationships among different cultures or geographical areas. Indeed, the presence of particular colourants, specific of one area or of one pictorial school, could indicate that artists coming from abroad were at work outside of their usual boundaries, or that pigments were imported from markets located at great distance. The case of a turquoise pigment found on a 12th century mural painting at the abbey of Novalesa (Piemonte, North-western Italy) is an example of what, according to the authors, should be seen as an example of travelling workers. Analytical evidences given by in situ XRF and FORS and by micro-invasive Raman, XRD and SEM-EDX measurements allowed identifying the rare pigment aerinite, an iron silicate extracted in the Pyrenees and only known to have been used in the medieval area comprising the Pyrenees and south-western France. Not only was its presence previously unreported in Italy, but even the layering of the pictorial layers was unusual. The aerinite layer lies under a thin, translucent layer of gypsum, which was perhaps applied in order to tune its hue and enhance the contrast with the more precious lapis lazuli also found in the mural painting. This unusual but significant identification strongly suggests that foreign painters coming from Pyrenees could have worked at Novalesa abbey in 12th century, reversing the previous hypotheses of a local production based on iconographic studies.

An original molecular approach to the use of clay minerals in the formulation of oil-based dyes and their sensitivity toward polar solvents - A case study

Several restorers of paintings have reported the sensitivity of oil paints toward polar solvents during the chemical cleaning of the surface of the pictorial layer. In this study, a novel mechanism for this phenomenon is described based on the chemical analysis of the pictorial layer of a nineteenth century painting and the swab used in the cleaning of this layer. The pigments used were characterized by FTIR and SEM-EDS and the presence of kaolinite, a clay mineral, was observed in all areas that showed sensitivity. The binder was characterized by GC–MS as a mixture of linseed and walnut oils. SEM analysis showed the presence of pigments adhered to the cotton as well as the presence of kaolinite. GC–MS results for the swab showed the absence of oil in the paint traces present. Thus, the oil and its degradation products are not sensitive toward the polar solvent, but only the pigment and the kaolinite. Since kaolinite is hygroscopic, it aids the leaching of the pigment of the oil layer onto the swab containing the polar solvent.

Applications of Raman spectroscopy in art and archaeology

Applications of Raman spectroscopy in art and archaeology

In situ non-invasive multianalytical methodology to characterize mosaic tesserae from the House of Gilded Cupids, Pompeii

Mosaics, one of the most important decorative artworks in the Roman culture, were usually elaborated with a set of tesserae joined with lime or others binders to form geometric or figurative decorations. The identification of both substrate and colored compounds of the tesserae is a challenge for chemists and archaeologists. In this work, two mosaics present in the House of Gilded Cupids from the Archaeological Park of Pompeii were analyzed in situ by non destructive techniques. Raman and Diffuse Reflectance Infrared Fourier Transform (DRIFT) spectroscopies were used for the molecular and mineralogical characterization, and hand-held energy dispersive X-ray fluorescence (HH-EDXRF) spectrometry and Laser Induced Breakdown Spectroscopy (LIBS) for the elemental analysis. LIBS in-depth analysis was performed to obtain insights about the thickness of the pictorial layer determining that the thickness of red and orange pictorial layers was higher than 140 μm. The results showed that white tesserae were mainly composed by calcite, while local black colored volcanic rocks were used to manufacture black tesserae. Red and orange tesserae were composed by a calcite-based matrix with a hematite pictorial layer applied over it. Orange color was obtained by diluting hematite in the calcite matrix. Principal component analysis (PCA) of the XRF data was performed to observe differences and/or similarities between the analyzed mosaics; the samples projection of the PCA showed clear groupings.

Characterization of biodegradation in a 17th century easel painting and potential for a biological approach

It is important to characterize the microorganisms involved in biodeterioration processes to understand their effects on cultural assets and to define an efficient strategy for protecting artworks, monuments, and buildings from microbiological recolonization. In this study, we analyzed the microbial communities dwelling on the verso (front) and recto (back) sides of a 17th century easel painting attributed to Carlo Bononi, an Italian artist of the first Baroque period. Cultivable bacteria and fungi colonizing the painting were isolated and identified in order to characterize the microbial community possibly involved in deteriorating the pictorial layer of the painting. The isolated bacterial strains belonged to the Staphylococcus and Bacillus genera. Furthermore, culture-dependent techniques and SEM/EDS analyses revealed the presence of filamentous fungi of the genera Aspergillus, Penicillium, Cladosporium, and Alternaria. The chemical compositions of pigments were consistent with typical 17th century paintings, and some of the identified pigments, namely red lac and red and yellow earths, could be exploited as nutrient sources by painting-associated microorganisms. The study also evaluated, in vitro, the potential decontaminating activity of a biocompound, containing spores of Bacillus subtilis, Bacillus pumilus, and Bacillus megaterium. The results indicated the ability of this biocompound to counteract the growth of contaminating microorganisms that are potentially dangerous to the painting, suggesting the potential use of these microorganisms to prevent biodeterioration of artworks.

Confocal Imaging at 0.3 THz With Depth Resolution of a Painted Wood Artwork for the Identification of Buried Thin Metal Foils

A compact confocal terahertz microscope working at 0.30 THz based on all-solid-state components is used to locate buried thin metal foils in a painted wood artwork. Metal foils are used for decoration, and their precise localization under the pictorial layer is relevant information for conservation scientists and restorers, which can neither be obtained by X-ray radiography nor by spectroscopic imaging in the infrared, as we directly show here. The confocal microscopy principle based on the spatial pinhole concept is here implemented by positioning the first focus of an ellipsoidal reflector at the phase center of horn antennas coupled to Schottky diode detector and emitter mounted in rectangular waveguide blocks, together with an optical beamsplitter. The second focus of the reflector is mechanically scanned inside the sample in three dimensions. The predictions of diffraction theory for a confocal microscope at an imaging wavelength of 1.00 mm with numerical aperture of 0.53 are verified experimentally (1.2 and 2.8 mm for the lateral and the axial resolution, respectively). These values of resolution allow a precise determination of the position of buried metal foils in an ancient piece of art hence making restoration interventions possible.

Microscopic Analysis of Wall Painting Techniques: Laboratory Replicas and Romanesque Case Studies in Southern Switzerland

ABSTRACTThe identification of painting techniques is an important aspect of any research related to historical, artistic, and conservation issues in the field of wall paintings conservation. There are a variety of different methodological approaches that can be used to identify wall painting techniques. In this study, the application of optical (PLM) and electron (SEM-EDX) microscopy was explored as they are complementary analytical techniques commonly used for micro-stratigraphic analysis of painted surfaces. Five replicas were prepared according to the technical procedures reported in medieval historical treatises, and the pigment was applied at different time intervals in order to monitor the modifications at the interface between the ground and pictorial layer. The comparison of data from the replicas with samples from Romanesque wall paintings in churches in Southern Switzerland and Northern Lombardy (Italy) allowed for an evaluation of the reliability of the proposed methodology and for the interpretation of the painting techniques.

Policromía original de las yeserías del Patio de las Doncellas del Real Alcázar de Sevilla. Materiales constitutivos y técnicas de ejecución

Esta investigación tiene la finalidad determinar la técnica y los materiales empleados en la policromía original de las yeserías de las galerías bajas del Patio de las Doncellas. Este emplazamiento forma parte de las construcciones realizadas por Pedro I (1356-1366) en el conjunto monumental del Alcázar de Sevilla, cuya importancia como ciudad palatina determinó su inclusión en la lista del Patrimonio Mundial de la UNESCO en el año 1987 junto a la Catedral y el Archivo de Indias. Su condición como residencia permanente de los monarcas españoles ha favorecido su conservación, pero también que haya sido muy intervenido desde su construcción. Esta sucesión de intervenciones es especialmente visible en las yeserías de dicho patio donde se distinguen repolicromados y encalados sucesivos que ocultan la delicadeza del relieve y los restos del color original, ofreciendo en la actualidad un aspecto grisáceo bastante lejano al del momento de su ejecución en el s. XIV en el que predominaba el color. Tras una pormenorizada revisión documental y un minucioso estudio de campo, se acometió la toma de micromuestras para estudiarlas mediante técnicas analíticas de estudio del Patrimonio Cultural -microscopía estereoscópica, microscopia óptica, microscopía electrónica de barrido (SEM/EDX), difracción de rayos X (XRD), espectroscopía infrarroja por transformada de Fourier (FTIR) o cromatografía gaseosa entre otras (GC-MS)- a partir de las cuales poder identificar las características del mortero, la composición de la capa pictórica y el aglutinante empleado, determinándose de esta manera la existencia de restos de policromía original.

Las pinturas murales de Castulo. Primeras aportaciones a la caracterización de materiales y técnicas de ejecución

En este artículo se presenta la investigación que se está llevando a cabo sobre las pinturas murales de la Sala del Mosaico de los Amores en el Conjunto Arqueológico de Castulo, en Linares (Jaén). Durante la campaña efectuada en el año 2011, se descubrió una estancia que albergaba una decoración musivaria y parietal de gran calidad datada en el s. I-II d.C. Parte de esa decoración parietal, concretamente la correspondiente al muro oeste, fue encontrada derrumbada sobre el pavimento, y trasladada a los laboratorios de la Universidad de Granada para su intervención de consolidación y restauración. Dado que apenas existía información sobre pintura mural en Castulo, se está realizando un estudio de las pinturas, en el que se está llevando a cabo la caracterización de materiales y de su técnica de ejecución, como paso previo a su restauración. Estos análisis han permitido identificar una capa pictórica muy rica, constituida por tonos verdes, rojos, ocres, blancos y negros, entre los que destacan pigmentos de gran calidad como el azul egipcio, además de otros que normalmente se encuentran en la paleta romana como el minio, la tierra roja, el negro de hueso o el blanco de cal.

Maya Lime Mortars—Relationship between Archaeomagnetic Dating, Manufacturing Technique, and Architectural Function—The Dzibanché Case

Researchers have related the manufacturing technique of plasters and stucco in the Maya area with their period of production but not with their architectural function. In this paper, we establish a relationship between those three features (manufacturing technique, age, and architectural function) in the plasters of the Maya site of Dzibanché in southern Quintana Roo. Dzibanché has abundant remains of stuccos and plasters found mainly in three buildings (Plaza Pom, Pequeña Acrópolis, and Structure 2). We used thin sections, SEM and XRD, and archaeomagnetic dating processes. The pictorial layer of Structure 2 was the earliest (AD 274–316 and the stuccoes and plasters of the other two buildings were dated to the Middle Classic (AD 422–531), but we obtained different archaeomagnetic dates for the red pigment layers found in the buildings of the Pequeña Acrópolis and thus we were able to determine their chronological order of construction. The raw materials and proportions were carefully chosen to fulfil the mechanical necessities of the architectonic function: different proportions were found in plasters of floors, in the external walls, and inside the buildings; differences between earlier and later plasters were also detected.

Pink discoloration on frescoes from Hurezi Monastery, Romania

Abstract A multianalitical approach based on optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction, grain size distribution and microbiological methods has been applied to characterize pink discoloration on the surface of both original painting and lime-mortar infillings of the frescoes of the refectory from the Hurezi Monastery, Romania. Polarized microscopy, the study of the cross-sections, X-ray diffraction and grain size distribution pointed out the characteristics of materials and led to a better analysis of composition and the availability to be colonized. Thick layers of bacteria developed around and into enlarged pores led to the alteration of substrate pore sizes and changes of moisture circulation. Acting simultaneously with efflorescences, disaggregation and fragmentation of the mortar and pictorial layer take place. Microbial origin of pink discoloration detected by OM and SEM was confirmed by culture based methods. The present study points out the analytical methods for identification of pink aesthetical damage of mural painting and its biological origin.