Nati Salvadó

Identification of copper-based green pigments in Jaume Huguet's Gothic altarpieces by Fourier transform infrared microspectroscopy and synchrotron radiation X-ray diffraction

The scientific investigation of ancient paintings gives a unique insight into ancient painting techniques and their evolution through time and geographic location. This study deals with the identification of the green pigments used by one of the most important Catalan masters in Gothic times, Jaume Huguet. Other pigments and materials have also been characterized by means of conventional techniques such as optical microscopy, scanning electron microscopy and Fourier transform infrared spectroscopy. Synchrotron radiation X-ray diffraction has been used to produce maps of phases at a spatial resolution of 100 microm across chromatic layers.

Identification of reaction compounds in micrometric layers from gothic paintings using combined SR-XRD and SR-FTIR

Synchrotron radiation X-ray diffraction (micro-SR-XRD) and Fourier transform infrared spectroscopy (micro-SR-FTIR) are used in the non-destructive identification of reaction and aging compounds from micrometric ancient painting layers. The combination of the micrometer size and non-destructive nature of the techniques together with the high resolution and brilliance of the synchrotron radiation has proved to be a procedure most advantageous for the study of reaction, aging and degradation processes. Copper, lead and calcium carboxylates and oxalates are determined in the chromatic, preparation and alteration layers from 15th century egg tempera and oil paintings. Their nature and crystallinity have been assessed. Some hypothesis about the mechanisms of development of both carboxylates and oxalates are presented.

SR-XRD and SR-FTIR study of the alteration of silver foils in medieval paintings

AbstractAltarpieces and polychrome carved wood from the fifteenth century AD usually exhibit golden and silvery areas by the application of a very thin foil of metal. The metal foils were normally protected from the atmosphere by a varnish or resin which maybe either preserved or absent. Moreover, they were glued to the background surface by adhesive substances (egg yolk, drying oil or animal glue). The high proportion of the glueing substances often renders the development of reaction compounds. With time, silver alters blacken or simply disappear completely. In this paper, we study the alterations to metal foils from a selection of fifteenth century artworks showing different glueing agents, organic coatings and several degrees of conservation of the organic coatings and metal leafs. The submillimetric layered structure and the high variability and low amount of most of the compounds present in the different layers, as well as their differing nature (organic and inorganic) make the use of micron-sensitive high-resolution techniques essential for their study. In particular, the high resolution, high brilliance and small footprint renders synchrotron radiation most adequate for their study. SR-XRD was performed to identify the reaction compounds formed in the different layers; μFTIR was used at to identify the silver protecting organic coatings, the metal foil glueing layers and the corresponding reaction compounds. The results obtained suggest that atmospheric corrosion is the dominant mechanism, and therefore that the degree of corrosion of the metal foils is mainly related to the conservation state of the protecting coatings. FigureSampling point, MO image from surface of the sample and SEM image from polish cross-section of the sample

Ageing of resin from Pinus species assessed by infrared spectroscopy

AbstractResins obtained from Pinus genus species have been widely used in very different fields throughout history. As soon as the resins are secreted, molecular changes start altering their chemical, mechanical and optical properties. The ageing processes are complex, and the chemical and structural changes associated with resin degradation are not yet fully known. Many questions still remain open, for instance changes happening in pimaranes, one of the two diterpenoid constituents of the resin. A systematic study of the ageing process of Pinus resins is done through Fourier transform infrared spectroscopy (FTIR) using chemical standards and complementing the obtained results with gas chromatography coupled to mass spectrometry (GC/MS) analysis when necessary. Moreover, long-term degradation processes are also investigated through the analysis of a selection of dated historical resins. This study overcomes the limitations of GC/MS and brings new information about the reactions and interactions between molecules during Pinus resin ageing processes. It also provides information about which bonds are affected and unaffected, and these can be used as specific markers of the degradation and of the resins themselves. Graphical AbstractChanges in the IR spectral features due to the Pinus resin ageing processes

New insights on blue pigments used in 15th century paintings by synchrotron radiation-based micro-FTIR and XRD

The blue pigments used on altarpieces in the 15th century in Catalonia and Crown of Aragon are principally composed of the azurite mineral. To a lesser extent, lapis lazuli, also of mineral origin, was used and occasionally in the background areas and outlining the principal figures, indigo (of vegetal origin) was used for the chromatic preparation layer. Data from several altarpieces belonging to well-known artists of that time are analysed by synchrotron radiation X-ray diffraction (SR-XRD), micro-infrared spectroscopy (μ-FTIR), synchrotron radiation micro-infrared spectroscopy (μSR-FTIR), Raman spectroscopy, and scanning electron microscopy with X-ray microanalysis (SEM-EDS). X-ray diffraction and infrared spectroscopy in association with synchrotron radiation have proven to be especially useful due to the micron-sized spot size, high brilliance and energy tunability, which help to obtain good separation of signals coming from different phases/substances and determine their localization in the various paint layers. The examples presented illustrate the potential of each analytical technique for the identification of the type of material present in the 15th century paintings. Moreover, the natural origin and composition of the pigments and their distribution in the paint layers are determined and some correlations with other contemporary paintings are proposed. Finally, the alteration compounds related to blue pigments are determined in each case.

Nature and origin of black spots found on Miró paintings: a non-invasive study

The degradation mechanism of cadmium pigments in an oil painting by Joan Miro is determined and reproduced. All possible chemical reactions leading to the observed alteration are checked in laboratory conditions. The behaviour of the different materials (support, pigments and binding medium) are determined. The study of the reaction and products is made using optical microscopy, scanning electron microscopy (SEM) with an energy dispersive X-ray detector, Fourier transform infrared spectroscopy and X-ray diffraction.

Optimal Sample Preparation for the Analysis of Micrometric Heterogeneous Samples

Precise microanalytical techniques are essential in many fields such as cultural heritage materials, showing complex layered microstructures containing a wide range of materials of diverse nature and hardness. Noninvasive sample manipulation and preparation is required to avoid, as much as possible, sample contamination, which may strongly limit the materials identification. The method proposed consists in the application of thin gold or carbon protecting layers before embedding the samples in synthetic resin for microtoming. The validity and optimal procedure is checked for those materials most often found on the surface of paintings: varnishes (natural resins and wax). An artwork sample is similarly prepared and analyzed by optical microscopy (OM), scanning electron microscopy (SEM/EDS), micro-infrared spectroscopy (μFTIR/μSR-FTIR), and X-ray diffraction (μSR-XRD) with synchrotron light.

Markers, Reactions, and Interactions during the Aging of Pinus Resin Assessed by Raman Spectroscopy

The resin extracted from the species of the Pinus genus (Pinaceae family) is a widely used material. Primarily, resins are made up of two types of diterpenoids: abietanes and pimaranes. Their composition changes with aging, affecting their chemical and physical properties; however, the chemical changes that occur during aging are not yet fully known. Understanding the evolution of pimaranes and abietanes and the chemical composition of the aged resins is essential to make the most of this substance and of its derivatives. A systematic study of the aging of Pinus resin with Raman complemented with infrared (IR) spectroscopy was carried out. This study provided new information about the interactions among the constituting molecules in resins aged over many years. In particular the formation of intermolecular hydrogen bonds in aged samples was detected for the first time, and the formation of acid anhydrides from the reaction between pimaranes was demonstrated. Furthermore, Raman and IR spectra band assignments are proposed, and the specific markers of the main compounds of the resin are tagged. This will facilitate the qualitative analysis of resin compounds.

Low molecular weight organic acid salts, markers of old fungi activity in wall paintings

Micro-Infrared Spectroscopy (μSR-FTIR) and X-ray diffraction (μSR-XRD) with synchrotron light, Gas Chromatography/Mass Spectrometry (CG/MS), Optical Microscopy (OM) and Scanning Electron Microscopy (SEM/EDS) were used to identify and obtain the distribution of complex mixtures of calcium salts of low molecular weight organic acids (LMWOA) in micro-layered micro-samples. Filamentous fungi produce LMWOA that can react with metal cations producing stable salts. These substances were found in the dark spots covering the surfaces of Saint Michaels Chapel wall paintings of the Royal Monastery of Pedralbes in Barcelona linking them to old fungi activity. The presence of glycerol likewise related to the fungi activity is also identified in the layers.

Microanalytical study of luster glazed gilding and silvering from Baroque altarpieces

Abstract Lustering, a technique which involved the application of coloured translucent glazes over gilding and silvering was widely used to enrich and decorate altarpieces in the Baroque period. The decorations consist of a micrometric multilayered structure including several color glazes, metallic leaves and bole applied over a plaster ground. The collection of Baroque altarpieces, the oldest dating 1671 and the newest 1775 from the cathedral of Tortosa (Catalonia), is a perfect case of study of the materials used and the techniques employed throughout the period. Further information is obtained from the analysis of the reaction and aging compounds resulting from the interaction among the compounds present in the layers and between the different layers. A combination of sensitive analytical techniques, Synchrotron based μ-XRD and μ-IR and SEM-EDS which enabled the luster samples to undergo analysis without altering their original layered microstructure were selected. The nature of the compounds used to produce the yellow, green, red and blue glazes (pigments, pigment lakes and resins), metallic leaves and boles is presented. Relevant information from historical and conservation viewpoints about the origin and nature of the materials used, the making of the lusters and their reactivity and aging are also discussed.