Sophia Sotiropoulou

Ochre-differentiation through micro-Raman and micro-FTIR spectroscopies: application on wall paintings at Meteora and Mount Athos, Greece

The most widely-used inorganic pigments of Byzantine and post-Byzantine hagiography are earth pigments called ochres such as, red and yellow ochres, limonite, goethite, raw and burnt sienna, caput mortuum and hematite. The present experimental work proposes a technique of differentiation that allows one to distinguish among all the different kinds of iron oxides, thereby providing a better understanding of the painting technique used on portable icons and wall paintings. The ratios between the main spectroscopic peaks, attributable to the major components usually present in ochres, were calculated and compared, one against the another, from the spectra obtained through micro-Raman spectroscopy. Elementary composition is also revealed through a scanning electron microscopy (SEM) analysis. The possibility for detailed study on a particular Byzantine ochre palette can thus be performed based on the small differences in its nature and composition. These differences can first be observed and then measured among all of the natural earth pigments, through microRaman and microFTIR spectroscopies.

Panselinos’ Byzantine wall paintings in the Protaton Church, Mount Athos, Greece: a technical examination

Abstract The sole surviving fresco paintings of Manuel Panselinos (13th century AD), one of the most celebrated Greek iconographers of the Byzantine era, are located in the Protaton Church (10th century AD) on Mount Athos, Greece. This paper presents an examination and technical analysis of 15 representative thematic scenes, covering an area of approximately 65 m 2 , from these monumental works of art. The following exhaustive study and documentation of both the original and the subsequently restored areas of the wall paintings were made possible by using various imaging techniques, including visible and ultra-violet photography, infrared reflectography, colour measurements and representation. The chemical identification of the pigments, binders and layer stratigraphy was achieved through the use of visible and ultra-violet fluorescence microscopy, micro-Raman spectroscopy, Fourier transform μspectroscopy (μFTIR), X-ray diffraction (XRD), and scanning electron microscopy with energy dispersive analysis (SEM-EDS) and electron probe microanalysis (EPMA). A collaborative analysis, its results demonstrate that the paintings were executed in both the true fresco and lime-painting techniques. They have also established Panselinos’ choice of materials and colour palette. We believe this study to be an important and necessary prerequisite for the future preservation and restoration of these unique frescoes.

Application of the Kubelka–Munk Correction for Self-Absorption of Fluorescence Emission in Carmine Lake Paint Layers

The variations of the fluorescence emission of carmine lake travelling through an absorbing and scattering medium, such as a paint layer, were investigated by ultraviolet (UV)–visible absorption, fluorescence spectroscopy, and imaging techniques. Samples of the lake were studied in dilute and saturated solutions, on a reference test panel and a real case study. Relevant spectral modifications have been observed as a function of the lake concentration mainly consisting of a fluorescence quenching, red shift of emission maxima, and deformation of emission band. The application of a correction factor based on the Kubelka–Munk model allowed fluorescence spectra obtained in solution and on painted samples of known composition to be compared and correlated, highlighting that the fluorescence of the lake within paint layers is affected by both self-absorption and aggregation phenomena. This approach has been successfully applied on a painting by G. Vasari for the noninvasive identification of carmine lake. The results reported here emphasize the necessity of taking physical phenomena into account in the interpretation of the fluorescence spectra for a proper and reliable characterization and identification of painting materials in works of art.

Material aspects of icons. A review on physicochemical studies of Greek icons.

Holy icons created in the Byzantine era are a vital entity in Orthodox Christianity, a living tradition unbroken over more than 1500 years. The importance of these symbolic representations has inspired interdisciplinary studies to better understand the materials and process of their construction. Researchers from a variety of fields are working together to place icons in their proper historical and cultural framework, as well as to develop long-term conservation strategies. In this Account, we review very recent analytical results of the materials and painting methods used in the production of Byzantine iconography. The care of icons requires particular attention because of their function; icons are objects of veneration and, for the most part, still stand in todays churches to serve ritual practices. Accordingly, they are affected by random, fluctuating environmental conditions aggravated by public access. Because of the holiness of the icons, the typical tradition of the church is to periodically restore the depicted scenes, either by retouching any defects or by partial or complete overpainting. These interventions greatly increase the complexity of the paint stratigraphy. To reveal the extent and quality of the original painting under several historical overpaintings or dirt overlays on the icon, researchers usually pursue a manifold approach, combining complementary multispectral imaging and spectroscopic techniques nondestructively. Unfortunately, a visual and exhaustive spectroscopic examination of a minimum number of cross-sectional microsamples is almost always necessary to clarify the structure of the paint layers and map the constituent materials identified therein. A full understanding of these details is critical for assessing the painting methods, stylistic conventions, and compositional concepts that render the different iconographic details. Cross-sectional micro-Raman spectroscopy, although time-consuming, now affords the direct identification of the distinct grains of almost all of the inorganic pigments and inert components included in the paint layers. Micro-Raman studies are complemented and cross-checked by micro-FTIR and scanning electron microscopy-energy dispersive spectroscopy (SEM-EDS) studies. This approach is essential in documenting the evolution of the materials and techniques used in creating icons over the centuries. Analytical data on Greek icons are now available for comparison with similar results from other important schools of iconography, such as in the eastern Mediterranean, the Balkans, or Russia, or, further, with Western schools of painting. The research constitutes a reference base for identifying and solving analytical problems, such as those related to the organic materials found in icons that have not yet been systematically studied. Moreover, the results on icons are also generally applicable to important analytical issues encountered in studying any multilayered paint stratigraphies.

Physicochemical characterization and provenance of colouring materials from Akrotiri-Thera in relation to their archaeological context and application

An assemblage of approximately 500 colouring materials and objects related to their use, found in different contexts and forms at Akrotiri, Thera, was recently investigated. The items date to the Early, Middle and Late Cycladic Bronze Age (c. 3000–1600 bc) and include materials or pigments found in their natural state, in specifically made forms or inside vessels. Some of the contexts do not provide any indication of the pigments’ use, storage, trade or application. Among the investigated materials, which include red and yellow ochres and blue riebeckite, are those that can be associated with pigments that were widely used in the past in wall paintings or to decorate pottery. There is also evidence for the selective use of purple pigments, which were derived from shellfish, in wall paintings. However, there are other raw colouring materials, such as lead pigments that have not been previously known to have been used in wall paintings or in any other applications during the prehistoric period in the Aegean. A thorough macro- and microscopic visual examination of the quality and morphology of these items enabled the identification of physical features (colour, homogeneity, grain size and shape) that indicate their nature or degree of processing. To identify the mineral composition of the pigments and to investigate their provenance from a geological perspective, quantitative X-ray diffraction (XRD) analysis was conducted. For those samples requiring additional information on their composition and for the refining or confirming of the XRD data, scanning electron microscopy combined with energy dispersive X-ray spectroscopy (SEM-EDX), micro-Raman and Fourier transform infrared (FT-IR) spectroscopies were performed. This work is part of a larger project, supported by Institute for Aegean Prehistory, that aims to clarify major archaeological queries that are not restricted to the identification of the nature, composition and provenance of the colouring materials but extend to aspects of their selection, preparation and application techniques used during the Early to the Late Bronze Age.

Improving FTIR imaging speciation of organic compound residues or their degradation products in wall painting samples, by introducing a new thin section preparation strategy based on cyclododecane pre-treatment

AbstractFourier transform infrared (FTIR) imaging in transmission mode, employing a bidimensional focal plane array (FPA) detector, was applied for the detection and spatially resolved chemical characterisation of organic compounds or their degradation products within the stratigraphy of a critical group of fragments, originating from prehistoric and roman wall paintings, containing a very low concentration of subsisted organic matter or its alteration products. Past analyses using attenuated total reflection (ATR) or reflection FTIR on polished cross sections failed to provide any evidence of any organic material assignable as binding medium of the original painting. In order to improve the method’s performance, in the present study, a new method of sample preparation in thin section was developed. The procedure is based on the use of cyclododecane C12H24 as embedding material and a subsequent double-side polishing of the specimen. Such procedure provides samples to be studied in FTIR transmission mode without losing the information on the spatial distribution of the detected materials in the paint stratigraphy. For comparison purposes, the same samples were also studied after opening their stratigraphy with a diamond anvil cell. Both preparation techniques offered high-quality chemical imaging of the decay products of an organic substance, giving clues to the painting technique. In addition, the thin sections resulting from the cyclododecane pre-treatment offered more layer-specific data, as the layer thickness and order remained unaffected, whereas the samples resulting from compression within the diamond cell were slightly deformed; however, since thinner and more homogenous, they provided higher spectral quality in terms of S/N ratio. In summary, the present study illustrates the appropriateness of FTIR imaging in transmission mode associated with a new thin section preparation strategy to detect and localise very low-concentrated organic matter subjected to deterioration processes, when the application of FTIR in reflection mode or FTIR-ATR fails to give any relevant information. Graphical AbstractVisible image of a thin section, C12H24 pre-treated, originating from prehistoric wall paintings at Akrotiri, Thera (Greece). FTIR images representing the spatial distribution of the consolidant, the minerals: wollastonite, riebeckite, and a proteinaceous binder. The size of the FTIR images is 170 × 340 μm2

A technical step forward in the integration of visible-induced luminescence imaging methods for the study of ancient polychromy

Photo-induced luminescence imaging techniques, such as UV-induced visible luminescence (UVL) and the more recently developed technique of visible-induced infrared luminescence (VIL), have been invaluable for the study of ancient polychromy, allowing the detection and mapping of luminescent materials, such as varnishes, consolidants, organic binders, and crucially, traces of pigments, organic and inorganic, that are often not visible to the naked eye. In the context of works from the Hellenistic period onwards, the detection of two pigments, Egyptian blue and rose madder lake, has been particularly pivotal in advancing the field. Current conventional methodologies for the digital mapping of these two luminescent pigments rely on the separate application of two techniques (VIL and UVL), each requiring a different illumination source and acquisition set-up. In this study, a novel approach is proposed, combining the use of visible-induced infrared luminescence and visible-induced visible luminescence to locate these two pigments. As the source of illumination in both cases is the same system of LEDs, the set-up has the advantage of requiring only minor filter changes between luminescence modes. The increased portability and safety compared to the use of methodologies that employ UV radiation represent notable advantages of this integrated system. The interchangeability between highly selective excitation sources, also significantly simplifies the experimental set-up and the need to adjust the object or equipment between acquisitions, ensuring better reproducibility of the data acquired and facilitating any post-processing procedures. This results in a user-friendly methodology for both experts and non-specialists alike. Three Hellenistic period terracottas; two from Canosa di Puglia, Italy (270–200 BC) and one from Myrina, Turkey (c. 100 BC), all characterised by large well-preserved areas of decoration in Egyptian blue and red lake, were studied in order to trial the approach. Comparisons were made with the more standard techniques of VIL and UVL, and it was shown that the combined method proposed efficiently detects and maps both of these pigments with analogous results to those obtained by more established methodologies. The observations made from the multispectral images acquired were verified by analysis of small samples of the pigments, using FTIR and Raman spectroscopy and HPLC-DAD analysis.

The effect of TiO2 component on the properties of acrylic and urea-aldehyde resins under accelerated ageing conditions

Abstract Synthetic resins were introduced in paintings conservation during the 1930s, as an alternative to natural resins, due to their superior resistance to degradation. Their composition usually includes a small amount of additives, such as titanium dioxide. The objective of this work is to study the effect of TiO2 additive on the durability of Paraloid B72 (acrylic resin) and Laropal A81 (urea-aldehyde condensation polymer), both used in art conservation, against photochemical degradation. A methodology involving separating particulate TiO2 from the organic fraction of the resins has been applied, followed by accelerated ageing of the resins in their commercial (C) and modified (M, i.e. after TiO2 removal) has been implemented. The morphological characteristics of resin films were examined through scanning electron microscopy (SEM). Chemical changes, colour properties and photo-chemical stability of the resins were studied with FTIR, UV-Vis absorption spectroscopy and spectro-colorimetry. The results showed a considerably different behaviour between the C and M states of both materials. In particular, C-Paraloid B72 collapses after prolonged irradiation, but within a certain time frame it appears to be relatively stable; on the other hand, C-Laropal A81 is considerably destabilized in comparison to its M state. It can be suggested that TiO2 acts as a UV-blocker for the underlying pigment layers, at the expense of resins’ stability.