Up to 70 % of the oil paintings conserved in collections present metal soaps, which result from the chemical reaction between metal ions present in the painted layers and free fatty acids from the ...lipidic binders. In recent decades, conservators and conservation scientists have been systematically identifying various and frequent conservation problems that can be linked to the formation of metal soaps. It is also increasingly recognized that metal soap formation may not compromise the integrity of paint so there is a need for careful assessment of the implications of metal soaps for conservation. This review aims to critically assess scientific literature related to commonly adopted analytical techniques for the analysis of metal soaps in oil paintings. A comparison of different analytical methods is provided, highlighting advantages associated with each, as well as limitations identified through the analysis of reference materials and applications to the analysis of samples from historical paintings.
Conservation and Heritage scientists frequently face challenging issues related to metal soaps phenomena in oil paint systems. This review provides a critical overview of analytical techniques available for the identification, localisation and study of the presence of metal soaps. Advantages and disadvantages of each technique are discussed and the comparison between data collected from ad hoc and real painting samples is reported.
The IR and Raman spectra of alizarin, purpurin, kermesic acid, and carminic acid have been computed performing density functional theory calculations at the B3LYP/6‐31G(d) level of theory. The ...computational approach adopted has been validated on the basis of a series of calculations with different level of theory on the anthraquinone molecule, the common moiety of these dyes. The computed vibrational frequencies have been adopted as a guideline to propose the vibrational assignment of the dyes and to obtain useful information on the Raman spectra of their aluminum complexes.
The Victoria and Albert Museum holds an important portrait of the Jamaican scholar and writer Francis Williams (c.1692/97–1762), portrayed as a scholar in his study. It is believed to have been ...painted around 1745 by an unknown artist, but the circumstances of its production are unknown. A technical examination of the painting was performed using x‐radiography and infrared reflectography (IRR), macro x‐ray fluorescence scanning (XRF), digital microscopy, scanning electron microscopy with energy‐dispersive x‐ray spectroscopy (SEM–EDX) and reflectance imaging spectroscopy in the short‐wave infrared (SWIR). XRF, IRR and reflectance imaging spectroscopy in the SWIR revealed the distribution of inorganic pigments including lead white, earth pigments, Prussian blue, vermilion, orpiment (or pararealgar) and bone or ivory black. Pentimenti and a different sketched landscape were observed in the IRR images, highlighting changes in the final composition. Three‐dimensional (3D) digital microphotography provided additional historical and contextual information through the observation of book titles and details. High‐resolution digital imaging complemented analytical data. Results of the technical examination revealed the material composition and the development of the painting, contributing to shed new light on the production of the portrait, the history and significance of the portrait.
The cultural heritage community is increasingly exploring synchrotron radiation (SR) based techniques for the study of art and archaeological objects. When considering heterogeneous and complex ...micro-samples, such as those from paintings, the combination of different SR X-ray techniques is often exploited to overcome the intrinsic limitations and sensitivity of the single technique. Less frequently, SR X-ray analyses are combined with SR micro-photoluminescence or micro-Fourier Transform Infrared spectroscopy, which provide complementary information on the molecular composition, offering a unique integrated analysis approach. Although the spatial correlation between the maps obtained with different techniques is not straightforward due to the different volumes probed by each method, the combination of the information provides a greater understanding and insight into the paint chemistry. In this work, we discuss the advantages and disadvantages of the combination of X-ray techniques and SR-based photoluminescence through the study of two paint micro-samples taken from Pablo Picasso's Femme (1907). The painting contains two cadmium yellow paints (based on CdS): one relatively intact and one visibly degraded. SR micro-analyses demonstrated that the two Cd-yellow paints differ in terms of structure, chemical composition, and photoluminescence properties. In particular, on the basis of the combination of different SR measurements, we hypothesize that the degraded yellow is based on nanocrystalline CdS with high presence of Cd(OH)Cl. These two characteristics have enhanced the reactivity of the paint and strongly influenced its stability.
The characteristics of commercially available refined and bodied linseed and tung oils, used as binders in the production of armour paints after historic recipes, are explored. Employed as ...anticorrosive paints mainly from the 1920s to 1960s, armour paints are greener alternatives that can be used for protection in industrial heritage conservation. Using a multi-analytical approach, chemical and physical properties of the fresh oils and solid films before and after accelerated ageing (ISO 16474-2:2013) were investigated to better understand which features are beneficial for the technical function of armour paints. Tests included measurements of density, the refractive index, insoluble impurities, alkaline impurities, the water content, the iodine value, the saponification value, the free fatty acid concentration, the acid value, the peroxide value and colour (Lovibond) and cold tests. The characterisation of the fresh oils using molecular analysis with FTIR and GC-MS revealed the complexity of the commercial formulations, for which additions of semi- and non-drying oils were detected. The results show that organic paint binders follow complex chemical reactions (such as oxidation and decrease of unsaturation being variable or swelling following water-immersion tests), with implications for their suitability for use in protection.
In conservation, science semiconductors occur as the constituent matter of the so-called semiconductor pigments, produced following the Industrial Revolution and extensively used by modern painters. ...With recent research highlighting the occurrence of various degradation phenomena in semiconductor paints, it is clear that their detection by conventional optical fluorescence imaging and microscopy is limited by the complexity of historical painting materials. Here, we illustrate and prove the capabilities of time-resolved photoluminescence (TRPL) microscopy, equipped with both spectral and lifetime sensitivity at timescales ranging from nanoseconds to hundreds of microseconds, for the analysis of cross-sections of paint layers made of luminescent semiconductor pigments. The method is sensitive to heterogeneities within micro-samples and provides valuable information for the interpretation of the nature of the emissions in samples. A case study is presented on micro samples from a painting by Henri Matisse and serves to demonstrate how TRPL can be used to identify the semiconductor pigments zinc white and cadmium yellow, and to inform future investigations of the degradation of a cadmium yellow paint.
This work proposes the virtual restoration of the Bodhidharma polychrome sculpture from the Lingyan Temple in China. Based on scientific analyses and simulation experiments, exterior colours and ...textures were virtually restored by combining 3D scanning and multi-view 3D reconstruction. At the same time, an efficient cultural relics high-fidelity information 3D modelling method was proposed. Colours and textures are essential for polychrome cultural relics, reflecting the historical appearance and technology. Due to long periods of natural ageing and the destruction of environmental factors, the colours and textures of polychrome sculptures are often altered or radically changed, making it difficult for people to appreciate the initial appearance. With the rapid development of digital technology and high-fidelity 3D modelling, virtual reality technology allows us to restore the appearance of cultural relics. This study expands the dimension of cultural relics exhibition, provides new perspectives for archaeology, art history and cultural heritage research, and provides a reference for the virtual restoration and digitalised archive of other cultural relics.
In conservation science, the identification of painting materials is fundamental for the study of artists’ palettes, for dating and for understanding on-going degradation phenomena. For these ...purposes, the study of stratigraphic micro-samples provides unique information on the complex heterogeneity of the pictorial artworks. In this context, we propose a combined-microscopy approach based on the application of time-resolved photoluminescence (TRPL) micro-imaging and micro-Raman spectroscopy. The TRPL device is based on pulsed laser excitation (excitation wavelength = 355 nm, 1 ns pulse width) and time-gated detection, and it is suitable for the detection of photoluminescent emissions with lifetime from few nanoseconds to hundreds of microseconds. In this work, the technique is beneficially applied for identifying different luminescent semiconductor and mineral pigments, on the basis of their spectral and decay kinetic emission properties. The spatial heterogeneities, detected in the micro-sample, are investigated with Raman spectroscopy (785-nm in CW mode) for a further identification of the paint composition on basis of the molecular vibrations associated with the crystal structure. The effectiveness and limits of the proposed combined method is discussed through analysis of a corpus of stratigraphic micro-samples from Russian Avant-garde modern paintings. In the selected samples, the method allows the identification of modern inorganic pigments such as cadmium-based pigments, zinc white, titanium white, chrome yellow, ultramarine and cinnabar.
The characteristics of armour paints, historically used to protect ferrous industrial heritage, are explored. Amour paints contain lamellar and highly reflexive pigments of micaceous iron oxide (MIO) ...and metallic, leafing aluminium, bound in linseed oil and linseed oil–tung oil mixtures, on an inhibitive and soap-forming linseed oil primer (red lead). It is the first study of the binding media used for historical armour paints and investigates the chemical and physical ageing of armour paints using a multianalytical approach. Naturally aged examples are compared to accelerated aged replica armour paint, and to historical paints. The ageing and degradation reactions are assessed by complementary GC–MS and FTIR, together with measurements of wettability, hardness and surface colour. The historical paint formulations include linseed oils and alkyd binders. The results confirm that the leafing effect of aluminium pigments results in only a small concentration of binder at the surface: the paints studied reflect light and form a strong chemical and physical barrier. Linseed oils and tung oil mixtures have been proven to be suitable for the production of armour paints, but the evaluation of ageing and assessment of physical changes will require further investigation.
The identification of colorants in historic plastics is a methodological and analytical challenge. Although deformulation is performed by the plastics industry, in the case of historical objects, ...sampling is often impossible, and in situ protocols are needed. The accurate identification of colorants provides insights into historical plastic formulations, supports planning of conservation studies, and critical data for objects that already exhibit color change (e.g. fading). Indeed, colorants may degrade following exposure to light, and color changes have been reported for plastic objects. The analysis of colorants remains a challenge, and microsampling is usually required. Successful identification of red pigments from thirty historical plastics is reported following a new in situ analytical protocol based on Raman microscopy. Information about other pigments, fillers and plastic polymers are reported. Fading has been observed in the historical plastic objects containing Pigment Red 53.
The successful use of Raman microscopy for the in situ identification of organic red pigments in historical plastic objects is demonstrated. An in situ multi‐analytical protocol for the study of organic red pigments is proposed. The novelty of the protocol lies on the analytical sequence of the techniques, combination of the information collected by elemental and vibrational analyses and final molecular identification of the organic red pigments by Raman.
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