Non-invasive detection of lead carboxylates in oil paintings by in situ infrared spectroscopy: How far can we go?

This paper demonstrates the efficacy of portable mid-infrared spectroscopy as a diagnostic tool for revealing the presence of lead carboxylates on artworks, in situ, without sampling. Samples of cerussite and hydrocerussite - the main components of lead white - were separately mixed with linseed oil, and artificially aged in two steps. Their compositional changes have been monitored over time by infrared spectroscopy in two investigation modes: absorption (benchtop instrument) and reflection (portable instrument), and by XRD spectroscopy. Each component of lead white showed different behavior depending on aging conditions, giving important information about the degradation products which are found in real cases. The accordance of results obtained in both modalities demonstrates that portable FT-MIR is a reliable technique for individuating and identifying lead carboxylates directly on paintings. Examples of the efficacy of this application are provided, by studying paintings from the 17th and 18th centuries.

Handheld new technology Raman and portable FT-IR spectrometers as complementary tools for the in situ identification of organic materials in modern art.

A non-invasive approach has been carried out to characterize painting materials used in modern artworks conserved in the art collection of Carandente's museum at Palazzo Collicola in Spoleto (Italy). This work is focused on the cross-validation of the handheld BRAVO Raman spectrometer, that uses a sequentially Shifted Excitation (SSE) to mitigate fluorescence, for the characterization specifically of organic materials. The analytical procedure, combining XRF, Raman and reflection infrared spectroscopy, allowed a complete characterization of the artists' palettes; particularly eight different synthetic dyes belonging to the class of pigment red (PR) and pigment yellow (PY.), synthetic and traditional binders, such as alkyd resin and lipids have been easily identified.

A vibrational spectroscopic and principal component analysis of triarylmethane dyes by comparative laboratory and portable instrumentation.

This contribution examines the utility of vibrational spectroscopy by bench and portable Raman/surface enhanced Raman and infrared methods for the investigation of ten early triarlymethane dye powder references and dye solutions applied on paper. The complementary information afforded by the techniques is shown to play a key role in the identification of specific spectral marker ranges to distiguish early synthetic dyes of art-historical interest through the elaboration of an in-house database of modern organic dyes. Chemometric analysis has permitted a separation of data by the discrimination of di-phenyl-naphthalenes and triphenylmethanes (di-amino and tri-amino derivatives). This work serves as a prelude to the validation of a non-invasive working method for in situ characterization of these synthetic dyes through a careful comparison of respective strengths and limitations of each portable technique.

Identification of animal glue and hen-egg yolk in paintings by use of enzyme-linked immunosorbent assay (ELISA).

We report the development of an indirect ELISA procedure for specific identification of chicken-egg yolk and animal glues in painting micro-samples. The results presented integrate previously published work on ELISA recognition of bovine ß-casein and chicken ovalbumin in painting materials. The integrated final ELISA procedure-optimised for protein extraction, immuno-reagent concentrations, blocking solution, incubation time, and temperature-enables multiplex identification, in single samples, of proteinaceous materials, i.e. chicken-egg yolk and albumen, animal glues, and bovine milk and/or casein, mainly used by painters in the past. The procedure has been systematically tested on laboratory models of mural and easel paintings, both naturally and artificially aged, to assess possible inhibitory effects on the immuno-reaction caused by inorganic painting materials (pigments and substrates) and by protein degradation resulting from aging processes. Real samples from case studies, which had previously been investigated and characterised by spectroscopy and chromatography, were successfully studied by use of the developed ELISA procedure. The commercial availability of all the immuno-reagents used, the affordable analytical equipment, and the specificity, sensitivity, and rapidity of ELISA make this method very attractive to diagnostic laboratories in the field of cultural heritage science. Possible further developments to the analytical potential of this technique include improvement of antibody performance and inclusion of other classes of bio-molecules as analytical targets.

FT-NIR spectroscopy for non-invasive identification of natural polymers and resins in easel paintings.

In the present study, the analytical strengths and limitations of near-infrared (NIR) spectroscopy to non-invasively characterize organic components in painting materials have been investigated. In spite of the increased amount of information available today from advanced modern analytical instrumentations dedicated to cultural heritage, the non-invasive identification of materials belonging to the wide class of organic compounds historically used in paintings is still a challenging task. Near-infrared spectroscopy offers several attractive features that make this technique particularly suitable to this purpose. In fact, it is non-invasive, allows for non-contact measurements in reflectance mode, gives molecular information on complex macromolecules, and can be performed on-site by means of portable devices. First-derivative transformation of reflectance spectroscopic data has been applied to provide a simple and fast way to deduce more information from NIR spectra. This approach has allowed spectral features to be identified that can be useful to distinguish different compounds belonging to the classes of lipids, proteins, and resins. To this purpose, at first, a spectral database of pure standard has been collected. Our analytical approach was then successfully validated on pictorial models reproducing the typical stratigraphy of an easel painting. As final step, the study of a real painting has been attempted and a drying oil, animal glue, and a terpenic natural resin, as well as an earth pigment were clearly identified, as cross-validated by GC-MS analysis.

Identification of proteins in painting cross-sections by immunofluorescence microscopy.

Immunofluorescence microscopy offers a highly specific analytical tool for unambiguous recognition and mapping of proteins in complex matrices. In the present work, the analytical potentials of immunofluorescence microscopy have been exploited to provide recognition of proteinaceous binders in painting cross-sections. An optimised analytical protocol is proposed for the identification of ovalbumin and of bovine serum albumin as markers of egg white and casein, respectively. The study has been carried out on laboratory model samples simulating both easel and mural paintings. The obtained results demonstrated the effectiveness of the method, suggesting the potential future use of immunofluorescence microscopy as a routine diagnostic tool in conservation science. Possible developments of the proposed methodology in order to improve the specificity of the method and its detection sensitivity are presented and discussed.