Characterization Of Painting Materials Research Articles

Black, Red and White: Characterization of Painting Materials on a Group of Bwa Masks from Burkina Faso

The distinctive and visually striking wooden masks associated with the Bwa culture in Burkina Faso, West Africa, are carved from a soft wood into different shapes and display various geometrical patterns and symbols according to their purpose. One of their characteristic features is the use of the colors black, red, and white, which evoke the three major rivers crossing the country: the Black, Red, and White Voltas. According to published accounts of scholars who have worked directly with the artists, the materials used to obtain these colors include reptile excrement for the white, iron-rich stones powdered and mixed with egg or plant gums for the red, and boiled Acacia seed pods for the black, as well as modern materials such as enamel paint in some cases. A group of four Bwa masks in the Arts of Africa collection of the Art Institute of Chicago was investigated using a complement of analytical techniques including Fourier transform infrared spectroscopy, scanning electron microscopy with energy dispersive spectroscopy, pyrolysis gas chromatography–mass spectrometry, and mass spectrometry-based proteomics to characterize their painting materials. The results obtained corroborate the published accounts, while also providing new insights into the nature of the coloring materials and the selection and substitution of pigments and binders. These findings highlight the complementary value of scientific research, in combination with fieldwork and artists’ accounts, to generate a fuller understanding and appreciation of this traditional artistic practice.

An Ancient Egyptian Multilayered Polychrome Wooden Sculpture Belonging to the Museo Egizio of Torino: Characterization of Painting Materials and Design of Cleaning Processes by Means of Highly Retentive Hydrogels

This contribution focuses on the conservation of an Egyptian wooden sculpture (Inventory Number Cat. 745) belonging to the Museo Egizio of Torino in northwest Italy. A preliminary and interdisciplinary study of constituent painting materials and their layering is here provided. It was conducted by means of a multi-technique approach starting from non-invasive multispectral analysis on the whole object, and subsequently, on selected micro-samples. In particular, visible fluorescence induced by ultraviolet radiation (UVF), infrared reflectography (IRR) and visible--induced infrared luminescence were used on the whole object. The micro-samples were analysed by means of an optical microscope with visible and UV light sources, a scanning electron microscope (SEM) with an energy-dispersive X-ray spectrometer (EDX), Fourier transform infrared (FT-IR) spectrometer, pyrolysis-gas chromatography/mass spectrometer (Py-GC/MS) and micro-particle induced X-ray emission (PIXE). The characterization of the painting materials allowed the detection of Egyptian blue and Egyptian green, and also confirmed the pertinence of the top brown layer to the original materials, which is a key point to design a suitable surface treatment. In fact, due to the water sensitiveness of the original materials, only few options were available to perform cleaning operations on this artwork. To setup the cleaning procedure, we performed several preliminary tests on mockups using dry cleaning materials, commonly used to treat reactive surfaces, and innovative highly water retentive hydrogels, which can potentially limit the mechanical action on the original surface while proving excellent cleaning results. Overall, this study has proved fundamental to increase our knowledge on ancient Egyptian artistic techniques and contribute to hypothesize the possible provenance of the artefact. It also demonstrated that polyvinyl alcohol-based retentive gels allow for the safe and efficient cleaning of extremely water sensitive painted surfaces, as those typical of ancient Egyptian artefacts.

A portable device for on site detection of chicken ovalbumin in artworks by chemiluminescent immunochemical contact imaging

The development of user-friendly devices for on site analysis and characterization of painting materials is one of the most challenging objectives in the diagnostics for cultural heritage. Thanks to the specificity of antigen–antibody reactions, immunological methods have been already successfully applied for the detection of proteins and for their localization within painting stratigraphies. Moreover, by combining the advantages of the immunological techniques with the high detectability offered by chemiluminescence detection, it has been possible to achieve good analytical performance and very low detection limits. This work was aimed at developing a portable analytical device for the detection of chicken ovalbumin (a protein found in egg tempera and in egg-based protective varnishes) in painting samples employing ready-to-use analytical cartridges and a thermoelectrically-cooled CCD camera as a chemiluminescence detector. The protein was extracted from using a simple procedure and revealed by a non-competitive immunoassay with chemiluminescence contact imaging detection. The assay was simple, fast and suitable for the detection of ovalbumin in small samples. This analytical system provided positive identification of ovalbumin in samples obtained from both fresh or artificially aged paint reconstructions and historical paintings. It might be easily employed in different contexts (such as small museums, restoration laboratories or even on site) by restorers to obtain prompt information during restoration actions, such as cleaning operations. In perspective this device could be also employed for the detection of other proteinaceous and organic painting components.

Effects of hazardous pollutants on the walls of Valence Aqueduct (Istanbul) by Raman spectroscopy, SEM–EDX and Geographical Information System

This study involves Raman spectroscopic (176–2900cm−1), SEM–EDX and Geographical Information System studies of the pollutants on the walls of Valence Aqueduct (Bozdoğan Kemeri), Istanbul, Turkey. Raman spectroscopy is a useful analytical method in characterization of painting materials and corrosion products. Especially, when it is not possible to take the samples from the place they exist, handheld Raman spectrometers play an important role to identify the materials in these samples. Furthermore, more information could be gathered when it is combined with SEM–EDX studies. On the other hand, regarding the cultural heritage, it is crucial to determine precise coordinates of the historical peninsula and the samples which have been exposed to pollutants, by Geographical Information Systems in order to study them and take precautions for the future. Handheld Raman spectrometer (NanoRam by B&WTek) allows recording of acceptable and good quality spectra of a large majority of minerals outdoors. Raman spectra of minerals and pollutants in this study were obtained using 785nm laser excitation source. Observed Raman bands are found at correct wavenumber positions within ±3cm−1 compared to reference values in the literature. Taking into account the resolution of the spectrometer (9cm−1), the results are still reliable and applicable on such systems. Areas of potential applications of these instruments include all kind of common geoscience work outdoors.

Localization of proteins in paint cross-sections by scanning electrochemical microscopy as an alternative immunochemical detection technique

The qualitative identification of proteinaceous substances, as well as their location within a complex paint stratigraphy, is one of the most challenging issues in the characterization of painting materials. Nevertheless, information on paint components represent a crucial task for studies concerning both the ancient painting techniques adopted and the state of conservation, being fundamental investigations for the selection of appropriate conservation actions. The present research was aimed at developing a new detection approach for the immunochemical localization of ovalbumin in paint cross-sections based on the use of scanning electrochemical microscopy (SECM). The immunochemical analyses were performed using an anti-ovalbumin primary antibody and a secondary antibody labelled with horseradish peroxidase (HRP). SECM measurements were performed in feedback mode using benzoquinone (BQ)/hydroquinone (H2Q) redox couple. In presence of hydrogen peroxide (H2O2), HRP catalyzes the re-oxidation of H2Q to BQ and the increment of BQ concentration in correspondence of the target protein was detected by SECM through the electrochemical reduction of the regenerated BQ at the microelectrode. Indeed, the localization of ovalbumin was possible thanks to a clear discrimination of SECM currents, achieved by the comparison of the measurements recorded before and after H2O2 administration, based on the HRP on/off approach. The method was evaluated both on samples from standard mocks-up and on a historical sample, collected from a Renaissance wood painting. The obtained results were promising, foreseeing a wider application of SECM on cultural heritage researches.

Characterisation of painting materials from Eritrea rock art sites with non-destructive spectroscopic techniques

Rock painting samples from Eritrean archaeological sites were studied by means of micro-Raman spectroscopy and proton-induced X-ray emission technique (PIXE). Hematite and manganese oxides/hydroxides were determined in red and black paints, respectively. Since colours do not contain carbon, the paintings cannot be dated with 14C. Moderate amounts of calcium carbonate or sulphate were also observed in most red drawings, while traces of phosphorus were found by PIXE only in a few red and black samples.

External beam applications to painting materials

The characterisation of painting materials has to overcome specific problems due to the special and precious characteristics of paintings. Sampling is hardly possible and is seldom so where it is most desirable. One has to be content with opportunities such as the presence of cracks or to limit the sampling near the edge of the frame. Nondestructive techniques must then be developed and external PIXE is one of the powerful available analytical tools; it may also be associated with complementary techniques such as X-ray fluorescence and external PIGME. Another major problem is related to the great heterogeneity of painting materials which are always a mixture of several components at the micrometric scale. The analysis has then to be complemented with other techniques (scanning electron microprobe, nuclear microbeam etc.) for a more accurate interpretation of the results given by the PIXE direct examination. Yet, the major difficulty lies in finding the way to build a real and constructive dialogue between the art historian and the physicist.