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

Abstract

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.

Surface Properties of Graffiti Coatings on Sensitive Surfaces Concerning Their Removal with Formulations Based on the Amino-Acid-Type Surfactants

“…However, it is worth mentioning that the film-forming coats of polymers typically employed to preserve, maintain, and renew the surfaces of the works of art or the monuments against the deterioration caused by weather conditions are removed using the nanostructured liquids in the extensive studies by the other authors [ 43 , 44 , 45 , 49 , 50 , 51 , 52 ]. The mechanism for removing this type of coating, so-called “dewetting”, has been well-described by Baglioni et al [ 51 , 52 ].…”

Experimentation on the removal of Paraloid B72R from the wooden surface of Egyptian artefacts from the National Archaeological Museum in Naples

“…Through the tests for the evaluation of the action time of the PVA-B hydrogel, it was verified that: within the first 60 seconds of contact, the hydrogel was only able to partially solubilize the aged Paraloid layer regardless of the film thickness, a complete removal of the resin was not observed in either case [10]. After the first minute of contact, the 5%-diluted Paraloid was completely swelled while the 10%-diluted Paraloid needed more insistence during the swab action to remove the Paraloid residue.…”

“…The limitation of Paraloid lies in its aging, with which the resin loses its inherent characteristics such as "reversible" behavior, transparency and flexibility. To overcome the problem related to the presence of Paraloid, a preliminary evaluation of the most widely used Paraloid removal systems in recent decades was carried out, which led to the selection of the cleaning system [5][6][7] best suited to the needs of our case: the high-viscosity polymer dispersion based on polyvinyl alcohol cross-linked with borax (Hydrogel PVA-B), selected for its mechanical properties such as its gentleness in solvent action, limiting the action at the interface, for its consistency that allows easy removal without leaving residue on the surface, and for its ability to retain organic solvents up to a maximum concentration of 30% [8][9][10]. Before using this cleaning system for the removal of Paraloid film from artifacts, an experiment was conducted to verify the effectiveness of this system and its applicability.…”

Experimentation of a PVA-Borax hydrogel for the removal of Paraloid B72® from artifacts of archaeological interest from the National Archaeological Museum in Naples, Italy

“…The next step was therefore to verify the effectiveness of the cleaning system that had been selected. At first, the action times of the hydrogel were evaluated through tests, whereby it was verified that: within the first 60 seconds of contact, the Hydrogel was only able to partially solubilise the aged Paraloid layer, regardless of the thickness of the film; complete removal of the resin was not observed in either case [14]. After the first minute of contact, the 5 %-diluted Paraloid was completely swelled while the 10 %-diluted Paraloid needed more insistence during the swab action to remove the Paraloid residue.…”