New Methodologies for the Conservation of Cultural Heritage: Micellar Solutions, Microemulsions, and Hydroxide Nanoparticles

Abstract

Modern civilization's inherited artworks have a powerful impact on society, from political, sociological, and anthropological points of view, so the conservation of our Cultural Heritage is fundamental for conveying to future generations our culture, traditions, and ways of thinking and behaving. In the conservation of cultural artifacts, scientists intervene in the degradation of often unique handcrafts, resulting from a delicate balance of aging, unpredicted events, environmental conditions, and sometimes incorrect previous restoration treatments, the details of which are often not precisely known. Nanoscience and nanotechnology are revolutionizing materials science in a pervasive way, in a manner similar to polymer chemistry's revolution of materials science over the preceding century. The continuous development of novel nanoparticle-based materials and the study of physicochemical phenomena at the nanoscale are creating new approaches to conservation science, leading to new methodologies that can "revert" the degradation processes of the works of art, in most cases "restoring" them to their original magnificent appearance. Until recently, serendipity and experiment have been the most frequent design principles of formulations for either cleaning or consolidation of works of art. Accordingly, the past has witnessed a number of actively detrimental treatments, such as the application of acrylic and vinyl resins to wall paintings, which can irreversibly jeopardize the appearance (or even the continued existence) of irreplaceable works of art. Current research activity in conservation science is largely based on the paradigm that compatibility of materials is the most important prerequisite for obtaining excellent and durable results. The most advanced current methodologies are (i) the use of water-based micelles and microemulsions (neat or combined with gels) for the removal of accidental contaminants and polymers used in past restorations and (ii) the application of calcium hydroxide nanoparticles for the consolidation of works of art. In this Account, we highlight how conservation science can benefit from the conceptual and the methodological background derived from both soft (microemulsions and micelles for cleaning) and hard (nanoparticles for consolidation) nanoscience. A combination of different nanotechnologies allows today's conservators to provide, in each restoration step, interventions respectful of the physicochemical characteristics of the materials used by artists. The "palette" of methods provided by nanoscience is continuously enriching the field, and the development of novel nanomaterials and the study of nanoscale physicochemical phenomena will further improve the performance of restoration formulations and our comprehension of degradation mechanisms.

Nanofluids and chemical highly retentive hydrogels for controlled and selective removal of overpaintings and undesired graffiti from street art

“…A previously formulated nanofluid, based on ethyl acetate and propylene carbonate [17][18][19], was combined with a poly(2-hydroxyethyl methacrylate (pHEMA)/ poly(vinylpyrrolidone) (PVP) semi-interpenetrated polymer network (sIPN) [16,20,21] and used to selectively remove a white acrylic modern paint from a white acrylic paint laid on a mortar sample. Cleaning results were, then, characterized by means of visual and photographic observation, optical microscopy, and FT-IR microreflectance investigation.…”

Nanomaterials for the cleaning and pH adjustment of vegetable-tanned leather

“…), and their low solvent content reduces the environmental impact. In fact, throughout the last decade, nanostructured fluids have been widely tested for the cleaning of mural paintings, and the results obtained have demonstrated that these systems are a valid alternative to the use of neat solvents [8][9][10][11]. However, for their use on watersensitive substrates, o/w microemulsions must be confined within a retentive network that allows their controlled release, so as to grant the removal of unwanted layers without excessive wetting of the surface.…”

Consolidation of Wall Paintings and Stone

“…As a result, the pictorial surface of the work of art can be disrupted (see Fig. 2.3) in a period of time ranging roughly from less than 10 to 50 years, the degradation being enhanced by fluctuations of temperature and relative humidity, and by pollution (Giorgi et al 2010a). For instance, the combination of the presence of a Mowilith film (vinyl acetate/acrylate copolymer) and salt crystallization produced in less than 10 years the irreversible loss of portions of original wall paintings in the archaeological site of Mayapan (Mexico, Post-Classic Age 1200-1450 BC), and degradation of paintings (e.g.…”