Twin-chain polymer networks loaded with nanostructured fluids for the selective removal of a non-original varnish from Picasso’s “L’Atelier” at the Peggy Guggenheim Collection, Venice

Abstract

This paper reports on the evaluation of a polyvinyl alcohol (PVA) "twin-chain" polymer network (TC-PN) combined with an oil-in-water nanostructured fluid (NSF) for the removal of a polyvinyl acetate (PVAc) varnish. Small Angle X-ray Scattering, Confocal Laser Scanning Microscopy, and Fluorescence Correlation Spectroscopy showed that the structure of the gel and the NSF are only minimally altered by loading the fluid into the gel. The NSF is partially free to diffuse through the network, but also interacts with the gel walls. During the cleaning, the dynamics of the fluid at the gel-substrate interface are controlled by the osmotic balance taking place among the interconnected pores. These features grant effective and controlled cleaning performances. The case study identified for this research is Pablo Picasso's The Studio (L'Atelier, 1928), one of the masterpieces in the Peggy Guggenheim Collection, Venice (PGC). In 1969 the oil painting, originally unprotected, was wax-lined and then varnished using a PVAc varnish. Over the years, the white shades of the painting have been compromised by the yellowing of the varnish and soiling of deposits. On painting mock-ups, the NSF-loaded hydrogels allowed the swelling and softening of PVAc varnish and wax layers, which were then removed with gentle mechanical action. Effective varnish and wax removal at the micron scale, and the absence of residues from the cleaning system (gel and NSF), were confirmed by Fourier Transform Infrared Spectroscopy (FTIR) 2D imaging. The effective and safe removal of the aged PVAc varnish and wax layer from the surface of the painting was then carried out using the same cleaning protocol successfully tested on the mock-ups, setting the NSF-loaded PVA TC-PNs as robust and reliable tools for the cleaning of sensitive works of art.

Advanced Materials in Cultural Heritage Conservation

“…Different properties can be conferred to the PVA 3D network by including in the formulation either PVP or a PVA with different molecular weight and hydrolysis degree [ 45 , 50 ]. The so-obtained new class of gels, namely PVA/PVA “twin-chain” networks, was developed and effectively used to remove surface soiling and aged varnishes from Picasso, Pollock, and Lichtenstein’s paintings [ 45 , 55 , 56 ]. The inclusion of the low-molecular weight PVA allows obtaining a network with a sponge-like interconnected porosity, which is significantly different from the pores of the single-PVA homologue gel.…”

“…Similar to pHEMA/PVP, also PVA-based hydrogels can be loaded with aqueous NSFs, thanks to the ability of the micelles to diffuse through the polymeric network without a significant alteration of either their structure or the gel’s [ 46 , 48 , 55 ]. The combination of NSFs and highly retentive hydrogels represent one of the most advanced and effective cleaning solutions today available to restorers and conservators.…”

How Science Can Contribute to the Remedial Conservation of Cultural Heritage

“…Recently, a new class of gels, PVA/PVA “twin‐chain” networks, have been synthesized and employed to remove surface dirt or aged coatings from Pablo Picasso, Jackson Pollock and Roy Lichtenstein's masterpieces, among others (Figure 4). [42,47,48] The presence of the lower‐molecular‐weight PVA (L‐PVA) produces, after the FT process, a final network with a sponge‐like interconnected porosity that differs from the tightly packed channel‐like pores of the single‐PVA analogue. The difference could play a fundamental role when it comes to absorb detached dirt from surfaces, with interconnected pores favoring the capture of dirt and its migration through the gel network.…”

“…Notably, both pHEMA/PVP and the PVA‐based hydrogels can be uploaded with o/w microemulsions, and the micelles are able to diffuse through the gel network without detrimental alteration of either their structure or the gel's [43,47,49] . This is an appealing solution when the cleaning power of aqueous nanostructured fluids is needed on a water‐sensitive surface, making the coupled system one of the most sophisticated tools currently available to conservators.…”

Removal of a Past Varnish Treatment from a 19th-Century Belgian Wall Painting by Means of a Solvent-Loaded Double Network Hydrogel

“…An organogel composed of 40% hydrolyzed polyvinyl acetate crosslinked with benzene-1,4-diboronic acid in 95:5 ethanol/water was able to eliminate varnish consisting of a mixture of shellac, drying oils, and pigment [ 20 ]. Recently, a PVA twin-chain gel loaded with a nanostructured fluid allowed the safe removal of a polyvinyl acetate varnish and wax layer from an oil painting by Pablo Picasso [ 21 ].…”