In January 2017, Sarah Nunberg (Conservator in private practice, Stockman Foundation Fellow at Pratt Institute) and Dr. Cindie Kehlet (Professor, Department of Math and Science, Pratt Institute) organized a four-day workshop on Nanotechnologies in Conservation at the Pratt Institute in Brooklyn, NY. Dr. Piero Baglioni and Dr. Rodorico Giorgi of the University of Florence Research Center for Colloids and Surface Science (CSGI) lectured on two EU-funded projects, NANOFORART and NANORESTART. The workshop focused on three of the technologies CSGI developed for conservation of cultural heritage: gels, microemulsions, and nanoparticle solutions. Conservators specializing in varied disciplines from institutions and private practices on the east coast attended the workshop.
CSGI has developed materials to address consolidation, cleaning and deacidification problems identified by colleagues in conservation, and continues to consult and collaborate internationally on a wide range of conservation projects. They have developed conservation products for cleaning and consolidation using nanotechnologies.
Conservators in all specialities have adopted the use of gels and thickeners for controlled cleaning of artworks. In the United States, over the past decades Richard Wolbers and Chris Stavroudis (among others) have introduced and popularized viscosity modifiers made of natural or synthetic polymers (e.g. Xanthan gum, Pemulen, Klucel, Carbopol, Velvesil plus). These materials allow conservators more options for tailoring cleaning solutions and restricting penetration into porous substrates.  Viscous solutions can limit solvent volatility, increase contact time, and combine immiscible solvents to form stabilized emulsions. More recently, physical gels made of polysaccharides (e.g. agar, gellan) have been used as “containers” for aqueous and some solvent cleaning applications.
While a variety of gels and thickeners have been readily adopted for use in treatment, concerns remain about controlling their application (e.g. conforming to different surfaces), specifying pore size, controlling solvent release and eliminating residues. Gels made of crosslinked polymers in semi-interpenetrating networks – such as those developed and introduced by CSGI – offer new options in the conservator’s toolkit. Imaging and analysis conducted by Baglioni and others has worked to identify and localize residues, and confirmed that the hydrogels and organogels do not leave a residue due to their structural and physiochemical properties.
At the workshop we worked with two types of CSGI hydrogels: chemical gels made of poly(2-hydroxyethyl methacrylate) (pHEMA)/ polyvinylpyrrolidone (PVP) formed by covalent bonds and physical gels made of polyvinyl alcohol (PVA)/ polyvinylpyrrolidone (PVP) or PVA/PVA formed with secondary bonds (dispersion forces or hydrogen bonds). Hydrogels are compatible with aqueous cleaning solutions, some polar solvents, and microemulsions (i.e. oil-in-water). CSGI’s chemical hydrogels are rigid, clear sheets that are cut to the size of the area treated. The physical gels are similar to Jello in consistency and texture, but clear and colorless. Another class of gels being developed by CSGI, organogels, open up a wider variety of solvent options.  Depending on the desired characteristics, these gels can be engineered to have different properties (e.g. elasticity, solvent retention, solvent compatibility) based on the polymers used, synthesis procedures, and degree of crosslinking.
Conservators often remove natural and synthetic adhesives and coatings from fine art surfaces by solubilizing the unwanted material. Solubilization risks incomplete removal, penetration into the substrate (especially if the substrate is porous), leaching out original materials, redeposition, and tidelines. Moreover, solubilization and removal of material must often be accompanied by mechanical action, which can damage sensitive underlying surfaces. Additionally, solubilization of aged coatings with neat volatile organic solvents often requires the use of polar, aromatic, or otherwise aggressive solvents that pose risks to the environment and human health.
Microemulsions are made from a micellar solution (a dispersion of surfactants formed when the concentration of surfactant exceeds a threshold value called the critical micellar concentration), in which a surfactant is used to contain a dispersed phase in a continuous phase (either water-in-oil or oil-in-water). Stable microemulsions can be extremely effective at cleaning because of the exponential increase in interphase surface area, where the cleaning activity occurs. As a result, smaller amounts of solvents are needed for highly effective cleaning solutions. Other microemulsion formulations have already been used in conservation for cleaning acrylic painted surfaces and plastics, as developed by Dow Chemical/Getty Conservation Institute/Tate. 
Several of the nanostructured solutions developed by CSGI can also work through dewetting (the opposite of surface wetting) instead of solubilization. In dewetting, the microemulsion activates and swells the polymer coating, forming a discrete layer that can be removed. Minimal mechanical action with a dry swab rolls off the swelled, dewetted polymer.
The CSGI microemulsions were initially developed for conservators working on wall paintings in Italy and Mexico that were deteriorating owing to aged acrylic and polyvinyl acetate coatings. The microemulsions can be used for removing synthetic polymers such as coatings or graffiti, but must be tested carefully for each application. Careful formulation is crucial: therefore it is important for conservators to work closely with CSGI to understand the product components and devise the best systems for their treatments.
As for the gels and viscosity modifiers described above, residues left behind from cleaning agents have been a major concern for those considering using emulsions and microemulsions for cleaning painted surfaces and plastics. For emulsions, high proportions of surfactants are sometimes needed to stabilize mixtures, and surfactant residues may attract dirt to the surface, or change surface gloss. Going forward CSGI and their research partners aim to identify self-degrading surfactants (that decompose without leaving a residue) for use in future conservation products. CSGI is also working to limit the amount of toxic solvents (such as methyl ethyl ketone) used in their microemulsions.
Nanoparticles (0.1-0.2 um in size) in suspension can be used for a variety of applications where penetration into surfaces is desirable. The main applications of nanoparticle solutions in conservation are for consolidating carbonate materials (i.e. stones or frescoes) and deacidifying paper and canvas. Nanoparticles can be dispersed in alcohol to form stable solutions, called nanoconsolidants. These can be applied to stabilize surfaces in preparation for subsequent treatment steps. As an example, they can be used to pre-consolidate friable wall paintings before salt removal, as they do not interfere with subsequent treatments or mobilize soluble salts. These treatments reproduce the original physiochemical properties of the artwork by undergoing the lime-cycle carbonation process, allowing crystals to bridge gaps as they form, effectively reconstituting the same binder as the original paint (inorganic CaCO3). Another application is to counteract and prevent acid hydrolysis in cellulosic materials: spraying Ca(OH)2 particles onto paper or canvas can effectively adjust and neutralize the material’s pH. 
After learning about the chemistry and principles behind these materials through Dr.Baglioni and Dr. Giorgi’s lectures, workshop participants experimented using a variety of mock-ups and artworks. We tested aqueous cleaning of paper and painted surfaces with the highly retentive chemical gels, microemulsions applied with cotton poultices and/or hydrogels for the removal of coatings on terracotta and fresco surfaces, and removal of acrylic paint covering oil paint, as well as applying solutions of Ca(OH)2 nanoparticles for fresco consolidation. As always, each conservator needs to develop a sense of the working properties of any tool or material to see how they will be useful. Dr Baglioni and Dr. Giorgi admirably contextualized the need for these materials, the underlying chemistry and physics, and the particular benefits these nanotechnologies provide.
The final day of the workshop focused on a project investigating the materials and restoration history of a Louise Nevelson painted wooden sculptural installation at St. Peter’s Church in Manhattan. A variety of treatment options were considered and tested, including chemical gels. Sarah Nunberg will present on this project at AIC:“Treatment of a White Louise Nevelson Installation” in the General Session, You Can’t Go It Alone.
Overall, the workshop was an extremely well-organized and exciting introduction to the vast applications of nanotechnologies in conservation. Dr. Baglioni, Dr. Giorgi, and their colleagues have published widely on their research, see the CSGI site for more information and selected references.
Thanks very much to Dr. Baglioni, Dr. Giorgi, the organizers, Pratt Institute, and the other participants for a wonderful and stimulating few days. Keep an eye out for the upcoming WAAC newsletter, which will feature a discussion of the practical use of these technologies.
 These materials are available for low cost directly from the University of Florence, per the arrangements of the EU funding source supporting this research: see the CSGI website (www.csgi.unifi.it). Reducing the environmental and human health impact is an important goal of CSGI’s projects. For an overview, see Giorgi, Rodorico, Michele Baglioni, Debora Berti, and Piero Baglioni. “New Methodologies for the Conservation of Cultural Heritage: Micellar Solutions, Microemulsions, and Hydroxide Nanoparticles.” Accounts of Chemical Research 43, no. 6 (June 15, 2010): 695–704. doi:10.1021/ar900193h.
 This was a key concern during development of these products and was tested with a variety of analytical techniques e.g. Focal plane array FTIR. See Domingues, Joana A. L., Nicole Bonelli, Rodorico Giorgi, Emiliano Fratini, Florence Gorel, and Piero Baglioni. “Innovative Hydrogels Based on Semi-Interpenetrating p(HEMA)/PVP Networks for the Cleaning of Water-Sensitive Cultural Heritage Artifacts.” Langmuir 29, no. 8 (February 26, 2013): 2746–55. doi:10.1021/la3048664.
 While these may seem unfamiliar to you at first glance, interpenetrating network polymeric gels are the same kind of technology used for making soft contact lenses.
 Organogels are described in greater detail in Baglioni, P. et al. 2015. Organogel formulations for the cleaning of easel paintings. Applied Physics A 121 (3): 857–868. doi:10.1007/s00339-015-9364-0 and Piero Baglioni, David Chelazzi, and Rodorico Giorgi. Nanotechnologies in the Conservation of Cultural Heritage: A compendium of materials and techniques. Springer Netherlands. 2015. DOI 10.1007/978-94-017-9303-2
 See “Mineral Spirits-Based Microemulsions: A Novel Cleaning System for Painted Surfaces” Bronwyn Ormsby, Melinda Keefe, Alan Phenix, Eleanor von Aderkas, Tom Learner, Christopher Tucker, and Christopher Kozak, Journal Of The American Institute For Conservation Vol. 55 , Iss. 1, 2016. Note that for all microemulsions, the phase diagrams describing stable formulations can be complex, and it is difficult to formulate these in most museum labs.
 See Giorgi et al. 2010 (full citation in reference 1)
 This work will also be presented at the 2017 Gels in Conservation Conference in London. (Nunberg, S. C. Kehlet, S. Alcala, C. Tomkiewicz, C. McGlinchy, M. Henry, J. Dittmer. “Conservation of a White Louise Nevelson Installation: Gel Systems Explored”) and has been submitted for review for the 18th Triennial ICOM-CC Conference in Copenhagen: Nunberg, S., C. Kehlet, S. Alcala, C. Tomkiewicz, C. McGlinchy, M. Henry, J. Dittmer. 2017. Conservation of a White Louise Nevelson Installation: Treatment Choices Based on Ethical Discussions and Analytical Studies.