Authors: Aline Assumpção and Souty Beskhyroun
There is a great need to develop and evaluate sustainable alternatives to traditional consolidants used in art conservation. These materials should be stable, reversible and chemically compatible with the original artwork itself. Nanoparticles make good sustainable consolidants due to their suspension stabilities, low toxicity mediums, higher reactivity, better compatibility and functional properties, and similar porosity to many substrates. 
Most studies on the use of nanomaterials for consolidating artwork have been focused on carbonate-based works of art (mural paintings, mortars, stones). . The loss of binder and the crystallization of salts are the main degradation processes for wall paintings, whereas loss of cohesion and biodeterioration are common issues in stone materials. Due to their adhesive power and accessibility, synthetic products were often used as a solution to these problems during the last few decades. However, their physicochemical incompatibility with many substrates had not been taken into consideration . The hydrophobic nature of these polymeric materials affects the water evaporation cycles of porous matrices and can lead to the internal crystallization of salts, which may in turn causes issues like the disruption of a painted surface.
Nanomaterials have been used for the consolidation of plaster and natural stone surfaces because their reduced scale increases their penetration and reactiveness . When dispersed in solvent, earth alkaline hydroxide nanoparticles such as calcium, magnesium, and barium hydroxides have been proven to be effective and durable consolidants that are compatible with many artwork matrices. For example, calcium hydroxide nanoparticles go through the process of carbonation, which causes the capillaries and cracks to be filled with CaCO3. This carbonated product acts as a binder with the same composition as the original material .
Inorganic nanoparticles are usually dispersed in a solvent as well, most commonly water or a short-chain alcohol. There are advantages to using these low-toxicity solvents instead of other consolidation systems. For example, the application of traditional synthetic polymers might require the use of more toxic solvents, either as mediums or in further cleaning treatments. Moreover, the increased reactiveness of nanosized particles reduces the amount of material used in the treatment.
Other novel nanoconsolidation solutions have also been studied in recent years. For instance, water-based formulations composed of nano-inorganic or nano-hybrid dispersions are available. These include nano-titania, nano-silica, nano-hydroxyapatite, and new organic polymeric consolidants, sometimes with the addition of inorganic nanoparticles to improve stability in outdoor environments. 
Nanocellulose has also been used for the consolidation of cellulosic materials such as canvas, paper, textiles, and wood because it offers high strength and stability and forms a translucent film. Interest in the material has been growing due to its non-toxicity and the fact that it is renewable and bio-degradable. Compatibility with the original substrate is another advantage of nanocellulose as compared to traditional consolidants. When used for the consolidation of canvases, nanocellulose appears to be an effective and environmentally-friendly alternative to synthetic polymers. Moreover, it presents no visible alteration of the canvas and a low depth of impregnation, which is advantageous in terms of reversibility .
Studies in this field are still in progress, but they suggest that nanomaterials are promising consolidants in terms of both efficacy and environmental impact. Using nanomaterials gives the conservator finer control over the treatment, so they offer a safer approach to conserving works of art.
Check our blog in the next few weeks to learn about the use of nanomaterials as sustainable coating materials!
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