NANOFORART

Impacts & Results

The projet came to and end in 2014, with many conclusions and innovant solutions for the objectives defined :

Consolidation of immovable works of art :

Due to several reasons (pollution, weathering, mechanical stress) wall paintings lose their original cohesion during time. When this happens a consolidation intervention has to be performed in order to recover the mechanical properties of the material and avoid the loss of the pictorial layer.

The project has produced several formulations for the consolidation of immovable works of art:

• Nanoparticles of calcium hydroxide dispersed in ethanol, 1-propanol or 2-propanol;
• Nanoparticles of magnesium hydroxide dispersed in 2-propanol;
• Nanoparticles of barium hydroxide dispersed in 2-propanol;
• Nanoparticles of strontium hydroxide dispersed in 2-propanol;
• Mixed formulation of calcium and barium hydroxide nanoparticles dispersed in 2-propanol.

The particles come at different possible concentrations (ca. 1-50 g/L), and different properties (e.g. size distribution, crystallinity) are possible, according to the conservation needs. The formulations are highly compatible with carbonate-based materials, such as wall paintings and carbonatic stone. Due to their compatibility, they represent an alternative to traditional consolidation materials used in restoration practice, for instance synthetic polymer coatings that exhibit poor compatibility with inorganic porous works of art and can produce detrimental effects in the long-term.

pH control of movable works of art : 

Acidity affects several types of artworks, leading to their weakening. For instance, cellulose-based artifacts, such as paper, wood and canvas exhibit loss of mechanical properties due to acid hydrolysis of cellulose. Collagen-based artifacts (parchment, leather) are also damaged by acidity excess. It is therefore necessary to counteract acidity through the application of an alkaline buffer on the endangered material.

The project has produced several formulations for the deacidification and pH control of movable works of art:

• Nanoparticles of calcium hydroxide dispersed in ethanol, 1-propanol, 2-propanol or cyclohexane
• Nanoparticles of magnesium hydroxide dispersed in 2-propanol Nanoparticles of calcium carbonate dispersed in 2-propanol or water
• Nanoparticles of calcium/magnesium or strontium carbonate dispersed in water Nanoparticles of calcium or magnesium carbonate dispersed in 2-propanol Nanoparticles of calcium carbonate dispersed in cyclohexane
• Magnesium oxide nanoparticles dispersed in water

The particles come at different possible concentrations (ca. 1-100 g/L), and different properties (e.g. size distribution, crystallinity) are possible, according to the conservation needs.

The use of nano-sized particles grants high reactivity to acids and CO2, the latter turns hydroxide into carbonate avoiding too high pH values on the treated fibers. The reduced size of the particles also favors their penetration through paper sizing. These systems represent an alternative to methods that use micronsized particles and precursors of hydroxide (or carbonate). The use of non-aqueous solvents makes these systems compatible with several water-sensitive substrates.

Cleaning of immovable works of art : 

Several undesirable materials can be found on the surface of wall paintings. Oily soil and dirt or organic compounds inappropriately applied during previous conservation workshops are some of the materials that must be removed from these work of arts. In several cases the removal of detrimental coatings prevents damage in the long-term (e.g. flaking of the surface layers).

The project has produced several formulations for the cleaning of immovable works of art, namely “oil-in-water” (o/w) nanostructured fluids where low amounts of organic solvents (content ranging from less than 5 to 25%) are dispersed as nano-sized droplets in water, with the help of surfactants. The different formulations offer a palette of possibilities in order to remove complex layers with different composition and polarity:

• o/w microemulsion containing ethyl acetate and propylene carbonate;
• o/w microemulsion containing xylene (or xylene and nitro-diluent, or xylene and ligroin);
• o/w microemulsion containing methyl ethyl ketone and/or butyl acetate or butanol.

These aqueous cleaning systems are particularly effective in the removal of oily soils without redeposition into the pores of the wall. They offer performances not achievable with traditional solvent cleaning and represent a new platform for conservation of work of arts. Nanostructured cleaning fluids (water-in-oil microemulsions, micellar solutions) are substantially based on water, with a drastically reduced solvent content while maintaining cleaning effectiveness. The environmental impact is therefore minimized, and the safety for the operator increased. Moreover, solvents and microemulsions can be confined in chemical gels that allow the control of the cleaning action while depressing the liquids' volatility, so that the safety of the cleaning systems is increased.

Cleaning of movable works of art: 

Cleaning of easel paintings is a very delicate operation, since detergent systems have to perform a selective and controlled action to remove grime, dirt and/or aged varnishes without affecting the underlying pictorial layer. Gels were usually used for this purpose. These systems offer quite good performances, but their nature makes them very hard to be removed from the cleaned surface and might produce irreversible damages to the pictorial layer.

The project has developed chemical hydrogels (based on a pHEMA/PVP semi-interpenetrated network) with different mechanical properties and retentiveness to adapt different conservation cases, where the both wetting of the surface and the amount/rate of removal of unwanted layers need to be controlled.

These innovative gels leave no residues on the surface of the painting and do not have the side effects of conventional gels. They can be loaded with pure solvents or with microemulsions leading to the most performing cleaning systems.

For more details on the project results and outcomes, consult the final compendium here.