CTS FOCUS 08 - The Future of Cleaning is Called Nevek®

The extracting and supporting properties of Agar-Agar have been known for several years and have been exploited to perform cleaning treatments on all kinds of substrates. Its main characteristic is the formation of rigid gels, useful whenever water must be used in a thickened form. 

When heated, the polysaccharide chains of Agar-Agar in aqueous dispersion distribute randomly, producing a fluid solution; upon cooling, they reorganize into tubular structures responsible for the characteristic rigid gel, within which water molecules are able to move.

The gelation process can be reversed indefinitely by heating and cooling, which is why these are referred to as thermoreversible gels. 

These gels have been studied since the 1960s, but only recently have in-depth investigations been carried out into their characteristics and their potential for cleaning works of art [1,2,3,4]. After a careful evaluation of the various Agar-Agar products available on the market, CTS selected a specific type in which the cleaning properties are optimized and removal is easier. This product was commercialized under the name Agar Art. 

Although Agar Art achieved good commercial success and has also been used for cleaning large surfaces [5,6], the full potential of these cleaning systems has not yet been completely exploited.

One of the factors that certainly slowed down their widespread adoption is the complexity of preparation: the powder must be weighed and dispersed in water, then heated for approximately ten minutes, after which any heat-sensitive reagents must be added. The gel must then be applied with a brush before cooling, or alternatively formed into solid sheets to place on the surfaces, if conditions allow. If hot application is required and the gel solidifies in the container during use, it must be reheated, often with the aid of a microwave oven.

As often happens, procedures that are simple in the laboratory become troublesome on-site, leading operators to prefer easier alternatives such as traditional cellulose pulp or sepiolite poultices.

A similar difficulty arises when carrying out small preliminary tests: restorers often wish to assess the effectiveness of certain reagents and identify the type of dirt to be removed through small test patches. However, the preparation process for Agar Art gels is too laborious for these preliminary tests, especially before the restoration site has been fully set up. 

Reflecting on these objective difficulties, and building on the experience of the company Aconerre, a homogenized gel formulation was developed, usable both cold and hot, in which it is extremely easy to dissolve a variety of reagents, from aqueous solutions to solvents.

With this latter property, it is clear that we are dealing with an even more versatile product. This new formulation, named NEVEK, overcomes the complexities associated with Agar use, broadening operational possibilities and simplifying procedures.

Derived from marine algae and free from synthetic materials, NEVEK presents no toxicity risks when handled correctly and is an environmentally sustainable material. 

As with Agar Art gels, NEVEK strongly retains water, allowing aqueous cleaning of surfaces by removing water-soluble substances without releasing free water deep into the substrate, thereby preventing the migration of salts that may be present in the support materials.

The water wets the interface between the gel and the surface, limiting penetration into the porous structure of materials such as plaster, stone, frescoes, and paintings.

All areas of restoration can benefit from the unique properties of this system, since NEVEK can support both aqueous solutions and all types of solvents, whether polar or non-polar. 

Among its possible applications, the main ones include:

• Removal of dirt and residues of old adhesives and protective coatings from stone surfaces, plaster, wall paintings, paintings on panel and canvas, paper, wood including polychrome wood, terracotta, archaeological artifacts, and more. 
• Extraction of salts from stone surfaces, mosaics, archaeological artifacts, and wall paintings. 
• Removal of varnishes from wood, including polychrome wood, paintings on panel and canvas, and stone materials. 
• Controlled moisture application with highly regulated diffusion of liquid water. 

NEVEK functions like a sponge, absorbing the solubilized material within itself, just as traditional Agar Art gels do, but it offers several advantages over rigid gels:

1. It is ready to use, since it can be applied cold and does not require the preparation procedures associated with powdered agar (weighing, dissolving, and heating). 
2. It has lower adhesion capacity and is particularly suitable for sensitive surfaces (lifting, disintegration, or heat-sensitive materials). 
3. Organic solvents, including non-polar solvents such as ligroin, can be added, creating a gel that behaves similarly to an oil-in-water emulsion. 
4. It can also be used in fluid form after heating, since the thermoreversible gel becomes liquid when heated. 

NEVEK can be applied by hand or with spatulas, and thanks to its thixotropic properties this is possible even on vertical surfaces. Its structure allows it to perfectly adapt to all surfaces, including irregular ones, and it is easy to remove, for example with a simple dry brush.

Because of its extremely low adhesion, its action is exceptionally gentle, avoiding the risk of detaching fragments. Removal is made even easier by interposing a sheet of Japanese paper. No rinsing is required, as the product leaves no residues. 

NEVEK can be heated in a microwave oven or bain-marie, obtaining a fluid phase that can be spread onto surfaces with a brush and then left to cool. In this way, the gel reforms, perfectly following the irregularities of the surface and absorbing water-soluble dirt.

The gel is then mechanically removed by gently lifting the film from the center toward the edges, possibly with the aid of wooden sticks.

If necessary, the product can be modified by incorporating substances that enhance its activity, up to a maximum of 30% by weight, using a simple mixer:

1. Aqueous solutions of surfactants, chelating agents, acids, and alkalis can be added, as with other gels; the release of the solution and the effect of these substances remain confined to the surface, limiting penetration into underlying layers. 
2. Solvents with varying polarity can also be added after preliminary testing. Again, solvent release into underlying layers is minimized. 

After these additions, the gel can no longer be reheated.

Contact times, to be established through testing, depend on the type of substrate, the material to be removed, environmental conditions, and how NEVEK has been modified. 

Application Examples

1. Preparation of a low-toxicity paint remover: add selected solvents to NEVEK, up to a maximum of 50% by weight, according to the type of varnish to be removed, until a homogeneous mixture is obtained. Apply to the varnish for a suitable period, then mechanically remove the NEVEK film together with the swollen varnish. 
2. Cleaning plaster, stone surfaces, and wall paintings: Agar gels have long been used on plaster and stone materials, also with additives such as surfactants and chelating agents. The versatility of this cleaning system makes it possible to develop various application methods suitable for multiple conservation issues. One example is the marble decoration of the Tornacoro in the Milan Cathedral [9]. More recent applications include frescoed surfaces and dry-painted wall decorations, such as the 14th-century murals in the Chapel of the Pedralbes Monastery in Barcelona [9]. 
3. Salt removal from stone materials: apply the product to the surface and remove after several hours. A study conducted by the Italian National Research Council (CNR) [8] demonstrated that NEVEK is as effective as hot-applied gel and that both are more efficient than preformed gel applications. Effectiveness can be enhanced with the addition of complexing agents such as EDTA or ammonium citrate. 
4. Removal of old vinyl glue films from the back of a canvas: add a 1:1 mixture of acetone and ethyl alcohol to NEVEK, in quantities not exceeding 50%. Mix until homogeneous. Apply to the vinyl glue film. After several hours, the swollen film detaches easily from the canvas without solvents penetrating into the underlying layers. 

BIBLIOGRAPHY

1. E. Campani, A. Casoli, P. Cremonesi, I. Saccani, E. Signorini. The Use of Agarose and Agar for the Preparation of “Rigid Gels”, translated by Diane Kunzelman. Quaderni del Cesmar7, No. 4, Il Prato, Padua, 2007. 
2. M. Anzani, M. Berzioli, M. Cagna, E. Campani, A. Casoli, P. Cremonesi, M. Fratelli, A. Rabbolini, D. Riggiardi. Rigid Agar Gels for the Cleaning Treatment of Plaster Objects. Quaderni del Cesmar7, No. 6, Il Prato, Padua, 2008. 
3. M. Anzani, A. Rabbolini. The Restoration of Stone Materials with Agar Agar Gels: the Plaster “La Bella Pallanza” and the Marble “Bust of a Woman” by Paolo Troubetzkoy, in Lo Stato dell’Arte, Proceedings of the 7th IGIIC National Congress, Naples, 8–10 October 2009, Nardini Editore, Florence, 2009. 
4. M. Anzani. Use of Rigid Agar Agar Gels for Cleaning Stone Materials, in Musso, S.F., Restoration Techniques. Utet Scienze Tecniche, PLT 43, 2013. 
5. M. Anzani, L. Borgioli, A. Rabbolini, A. Toniutti. S. Eugenio in Milan: 120 m² of Cleaning with Agar Agar, Proceedings of the 9th IGIIC Congress Lo Stato dell’Arte 9, Cosenza, 13–15 October 2011. 
6. A. Rava, W. Shank, P. Colombini, O. Chiantore, M. Picollo, V. Palleschi et al. Keith Haring in Pisa: Cleaning and Protection of an Acrylic Painting Exposed Outdoors. Scienza e Beni Culturali XXVIII, 2012. 
7. A. Sansonetti, M. Casati, J. Striova, C. Canevali, M. Anzani, A. Rabbolini. A Cleaning Method Based on the Use of Agar Gels: New Tests and Perspectives. 12th International Congress on the Deterioration and Conservation of Stone, New York, 2012. 
8. D. Gulotta, D. Saviello, F. Gherardi, L. Toniolo, M. Anzani, A. Rabbolini, S. Goidanich. Setup of a Sustainable Indoor Cleaning Methodology for the Sculpted Stone Surfaces of the Duomo of Milan. Heritage Science, 2014, 2:6. 
9. R. Senserrich-Espuñes, M. Anzani, A. Rabbolini, L. Font i Pagès. The Use of Agar Gels on the 14th-Century Wall Paintings in the Chapel of Sant Miquel at the Royal Monastery of Santa Maria de Pedralbes in Barcelona, in Lo Stato dell’Arte, Proceedings of the 13th IGIIC National Congress, Turin, 22–24 October 2015, Nardini Editore, Florence, 2015.