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Posted: Oct 22, 2007
Old world masterpieces may benefit from a nanotechnology cleaning
(Nanowerk Spotlight) In the art world, the topic of conservancy is a heated one. Some believe that the world’s most precious works of art should be allowed to age and die gracefully, while others believe they should be protected and restored at all costs. Art conservation and restoration is not a modern phenomenon. Within 20 years of its 1497 completion, one of the world’s most well-known and admired works of art, The Last Supper, was already beginning to show signs of wear and exposure. In 1726, the first of many restorations (or attempted restorations) occurred, followed by additional restorations in 1901, 1908, 1924, and 1951. The deterioration proved unstoppable, while the effects of pollution added to the masterpiece’s worsening condition. Between 1978 and 1999, another major restoration effort was undertaken. In 1981, the decision by the Vatican to restore the Sistine Chapel’s ceiling sparked a tremendous debate. Today, the Mona Lisa stirs similar debate. Although the world’s most famous painting has severe yellowing and shows other signs of aging (it is 500 years old after all), the Louvre has adamantly refused to even consider restoration or cleaning. You can’t really blame them. While the cleaning and restoration of the Sistine Chapel and the Last Supper has certainly improved their visibility, restoration is not an exact science and the process could save or destroy the famous work. In fact, much of the yellowing we see today on masterpieces such as the Mona Lisa and the Last Supper are the result of varnishes originally applied to protect the paintings. The process of cleaning and removing old varnish is a tedious and painstaking process, but Italian chemists may have found a much better, and safer, process with the help of nanoparticles.
The chemists, from the Center for Colloid and Surface Science (CSGI) research group at the University of Florence, under the direction of Professor Piero Baglioni, have created a nanomagnetic sponge that can absorb cleaning solutions, release them onto the surface of paintings, sculptures and other works of art, and then reabsorb the solutions, after the piece is cleaned. All of this occurs without the human hand ever coming into contact with the art.
Application of the nanomagnetic gel to a fresco painting realized in the laboratory for testing the gel efficacy for paraloid B72 removal. Left panel: white glaze shows the area treated with Paraloid, and the circle shows the area that will be used for gel treatment (grazing angle light). Center panel: gel treatment (normal light). Right panel: area cleaned by the removal of paraloid B72 (grazing angle light). (Reprinted with permission from American Chemical Society)
Although porous like a sponge, the material is actually a hard, solid hydrogel. The sponge is made by cross linking magnetic nanoparticles (CoFe2O4) through a polyethylene glycol and acrylamide polymer network. When polymerization is complete, the sponge can be immersed in water to achieve full saturation. According to the chemists, the nanomagnetic gel is hard enough to be handled with tweezers or cut with a knife or scissors. This is important because the gel can be cut into a specific shape for cleaning a particular area of the artwork. When cleaning is accomplished, the gel can be removed with a magnet. The nanomagnetic sponge can also be freeze-dried into a magnetic powder, which will reform the gel when rehydrated.
Gels are often used for cleaning artwork because they do not soak as deeply into the surface as liquid solvents. However, they are difficult to remove, often leaving residue on and beneath the surface. In addition, gels have proven unsatisfactory on porous surfaces such as wall paintings. According to the article, published in the June 2007 issue of the American Chemical Society’s journal Langmuir ("Nanomagnetic Sponges for the Cleaning of Works of Arts"), the nanomagnetic sponge appears to be particularly useful for removing Paraloid polymers from marble and frescos. Paraloid polymers, especially Paraloid B72, were once used extensively for art conservation. Unfortunately, as it ages, the resin tends to yellow and lose its chemical and mechanical properties causing damage to art and artifacts. Today, non-yellowing varnishes are used, but the old varnish must be removed first.
The Italian scientists tested the nanomagnetic sponge on a sample of painted marble that was treated with a Paraloid B72 solution eight years ago. According to the chemists, prior to the sponge application, the sample appeared glassy and yellow. After direct application of the microemulsion-loaded magnetic gel (application time varied from 10 minutes to two hours), the gel was removed using a magnet. To evaluate the efficiency of the removal process, the team employed the use of Microreflectance Fourier transform infrared (FTIR) spectrometry. According to the article, a comparison of spectra collected before and after the treatment showed that signals from the acrylate completely disappeared after the cleaning. Additional analysis through scanning electron microscope (SEM) and, in particular, the mapping of X-ray emission collected by energy dispersive X-ray spectrometry, provided clear evidence that no residue from the nanoparticles remained on the surface of the painting, and the polymer was completely removed. The scientists also tested the process on a damaged fresco, successfully demonstrating its use on plaster.
Although the article focuses on the use of the nanomagnetic sponge for art conservation and restoration, the authors suggest that the nanomagnetic gel will be useful for a variety of applications in cosmetics, biotechnology and detergents. “The overall system is particularly efficient in the uptake and release of the material contained in the loaded phase,” say the authors. “The nanomagnetic gel represents the most advanced and versatile system for cleaning and will have a dramatic impact on the conventional methods used in the conservation field and in several other fields where fine tuning of the release or uptake of confined material is required.”