Updated by Reginald Davey 15/06/23
In the past, restoration of paintings and other old artwork often involved the application of coatings such as acrylic resins to consolidate and protect them. However, acrylic resins drastically change the treated artwork’s optical properties and, in many cases, can accelerate their degradation.
This causes issues for more sympathetic restoration, which tries to preserve the original artwork as the artist intended it to be seen. Therefore, removing these coatings is of critical concern.
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The Problem With Conventional Restoration Coatings
The preservation of the world’s cultural heritage is an ongoing concern in the art restoration business. It is vitally important to arrest the aging and degradation of old artworks so that current and future generations can enjoy them for decades to come.
The inappropriate use of synthetic polymers and acrylic resins is a key issue in the restoration industry and has led to the damage of many important pieces of art.
Acrylic resins drastically change the treated artwork’s optical properties and, in many cases, can accelerate their degradation. This causes issues for more sympathetic restoration, which tries to preserve the original artwork as the artist intended it to be seen.
Wall art and murals are an intrinsic part of many medieval and Renaissance buildings, such as churches, villas, and municipal buildings. However, when they are coated with traditional acrylic and vinyl coatings, issues such as salt crystallization in the artwork’s pores can occur.
This leads to mechanical stresses within the paint layer itself, which is typically on the scale of a few to a hundred microns. Depending on environmental conditions, seemingly irreversible degradation can occur within just a handful of years or decades.
In addition, the aging of the coating itself can lead to drastic changes in the artwork’s physiochemical properties. This occurs in both the painting’s inorganic constituents and the polymer coatings. Factors such as reduced water vapor and gas permeability can contribute to accelerated degradation.
In the most extreme cases, the painted layer can completely detach from the underlying mortar surfaces or canvas. It is almost impossible to remove these damaging coatings from artwork with the use of neat organic solvents.
Removing Acrylic Coatings from Paintings on Walls
Over the past few decades, researchers have explored novel approaches to improve sympathetic restoration of old artworks. A 2010 study published in the journal Nanoscale by Italian researchers from the University of Florence developed new organic solvent delivery methods using micelles and microemulsions.
In the water continuous phase, nanodroplets of the organic phase are dispersed, which effectively lifts the polymer coating without damaging the underlying painted layer. This avoids polymer spreading in the artifact’s porous matrix.
Key to this soft-nanostructured process is the large interfacial area of the novel coating removal system, which amplifies interactions between it and the deleterious polymer coating. Novel nanofluids were formulated for the removal of Paraloid B72, a commonly used polymer coating composed of ethyl methacrylate/methyl acrylate.
The research demonstrated the effectiveness of a novel oil-in-water microemulsion composed of sodium dodecylsulfate, SDS, 1-PeOH, and small proportions of p-xylene and nitro diluent. 1-PeOH (1-pentanol) is employed as a co-surfactant. The “swollen” micellar system, termed EAPC, also contains propylene carbonate.
The system has some limitations, however, especially in removing coatings that use a combination of Paraloid B72 and Mowilith DM5. Additionally, the system encounters problems where both these coatings are applied sequentially.
Another paper published in 2021 demonstrated the effective removal of polymeric coatings from a Belgian neo-gothic wall painting. Original paint layers were obscured by varnish, which had browned over time since the artwork’s previous restorations.
The team developed a novel system that utilizes a solvent-loaded double network PVA/borax/agarose hydrogel. Testing various solvent mixtures revealed that the most effective system was hydrogel/10% propylene carbonate. Visual examinations, FTIR spectroscopy, and OM verified the results.
Acrylic Resin Removal from Paintings on Canvas
Removal of coatings from paintings on canvas presents a set of similar but distinct challenges for the design of novel restoration systems for acrylic resin removal.
A 2019 paper by researchers from the Sapienza University of Rome in Italy presented a case study on the use of novel microemulsion aged resin removal on a painting. The resin was applied in a previous restoration.
Oil in water (O/W) microemulsions of xylene (XYL) and EAPC were tested on the previously restored painting, with different results observed by the team. The XYL microemulsion was effective at removing acrylic polymers, whilst the EAPC microemulsion could be used for both acrylic and vinyl resin removal.
According to the paper, the XYL microemulsion system had the greatest effect on original artwork restoration, making it highly suitable for the removal of harsh varnish from paintings on canvas.
In Conclusion
Traditional acrylic and polymer resins, which have been used in artwork restoration and conservation for several decades, cause deleterious damage over time to paintings on both canvas and walls. Acrylic resin removal is a complex and delicate process.
A more sympathetic type of artwork restoration is needed to preserve the cultural heritage of many nations. In order to achieve this, many studies have concentrated on this critical research question in the art world, developing novel solvent/micelle and hydrogel systems to arrest or reverse the damage caused by previous efforts.
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Further Reading and More Information
Al-Emam, E et al. (2021) Removal of a Past Varnish Treatment from a 19th-Century Belgian Wall Painting by Means of a Solvent-Loaded Double Network Hydrogel Polymers 13:16 [online] mdpi.com. Available at:
https://doi.org/10.3390/polym13162651
Guizzo, S et al. (2019) Application of microemulsions for the removal of synthetic resins from paintings on canvas Natural Product Research 33:7 pp. 1015-1025 [online] sciencedirect.com. Available at:
https://doi.org/10.1080/14786419.2016.1244191
Baglioni, M et al. (2010) Removal of acrylic coatings from works of art by means of nanofluids: understanding the mechanism at the nanoscale Nanoscale 2 pp. 1723-1732 [online] pubs.rcs.org. Available at:
https://pubs.rsc.org/en/content/articlehtml/2010/nr/c0nr00255k
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