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Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments

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A special issue of Coatings (ISSN 2079-6412). This special issue belongs to the section "Surface Characterization, Deposition and Modification".

Deadline for manuscript submissions: closed (15 July 2024) | Viewed by 20809

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Special Issue Editor

Dr. Maduka Lankani Weththimuni

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Department of Chemistry, University of Pavia, Pavia, Italy
Interests: synthesis; characterization and applying of nanomaterials; nanocomposites; metal complexes; gels and polymers for different purposes (water purification, solar cells, sensors, nano-cleaning, making thin films as protective coatings, and consolidation and restoration of wood and stone artifacts)
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Special Issue Information

Dear Colleagues,

Why is Heritage Conservation and restoration necessary? It is necessary because Heritage sites (historical buildings, artifacts, sculptures, paintings, etc.) are symbols of history and are subject to several degradation processes and aging due to several factors. In particular, decay processes of historical materials related to physical and chemical phenomena occurring mainly in the presence of water, which is one of the most deteriorating factors, especially for porous materials (wood and stone). In addition, air pollution, dyes, and microorganism colonization are frequently related to the harmful degradation of building materials, which contribute to the decay of external historic buildings. Thus, the conservation and restoration of cultural heritage materials has become a necessity in a lot of countries. In addition to their intrinsic value, effective conservation and maintenance not only helps in preserving and safeguarding resources, but also in revitalizing local economies, and in bringing about a sense of identity, pride, and belonging to residents. For conservation and restoration purposes, numerous new materials and methods have been developed during the past decade. Toward this goal, we are assembling a Special Issue of Coatings, which aims to encourage researchers and to provide them with a platform to publish their novel studies. In this Special Issue, original research articles and reviews are welcome. Research areas may include (but are not limited to) the following:

Surface characterization methods;
New tools for the characterization purposes;
New materials and methods for surface cleaning;
Analyzing the decay processes;
New materials and methods for conservation (novel treatments);
Novel approach for restoration;
Durability assessments.

We look forward to receiving your contributions.

Dr. Maduka Lankani Weththimuni
Guest Editor

Manuscript Submission Information

Manuscripts should be submitted online at www.mdpi.com by registering and logging in to this website. Once you are registered, click here to go to the submission form. Manuscripts can be submitted until the deadline. All submissions that pass pre-check are peer-reviewed. Accepted papers will be published continuously in the journal (as soon as accepted) and will be listed together on the special issue website. Research articles, review articles as well as short communications are invited. For planned papers, a title and short abstract (about 100 words) can be sent to the Editorial Office for announcement on this website.

Submitted manuscripts should not have been published previously, nor be under consideration for publication elsewhere (except conference proceedings papers). All manuscripts are thoroughly refereed through a single-blind peer-review process. A guide for authors and other relevant information for submission of manuscripts is available on the Instructions for Authors page. Coatings is an international peer-reviewed open access monthly journal published by MDPI.

Please visit the Instructions for Authors page before submitting a manuscript. The Article Processing Charge (APC) for publication in this open access journal is 2600 CHF (Swiss Francs). Submitted papers should be well formatted and use good English. Authors may use MDPI's English editing service prior to publication or during author revisions.

Keywords

heritage sites
conservation
restoration
characterization
novel treatments
nanomaterials
green materials
self-cleaning surfaces
novel methods
durability

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Published Papers (11 papers)

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Editorial

Jump to: Research, Review

5 pages, 228 KiB

Open AccessEditorial

Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments

by Maduka L. Weththimuni and Maurizio Licchelli

Coatings 2023, 13(2), 457; https://doi.org/10.3390/coatings13020457 - 17 Feb 2023

Cited by 9 | Viewed by 2318

Abstract

Conservation is not the same thing as restoration [...] Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

Research

Jump to: Editorial, Review

35 pages, 7133 KiB

Open AccessArticle

Spectral- and Image-Based Metrics for Evaluating Cleaning Tests on Unvarnished Painted Surfaces

by Jan Dariusz Cutajar, Calin Constantin Steindal, Francesco Caruso, Edith Joseph and Tine Frøysaker

Coatings 2024, 14(8), 1040; https://doi.org/10.3390/coatings14081040 - 15 Aug 2024

Viewed by 976

Abstract

Despite advances in conservation–restoration treatments, most surface cleaning tests are subjectively evaluated. Scores according to qualitative criteria are employed to assess results, but these can vary by user and context. This paper presents a range of cleaning efficacy and homogeneity evaluation metrics for appraising cleaning trials, which minimise user bias by measuring quantifiable changes in the appearance and characteristic spectral properties of surfaces. The metrics are based on various imaging techniques (optical imaging by photography using visible light (VIS); spectral imaging in the visible-to-near-infrared (VNIR) and shortwave infrared (SWIR) ranges; chemical imaging by Fourier transform infrared (FTIR) spectral mapping in the mid-infrared (MIR) range; and scanning electron microscopy coupled with energy dispersive X-ray spectroscopy (SEM-EDX) element mapping). They are complemented by appearance measurements (glossimetry and colourimetry). As a case study showcasing the low-cost to high-end metrics, agar gel spray cleaning tests on exposed ground and unvarnished oil paint mock-ups are reported. The evaluation metrics indicated that spraying agar (prepared with citric acid in ammonium hydroxide) at a surface-tailored pH was as a safe candidate for efficacious and homogenous soiling removal on water-sensitive oil paint and protein-bound ground. Further research is required to identify a gel-based cleaning system for oil-bound grounds. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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21 pages, 6365 KiB

Open AccessArticle

Removing Aged Polymer Coatings from Porous Stone Surfaces Using the Gel Cleaning Method

by Maduka L. Weththimuni, Giacomo Fiocco, Alessandro Girella, Barbara Vigani, Donatella Sacchi, Silvia Rossi and Maurizio Licchelli

Coatings 2024, 14(4), 482; https://doi.org/10.3390/coatings14040482 - 14 Apr 2024

Cited by 1 | Viewed by 985

Abstract

Acrylic polymers were extensively used in past restoration practices, usually as consolidants or protecting agents. Their removal is often required because polymer coatings can improve some decay processes of stone substrates and, after ageing, may generate undesirable materials on the surface of artifacts. Therefore, the removal of old polymer coating from the surface of artifacts has become a common operation in the conservation of cultural heritage. As with other cleaning operations, it is a delicate process that may irreversibly damage the artifacts if not correctly carried out. The main aim of this study was to determine the appropriate cleaning procedure for efficiently removing old acrylic polymers (e.g., Paraloid B-72) from the surface of historical buildings. For this purpose, a polymer was applied to two different porous stone substrates (bio-calcarenite and arenaria stone). The hydrogel cleaning approach was used for the present study, as preliminary results suggested that it is the most promising polymer-removing method. The considered hydrogel (based on a semi-interpenetrating polymer network involving poly(2-hydroxyethyl methacrylate) and polyvinylpyrrolidone) was prepared and characterized using different techniques in order to assess the gel’s properties, including the gel content, equilibrium water content, retention capability, hardness, Young’s modulus, and morphology. After that, the hydrogel was loaded with appropriate amounts of nano-structured emulsions (NSEs) containing a surfactant (EcoSuf^TM), organic solvents, and H₂O, then applied onto the coated surfaces. Moreover, plain EcoSurf^TM in a water emulsion (EcoSurf/H₂O) was also used to understand the polymer-removing behavior of the surfactant without any organic solvent. A comparative study was carried out on artificially aged and unaged polymer-coated samples to better understand the cleaning effectiveness of the considered emulsions for removing decayed polymer coatings. The experimental results showed that the NSE-loaded hydrogel cleaning method was more effective than other common cleaning procedures (e.g., cellulose pulp method). In fact, only one cleaning step was enough to remove the polymeric material from the stone surfaces without affecting their original properties. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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12 pages, 9155 KiB

Open AccessArticle

Surface-Active Ionic-Liquid-Based Coatings as Anti-Biofilms for Stone: An Evaluation of Their Physical Properties

by Marika Luci, Filomena De Leo, Donatella De Pascale, Christian Galasso, Mauro Francesco La Russa, Sandra Lo Schiavo, Michela Ricca, Silvestro Antonio Ruffolo, Nadia Ruocco and Clara Urzì

Coatings 2023, 13(10), 1669; https://doi.org/10.3390/coatings13101669 - 23 Sep 2023

Viewed by 1433

Abstract

The biodeterioration of stone surfaces can be a threat to the conservation of built heritage. Much effort has been put into finding treatments and processes to mitigate biocolonization and its effects, both in terrestrial and underwater environments. Recently, the use of surfactant ionic liquids has been shown to have biocidal and antifouling effects on stone. However, little information is currently available on the morphological and physical properties of such coatings. In this paper, we report on the physical characterization of coatings based on an ionic liquid (IL) consisting of N-(2-hydroxyethyl)-N,N-dimethyl-1-do-decanaminium cation and a combination of bromide and dodecylbenzenesulfonate (DBS) anions in a molar ratio of 3:1, respectively. Nanosilica and tetraethyl orthosilicate were used as binders to promote the adhesion of the ionic liquid to the stone surface. The coatings were applied on Carrara marble samples and analyzed using Scanning Electronic Microscopy (SEM), static contact angles, colorimetric measurements and capillary water absorption. The resistance to UV radiation and seawater was also investigated. The results show that the IL behaves differently depending on the binder. The latter influences the arrangement of the IL and its wettability, which decreases in the case of NanoEstel, whereas this parameter increases in the case of Estel. In addition, the coatings show good resistance to the degradation agents. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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15 pages, 6344 KiB

Open AccessArticle

Proposal of New Natural Hydraulic Lime-Based Mortars for the Conservation of Historical Buildings

by Marco Destefani, Laura Falchi and Elisabetta Zendri

Coatings 2023, 13(8), 1418; https://doi.org/10.3390/coatings13081418 - 12 Aug 2023

Cited by 3 | Viewed by 1626

Abstract

NHL mortars are known to be compatible materials for the conservation of architectural heritage. To improve their properties with regard to salt resistance and lower their carbon footprint, NHL-based mortars with salt inhibitor agents were studied and different formulations were produced: NHL-based mortars (MSs), composed of natural hydraulic lime; and sand and cocciopesto mortars (MSCs), in which NHL, sand and brick powder were admixed with two different products, diethylenetriaminapenta and chitosan, in different concentrations. The mortar performance was tested against freeze–thaw and salt crystallization through immersion–drying cycles in a 14% sodium sulfate solution. The results highlighted that the addition of cocciopesto was effective in increasing the salt resistance, but increased the water intake during the freeze–thaw tests. The use of DTPMP produced less thixotropic mortars and decreased the water uptake, but worsened the salt resistance of hardened mortars. Chitosan allowed a good workability of fresh mortar; its water uptake was similar to the reference mortar and slightly increased the salt resistance. In the cocciopesto samples, both additives reduced the weight variation during freeze–thaw tests; meanwhile, for the lime samples, the additives increased the weight variation during the final cycles. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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10 pages, 2431 KiB

Open AccessArticle

Photonic Applications for Restoration and Conservation of 19th Century Polychrome Religious Wooden Artworks

by Victoria Atanassova, Monica Dinu, Sultana-Ruxandra Polizu and Roxana Radvan

Coatings 2023, 13(7), 1235; https://doi.org/10.3390/coatings13071235 - 11 Jul 2023

Cited by 1 | Viewed by 2389

Abstract

The present paper reports the multi-analytical approach for the removal of thick layers of metallic overpaints from a Brancovan iconostasis of the “Holy Trinity” church in Măgureni, România, which was built in 1694. After a restoration procedure at the beginning of the 20th century, the polychrome sculpture of the frame, which was initially gilded with a thin silver foil, was covered with a thick metallic overpaint layer imitating silver and gold. Currently, the conservation project of the church is focused on restoring the original aspect; thus, the overpainting that presented strong oxidation and soiling was removed. The adopted conservation methodology involved physicochemical characterization of the pictorial layers via optical microscopy, laser-induced breakdown spectroscopy, and Fourier-transform infrared spectroscopy, followed by the removal of the overpaints. The cleaning tests were performed by evaluating several methods in order to find the proper regime that would help preserve as much of the underlying polychrome layers as possible. Based on the tests, it was decided that the best solution was to use laser cleaning for the rough removal of the metallic paint overlayers and finalizing with chemical cleaning. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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14 pages, 4303 KiB

Open AccessFeature PaperArticle

UV-C Irradiation and Essential-Oils-Based Product as Tools to Reduce Biodeteriorates on the Wall Paints of the Archeological Site of Baia (Italy)

by Paola Cennamo, Roberta Scielzo, Massimo Rippa, Giorgio Trojsi, Simona Carfagna and Elena Chianese

Coatings 2023, 13(6), 1034; https://doi.org/10.3390/coatings13061034 - 2 Jun 2023

Cited by 2 | Viewed by 1281

Abstract

This study is aimed to compare, through laboratory experimentations, the efficiency of UV-C irradiation and an essential-oils-based product as tools to reduce the biofilm identified in a semi-hypogeum room located in the archaeological park of Baia, Italy. During this study, the autotrophic component of the original biofilm, mostly composed of Chlorophyceae and Cyanophycean, was isolated in the laboratory, while simultaneously, the composition of the pigments used for the fresco paintings was examined in situ through X-ray fluorescence. These examinations were necessary for the creation of test samples that were similar to the original surfaces and used for subsequent experiments. The plaster testers were contaminated with artificial biofilm, exposed to UV-C at a distance of 80 cm for a fixed time interval and treated with ESSENZIO©, a product based on oregano and thyme essential oils, to eradicate the biological species. The treatment’s effectiveness was then assessed by employing optical microscopy and spectrometric techniques applied to the areas previously occupied by the biofilm on the different test samples. To obtain an additional parameter to evaluate the treatments efficacy, the concentrations of the photosynthetic pigments were also measured by spectrophotometry. Results showed that biofilms were successfully removed by the irradiation of the surfaces and by the essential-oils-based product at a dilution of 50% in demineralized water with a time of application of 1 h and 30 min; in addition, no visible change of the pigments used on the testers were observed, demonstrating the high efficiency of the treatments against biodeteriogens. The two methods and their different mechanisms of action have provided interesting aspects that suggest a combined strategy to contrast and prevent biological growth in archaeological contexts. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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16 pages, 4718 KiB

Open AccessFeature PaperArticle

Agar Foam: Properties and Cleaning Effectiveness on Gypsum Surfaces

by Paulina Guzmán García Lascurain, Sara Goidanich, Francesco Briatico Vangosa, Marilena Anzani, Alfiero Rabbolini, Antonio Sansonetti and Lucia Toniolo

Coatings 2023, 13(3), 615; https://doi.org/10.3390/coatings13030615 - 14 Mar 2023

Cited by 4 | Viewed by 1944

Abstract

In the past decade, the usage of soft materials, like gels, has allowed for a better control of the water release process into the substrate for cleaning interventions. Agar—a natural polysaccharide harvested from algae—has been used to perform cleaning of stone materials, gypsum works, and paintings with remarkably positive results. Agar presents the great advantage of being cheap, easily available, fast to produce and not toxic, allowing for more sustainable conservation works. More recently, a new type of agar fluid, agar foam, promises further control of the water release and ease of application on delicate surfaces. In the present study, this new type of agar, CO₂ and N₂O foams, has been characterized and compared with the conventional sol/gel agar system. Moreover, the cleaning effectiveness of the agar foam was tested both in laboratory conditions and in two case studies: a historical gypsum from the porch framing of the Abbey of Nonantola, and the 20th century gypsum cast of the Pietà Rondanini by Michelangelo, located in the Sforza Castle in Milan. The obtained results show that foaming changes the sol-gel transition temperature of the agar gel as well as incrementing its dissipative behavior. When freshly applied, the foams flow with a reduced velocity, thus allowing a better control and ease of application. Once gelified, they act as a soft solid-like material, as shown by their rheological properties. Moreover, it was found that CO₂ foam slightly reduces the water release to the surface, while maintaining the moldability and ease of application. The study allows for the conclusion that agar foam offers an interesting alternative for delicate surfaces, with a non-coherent mineral deposit, and with complex geometries that often represent a challenge for the conventional agar applications Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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16 pages, 3775 KiB

Open AccessArticle

A New Green Coating for the Protection of Frescoes: From the Synthesis to the Performances Evaluation

by Raffaella Lamuraglia, Andrea Campostrini, Elena Ghedini, Alessandra De Lorenzi Pezzolo, Alessandro Di Michele, Giulia Franceschin, Federica Menegazzo, Michela Signoretto and Arianna Traviglia

Coatings 2023, 13(2), 277; https://doi.org/10.3390/coatings13020277 - 26 Jan 2023

Cited by 3 | Viewed by 2645

Abstract

This work presents the formulation and characterization of a new product for the protection of outdoor frescoes from aggressive environmental agents. The formulation is designed as an innovative green coating, prepared through a zero-waste one-pot-synthetic method to form silver nanoparticles (AgNPs) directly in a chitosan-based medium. The AgNPs are seeded and grown in a mixed hydrogel of chitosan, azelaic, and lactic acid, by the reduction of silver nitrate, and using calcium hydroxide as precipitating agent. The rheological properties of this coating base are optimized by the addition of a solvent mixture of glycerol and ethanol with a 1:1 volume ratio. The new formulation and two commercial products (Paraloid^® B72 and Proconsol^®) are then applied by brush to ad hoc mock-ups to be evaluated for chemical stability, color and gloss variations, morphological variation, hydrophobicity, and water vapor permeability via Fourier-transform infrared spectroscopy (FT-IR) in attenuated total reflection (ATR) mode, spectrophotometer analysis, stereomicroscope observations, UNI EN 15802, and UNI EN 15803, respectively. The results show that the application of the hybrid chitosan-AgNPs coating is promising for the protection of outdoor frescoes and that it can underpin the development of new products that address the lack of conservation strategies specifically designed for wall painting. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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Review

Jump to: Editorial, Research

47 pages, 6271 KiB

Open AccessEditor’s ChoiceReview

Recent Advances in the Application of Metal Oxide Nanomaterials for the Conservation of Stone Artefacts, Ecotoxicological Impact and Preventive Measures

by Marwa Ben Chobba, Maduka L. Weththimuni, Mouna Messaoud, Clara Urzi and Maurizio Licchelli

Coatings 2024, 14(2), 203; https://doi.org/10.3390/coatings14020203 - 4 Feb 2024

Cited by 3 | Viewed by 2265

Abstract

Due to the ongoing threat of degradation of artefacts and monuments, the conservation of cultural heritage items has been gaining prominence on the global scale. Thus, finding suitable approaches that can preserve these materials while keeping their natural aspect of is crucial. In particular, preventive conservation is an approach that aims to control deterioration before it happens in order to decrease the need for the intervention. Several techniques have been developed in this context. Notably, the application of coatings made of metal oxide nanomaterials dispersed in polymer matrix can be effectively address stone heritage deterioration issues. In particular, metal oxide nanomaterials (TiO₂, ZnO, CuO, and MgO) with self-cleaning and antimicrobial activity have been considered as possible cultural heritage conservative materials. Metal oxide nanomaterials have been used to strengthen heritage items in several studies. This review seeks to update the knowledge of different kinds of metal oxide nanomaterials, especially nanoparticles and nanocomposites, that have been employed in the preservation and consolidation of heritage items over the last 10 years. Notably, the transport of nanomaterials in diverse environments is undoubtedly not well understood. Therefore, controlling their effects on various neighbouring non-target organisms and ecological processes is crucial. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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26 pages, 825 KiB

Open AccessReview

Innovative Methodologies for the Conservation of Cultural Heritage against Biodeterioration: A Review

by Martina Cirone, Alberto Figoli, Francesco Galiano, Mauro Francesco La Russa, Andrea Macchia, Raffaella Mancuso, Michela Ricca, Natalia Rovella, Maria Taverniti and Silvestro Antonio Ruffolo

Coatings 2023, 13(12), 1986; https://doi.org/10.3390/coatings13121986 - 22 Nov 2023

Cited by 8 | Viewed by 1823

Abstract

The use of traditional biocidal products in cultural heritage has suffered a slowdown due to the risks related to human health and the environment. Thus, many studies have been carried out with the aim of testing innovative and environmentally friendly alternatives. In this framework, this review attempts to provide an overview of some novel potential products with biocidal action, tested to counteract the process of degradation of paper and stone materials due to microbial activity, keeping in mind the sustainability criteria. In particular, we have focused our attention on the testing of nanotechnologies, essential oils, DES (deep eutectic solvents) with low toxicity, and colloidal substances for conservation purposes. Full article

(This article belongs to the Special Issue Heritage Conservation and Restoration: Surface Characterization, Cleaning and Treatments)

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