Selected Aspects Regarding the Restoration/Conservation of Traditional Wood and Masonry Building Materials: A Short Overview of the Last Decade Findings

A Two-Step Surface Modification Methodology for the Advanced Protection of a Stone Surface

The biodeterioration of the natural surface on monuments, historical buildings, and even public claddings brings to the attention of researchers and historians the issues of conservation and protection. Natural stones undergo changes in their appearance, being subjected to deterioration due to climatic variations and the destructive action of biological systems interfering with and living on them, leading to ongoing challenges in the protection of the exposed surfaces. Nanotechnology, through silver nanoparticles with strong antimicrobial effects, can provide solutions for protecting natural surfaces using specific coupling agents tailored to each substrate. In this work, surfaces of two common types of natural stone, frequently encountered in landscaping and finishing works, were modified using siloxane coupling agents with thiol groups. Through these agents, silver nanoparticles (AgNPs) were fixed, exhibiting distinct characteristics, and subjected to antimicrobial analysis. This study presents a comparative analysis of the efficiency of coupling agents that can be applied to a natural surface with porous structures, when combined with laboratory-obtained silver nanoparticles, in reducing the formation of microbial biofilms, which are a main trigger for stone biodeterioration.

Cementless Compositions for the Restoration of White Stone Based on Lime Binder and Silicon Dioxide

The condition of architectural monuments is directly influenced by various factors, such as anthropogenic, natural, and technological, leading to the degradation of both structures and construction materials, ultimately resulting in irreversible damage. These factors diminish the quality of construction materials, contributing to alterations and the destruction of the appearance and structure of white stone. The primary objective of this research is to develop cement-free compositions for restoring ancient masonry materials. Tests were conducted at the BM Department of VlSU using modern equipment. New material compositions for restoration have been devised, combining lime and silicon dioxide with chemical additives to enhance adhesive and strength properties. Adhesive strength increases by 1.5 times with the addition of white soot (silicon dioxide). Moreover, the incorporation of silicon dioxide positively impacts compressive strength (from 10.6 to 15.6 MPa), surpassing the strength of composites without white soot by 1.5 times. XRD confirms the developed composite's similar phase composition to white stone, supported by optical microscopy and SEM results. Restoration composites based on these compositions exhibit homogeneous structures compatible with white stone and demonstrate high adhesion levels. These results make the proposed compositions promising for white stone restoration, ensuring structural and chemical compatibility with the restored surface.

Application of Inorganic Nanomaterials in Cultural Heritage Conservation, Risk of Toxicity, and Preventive Measures

Nanotechnology has allowed for significant progress in architectural, artistic, archaeological, or museum heritage conservation for repairing and preventing damages produced by deterioration agents (weathering, contaminants, or biological actions). This review analyzes the current treatments using nanomaterials, including consolidants, biocides, hydrophobic protectives, mechanical resistance improvers, flame-retardants, and multifunctional nanocomposites. Unfortunately, nanomaterials can affect human and animal health, altering the environment. Right now, it is a priority to stop to analyze its advantages and disadvantages. Therefore, the aims are to raise awareness about the nanotoxicity risks during handling and the subsequent environmental exposure to all those directly or indirectly involved in conservation processes. It reports the human-body interaction mechanisms and provides guidelines for preventing or controlling its toxicity, mentioning the current toxicity research of main compounds and emphasizing the need to provide more information about morphological, structural, and specific features that ultimately contribute to understanding their toxicity. It provides information about the current documents of international organizations (European Commission, NIOSH, OECD, Countries Normative) about worker protection, isolation, laboratory ventilation control, and debris management. Furthermore, it reports the qualitative risk assessment methods, management strategies, dose control, and focus/receptor relationship, besides the latest trends of using nanomaterials in masks and gas emissions control devices, discussing their risk of toxicity.

A Short Overview of Recent Developments in the Application of Polymeric Materials for the Conservation of Stone Cultural Heritage Elements

Stones are ones of the most ancient natural materials exploited by humans, with different uses, from tools to buildings, that have endured over time in better conditions than other objects belonging to cultural heritage. Given the importance of those silent witnesses of our past, as well as our duty to preserve all parts of cultural heritage for future generations, much effort was put into the development of materials for their consolidation, protection, self-cleaning, or restoration. Protection of ancient stone monuments and objects has gained the interest of researchers in the last decades in the field of conservation of cultural heritage. In this respect, the present paper aims to be a critical discussion regarding potential polymeric materials, which can be used in restorative and conservative approaches for stone materials of cultural heritage importance, against physical degradation phenomena. Recent advances in this area are presented, as well as the current bottle-necks and future development perspectives.

Some Methods for the Degradation-Fragility Degree Determination and for the Consolidation of Treatments with Paraloid B72 of Wood Panels from Icon-Type Heritage Objects

The main objective of this paper is to develop methods for assessing the deterioration of wooden panels of iconic heritage objects and the effectiveness of consolidation treatments, methods that are easy to apply to the field of wood restoration. During the research, four evaluation methods were identified, respectively: the density method, the excessive porosity method, the Brinell hardness method, and the Mark hardness method. Each method was exemplified on five wooden panels (icons), and when needed, degraded specimens were used and/or treated with Paraloid B72. One of the main conclusions of the research is that, although all methods are minimally invasive and do not require cutting of these heritage objects, the applicability of each is done depending on the type of degradation, often requiring a combined analysis between two or several methods. Additionally, the classification of the cultural good in one of the five degrees of embrittlement-degradation help to design a technological flow regarding the treatments of consolidation/restoration of the heritage object.

Density Functional Theory (DFT) as a Nondestructive Probe in the Field of Art Conservation: Small-Molecule Adsorption on Aragonite Surfaces

Humans have incorporated minerals in objects of cultural heritage importance for millennia. The surfaces of these objects, which often long outlast the humans that create them, are undeniably exposed to a diverse mixture of chemicals throughout their lifetimes. As of yet, the art conservation community lacks a nondestructive, accurate, and inexpensive flexible computational screening method to evaluate the potential impact of chemicals with art, as a complement to experimental studies. In this work, we propose periodic density functional theory (DFT) studies as a way to address this challenge, specifically for the aragonite phase of calcium carbonate, a mineral that has been used in pigments, marble statues, and limestone architecture since ancient times. Computational models allow art conservation scientists to better understand the atomistic impact of small-molecule adsorbates on common mineral surfaces across a wide variety of environmental conditions. To gain insight into the surface adsorption reactivity of aragonite, we use DFT to investigate the atomistic interactions present in small-molecule-surface interfaces. Our adsorbate set includes common solvents, atmospheric pollutants, and emerging contaminants. Chemicals that significantly disrupt the surface structure such as carboxylic acids and sulfur-containing molecules are highlighted. We also focus on comparing adsorption energies and changes in surface bonds, which allows for the identification of key features in the electronic structure presented in a projected-density-of-state analysis. The trends outlined here will guide future experiments and allow art conservators to gain a better understanding of how a wide range of molecules interact with an aragonite surface under variable conditions and in different environments.

Recent Developments in the Application of Inorganic Nanomaterials and Nanosystems for the Protection of Cultural Heritage Organic Artifacts

Cultural heritage (CH) represents human identity and evidence of the existence and activities that people have left over time. In response to the action of aggressive degrading factors, different materials have been developed and used to protect cultural heritage artifacts. The discovery of optimal materials for this purpose also raises several problems, mainly related to their compatibility with the support material, the most important aspect being that they must preserve their aesthetic characteristics. In this context, the present review paper aims to provide a critical discussion about the possibilities of using different inorganic nanomaterials and recipes for the conservation of cultural heritage objects of organic nature (such as paper, wood, and other support materials). In addition, also are covered different aspect concerning protection mechanisms and application methods as well as future perspectives in this area.

Bioconservation of Historic Stone Buildings—An Updated Review

Cultural heritage buildings of stone construction require careful restorative actions to maintain them as close to the original condition as possible. This includes consolidation and cleaning of the structure. Traditional consolidants may have poor performance due to structural drawbacks such as low adhesion, poor penetration and flexibility. The requirement for organic consolidants to be dissolved in volatile organic compounds may pose environmental and human health risks. Traditional conservation treatments can be replaced by more environmentally acceptable, biologically-based, measures, including bioconsolidation using whole bacterial cells or cell biomolecules; the latter include plant or microbial biopolymers and bacterial cell walls. Biocleaning can employ microorganisms or their extracted enzymes to remove inorganic and organic surface deposits such as sulfate crusts, animal glues, biofilms and felt tip marker graffiti. This review seeks to provide updated information on the innovative bioconservation treatments that have been or are being developed.

A Multi-Technique Approach to Evaluate the Surface Properties of Heat-Treated Chestnut Wood Finished with a Water-Based Coating

The aim of the present work is to investigate the surface properties and the effect of a water-based coating on chestnut wood (Castanea sativa Mill.), both untreated and thermally treated. Chestnut is very common throughout the Mediterranean region and its wood is widely used as timber, especially in Central Italy, to build window fixtures and doors which have to be decay-resistant, even in historical buildings. Traditional techniques have been used in combination with Hyperspectral Imaging which had never been used before to examine thermally treated wood. Specifically, colour, roughness, micro-hardness, wear and contact angle measurements have been performed on untreated and thermally treated chestnut wood, covered by a commercial water-based coating named Idrolinfo. Hyperspectral analysis has been demonstrated to be appropriate to discriminate the heat treatment and the presence of the water-based product. The applied techniques showed that the best performances are obtained with the 170 °C heat treatment. The water-based coating demonstrated its validity when applied to untreated and heat-treated wood at 140 °C and 170 °C. The main findings showed that chestnut wood increased or maintained its properties if treated at those temperatures without undergoing a major colour change, acquiring good hydrophobicity, both if uncoated or treated with the water-based coating.

Emergence of Polymeric Material Utilising Sustainable Radiation Curable Palm Oil-Based Products for Advanced Technology Applications

In countries that are rich with oil palm, the use of palm oil to produce bio-based acrylates and polyol can be the most eminent raw materials used for developing new and advanced natural polymeric materials involving radiation technique, like coating resins, nanoparticles, scaffold, nanocomposites, and lithography for different branches of the industry. The presence of hydrocarbon chains, carbon double bonds, and ester bonds in palm oil allows it to open up the possibility of fine-tuning its unique structures in the development of novel materials. Cross-linking, reversible addition-fragmentation chain transfer (RAFT), polymerization, grafting, and degradation are among the radiation mechanisms triggered by gamma, electron beam, ultraviolet, or laser irradiation sources. These radiation techniques are widely used in the development of polymeric materials because they are considered as the most versatile, inexpensive, easy, and effective methods. Therefore, this review summarized and emphasized on several recent studies that have reported on emerging radiation processing technologies for the production of radiation curable palm oil-based polymeric materials with a promising future in certain industries and biomedical applications. This review also discusses the rich potential of biopolymeric materials for advanced technology applications.

Gap-Fillers for Wooden Artefacts Exposed Outdoors—A Review

Conservation of wooden artefacts that are exposed outdoors, mainly in open-air museums, is a very complex and difficult issue that aims to preserve both the integrity and aesthetics of valuable objects. Unceasingly subjected to several factors, such as alternating weather conditions and the activities of microorganisms, algae, and insects, they undergo continuous changes and inevitable deterioration. Their biological and physical degradation often results in the formation of gaps and cracks in the wooden tissue, which creates a need not only for wood consolidation, but also for using specialist materials to fill the holes and prevent further degradation of an object. To ensure effective protection for a wooden artefact, a filling material must both protect the wood against further degradation and adapt to changes in wood dimensions in response to humidity variations. A variety of substances, both organic and inorganic, have been used for conservation and gap filling in historic wooden objects over the years. The filling compounds typically consist of two components, of which one is a filler, and the second a binder. In the case of inorganic fillers, plaster has been traditionally used, while the most popular organic fillers were wood powder, wood shavings, and powdered cork. As with binders, mainly natural substances have been used, such as animal glues or waxes. Nowadays, however, due to the lower biodegradability and better physicochemical properties, synthetic materials are gaining popularity. This article discusses the types of filling compounds currently used for gap filling in wooden artefacts exposed outdoors, outlining their advantages and drawbacks, as well as future perspective compounds. It appears that particularly composite materials based on natural polymers deserve attention as promising filling materials due to their high elasticity, as well as similarity and good adhesion to the wooden surface. Their main shortcomings, such as susceptibility to biodegradation, could be eliminated by using some modern, bio-friendly preservatives, providing effective protection for historic wooden artefacts.

Improving the Protective Properties of Shellac-Based Varnishes by Functionalized Nanoparticles

Shellac is a natural varnish still known as one of the most elegant finishes for furniture and musical instruments, and currently used for restoration and refinishing of wooden antiques. However, it displays some limitations such as (i) sensitivity to alcoholic solvents (ii) softness of the coating, and (iii) considerable weathering due to photo- and bio-degradation. Hence, the main aim of this study was to improve the properties of shellac-based finish by introducing functionalized nanoparticles. Two inorganic nano-sized materials were considered: ZnO that was expected to reduce photo- and bio-degradation problems, and ZrO2 that was expected to improve the hardness of the varnish. Nanoparticles were synthesized and treated with a bifunctional silane coupling agent. Both plain and functionalized nanoparticles were extensively characterized using different experimental techniques. Functionalized nanoparticles were grafted on shellac through a reaction involving the epoxy-rings introduced on their surface. The resulting modified varnishes were applied on maple wood specimens according to traditional procedures. Different instrumental techniques and testing methods were used to characterize both nano-sized materials and the corresponding nanocomposites, as well as to evaluate the performance of the new coatings. The investigated composite materials display the same aesthetic appearance as plain shellac, while some other properties were improved. In particular, both nanocomposites are distinctly less soluble in alcohols than plain shellac and display antifungal properties. Moreover, coating containing functionalized ZnO nanoparticles displays photo-protection behavior, while shellac modified with ZrO2 nanoparticles exhibits a higher hardness when compared to the traditional varnish.

Non-Destructive Detection of Pentachlorophenol Residues in Historical Wooden Objects

Wood is a natural polymeric material that is an important constituent of many heritage collections. Because of its susceptibility to biodegradation, it is often chemically treated with substances that can be harmful to human health. One of the most widely used wood preservatives was pentachlorophenol (PCP), which is still present in museum objects today, although its use has been restricted for about forty years. The development of non-destructive methods for its determination, suitable for the analysis of valuable objects, is therefore of great importance. In this work, two non-destructive solid-phase microextraction (SPME) methods were developed and optimized, using either headspace or contact mode. They were compared with a destructive solvent extraction method and found to be suitable for quantification in the range of 7.5 to 75 mg PCP/kg wood at room temperature. The developed semi-quantitative methods were applied in the wooden furniture depot of National Museum of Slovenia. PCP was detected inside two furniture objects using headspace mode. The pesticide lindane was also detected in one object. The indoor air of the depot with furniture was also sampled with HS SPME, and traces of PCP were found. According to the results, SPME methods are suitable for the detection of PCP residues in museum objects and in the environment.

A User-Friendly Tool to Characterize the Moisture Transfer in Porous Building Materials: FLoW1D

This paper presents a user-friendly tool—FLoW1D (One-Dimensional Water Flow)—for the estimation of parameters that characterize the unsaturated moisture transfer in porous building materials. FLoW1D has been developed in Visual Basic for Applications and implemented as a function of the well-known Microsoft Excel© spreadsheet application. The aim of our work is to provide a simple and useful tool to improve the analysis and interpretation of conventional tests for the characterization of the hygric behavior of porous building materials. FLoW1D embraces the conceptual model described in EN 15026 for moisture transfer in building elements, and its implementation has been verified and validated correctly. In order to show the scope of the code, an example of an application has been presented. The hygric characterization of the limestone that is mostly employed in the Cathedral of Santa Maria and San Julian in Cuenca (Spain) was conducted based on an analysis of the conventional water absorption by capillarity tests (EN 15801).