Among innovative gel formulations for metal conservation, a sustainable organogel based on bioderived polyhydroxybutyrate (PHB), ethyl lactate (EL) and chelating agents has been lately explored, bringing promising results. However, since ligands are usually found in the form of aqueous solutions, both the hydrophobicity of PHB and the not ideal mixture of EL in water should be considered. In this regard, we have developed a PHB-EL organo-gel, containing the chelating water solution in the form of a water-in-oil (W/O) Pickering emulsion stabilized by hydrophobized halloysite clay nanotubes (HNTs). The HNTs hydrophobization has been achieved by selective functionalization of outer surface with a cationic surfactant (hexadecyltrimethylammonium bromide). The stabilization mechanism of hydrophobized nanotubes to the inverse Pickering emulsion gels has been studied by combination of several methods, including morphological analysis, surface characterization and rheology. Then, the removal capacity of the gel systems toward corrosion layers from a copper substrate has been tested. Both the cleaning efficiency and the release of residues on the treated surfaces have been analyzed. A controlled cleaning has been obtained through the systematic regulation of the gel application time. Therefore, this work proposes an optimization of the previously studied organo-gel, obtaining a system with a more homogeneous structure due to the action of W/O Pickering emulsion.

Silver has been widely used for art and heritage objects throughout history, due to its excellent ductility, malleability and brilliant metallic lustre. However, silver objects tarnish over time and must be regularly treated to maintain their appearance. In conservation and heritage studies, naturally or artificially aged silver mock-ups are often used to simulate the tarnishing conditions of valuable historical silver objects. Over the last few decades, many research groups have proposed different aging protocols. In this paper, we reviewed the silver aging protocols employed in recent studies in the field. Although the chemistry-based aging methods are most widely used, issues regarding alterations of the tarnish stratigraphy and negative influences on environment and operator safety should not be neglected. This review aims to provide important references for conservators, scientists and researchers to select safe and suitable aging methods for building their own mock-up systems, and to encourage the development of more sustainable aging protocols for future conservation of historical silver objects.

We present a preliminary study of the cleaning of artificially tarnished silver mock-ups with several greener materials, including sodium glycinate, ethylenediamine-N,N'-disuccinic acid (EDDS), saponin, and deep eutectic solvents (DESs), in comparison to a commercial silver polish product. While sodium glycinate, EDDS and saponin did not show substantial cleaning effects on light silver tarnish, a two-step method combining (i) oxidative DESs and (ii) sodium glycinate-based suspension proved effective for the removal of heavy tarnish. However, observations via colorimetry, interferometry microscopy, optical microscopy, and scanning electron microscopy showed that this two-step method could lead to surface roughening. While clear scratches and over-polishing issues were observed on coupon surfaces cleaned by the commercial silver polish product, the use of a slurry composed of sodium glycinate, citric acid, glycerol and water resulted in optimal cleaning effects, despite its relatively low cleaning rate. (c) 2025 The Authors. Published by Elsevier Masson SAS. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/)

Due to the high values of historical silver artefacts, artificially aged mock-ups are often used for the development of conservation concepts and treatments in the field of conservation and heritage study. However, some chemicals used in recent aging methods have the risks of being toxic and environmentally harmful. We have tested and improved green aging protocols based respectively on boiled egg white and albumin solution on both sterling silver and pure silver coupons. The artificially created tarnish layers on the coupons showed high homogeneity and reproducibility. We identified the successive phases formed on the sterling silver coupons during the aging process with albumin solution through X-ray diffraction analysis: (1) stromeyerite (AgCuS), (2) coexistence of stromeyerite, jalpaite (Ag3CuS2) and sub-sulphide (Ag8S), (3) intermediate phases progressing towards Ag and Cu sulphides. Raman spectroscopy confirmed that adapting the quantity of reagents and exposure time during the aging process resulted in tarnish composition close to that observed on naturally tarnished reference objects. Changes in the surface morphology of the coupons were monitored by optical microscopy and scanning electron microscopy. While sulphidation dominated the tarnishing process, we observed that albumin solution aged samples showed an initial predominance of oxidation. Surface microstructures consisting of islands or rings of various sizes were observed on several albumin solution aged coupons. Measurements via Kelvin probe force microscopy and atomic force microscopy showed that the formation of these structures was linked to the accumulation of corrosion products.

Hyperspectral imaging (HSI) provides high-resolution recording of the spectral information at every spatial point (pixel) of an object throughout a contiguous range of wavelengths. This paper reports an attempt at exploring the application of HSI in transmittance mode for the identification and quantification of corrosion in transparent historical glass, which is difficult to identify by visual inspection. This was done using model glass samples mimicking historical composition and subjected to artificial ageing in the presence of volatile organic compounds. Hyperspectral images of unaged and aged glass samples were recorded with two cameras covering visible and near infrared (VNIR, 400–1000 nm) and short-wave infrared range (SWIR, 1000–2500 nm) using a custom-made HSI set-up in transmission mode. The HSI data were further processed to classify and visualize corrosion in different ageing environments and ageing periods. The results show that HSI can be employed as a valuable tool to assess glass corrosion at early stages, especially by analysing the SWIR spectral region—which shows the water absorption by the glass matrix due to corrosion.

An innovative green organogel was designed to simultaneously tackle inorganic compounds (i.e., iron corrosion) and organic substances (i.e., acrylic coatings) as undesired materials possibly present on the surface of altered indoor metal artworks. Poly-3-hydroxybutyrate (PHB), ethyl lactate (EL), and deferoxamine B (DFO) were employed in the formulation as thickening agent, organic solvent, and complexing agent, respectively, aiming to propose a sustainable and less harmful chemical cleaning method for metal care. The components were selected because they are bio-sourced, renewable, biodegradable, and non- or low-toxic materials. A multi-modal protocol of analysis was carried out to characterise the newly designed PHB-EL-DFO organogel. The cleaning performance of the novel formulation was assessed on mild steel mock-ups presenting both corrosion and organic coating to be removed. The conducted multi-analytical approach verified that the PHB-EL-DFO gel was able to tackle the two undesired materials simultaneously in an adjustable and easy-to-use way thanks to a modular application.

Lacquered brass objects are widely present in scientific and technical heritage collections. Localized atmospheric corrosion occurs on the metal when the coating fails to play its protective role. Although lacquered brass objects are not necessarily endangered by this phenomenon, the presence of dark, unpleasant corrosion spots alters the surface appearance, affecting the readability of the objects. Conservators are therefore frequently asked to clean these surfaces. We hereby present the results of a study conducted in the framework of the CleanLaB (Cleaning of Lacquered Brass) project at the Haute Ecole Arc of Neuchâtel for the cleaning of lacquered brass. This work investigates the effects of several gelled cleaning systems applied on artificially aged, lacquered brass samples to remove the corrosion products without affecting the integrity of the coating. The performance of complexing agents commonly used in conservation was compared on lacquered brass mock-ups coated with shellac resin by means of multiple non-invasive characterization and imaging techniques. The tests included conventional complexing agents like sodium citrate and disodium ethylenediaminetetraacetic acid, as well as a bio-originated system based on deferoxamine, a microbial metal chelator investigated as a green alternative in cleaning formulations.

Jean Dunand (1877-1942) was a European artist internationally appreciated at his time for his innovative Art D & eacute;co housewares made of hammer-beaten copper-based alloys, known as dinanderie. Still uncertain was the nature of the constituting materials; therefore, for the first time, three objects, namely, a bowl, a trinket bowl and a vase, were the target of a multi-modal work of characterisation. Mobile or benchtop X-ray fluorescence, Fourier-transform infrared (FTIR) and Raman spectroscopies were used to adapt the analyses to the shape and size of the artefacts. Elemental analysis verified that the vase consisted of brass Cu70Zn30, whereas the bowl and the trinket bowl were made of nickel silver Cu70Zn19Ni11. The black finishing present on all the artefacts was related to tenorite by Raman spectroscopy, ascribing the patina to an intentional artist's willing and not to spontaneous tarnishing processes. Metal soaps of copper and zinc were documented as degradation products by FTIR spectroscopy. The drawings adorning the vase and the trinket bowl were identified as silver-based, contrary to what was hypothesised by conservators (i.e., tin-based) due to conventional Dunand's inlaying technique. Besides single-point analysis, Raman mapping was performed in-situ, applying for the first time a Virsa (TM) Raman Analyser (Renishaw) in the field of cultural heritage. The fibre-optic-coupled instrument allowed to comply constantly with the artefacts' geometry thanks to the modular probe and the motorised focus-tracking stand. The synergic combination of elemental and vibrational analyses resulted successful, providing new and unique information on artist's technique in view of possible restoration interventions.

In the field of cultural heritage, the use of natural gels is rising for the application of active agents. Here, two natural polymers are assessed: agar, a pioneer hydrogel for conservation treatments, and chitosan, a rather novel and metal-binding gel. For chitosan, a state-of-the-art based formulation (CS–ItA–LCys) is evaluated as it was reported for silver-complexing properties. It is evaluated whether these polymers can withstand the addition of the chelating compound deferoxamine, which is a bacterial siderophore. This allows for the obtainment of completely bio-sourced gel systems. A Fourier-transformed (FT) infrared spectroscopy characterization is performed, completed with rheological measurements and Cryo-Scanning Electron Microscopy (cryo–SEM) to investigate the physico–chemical properties of the gels, as well as their interaction with deferoxamine. Both polymers are also tested for their inherent complexing ability on silver ions using FT–Raman spectroscopy. A multi-analytical comparison shows different microstructures, in particular, the presence of a thick membrane for chitosan and different mechanical behaviors, with agar being more brittle. Neither hydrogel seems affected by the addition of deferoxamine; this is shown by similar rheological behavior and molecular structures in the presence or absence of the chelator. The intrinsic abilities of the chitosan formulation to make silver complex are demonstrated with the observation of two peaks characteristic of Ag–S and Ag–O bonds. Agar and chitosan are both proven to be reliable gels to act as carriers for bio-based active agents. This paper confirms the potential asset of the chitosan formulation CS–ItA–LCys as a promising gel for the complexation of soluble silver.

This article discusses the value of ethnographic objects in museums and collections, and the challenges of preserving them due to their complex composition and poly-materiality. Specifically, the study focuses on the formation of metal soaps on objects made of metal in contact with leather or wood parts. The study proposes a collaborative approach between conservators and scientists to identify and understand the metal soaps present on a selection of objects from the Ethnographic Museum at the University of Zurich. The authors wish to raise awareness about material alteration in ethnographic collections and museum contexts and to promote communication between different actors in the field, while enabling conservation professionals to confirm the formation of a class of degradation products in the absence of specific analytical techniques.

One of the most challenging types of artifact occurring within museum collections is unstable chloride-contaminated archaeological iron. A high chloride concentration causes cracking, flaking and leads to full mineralization, in effect making objects fragile. Consequently, removal of chloride ions plays a key role in stabilization treatment, while preserving the integrity of the corroded iron object. Despite the variety of stabilization methods, all have significant disadvantages, including a lack of sustainability. Within the framework of the Horizon Europe project GoGreen the potential of microbial biosorption to stabilize archaeological iron artefacts is being investigated. Dry biomass of the fungi Meyerozyma sp. and Saccharomyces cerevisiae was studied to remove chloride ions. Preliminary tests were carried out on artificially-aged steel samples. To assess the activities of the microorganisms' functional groups and biosorption capabilities as a potential green stabilization treatment, analytical techniques including FTIR, Raman spectroscopy, and SEM-EDX were used. The results demonstrate two promising paths for the development of green stabilization treatments based on fungal biomass: passive adsorption into the cell wall and conversion of reactive corrosion products into more stable compounds. The use of microbial biomass opens up promising perspectives for the development of more sustainable solutions in archaeological iron stabilization, while avoiding the generation of toxic waste in our environment. Uno de los tipos de artefactos m & aacute;s desafiantes que se encuentran en las colecciones de los museos es el hierro arqueol & oacute;gico inestable contaminado con cloruro. Una alta concentraci & oacute;n de cloruro provoca grietas, descamaci & oacute;n y conduce a una mineralizaci & oacute;n completa, lo que de hecho vuelve los objetos fr & aacute;giles. En consecuencia, la eliminaci & oacute;n de iones cloruro juega un papel clave en el tratamiento de estabilizaci & oacute;n, preservando al mismo tiempo la integridad del objeto de hierro corro & iacute;do. A pesar de la variedad de m & eacute;todos de estabilizaci & oacute;n, todos tienen desventajas importantes, incluida la falta de sostenibilidad. En el marco del proyecto GoGreen de Horizonte Europa, se est & aacute; investigando el potencial de la biosorci & oacute;n microbiana para estabilizar artefactos arqueol & oacute;gicos de hierro. Biomasa seca de los hongos Meyerozyma sp. y Saccharomyces cerevisiae fue utilizada para eliminar iones cloruro. Se llevaron a cabo pruebas preliminares con muestras de acero envejecidas artificialmente. Para evaluar las actividades de los grupos funcionales de los microorganismos y las capacidades de biosorci & oacute;n como posible tratamiento de estabilizaci & oacute;n verde, se utilizaron t & eacute;cnicas anal & iacute;ticas que incluyen FTIR, espectroscop & iacute;a Raman y SEM-EDX. Los resultados demuestran dos caminos prometedores para el desarrollo de tratamientos de estabilizaci & oacute;n ecol & oacute;gicos basados en biomasa f & uacute;ngica: la adsorci & oacute;n pasiva en la pared celular y la conversi & oacute;n de productos reactivos de corrosi & oacute;n en compuestos m & aacute;s estables. El uso de biomasa microbiana abre perspectivas. prometedoras para el desarrollo de soluciones m & aacute;s sostenibles en la estabilizaci & oacute;n del hierro arqueol & oacute;gico. evitando al mismo tiempo la generaci & oacute;n de residuos t & oacute;xicos en nuestro entorno.

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.

Metal soaps, the organic salts resulting from the interaction of fatty acids and metal cations, arouse interest in the scientific field because of their versatility in a great range of chemical applications as well as because of the mechanism of their formation during degradation processes. This article presents a review of the synthetic pathways used to produce metal soaps, their relevant physico-chemical properties, and how these reflect in their applications. Common industrial uses of metal soaps are reported, with a particular focus on those applications, such as cosmetics, paints, and coatings, that have an impact on the cultural heritage field. In addition, the occurrence of metal soaps in cultural heritage studies is presented, ranging from archaeological and ethnographic artefacts to fine art objects, and discussed per class of materials. An overview of the presence or absence of metal soaps in historical artefacts due to the interaction of metal parts or mineral pigments with fatty acids is given herein. This collection shows a variety of situations in which metal soaps—particularly lead, zinc and copper soaps—can form on composite objects made of different materials such as wood, leather and fatty-acid-containing materials (e.g., waxes), in the presence of metal, metal alloys or pigments.

The research study is aimed to design innovative bio-gel formulations able to tackle altered historical metal artworks in a green and sustainable perspective. The target of the research is the removal of undesired or altered materials of both inorganic (i.e., corrosion and tarnishing) and organic nature (i.e., protective coatings). The designed gel systems are initially assessed on mock-ups. Iron-, copper- and silver-based substrates, chosen as mostly present in historical metal collections, are chemically aged to form corrosion on the surface. Alternatively, they are coated with organic protectives (i.e., acrylic and nitrocellulose varnish) that are mostly used for indoor metal care. After multi-modal analytical assessment to check the action and safety of the gels on the metal mock-ups, the developed solutions are applied on real cases, thanks to the strong and fruitful collaboration with curators and conservators of metal artworks.

Bioderived alternatives to commonly used complexing agents for the cleaning of iron artworks are sought for their natural origin and better biodegradability. Indeed, complexing agents currently used for the removal of undesired corrosion products from iron artworks can be difficult to control and their environmental impact is often overlooked. This paper studies the use of siderophores, focusing on the ability of one of them, deferoxamine, to be employed as an active agent loaded in polysaccharides hydrogels, on corrosion phases. Preliminary tests were conducted on artificially aged steel samples and further studies were performed on naturally corroded steel to assess the most performing application parameters. Long-term behavior of cleaned surface was assessed. Cleaning outcomes were compared with those obtainable with disodium ethylenediaminetetraacetic acid using optical microscopy, colorimetry and atomic absorption spectroscopy as well as Infrared and Raman micro-spectroscopies. Among the different gelling agents evaluated, agar applied when hot and gellan gum prepared at room temperature were the most effective gel formulations and agar left few residues over the treated surfaces. The protocol was then tested on altered steel artifacts belonging to heritage institutions in France. Encouraging outcomes in the removal of iron corrosion phases with green approaches are here presented.

An innovative bio method was investigated to extract harmful iron and sulfur species from waterlogged wood samples. The method was compared with a chemical treatment. Both approaches were applied on lacustrine and marine samples, from different wood genera, to evaluate the versatility of the proposed bio method. Non-invasive and non-destructive methods were carried out to investigate both bio-based and chemical treatments. The result was that some wood genera were more affected by the bio approach, with a clear distinction between lacustrine beech and pine against oak and lime wood species. The chemical approach showed potential harm for the wooden structure, with acidic pH values and an increase of maximum water content, both implying degradation of the wood structure. In terms of extraction, no iron or sulfur products were detected by Raman spectroscopy on biologically treated samples, in agreement with extraction rates calculated. It was also suggested that iron bonded to wood was extracted with the chemical approach, and calcium content affected by both approaches.