Testing of the siderophore deferoxamine amended in hydrogels for the cleaning of iron corrosion

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

Biologically Derived Gels for the Cleaning of Historical and Artistic Metal Heritage

In the general global rise of attention and research to seek greener attitudes, the field of cultural heritage (CH) makes no exception. In the last decades, an increasing number of sustainable and biologically based solutions have been proposed for the protection and care of artworks. Additionally, the safety of the target artwork and the operator must be kept as core goals. Within this scenario, new products and treatments should be explored and implemented in the common conservation praxes. Therefore, this review addressing metal heritage is aimed to report biologically derived gel formulations already proposed for this specific area as reliable tools for cleaning. Promising bio-gel-based protocols, still to be implemented in metal conservation, are also presented to promote their investigation by stakeholders in metal conservation. After an opening overview on the common practices for cleaning metallic surfaces in CH, the focus will be moved onto the potentialities of gel-alternatives and in particular of ones with a biological origin. In more detail, we displayed water-gels (i.e., hydrogels) and solvent-gels (i.e., organogels) together with particular attention to bio-solvents. The discussion is closed in light of the state-of-the-art and future perspectives

Biopulitura di artefatti metallici in collezioni storiche

Un approccio interdisciplinare innovativo, che fonde le scienze naturali e la conservazione dei beni culturali, è il principio cardine dei temi di ricerca sviluppati fra la Haute Ecole Arc Conservation Restauration e l’Università di Neuchâtel in Svizzera. La ricerca mira a formulare bio-gel innovativi, in grado di trattare la superficie alterata di opere in metallo in un’ottica verde e sostenibile. Grande attenzione è rivolta alle componenti dei sistemi gel (agenti addensanti, solventi ed agenti chelanti), al fine di selezionare solo materiali di origine biologica, biodegradabili, e non tossici. In particolare, in questo contributo vengono presentate le potenzialità di agenti complessanti di origine naturale denominate “siderofori”, quale possibile alternativa sostenibile ed efficace rispetto alle sostanze sintetiche e tossiche, comunemente impiegate nella conservazione dei metalli (es. sale di sodio acido etilendiamminotetraacetico - Na2EDTA). In parallelo, i bio-solventi sono esplorati come metodo alternativo e più ecologico per la rimozione di rivestimenti organici protettivi. Difatti, questa classe di solventi organici deriva da fonti rinnovabili e da naturali processi metabolici di origine microbiologica, e negli ultimi decenni sono attentamente scrutinati per evitare l’utilizzo di solventi nocivi ed inquinanti (es. acetone, acqua ragia) largamente utilizzati nell’industria così come nel campo dei beni in metallo. La ricerca qui presentata è quindi orientata verso la rimozione di materiali indesiderati o alterati sia di natura inorganica (corrosione e tarnishing) che organica (rivestimenti protettivi). I sistemi gel sono inizialmente valutati su mock-up metallici. I substrati a base di ferro, rame e argento, scelti in quanto maggiormente presenti nelle collezioni storiche di oggetti in metallo, sono invecchiati chimicamente per corroderne la superficie. In alternativa, sono rivestiti con protettivi organici (ad esempio, vernici acriliche ed alla nitrocellulosa) ampiamente utilizzati per la cura degli oggetti storici in metallo. Dopo una valutazione analitica multimodale atta a verificare l’azione e la sicurezza dei gel sui mock-up metallici, le soluzioni HELIX sono applicate su casi reali, grazie alla stretta e proficua collaborazione con curatori e conservatori di beni artistici in metallo

Biocleaning of historical metal artworks ::innovative green gels amended with microbial derivatives

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

Exploiting Biologically Synthetized Chelators in Conservation ::Gel-based Bio-cleaning of Corroded Iron Heritage Objects

The complexing agents widely 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 compares the efficiency of deferoxamine B (DFO), a siderophore synthetised by the bacterium Streptomyces pilosus, with that of disodium ethylenediaminetetraacetic acid (Na2EDTA) in the removal of iron corrosion phases. Several bio -derived hydrogels were exploited as carriers and preliminary tests were carried ou on naturally aged samples. The investigated parameters included siderophore concentration, treatment duration and potential reapplication, as well as a reliable application protocol. Cleaning efficacy was evaluated using optical microscopy, colourimetry and Raman spectroscopy. The result showed the comparable cleaning efficiency of DFO and Na2EDTA at neutral pH. However, the DFO-hydrogel performed better on iron rust. A frequent renewal of the treatment formulation ensured more effective cleaning. Among the different carriers tested, agar gels applied when hot and gellan gum gels prepared at room temperature were the most effective, and left few residues on the treated surfaces. The methodology was then tested on altered steel artefacts belonging to heritage institutions in Nantes (France). The encouraging outcomes point the way to a more sustainable approach to treating historical iron artworks