Search Results (13)

The early detection of bronze disease is a significant challenge not only in conservation science but also in various industrial fields that utilize copper alloys (i.e., shipbuilding and construction). Due to the aggressive nature of this corrosion pathway, developing methods for its early detection is pivotal. The presence of copper trihydroxychlorides is the main key indicator of the ongoing autocatalytic process. Commonly used for pigment identification, reflectance imaging spectroscopy (RIS) or fiber optics reflectance spectroscopy (FORS) was recently employed for mapping atacamite distribution in extended bronze corrosion patinas. In this work, we detected the onset of bronze disease using visible–near-infrared (VIS-NIR) multispectral reflectography, which allowed for disclosing features that were poorly detectable to the naked eye. The image cube was analyzed using the spectral correlation mapper (SCM) algorithm to map the distribution of copper trihydroxychlorides. FORS and Raman spectroscopy were employed to characterize the patina composition and validate RIS data. A set of bronze samples, representative of Florentine Renaissance workshops, was specifically realized for the present study and artificially aged at different corrosion stages. Full article

Hypogea are natural or artificial spaces located underground often of great interest from an anthropological, archeological, religious, artistic, or historic point of view. Due to their features, these environments usually present conservative problems and biological colonization could be considered as one of the main threats. The present three-year study was carried out by specialists of the Central Institute for Restoration of Rome (ICR) in the hypogeous site preserved in the Roman Archeological Museum of Positano (Positano MAR) and focused on characterizing biological alterations present on the mural paintings; setting up efficient strategies and protocols for biodeterioration control; and monitoring the efficacy of direct and indirect interventions. Patinas with different morphologies were analyzed through microscopic observations, cultural analyses and next-generation sequencing. The results proved that the alterations comprised a great variety of microorganisms forming very distinct communities, differently distributed over space and time. The main taxa represented were bacteria of phyla Pseudomonadota and Actinomycetota, fungi belonging to the genus Fusarium and Gliocladium, and algae of the genus Chlorococcum. Preservation protocols were set up considering the alterations’ composition and included the application of biocides, limiting daily temperature changes, decreasing illuminance values on painted surfaces, and the screening of natural light sources. Full article

The study of characterisation and production of artificial patinas plays a key role in the field of cultural heritage. In particular, artistic patinas should be considered as an integral part of the artworks, as they are deliberately produced by artists and metalworkers as a part of their artistic design. Therefore, it is important to achieve a good knowledge of their composition and corrosion behaviour in order to setup and perform optimal conservation strategies for their preservation. In addition, the possibility of realising laboratory patinas that are as representative as possible of natural corrosion layers is important for the realisation of laboratory specimens which can be used as reliable model systems (mock-ups) for the study of degradation mechanisms and conservative treatments. For this work, both artistic and laboratory patinas have been considered and investigated. In particular, six different artistic patinas produced by Fonderia Artistica Battaglia were characterised. Moreover, a series of laboratory patinas was produced according to chemical procedures adapted from those already reported in the literature. The patina morphology was evaluated by stereomicroscopy observations, their composition was analysed by means of FTIR and XRD analysis and their corrosion behaviour was evaluated by LPR and EIS measurements. Finally, the LPR and EIS analysis have pointed out the low protection provided by the corrosion layers of artistic patinas. In regard to laboratory patinas, the optimized procedures of production were found to be effective for the realization of the main corrosion products of copper-based surfaces. From an electrochemical point of view in particular, quite different electrochemical behaviours were observed on artificial corrosion layers with the same chemical composition. Full article

Copper trihydroxychlorides, which are known as “bronze disease”, are dangerous corrosion products that compromise the stability and conservation of bronze sculptures. Here, we performed artificial patina corrosion experiments on quaternary bronze (Cu-Zn-Sn-Pb) to examine the corrosion behavior of the chloride patina commonly found in bronze objects in marine environments. The chromaticity and reflectance of the patina in the context of the corrosion products indicate that copper trihydroxychloride, which is commonly found in a single color in marine environments, was produced early in the corrosion experiment. Furthermore, the corrosion of bronze had different effects on the alloying elements, contrary to pure copper corrosion. The chloride patina formed a single patina layer of copper trihydroxychlorides. This patina layer was divided into the outer porous powder and inner uniform layers. Furthermore, the interaction of oxygen in the atmosphere with the corrosion layer and internal oxidation of tin in the alloy promoted powdering. These results provide important basic data for research on sculpture conservation and corrosion characteristics, such as changes in color, chemical composition, and corrosion products on the patina surfaces of outdoor bronze sculptures. Full article

Copper alloys interact with air pollutants to form corrosion products and, consequently, a patina on outdoor bronze sculptures. In this study, corrosion experiments were conducted to clarify the corrosion behaviors of artificial sulfide patina in an urban–industrial environment on a quaternary bronze alloy (Cu–Zn–Sn–Pb) with a composition and metallurgical properties similar to those of outdoor bronze sculptures. The correlation between the chromaticity and reflectance of the patina revealed increasing brochantite with the corrosion of the patina and an association between the chromaticity a^* and patina growth. Cuprite and brochantite were distinguished, and the point at which brochantite covered the patina surface was determined. The quantitative changes in brochantite were mainly influenced by physical causes such as the crystal size and patina layer thickness as well as by Cu²⁺ ions working as color formation ions moving to the outermost layer. Atmospheric corrosion of the alloy resulted in reduced Cu and Zn contents and increased Sn and Pb contents. The patina consisted of brochantite in the outermost layer and cuprite and cassiterite in the inner layers. These findings should clarify corrosion characteristics such as the surface color, composition, and changes in corrosion products of outdoor bronze sculptures and contribute toward their preservation. Full article

The influence of plasma-reduction treatment on iron and copper compounds at different oxidation states was investigated in this study. For this purpose, reduction experiments were carried out with artificially generated patina on metal sheets and with metal salt crystals of iron(II) sulfate (FeSO₄), iron(III) chloride (FeCl₃), and copper(II) chloride (CuCl₂), as well as with the metal salt thin films of these compounds. All the experiments were carried out under cold low-pressure microwave plasma conditions; the main focus was on plasma reduction at a low pressure in order to evaluate an implementable process in a parylene-coating device. Usually, plasma is used within the parylene-coating process as a supporting tool for adhesion improvement and micro-cleaning efforts. This article offers another useful application for implementing plasma treatment as a reactive medium in order to apply different functionalities by an alteration in the oxidation state. The effect of microwave plasmas on metal surfaces and metal composite materials has been widely studied. In contrast, this work deals with metal salt surfaces generated from a solution and the influence of microwave plasma on metal chlorides and sulfates. While the plasma reduction of metal compounds commonly succeeds with hydrogen-containing plasmas at high temperatures, this study shows a new reduction process that reduces iron salts at temperatures between 30 and 50 °C. A novelty of this study is the alteration in the redox state of the base and noble metal materials within a parylene-coating device with the help of an implemented microwave generator. Another novelty of this study is treating metal salt thin layers for reduction purposes in order to provide the opportunity to include subsequent coating experiments to create parylene metal multilayers. Another new aspect of this study is the adapted reduction process of thin metal salt layers consisting of either noble or base metals, with an air plasma pre-treatment prior to the hydrogen-containing plasma-reduction procedure. Full article

The bronze patina is aesthetically pleasing and enhances the corrosion resistance of the metallic object. This corrosion product layer can develop naturally, through aging or artificially. However, artificial methods require substances that are hazardous to human health and the environment. In this study, a sustainable approach to patina development, based on the anodic polarization of a 85.5Cu-4.2Pb-4.5Sn-5.7Zn copper alloy immersed in 0.1 M NaCl + 0.01 M NaHCO₃ were characterized using polarization curves, chronoamperometry, electrochemical impedance spectroscopy, electrochemical noise measurements, X-ray diffraction, and scanning electron microscopy. The results indicate that the anodic potential modifies the current density as well as the diffusion coefficient of oxygen associated with a thicker corrosion product layer. Electrochemical Impedance spectroscopy and electrochemical noise show that the porous behaviour and corrosion resistance increases as the potential becomes more anodic due to the formation of a protective layer. This behaviour corresponded with the results acquired by chronoamperometry. The surface characterization shows that the potential applied changes the surface morphology and composition of the corrosion products, being identified the crystalline phases of nantokite and atacamite although Cu, Cl, O, Zn, and Pb elements were also detected. Full article

Copper alloy artworks are particularly subjected to chloride attack, which may trigger bronze disease. Therefore, early identification of the phenomenon is crucial in order to stabilize the reactive copper chloride (CuCl) and remove the harmful corrosion products (atacamite and polymorphs). Confocal Raman Microspectroscopy (CRM) has proven to be effective for the detection of small amounts of atacamite, ascribable to the initial phases of corrosion. The handling of bronze artworks is often difficult or even impossible given their large size and weight, and sampling is not always allowed, making the use of portable instruments mandatory for on-site diagnostics. This paper proposes a method for the early detection of corrosion using non-invasive approaches. In this work, we present the results obtained from a set of artificially aged bronze samples with a suite of either laboratory (bench-top) or field (portable/transportable) instruments with the aim of highlighting their characteristics and performances in the diagnosis of bronze disease. Raman spectroscopy, Fiber Optics Reflectance Spectroscopy (FORS), Optical Coherence Tomography (OCT), and Scanning Electron Microscopy (SEM) were applied for chemical and morphological characterization of the samples. Full article

The new bronze objects of art are almost always patinated before their exposure outdoors or indoors. Among the many patination methods used by practitioners, sulphide patination is one of the most common techniques. The aim of this work is to examine the corrosion behaviour of sulphide patinated bronzes under various aging conditions, including continuous immersion in simulated urban rain, alternating wet/dry cycles, and exposure to corrosion chamber with NO₂ gas. The study was conducted on three types of bronzes with varying tin content. Corrosion characterisation of patinated bronze samples was performed by the means of electrochemical impedance spectroscopy and polarization measurements. Chemical composition and morphology of sulphide patinated bronze surface was examined by infrared spectroscopy and scanning electron microscopy. Obtained results show that freshly patinated bronze surfaces exhibit low corrosion resistance that gradually improves over time. An increase in corrosion resistance strongly depends on aging conditions, and it appears to be the highest under continuous immersion conditions. Full article

The article deals with the preparation of artificial copper pigment based on brochantite. The pigment was prepared by slow additions of sodium hydroxide solution into the solution of copper sulphate. The studied parameters were addition rate, solutions concentrations, ferrous ion addition, and filtration time. The prepared pigments were evaluated by means of X-ray diffraction and spectrophotometry. Subsequent pigment immobilization in an acrylate varnish was also studied. Observed parameters were influenced by solvent type, mechanical or chemical dispersion, and natural aging in an aggressive outdoor atmosphere. Pigment containing varnishes were evaluated by means of spectrophotometry, optical profilometers, and pull-off test. Slow hydroxide addition allows the formation of brochantite pigment. Fast filtration limits backward pigment decomposition. Ferrous ion improves pigment color closer to natural copper patina. The ideal immobilization procedure includes ethylacetate as a solvent and mechanical dispersion. The varnish filled with pigment provides sufficient adhesion to the metallic copper substrate as well as long-term color stability in the outdoor atmosphere. Full article

The requirements for the formation of a protective patina on conventional weathering steels (WS) are well known in the scientific literature related to civil structures. However, these criteria are not always given due consideration when WS is used in cultural heritage, as in the case of sculptural work. An artificial patina was produced simulating artists’ working procedures using a direct patination technique, applying a solution of 10% H₂SO₄ on WS specimens. These were exposed for two years in the urban atmosphere of Madrid along with weathering steel specimens without artificial patina, called natural patina. The patinas generated have been analyzed using colorimetry, micro-Raman spectroscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD) and thickness measurements.The artificial patina color formed hardly differs from the color that the natural patina acquires from practically the beginning of its formation in the atmosphere of Madrid. After two years, the atmospheric corrosion rate of patinated WS is lower than 6 µm/year. The sulfuric acid treatment accelerates the protective ability of the patina with respect to the natural patina according to the ratio goethite to lepidocrocite (α/γ). Chromium-rich goethite is located in the inner part of the artificial patina as well as chromium-rich ferrihydrite. Ferrihydrite may act as a precursor of nanophasic goethite. Full article

Natural copper patina is usually formed over several decades. This work investigates the possibility of obtaining a stable artificial patina based on brochantite in a more reasonable time. The patination process was based on patina formation from a humid atmosphere containing sulphur dioxide. The studied parameters were humidity (condensation and condensation/drying), sulphur dioxide concentration (4.4–44.3 g·m⁻³) and surface pre-treatments (grinding, pre-oxidation and pre-patination) prior to the patination process. Samples were evaluated by mass change, digital image analysis, spectrophotometry, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS) and X-ray diffraction (XRD). A resistometric method was employed in order to observe the patina formation continuously during the exposure. Conditions inside the chamber were monitored during the exposure (pH of water and concentration of SO₂ in gaseous phase). According to XRD, it was possible to deliberately grow a brochantite patina of reasonable thickness (approx. 30 µm), even within a couple of days of exposure. The drying phase of the condensation cycle increased the homogeneity of the deposited patina. Formation kinetics were the fastest under a condensation/drying cycle, starting with 17.7 g·m⁻³ sulphur dioxide and decreasing dosing in the cycle, with an electrolyte pH close to 3. The higher sulphur dioxide content above 17.7 g·m⁻³ forms too aggressive a surface electrolyte, which led to the dissolution of the brochantite. The pre-oxidation of copper surface resulted in a significant improvement of patina homogeneity on the surface. Full article

In this study, we demonstrate a rapid treatment method for producing a needle-like nanowire structure on a hot-dip galvanized sheet at a temperature of 50 °C. The processing method involved only supercritical carbon dioxide and water to induce a reaction on the zinc surface, which resulted in growth of zinc hydroxycarbonate nanowires into flower-like shapes. This artificial patina nanostructure predicts high surface area and offers interesting opportunities for its use in industrial high-end applications. The nanowires can significantly improve paint adhesion and promote electrochemical stability for organic coatings, or be converted to ZnO nanostructures by calcining to be used in various semiconductor applications. Full article