Preservation of Metallic Cultural Heritage

doi:10.1016/B978-044452787-5.00172-4

Reference Module in Materials Science and Materials Engineering

Shreir's Corrosion

Volume 4, 2010, Pages 3307-3340

https://doi.org/10.1016/B978-044452787-5.00172-4 Get rights and content

The ethics and rationale that underpin the preservation of cultural metals are outlined and their influence on the conservation process is examined via a review of treatment strategies illustrated by example. Citing current and formative research into treatments illustrates the role of corrosion science in conservation. Topics that merit further study and research are highlighted wherever appropriate.

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Cited by (38)

Protective coatings for metallic heritage conservation: A review
2023, Journal of Cultural Heritage
The study and development of protective coatings for metallic heritage is a topic of continuous research, with the main objective of ensuring the protection of the object for as long as possible. The limitations imposed by conservation and restoration criteria, together with the diversity of factors involved, make metal protection an unresolved subject. In addition to the nature of the protective coating, different factors can influence its effectiveness, which may mean that one type of protection performs well in a certain environment or on one type of metal and not on another. Therefore, the main objective of this work is to provide a comprehensive review of the coatings used in the conservation of metallic heritage from the last decades to the present day. Studies carried out on coatings of the different families according to their nature/composition (waxes, acrylic resins, nitrocellulose lacquers, fluoropolymers, carboxylates, organosilanes compounds and other coatings) have been reviewed, considering the substrate, application, weathering and examination.
Metallurgical characterization of a failed A106 Gr-B carbon steel welded condensate pipeline in a petroleum refinery
2022, International Journal of Pressure Vessels and Piping
Citation Excerpt :
During corrosion of iron, the pipe surface in the presence of dissolved oxygen can be gradually transformed into a massive layer of corrosion products with a rust-colored. Corrosion products, which are commonly detected in the surface layer with higher oxidation states, are mostly goethite (α-FeOOH) and lepidocrocite (γ-FeOOH) [21–26]. Besides goethite and lepidocrocite, which are mostly crystalline and can be easily detected by X-ray diffraction (XRD), there may also be crystalline corrosion products which didn't appear in the XRD pattern in XRD pattern because of their small amount.
A condensate pipeline made of carbon steel alloy with grade A106-Gr.B, had a leakage in the form of a pinhole at the girth weld after 16 years of operation. Visual examination, optical and scanning electron microscopy (SEM), coupled with energy-dispersive X-ray spectroscopy (EDS), chemical analysis, and hardness measurements were performed on the failed pipeline samples. Visual examination of the inner surface of the circumferential weld line showed many types of welding defects, as well as severe localized corrosion pits in the weld zone at the bottom of the pipe surface. The microscopic analysis shows that the localized corrosion attack is the root cause of the pipe failure. XRD patterns of the inner surface of the failed pipe emphasizes a formation of corrosion products of iron oxyhydroxides such as Lepiodocrocite (Fe + 3O(OH)), and Goethite (FeO(OH)). Additionally, the foreign elements of aluminum, and chlorine, detected by the EDS analytical results promote under-deposit corrosion, particularly in regions with stagnant water, i.e., at 6 O'clock pipe position.
An innovative multi-component fluoropolymer-based coating on outdoor patinated bronze for Cultural Heritage: Durability and reversibility
2020, Journal of Cultural Heritage
Citation Excerpt :
The features of coatings, environments of exposure and conditions of metallic surfaces at the moment of coating application should be considered when protective treatments are chosen. Furthermore, in Cultural Heritage coatings must fulfil strict requirements, as ease of application, minimal aesthetical impact, protective performance, long-term durability, non-toxicity, reversibility and re-applicability [1]. In recent years, several studies proposed innovative protective coatings with peculiar features, such as organosilane-based [2–9] or eco-friendly coatings [10–13].
The application of protective coatings for the conservation of outdoor metallic artworks is currently considered the best approach actively employed. This paper focuses on the evaluation of the protectiveness of an optimised fluorosilane (FA-MS) coating with low occupational hazard impact and high inhibition efficiency. FA-MS coating was applied on a typical historical as-cast bronze (Cu-Sn-Zn-Pb), artificially patinated by synthetic acid rain dropping, to simulate natural unsheltered patinas. Subsequently, the patinated bronze was coated by brushing and then artificially aged by synthetic rain dropping. In order to investigate the coating-patina system, a multi-analytical approach was applied including scanning electron microscopy coupled with elemental analysis (FEG-SEM with EDS), microstructural analysis of cross-sections produced by Focused Ion Beam milling (FIB) and X-ray Photoelectron Spectroscopy (XPS). The coating homogenously covered the whole patinated surface producing a transparent layer few μms thick. The weathering solutions were also analysed for the assessment of metallic cations release. FA-MS showed excellent protective performances for the patinated bronze exposed to simulated outdoor conditions. Very high values of inhibiting efficiency in terms of metal release in the weathering solutions (up to 99%) were measured.
In order to investigate all the necessary requirements for application in conservation field, the durability of FA-MS was also tested on a real bronze artistic casting, in terms of limiting the alloy composition changes (measured by in situ XRF) over time. A good durability of the coating was observed during the ongoing field exposure test.
Lastly, reversibility of FA-MS was investigated by applying different mechanical cleaning methods, such as brushing and blasting. The reversibility was assessed by the evaluation of the morphology (colour change, surface roughness and optical microscopy) and the composition (SEM-EDS and Py-GC-MS chromatography) of the cleaned surfaces. Cleaning by brushing proved to be an efficient method for removing this coating without significantly altering the bronze patina.
Metabolic processes applied to endangered metal and wood heritage objects: Call a microbial plumber!
2020, New Biotechnology
While often considered as harmful for cultural heritage, microorganisms can also be used for its safeguarding. The methods used so far for the conservation-restoration of cultural heritage are often unsatisfactory in terms of efficiency and durability. Inhibitors or complexing agents are also toxic and pose potential threats to human health and to the environment. Microbial-based technologies can provide sustainable solutions for heritage conservation-restoration using ecologically friendly biological treatments. Over the last decades, the development of biological methods and materials has become a significant alternative for the preservation of ancient heritage. Of particular note, microbial metabolisms are exploited to consolidate, clean, stabilize or even protect surfaces of cultural items. Taking advantage of unique properties of microorganisms, reactive corrosion products are extracted or converted into biogenic minerals that provide the treated surfaces with long-term stability. Examples of the techniques proposed include the formation of passivating biogenic layers that can be applied for preservation of metal-based heritage, as well as the development of methods for the preventative removal of iron species from waterlogged wood. This review presents the current advance made in research aiming to preserve copper- and iron-based artefacts, in particular sculptures but also archaeological objects, as well as in the development of a method for the extraction of iron species from waterlogged wood.
Comparison of a bio-based corrosion inhibitor versus benzotriazole on corroded copper surfaces
2018, Corrosion Science
This research aims to characterize and compare the protective behaviour of a bio-based treatment versus benzotriazole (BTA) for the preservation of copper-based artefacts affected by active corrosion induced by copper chlorides. For this, the treatments were applied on artificial copper hydroxychlorides produced on copper sample. Their inhibition performance was then investigated by Scanning Electron Microscopy, Infrared Spectroscopy and Electrochemical Impedance Spectroscopy. Results showed few BTA-Cu complexes formed and poor protectiveness of the BTA treatments. In contrast, the bio-based treatment resulted in the conversion of almost all copper hydroxychlorides into copper oxalates, providing a more efficient corrosion inhibition.
Chitosan-based coatings for corrosion protection of copper-based alloys: A promising more sustainable approach for cultural heritage applications
2018, Progress in Organic Coatings
Citation Excerpt :
In this scenario, the use of eco-friendly polymeric materials obtained from renewable sources, which act both as barrier layer and reservoir for corrosion inhibitors, is an attractive approach for the development of reliable, sustainable and active protective coatings [6–11]. The choice of natural polymers that are soluble in water-based solutions may avoid the use of harmful solvents (as toluene, acetone, white spirit and xylene) that are necessary for the application and removal of commonly used commercial protective coatings, consisting of BTA dispersed in acrylic resins (Paraloid B72™, 70 methylmethlacrylate/30 ethyl acrylate copolymer) or microcrystalline waxes [2]. Therefore the development of innovative water-soluble products is mandatory, especially for conservation interventions on unmovable works of art.
The attractive physicochemical properties of chitosan make its derived materials promising candidates for the reliable and sustainable corrosion protection of metallic substrates. In this work, chitosan-based coatings embedding different corrosion inhibitors, i.e. benzotriazole (BTA) and mercaptobenzothiazole (MBT), were investigated for the protection of copper-based alloys, with the aim to extend their application to the preservation of works of art exposed to indoor atmosphere. The composition of the formulations was optimized paying particular attention to their potential application in the field of cultural heritage. To assess the efficacy of the coatings, tailored accelerated corrosion tests were carried out on bare and coated bronze substrates. Coated and uncoated alloy disks were characterized before and after corrosion treatments by optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy and Fourier transform infrared spectroscopy. Moreover, an image analysis protocol was defined to evaluate the extent of surface modifications after degradation treatments. The obtained results revealed that the chitosan-based coatings containing BTA and MBT fulfil the aesthetic criteria required in the field of cultural heritage and are able to inhibit the corrosion of bronze alloys. It is worth noting that a synergic effect between the chemical protection provided by the inhibitors and the physical one provided by the polymer matrix was observed. Our findings demonstrate that the developed systems are suitable for a reliable and more sustainable protection of indoor bronze artefacts, thus representing a promising alternative to commercial products and particularly taking advantage from the use of non-harmful solvents for their application and removal.

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4.43 - Preservation of Metallic Cultural Heritage