Archaeological Iron Artefacts Research Articles

Developing a quantitative multimodal and multi-scale, fully non-destructive technique for the study of iron archaeological artefacts

This article presents the methodology and initial findings of the SNSF Sinergia project CORINT. The project's objective is to elucidate the corrosion mechanisms affecting iron-based structures entrapped in various porous media. This paper focuses specifically on iron archaeological artefacts (IAAs) in soil. A novel multimodal quantitative imaging technique, which integrates neutron and X-ray computed tomography (NX-CT), is under development for non-destructive examination of corrosion processes. The method involves registering and fusing neutron and X-ray tomography data, followed by Gaussian mixture model (GMM) clustering for phase segmentation. Imaging was conducted on two IAAs, Vrac C and BdC1. Additionally, random cross-sections of these samples underwent analysis through optical microscopy, µRaman spectroscopy, and SEM-EDS to characterize and correlate corrosion layers with NX-CT results. This study yields valuable insights into the corrosion of IAAs, enabling the non-destructive investigation of corrosion processes in porous media. The implications extend beyond the preservation of cultural heritage, to the examination of long-term corrosion behaviors in contemporary iron structures, steel within concrete, and nuclear waste disposal plans.

Green Alternatives for Archaeological Iron Stabilization

ABSTRACT 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.

Structural and spectroscopic study of well-developed crystals of parahibbingite, β-Fe2(OH)3Cl, formed from terrestrial weathering of the Muonionalusta iron meteorite

AbstractParahibbingite [β-Fe2(OH)3Cl], a new mineral recently described from ultramafic rocks in the Bushveld Complex, South Africa, has been found to form millimetric well-developed crystals as a terrestrial weathering product of the Muonionalusta iron meteorite. The mineral, initially identified by means of Raman spectroscopy, was found in a small cavity within a crust of rust on a granitic rock fragment that was in direct contact with the alteration crust of a meteorite specimen, collected in the Kitkiöjärvi area, Sweden. Its crystal structure was refined from single-crystal X-ray diffraction data (R1 = 0.0331) in the space group R$\bar{3}$m [a = 6.9362(4), c = 14.673(1) Å and V = 611.35(7) Å3 for Z = 6], thus confirming the structural model of synthetic β-Fe2(OH)3Cl. It consists of a network of octahedrally coordinated Fe2+ atoms alternately arranged in triangular and Kagomé layers, stacked along the c axis. The H atom position was determined, showing O–H⋅⋅⋅Cl bonds, which provides a further link between layers. Parahibbingite is found to be not only an important constituent of the corrosion system of archaeological iron artefacts but can also play an important role as an alteration product of iron meteorites.

An overview of modern ways of cleaning from rust and preservation of iron historical artefacts

This overview focused on the recent advances in rust cleaning and conservation of iron-based historical artefacts. Archaeological iron artefacts undergo various forms of corrosion, including soil and atmospheric. In general the main corrosion products are goethite α-FeO​​(OH), acaganeite β-FeO (OH), lepidocrocite γ-FeO (OH), magnetite Fe3O4, siderite FeCO3, vivanite Fe3(PO4)2 ∙ 8H2O, etc. A number factors contribute to the process corrosion, but Cl- anion embedded in the crystal lattice of acagenite is crucial. It has been considered corrosion product removers from the artefact surface, and found out that all of them should contain inhibitors slowing down the interaction of the artefact iron core with acids. Organic acids, in particular citric, maleic and acetic acids are considered to be non-aggressive and environmental-friendly. After removing corrosion product layer, iron historical heritages are affected by atmospheric corrosion thus stabilizing substances and protective coatings must be applied. The most common protectors are tannin-iron complex compounds, which provide an anti-corrosion coatings and prevent further destruction of artefacts. Preservation of iron-based historical artefacts with synthetic polymer waxes, resins and synthetic polymers is thought to be promising.

Modeling ‘dry’ OCP measurements to characterize archaeological iron corrosion II: Short-time transients

• “Dry” open circuit potential-time measurements are recorded for archaeological iron objects. • Theoretical modeling of short-time (<1 min) transients is presented. • Effective RC parameters can be evaluated from a nano-pitting corrosion model. • RC parameters provide information on the type and degree of corrosion. Short-time transients recorded in “dry” open circuit potential (OCP) measurements performed on archaeological iron artifacts are modeled based on their ascription to pitting corrosion events. Three types of short-time transients can be discerned, the two first ones yielding approximately exponential growth and decay curves apparently driven by charging/discharging processes. A third type of transients that consists of sharp rising/decay involving successive anodic and cathodic excursions over the background OCP vs. time curve is described assuming a logistic variation of charge transfer in dissolution/repassivation steps of pit evolution. Theoretical modeling is in agreement with experimental data for a set of archaeological iron objects.

Experience of Ultrasonic Use to Stabilize Archaeological Iron Artifacts with Active Corrosion

Of all the complex problems of museum storage of archaeological objects, iron objects represent one of the most difficult. In the process of corrosion, an iron object passes through several stages, from oxidation of the metal surface to full mineralization. The greatest problem consists of the items in the stages of oxidation, when the metal is almost completely corroded and converted into minerals. Mineral peels exfoliate under the influence of active corrosion, leading to a loss of historical significance of the object. In the world’s practice of archaeological iron conservation, there are several different ways of stabilization, but none of them can guarantee the integrity of the iron artifact during its museum storage. To date, the most effective conservation method of stabilizing archaeological iron is alkaline sulfite treatment. However, this method has a number of drawbacks, the main of which is the duration of the stabilizing treatment. The authors consider the possibility of increasing the efficiency of the method of processing archaeological iron objects in an alkaline sulfite solution by means of ultrasonic solution activation. In the course of the experimental study, it has been established that the use of ultrasonic in alkaline sulfite treatment hugely increases the efficiency of the method.

Evaluation of Inhibition Efficiency of Oak Galls Extract as a Green Corrosion Inhibitor of Archaeological Iron Artifacts in the Atmospheric Environment

Abstract The aim of this work is to investigate the effectiveness of oak galls extract (OGE) as a green corrosion inhibitor from natural resources to prevent the corrosion of archaeological iron artifacts in atmospheric environments. The inhibition efficiency has been evaluated by measuring the weight loss of the treated coupons after exposure to 85% RH in a humidity chamber, Potentiodynamic polarization and electrochemical impedance spectroscopy (EIS) techniques. Also, the morphology of an adsorbed film on the surface was investigated by scanning electron microscopy and optical microscope. The influence of OGE on changing the original appearance of the surface was also evaluated using visual examination and colorimetric measurements. The measurements results revealed that OGE gave high inhibition efficiency reaching approximately 95% of 6% concentration. Based on the study results, OGE can be proposed as an efficient green inhibitor for iron artifacts.

Multi-classifier majority voting analyses in provenance studies on iron artefacts

The main objective of this paper is to propose an approach for identification of provenance of archaeological iron artefacts making use of major oxides and trace elements. For this purpose, seven classifiers were built on the basis of the following techniques: Linear Discriminant Analysis (LDA), Support Vector Machine (SVM), Random Forests (RF), Naïve Bayes (NB), K-Nearest Neighbours (KNN), Recursive Partitioning and Regression Trees (RPART) and Kernel Discriminant Analysis (KDA). A final assignment of a given observation to a regional class was carried out on the basis of results provided by all classifiers using a majority voting technique. The proposed approach was first tested on experimental slag and then it was applied to actual archaeological data. It is hoped that this method can become part of a new integrated approach which will consider all available types of data, such as major and trace elements and isotopic ratios.

A novel technology for the corrosion protection of iron archaeological artefacts using parylene base removable bilayer

Abstract Combinations of different acrylic resins and microcrystalline waxes are most often used for conservation and preservation these days. However, their properties are not sufficient and satisfactory in many ways. A novel barrier coating for the conservation of iron archaeological artefacts composed of parylene C polymer and Laksil lacquer is proposed within this article. Parylene C is a commercial name of poly(chloro-p-xylylene) polymer, and it was prepared via modified chemical vapour deposition. Parylene removability was ensured through the xylene soluble interlayer made of Laksil silicone-acrylic lacquer which was applied between a protected iron model substrate and parylene thin film. The corrosion tests in salt spray showed excellent barrier properties of Laksil/parylene bilayer. The surface roughness measured by the profilometry and the surface morphology shown by the SEM displayed the synergic effect between the Laksil and parylene layer which leads to the exceptional barrier and anticorrosion function of Laksil/parylene bilayer. First, the Laksil layer flattened out rough surface of a substrate; second, thereon deposited parylene film became smooth and defect free and acted as a good diffusion barrier. The colouristic measurements proved that the bilayer does not change the appearance of item, in terms of colour. The EDX and TGA confirmed entirely successful removal of bilayer and thus the reversibility of conservation treatment is enabled. The characteristics of Laksil/parylene bilayer were compared with the conventional conservation coating composed of Paraloid B72 acrylic resin and Revax microcrystalline wax prepared by professional conservators. The Laksil/parylene bilayer demonstrated significantly superior properties in this comparison.

Electrical properties of iron corrosion layers formed in anoxic environments at the nanometer scale

The electrical properties of the corrosion layers on archaeological iron artefacts were determined by Conductive Atomic Force Microscopy. Different corrosion products were studied: FeII carbonates, magnetite entrapped in the carbonate, and iron sulfides. The results indicate that the ferrous carbonate matrix is insulating, and that magnetite and iron sulfides have a conductive character, although these phases are not systematically connected to the metal. This suggests that electrons produced by the anodic dissolution of metal would be conducted to the external part of the corrosion product layer through a three-dimensional network of connected magnetite strips passing through the ferrous carbonate matrix.

Stabilization treatment of cultural heritage artefacts: In situ monitoring of marine iron objects dechlorinated in alkali solution

The preservation of archaeological iron artefacts necessitates stabilization treatments. For this study, such treatments were applied, in aerated and deaerated NaOH solutions, to Roman iron bars excavated from a marine site in order to understand the evolution of corrosion layers composed of ferrous hydroxychloride β-Fe2(OH)3Cl. Their transformation was monitored in situ by micro-diffraction under synchrotron radiation and characterized ex situ using multi-scale complementary analytical tools. The formation of transient phases such as ferrous hydroxide Fe(OH)2 was identified in both media and chlorinated green rust GR(Cl−) occurred in aerated solutions, showing the influence of dissolved oxygen on the transformation processes.

Role of previously formed corrosion product layers on sulfide-assisted corrosion of iron archaeological artefacts in soil

Iron archaeological nails (16th century) were used as representative of the mild steel structures envisaged for the storage of nuclear waste. The influence of sulfide species on the corrosion behavior of the nails was investigated via the thorough description of the modifications undergone by the corrosion products surrounding the metal after re-immersion in deaerated sulfide solution. The only observed modification was the formation of FeS at the corrosion product layer/soil interface. The corrosion product layer, mainly composed of FeCO3, acts as protective barrier, the reactivity of FeCO3 preventing sulfide species to reach the metal and influence the corrosion process.

Iron and Fungal Physiology: A Review of Biotechnological Opportunities.

Iron is an essential inorganic micronutrient. Because of its low toxicity only a few studies have dealt with the importance of iron in fungal physiology. Most of the studies published so far focus on iron sequestration by animal fungal pathogens, iron uptake by mycorrhizal fungi, or iron redox activities by fungal wood degraders. However, a general overview on the relationship between fungal physiology and iron is still lacking. In this review we present a summary of the types of physiological activities that participate in iron homeostasis in fungi and how these activities can be used for the development of original biotechnological applications in relationship to iron-containing matrices. Concrete examples of biotechnological applications involving iron and fungi are also discussed. In the last part, a specific research project in biotechnology focusing on the use of fungi for the conservation of archaeological objects in iron is described in detail. This project aims at developing a new conservation-restoration method to preserve archaeological iron artifacts exploiting the ability of fungi to transform anduptake iron. Preliminary results obtained in this project regarding iron-reduction, iron uptake, and biogenic formation of iron minerals are presented and discussed.

Effect of natural and synthetic iron corrosion products on silicate glass alteration processes

Glass long term alteration in the context of high-level radioactive waste (HLW) storage is influenced by near-field materials and environmental context. As previous studies have shown, the extent of glass alteration is strongly related to the presence of iron in the system, mainly provided by the steel overpack around surrounding the HLW glass package. A key to understanding what will happen to the glass-borne elements in the geological disposal lies in the relationship between the iron-bearing phases and the glass alteration products formed.In this study, we focus on the influence of the formation conditions (synthetized or in-situ) and the age of different iron corrosion products on SON68 glass alteration. Corrosion products obtained from archaeological iron artifacts are considered here to be true analogues of the corrosion products in a waste disposal system due to the similarities in formation conditions and physical properties. These representative corrosion products (RCP) are used in the experiment along with synthetized iron anoxic corrosion products and pristine metallic iron. The model-cracks of SON68 glass were altered in cell reactors, with one of the different iron-sources inserted in the crack each time. The study was successful in reproducing most of the processes observed in the long term archaeological system.Between the different systems, alteration variations were noted both in nature and intensity, confirming the influence of the iron-source on glass alteration. Results seem to point to a lesser effect of long term iron corrosion products (RCP) on the glass alteration than that of the more recent products (SCP), both in terms of general glass alteration and of iron transport.

Corrosion product transformations in alkaline baths under pressure and high temperature: The sub‐critical stabilisation of marine iron artefacts stored under atmospheric conditions

In the context of conservation of ferrous cultural heritage, dechlorination processes of archaeological iron artefacts are studied in subcritical conditions which consist of immerging an artefact inside an alkaline bath under pressure (30 bar) and temperature (160 °C). Submarine archaeological environments lead to the presence of chlorides inside the corrosion layers. After exposure to the atmosphere following excavation, initial corrosion phases evolve. Chlorides remain trapped inside the structure of corrosion products particularly during the crystallisation of akaganeite. Stabilisation treatment objectives are to remove chlorides from the corrosion layers and to obtain more stable phases. A Roman archaeological bar has been studied on cross‐section before and after treatment in sub‐critical conditions. Less stable phases, such as ferrihydrite and akaganeite, transformed into hematite. That was confirmed by the use of synthetic and pure phases treated in the same conditions. The presence of goethite before and after the treatment in the corrosion profile raises the question of its reactivity during dechlorination process. Akaganeite has been synthesised and compared to archaeological powder sampled on an artefact. The results highlight reactivity differences indicating that sub‐critical transformation processes are not only dependent on the nature of phases but also on intrinsic physical characteristics.

Structural characterization of corrosion product layers on archaeological iron artifacts from Vigna Nuova, Crotone (Italy)

Abstract A collection of archaeological iron artifacts, whose age could be assigned from the Iron Age up to the post–medieval period, and coming from the Archaeological National Museum of Crotone (Calabria, Italy) were investigated. They show evident forms of degradation although they were restored around twenty years ago. The aim of this work was to study the chemistry of the corrosion layers formed on the iron artifacts. Techniques such as optical and electronic microscopies (OM and SEM-EDS), X-Ray diffraction (XRD), Ion Chromatography, ATR/FTIR Spectroscopy and Micro-Raman Spectroscopy have been applied. It was found that corrosion products are mainly made up of goethite, maghemite, magnetite, hematite, lepidocrocite and ferrihyidrite. Akaganeite was often found at the interface between the corrosion products and the core of the metal. This could be considered as the main cause of the rapid post-restoration deterioration of iron objects investigated.

What effect does siderite crystal growth have on chlorides and potential information within the corrosion products of archaeological iron artefacts?

In anoxic, carbonated and slightly acidic burial environments, the growth of siderite crystals on archaeological iron has been attributed a passivating effect on the corrosion process. By creating a simplified, though similar environment (optimized for siderite growth), the aim of this project was to observe how the growth of siderite crystals within the corrosion crust of archaeological iron objects would affect both the corrosion crust and its chloride content.

Monitoring stabilizing procedures of archaeological iron using electrochemical impedance spectroscopy

A methodology for monitoring washing procedures applied to stabilize archaeological iron is described. It is based on the combination of voltammetry of microparticles (VMP) with electrochemical impedance spectroscopy (EIS). A semi-empirical approach is used where the impedances at low and high frequencies were related with the fraction areas of passive and corrosion layers generated during the stabilizing treatment, the thickness, and the porosity of the corrosion layer. The variation of such parameters with the time of washing was determined from EIS data for four types of desalination procedures using concentrated NaOH and/or Na2SO3 aqueous solutions on archaeological iron artifacts. After 2 months of treatment, EIS data indicate that an essentially identical “stable” state was attained in all cases, as confirmed by the formation of a passive magnetite layer identified in VMP measurements while the rate of variation of corroded surface and porosity at short washing times varied significantly from one stabilization procedure to another.

Characterization of the corrosion layer on iron archaeological artefacts from K2 (825–1220 AD), an archaeological site in South Africa

A study of the composition and phase distribution of the corrosion layers on three ferrous objects, excavated at K2 (Bambandyanalo), an archaeological site in South Africa, was conducted. The objective of the study was to obtain information that can contribute to conservation procedures to be performed on the iron artefacts from this site. Examination of cross sections by means of energy-dispersive X-ray spectroscopy coupled to a scanning electron microscope (SEM–EDX), X-ray powder diffraction (XRD), and micro-Raman spectroscopy revealed the same corrosion composition and structure for all the objects under study, namely an internal layer adjacent to the metal surface with ghost inclusions and an external layer containing quartz grains. The study also revealed that the presence of magnetite (Fe3O4), maghemite (γFe2O3), and lepidocrocite (γ-FeOOH) within the internal layer is the only difference between the chemical compositions of iron corrosion products within the two layers. The results also made it possible to retrace the corrosion history during burial and long-term storage.

Mechanisms of the dechlorination of iron archaeological artefacts extracted from seawater

Treatments based on the immersion of iron artefacts in NaOH or KOH solutions with or without cathodic polarisation of the metal core, used for conservation purposes, were applied to Gallo-Roman iron ingots excavated from the Mediterranean Sea. The transformation of the initial layer of β-Fe 2(OH) 3Cl was followed with time. The resulting phases were characterised by a complete set of multi-scale complementary techniques. It could be demonstrated that the main process involved successively the transformation of β-Fe 2(OH) 3Cl into Fe(OH) 2 and the oxidation of Fe(OH) 2 into α-/δ-FeOOH and magnetite. Cathodic polarisation accelerated, via migration processes, the removal of chloride ions.