Application of Modified Tafel Analysis to the Identification of Corrosion Products on Archaeological Metals Using Voltammetry of Microparticles

An operational modification of Tafel analysis, applied to the intermediate region of square wave voltammetric curves, devoted to the identification of corrosion products on archaeological metal, is described. This is based on the voltammetry of microparticles methodology using conventional abrasive conditioning of the electrode, as well as ‘one‐touch’ and layer‐by‐layer techniques. The proposed methodology is applied to the identification of copper and silver corrosion products in mediaeval silver‐copper coins from the Libertad street hoard in Valencia (Spain).     

Dating Archaeological Strata in the Magna Mater Temple Using Solid‐state Voltammetric Analysis of Leaded Bronze Coins

The application of solid state electrochemistry techniques for dating archaeological strata using lead‐containing bronze coins is described. The proposed methodology was applied to samples coming from the Roman archaeological site of Magna Mater Temple (Rome, Italy) occurring in different strata dating back between the second half and the end of the 4^th century A.D. and the 20^th century. The voltammetric signatures of copper and lead corrosion products in contact with aqueous acetate buffer, as well as the catalytic effects produced on the hydrogen evolution reaction, were used for establishing the age of different strata and dating coins belonging to unknown age. Voltammetric data were consistent with a theoretical approximation based on a potential rate law for the corrosion process.     

Modeling Corrosion of Archaeological Silver‐Copper Coins Using the Voltammetry of Immobilized Particles

Two complementary models to describe the long‐term corrosion of silver‐copper coins, based on potential rate laws for smooth corrosion and those combined with diffusive law, for gross corrosion, are proposed. Theoretical kinetics can be tested using signatures of copper and silver corrosion products using the voltammetry of immobilized particles technique. The method is applied to silver coins minted during the 13^th–14^th centuries from the Libertad street hoard in Valencia (Spain) using non‐invasive one‐touch graphite pencil sampling. Voltammetric features yield functional dependences in agreement with the proposed model potentially useful for distinguishing between different mints.     

Multianalytical study of corrosion layers in some archaeological copper alloy artefacts

Corrosion layers in some copper and bronze archaeological objects from Haft Tappeh archaeological site, southwest Iran, were studied. For this purpose, optical microscopy, scanning electron microscopy with energy dispersive X‐ray microanalysis, micro‐Raman spectroscopy and X‐ray diffraction methods were applied to observe corrosion stratigraphy and their characteristics as well as identification of chemical composition and phase determination of different corrosion layers. Based on optical and electron microscopy, three different corrosion strata were identified in cross section of different metallic objects including various red, green, white‐grey powdery and dark internal compact layers. Scanning electron microscopy with energy dispersive X‐ray microanalysis on different corrosion layers revealed that Cu, Sn and Cl are the main elements in the chemical composition of different layers. Tin‐rich phases were detected in white‐grey and dark layers that may be formed because of the internal oxidation of tin as well as the decuprification (selective dissolution of copper) phenomena occurring during long‐term burial period in the soil. Also, the XRD and micro‐Raman spectroscopy results proved that the main corrosion products are nantokite (CuCl), copper trihydroxychlorides and copper oxides. The combination of these analytical methods allows us to explore the surface and internal corrosion layers of the archaeological copper and bronze samples, and major interest is on studying their chemistry, microstructural properties and corrosion stratigraphy. Copyright © 2015 John Wiley & Sons, Ltd.     

Characterisation of pigments and corrosion patinas by means of micro-Raman spectroscopy

New applications of micro-Raman spectroscopy are presented here for the investigation of colouring agents in a wax model of plant and of corrosion products on metal artworks. A late 1700 wax model of Camellia japonica L. was studied in order to characterise the nature of white, red and green colours of petals and leaves. White and red colours of petals were identified as pigments of baryte and a mixture of cinnabar and carmine lake, respectively. Fragments taken from leaves with different green hues were also studied; only yellow grains were isolated in this case which were identified as orpiment and yellow chrome. The applicability of micro-Raman spectroscopy to the study of corrosion products on metal objects is presented here for iron archaeological artefacts and for lead samples taken from the cupolas of the Consolata Sancturay in Turin. Analysis of blackish and reddish corrosion patinas entirely covering the archaeological iron objects led to the identification of magnetite and maghemite, goethite and lepidocrocite, respectively. As to lead fragments, the main corrosion product was lead sulphate, and minor amounts of lead carbonate, nitrate and oxide (litharge) were also found.     

Application of thermomagnetometry to corrosion studies of archaeological iron

Summary Thermomagnetometry has been applied to mineralized archaeological iron samples and samples from accelerated corrosion tests. It has successfully quantified the degree of corrosion, measured by the loss of iron, as well as the amount of magnetite formed and water held in the corrosion and adhered soil layers. Thermomagnetometry, thermogravimetric analysis and differential scanning calorimetry have been applied to the reported corrosion products from archaeological iron. Fourier transform infra-red and Raman spectroscopies and X-ray diffraction analyses were undertaken on the residues and at intermediate heating stages, where the thermal analyses indicated, to identify the reaction products.     

Electrochemical Characterization of Corrosion Products in Leaded Bronze Sculptures Considering Ohmic Drop Effects on Tafel Analysis

The characterization of corrosion products in leaded bronze based on the voltammetry of immobilized particles methodology is described. Voltammetric data, supported by Fourier transform infra‐red spectroscopy, field emission scanning electron microscopy‐energy dispersive X‐ray microanalysis (FESEM‐EDX) and scanning electrochemical microscopy (SECM) allow the identification of copper and lead corrosion materials. The mutual influence of such products is modeled upon considering uncompensated ohmic drops in the Tafel analysis of the rising portion of the respective voltammetric signals for their electrochemical reduction.     

A Study on Corrosion Processes of Archaeological Glass from the Valencian Region (Spain) and its Consolidation Treatment

The combined use of scanning electron microscopy/energy dispersive X-ray microanalysis (SEM/EDX) and square wave voltammetry (SQWV), is used for studying the corrosion processes that have taken place in buried glass from different archaeological sites in the Valencian Region (Spain). The procedures permit a parallel investigation of morphology and chemical composition. Determination of the chemical composition of the glasses and their alteration crust and identification of the elements responsible for the colour has been also carried out using energy dispersive X-ray microanalysis. The electrochemical response of samples attached to paraffin-impregnated graphite electrodes reveals the presence of different iron and manganese oxide species in the browning areas of the corroded glass. Image analysis applied to microphotographs obtained by means of SEM led to the determination of morphological parameters concerning the corrosion phenomena occurring on the surface of the fragments such as thickness of the corrosion layer and its laminated structure. Additionally, measurement of the thickness of the film of polymer used as coating in the consolidation treatments has been carried out using cryo-scanning electron microscopy (cryo-SEM) combined with image analysis.     

Characterization of Egyptian bronze archaeological artifacts

This paper presents the results of in situ non‐destructive X‐ray fluorescence determination of the chemical analysis of a collection of ten bronze statues that are on display at the Egyptian museum of Cairo. The statues are from the late period of the ancient Egyptian history. In addition, destructive technique X‐ray diffraction analysis was applied on 11 damaged archaeological objects to determine the corrosion products and the alloy compositions. Specimens of the latter objects were subjected to metallographic examinations to determine the microstructure of the alloy. Surprisingly, the results indicated that all ten statues and 10 of the 11 damaged objects were made of lead – bronze alloy; the percentage of the lead varied from 3.43 to 18.04, the tin varied from 2.53 to 10.67. The chemical composition of the patina on eight damaged objects is essentially composed of (Cu₂O) cuprite for all objects in addition to other compounds such as (SnO₂) cassiterite in two objects, (PbCO₃) cerussite in three other objects and (Cu₂(OH)₃Cl) atacamite or (Cu(OH)₃Cl) paratacamite in two other objects. The formation of chlorides and carbonate resulted from the interaction between surrounding environment and the alloy. The results of the metallographic examinations indicated a non‐homogenous structure and the increase of the lead content increases the globular lead particles. In spite of this condition, the galvanic corrosion tendency when the alloy is exposed to moist air or soil is not possible as lead compounds are electrically insulating. Another advantage for using leaded bronze in making statues is being heavy and thus leads to stability. Copyright © 2012 John Wiley & Sons, Ltd.     

MALDI‐FT‐ICR‐MS for archaeological lipid residue analysis

Soft‐ionization methods are currently at the forefront of developing novel methods for analysing degraded archaeological organic residues. Here, we present little‐used soft ionization method of matrix assisted laser desorption/ionization‐Fourier transform‐ion cyclotron resonance‐mass spectrometry (MALDI‐FT‐ICR‐MS) for the identification of archaeological lipid residues. It is a high‐resolution and sensitive method with low limits of detection capable of identifying lipid compounds in small concentrations, thus providing a highly potential new technique for the analysis of degraded lipid components. A thorough methodology development for analysing cooked and degraded food remains from ceramic vessels was carried out, and the most efficient sample preparation protocol is described. The identified components, also controlled by independent parallel analysis by gas chromatography‐mass spectrometry (GC‐MS) and gas chromatography‐combustion‐isotope ratio mass spectrometry (GC‐C‐IRMS), demonstrate its capability of identifying very different food residues including dairy, adipose fats as well as lipids of aquatic origin. The results obtained from experimentally cooked and original archaeological samples prove the suitability of MALDI‐FT‐ICR‐MS for analysing archaeological organic residues. Sample preparation protocol and identification of compounds provide future reference for analysing various aged and degraded lipid residues in different organic and mineral matrices.     

Potential Application of Voltammetry of Microparticles for Dating Porcine Blood‐based Binding Media used in Taiwanese Architectural Polychromies

A method for dating Hemoglobine‐containing archaeological samples using the voltammetry of microparticles is described. This is based on the record of the voltammetric response of such materials attached to paraffin‐impregnated graphite electrodes in contact with aqueous acetate buffer. Signals attributable to the Fe^III/Fe^II iron couple and their catalytic enhancement in the presence of H₂O₂ can be correlated, via first‐order reaction kinetics, with the time of aging of the samples. The method has been applied to the study and dating of the polychromed architectural decoration of different parts of the architectural complex of the Longshan Temple in Lukang (18^th century, Taiwan).     

Use of a Commercially Available Wood‐Free Resin Pencil as Convenient Electrode for the ‘Voltammetry of Microparticles’ Technique

A wood‐free resin pencil comprised of a lead made of graphite particles dispersed in a polymeric matrix is proposed as a convenient low‐cost electrode for the ‘Voltammetry of Microparticles’ technique instead of paraffin impregnated graphite rods. The pencil electrode was successfully applied for the characterization of insulating (Prussian blue, zeolites) and conductive (silver selenide, pyrite) microparticles in various media. The voltammetric responses were comparable to, sometimes even better than, those obtained with applying other electrochemical techniques.     

Advanced mono‐ and multi‐dimensional gas chromatography–mass spectrometry techniques for oxygen‐containing compound characterization in biomass and biofuel samples

A wide variety of biomass, from triglycerides to lignocellulosic‐based feedstock, are among promising candidates to possibly fulfill requirements as a substitute for crude oils as primary sources of chemical energy feedstock. During the feedstock processing carried out to increase the H:C ratio of the products, heteroatom‐containing compounds can promote corrosion, thus limiting and/or deactivating catalytic processes needed to transform the biomass into fuel. The use of advanced gas chromatography techniques, in particular multi‐dimensional gas chromatography, both heart‐cutting and comprehensive coupled to mass spectrometry, has been widely exploited in the field of petroleomics over the past 30 years and has also been successfully applied to the characterization of volatile and semi‐volatile compounds during the processing of biomass feedstock. This review intends to describe advanced gas chromatography–mass spectrometry‐based techniques, mainly focusing in the period 2011–early 2020. Particular emphasis has been devoted to the multi‐dimensional gas chromatography–mass spectrometry techniques, for the isolation and characterization of the oxygen‐containing compounds in biomass feedstock. Within this context, the most recent advances to sample preparation, derivatization, as well as gas chromatography instrumentation, mass spectrometry ionization, identification, and data handling in the biomass industry, are described.     

Ancient coins: cluster analysis applied to find a correlation between corrosion process and burial soil characteristics

Although it is well known that any material degrades faster when exposed to an aggressive environment as well as that "aggressive" cannot be univocally defined as depending also on the chemical-physical characteristics of material, few researches on the identification of the most significant parameters influencing the corrosion of metallic object are available.A series of ancient coins, coming from the archaeological excavation of Palazzo Valentini (Rome) were collected together with soils, both near and far from them, and then analysed using different analytical techniques looking for a correlation between the corrosion products covering the coins and the chemical-physical soil characteristics. The content of soluble salts in the water-bearing stratum and surfacing in the archaeological site, was also measured.The obtained results stress the influence of alkaline soils on formation of patina. Cerussite, probably due to the circulation of water in layers rich in marble and plaster fragments, was the main corrosion product identified by X-ray Diffraction (XRD). Copper, lead and vanadium were found in soil surrounding coins. By measuring conductivity, pH and soluble salts content of the washing solutions from both coins and soils, we could easily separate coins coming from different stratigraphic units of the site.Data were treated by cluster and multivariate analysis, revealing a correlation between part of the coins and the nearby soil samples.     

Dating Archaeological Copper/Bronze Artifacts by Using the Voltammetry of Microparticles

A method for dating copper/bronze archaeological objects aged in atmospheric environments is proposed based on the specific signals for cuprite and tenorite corrosion products measured through the voltammtry of microparticles method. The tenorite/cuprite ratio increased with the corrosion time and fitted to a potential law that yielded a calibration curve usable for dating purposes.     

Species identification by analysis of bone collagen using matrix‐assisted laser desorption/ionisation time‐of‐flight mass spectrometry

Species identification of fragmentary bone, such as in rendered meat and bone meal or from archaeological sites, is often difficult in the absence of clear morphological markers. Here we present a robust method of analysing genus‐specific collagen peptides by mass spectrometry simply by using solid‐phase extraction (a C18 ZipTip®) for peptide purification, rather than liquid chromatography/mass spectrometry (LC/MS). Analysis of the collagen from 32 different mammal species identified a total of 92 peptide markers that could be used for species identification, for example, in processed food and animal feed. A set of ancient (>100 ka@10°C) bone samples was also analysed to show that the proposed method has applications to archaeological bone identification. Copyright © 2009 John Wiley & Sons, Ltd.     

Identification strategies for flame retardants employing time‐of‐flight mass spectrometric detectors along with spectral and spectra‐less databases

In the past, the preferred strategy for the identification of unknown compounds was to search in an appropriate mass spectral database for spectra obtained using either electron ionisation (GC‐MS analyses) or collision‐induced dissociation (LC‐MS/MS analyses). Recently, an increase has been seen in the use of accurate mass instruments and spectra‐less databases, based on monoisotopic accurate mass alone. In this article, we describe a systematic workflow for the screening and identification of new flame retardants. This approach utilises LC‐quadrupole‐time‐of‐flight MS and spectra‐less databases based only on monoisotopic accurate mass for the identification of ‘unknowns’. An in‐house database was built, and the input parameters used in the data analysis process were optimised for flame retardant chemicals, so that it can be easily transferred to other laboratories. The procedure was successfully applied to dust, foam and textiles from car interiors and indoor consumer products. The developed method was demonstrated for the main new flame retardant present in Antiblaze V6 and for the three unreported reaction by‐products/impurities present in the same technical mixture. Copyright © 2015 John Wiley & Sons, Ltd.     

Integrated analytical methodologies for the study of corrosion processes in archaeological bronzes

The investigations on structure and micro-chemical composition of archaeological metal alloys are needed in archaeometry. The aim of this study is devoted both to acquire information about their provenance and production technology, and to improve our understanding about the corrosion processes. In this paper we present the study of the corrosion phenomena of bronze samples, laboratory-made according to binary, ternary and quaternary alloys typical of Roman archaeometallurgical production through an integrated methodology based on the use of non or micro invasive physical techniques. Among the analysed samples, two were artificially aged through burial in the archaeological site of Tharros, along the west coast of Sardinia (Italy). The corrosion products, typical of the bronzes in archaeological sites near the sea, have been characterized by non invasive and micro-destructive measurements. In particular, the corrosion patinas were examined through optical microscopy, scanning electron microscopy and microanalysis, X-ray fluorescence and laser ablation spectroscopy. The use of integrated technologies allowed us to determine both the elemental composition and surface morphology of the patina, highlighting the correlation between patina nature and chemical composition of the burial context. Moreover, data obtained by the laser-induced breakdown spectroscopy along the depth profile on the samples, have yielded information about the stratigraphic layers of corrosion products and their growth. Finally, the depth profiles allowed us to verify both the chemical elements constituting the patina, the metal ions constituting the alloy and the occurrence of migration phenomena from bulk to the surface.     

Electrochemical identification of metal ions in archaeological ceramic glazes by stripping voltammetry at graphite/polyester composite electrodes

The electrochemical response of metal ions in different samples of coloured ceramic tin-lead glazes attached to graphite/polyester composite electrodes is described. In addition to the ubiquous signals for lead, reductive dissolution processes are followed by anodic stripping peaks for Co, Cu, Sb, Mn, Sn and Fe, enabling the direct identification of such elements in microsamples proceeding from archaeological glazed tiles from Valencia (Spain) workshops (16th-18th century). Additional anodic and cathodic peaks corresponding to redox processes involving metal species in solution generated during stripping processes are also used. Peak potentials, Tafel plots and shape parameters are used for characterising the different species.     

Quantitation of Metal Ions in Archaeological Glass by Abrasive Stripping Square‐Wave Voltammetry Using Graphite/Polyester Composite Electrodes

A method for identifying Co, Cu, Sb, Sn, Fe, Zn, and Zr pigments in glasses using square‐wave voltammetry as the detection mode is described. It is based on the abrasive attachment of glass microsamples to graphite/polyester composite electrodes. Sample amounts less than 1 μg are used allowing for the study of archaeological samples. In all cases well‐defined anodic stripping peaks corresponding to the oxidation of metal deposits generated at potentials ranging from ?0.6 to ?1.6 V (vs. SCE) are obtained. This response is in agreement with that displayed by the corresponding metal oxides. Quantitative estimates of the relative population of metal ions in glasses are obtained from peak area measurements with an accuracy comparable to that obtained with SEM/EDX.