Photoageing of Baltic amber – Influence of daylight radiation behind window glass on surface colour and chemistry

The aim of this study was to provide evidence about the interaction between Baltic amber and daylight behind window glass, essential to understanding the mechanisms by which the material degrades in museum environments and to propose techniques for preventive conservation based on the control of environmental parameters where amber objects are stored or displayed. To investigate the photodegradation of Baltic amber, the methodology consisted of artificial ageing, in order to initiate degradation of model amber samples, and non-destructive analytical techniques, in order to identify and quantify changes in colour and chemical properties. Prism-shaped samples, obtained from a large amber piece, were exposed to different microclimatic conditions, subjected to accelerated photoageing and analysed by spectrocolorimetry, infrared spectroscopy and Raman spectroscopy. The experiments provided results about surface discolouration, oxidation of the molecular structure and breakdown of unsaturated carbon-carbon bonds in various environmental conditions, confirming the degrading role of daylight behind window glass. The conclusions of this study can be applied to the development of techniques for preventive conservation of museum collections containing amber objects.     

LC-MS and FT-IR characterization of amber artifacts

This work focuses on using analytical methods, such as Fourier transform Infrared spectroscopy (FTIR) and high performance liquid chromatography (HPLC) with mass spectrometry (MS) detection to assess archaeological and geological amber. The main goal of this study is to apply the previously developed and optimized analytical methods in verifying criteria to ascribe and characterize the origin of materials found in archaeological sites. The proposed LC-MS method was successfully applied for the quantification of succinic acid content both in geological and archaeological samples of amber and offers excellent linearity between 0.1 and 5??g mL^?1. The developed FTIR method provided some criteria which is able to differentiate between Baltic and Romanian amber (Romanite) that furthermore validates on archaeological amber artefacts.      

Mass spectrometry in the characterization of ambers. I. Studies of amber samples of different origin and ages by laser desorption ionization, atmospheric pressure chemical ionization and atmospheric pressure photoionization mass spectrometry

Amber is a fossil resin constituted of organic polymers derived through complex maturation processes of the original plant resin. A classification of eight samples of amber of different geological age (Miocene to Triassic) and geographical origin is here proposed using direct mass spectrometric techniques, i.e. laser desorption ionization (LDI), atmospheric pressure chemical ionization (APCI) and atmospheric pressure photoionization (APPI), in order to obtain a fingerprint related to the amber origin. Differences and similarities were detected among the spectra with the four methods, showing quite complex spectra, full of ionic species in the mass range investigated (up to m/z 2000). The evaluation required statistical analysis involving multivariate techniques. Cluster analysis or principal component analysis (PCA) generally did not show a clear clustering with respect to the age of samples, except for the APPI method, which allowed a satisfying clustering. Using the total ion current (TIC) obtained by the different analytical approaches on equal quantities of the different amber samples and plotted against the age, the only significant correlation appeared to be that involving APPI. To validate the method, four amber samples from Cretaceous of Spain were analyzed. Also in this case a significant correlation with age was found only with APPI data. PCA obtained with TIC values from all the MS methods showed a fair grouping of samples, according to their age. Three main clusters could be detected, belonging to younger, intermediate and older fossil resins, respectively. This MS analysis on crude amber, either solid or extract, followed by appropriate multivariate statistical evaluation, can provide useful information on amber age. The best results are those obtained by APPI, indicating that the quantity of amber soluble components that can be photoionized decreases with increasing age, in agreement with the formation of highly stable, insoluble polymers.     

Analytical methods to differentiate Romanian amber and Baltic amber for archaeological applications

The study aims to establish several definite criteria which will differentiate Romanian amber and Baltic amber to certify the local or Baltic origin of the materials found in archaeological sites on the Romanian territory, by using light microscopy and performing analytical methods, such as Fourier transform infrared spectroscopy-variable angle reflectance and liquid chromatography with mass spectrometry detection. Experiments especially by Fourier transformed infrared spectroscopy, were applied to a wide range of samples with controlled origin. The methods were optimised and resulted in premises to apply the techniques to analysis of the archaeological material.      

Direct Determination of Aluminum in Archaeological Clays by Laser‐Induced Breakdown Spectroscopy

Abstract

Instrumental techniques that allow the direct analysis of solids with little or no sample preparation are particularly important for the evaluation of samples that are difficult to analyze such as refractory or geological materials. Laser‐induced breakdown spectroscopy (LIBS) is a promising technique for the direct, rapid analysis of elements in solid materials with minimal sample preparation. The main advantages over wet techniques are virtual nondestructiveness and analysis speed. The goal of this work is the direct determination of aluminum of archaeological pieces using laser‐induced breakdown spectroscopy. The corresponding signals of metals were interpolated from calibration graphs of different salts of the metals. The matrix effects from the direct determination of these elements were thoroughly investigated. The potential of this technique for direct quantitative analysis of real archaeological materials (from Department of Ancient Science, University of Zaragoza) was evaluated, and the reproducibility of LIBS spectra from different archaeological samples was measured as a function of the number of laser shots. Finally, the results from LIBS are compared with those obtained by laser ablation inductively coupled plasma mass spectrometry.     

Surface yellowing and fragmentation as warning signs of depolymerisation in Baltic amber

It is well known that the surrounding environment affects the initiation and rate of degradation of Baltic amber, causing changes in visual and mechanical properties. However, the mechanisms by which oxygen, the most important agent of degradation, causes those alterations are still unknown. Knowledge of such mechanisms would allow developing more efficient preventive conservation measures for amber artefacts in museums than those available today. In this study, an experiment using accelerated thermal ageing was conducted on representative Baltic amber samples. Changes in colour, topography and chemical properties were assessed regularly using non-destructive techniques, to identify the degradation phenomena which play a significant role during the discolouration and fragmentation processes of amber surfaces. The breakdown of the amber polymer chains, caused by oxidative radical reactions, was determined by means of FT-Raman spectroscopy and involved the formation of olefinic bonds in the terminal position. This depolymerisation process was correlated to modifications in colour, particularly yellowing, and in topographic features, analysed by spectrocolorimetry and confocal profilometry respectively. Thus, surface yellowing and fragmentation of amber objects in museum collections may act together as indicators of progressive depolymerisation.     

Characterization of prehistorical glass beads excavated from Khao Sam Kaeo (Chumphon, Thailand) using PIXE and SEM–EDS

It was proved that non-destructive and non-sampling methods were used to analyze the composition of the archaeological glasses. Glass has been used in ornaments and decoration in Thailand for thousands of years. In this study, glass bead fragments found from the archaeological site at Khao Sam Kaeo, Chumphon Province, southern Thailand were analyzed by the proton induced X-ray emission spectroscopy (PIXE) and scanning electron microscope coupled with energy dispersive X-ray fluorescence spectroscopy (SEM?CEDS). The composition analysis showed that copper was mainly presence as the colorant. Titanium, common impurity in sand, was all present in the glass bead samples. Furthermore, this type of glass almost spread over the various sites in this region that demonstrated the long distance or exchange connections. Finally, PIXE and SEM?CEDS have been used to be the efficient techniques to analyze the archaeological objects, especially the glassy materials, to understand their characteristics and how they were produced in ancient times.     

Raman spectroscopic study on archaeological glasses in Thailand: ancient Thai glass

Glasses have been used as ornamental and decorative objects in Thailand for several hundred years as seen in archaeological artifacts, such as glass beads found throughout the regions. Decorative glasses can generally be seen as architectural components in Buddhist temples and old-styled palaces. They came in various colors ranging from transparent to amber, blue, green and red of different shades and tones. Fragments of archaeological glass samples were characterized for the first time using Raman spectrophotometer with the aim of obtaining information that would lead to the identification of the glass samples by means of laser scattering. The samples were also investigated using other techniques, such as proton induced X-ray emission spectroscopy, scanning electron microscopy cooperated with energy dispersive X-ray fluorescence spectrometer and synchrotron radiation to induced X-ray fluorescence. The results showed that they were mostly lead-silica based glasses whose colors were induced by metal ions. The differences in chemical compositions were confirmed by Raman signature spectra.     

Identification of volatile degradation products from Baltic amber by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry

The aim of this study was to test and develop techniques for the detection and identification of volatile compounds released as degradation products by Baltic amber. During a preliminary investigation, the off-gassing of acidic volatiles was detected through the corrosion of lead coupons. The corrosive compounds released by the material were then identified as formic acid and acetic acid by headspace solid-phase microextraction coupled with gas chromatography–mass spectrometry. During an advanced investigation, based on the use of artificial ageing to initiate degradation of model amber samples in different microclimates, the detected formic acid and acetic acid off-gassing appeared to be more intense in a dry environment with normal oxygen concentration. The release of formic and acetic acids by the amber was likely the result of radical reactions which should be investigated in further studies.     

Raman spectroscopic analyses of preserved historical specimens of human hair attributed to Robert Stephenson and Sir Isaac Newton

The Raman spectra of two historical specimens of human hair attributed to the engineer Robert Stephenson and scientist Sir Isaac Newton, preserved in private collections are reported. Comparisons are made with the Raman spectra of modern hair specimens and with hair from archaeological excavations. The hair spectra collected with a laser excitation of 785 nm are of a better quality than those collected using 1064 nm. The historical hair specimens are remarkably well-defined spectroscopically in terms of the amide I vibrational mode and the [small nu](SS), ascribed to a predominantly gauche-gauche-gauche CSSC conformation. The contrast with degraded hair specimens recovered from archaeological excavations is striking. The presence of a weak feature near 2590 cm(-1) in the hair samples attributed to a [small nu](SH) vibration could be indicative of a reduction process operative on the CSSC cystine keratotic linkages and a possible origin of this is bacterial biodegradation identified histologically. This study demonstrates the molecular information available from non-destructive Raman spectroscopic analysis from single hair shafts or small bundles of fibres which complements information available from histological and destructive analytical techniques for rare biological specimens subjected to conservation or curation procedures in museums or private collections.     

Thermal desorption/gas chromatography/mass spectrometry approach for characterization of the volatile fraction from amber specimens: A possibility of tracking geological origins

Research on the chemical composition of fossil resins has evolved during the last decades as a multidisciplinary field and is strongly oriented toward the correlation with their geological and botanical origin. Various extraction procedures and chromatographic techniques have been used together for identifying the volatile compounds contained in the fossil resin matrix. Hyphenation between thermal desorption (TD), gas chromatography (GC) and mass spectrometry detection (MS) has been chosen to investigate the volatile compounds fraction from ambers with a focus on Romanite (Romanian amber) and Baltic amber species. A data analysis procedure was developed for the main purpose of fingerprinting ambers based on the MS identity of the peaks generated by the volatile fraction, together with their relative percentual area within the chromatogram. Chromatographic data analysis was based entirely on Automated Mass Spectral Deconvolution & Identification System (AMDIS) software to produce deconvoluted mass spectra which were used to build-up a mixed mass spectra and relative retention scale library. Multivariate data analysis was further applied on AMDIS results with successful discrimination between Romanite and Baltic ambers. A special trial was conducted to generate pyrolysis “like” macromolecular structure breakdown to volatile compounds by gamma irradiation with a high absorbed dose of 500 kGy. Contrary to our expectations the volatile fraction fingerprints were not modified after irradiation experiments. A complementary non-destructive new approach by ESR spectroscopy was also proposed for discriminating between Romanite and Baltic ambers.     

Surface-analytical studies on environmental and geochemical surface processes.

The surface chemical compositions of solid samples from environmental and geological sources can differ from the bulk or average compositions, because of changes caused by adsorption, dissolution, oxidation, etc. Accordingly, analytical information on surface layers is important for a better understanding of the environmental chemistry involving solid surfaces. The rapid development of surface-analytical techniques has enabled us to probe the surface chemistry of environmental and geological solid samples of complex composition. This article demonstrates some examples of important items of information that can be obtained by applying surface-analytical techniques, such as X-ray photoelectron spectroscopy and secondary ion mass spectrometry, to environmental and geological samples. The surface analysis of fly ashes, soils, sediments and weathered silicate minerals is reviewed.     

Three-dimensional micro-XRF investigations of paint layers with a tabletop setup

The non-destructive investigation of art and archaeological objects with depth sensitivity is now possible using 3D micro-XRF spectroscopy. More detailed answers for questions on painting techniques, on the pigment palette, on the production processes and indirectly on dating or provenancing of objects are accessible now. This was already illustrated by the investigation of Mughal miniatures with a confocal setup at the synchrotron source BESSY.In this paper we demonstrate the feasibility of 3D micro-XRF spectroscopy with a tabletop setup and discuss its sensitivity in comparison to the synchrotron-based setup. Investigated objects are glass standards and also prepared paint layers. Perspectives for other types of studies are proposed.     

Molecular characterisation of birch bark tar by headspace solid-phase microextraction gas chromatography-mass spectrometry: a new way for identifying archaeological glues

To develop an analytical methodology, as non-destructive as possible, suitable for the identification of natural substances from archaeological origin, we studied the potentiality of solid-phase microextraction (SPME) for analysing birch bark tar, an adhesive commonly used during ancient times. First of all, birch bark tars were produced by a controlled heating of birch bark. The two kinds of samples obtained using different processes of fabrication, one at liquid state, the second one at solid state, were then analysed by headspace HS-SPME-GC-MS. Different conditions of sample treatment were tested (two different fibre coatings, various times and temperatures of extraction) in order to suggest optimal conditions for the analysis of birch bark tar. Both samples were shown to be rich in volatile organic components. Two main groups of constituents, namely phenolic compounds issued from lignin or tannin known to be present in bark and sesquiterpenoid hydrocarbons, secondary metabolites largely distributed in the plant kingdom, were detected for the first time in birch bark tar. HS-SPME-GC-MS appears thus to be a very efficient method for investigating the volatiles emitted by plant tars and could be further used for the study of birch bark tar samples issued from archaeological context.     

First elemental imaging experiments on a combined PGAI and NT setup at the Budapest Research Reactor

The European collaboration “ANCIENT CHARM” () aims to develop new non-destructive neutron techniques to image the internal composition of complex archaeological objects in order to answer various archaeological questions. Among these techniques, prompt gamma activation imaging (PGAI) and neutron tomography (NT) form a unique combination which can determine the 3D distribution of most elements in objects with a non-destructive procedure. A spatial resolution better than 2 mm has already been achieved in a moderately scattering matrix material.     

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.     

Improved procedure for protein binder analysis in mural painting by LC-ESI/Q-q-TOF mass spectrometry: detection of different milk species by casein proteotypic peptides

Diagnostic techniques applied to the field of cultural heritage represent a very important aspect of scientific investigation. Recently, proteomic approaches based on mass spectrometry coupled with traditional spectroscopic methods have been used for painting analysis, generating promising results for binder’s protein identification. In the present work, an improved procedure based on LC-ESI/Q-q-TOF tandem mass spectrometry for the identification of protein binders has been developed for the molecular characterization of samples from an early-twentieth-century mural painting from the St. Dimitar Cathedral in Vidin, Bulgaria. The proteomic investigation has led to the identification of both egg white and egg yolk proteins, according to traditional old recipes for tempera paintings. In addition, beyond the egg components, the presence of caseins was also revealed, thus suggesting the use of milk as binding medium, fixative or stabilising agent. Furthermore, for the first time, the capability to discriminate the milk origin on the basis of alpha casein proteotypic peptides is reported, that are diagnostic for a given species, thus opening interesting perspectives in art and archaeological fields.     

Development of a micro-X-ray fluorescence system based on polycapillary X-ray optics for non-destructive analysis of archaeological objects

A new micro-X-ray fluorescence (micro-XRF) system based on rotating anode X-ray generator and polycapillary X-ray optics has been set up in XOL Lab, BNU, China, in order to be used for analysis of archaeological objects. The polycapillary X-ray optics used here can focus the primary X-ray beam down to tens of micrometers in diameter that allows for non-destructive and local analysis of sub-mm samples with minor/trace level sensitivity. The analytical characteristics and potential of this micro-XRF system in archaeological research are discussed. Some described uses of this instrument include studying Chinese ancient porcelain.     

Prompt gamma activation analysis for non-destructive characterization of chipped stone tools and raw materials

Recently, several archaeometrical projects were started on the prehistoric collection of the Hungarian National Museum. Among the analytical methods applied, non-destructive prompt gamma activation analysis (PGAA) has a special importance. Based on major-and trace components, characterization of stone tools and their raw materials were performed. Until now, 160 pieces from Carpathian Basin and from the surrounding area (Romania, Croatia, Ukraine, Poland and the Mediterranean region) have been analyzed, including both archaeological and geological pieces. Obsidian and Szeletian felsitic porphyry objects adequately separable with PGAA. Identification of high silica silex categories, however, is much more difficult.     

A spectrometric and chromatographic approach to the study of ageing of madder (Rubia tinctorum L.) dyestuff on wool

In this work, the lightfastness of wool textile samples, dyed with madder and its principal components alizarin and purpurin, was investigated using two complementary experimental techniques: absorption and emission UV-vis spectroscopy and chromatography (HPLC-PDA). Spectroscopic techniques were used to follow the time course of ageing, whereas chromatography was applied to determine relative compositional changes that occurred after exposure of wool dyed samples to natural and artificial ageing. The results from the two techniques integrate well each other and provide complementary and useful indications about the sensitivity of the dyed textiles to ageing, showing that purpurin is the principal component responsible for the spectral and chromatic properties of madder as well as for its degradation. The fading of both the fibre and dye is reduced in the presence of alum and in the absence of oxygen. The multi-analytical approach used highlights the potential of the UV-vis spectroscopy for the investigation of dyes on textiles. The great sensitivity of the spectrofluorimetry makes this technique particularly promising for a non-destructive study of dyes on works of art.