Olivier Schalm

Use of microscopic XRF for non‐destructive analysis in art and archaeometry

The various application possibilities of microscopic x-ray fluorescence and associated methods for the characterization and provenance analysis of objects and materials of cultural heritage value are discussed by means of a number of case studies. They include the trace analysis of historic glass, the analysis of corroded coins and statues in bronze and silver and the study of inks on historical documents. These studies are conducted by means of micro-XRF instruments installed at synchrotron beamlines and by means of laboratory equipment, some of which is easily transportable to the museum or archaeological site where the objects of interest are located. Copyright

A flexible and accurate quantification algorithm for electron probe X-ray microanalysis based on thin-film element yields

Abstract Quantitative analysis by means of electron probe X-ray microanalysis (EPXMA) of low Z materials such as silicate glasses can be hampered by the fact that ice or other contaminants build up on the Si(Li) detector beryllium window or (in the case of a windowless detector) on the Si(Li) crystal itself. These layers act as an additional absorber in front of the detector crystal, decreasing the detection efficiency at low energies (

The colour of silver stained glass—analytical investigations carried out with XRF, SEM/EDX, TEM, and IBA

Glass treated on its surface with silver compounds and an aluminosilicate, such as ochre or clay, at higher temperatures (between 550 and 650 °C) accepts a wide variety of a yellow colour. It is the aim of this study to investigate the parameters of the manufacturing process affecting the final colour of silver stained glass and to correlate them with the final colour and colour intensity. Therefore, defined mixtures of ochre and a silver compound (AgCl, AgNO3, Ag2SO4, Ag3PO4, Ag2O) were prepared and applied on soda-lime glass. The firing process was modified within the range from 563 to 630 °C and glass samples were analysed after treatment with energy dispersive X-ray fluorescence analysis (EDXRF), scanning electron microscopy (SEM/EDX), transmission electron microscopy (TEM), as well as ion beam analysis (IBA) with an external beam. Within the scope of IBA simultaneous measurements using particle-induced X-ray emission (PIXE), particle-induced gamma-ray emission (PIGE), and Rutherford backscattering spectrometry (RBS) were carried out in order to obtain the thickness of the Ag-rich surface layer and the depth distribution of Ag. By means of TEM the microstructure of the silver particles was visualised. XRF results show that the lowest amount of Ag could be detected on glass samples treated with silver stain mixtures containing AgCl and Ag2O. A low kiln temperature (e.g. 563 °C) results in a higher silver concentration at the surface and lower penetration depths. Furthermore, the results obtained with SEM/EDX at cross-sections of the glass samples could be confirmed by PIXE, PIGE, RBS, and TEM.

Electrochemical photodegradation study of semiconductor pigments: influence of environmental parameters.

Chemical transformations in paintings often induce discolorations, disturbing the appearance of the image. For an appropriate conservation of such valuable and irreplaceable heritage objects, it is important to have a good know-how on the degradation processes of the (historical) materials: which pigments have been discolored, what are the responsible processes, and which (environmental) conditions have the highest impact on the pigment degradation and should be mitigated. Pigment degradation is already widely studied, either by analyzing historical samples or by accelerated weathering experiments on dummies. However, in historic samples several processes may have taken place, increasing the complexity of the current state, while aging experiments are time-consuming due to the often extended aging period. An alternative method is proposed for a fast monitoring of degradation processes of semiconductor pigments, using an electrochemical setup mimicking the real environment and allowing the identification of harmful environmental parameters for each pigment. Examples are given for the pigments cadmium yellow (CdS) and vermilion (α-HgS).

Composition of 15–17th Century Archaeological Glass Vessels Excavated in Antwerp, Belgium

In the beginning of the 16th century, Antwerp (Belgium) was one of the largest ports of Europe and an important centre for the manufacture and import of glassware, especially for Venetian and fagon-de-Venise glass vessels. As a result, archaeological excavations in the historical centre of Antwerp have yielded a number of important glass finds from the 15th until the 17th century. Within this extensive collection, several typological categories of glass vessels can be distinguished. The major and trace composition of a series of 96 representative glass objects was determined by means of EPXMA (electron probe X-ray micro analysis) and μ-SRXRF (synchroton radiation induced X-ray fluorescence analysis). Four major compositional types could be distinguished. The correlation between object composition, colour and type is discussed. Special emphasis is placed on the composition of the facon-de-Venise or Venetian glass objects found in Antwerp and on the comparison of this composition to that of glass of the same type found in other locations in Europe.

Spread of façon-de-Venise glassmaking through central and western Europe

Abstract The major and trace composition of a series of 16th century glass fragments, originating from the ruins of different 15–17th century castle sites in the neighborhood of Ljubljana (Slovenia) was determined. The resulting compositions are compared to those obtained from archaeological glass finds originating from Ljubljana city center, Antwerp (Belgium) and Venice (Italy). In these urban centers, historic documents describe the existence of a flourishing glass making and working industry in the 16th century. Electron probe X-ray microanalysis (EPXMA) combined with microscopic synchrotron induced X-ray fluorescence (μ-SRXRF) was used to analyze the glasses from the Slovenian castles and from Antwerp while ion beam analysis (proton induced X-ray and γ-emission PIXE/PIGE) was used for the Ljubljana samples. A comparison of the major glass compositions of the latter glass samples obtained by means of EPMA and the ion beam methods revealed that the differences between the two sets of data are generally smaller than 10%, except in the case of concentrations smaller than 1% w/w where typical values of 20% of relative deviation are encountered. In contrast to Antwerp, where both local and Venetian glass compositions are encountered, the Ljubljana and Slovenian castle glasses feature a composition that closely resembles that of Venetian vitrum blanchum glass.

Micro and Surface Analysis in Art andArchaeology

A variety of instrumental analytical techniques can be applied to the physical and chemical examination of works of art and archaeology. In this paper, a few examples are discussed of the application of micro-analytical chemistry in this interdisciplinary field. The following subjects from the experience of our laboratory, in collaboration with several specialized institutes, were selected: Early Bronze Age ceramic crucibles, residues and powders from Goltepe, South Central Turkey, have been analysed using surface analytical techniques to investigate potential evidence of tin smelting. The study indicates that the crucibles were used for processing of tin and gives clear evidence of a local tin industry. Roman glass from a collection of objects discovered in Qumrân near the Dead Sea was used to study the corrosion of glass objects in a particularly stable environment over a period of nearly 2000 years. The corrosion of a series of glass-in-lead windows from St. Michael and St. Goedele’s Cathedral, Brussels, was studied using electron probe microanalysis and micro X-ray fluorescence. New views can be formulated on the corrosion mechanism, which appears to be a complex multiphase process under the influence of atmospheric pollution. A few preliminary results are discussed for the analysis of glass paintings, in particular carnation red glass paints.

Characterization of the main causes of deterioration of grisaille paint layers in 19th century stained-glass windows by J.-B. Capronnier☆

Abstract Twenty-seven glass fragments containing dark coloured grisaille paint layers of different qualities were collected from ten windows of the cathedral St. Michael & St. Gudule in Brussels (Belgium). The windows were made by J.-B. Capronnier (1814–1891) and cover the period between 1843 and 1878. The samples were cross-sectioned and examined in an electron microscope. Grisaille paint layers are not homogeneous and therefore, it is not meaningful to characterize them in terms of their average composition. Instead, parameters such as granularity, the number of residual gas bubbles per running millimetre of paint, the type of pigments, and the thickness of the paint layer were used to characterize them. The microscopic morphology allows a classification of the grisaille paint layers in four groups, every group associated with a quality level. Moreover, the main causes of the accelerated degradation of some of these paint layers could be explained. The classification made it possible to distinguish two periods in the work of Capronnier: (1) the early period (1843–1848) is characterized by the presence of either single granular paint layers or of double-layered systems consisting of a granular paint layer on top of a well-melted paint layer. The granular grisaille paint layers tend to pulverize; (2) the later period (1848–1878) is characterized by the presence of only well-vitrified paint layers. No sign of deterioration was found on the well-vitrified paint layers.

Application of auxiliary signals in x-ray fluorescence and electron microprobe analysis for density evaluation

Information included in auxiliary signals, i,e. incoherently and coherently scattered signals and transmitted beam intensities in x-ray fluorescence analysis (XRF), a selected channel in the scattered white synchrotron radiation and in the contents of selected hremsstrahlung channels in electron microprobe analysis (EMPA), can be extracted and exploited to complete the results of analyses. Such additional information is much more detailed when the devices are operating in the microprobe mode; however, this is not a necessary condition. The theoretical basis for the use of the auxiliary signals, in the sense proposed in this paper, is discussed. In situations where the main component is of essentially constant chemical composition but with variable density through the sample (wood of living trees, petrified wood, stalactites, coral structures-in general natural periodic structures) or with inclusions inside, the application of two kind of signals is preferable in XRF: the transmitted and scattered signal. For light organic matrices (cellulose, plastics), the information included in the Rayleigh or Compton signal is reversed in relation to the information from the transmission signals. The selected hremsstrahlung signal or the signal from the secondary electron spectrum can serve the same purpose if EMPA analysis is performed. In general, these signals provide auxiliary knowledge about the density of objects. An especially interesting situation is when the object is a chemical negative of the original, such as the distribution of silica in some kinds of petrilied wood with respect to the distribution of the cellulose in the original wood. Many original results of analyses are shown. Intercomparisons of the transmission images with the reversed scattered scans in light matrices are still scarce, while the observation of bremsstrahlung or secondary electron scans (in EMPA) and their scattered or transmission analogues (in XRF) for objects and their chemical negatives is demonstrated for the first time. Comprehensive results of the analyses of petrified wood and stalactites (EMPA and XRF) are presented.

Analysis of speleothems by electron and X-ray microprobes

A piece of stalagmite from a cave in Winthertore, Belgium, was analysed by the use of capillary tabletop and synchrotron versions of X-ray microprobes and then by the electron microprobe. The potential of these microprobes was tested for the first time in the study of such specific periodic objects. Indirect measurements of the morphology/density of samples were made by the use of Compton and Rayleigh scattered radiation in the X-ray tabletop microprobe and a selected channel in white scattered radiation in the X-ray synchrotron microprobe. In the electron microprobe, the linear profile extracted from the grey-scale transformation of the secondary electron image was used for the same purpose. The elemental analyses were superimposed on the density characteristics of the samples. The inclusions of iron and silicon, measurements of the magnesium/calcium/strontium/barium ratio, profiles of anionic species and the noticeable presence of iodine were among the most important findings. Some of the measured parameters probably allow the creation of thermometric scales for the potential estimation of the climatic conditions during the deposition of the calcite material.