Article

The Eye of the Medusa - XRF Imaging Reveals Unknown Traces of Antique Polychromy

Authors:
  • INSIGHT (Institute for the Study and Integration of Graphical Heritage Techniques)
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Abstract

The colorful decoration of statues and buildings in antique times is commonly described by the term Antique Polychromy. It is well known among scholars but less so in the interested public and its exact form is subject of ongoing research. In this paper we discuss results obtained from the Frieze of the Siphnian Treasury from the Sanctuary of Delphi (Greece). We will present the first applica-tion of a mobile instrument for macro-XRF imaging in the investigation of the Antique Polychromy and show that it allows to find significant traces not visible to the naked eye and not detectable by XRF spot measurements or any other mobile, non-invasive method. These findings allow for a partial reconstruction of the polychromy. Further, we present a novel approach to correctly interpret artifacts resulting from changes of the detection geometry in the investigation of complexly shaped samples by XRF imag-ing. This approach is based on the 3D surface model acquired by photogrammetry and fundamental parameter calculations.

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... Lastly, systematic studies have been conducted on the remains of paint on marble sculptures, but few analytical publications contain a description of the analytical methodology (Brons et al. 2020;Magrini et al. 2019;Bracci et al. 2020;Alfeld et al. 2017;Aggelakopoulou and Bakolas 2022;Abbe and Şare Ağtürk 2019). The commonly defined noninvasive standard protocol involves the use of multispectral imaging and video microscopy coupled with non-invasive punctual spectroscopies (Raman, XRF, FTIR) corresponding to the areas where the remains of colour are observed (Østergaard 2018). ...
... The commonly defined noninvasive standard protocol involves the use of multispectral imaging and video microscopy coupled with non-invasive punctual spectroscopies (Raman, XRF, FTIR) corresponding to the areas where the remains of colour are observed (Østergaard 2018). However, as has been demonstrated in an earlier publication (Alfeld et al. 2017), spot analysis makes it difficult to match visual observation with physico-chemical data. Consequently, contaminations from soil or from the iron elements that connect the different parts of the marble statues can be misinterpreted as traces of pigments. ...
... The position of the X-ray tube, detector and collimator was fixed by a 3D-printed plastic holder. The instrument was previously described elsewhere (Alfeld et al 2017). 18 scans were carried out on the objects discussed in this article. ...
Article
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... This problem was addressed by using fundamental parameter calculations in combination with photogrammetry, i.e., the calculation of an object's 3D shape based on series of photographs. Results are shown in Fig. 6 [122]. ...
... Similar, as discussed above, fundamental parameter based calculations were used, not to correct for differences in stratigraphy but in object shape and thus measurement geometry of painted 6th century BC marble statues, based on 3D models obtained with photogrammetry [122]. ...
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Article
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... MA-XRF has been used for the investigation of the distribution of ancient pigments at synchrotron radiation sources [12][13][14] and one mobile application has been reported [15]. Mobile hyperspectral reflectance imaging has not yet been applied to the study of ancient pigment use. ...
... In this publication we describe the investigation of ancient polychromy on the Frieze of the Siphnian Treasury (6th century BC) in the Delphi Archaeological Museum (Greece), described in detail in Section 2.1. In a previous study on the same object we showed the value of MA-XRF to reveal traces of pigments hidden under soil encrustation on the head of Medusa on the shield of Achilleus (shown in the right of the photograph in Fig. 4) and used the combination of a 3D model obtained by photogrammetry and fundamental parameter calculations to address the complex shape of the object [15]. ...
... Spot measurements were done with 300 s/ spot. The instrument is virtually identical to the one used previously [15] with the exception of the changed detection angle and shown in Fig. 1. ...
Article
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Article
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... For a 300 s measurement they were found to be between 120 ppm (Ca, Z = 20) and 22 ppm (Cu, Z = 29) for elements heavier than Ca (Z = 20). The instrument has been previously described elsewhere [11]. ...
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... V. Brinkmann has since 1981 studied in detail the sculptures of the Temple of Aphaia in Aegina and the Greek tombstones in Munich sculpture Museum and focused on the application of new methods in photographic technique to the discovery and documentation of ancient colours with emphasis on their potential diagonal lighting (Vlasopoulou 2012;Brinkmann 2007). As for Delphi archaic monuments with coloured remains notable is the extensive report to the multi-coloured frieze of the Siphnian treasury (Brinkmann 1994;Alfeld et al., 2017). ...
Article
Non-destructive analysis by means of portable X-ray flourescence (pXRF) and Raman spectroscopy of color traces on sculptures and architectural parts from the Delphi Museum, Phokis, Greece, are presented. These sculptures and architectural parts are dated to the Archaic period (7th-6th c. B.C.). The main question to be answered is the mineral/pigment used for each part and therefore to reconstruct the color palette of the artists. For this research, sixteen archaeological exhibits of the Delphi museum were analyzed with two different spectroscopies, and the white, red, black, yellow and blue pigments were identified.
... Paleontological objects (fossilized remains of animals and plants) have the potential to preserve remnant chemistry of the original organism (some constrained by specific biomarkers). Such fossils include mineralized soft Sciau et al. (2006), Liu et al. (2007), Lynch et al. (2007), Mirguet (2009), Leon et al. (2010, Jackson et al. (2013Jackson et al. ( , 2014Jackson et al. ( , 2017, Dejoie et al. (2014aDejoie et al. ( , b, 2015, Leon et al. (2015), and Bertrand et al. (2017) Advanced Photon Source ( 1-5 μm 2 Dredge et al. (2015Dredge et al. ( , 2017, MacLeod (2015), Popelka-Filcoff et al. (2015, Jones et al. (2016), Thurrowgood et al. (2016, Alfeld andde Viguerie (2017), de Jonge et al. (2017), Sharp-Paul (2017), Kirkwood et al. (2018), Ryan et al. ( , 2014Ryan et al. ( , 2018, Paterson et al. (2011), andHoward et al. (2012) XAS Riesemeier et al. (2005), Reiche et al. (2006Reiche et al. ( , 2011, and Radtke et al. (2013Radtke et al. ( , 2016 CHESS μm Swanston et al. (2012Swanston et al. ( , 2015, Michelin et al. (2013), Rouchon and Bernard (2015), and Alleon et al. (2016aand Alleon et al. ( , 2017 Canadian Light Source ( Michelin et al. (2013), Rouchon and Bernard (2015), Alleon et al. (2016aAlleon et al. ( , 2017, and Gueriau et al. (2017) 11ID-1 SGM ∼20-100 μm diameter Bergmann ( , 2007Bergmann ( , 2011, Bergmann and Knox (2009, Larson et al. (2010), Sadeghi and Bergmann (2010), Edwards et al. (2011aEdwards et al. ( , b, 2013Edwards et al. ( , 2014Edwards et al. ( , 2016Edwards et al. ( , 2018, Wogelius et al. (2011), Manning et al. (2013), Anne et al. (2014Anne et al. ( , 2017Anne et al. ( , 2018, Barden et al. (2015a, b), Egerton et al. (2015), Harazim et al. (2015), Gueriau et al. (2017), and Gibson et al. (2018) 10-2 Bertrand et al. (2011), andHoerlé et al. (2016) tissue that is not seen in the visible light spectrum and is often overlooked in such fossils. This additional information can lead to a better understanding of the pigmentation, anatomy, development and growth stage, diet, and even health of the organism prior to death. ...
... For many centuries these material expressions were thought to have been monochromatic-given the lack of empirical evidence confirming their polychromy; a paradigmatic illustration of a past idealized as pure and white [1,2]. These works are now seen in their original polychrome as the result of varied chemical analyses [3,4]. In a similar fashion, the Pre-a1111111111 a1111111111 a1111111111 a1111111111 a1111111111 followers to, "undo the vault where the idol was and break him in front of everyone" [32:133] (S1 Text). ...
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Pachacamac is the name of the 15th-16th century Inca sanctuary on the Peruvian coast as well as the name of one of the principal oracles of Inca divinities. This effigy would have been destroyed by Pizarro in 1533 during his visit to the great monumental complex, and as such the originality and antiquity of the wooden statue—the so-called Pachacamac Idol—have been the subject of much controversy and debate. We present here previously unpublished dates that confirm its manufacture during the Middle Horizon (AD 500–1000), as well as evidence of its original polychromy. Traces of colors were observed on its different sections with portable microscopy and analyses with two different X-Ray Fluorescence spectrometry techniques, leading to identification of yellow, white, and red mineral pigments, including the presence of cinnabar. Dated between the 8th and 9th centuries, the statue would have been worshipped for almost 700 years, from the time of its creation to the time of the Spanish conquest, when Pachacamac was a major place of pilgrimage. These data not only offer a new perspective on Pachacamac’s emblematic sacred icon, but also on the colorful practices of the Pre-Hispanic Andes.
... Paleontological objects (fossilized remains of animals and plants) have the potential to preserve remnant chemistry of the original organism (some constrained by specific biomarkers). Such fossils include mineralized soft Sciau et al. (2006), Liu et al. (2007), Lynch et al. (2007), Mirguet (2009), Leon et al. (2010, Jackson et al. (2013Jackson et al. ( , 2014Jackson et al. ( , 2017, Dejoie et al. (2014aDejoie et al. ( , b, 2015, Leon et al. (2015), and Bertrand et al. (2017) Advanced Photon Source ( 1-5 μm 2 Dredge et al. (2015Dredge et al. ( , 2017, MacLeod (2015), Popelka-Filcoff et al. (2015, Jones et al. (2016), Thurrowgood et al. (2016, Alfeld andde Viguerie (2017), de Jonge et al. (2017), Sharp-Paul (2017), Kirkwood et al. (2018), Ryan et al. ( , 2014Ryan et al. ( , 2018, Paterson et al. (2011), andHoward et al. (2012) XAS Riesemeier et al. (2005), Reiche et al. (2006Reiche et al. ( , 2011, and Radtke et al. (2013Radtke et al. ( , 2016 CHESS μm Swanston et al. (2012Swanston et al. ( , 2015, Michelin et al. (2013), Rouchon and Bernard (2015), and Alleon et al. (2016aand Alleon et al. ( , 2017 Canadian Light Source ( Michelin et al. (2013), Rouchon and Bernard (2015), Alleon et al. (2016aAlleon et al. ( , 2017, and Gueriau et al. (2017) 11ID-1 SGM ∼20-100 μm diameter Bergmann ( , 2007Bergmann ( , 2011, Bergmann and Knox (2009, Larson et al. (2010), Sadeghi and Bergmann (2010), Edwards et al. (2011aEdwards et al. ( , b, 2013Edwards et al. ( , 2014Edwards et al. ( , 2016Edwards et al. ( , 2018, Wogelius et al. (2011), Manning et al. (2013), Anne et al. (2014Anne et al. ( , 2017Anne et al. ( , 2018, Barden et al. (2015a, b), Egerton et al. (2015), Harazim et al. (2015), Gueriau et al. (2017), and Gibson et al. (2018) 10-2 Bertrand et al. (2011), andHoerlé et al. (2016) tissue that is not seen in the visible light spectrum and is often overlooked in such fossils. This additional information can lead to a better understanding of the pigmentation, anatomy, development and growth stage, diet, and even health of the organism prior to death. ...
... 10 Chemical imaging methods can be divided into two distinct categories of elemental or molecular species information. On the one hand, there are elemental mapping/imaging techniques 11 such as X-ray fluorescence (XRF), 12 laser ablation (LA)-inductively coupled plasma-mass spectrometry (ICP-MS), 13 and glow discharge (GD) plasmas. 14 These techniques provide information on how certain elements are distributed across and within a structure. ...
Article
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... However, artists purposefully create paintings with topographical surface to provide a level of plasticity and depth. This is particularly interesting for painted marbles from Roman or Greek antiquity [2,7] where correction for variation in the surface was made in post processing. However, not all image distortion is recoverable and may more easily be avoided when capturing an image. ...
Chapter
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... The technique is relatively fast; the acquisition time naturally depends on the dimensions of the area of analysis and the dimensions and characteristics of the instrument employed. Numerous types of equipment are available nowadays, ranging from small and easy-to-transport instruments customized for the analysis of areas of only a few cm 2 [2,3] to massive scanners allowing large areas to be analysed in a reasonably short acquisition time [4][5][6]. ...
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Chapter
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Paintings are near-planar objects with material characteristics that vary widely. The fact that paint has a material presence is often overlooked, mostly because we often encounter these artworks in the form of two-dimensional reproductions. Capturing paintings in the third dimension is not only important for study, restoration and conservation, but it also inspires 3D printing methods1, particularly through the high demands it makes on reproducing color, gloss and texture. A hybrid solution between fringe projection and stereo imaging is proposed as 3D imaging method, with a setup involving two cameras and a projector. Fringe projection is aided by sparse stereo matching to serve as image encoder. These encoded images processed by the stereo cameras solve the correspondence problem in stereo matching, leading to a dense and accurate topographical map, while simultaneously capturing the composition of the painting in full color. The topographical map and color data are used to make hardcopy 3D reproductions, using a specially developed printing system. Several paintings by Dutch masters Rembrandt and Van Gogh have been scanned and reproduced using this technique. These 3D printed reproductions have been evaluated by experts, both individually and in a side-by-side comparison with the original.
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The analytical aspects of the investigation of 'Flower Still Life' by Vincent van Gogh and its underlying composition, showing two wrestlers by scanning macro-X-ray Fluorescence Analysis (MA-XRF) was reported. In MA-XRF the painting is excited by an X-ray millibeam to emit X-ray fluorescence radiation. Through the energy of the recorded fluorescence radiation the elements present in the analyzed spot can be identified. The painting was mounted on a motor stage behind the normal experimental table and moved continuously through the beam for scanning. The beam size was defined by a set of slits placed at the end of the experimental table. MA-XRF scans were performed with a step size of 1 mm and a dwell time of 3.6 s. The sample was cross-sectioned and examined using high-resolution microscopic methods. The correction of absorption effects in the Zn-maps allowed to remove otherwise misleading artifacts from hidden layers, so that a more realistic impression of the hidden portrait is gained.
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Scanning macro-X-ray fluorescence analysis (MA-XRF) is rapidly being established as a technique for the investigation of historical paintings. The elemental distribution images acquired by this method allow for the visualization of hidden paint layers and thus provide insight into the artist's creative process and the painting's conservation history. Due to the lack of a dedicated, commercially available instrument the application of the technique was limited to a few groups that constructed their own instruments. We present the first commercially available XRF scanner for paintings, consisting of an X-ray tube mounted with a Silicon-Drift (SD) detector on a motorized stage to be moved in front of a painting. The scanner is capable of imaging the distribution of the main constituents of surface and sub-surface paint layers in an area of 80 by 60 square centimeters with dwell times below 10 ms and a lateral resolution below 100 μm. The scanner features for a broad range of elements between Ti (Z = 22) and Mo (Z = 42) a count rate of more than 1000 counts per second (cps)/mass percent and detection limits of 100 ppm for measurements of 1 s duration. Next to a presentation of spectrometric figures of merit, the value of the technique is illustrated through a case study of a painting by Rembrandt's student Govert Flinck (1615–1660).
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3D imaging sensors for the acquisition of three dimensional (3D) shapes have created, in recent years, a considerable degree of interest for a number of applications. The miniaturization and integration of the optical and electronic components used to build them have played a crucial role in the achievement of compactness, robustness and flexibility of the sensors. Today, several 3D sensors are available on the market, even in combination with other sensors in a "sensor fusion" approach. An importance equal to that of physical miniaturization has the portability of the measurements, via suitable interfaces, into software environments designed for their elaboration, e.g., CAD-CAM systems, virtual renders, and rapid prototyping tools. In this paper, following an overview of the state-of-art of 3D imaging sensors, a number of significant examples of their use are presented, with particular reference to industry, heritage, medicine, and criminal investigation applications.
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The X-ray fluorescence imaging technique allows not only imaging but also identification of the hidden paint layers what makes it much more versatile tool than X-ray radiography. One of main disadvantages of this method is fact that the characteristic X-rays from deeper paint layers are absorbed in the covering layers. This effect manifests itself in a form of artefacts that impede proper interpretation of the acquired images. In this work it is shown that the methodology of correction of the inter-layer absorption effects can be extended to the case of polychromatic excitation. Additionally, the new approach of determination of the optimal correction parameters was presented. The methodology was tested with use of test painting and mock-up painting measured with table-top micro-XRF setup.
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Macro-X-ray fluorescence (XRF) is a newly commercially available research tool very useful in the examination of artwork. Its novelty lies in its ability to create maps of the distribution of chemical elements on scales of a few milimetres. In this contribution, its use together with optical coherence tomography (OCT) in the inspection of an illuminated manuscript is reported for the first time. The former technique is used both for mapping the elemental distribution over large parts of the folios - including illuminated initials - and for quantitative analysis of the composition of the smalt pigment, as well as of changes in the composition of iron-gall ink at different pages. The latter, by providing cross-sectional images of painted details, helps in interpreting the XRF results. All of the results shown relate to the examination of a late sixteenth-century-illuminated parchment manuscript (a gradual) originating from the Convent of the Benedictine Sisters in Lviv in the Ukraine. © The International Institute for Conservation of Historic and Artistic Works 2015.
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Samples with non-planar surfaces present challenges for X-ray fluorescence imaging analysis. Here, approximations are derived to describe the modulation of fluorescence signals by surface angles and topography, and suggestions are made for reducing this effect. A correction procedure is developed that is effective for trace element analysis of samples having a uniform matrix, and requires only a fluorescence map from a single detector. This procedure is applied to fluorescence maps from an incised gypsum tablet.
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Hidden, sub-surface paint layers and features contain valuable information for the art-historical investigation of a painting's past and for its conservation for coming generations. The number of techniques available for the study of these features has been considerably extended in the last decades and established techniques have been refined. This review focuses on mobile non-destructive subsurface imaging and depth profiling techniques, which allow for the in-situ investigation of easel paintings, i.e. paintings on a portable support. Among the techniques discussed are: X-ray radiography and infrared reflectography, which are long established methods and are in use for several decades. Their capabilities of element/species specific imaging have been extended by the introduction of energy/wavelength resolved measurements. Scanning macro-X-ray fluorescence analysis made it for the first time possible to acquire elemental distribution images in-situ and optical coherence tomography allows for the non-destructive study the surface paint layers in virtual cross-sections. These techniques and their variants are presented next to other techniques, such as Terahertz imaging, Nuclear Magnetic Resonance depth profiling and established techniques for non destructive testing (thermography, ultrasonic imaging and laser based interference methods) applied in the conservation of historical paintings. Next to selected case studies the capabilities and limitations of the techniques are discussed.
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This work presents the recent developments of xraylib, an ANSI C library that provides convenient access to a large number of X-ray related databases, with a focus on quantitative X-ray fluorescence applications. The enhancements include improved X-ray fluorescence production cross sections that take into account cascade effects and M-lines, as well as revised line energies, atomic level widths, Compton broadening profiles etc. A full overview of the complete application programming interface is presented.
Chapter
IntroductionBasic Principles X-ray Wavelength and Energy ScalesInteraction of X-rays with MatterPhotoelectric EffectScatteringBremsstrahlungSelection Rules, Characteristic Lines and X-ray SpectraFigures-of-merit for XRF SpectrometersInstrumentation X-ray SourcesX-ray DetectorsWavelength-dispersive XRFEnergy-dispersive XRFRadioisotope XRFTotal Reflection XRFMicroscopic XRFMatrix Effects Thin and Thick SamplesPrimary and Secondary Absorption, Direct and Third Element EnhancementData Treatment Counting StatisticsSpectrum Evaluation TechniquesQuantitative Calibration ProceduresError Sources in X-ray Fluorescence AnalysisSpecimen Preparation for X-ray FluorescenceAdvantages and Limitations Qualitative AnalysisDetection LimitsQuantitative ReliabilitySummary X-ray Wavelength and Energy ScalesInteraction of X-rays with MatterPhotoelectric EffectScatteringBremsstrahlungSelection Rules, Characteristic Lines and X-ray SpectraFigures-of-merit for XRF Spectrometers X-ray SourcesX-ray DetectorsWavelength-dispersive XRFEnergy-dispersive XRFRadioisotope XRFTotal Reflection XRFMicroscopic XRF Thin and Thick SamplesPrimary and Secondary Absorption, Direct and Third Element Enhancement Counting StatisticsSpectrum Evaluation TechniquesQuantitative Calibration ProceduresError Sources in X-ray Fluorescence AnalysisSpecimen Preparation for X-ray Fluorescence Qualitative AnalysisDetection LimitsQuantitative Reliability
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Interpretation of X-ray fluorescence images of archeological artifacts is complicated by the presence of surface relief and roughness. Using two symmetrically arranged fluorescence detectors in a back-reflection geometry, the proper X-ray fluorescence yield can be distinguished from intensity variations caused by surface topography. This technique has been applied to the study of Roman inscriptions on marble.
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This article illustrates the analysis by synchrotron micro-analytical techniques of an azurite painting presenting greenish chromatic degradation. The challenge of the experiments was to obtain the spatial distribution of the degradation products of azurite. Copper hydroxychlorides, carbonates and copper oxalates have been mapped by SR FTIR imaging of cross sections in transmission mode. To complement the information, Py/GC/MS and GC/MS techniques were applied in order to characterize the binding media and organic materials present as well as their degradation products. Results contribute to a better understanding of the decay of blue areas in ancient paintings not only from the particular point of view of azurite weathering, but also by adding information regarding the oxalates’ formation and their distribution in painting samples. Synchrotron radiation demonstrates its capability for the mapping in painting cross sections.
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A user friendly program for X-ray fluorescence analysis has been developed at the European Synchrotron Radiation Facility. The program allows interactive as well as batch processing of large data sets and it is particularly well suited for X-ray imaging. Its implementation of a complete description of the M shell is particularly helpful for analysis of data collected at low energies. The code is platform independent (Linux, Windows, MacOS X, Solaris …) and it is freely available for non-commercial use. Description of the algorithms used and practical examples are presented.
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Quantitative estimate of elemental composition by spectroscopic and imaging techniques using X-ray fluorescence requires the availability of accurate data of X-ray interaction with matter. Although a wide number of computer codes and data sets are reported in literature, none of them is presented in the form of freely available library functions which can be easily included in software applications for X-ray fluorescence. This work presents a compilation of data sets from different published works and an xraylib interface in the form of callable functions. Although the target applications are on X-ray fluorescence, cross sections of interactions like photoionization, coherent scattering and Compton scattering, as well as form factors and anomalous scattering functions, are also available.
Article
A newly developed spectrometer for energy-dispersive micro X-ray fluorescence spectrometry has been designed for the demands of archaeometry. ArtTAX combines the advantages of non-destructive and sensitive multi-elemental analysis at sub-mm resolution with the possibility of working outside the laboratory. The spectrometer consists of an air-cooled, low-power molybdenum tube, new generation polycapillary X-ray optics, a silicon drift detector without the need for liquid-nitrogen cooling, a CCD camera, and three light diodes for sample positioning. The motor-driven measurement head is fixed on a x,y,z-flexible tripod support which can be assembled and dismantled within minutes. The spot size of the primary X-ray beam was determined to be 94 microm for the Cu(Kalpha) energy, the detection limits are in a range of a few tens of microg g(-1) for the medium energy-range in glass. Additional open helium purging in the excitation and detection paths enables the determination of elements down to sodium, thus avoiding vacuum conditions or a size-limiting sample chamber. A selection of qualitative and quantitative results on pigment, metal, glass, and enamel analyses are presented to show the potential of ArtTAX in the field of art and archaeology.
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The conservation of the polychromy of the terracotta army of the first Chinese emperor Qin Shihuangdi represents a special problem because of the deterioration of the ground layer consisting of organic material. This was triggered due to it having spent more than 2200 years in water-saturated soil. The consolidation of the polychromy was achieved through polymerisation of a specially adapted combination of monomers.
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