1,721,033 research outputs found
True versus forged in the cultural heritage materials : the role of PXRF analysis
No full textForensic and cultural heritage scientific analyses have several similarities. Indeed, they both deal with unique, ‘precious’ and often
quantitatively very limited objects, which have to be preserved as much as possible. Whenever analytical examination is needed,
similar requirements have to bemet. Furthermore, also in cultural heritage, field scientists are looking for answers about the story
behind the artefact, trying to help discovering its provenance, proving its authenticity or supporting a conscious restoration
(a wrong knowledge about ancient material caused destructive conservation intervention even in recent times).
Energy dispersive X-ray fluorescence analysis is thus one of the best approaches mainly for the possibility to perform both
qualitative and quantitative analyses without losing sample. Moreover, last generation handheld spectrometers allow to perform
analytical investigation almost anywhere.
In the present paper, after a brief excursus about the possibility of getting answers through energy dispersive X-ray fluorescence
analysis for the most common archaeometric materials, we present a few peculiar case studies in which scientific examination
proved to be helpful in solving historical and archaeological uncertainty
Di mescole e di strati : i pigmenti di Mantegna nella pala di San Zeno secondo le analisi integrate EDXRF e vis-RS
No full textEvaluation of effects of irregular shape on quantitative XRF analysis of metal objects
No full textQuantitative XRF analysis of metal alloys can be obtained by using the general fundamental parameter method based on the comparison of x-ray line fluorescence intensities with those obtained from reference standard pellets in identical experimental conditions. Corrections for auto absorption and secondary excitation effects are fundamental to obtaining quantitative results.
When analyzing a real object with irregular, or at least nonpellet-shaped, geometry and/or of incorrect positioning, an additional correction factor for x-ray fluorescence line intensities must be entered.
In this paper we review the problem of the contributions to the error specific to an irregular surface or incorrect positioning intrinsic to the fundamental parameter method, in the more enlarged context of considering a real experimental setup in which irradiation and detection angles are not exactly constant, as assumed in the fundamental parameter method. They are accounted for by the corrective irregular shape factors.
In principle, these factors must be separately calculated for each value of excitation and characteristic x-ray energies, and the relative precision in the quantitative determination of elemental concentrations with the fundamental parameter method can be estimated from the relative amplitude of the variation of shape factor values depending on the exciting energy spectrum. One obtains the result that the correction due to irregular shape or incorrect positioning of the object under examination tends to the limit 1, or, more generally, to a constant value independent of the excitation and emission x-ray energies in the limiting case where the direction of the exciting radiation coincides with that of the detected fluorescence x-rays.
The results of calculations of the relative precision of XRF quantitative analysis are shown for gold-based alloy objects in some specific cases of surface roughness and positioning of the object. Dispersion around the nominal values for the angles of incoming and outgoing x-ray directions is assumed as determined by the geometric conditions in two selected instrumental setups. A nominal value of 45 degrees was assumed for both the angles in the first case. In the second case, we considered an irradiation setup where the condition of coincidence for incoming and outgoing x-ray directions is nearly achieved by employing an annular silicon drift detector (SDD) with a central hole, which allows the passage of the exciting x-rays.
An interesting result obtained in the latter case is that, looking only at the dependence on the irregular shape, an attainable precision on the order of < 1%o can be achieved.
In view of the possible applications of quantitative XRF analysis to jewellery, employing SDD detectors capable of very high counting rates should allow a statistical error under the above-mentioned limit in a reasonably short measuring time.
However, concerning the error deriving from intrinsic x-ray tube instability, an investigation aimed at achieving a stable enough system is still needed
In situ EDXRF analyses on Renaissance plaquettes and indoor bronzes patina problems and provenance clues
No full textThe preliminary work for the edition of the complete catalogs of Civic collections of Vicenza (Italy) was an occasion to study by energy dispersive x-ray fluorescence (EDXRF) about 30 small bronzes and plaquettes of Italian Renaissance. It was necessary to perform in situ analyses directly in the museum without any possibility of sampling or cleaning the objects. We report the results of quantitative analysis on principal and trace elements; moreover, patina problems and the possible clues for raw materials provenance are faced
Dalla ricostruzione degli strati originali ai materiali di Cavenaghi. La campagna di analisi non invasive sulla Madonna con il Bambino e un coro di cherubini di Mantegna in Brera
No full textArchaeometric study of shells of Helicidae of the Edera Cave (North-Eastern Italy)
No full textThe Edera Cave, near Aurisina in the Trieste Karst, retains a stratigraphy that extends from
the Mesolithic to the modern era. At Sauveterrian layers, many specimens of Helix cincta
are present, which are considerably crushed, and a small percentage of which are also
blackened. Chemical analyses show that the blackened specimens were exposed to a
temperature of between 500 and 550°C, and suggest that many others were destroyed by fire
at temperatures of above 700°C. Consequently, only a part of the Helix cincta shells is
assumed to be the residue of human meals, since several factors render plausible an
accidental combustion of shells already present in the ground before the lighting of
Mesolithic hearth
Micro-Raman on flax fibers: ageing fingerprints in spectra
No full textFlax fiber (Linum usitatissimum) is probably the earliest textile material and holds a great archaeological interest [1]. The possibility to define a connection between ageing and molecular characteristics is thus a concrete purpose aiming to help indirect dating. The flax fibers mainly consist of cellulose, hemicellulose, lignin and pectic material.
Vibrational spectroscopy, and in particular Raman spectroscopy, has been already used to give a non-destructive characterization of archaeological flax fabrics [2,3]. While larger acquisition areas and IR excitation (exc = 1064 nm) were used in [3], in the present work micro-Raman spectroscopy and visible-excited fluorescence spectroscopy were applied to 24 micrometric-sized fibers from historical linen (dating from about 3000 B.C. to the XVII cent.) and 12 crude or treated modern fibers. Micro-Raman and micro-fluorescence spectra were acquired respectively by means of a JASCO NRS-5000 Raman system (exc = 785 nm) and of a JASCO RMP-100 microprobe coupled with a Lot Oriel MS25 spectrometer and with a frequency-doubled Nd:YAG laser (exc = 532 nm).
In the examined spectral range, from 70 cm-1 to 2600 cm-1, the ratio between 1121 cm-1 and 1096 cm-1 bands has been proved to be a possible signature of ageing [4,5]. Evaluating the above-mentioned band ratio (I1121 cm-1/ I1096 cm-1) after baseline correction, micro-Raman spectra show that modern samples exhibit a quite constant ratio value of 0.85±0.05, which diminishes (up to 0.7) if the linen fiber is heated or bleached. Fibers form archaeological linen show a reduced value for the ratio, that decreases to about 0.5 depending on the age and on the conservation conditions. It should be emphasized that for the most ancient samples or the most severely aged modern samples, the above ratio could not be determined due to the high fluorescence background overlapping the Raman signals.
As the possible presence of non-cellulosic carbohydrates in the linen fiber can produce a different spectral pattern, especially in the 280-600 cm-1 region, with variations of relative signal intensities, multiple spectra relative to the same fibers must be acquired, selected and averaged, thus reducing also the possible contribution of extraneous material.
A Pearson correlation value of about 0.7 between the intensity of the fiber fluorescence emission and the age of the flax samples is also obtained, showing variations mainly due to the possible influence of other features such as contamination from organic substances (balms, dyes etc.).
In conclusion, this study opens a perspective on the possibility of a truly micro-destructive investigation of ancient textiles, exploiting the molecular specificity of spectroscopic techniques.
[1] E.J.W. Barber, Prehistoric Textiles, Princeton University Press, Princeton, NY, USA, 1991, p.12
[2] H. G.M. Edwards, D. W. Farwell, D. Webster, Spectrochemica Acta A, 53, 1997, 2383.
[3] G. Fanti, P. Baraldi, R. Basso, A. Tinti, Vibrational Spectroscopy 67, 2013, 61.
[4] H. G.M. Edwards, N. F. Nikhassan, D. W. Farwell, P. Garside, P. Wyeth, J. Raman Spectrosc. 37, 2006, 1193.
[5] A. Jahan, M.W. Schröder, M. Füting, K. Schenzel, W. Diepenbrock, Spectrochemica Acta A, 58, 2002, 2271
EDXRF quantitative analysis of chromophore chemical elements in corundum samples
No full textCorundum is a crystalline form of aluminum
oxide (Al2O3) and is one of the rock-forming minerals.
When aluminum oxide is pure, the mineral is colorless, but
the presence of trace amounts of other elements such as
iron, titanium, and chromium in the crystal lattice gives the
typical colors (including blue, red, violet, pink, green,
yellow, orange, gray, white, colorless, and black) of
gemstone varieties. The starting point for our work is the
quantitative evaluation of the concentration of chromophore
chemical elements with a precision as good as possible to
match the data obtained by different techniques as such as
optical absorption photoluminescence. The aim is to give
an interpretation of the absorption bands present in the NIR
and visible ranges which do not involve intervalence charge
transfer transitions (Fe2+ → Fe3+ and Fe2+ → Ti4+),
commonly considered responsible of the important features
of the blue sapphire absorption spectra. So, we developed a
method to evaluate as accurately as possible the autoabsorption
effects and the secondary excitation effects which
frequently are sources of relevant errors in the quantitative
EDXRF analysis
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