Giovanni Buccolieri

Portable equipment for energy dispersive X-ray fluorescence analysis of Giotto’s frescoes in the Chapel of the Scrovegni

Abstract Photon induced energy dispersive X-ray fluorescence (EDXRF) analysis is a valuable technique for the study of works of art, because it is nondestructive, multielemental, simple and relatively inexpensive. For this reason EDXRF is a very popular analytical technique in archaeometry. Portability of EDXRF equipments is extremely useful and almost mandatory in many cases, such as analysis of frescoes, of large paintings, bronzes, brasses and gold alloys, and so on, especially when located in museums. EDXRF analysis generally involves an area of a few mm2, and a thickness between μm and fractions of mm and, therefore, the analysis is superficial and dependent on the surface conditions. The frescoes by Giotto in the “Chapel of the Scrovegni” in Padua were systematically analysed in the period July 2001–March 2002 in more than 300 points, before, during and after restoration, in order to detect the possible presence of superficial sulphur and to test various sulphur cleaning procedures. Further all pigments were systematically analysed in order to determine their composition. Golden haloes were also analysed and different pigment layers were detected under the gold leaf; from the EDXRF analysis the attribution of chemical elements to the proper layer was possible.

Monitoring of total and bioavailable heavy metals concentration in agricultural soils

The aim of this paper is to evaluate total and bioavailable concentration of heavy metals in agricultural soils in order to estimate their distribution, to identify the possible correlations among toxic elements and the pollution sources, to distinguish the samples in relation to sampling site or to sampling depth, and to evaluate the available fraction providing information about the risky for plants. In particular, we reinvestigated total concentrations of As, Be, Cd, Cr, Cu, Fe, Hg, Mn, Ni, Pb, Sb, V, and Zn and available concentrations of As, Be, Cd, Cr, Cu, Hg, Ni, Pb, Sb, and Zn in soil from Apulia (Southern Italy). Analytical results showed that total concentrations, for all soils, are in the range permitted by regulations in force in Italy, but some soils evidence slight enrichment of Cd, Cr, Cu, Pb, and Zn. All the heavy metals in the available fraction were below the detection limits of the analytical techniques used except Cu, Ni, Pb, and Zn.

Particulate matter characterization at a coastal site in south-eastern Italy

Several samples of airborne particulate matter (PM), collected from 6th November to 6th December 2003 at a coastal site in the south-east of Italy, have been analyzed by different techniques to characterize elemental composition and morphological properties of the inorganic PM fraction and obtain preliminary results on anthropogenic contributions. Al, Cr, Cu, Fe, Mn, V, Pb, Ti, Ca and Zn mass concentrations, evaluated by an inductively coupled plasma atomic emission spectrometer, account for up to l% of the bulk PM mass in the investigated samples. According to geochemical calculations, Ca, Al, Fe and Mn are predominantly of crustal origin, while Cr, Cu, Pb, V, Ti and Zn heavy metals are of anthropogenic origin. Ion chromatography analyses have identified sulfate (SO(4)(2-)) nitrate (NO(3)(-)), sodium (Na(+)), and ammonium (NH(4)(+)) as the main ionic components accounting for up to 38% of the total PM mass and up to 90% of the total ionic mass. Besides ion chromatography, X-ray energy dispersive (EDX) microanalyses have revealed the high variability of Cl: its weight concentration varies from about 24% to below the detection limit (>or=0.5%) in the investigated samples. The marked anti-correlation between the excess of S and the Cl/Na ratio has allowed inferring that reactions between sea salt particles and acidic sulfates, which liberate HCl gas to the atmosphere leaving particles enriched in non-sea-salt sulfates, have significantly contributed to chloride depletion. Morphological analyses by scanning electron microscopy have shown that about 90% of the total sampled particles have a diameter <or=5 microm.

A portable apparatus for energy-dispersive X-ray fluorescence analysis of sulfur and chlorine in frescoes and stone monuments

Abstract A simple and portable equipment was constructed, based on the energy dispersive X-ray fluorescence. It is composed of a small size X-ray tube, a thermoelectrically cooled Si-PIN detector, and a multi channel analyzer. The tube has a Pd anode, and works at 3–30 kV, 0.1 mA. At 3–5 kV, it emits Pd-L lines and bremsstrahlung radiation, and therefore is suited to the analysis of low atomic number elements, such as P, S, Cl. Working at 30 kV the tube emits Pd-K lines and bremsstrahlung radiation, and is able to excite medium atomic number elements up to tin (K-lines) and high atomic number elements (L-lines). The Si-PIN detector has a 25 μm Bc-window and energy resolution of about 190 eV at 5.9 keV. It has a thickness of about 300 μm and thus an efficiency rapidly decreases at energies larger than about 20 keV. The equipment is completed by a portable multi channel analyzer. The described system was first tested in Laboratory and then employed to analyze mainly sulfur and chlorine in the follwoing frescoes and monuments: • frescoes of Piero della Francesca (church of S. Francesco, Arezzo) • frescoes of Domenichino (cathedral of Fano) • Roman frescoes (church of S. Clemente, Rome) • lapideous altars (church of S. Croce, Lecce).

Exposure to static magnetic field stimulates quorum sensing circuit in luminescent Vibrio strains of the Harveyi clade.

In this study, the evidence of electron-dense magnetic inclusions with polyhedral shape in the cytoplasm of Harveyi clade Vibrio strain PS1, a bioluminescent bacterium living in symbiosis with marine organisms, led us to investigate the behavior of this bacterium under exposure to static magnetic fields ranging between 20 and 2000 Gauss. When compared to sham-exposed, the light emission of magnetic field-exposed bacteria growing on solid medium at 18°C ±0.1°C was increased up to two-fold as a function of dose and growth phase. Stimulation of bioluminescence by magnetic field was more pronounced during the post-exponential growth and stationary phase, and was lost when bacteria were grown in the presence of the iron chelator deferoxamine, which caused disassembly of the magnetic inclusions suggesting their involvement in magnetic response. As in luminescent Vibrio spp. bioluminescence is regulated by quorum sensing, possible effects of magnetic field exposure on quorum sensing were investigated. Measurement of mRNA levels by reverse transcriptase real time-PCR demonstrated that luxR regulatory gene and luxCDABE operon coding for luciferase and fatty acid reductase complex were significantly up-regulated in magnetic field-exposed bacteria. In contrast, genes coding for a type III secretion system, whose expression was negatively affected by LuxR, were down-regulated. Up-regulation of luxR paralleled with down-regulation of small RNAs that mediate destabilization of luxR mRNA in quorum sensing signaling pathways. The results of experiments with the well-studied Vibrio campbellii strain BB120 (originally classified as Vibrio harveyi) and derivative mutants unable to synthesize autoinducers suggest that the effects of magnetic fields on quorum sensing may be mediated by AI-2, the interspecies quorum sensing signal molecule.

Laser ablation threshold of cultural heritage metals

In this work we determined experimentally the threshold fluence of the most common metals found in cultural heritage, e.g. copper, silver and their alloys. We carried out the ablation process in air at atmospheric pressure with 8 ns pulsed Nd:YAG and 23 ns pulsed KrF lasers, at 532 and 248 nm, respectively. We irradiated every target by a fixed number of laser shots (repetition rate of 1 Hz) at several laser fluence values. Then, the resulting craters were characterized by a stylus surface profiler in order to obtain the dependence of ablation rate on laser fluence F. Here, we defined the ablation raate as ablated matter thickness for single laser pulse, x. Therefore, we identified the ablation threshold fluence, Fth, as the fluence value below which no ablation process would occur.

Experimental results of UV laser cleaning on a silver Carlino coin

Silver artefacts and particularly ancient silver artefacts present the serious problem of turning black due to ambient contamination. The black colour is the consequence of a layer forming on the surface made of acanthite and jalpaite; both compounds are sulphur composts. Recently, a UV laser cleaning technique has demonstrated to be very promising in the processing of cultural artefacts. To operate on artefacts without contaminating the bulk, we first determined the laser fluence threshold of the bulk; second, we controlled the surface compounds, and finally we operated the laser irradiation. In this work, we utilised certified silver and silver/copper samples in order to perform preliminary studies. The threshold fluences we found were 780 and 510 mJ/cm2 for the pure Ag and for the Ag/Cu alloy, respectively. The jalpaite concentration on the Ag/Cu sample increased after a laser dose of 25 J/cm2, whereas for a higher laser dose its value lowered, pointing out that complex processes take part during the laser application. We successfully applied the technique on a Carlino coin made of silver coined in 1689 under King Carlo II. The analyses were performed by two different techniques that are able to find the percentage of elements and the chemical compounds: the energy dispersive X-ray fluorescence and the X-ray diffractometer spectrometer. We found that the sulphur concentration decreased upon the increase of the laser dose. Operating on the coin up to a dose of 280 J/cm2, the sulphur concentration deceased by up to 20%, while the coin looks clearer just after 50 J/cm2.

Selective laser cleaning of chlorine on ancient coins

Results about the efficiency of the laser cleaning on the reduction of corrosion products from the surface of ancient coins are reported. In this work an ancient copper coin datable from 1500 to 1600 A.D. and a UV excimer laser were utilized. The goal of this work consists to study the potentiality of UV laser treatment in the reduction of the chlorine concentration on the coin surface which is the main responsible of the corrosion processes of the ancient coins. We used Energy Dispersive X-Ray Fluorescence (EDXRF) and X-Ray Diffraction (XRD) techniques to estimate the chemical composition of the coin surface, before and after UV excimer laser cleaning. In particular, we measured the chlorine, copper and calcium concentrations. We found that a radiation dose of about 19 J/cm2 was able to reduce the chlorine concentration from 2.3 % w/w to 0.6 % w/w without damaging the metal bulk.

Nondestructive Analysis of Silver Coins Minted in Taras (South Italy) between the V and the III Centuries BC

This work enters in an interdisciplinary research project involving the archaeometrical analysis of ancient silver coins minted in the Greek colony of Taras (the modern south Italian town of Taranto) between the V century BC and the III century BC. In this work, by comparing the results obtained from X-ray microanalysis data acquired from the least corroded surface areas and the cross-section of coins from SEM-EDX and from XRF analysis, we have demonstrated that analysed coins exhibited a corrosion layer no more than 25 μm and that surface silver enrichment was less than 1 wt%. Thus, the data obtained by using X-ray microanalysis from surface may not significantly differ from the original bulk composition. Our results demonstrate that the silver content in the coins decreases considerably ranging from about 97% for the older down to 80% for the ones of 3rd Evans period (300–270 BC), corresponding to the significant social change in the period.

Analysis of selective laser cleaning of patina on bronze coins

The patina, is the result of a large number of chemical, electrochemical and physical processes which occur spontaneously during interaction of metal surfaces with the environment. In this work we want to analyze and remove the patina in artefacts, exposed to atmosphere for various decades. Here, experimental results about the laser cleaning of bronze coins by KrF (248 nm) and Nd:YAG (532 nm) lasers are reported. Both laser wavelengths were efficient to reduce the chlorine concentration on the surface of the coins more than 80 %, as demonstrated by Energy Dispersive X-Ray Fluorescence analyses.