Reproducibility, Precision and Trueness of X-Ray Fluorescence Data for Mineralogical And/Or Petrographic Purposes (original) (raw)
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Recent work aimed at provenancing metal slag from Sagalassos, south-west Turkey, as part of a study investigating the Roman iron industry in the area. Although previously samples of the slag material had been exported from the country for the purposes of analysis, a method of analysing the materials in-situ was required. It was decided that the best technique for achieving ‘in-the-field’ results would be handheld X-ray fluorescence spectrometry (HH-XRF). A series of laboratory based tests were first performed in order to determine the ideal working parameters for the HH-XRF and the best method for preparing the samples. The results indicated that different slag (i.e. Ti-rich/poor) could clearly be distinguished amongst the powdered samples. A total of 45 metal slag were analysed in the field in order to see whether the slag could be qualitatively characterised based on provenance. The results of the field study indicated two principle groups (a high Ti – Zr group and a low Ti – Zr group). The Ca and Mn contents also split the data into two groups but these were not consistent with the previous Ti – Zr groups. These differences could be related to the choice of ores and fluxes used for iron production.
Portable X-rays Fluorescence (pXRF) represents one of the most effective tools for in situ, non-destructive elemental analysis, which has a valuable application in the study of ceramic production. However, whilst the qualitative assessment of the composition of artefacts is reliable, the quantitative analysis can be biased by some limitations, due to instrumental features or materials properties. The analysis of ceramic materials is particularly challenging due to the lack of representative calibrations and standards, as well as the low density and poor homogeneity of samples. In this contribution, a method is proposed to fingerprint a ceramic production through pXRF analysis. At the site of Montelabate (Perugia) in central Italy four kilns were excavated revealing a production of amphorae. This site was therefore selected as a suitable case study for fingerprinting a ceramic production. After qualitative analysis, representative calibration standards were created based on different commercial clays and feldspars. These can help overcoming the well-known matrix effect, both physical and chemical, and may offer a representative and reproducible standard to be used in different laboratories. Alongside the precise assessment of composition, the possibility to fingerprint a production was also assessed using a different method, based on the intensity ratio between selected elements. The relevant elements were chosen based on their correlation and non-correlation. Correlated elements were attributed to the raw clay used for ceramic production and non-correlated elements were attributed to the specific fabric recipe. Accordingly , some benchmarks to identify the clays and fabric used in the site of Montelabate were identified. Amphorae found at other ancient commercial sites in the area of Rome were therefore also compared with these benchmarks in order to assess their provenience.
The archaeological exploration of the Ognina islet, near Syracuse, Sicily, carried out in 1964 provided the evidence of a long term prehistoric occupation between the Neolithic and the Middle Bronze Age. Maltese style ceramics were found in the Early and Middle Bronze Age layers. The small group of imports, belonging to the Thermi Ware, was found in connection with the local Castelluccian Ware (EBA), while the Borġ in-Nadur ware, also Maltese in style, was related with local Thapsos ceramics (MBA). In 2012, during a fieldwork, a large amount of ceramics were recovered, among which were some new examples of Thermi and Borġ in-Nadur wares, as well as large amounts of Castelluccian and Thapsos pottery. In order to ascertain whether the Maltese type pottery was imported from that small island, a program of archaeometric analyses was established. Diagnostic samples belonging to both Maltese-like and Sicilian pottery classes were analysed with destructive thin sectioning and X-ray fluorescence spectrometry (XRF) and subsequently with nondestructive pXRF together with a sample of Sicilian clay taken from the source closest to the islet. The analyses demonstrated that the two Thermi Ware samples were locally produced, while three out of four Borġ in-Nadur pieces were produced in Malta and one was produced in Sicily. L’esplorazione archeologica dell’isolotto di Ognina, Siracusa, effettuata nel 1964 ha fornito la prova di un’occupazione preistorica a lungo termine tra il Neolitico e l’Età del Bronzo Medio. Le ceramiche maltesi sono state trovate negli strati dell’età del Bronzo Antico e Medio. Il piccolo gruppo di importazioni, appartenente alla Thermi Ware, è stato trovato in connessione con il locale Castelluccian Ware (EBA), mentre gli esemplari Borġ in-Nadur, anch’esso in stile maltese, era in relazione con la ceramica locale di Thapsos (MBA). Nel 2012 è stata recuperata una grande quantità di ceramiche, tra cui alcuni nuovi esempi di articoli di Thermi e Borġ in-Nadur, nonché grandi quantità di ceramica di Castelluccian e Thapsos. Per accertare se il tipo di ceramica maltese fosse importato da quella piccola isola, fu stabilito un programma di analisi archeometriche. Campioni diagnostici appartenenti a classi ceramiche siciliane e siciliane sono stati analizzati con sezioni sottili distruttive e X-ray fluorescence spectrometry tradizionale (XRF) e successivamente portatile e non distruttivo (pXRF) insieme a un campione di argilla siciliana prelevato dalla sorgente più vicina all’isoletta. Le analisi hanno dimostrato che i due campioni di Thermi Ware sono stati prodotti localmente, mentre tre su quattro pezzi Borġ in-Nadur sono stati prodotti a Malta e uno è stato prodotto in Sicilia.
Chemical analysis is a well-established procedure for the provenancing of archaeological ceramics. Various analytical techniques are routinely used and large amounts of data have been accumulated so far in data banks. However, in order to exchange results obtained by different laboratories, the respective analytical procedures need to be tested in terms of their inter-comparability. In this study, the schemes of analysis used in four laboratories that are involved in archaeological pottery studies on a routine basis were compared. The techniques investigated were neutron activation analysis (NAA), X-ray fluorescence analysis (XRF), inductively coupled plasma optical emission spectrometry (ICP-OES) and inductively coupled plasma mass spectrometry (ICP-MS). For this comparison series of measurements on different geological standard reference materials (SRM) were carried out and the results were statistically evaluated. An attempt was also made towards the establishment of calibration factors between pairs of analytical setups in order to smooth the systematic differences among the results.