Assessing the applicability of portable X-ray fluorescence spectrometry for obsidian provenance research in the Maya lowlands

Recent innovations in portable energy-dispersive X-ray fluorescence (PXRF) spectrometry have increased its utility for the geochemical characterization of obsidian artifacts for archaeological provenance research. However, concerns over the utility of PXRF instrumental analyses have been raised, focused on the validity and reliability of the geochemical data produced. Here we adopt the framework of Richard Hughes (On Reliability, Validity, and Scale in Obsidian Sourcing Research, 1998), whereby reliability addresses instrument stability and issues of measurement while validity pertains to an instrument’s ability to discern geochemical source provenance. This is done in order to test the utility of PXRF instruments for archaeological provenance research. k-Means cluster analysis was used to test the accuracy of PXRF through statistical comparison of data acquired via laboratory and portable energy-dispersive XRF instruments. Multivariate analysis was employed to demonstrate obsidian source representation at two Classic Maya archaeological sites in southern Belize – Uxbenká and Ek Xux – and to test the validity of data obtained from a PXRF instrument in answering archaeological research questions pertaining to regional interactions between lowland Maya polities. Results suggest that portable XRF instruments produce internally consistent results. However, data acquired from a PXRF instrument are not statistically equivalent to other XRF instruments. This is to say that while PXRF is not a reliable technique, it is valid for questions pertaining to geochemical source representation.     

pXRF: a study of inter-instrument performance

Integrating portable X-ray fluorescence (pXRF) instrumentation into archaeological investigations has generated as much interest as skepticism because several characteristics of the technique limit analytical accuracy and precision. This paper seeks to explore inter-instrument performance in order to assess the potential pXRF instrumentation has in examining the elemental composition of lithic raw materials. Two pXRF instruments, Delta and Omega models both manufactured by Olympus Innov-X Systems, were utilized to obtain the trace element signatures of five fine-grained volcanic sources and four obsidian sources in the Great Basin. We compared the two portable instruments to a wavelength-dispersive instrument extensively calibrated with geologic standards and to a commercial benchtop energy-dispersive system. Our results suggest that the relationships between the data produced by these different instruments are complex, and as we look to the future of pXRF use in archaeological analysis we argue that that the same strict protocols applied in laboratory-based XRF analyses, involving instrument calibration, evaluation of inter-instrument performance, and comparison to accepted geologic standards, need to be applied in pXRF analysis.     

Sceattas in Anglo-Saxon Graves

ANGLO-SAXON SILVER PENNIES (sceattas) are rare as gravegoods, but their provision was a regular element of burial practice in a small minority of later 7th-century-furnished inhumations and later burials. Although the number both of coins and burials is very small, they show patterns of deposition and treatment that have both a cultural and a broader chronological significance. This sample provides a window on social and symbolic attitudes to the coinages as elements of the broader material culture of contemporary society, and constitutes important corroborating evidence that the Primary Phase issues embodied a new degree of monetisation in 7th-century England.     

Evaluating effects of chemical weathering and surface contamination on the in situ provenance analysis of building stones in the Cuzco region of Peru with portable XRF

As the only type of instrument capable of determining artifact geochemistry in a wide variety of settings, portable X-Ray Fluorescence (PXRF) may be frequently utilized as probably the best option for collecting data when removal of objects in part or in whole is unfeasible. However, using PXRF in circumstances where sample selection and preparation diverge from standards developed for lab-based instrumentation requires assessing the impact of new and potentially limiting factors to establish the validity of the method in these new contexts. Here we examine the effects of surface contamination and chemical weathering on the ability to assess provenance of igneous building stones used in the Cuzco region of Peru. Surface contamination was assessed through comparing low-impact cleaning methods on diorite and andesite blocks, and weathering was examined by comparing weathered vs. fresh surfaces of samples from two andesite quarries. In general, the lightest elements were most impacted by contamination and weathering while measurements of many of the heavier elements commonly used in provenance studies were relatively unaffected. Concentrations of Pb and Zn were problematic in the urban context of Cuzco because of pollution. Ability to determine provenance of building stones within those limitations (i.e., the validity of this application of PXRF) was demonstrated in a preliminary study by comparing measurements from uncleaned, exposed building stones in the region to fresh quarry samples.     

Materials Characteristics of Roman and Arabic Mortars and Stuccoes from the Patio De Banderas in the Real Alcazar of Seville (Spain)

This study discusses the materials and traditional knowledge used in the manufacture and application of lime mortars and stuccoes by Romans and Arabs in Seville (southern Iberian Peninsula). All of the samples studied contain calcite as a binder, combined with aggregates based on river sand from the filling materials of the Guadalquivir River's depression, located in the vicinity of the Real Alcazar Palace in Seville, Spain, where the artefacts were discovered. The Romans used high‐quality production technology, as evidenced by the careful selection of raw materials as well as by the adequate binder‐to‐aggregate ratio and the elevated homogeneity of the mortars and stuccoes. The suitable distribution of aggregates resulted in higher density values for Roman fragments than for Arabic ones. Results derived from Arabic samples suggest a decline in technology manufacture over time. This work provides useful information, particularly regarding the Roman and Arabic periods in the Iberian Peninsula. The analytical techniques employed in this study were X‐ray diffraction (XRD), X‐ray fluorescence (XRF)—using conventional and portable systems, scanning electron microscopy (SEM), petrographic microscopy, differential thermal analysis/thermogravimetry (DTA/TG), particle‐size analysis and mercury intrusion porosimetry.     

Handheld Portable X‐Ray Fluorescence of Aegean Obsidians

We tested two portable XRF instruments (with different technologies) using two correction schemes (‘soils’ and ‘mining’) with both factory‐set calibrations and linear regression calibrations derived from published data. All four Aegean obsidian sources, including Sta Nychia and Dhemenegaki on Melos, were distinguished in each case. The newer instrument provided better ‘off‐the‐shelf’ accuracy than the older instrument, but calibrations negated these differences. The newer model also offered superior precision for most elements, despite measuring specimens for shorter times. Both correction schemes for the newer instrument resulted in almost equal precision, meaning that either may be used for successful Aegean obsidian sourcing.     

Compositional Analysis of 14th–15th Century Enamels from the Altar of San Giovanni in Florence: an Integrated Study by Portable X‐Ray Fluorescence and Electron Probe Microanalysis

The enamels of the Altar of San Giovanni, from the Baptistery of Florence, were investigated using both non‐invasive and micro‐invasive analysis in order to elucidate the glass melting and colouring techniques. A few fragments detached from the altar and recovered by the restorers were analysed in cross‐section by electron probe microanalysis. Moreover, non‐invasive investigations by portable XRF allowed a large number of enamelled plaques to be investigated. The results showed a good agreement between the two techniques and made it possible to identify similarities or differences in the enamels of the three manufacturing periods of the altar.     

Spinning Yarns: The Archaeological Evidence for Hand Spinning and its Social Implications,c ad 1200–1500

THIS PAPER EXAMINES the archaeological evidence for hand spinning in medieval Britain from c 1200 to c 1500. Ceramic, stone and baked clay spindle whorls have dominated the excavated finds, but a new corpus of lead-alloy spindle whorls, recorded through the Portable Antiquities Scheme and Scottish Treasure Trove, is presented here. Analysis of the metal whorls’ distribution, manufacture, dating and decoration is provided, illuminating the wide social and economic contexts in which they were used. From memento mori of pious spinners to sexually potent objects representative of lubricious gossips, the ubiquitous spindle whorl was a universal tool that had a powerful agency. The artefacts are small finds embodying daily life but also tie into the wider national economy of the High and Late Middle Ages.     

Down at the old Ship and Ball — taverns,trade and daily life in the London Borough of Southwark

SUMMARY: Archaeological excavations in Southwark over the past 50 years have proved to be a very prolific source of evidence for the material culture of people living in this part of London from the 16th century onwards. This lecture, the fourth held by SPMA in honour of the late Geoff Egan, focuses on a remarkably rich and varied assemblage of 17th- and 18th-century artefacts excavated on a site in Tanner Street in 2012. Covering a wide spectrum of activities, occupations and levels of society, these include ceramics, glass, clay tobacco pipes, pewter, copper-alloy, wood, leather, bone and ivory, with objects as diverse as cloth seals, spoons, book mounts, wine bottles and glasses, bird feeders and a mallet for playing pall mall, and sources ranging from the English Midlands to the Far East.     

便携式X射线荧光现场分析壁画颜料适用性研究——以西藏拉萨大昭寺壁画为例

便携式X射线荧光光谱仪作为快捷的无损分析技术,广泛应用于壁画文物的现场分析中.本文利用便携式X射线荧光光谱仪分析了西藏拉萨大昭寺转经廊壁画,选取部分样品,利用实验室X射线荧光分析,发现所分析颜料的主要显色元素具有一致性,并利用拉曼光谱确定了壁画颜料的成分.通过比较研究,发现便携式X射线荧光光谱仪可确定大部分色彩较为纯正的颜料的成分,同时,由于西藏拉萨大昭寺壁画颜料的杂多性,对于含砷的橙色颜料、含砷或含铅与含铁的黄色颜料、含铜砷的绿色颜料、含钙硫的白色颜料、群青与孔雀石的混合颜料则需结合拉曼光谱确定之.本研究工作显示,利用便携式X射线荧光光谱仪开展现场检测,可极大地减少实验室分析样品的取样数量,有利于壁画颜料的无损分析与微损分析.