Crombé, Philippe

Degryse, Patrick

Teetaert, Dimitri

Vanhaecke, Frank

Vanmontfort, Bart

Vannoorenberghe, Marieke

English

Ghent University Academic Bibliography

SELECTIVE MULTI-ELEMENT ANALYSIS OF THE CLAY FRACTION IN ANCIENT POTTERY BY LASER ABLATION – INDUCTIVELY COUPLED PLASMA – MASS SPECTROMETRYMarieke Vannoorenberghe1, Dimitri Teetaert2, Bart Vanmontfort3, Patrick Degryse4, Philippe Crombé2, Frank Vanhaecke11 Ghent University, Department of Chemistry, Atomic and Mass Spectrometry (A&MS) research group, Krijgslaan 281 – S12, 9000, Ghent, Belgium2 Ghent University, Department of Archaeology, Prehistory of Europe research group, Sint-Pietersnieuwstraat 35, 9000, Ghent, Belgium3 KU Leuven, Department of Archaeology, Art History and Musicology, Archaeology group, Celestijnenlaan 200E, 3001 Leuven, Belgium4 KU Leuven, Department of Earth and Environmental Sciences, Geology group, Celestijnenlaan 200E, 3001 Leuven, BelgiumIntroductionIn the past two decades, laser ablation–inductively coupled plasma–mass spectrometry (LA-ICP-MS) has become an interesting alternative to the bulk solution methods for elemental analysis of pottery clay with the aim of provenance determination. The current study investigates the capabilities and limitations of selective LA-ICP-MS analysis of the clay fraction in thin sections of sediments and pottery in comparison to those of the more common bulk analysis techniques.1) Choice of calibration methodDifferences in ablation behaviour between clay material and glass cause concentration values that are systematically biased when using external calibration without internal standard (IS) correction. A sum normalization approach whereby the concentration of Si as internal standard is initially estimated to be 30 weight percent (wt%) and is afterwards corrected by assuming the sum of all oxide concentrations to be 100 wt% produces nearly identical results as an external calibration approach whereby the bulk Si concentration from the certificate is taken as IS. Conclusions and outlook1) The sum normalization approach and external calibration with an IS correction provide similar results. This implies that upfront knowledge about the concentration of the IS in the samples is not crucial.1) LA-ICP-MS analysis effectively excludes inclusions in pottery clay from the analysis. This implies that temper added by the potter which could complicate comparison between pottery and sediment can be avoided.Future research will shed light on the high recovery for some elements in the NIST SRM 679 Brick Clay. In addition, LA-ICP-MS analysis on thin sections of sediments from the direct surrounding of the site Spiere-de-Hel will be performed in order to compare the chemical composition with that of the pottery to answer hypotheses of plausible provenance.AcknowledgementThe research foundation flanders (FWO) is acknowledged for its financial support under the form of a PhD fellowship for fundamental research.References[1] Vanmontfort, B. (2004) Converging worlds. The Neolithisation of the Scheldt basin during the late fifth and early fourth millenium cal BC.  (PhD thesis, Leuven University, Belgium)[2] Lamberts, M. (2015) Petrografisch en chemisch onderzoek van het midden-neolithisch aardewerk van de site Spiere-de-Hel, België. (Master's thesis, Leuven University, Belgium)[3] Jochum, K.P. et al. (2007) GeoReM: A New Geochemical Database for Reference Materials and Isotopic Standards, Geostandards and Geoanalytical research 29 (3), 333-338Materials and methods1) A pressed, baked and polished pellet of NIST SRM 679 Brick Clay has been analysed repeatedly by LA-ICP-MS and the data was processed with different calibration approaches based on a calibration set of glass standards. The elemental concentration results were compared with the reference values from the GeoRem database3.2) The clay fraction in 30 thin sections of pottery from the middle Neolithic site ‘Spiere-de-Hel’ has been analysed by LA-ICP-MS and the results are compared to those obtained in previous bulk analyses of the same pottery by inductively coupled plasma – optical emission spectroscopy (ICP-OES).1,2The Instrumentation used for the LA-ICP-MS analyses consists of an Analyte G2 ArF*excimer-based-deep UV laser system from Teledyne Cetac Technologies and an Xseries II quadrupole-based ICP-mass spectrometer from ThermoScientific.2) The use of thin sectionsMiddle Neolithic pottery consists of multiple fractions forming a very heterogeneous material. Non-clay fractions can be added by the potter (temper) or can be naturally present in the sediment.  In the pottery from the site Spiere-de-Hel, chunks of flint have been added by the potter and form the most prominent inclusions.Inspection of the SiO2 concentration in 30 pottery sherds from Spiere-de-Hel as obtained by LA-ICP-MS reveals a systematically lower concentration for SiO2 compared with previous bulk-ICP-OES analyses. The concentrations of other elements are accordingly higher because of the dilution effect. The difference of SiO2 concentration between the two techniques correlates with the amount of petrographically estimated SiO2 inclusions (chunks of flint and quartz grains in the sand/silt fraction).Fig. 1 Partially reconstructedflask from the site Spiere-de-Hel1Fig. 5 Typical microphotograph of a thinsection of the pottery from Spiere-de-Hel.1Fig. 2 a) pressed pellet (Ø=13mm), b) sherd afterthin sectioning, c) thinsectionFig. 3 Bias between the results obtained for a pressed pellet of NIST SRM 679 and the corresponding GeoReM reference values.3Advantages ChallengesNo digestion stepSpatially resolved analysisDirect solid sampling without internal standardLimited amount of clay reference materialsFig. 4 a) Scatterplot with the concentrations of SiO2 and Al2O3 in 30 thin sections from Spiere-de-Hel as obtained using LA-ICP-MS and ICP-OES,b) difference between SiO2 concentration in 30 thin sections of pottery from Spiere-de-Hel as obtained using LA-ICP-MS and ICP-OES as afunction of the petrographically estimated amount of SiO2 inclusions.a)b)c)Clay matrixBurnt organicmaterialAdded by the potter or naturally present in the clayChunks of flintAdded by the potterQuartz in silt/sandfractionContactmarieke.vannoorenberghe@ugent.bewww.ams.ugent.beUniversiteit Gent@ugentGhent University-80-60-40-20020406080100120140160Li Na Mg Al Si K Ca Sc Ti V Cr Mn Fe Co Ni Cu Zn Rb Sr Y Zr Nb Sn Sb Cs Ba La Ce Pr Nd Sm Eu Gd Tb Dy Ho Er Tm Yb Lu Hf Pb Th Uexternal calibration + IS sum normalization External calibration - IS303540455055606570750 10 20 30 40SiO 2(wt%)Al2O3 (wt%)LA-ICP-MS ICP-OES-30-25-20-15-10-500 10 20 30 40 50 60ConcentrationSiO 2(LA-ICP-MS -ICP-OES) (wt%)Amount of SiO2 inclusions estimated petrographicallya) b)

Selective multi-element analysis of the clay fraction in ancient pottery by laser ablation-inductively coupled plasma-mass spectrometry

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Selective multi-element analysis of the clay fraction in ancient pottery by laser ablation-inductively coupled plasma-mass spectrometry

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