Analysis of the CHARM Cu‐alloy reference materials using excimer ns‐LA‐ICP‐MS: Assessment of matrix effects and applicability to artefact provenancing

Abstract

Excimer nano‐second laser ablation inductively coupled plasma mass spectrometry (ns‐LA‐ICP‐MS) is an important tool in chemical characterization of Cu alloys. However, variable matrix‐induced elemental fractionation in Cu alloys poses a significant challenge. We systematically investigate this issue by analysing the Cultural Heritage Alloy Reference Material Set (CHARM) of Cu alloy targets. The extent to which silicate glass reference materials can be used when analysing Cu alloy targets is determined, as is the optimal internal standard, for a wide range of Cu alloy compositions. Analyses were further optimized by quantitative assessments of the use of CHARM end‐member materials as external standards for other CHARM Cu alloy targets. The variable magnitude of the observed matrix effects is most readily explained by variations in Cu/Zn ratios and resulting differences in melting and boiling points, compared with external reference materials, making the Zn‐rich Cu alloy targets most prone to matrix effects. With the correct choice of an external matrix‐matched standard (Pb‐rich CHARM reference material 32X LB14F) and internal element standardization, an accuracy of < 20% can be achieved for virtually all elements of interest in brass and bronze artefacts, which is a significant improvement compared with the use of glass external reference materials.

Assessment of the deterioration process of copper alloys: a case study of Central Lithuanian crossbow brooches with a triangular foot

“…1. Distribution of crossbow brooches with triangular feet: Aukštadvaris (1), Alytus (2), Berčiūnai (3), Dauglaukis (4), Eiguliai (5), Griniūnai (6), Juostininkai (7), Kairėnėliai (8), Kalniškiai-Bažavalė (9), Linksmėnai (10), Marvelė (11), Meldiniai (12), Obeliai (13), Pamarnakis (14), Pamušiai (15), Pašušvys (16), Pernarava (17), Plauciškiai (18), Plinkaigalis (19), Raginėnai (20), Riklikai (21), Rinkšeliai (22), Tūbausiai (23), Ukmergė (24), Upytė (25), Veršvai (26) and Vosgėliai (27) (by A. Tautavičius and U. Budvydas, updated by A. Vasiliauskaitė and drawn by A. Vasiliauskaitė) three subtypes which are not described in detail here, as the typology is not relevant for this paper. The brooches examined here were found in the inhumation graves of males, females and children (Fig.…”

“…The analysis of the brooches was performed using a portable Niton XL3t XRF spectrometer (power 2 W, voltage 50 kV, detector area ~50 mm 2 and manufacturer Thermo Fisher in the 'General Metals' mode). The cultural heritage alloy reference material set with 5 CHARM standards (bronze alloy, leaded bronze, brass alloy, leaded brass and gunmetal) was used for the analysis [15][16][17]. Each find was irradiated in at least two locations (for 30 s).…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…Steenstra et al have described the analysis of the cultural heritage alloy reference materials (CHARM) set of Cu-alloys using excimer ns LA-ICP-MS and assessed the matrix effects and its applicability to artefact provenancing. 366 The extent of the matrix effects was very variable between different alloys. This was attributed to the variation in the Zn/Cu ratio, with those samples rich in Zn significantly affecting the melting and boiling points (and hence, laser ablation properties).…”

Standardization procedure to provide a unified multi-method elemental compositional dataset, application to ferruginous colouring matters from Namibia

“…During this project, Heginbotham and colleagues (2015) have developed XRF inter-laboratory standardization for copper alloys characterization. Maximum Fe2O3 content in these alloys is of 1.4 ± 0.9 % (32X SN5A) (Heginbotham et al, 2015 ;Steenstra et al, 2021). Ferruginous colouring materials usually have a Fe2O3 content comprised between 10 to 90 %.…”