Characterization of slag inclusions in iron objects

Abstract : Tracing the origins of iron artifacts generates great interest in iron metallurgy. Chemical analysis of non-metallic slag inclusion (SI) entrapped in iron produced in bloomery furnaces is an efficient mean for provenance studies as, within their composition, SI do not only carry the conditions of production but also the chemical signature of the iron ore initially used. The analytical protocol is a three stage process: (a) metallographic identification and selection of SI, (b) characterization of their main component using SEM-EDX, (c) traces element determination using LA-ICP-MS. LA-ICP-MS analysis allows to quantify up to 39 trace elements in the fayalitic-rich matrix of SI with detection limits at the ppm level. Compositional ratios are then compared with one another and to the chemical signature of previously analysed regions of production. The methodology was applied on iron armatures from the cathedral of Bourges to study their fabrication, their installation in the building and their provenance. Results obtained allow a better understanding of the role of these armatures and the supply of this construction site.