Archaeointensity of nineteenth-century Scottish firebricks from a foundry in Melbourne, Australia: comparisons with field models and magnetic observatory data

An archaeomagnetic intensity study was conducted on nineteenth-century firebricks manufactured in Scotland and used in an iron foundry in Melbourne, Australia, between 1842 and 1864 CE. Archaeointensity results obtained from bricks with a single component of magnetization gave values of 61.45 + 0.89 and 61.92 + 6.84 μT. These values are in agreement with historical absolute intensity measurements taken at the Melbourne geomagnetic observatory between 1858 and 1863 CE (61.17 + 0.078 μT) and with the gufm1 model based on mariners’ data. A high-temperature vector component, presumably acquired at the time of manufacture in Scotland, was isolated in certain firebricks and an archaeointensity of 48.3 + 8.39 μT was obtained, which is consistent with the gufm1 model for Scotland at this time (48.79 μT). The dual archaeointensity record of the firebricks supports their geographical provenance, highlighting the potential for archaeointensity data to be used in archaeological artefact-sourcing studies, whilst anomalously high intensities recorded in one of the bricks highlight potential contamination issues from non-Earth magnetic fields in archaeometallurgical contexts. The new Melbourne archaeointensity data are the most precisely dated archaeomagnetic data produced so far for Australia.