A small aqua-coloured glass bead is placed in the ‘analytical chamber’ of a specialised machine. It is a large piece of kit – four times bigger than those chunky photocopiers that populate workplaces – and incredibly noisy. A built-in camera allows us to watch what is happening inside. Flashing lights appear, as the bead is perforated by a laser beam that acts as a microscopic drill. The resulting hole, though, is so small that it is invisible to the naked eye. Despite this, the minute amount of material extracted during the process can be studied to tell us much about the bead. In particular, using this sample to determine the origin of the glass can help us learn more about ancient trade networks.
The bead in question was found at a hilltop sanctuary at the Timpone della Motta, near the modern town of Francavilla Marittima in southern Italy. It had been buried alongside hundreds of other glass beads, as well as fragments of pottery vessels, terracotta figurines, and bronze objects in a ritual deposit dating to the first half of the 6th century BC. Thousands of burned and heavily fragmented bones from sheep were also thrown into the deposit. Thanks to the scientific analyses, we now know that our glass bead had travelled a long distance before it entered the earth at the sanctuary.
1st millennium BC. IMAGE: Danish Institute in Rome
Ancient glass and modern science
The glass bead is one of 32 such objects that took another lengthy journey after their discovery at the Timpone della Motta sanctuary. They travelled from Italy to central France, and specifically to a scientific laboratory in Orléans (IRAMAT-CEB, Institut de recherche sur les archéomatériaux, at CNRS, Le Centre national de la recherche scientifique). In this lab, 26 of the best-preserved beads were analysed using the method just described – a technique that is known to specialists as LA-ICP-MS (laser ablation inductively coupled plasma mass spectrometry). It allows archaeologists to determine the chemical composition of the glass without chopping off and destroying a sizable chunk of the bead. It is an ideal method for analysing small artefacts. Glass is not the only material that can be studied using LA-ICP-MS. Gold and silver coins, jewellery, and precious stones like garnet, obsidian, and emerald are also counted among frequent visitors to the lab.
