Reassessing early copper metallurgy : insights from the prehistoric site of Orti Bottagone, Tuscany

Abstract

This research focuses on the study of the metallurgical assemblage discovered at the Final Neolithic (early 4th millennium BC) site of Orti Bottagone, Tuscany (Italy). It has two objectives: understanding the copper reduction technology employed at the site and exploring the feasibility of one-step sulphide ore reduction experimentally. The overarching goal is to comprehend how prehistoric smiths might successfully have smelted sulphide ores at a time when most were still engaged in the reduction of copper oxides and carbonates. The answer, although based on evidence from a single site, has important implications for our understanding of technological change in Western Europe. Traditional belief has it that metal technology progressed from the working native copper in the Neolithic to the small-scale smelting of copper oxides and carbonates in the Chalcolithic and the large-scale reduction of copper sulphides in the Bronze Age. However, recent research has challenged this belief, highlighting that sulphide ores were already being reduced in the Chalcolithic, when most communities still relied on copper oxides and carbonates. Orti Bottagone can shed light on the transition from oxide/carbonate to sulphide smelting due to its early chronology and its location at the heart of a copper-rich ore district. The research has employed a multi-analytical approach, combining materials science and experimental archaeology. Several samples of slags and a crucible fragment were analysed using Optical and Digital Microscopy (OM and DM), X-ray Powder Diffraction (XRD), X-Ray Fluorescence (pXRF) and Scanning Electron Microscopy coupled with Energy Dispersive Spectrometry (SEM-EDX). Slag analysis has revealed that, at Orti Bottagone, copper was obtained from sulphide-rich charges through an immature slagging process. The experimental reconstruction of the process showed that sulphide ores were likely smelted through a one-step process without any roasting. These findings indicate that sulphide ores could be reduced at the initial stages of metallurgy under conditions that, although inefficient, secured the transformation of the ore into metal.