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Scientific investigations and archaeometric studies have played a major role in the field of archaeology, especially with regard to materials transformed through human activity, like metals. Metals are generally investigated through metallography and Scanning Electron Microscopy (SEM), which required sampling or surface preparation. Neutron techniques instead are able to provide the bulk properties of metals in a non-invasive way.
In this work we present a neutron imaging study of a Chinese bimetallic sword fragment from 2nd-1st century BCE. In particular, white beam Neutron Tomography (NT) and Neutron Resonance Transmission Analysis (NRTA) have been applied, using the IMAT and the INES beamlines of the ISIS pulsed neutron source in the UK, respectively.
The earliest example of bimetallic weapons in China dates as early as the Shang Dynasty (1600–1100 BCE), where meteoric iron and bronze were combined to forge weapons [1]. With the discovery of iron smelting technology during the Spring and Autumn Period (770–473 BCE), bimetallic swords with bloomery iron and bronze became more common [2]. They have been found in many parts of central China.
The sword fragment investigated has an iron blade mounted on a studded bronze grip (probably for a twine binding) and a ricasso with three long spikes protruding on each side. The object resembles two published examples with similar form of hilts [3, 4] listed as originating from burials investigated in the mountainous regions of Longpaozhai, in the Min River Valley (Central Sichuan), dating from the 2nd or 1st century BCE. Similar swords are also found further north and may have been introduced from further west.
NT allowed us to study the inner morphology of the sword, revealing details of its conservation status and the forging and/or casting of the different components. NRTA provided a 2D map of the elemental composition of the artefact, indicating the nature of the bronze alloy of the grip (whether tin bronze, leaded tin bronze, or arsenical tin bronze) and of the iron blade.
The study presented was complemented by Neutron Diffraction, Neutron Resonance Capture Analysis (NRCA), and negative muons, providing a full characterisation of the object in terms of alloy composition, microstructural characterisation and elemental information, in a non-destructive way.
References:
[1] http://en.cnki.com.cn/Article_en/CJFDTOTAL-WWBF2002S1027.htm
[2] IHTAN Derui, 2002. Study on bimetallic bronze swords in ancient China, Sciences of Conservation and Archaeology, The 69th WFC Paper
[3] M. Orioli, 1994. Pastoralism and nomadism in South-West China: a brief survey of the archaeological evidence, in The Archaeology of the Steppes, Methods and Strategies, papers from the International Symposium held in Naples 9-12 November 1992, 87–108
[4] Kaogou Xuebao (Acta Archaeologica Sinica) 1977.2
