Phase identification and alloy composition of historic Indian bronze gongs and cymbals by SR-XRD and PIXE

Abstract

The aim of this paper is to better understand the manufacturing process of high tin bronze gongs and cymbals by analyzing a corpus of museum musical instruments using different non destructive and non invasive techniques. Two main factors were taken in account in this study : alloy composition and heat treatments. The particular type of heat treatments performed for the making of high tin bronze gongs and cymbals is water quenching, which produces characteristic martensitic phases. The first factor, alloy composition, was investigated using Particle Induced X-ray Emission (PIXE) at the NewAGLAE particle accelerator. The second factor, the presence of quenching, was studied using Synchrotron Radiation X Ray Diffraction (SR-XRD) at the SOLEIL Synchrotron, at the DiffAbs beamline. This analysis allows for the identification of the metastable crystalline phases that act as a marker for the use of quenching in the manufacture of musical instruments. The heritage objects were investigated alongside an ensemble of lab-produced model samples that allow the use of other destructive characterization techniques, such as optical metallography. By processing the diffraction data using several methods, including Principal Component Analysis, the identification of martensitic phases in the musical instruments was achieved. Microstructural parameters were also discussed using azimuthal scanning by processing the 2D diffraction images and the variations in the diffraction intensity along the azimuthal direction. These results enable a better understanding of the use of high tin bronze alloys for gongs and cymbals.