Gold and sweat: A science-based investigation of the Chinese method of black patination

Abstract

The patination of copper alloys using chemical means to turn their surfaces black is well-documented historically in China and Japan, and purportedly used in ancient Egypt, Greece, Mycenae, and the Roman world, but we know remarkably little about the origins and eventual transmission of this technology. To solve this question, there is the need to compare the materials and technologies used in different cultures, as well as to understand the corresponding patination mechanisms. Here we present the results of an experimental and analytical project that sought to reproduce and study a traditional patination method recorded in China. This involved the patination of copper alloys containing small amounts of precious metals, which were coloured by natural sweat through handling. Based on the analysis by colorimetry, OM, pXRF, SEM-EDS, XRD, Raman, and UV–VIS spectroscopy of experimental tokens and historic artefacts at the British Museum, we explain the effects of tin, silver and gold in the colour and texture of the black patinated materials, as well as the role of sweat and handling. We propose a detailed explanation for the mechanism of patination by handling, making emphasis on the role of precious metals and tin in the patina formation, and present a model of patination that will allow for comparison with patinated materials from other regions and periods.