Alloys of Japanese Patinated Metalwork

Abstract

Alloying to create polychrome effects in metalwork was developed into an important art form in Japan and was mainly used for small items of sword furniture. This paper builds on an analytical study published in 1991 on selected items from the British Museum collection of tsuba, largely dating to the 18th and 19th centuries, 1) and extends it with analyses of the copper alloys of a wider range of objects, some from other collections. The alloys were analysed using micro X-ray fluorescence spectrometry (μXRF). Additional examinations were carried out using optical microscopy and scanning electron microscope (SEM) equipped with Energy Dispersive X-ray analysis (EDX).The results of the analyses carried out so far suggest that it is possible to track the introduction to Japan of the liquation process to de-silver copper by identifying copper objects of increasing purity after the end of the 16th century. Secondly, after this period, arsenic is rarely found in copper and copper alloys with the notable exception of a number of shakudo alloys, which confirms that a choice was being made to add arsenic deliberately to produce an enhanced patina.

Effects of alloy composition in traditional Japanese shakudo patination

“…There have been some suggestions that the presence of arsenic may also modify patina colour in shakudo (e.g. [18]), but because of health and safety considerations, it could not be included in this study.…”

2015 Atomic Spectrometry Update – a review of advances in X-ray fluorescence spectrometry and their applications

“…Interpretations were made of the presence and measured concentrations of Sn (higher levels result in a golden surface to the alloy), Pb (proposed to be a deliberate addition even at low concentrations), Fe and Zn (believed to be non-intentional additions to the alloy originating from copper ores used in smelting) and As (originating from Limassol Forest ores or the recycling of Early and Middle Bronze Age artefacts). As a result of the analysis of patinated metalwork from Japan, mainly using m-XRF instrumentation, La Niece and co-authors 327 suggested that it was possible to track the introduction to Japan of the liquidation process to de-silver copper by the identication of copper objects of increasing purity. In addition, their results indicated the deliberate addition of As to certain alloys to produce an enhanced patina.…”