A Better Shade of Black: Effects of Manufacturing Parameters on the Development of Ancient Black Bronzes*

Abstract

Copper alloys with controlled contents of Sn, Ag and Au were treated with methods and solutions that mimic those used in ancient and traditional procedures for the production of black bronze. Examination of the resulting patinas with colorimetry, SEM–EDS, TEM, Raman spectroscopy and XRD revealed no systematic differences according to the fabrication method, whereas patina homogeneity and colour in those alloys that did not contain precious metal were affected by superficial work. Patina microstructure determines adherence and coverage, and depends upon the solution used irrespective of the alloy composition, but the colour of the patina is mainly related to the alloy composition. Gold promotes the development of cuprite, slowing the oxidation to tenorite in the corrosion process. Gold additions produce a more uniform patina as well as a desirable blue–black tone, which is likely to have been a factor in alloy selection.

Effects of alloy composition in traditional Japanese shakudo patination

“…The earlier experiments [17] also showed that the most successful patinas, comprising compact and homogeneous layers of fine grains covering the entirety of the sample surface, were obtained using a copper acetate treatment solution, the main documented ingredient to have been used in Japanese patination. Therefore, in the present study, the patination was performed on a hotplate with a copper acetate solution (0.4 g in 100 ml of deionised water).…”

“…The experimental method was based on the results of the pilot study described in Benzonelli et al [17]. We produced replica tokens of eight alloys, four of which were included in the original experiments: Cu 100 , Cu 95 Sn 5 , Cu 97 Au 3 , and Cu 89 Sn 5 Au 3 Ag 3 plus four new compositions: Cu 97 Ag 3 , Cu 92 Sn 5 Au 3 , Cu 92 Sn 5 Ag 3 , and Cu 94 Au 3 Ag 3 , where subscripts indicate the composition in wt.%.…”

“…This paper focuses on the patination technique used to produce shakudō and shibuichi and builds on preliminary experiments discussed in Benzonelli et al [17]. We report experimental replication of patinas in order to investigate the relationship between production technology, alloy composition (in particular, the presence of gold, silver, and tin), and the physico-chemical characteristics of the patina.…”

Abrasiva

“…• Lehm (Sugimori 2004;Benzonelli et al 2017Benzonelli et al , 1042 414 When thinking of "natural" grinding and polishing agents, mainly sandstone, quartz sand and maybe natural emery spring to mind. Old handbooks for craftsmen and workshop equipment -plus a very few sources of information from antique authors -deal with many other substances which could either be used for sanding or for polishing.…”

Distribution and acquisition of metals in the 2nd millennium BC near east

“…1060 Ogden 1993, 40-2;Demakopoulou et al 1995. See also Aruz et al 2008Cockrell 2009, 85-9;Benzonelli et al 2017, 11-3. 1061Demakopoulou et al 1995Giumlia-Mair 2012, 107, 111-14.…”