Characterization of bronze disease for conservation purposes

The present research study is based on the master’s thesis work performed at the Conservation and Restoration Centre “La Venaria Reale”. It focuses on the archaeometric investigations of the archaeological bronze basin with reference number 15007 and dated to the first century AD. The find was unearthed from the Insula Occidentalis site in the Vesuvian area of Pompeii in the 1970s. More specifically, the basin was found in the grand complex of Marcus Fabius Rufus’s House and the House of the Golden Bracelet. Then, it was stored at “Casa Bacco” deposits until 2015. [1] However, there was a lack of information about the specific context of the finding and the original purpose of the basin was unknown. Moreover, the find showed a highly fragmentary state, with several missing pieces and greenish patinas. Here, the coupling of different techniques, such as ultraviolet photography, X-ray radiography, and vibrational spectroscopies allowed for evaluating the conservation state of the basin. Furthermore, the combination of microRaman analysis and X-ray powder diffraction was performed to in-depth characterize the corrosion patinas of three micro-fragments and a little amount of powder gently detached from the basin. The results of the scientific investigations reveal the presence of a stratified structure made up of layered copper corrosion compounds, which can be related to the bronze disease phenomenon. The detection of paratacamite and clinoatacamite ((Cu)2(OH)3Cl) and of copper sulfide (covellite, CuS) reflected the long-term exposure in chloride-rich and anaerobic environments, like marine and volcanic sites. [2] Moreover, the identification of polybasite ([(Ag,Cu)6(Sb,As)2S7][Ag9CuS4]) allowed getting insight into the chemical composition of the cupper-based alloy and manufacturing process. [3] Thus, the archaeometric investigation offered the possibility to unambiguously identify corrosion products and integration materials employed in former restoration works. The obtained results proved to be precious for optimizing the restoration and conservation interventions of archaeological bronze artefacts. [1] Ciardiello R., La casa del bracciale d’oro, in: Aoyagi M., Pappalardo U., Pompei Insula Occidentalis, Valtren, 2006, 71–560. [2] Scott D. A., Copper and bronze in art: corrosion, colorants, conservation, Getty Publications, Los Angeles, 2002, 125- 126. [3] Pelton A., Stamatakis M. G., Kelepertzis E., Panagou T., The Origin and Archaeometallurgy of a Mixed Sulphide Ore for Copper Production on the Island of Kea, Aegean Sea, Greece, Archaeometry, 57 (2) (2015) 318–343.