Characterisation of Archaeological High-tin Bronze Corrosion Structures

ABSTRACT

Since ancient times, the use of high-tin bronze alloys (>17 wt.%) has been mainly limited to the production of specific objects such as mirrors and bells. High-tin bronzes can show distinctive colour reflection, as well as mechanical properties and corrosion resistance that clearly distinguish them from the classical bronze composition (with 8–12 wt.% tin). In the present study samples of archaeological high-tin bronze bells were studied by optical microscopy, SEM-EDX, and Raman imaging with the aim of characterising their microstructural long-term corrosion patterns. Results show the presence of high quantities of δ phase, when compared to the classical bronze composition, which makes some corrosion structures more visible in these alloys. The corrosion morphologies show selective corrosion of different metal phases along depth of corrosion, which were attributed to different oxygen potentials. This study proposes a classification of four types of corrosion structures occurring in two-phase bronzes as a consequence of aeration conditions during burial time and aeration within the corrosion structure.

KEYWORDS:

• Archaeological artefacts
• bells
• high-tin bronze
• long-term corrosion

Disclosure statement

No potential conflict of interest was reported by the author(s).

Additional information

Funding

Part of this work was carried out in the framework of the projects: ‘Singing Bronze’, funded by Banco Santander through the prize Santander/NOVA 2016; ‘IberianTin’ (PTDC/HAR-ARQ/32290/2017), funded by European Regional Development Fund funds through the regional program of Lisbon and through national funds through the Fundação para a Ciência e a Tecnologia (FCT) (Foundation for Science and Technology); and UID/CTM/50025/2019 granted to CENIMAT/i3N, financed through FEDER funds by COMPETE 2020 and national funds through FCT.