Bronzes with high tin content: long term corrosion evolution

Ana Sofia Saraiva, Elin Figueiredo, Rui J.C. Silva.

aDep. Conservação e Restauro, FCT-UNL, 2829-516 Caparica, Portugal

bCENIMAT/I3N, Dep. of Materials Science, FCT, Universidade Nova de Lisboa, Caparica, Portugal 

High-tin bronzes with 20-25 wt.% Sn have been used in bell foundry since antiquity. The use of a bronze alloy with 4 parts of copper to 1 part of tin has been proposed as superior in terms of mechanical resistance and sound resonance from as early as the 5th century BC in Ancient China. Since then, this alloy has been used worldwide and has been named bell metal.

During my Master’s thesis I studied archaeological bell fragments from different locations of the Portuguese territory and from a time span from the 13th to the 19th centuries by optical microscopy (OM), scanning electron microscopy with energy dispersive spectroscopy (SEM-EDS) and Raman spectroscopy with the aim of characterize microstructural corrosion patterns.

A new classification in four main types of corrosion structures occurring in high-tin bronzes is proposed as a variation of oxygen potential conditions during burial and based on various corrosion patterns associated to selective corrosion of different metal phases.