Istituto di Scienze Marine     
Letardi P., Golfomitsou S. Atmospheric corrosion of bronze: a field exposure study of the correlation of environmental data with patina growth in a urban-marine environment. In: Metal2013 - Interim Meeting of the ICOM-CC Metal Working Group (Edimburgo, 16-20 settembre 2013). Proceedings, pp. 157 - 162. Ewan Hyslop, Vanesa Gonzalez, Lore Troalen, Lyn Wilson (eds.). Historic Scotland and International Council of Museums, 2013.
Field exposure of copper alloy coupons in harsh environmental conditions, such as those of Genoa harbour, has been found to be more severe than laboratory exposure with artificial rain. The CNR-ISMAR exposure site (SMS), located inside Genoa harbour, presents an extremely harsh environment with high levels of chlorides and humidity fluctuations which typically accelerate corrosion. Over the last few years, a number of bronze coupons have been exposed on an outdoor rack located at SMS in standard conditions (45 to the horizontal and facing south) with the aim of producing naturally corroded specimens for the testing of protective coatings. Corrosion monitoring was carried out using several techniques (including X-ray diffraction (XRD), colour, and eddy current thickness measurements). Meteorological data (temperature, relative humidity, atmospheric pressure, precipitation events, and wind velocity) from weather station located at the exposure site were also collected. Although the relationship between these factors and corrosion rate has been discussed, their relationship with the type of corrosion products and the development of patina is yet to be clarified. Preliminary analysis shows that the patina thickness grows quickly in the first 3 months with a much slower increase over the next 27 months. XRD data shows the formation of cuprite from the very beginning of exposure, with an increasing amount of hydroxychlorides and brochantite detectable later on. This paper discusses how environmental parameters affect patina development by analysing some of the available data within a statistical framework to gain a better understanding of how local environmental parameters associate with the corrosion patterns, which in turn affects conservation decisions. The systematic approach adopted will help in the development of standardised methods to assess naturally corroded coupons to be used for testing conservation treatments for outdoor bronze monuments.
Subject bronze
atmospheric corrosion
statistical methods

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