Quantitative Oddy test by the incorporation of the methodology of the ISO 11844 standard: A proof of concept

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• '3 in 1′ Oddy test was used to evaluate harmful materials for metallic cultural heritage. • Unlike the original Oddy test setup, metal coupons were hung from glass hooks. • Quantitative evaluation of Oddy test was performed as a complement to the visual rating. • Electrolytic cathodic reduction for silver and copper and mass gain for lead. • Quantitative methods allow selecting the safest material from those rated as suitable. The Oddy test is a preventive conservation tool that helps to preserve real objects of cultural significance. To do this, it uses silver, copper and lead coupons as corrosion dosimeters. Despite its utility and extensive experience, one of its limitations is the lack of a quantitative assessment method to avoid the subjectivity of visual examination and numerically rank the tested materials into suitable (permanent or temporary) and unsuitable. To address these issues, we present a proof of concept for the incorporation of the methodology of the ISO 11844-2 standard into the assessment stage of the '3 in 1′ Oddy test. And so, use standardized quantification methods of corrosion rate for metal coupons such as electrochemical reduction for silver and copper coupons and gravimetric methods for lead coupon. A traditional '3 in 1′ Oddy test has been performed to evaluate four materials known for their harmful nature to metallic cultural heritage: oak wood, medium density fibreboard (MDF), wool and leather. The electrochemical reduction method yields excellent results for copper and silver, allowing quantifying the corrosion even for the lightest tarnishing of the metal coupons that act as control or reference. For example, in the absence of contaminant-emitting material, the silver coupon lost 0.12 nm of thickness due to corrosion of the own conditions of the Oddy test (60 °C and 100%RH). Mass gain is also a convenient method with enough sensitivity to rank the corrosion of lead. It has been shown that the ranking established by visual inspection alone can be misleading, rating similarly materials that produce large differences in corrosion rates. Moreover, in the case of copper, the visual rating of the tested materials does not agree with that obtained from electrochemical reduction. Further research is needed to establish the limits of this methodology, but results presented here demonstrate the feasibility and utility of this approach.