Micro Raman investigation on corrosion of Pb‐based alloy replicas of letters from the museum Plantin‐Moretus, Antwerp

Abstract

To better understand corrosion behaviour of lead (Pb)-based alloys exposed to volatile organic compounds – specifically acetic\ud and formic acid – a preliminary research has been carried out on laboratory-made samples replicating such alloys. Replicas have\ud been manufactured by simulating specific types of Pb-based alloys, with antimony (Sb) and tin (Sn) as alloying elements, in order to\ud characterise corrosion products and evaluate the influence of each alloying element. Replicas were cast in a refractorymould and later\ud placed in size-specific desiccators and exposed to concentrated acetic and formic acid vapours for 15 days. Each specimen was also\ud subjected to gravimetric measurements and periodically monitored in order to understand the corrosion behaviour. Micro Raman\ud Spectroscopy (μRS) and Scanning Electron Microscopy together with energy Dispersive X-Ray Spectroscopy were used for the characterisation\ud of Pb-based replicas. Results showed the presence of typical corrosion products – more or less hydrated forms of Pb and Sn\ud acetates and formates – and also a sudden increase in the volume and brittleness of some Sb-rich specimens as well as the presence of\ud seldom-detectedmetallic Sb peakswith μRS. In this perspective, the influence of Sb as an alloying element on the corrosion of Pb-based\ud artefactsmay generate serious problems when such objects have to be restored and particular attention should be given to conservation/\ud stabilisation procedures

Historical Type in the Collection of the Plantin-Moretus Museum in Antwerp from a Metal Conservator's Point of View

“…Recent research has shown that the presence of antimony strongly promotes the corrosion of lead. 33 This was also recorded in the analysis of the heavily corroded type objects from the Plantin-Moretus Museum collection. There, it became clear that type with high levels of antimony and no (or very low amounts) of tin were prone to a severe corrosion process.…”

The formation of formates: a review of metal formates on heritage objects

“…At lower acid concentrations lead formate hydroxide (ICDD 14-0831) was detected in these lab experiments, instead of neutral lead formate but this compound has yet not been reported on heritage objects. The influence of the alloying elements tin and antimony on corrosion by organic acids has been studied on letter replicas [66].…”

Recent advances in linear and non‐linear Raman spectroscopy. Part IX

“…Ghiara and co‐workers carried out a micro‐Raman investigation on corrosion of Pb‐based alloy replicas of letters from the museum Plantin‐Moretus, Antwerp. In this work's perspective, the influence of Sb as an alloying element on the corrosion of Pb‐based artifacts may generate serious problems when such objects have to be restored, and particular attention should be given to conservation/stabilization procedures . Gutman et al .…”