Abstract
Contact corrosion and atmospherically mediated corrosion represent significant challenges in the conservation of musical instruments, as observed in the collections of the Norwegian Museum of Music (NM-RR), part of the Museums of Southern Trøndelag (MiST). Metal components, particularly steel strings, may corrode when in contact with materials such as fabrics, plastics, wood, or leather. This project aimed to identify the material combinations most frequently associated with contact corrosion in musical instrument collections, understand the underlying degradation mechanisms, and evaluate corrosion-mitigating approaches.
A survey of approximately 1260 musical instruments in 12 European museums revealed that 14% contained material combinations that are at particular risk of contact corrosion. To facilitate future data collection, a web-based survey tool was developed, and results are continuously collected and disseminated through the website instrumentcorrosion.com. Based on the survey, two material combinations were found to be particularly problematic: steel strings in contact with stringing braids in keyboard instruments and steel strings in contact with plastics in stringed instruments. Historic samples of steel strings, string braids, and plastics were examined to identify appropriate modern proxy materials for use in laboratory experiments. The microstructure and elemental composition of modern steel strings were analysed using scanning electron microscopy with energy-dispersive X-ray spectroscopy (SEM-EDS) and inductively coupled plasma mass spectrometry (ICP-MS). The stringing braids consisted of wool fibre-based felts, and the plastic responsible for corrosion observed on steel strings was identified as cellulose nitrate (CN) using infrared spectroscopy.
Laboratory exposure studies were conducted to examine specific degradation mechanisms. Modern artificially aged CN and model atmospheres containing nitrogen dioxide and acetic acid were used to generate corrosive environments in laboratory studies. The corrosivity of the generated environments was investigated through accelerated corrosion tests involving silver, copper, iron, and lead coupons, as well as steel strings. Cathodic reduction and gravimetry were used to quantify corrosion rates. Corrosion products formed on metals exposed to CN or felt environments were characterised. The presence of nitrogen- or sulphur-containing compounds in the corrosion products demonstrated the incorporation of volatile species released from degrading CN or felt, respectively.
Corrosion-mitigation approaches included coatings and volatile corrosion protection. One thin-film coating, three polymer coatings, six volatile corrosion inhibitors (VCIs), one cellulose-based adsorbent, and three humidity-controlling saturated salt solutions were evaluated. One VCI and the cellulose-based adsorbent provided the most promising protection against CN emissions. In addition, these treatments appeared to slow the degradation of CN. A potential impact of VCIs on organic materials was assessed using a modified Oddy test with textile yarns. One VCI was found to induce cross-linking in the fibres present in the tested yarns.
Overall, the use of adsorbents and volatile corrosion protection is a promising approach for safeguarding steel strings in musical instruments, provided that its effects on organic materials are considered. The non-contact application of these methods is particularly advantageous for conservation practice. The experimental approaches developed in this project are adaptable to well-equipped conservation laboratories, providing a practical basis for conservation applications and future research in conservation and corrosion science.