When Glass and Metal Corrode Together, V: Sodium Copper Formate

ABSTRACT

A sodium copper formate, first described in 2002, can also form on copper alloys with sodium originating from soda glass hydrolysis. The frequent occurrence (50% of 250 cases of glass-induced metal corrosion) is due to the presence of formaldehyde emissions in storage and its direct reaction to formate in the alkaline surface films. The compound can be produced without the presence of acetate when chalconatronite or metal coupons immersed in soda solution are exposed to formaldehyde vapours. The crystal structure, derived from X-ray powder diffraction, yielded the sum formula Cu₄Na₄O(HCOO)₈(OH)₂·4H₂O. Except for the absence of acetate in the structure, this is in good agreement with the 2002 publication. To assess which kind of combined glass/metal objects are affected, a number of large museum collections were surveyed. Sodium copper formate was detected as a corrosion product using mainly micro-Raman spectroscopy, for instance, on 18 painted Limoges enamels, eight glass vessels with metal mountings, glass beads on metal wire from 11 bridal crowns, nine Christmas tree balls with wire decoration, 40 pieces of jewellery with glass gems, three daguerreotypes, and one miniature with cover glasses.

KEYWORDS:

• Glass corrosion
• copper alloys
• sodium copper formate
• indoor pollutants
• Raman spectroscopy
• X-ray powder diffraction

Acknowledgements

The authors gratefully acknowledge Dirk Kirchner and Georg Wange (German Mining Museum, Bochum) for taking the FE-SEM images and performing the IEC analyses. Christoph Krekel and Julia Schultz (Stuttgart Conservation Science department) made the Raman measurements possible. This research would not have been possible without the cooperation of numerous museums which allowed access to collections and made samples available for analyses. We are grateful for the support and useful information to a large number of colleagues including Julia Day (The Frick Collection), Fi Jordan (Victoria and Albert Museum), Birgit Schwahn (sample of the Herzog Anton Ulrich-Museum), Guus Verhaar (Rijksmuseum Amsterdam), Cátia Lamerton Viegas Wesolowska (samples of the National Museum, Warsaw), Silke Nienstedt (Focke-Museum, Bremen), Anne Becker (Museumslandschaft Hessen Kassel), Annika Dix and Stefan Oed (Germanisches Nationalmuseum), Heiner Grieb (Kunstsammlungen der Veste Coburg), Astrid van Giffen and Stephen Koob (Corning Museum of Glass), Margarete Pavaloi (Völkerkundemuseum der von Portheim Stiftung Heidelberg), Martin Ledergerber (Schweizerisches Nationalmuseum), Ina Sahl (Franziskanermuseum Villingen Schwenningen), Silke Beiner-Büth (Hamburg Museum), Rosa Pittà-Settelmeyer (Rosgartenmuseum Konstanz), Rainer Richter (Staatliche Kunstsammlungen Dresden), Monica Galeotti (Opificio delle Pietre Dure) and Paolo Belluzzo (samples of the Museo Sistino Vescovile) as well as to Isabel Keller and Stephanie Wümmers (former Stuttgart MA Objects’ Conservation students).

Disclosure statement

No potential conflict of interest was reported by the authors.

ORCID

Andrea Fischer http://orcid.org/0000-0001-9496-5097

Additional information

Funding

The GIMME Project was funded by the Friede Springer Stiftung, Germany and is published in full in the PhD thesis of Fischer (2016).