Exploring the use of Acidithiobacillus Ferrooxidans for the removal of Sulphides from Tarnished Silver

Main Article Content

Giel Scheepers
Rijksmuseum Amsterdam, Conservation & Science, Metals Conservation; Utrecht University, Faculty of Science, Department of Biology, Microbiology
http://orcid.org/0000-0003-3128-9436
Margot Koster
Utrecht University, Faculty of Science, Department of Biology, Microbiology
http://orcid.org/0000-0003-1810-242X
Joosje van Bennekom
Rijksmuseum Amsterdam, Conservation & Science, Metals Conservation
http://orcid.org/0000-0001-8977-2805

Abstract

Tarnished silver objects contain a black layer of silver sulfide. Current cleaning methods are not suitable for fragile objects, therefore, this exploratory study set out to develop a new biology-based method to clean silver. The extremophile bacterium Acidithiobacillus ferrooxidans was considered the most promising candidate, because of its ability to oxidize metal sulfides. The bacterium indirectly removed silver sulfide from tarnished silver coupons, through the generation of ferric iron. However, this procedure etched the silver. It was investigated whether A. ferrooxidans was able to directly oxidize silver sulfide in the absence of iron. However, no removal of silver sulfide was observed.

Keywords: Silver, Fragile silver, Silver sulfide, Tarnish removal, A. ferrooxidans, Bio-inspired innovation

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