The use of nanostructured fluids for the removal of polymer coatings from a Nuxalk monumental carving – exploring the cleaning mechanism

While undertaking treatment of a monumental Northwest Coast wooden carving at the American Museum of Natural History, conservators encountered a difficult cleaning challenge. The 19th century painted red cedar carving served as a house entry pole in the Nuxalk village of Bella Coola in the province of British Columbia, Canada. The painted surface was weathered by years out of doors in front of the house of Chief Pootlass and obscured by darkened museum-applied coatings and grime acquired during more than 100 years of open display at the museum. The methods used to reduce the grime and cellulose nitrate coating found on the surface overall were not successful when applied to the green painted areas on the bottom of the pole, as it was covered with an additional coating of poly(vinyl acetal) resin. The present work reports on the testing and use of aqueous nanostructured fluids (NSFs) and hydrogels for succesfully cleaning these areas, where other methods could not be used safely. There have only been a few published examples of these recently developed cleaning fluids and gels being used on art objects and this is the first known use on this type of material. Further analyses were performed following the cleaning. Micro-reflectance FTIR, optical microscopy, SEM-EDX, and NMR were used to characterize paint and coating samples taken from the carving. In addition, laboratory tests were performed to evaluate the response of poly(vinyl acetal) to a selection of NSFs, providing an understanding of the mechanisms underlying the successful cleaning performed on the pole by the conservators.