Effective cleaning of copper stained calcareous stone

Kim Pilkjær Simonsen,Takayoshi Suzuki,Sanne Spile,Jesper Bendix

doi:10.1186/s40494-016-0102-5

Kim Pilkjær Simonsen, Takayoshi Suzuki + Show 2 more

Open Access

https://doi.org/10.1186/s40494-016-0102-5

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Abstract

Light calcareous stone materials used in connection with cultural heritage objects, such as pedestals, or used as wall facings in connection with bronze statues or joints often show green staining due to the corrosion products from the bronze elements. The green stains alter the appearance of the monument and thus disrupt the original intention. Due to this, several cleaning methods, often involving ammonia, have been developed for removal of copper stains from stone surfaces. This paper describes a new, highly efficient method for cleaning copper stains from calcareous stone by introducing the chelating agent ethylenediamine in a poultice consisting of Laponite® RD, Arbocel® BC1000 and CMC. Cleaning experiments were performed on marble and on a calcareous sandstone plinth contaminated with natural copper corrosion products due to outdoor exposure of an untreated bronze statue. The cleaning results were evaluated by visual observations. The chemical cleaning of copper stained calcareous stone surfaces has been investigated and a new method for removal of copper stains has been developed. A solution of 0.1 M ethylenediamine in a poultice consisting of Laponite® RD/Arbocel® BC1000/CMC has shown to be an effective, economical, and fast do-it-yourself method.

Highlights

ConclusionThe chemical cleaning of copper stained calcareous stone surfaces has been investigated and a new method for removal of copper stains has been developed
Light calcareous stone materials used in connection with cultural heritage objects, such as pedestals, or used as wall facings in connection with bronze statues or joints often show green staining due to the corrosion products from the bronze elements
To investigate whether the ethylenediamine-laponite poultice could be effective in spring and autumn, the experiments on the sandstone plinth were performed in the lapidarium having T = 6–13 °C and RH = 100–75 %

Summary

Conclusion

Cleaning of copper stained calcareous stone was investigated by the use of ethylenediamine as a cleaning agent in the newly developed poultice containing Laponite® RD, Arbocel® BC1000 and CMC. A mixing ratio of Laponite® RD/Arbocel® BC100 = 1:1 + 5 % CMC in 0.1 M ethylenediamine solution gave a fast and efficient cleaning of copper stained calcareous stone material in the laboratory. The laboratory conditions represent ambient temperature in the summer months in the Nordic countries, the normal period for cleaning of outdoor stone monuments The use of this poultice-mixing ratio at lower temperatures and higher RH resulted in longer drying time of the poultice, a longer cleaning time. Even though it is possible to remove copper stains on outdoor monuments at temperature lower than 20–25 °C, working in the warm summer months gives the best conditions for application and drying of the poultice and the fastest cleaning results.

Background

Results and discussion