Copper(II) hydroxide on artefacts: Corrosion,conservation, colourants |
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| Authors: | Britta Schmutzler Gerhard Eggert Charlotte F Kuhn-Wawrzinek |
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| Institution: | 1. Institute of Conservation Sciences, State Academy of Art and Design Stuttgart, Germany;2. Objects Conservation, State Academy of Art and Design Stuttgart, Germany;3. Institute of Inorganic Chemistry, University of Stuttgart, Germany |
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| Abstract: | Copper(II) hydroxide (as the rarely occurring mineral spertiniite) is formed under alkaline, oxidising conditions. It has been observed as a naturally occurring corrosion product of brass in sea water. But most occurrences on copper alloys are due to conservation treatments using basic solutions (sodium hydroxide or ammonia) or to intentional patination. Classical brass centrepieces (c. 1800), ‘cleaned’ with ammonia solution, developed a blue spertiniite patina in gaps, where evaporation was hindered. Additional to the danger of stress corrosion cracking this is another reason now outlawing this treatment. Copper pigment layers will transform to copper hydroxide when exposed to bases. The treatment of basic copper salts with bases has been used intentionally in the production of Bremen blue and similar pigments which can be composed of copper hydroxide as well. |
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| Keywords: | Ammonia Brass Bremen blue Copper alloys Copper(II) hydroxide Copper pigments Spertiniite Stress corrosion cracking |
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