No abstract

Since the mid sixties Cor-Ten 1 steel became one of the most famous materials for outdoor sculptures until today. This material was used by many artists because of its good weather resistance. Due to not always suitable ranges of application many significant problems in the field of conservation appeared.These were surveyed in a project of the study programme 'Object Conservation' at the State Academy of Art and Design Stuttgart with special focus on the material and its protective rust layers, the premises for its protection, different cases of significant damage and their causes, the potential of preventive conservation and practised interventive methods.Although it seems to be in some way a contradiction in itself to coat a weathering steel, this has often been done in hands-on conservation to overcome corrosion problems. Therefore different coating materials already in use for outdoor metal sculptures were tested on Cor-Ten coupons in the framework of the CONSIST project in the Deutsches Bergbau-Museum Bochum (DBM). Cor-Ten B samples were covered with different coating materials such as: microcrystalline waxes, waxes used in technical corrosion protection, an acrylic resin and a polyurethane resin. The sheets were then weathered for 2 months in a climate chamber with a relative high humidity (but also drying cycles) and a climate chamber with a periodic changing relative high rate of SO 2 gas and humidity using standard protocols developed at DBM in earlier projects. The effectiveness of the protective function of each coating materials is compared, consequences for practical applications discussed.

Corroding glass forms alkali(ne) surface films, which may lead to special metal corrosion products in the contact zone, for example different sodium copper carbonates or basic sodium lead carbonate. Sodium copper formate acetate was found on objects exposed to long term emissions from wood. A higher pH value may also lead to basic compounds, which normally do not form, e.g. the newly characterised Cu 2 (OH) 3 HCOO. The alkaline films also create a reactive environment for the formation of formates from formaldehyde (e.g. emitted from glues) due to the Cannizzaro reaction or possibly from the neglected pollutant carbon monoxide. Further products containing, for example, potassium or sulphate may be expected.

Cu3(CH3COO)2(OH)4 a historic blue verdigris pigment phase was synthesised and characterised by its spectroscopic and magnetic properties.