Technologies for conservation of copper alloy monuments

Investigation of corrosion processes of different copper
alloys according to certain environments, and develop
special conservation therapies. (Outdoor bronze monuments

Metal works of art are impaired in their outward appearance by the influence of corrosive substances. The damage is greatest - just as in the case of the problems connected with stone corrosion - to objects in the open air. The damage caused to the objects which, in a very simplified manner, is often attributed to the high level of SO2, can in extreme cases lead to the destruction and subsequent loss of the work of art. The aim of COPAL is to investigate corrosion processes of different copper alloys according to certain environments, and to develop special conservation therapies. Practically every country partner selects one representative outdoor bronze monument for investigation. The criteria for selection are: - cultural reference - no practical conservation work in combination with the selected monument within the next 5 years - existence of as many data as possible concerning aspects such as casting technique, materials used, techniques of construction, patination, conservation therapies already carried out in the past, etc. - selection should be within the range of a certain chemical composition: Pb .. 0-14% Zn .. 0-16% Sn .. 0-12% Mi .. 0-2% Fe, As, Sb up to 0.6% It is to be noted that a certain non-homogeneity of chemical composition appears within one monument and has to be taken into account as well. After sampling in-situ - using a special sampling device - the chemical composition is analysed and the different metallographic structures of the monument samples are investigated. According to these results, sample plates are recast, concerning only chemical compositions of the alloys, but also a network of possible metallographic structures that occur within the selected monuments. The sample plates are defined in sizes of 20 x 40 mm, 2 mm thickness. Two different kinds of surface treatment will be performed: - polished - sandblasted both under exactly defined conditions. These sample plates are distributed among the partner institutions, each only taking over those sample plates that fit the chemical compositions and metallographic structures of the one selected monument. The plates are to be exposed in-situ in the nearest possible neighbourhood of the monument. The aim of this exposition is: - to build up natural patinas according to the special environment - to investigate the corrosion processes according to the special environment. Environmental data should be provided through measurements. Some part of the exposed plates will be used after some years as naturally corroded plates for testing and developing special conservation treatments in a further project, thus considering relevantly corroded bronze surfaces and not blank ones. In addition, to exposition experiments in-situ, artificial weathering is carried out to study the corrosion processes in-vitro under defined conditions including synergetic effects of air pollutants. While in the neighbourhood of the selected monuments only those sample plates are exposed that show relevance to the monuments concerning chemical composition and metallographic structures, the artificial weathering will be carried out for all kinds of sample plates under defined conditions. Some selected representative conservation products are going to be tested on the blank alloy surfaces (polished and sandblasted) with the help of artificial weathering: - Polyacryl - Polymethane - Polyester - Epoxide resin varnish - combination of hard paraffin with microcrystalline wax - combination of epoxides with polyethylene waxes. The results of these investigations should deliver basic information before carrying out these tests that will take place in a further step using the naturally corroded sample plates. It has to include treatment of already corroded surfaces bearing naturally built up patina layers that - partially - have to be taken care of during conservation of the monument. The techniques being used are: - specially developed sampling technique for bronze monuments - recasting of bronze alloys using a specially developed device - exposition of sample plates according to already existing standards - artificial weathering using a specially developed device concerning synergetic effects of air pollutants - chemical analysis using AAS (atomic absorption spectrophotometry) - SEM-EDS (scanning electron microscopy - energy dispersive system) - patina layer studies using FT-TR (Fourrier transformed infrared spectrophotometry) - patina layer studies using XRD (X-ray diffraction) - patina layer studies using Ion Chronometography. The selected monuments are: * AUSTRIA: Monument of Emperor Joseph II (1795-1807) in Vienna * GERMANY: Monument of King Maximilian II in Munich * SWEDEN: monument of King Gustav II Adolf (1854) in Goeteborg. 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1 000 000.00€
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