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Content archived on 2024-04-19

New Conservation Methods for Outdoor Bronze Sculptures -

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Coatings designed to protect outdoor bronze sculptures from corrosion and deterioration are being tested, in particular organic inorganic copolymers (organically modified ceramics (ORMOCER)). Different substrates, untreated or with artificial patina, are protected with different kinds of ORMOCER coating and compared with corresponding samples with conventional coatings (eg wax) and with untreated samples. Artificial weathering methods are used, including exposures close to natural weathering as well as exposure conditions which accelerate the corrosion (exchange in humidity and temperature, continuous condensation, ultraviolet (UV) test, atmospheres with high sulphur dioxide content). The corrosion progress of the samples is analysed by light microscopy (LM), scanning electron microscopy (SEM) (surface and cross section), X-ray microanalysis and infrared (IR) spectroscopy. The experiments are completed by several adhesion tests and investigations of the reversibility of the lacquer as well as electrochemical measurements.
Works of art standing outdoors are endangered by environmental impact, which accelerates their natural degredation. Unsheltered metal objects, like bronze sculptures, originally polished, waxed or artificially painted, are susceptible to corrosion due to the attack of rain or condensed water and pollutants. The surface changes in colour, in chemical composition and in the amorphous character of the patina. Preserving the artistic intention of these art objects has induced conservators to reflect about methods of maintenance. Currently available coating systems have proved to have only a restricted long-term stability (about 5 to 10 years). This is not ideal from a conservation point of view, since failed treatments have to be repeated within a short time, thus raising the costs of maintenance. A promising attempt has been made to introduce a new class of material for the protection of outdoor bronze sculptures: organic-inorganic copolymers (organically modified ceramics), incorporating properties of organic and inorganic materials. A multidisciplinary team of experts in surface coating technology, metal corrosion and bronze conservation from different countries worked together for two years, developing the new material and testing for the given purpose. The efficacy of various Ormocer systems as protective coatings was evaluated on a large number of different bronze substrates simulating uncorroded as well as patinated surfaces. The laboratory phase included extended test series of the coated samples to optimize adhesion properties and long-term stability. The protective treatments were evaluated according to the results of a broad variety of analytical methods after exposing the samples to accelerated weathering. At the end of the project, promising Ormocer coatings were applied to two bronze busts and one original statue. Their long-term exposure outdoors will demonstrate the performance of the proposed treatment under natural weathering conditions. The results obtained from these pilot studies will direct future research on Ormocers as new coating systems for massive outdoor sculptures.

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