Comprehensive studies of patinas on Renaissance bronze statuettes with laboratory, synchrotron and neutron-aided techniques

The spatial distribution of constituents in the patina of Renaissance hollow bronze statuettes adds a new dimension to bulk microanalytical data. Studies of the chemical stratigraphy of patina on bronze statuettes reveal interesting composites consisting of primary layers reflecting dezincification, secondary layers with botryoidal copper sulphate structures and applied organic layers with a chaotic internal structure. To characterize the patina structure fully, various macro and microanalytical 2 and 3-D imaging approaches are combined. Intact patinas have intricate secondary layers developed from mineralising copper metal soaps that suggest a period of slow development. Further organic-rich layers seal and preserve these layers in protected areas of the statuettes, for example in the hair. The absence of these secondary layers changes not only the quality of the patina but may also be an indication of questionable authenticity and/or invasive repairs.