New insights into alloy compositions: studying Renaissance bronze statuettes by combined neutron imaging and neutron diffraction techniques

Abstract

Until recently the inside parts of hollow cast Renaissance bronze statuettes were concealed, yet they hold important information on the production techniques used in the manufacture of these fine works of art. For that specific reason the inside of the sculptures have been made visible using a neutron imaging technique (tomography) at the Paul-Scherrer Institut, Villigen, Switzerland. This method allowed us to study the internal structure of a bronze sculpture and provided an indication of different material compositions. Since sample taking is not advised on these precious works of art, different non-destructive methods had to be investigated to obtain more specific information on the compositions of the inner parts. This research focuses on analyzing pre-determined small volumes selected from neutron tomographies. With this approach it has become possible to study the material compositions and crystalline structures of these statuettes with a millimetre-sized gauge volume placed at any selected point within the object, using time-of-flight neutron diffraction in the setup of ENGIN-X at the ISIS facility at the Rutherford Appleton Laboratory, UK. Analysis of a Renaissance statuette from the Rijksmuseum, a Striding Nobleman, gives evidence of the different copper alloy compositions of superficial and internal parts but also shows small amounts of ferrite present which until recently was not reported for Renaissance bronzes. The alloy is magnetic due to the ferrite, and strong rare-earth magnets were used to establish whether or not other Renaissance bronzes and brasses contain ferritic iron. A combined application of neutron techniques leads to a better understanding of the production techniques and will, in general, help to advance the analytical studies of these marvelous objects.