Lustre decorations were widely used in the Renaissance period and can be seen in the famous pottery found at Deruta and Gubbio in Italy (see photo). Two years ago it was discovered that the decorations consist of a thin metal-glass layer that contains silver and copper nanoparticles. These nanoparticles are between 5 and 100 nanometres in diameter and produce brilliant iridescent reflections of ‘gold’ and red. Although much has been written on the history of these objects, there is little scientific information available on the lustre technique itself.

Bruno Brunetti of the University of Perugia and colleagues from Perugia, the universities of Padova and Venice, and the European Synchrotron Radiation Facility (ESRF) in Grenoble studied original samples of Umbrian pottery using non-destructive techniques that include Rutherford backscattering spectrometry, optical absorption spectroscopy and x-ray fluorescence. Extended x-ray absorption fine structure measurements were carried out at the GILDA beamline at the ESRF.

The researchers found that the ‘gold’ colours came from silver nanoparticles and copper ions distributed in a thin layer some 60 to 120 nanometres deep. The silver and copper were present in concentrations of about 20% and 1-3 % respectively by weight. Red colours were produced by copper nanoparticles and ions present in a concentration of about 8% within a layer some 60 to 180 nanometres deep.

The Italian team believe that copper and silver were deposited using methods that are surprisingly similar to those used to make modern metal-glass composites.