Evidence of nucleation and growth of metal Cu and Ag nanoparticles in lustre: AFM surface characterization

Lustre is one of the most interesting ancient ceramic decorations. Recent studies demonstrated that lustre correspond to a nanostructured thin layer formed by metallic copper and metallic silver nanocrystals embedded in a glass matrix. The aim of this paper is to improve the comprehension of lustre nature and the mechanisms of its formation focusing special attention on glaze surface nanotopography and the crystalline particles size and distribution. Lustre reproductions were studied during the lustre formation process and compared to medieval lustre layers. Lustre reproductions and ancient lustre surfaces were observed by means of White Light Interferometry, Atom Forces Microscopy, X-ray Diffraction and Electron Microprobe. These observations shown that lustre layer does not appear as a superimposed layer on the top of the glaze but as a surface roughness resulting by the nanocrystals growth inside the glassy matrix. Chemical Microprobe Analysis of lustre reproductions indicates that Cu and (later) Ag are introduced into the glaze by ion-exchange with alkalis (Na and K) from the glaze. White Light Interferometry and Atomic Forces Microscopy showed that surface roughness increase during the lustre formation process as a result of metal nanoparticles growth. Silver particles appear heterogeneously distributed and have a smaller size and higher roughness than copper particles on ancient lustre. This paper confirmed that lustre formation process involves two steps process: ion exchange and crystallization (nucleation and crystal growth) of Cu and Ag metal nanoparticles inside the glassy matrix.