Nanoscale engineering of gold particles in 18th century Böttger lusters and glazes

By exploring the manufacturing methods of historic objects, cultural heritage studies can yield new insights into the history of technology. The required tunability of processing steps, however, is often unknown and the underlying physics and chemistry that provide insight into the object’s properties may also be lacking. A case in point is Böttger luster, a purple overglaze decoration famous for its distinctive iridescence, produced in the Meissen Manufactory from its earliest Böttger period (1710–1719) to around 1735. The iridescence of Böttger luster distinguishes it from contemporaneous purple glazes, motivating the exploration of what compositional and structural features give rise to this optical phenomenon. In this study, historic samples of Böttger luster and Purple of Cassius from Meissen are characterized and compared microscopically. The composition of both overglaze enamels is presented, including results from scanning transmission electron microscopy (STEM)-energy-dispersive X-ray spectroscopy (EDX) analyses. It was found that the iridescence and purple color of Böttger luster is due to the presence of gold nanoparticles in the glaze of the porcelain. Of specific interest is how the underlying physics of scattering and interference of the nanoparticle array is responsible for the iridescence that distinguishes Böttger luster from other gold-based purple colorants, including Purple of Cassius. Coupling these results with prior findings of Meissen porcelains, the glazes were recreated and characterized using scanning electron microscopy (SEM)-EDX, X-ray diffraction (XRD), and ultraviolet-visible spectroscopy (UV-Vis), offering insights into compositional requirements to produce purple luster.