Golden-like luster decorations on glazed ceramics from early Islamic times (9-12th centuries AD) consist of a nanocomposite submicrometric layer made of silver metal nanoparticles. The color and golden-like reflectivity of these decorations are dominated by the nonlinear optical response and Mie scattering of the silver nanoparticles. We demonstrate that the enhanced golden-like reflectivity occurs only for dense nanoparticulated layers and that they were obtained by adding PbO to the alkaline glaze. This resulted in reduced diffusivity of silver in the glaze leading to more concentrated and thinner luster layers that formed closer to the glaze surface. The result obtained adds new insights into the high technological level attained during Islamic times and also has important historical implications, giving both new clues concerning the lead enrichment of the glazes during this period, and some basis for the medieval Alchemy search for the production of "gold" from other metals.