Luster Pottery from the Thirteenth Century to the Sixteenth Century: A Nanostructured Thin Metallic Film Josefina Pe ´rez-Arantegui, ² Judit Molera, ‡,§ Angel Larrea, ¶ Trinitat Pradell, § and Marius Vendrell-Saz ‡ Departamento de Quı ´mica Analı ´tica, Universidad de Zaragoza, 50009 Zaragoza, Spain; Departament de Cristal.lografia i Mineralogia, Universitat de Barcelona, 08028 Barcelona, Spain; Instituto de Ciencia de Materiales de Arago ´n, Universidad de Zaragoza–CSIC, 50015 Zaragoza, Spain; and ESAB, Universitat Polite `cnica de Catalunya, 08026 Barcelona, Spain Ilaria Borgia, ²² Brunetto G. Brunetti, ²² Franco Cariati, ‡‡ Paola Fermo, ‡‡ Marcello Mellini, §§ Antonio Sgamellotti, ²² and Cecilia Viti §§ Dipartimento di Chimica, Universita’ di Perugia, 06123 Perugia, Italy; Dipartimento CIMA, Universita’ di Milano, 20133 Milano, Italy; and Dipartimento di Scienza delle Terra, Universita’ di Siena, 53100 Siena, Italy Luster is a decorative metallic film that was applied on the surface of medieval glazed pottery. It can be obtained via the low-temperature (650°C), controlled reduction of copper and silver compounds. In this paper, we show that luster is a thin layered film (200 –500 nm thick) that contains metallic spherical nanocrystals dispersed in a silicon-rich matrix and has a metal-free outermost glassy layer that is 10 –20 nm thick. Silver nanocrystals seem to be separated from those of copper, forming aggregates 5–100 m in diameter. This composite structure exhibits optical properties that are dependent on both the particle size and the matrix. Luster is indeed the first reproducible nanostructured thin metallic film that was made by humans. I. Introduction N ANOMETER-SIZED metallic particles suspended in melt glasses have been used for centuries to produce colored glassware. 1 Recently, it has been found that composites that are characterized by a much-higher local concentration of metal nanoclusters than that in melt glasses can be synthesized via different techniques, such as radio-frequency sputtering, ion implantation, or sol– gel deposition followed by annealing in a reducing hydrogen/nitrogen atmosphere. 2–4 These composites exhibit third-order susceptibili- ties that are several hundred times larger than those in common colloidal melt glasses. They are promising materials for all optical systems—that is, for switching, routing, and signal processing devices to be able to work in optical-fiber communications at much-higher speed than electronics. 5 Here, using a physicostruc- tural study on ancient ceramics, we show that high-density thin films of silver and copper nanoclusters already have been pro- duced in Middle-Age- and Renaissance-era glazed pottery, to exploit their peculiar optical properties for decorative purposes. These decorations, which are characterized by beautiful metallic reflections and iridescence (mainly goldlike or copperlike), are known as luster (see Fig. 1). The earliest luster pottery was made in Iraq in the ninth century. 6 The Islamic technology of production spread to Egypt, Persia, and Spain during medieval times, following the expansion of Arabian culture. The first examples of luster that was made in Spain were found in Murcia and date back to the twelfth century AD. 7 Later, during the fourteenth and fifteenth centuries, luster pottery was produced largely in Manises, Paterna, and other centers. 8 From Spain, luster was introduced into the Italian peninsula, where it was used to decorate the splendid majolicas that were produced in central Italy (for example, in Deruta 9 and Gubbio 10 ) during the fifteenth and sixteenth centuries. Historical documentation 11–14 indicates that the luster was obtained using a procedure that is analogous to the synthesis of modern, thin, nanostructured metallic films. It was prepared by annealing a mixture of copper and silver compounds, clay, ochre, and other optional substances on previously tin-glazed pottery, under a reducing atmosphere. The luster, which was mixed with water and vinegar, was applied by hand using a brush. Although the metallic character of the film has not been clearly demonstrated until recently, the reducing atmosphere was generally thought to be responsible for the reduction of the copper and silver compounds to their metal counterparts, in the form of thin metallic films. Luster decorations were applied on previously glazed pottery (lead, alkaline, or mixed glaze) and opacified, in most cases, by the presence of cassiterite (SnO 2 ) particles. 15 The reduction firing was performed at temperatures that were high enough to soften the glaze, thus ensuring a good adherence of the luster film, but low enough to avoid dissolution of the luster into the glaze. No historical data are available on the firing temperatures that were used in the luster production. However, our studies on the technology of production of lead glazes and tin opacified lead glazes 15 have indicated that the temperature should not reach 700°C, because the glaze melts near this temperature. On the other hand, at temperatures of 650°C, the glaze does not soften enough to ensure the adherence of the luster. When the temperature and atmosphere were controlled correctly, the residue of the applied mixture did not adhere to the glaze and could be burnished off. This phenomenon is consistent with a metallurgical process whereby metallic particles are deposited in the glaze surface after the reduction of the original compounds; the burnished residue contains scoria, as a result of the metallurgy. Different recipes were used to obtain different luster colors and, as ancient documents and archaeological findings indicate, the R. K. Brow—contributing editor Manuscript No. 188717. Received February 28, 2000; approved September 20, 2000. ² Dept. de Quı ´mica Analı ´tica, Universidad de Zaragoza. ‡ Dept. de Cristal.lografia i Mineralogia, Universitat de Barcelona. § Instituto de Ciencia de Materiales de Arago ´n, Universidad de Zaragoza–CSIC. ¶ ESAB, Universitat Polite `cnica de Catalunya. ²² Dept. di Chimica, Universita ´ di Perugia. ‡‡ Dept. CIMA, Universita ´ di Milano. §§ Dept. di Scienza delle Terra, Universita ´ di Siena. J. Am. Ceram. Soc., 84 [2] 442– 46 (2001) 442 journal